Table of Contents

As filed with the Securities and Exchange Commission on August 30,October 1, 2019

Registration No. 333-             

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

PHIO PHARMACEUTICALS CORP.

(Exact name of Registrant as specified in its charter)

257 Simarano Drive, Suite 101

Marlborough, Massachusetts 01752

(508) 767-3861

(Address, including zip code, and telephone number, including area code, of Registrant’s principal executive offices)

Gerrit Dispersyn, Dr. Med. Sc.

President & CEO

Phio Pharmaceuticals Corp.

257 Simarano Drive, Suite 101

Marlborough, Massachusetts 01752

(508) 767-3861

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Approximate date of commencement of proposed sale to the public:

As soon as practicable after the effective date of this Registration Statement.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box.☒

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act.☐

CALCULATION OF REGISTRATION FEE_______________________

The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act, or until the registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

The information in this preliminary prospectus is not complete and may be changed. These securities may not be sold until the registration statement filed with the Securities and Exchange Commission is effective. This preliminary prospectus is not an offer to sell these securities, nor doesand it seekis not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

Subject to completion, dated August 30,October         , 2019

PRELIMINARY PROSPECTUS

Preliminary Prospectus

Up to 8,125,946 Shares of Common Stock

This prospectus covers

Up to             Units (each Unit consisting of one share of Common Stock and one Warrant to

purchase one share of Common Stock)

Up to            Pre-funded Units (each Pre-funded Unit consisting of one Pre-funded Warrant to

Purchase one share of Common Stock and one Warrant to purchase one share of Common Stock)

Shares of Common Stock Underlying the offerPre-funded Warrants and sale

            Shares of Common Stock Underlying the Warrants

We are offering up to         8,125,946 sharesunits (each unit consisting of one share of common stock and one warrant to purchase one share of our common stock) at a public offering price of $       per unit. Each warrant included in the units has a per share exercise price of $       .

We are also offering to those purchasers whose purchase of units in this offering would result in the purchaser, together with its affiliates and certain related parties, beneficially owning more than 4.99% of our outstanding common stock following the consummation of this offering, the opportunity to purchase, in lieu of the number of units that would result in ownership in excess of 4.99% of our outstanding common stock, pre-funded units (each pre-funded unit consisting of one pre-funded warrant to purchase one share of our common stock $0.0001 par value, by Lincoln Park Capital Fund, LLC (“Lincoln Park” orand one warrant to purchase one share of our common stock) at a public offering price equal to the “Selling Stockholder”)price per unit being sold to the public in this offering minus $0.01. Each pre-funded warrant included in the pre-funded units will have a per share exercise price of $0.01. The pre-funded warrants contained in the pre-funded units will be exercisable immediately and may be exercised at any time until the pre-funded warrants are exercised in full. Each warrant included in the pre-funded units has a per share exercise price of $       . The warrants to purchase one share of our common stock contained in the units and pre-funded units will be exercisable beginning on the date of issuance and will expire on thefifth anniversary of the date of issuance.

For each pre-funded unit we sell, the number of units we are offering will be decreased on a one-for-one basis. The units and pre-funded units have no stand-alone rights and will not be certificated or issued as stand-alone securities. The shares of common stock, being offered to the Selling Stockholder have been or maypre-funded warrants and warrants comprising such units are immediately separable and will be issued pursuant to the purchase agreement dated August 7, 2019 that we entered into with Lincoln Park (as amended on August 20, 2019, the “Purchase Agreement”). See “The Lincoln Park Transaction” for a description of the Purchase Agreement and “Selling Stockholder” for additional information regarding Lincoln Park. The prices at which Lincoln Park may sell the Shares will be determined by the prevailing market price for the Shares or in negotiated transactions.

We are not selling any securities under this prospectus and will not receive any of the proceeds from the sale of the Shares by the Selling Stockholder.

The Selling Stockholder may sell the shares of common stock describedseparately in this prospectus in a number of different ways and at varying prices. See “Plan of Distribution” for more information about how the Selling Stockholder may sell the shares of common stock being registered pursuant to this prospectus. The Selling Stockholder is an “underwriter” within the meaning of Section 2(a)(11) of the Securities Act of 1933, as amended (the “Securities Act”).

We will pay the expenses relating to the registration under the Securities Act of the offer and sale by Lincoln Park of the shares covered by this prospectus, including legal and accounting fees.offering.

Our common stock is currently quotedlisted on theThe Nasdaq Capital Market under the symbol “PHIO”. The closing price of our common stock on August 29,September 30, 2019, as reported by Nasdaq, was $0.3301$0.2751 per share. We do not intend to apply for listing of the pre-funded warrants or the warrants on any securities exchange or other trading system. 

There is no established public trading market for the pre-funded warrants or warrants, and we do not expect a market to develop. Without an active trading market, the liquidity of the pre-funded warrants and warrants will be limited. We have assumed a public offering price of $      per unit, the last reported sale price for our common stock as reported on The Nasdaq Capital Market on October      , 2019, and $      per pre-funded unit. The actual offering price per unit or pre-funded unit will be negotiated between us and the underwriter based on the trading of our common stock prior to the offering, among other things, and may be at a discount to the current market price. Therefore, the assumed public offering price used throughout this prospectus may not be indicative of the final offering price.

You should read this prospectus, together with additional information described under the headings “Incorporation of Certain Information by Reference” and “Where You Can Find More Information,” carefully before you invest in our securities.

Investing in our securities involves a high degree of risk. In reviewing this prospectus,Before making any investment in these securities, you should consider carefully the risks and uncertainties described in the section entitled “Risk Factors”“Risk Factors” beginning on page 46 of this prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense. The securities are not being offered in any jurisdiction where the offer is not permitted.

We have granted the underwriter the option to purchase up to          additional shares of common stock at a purchase price of $           per share and/or warrants to purchase up to an aggregate of shares of common stock at a purchase price of $0.01 per warrant with an exercise price of $        per share, less the underwriting discounts and commissions, solely to cover overallotments, if any. The underwriter may exercise its option at any time within 30 days from the date of this prospectus. If the underwriter exercises the option in full, the total underwriting discounts and commissions payable by us will be $            , and the total proceeds to us, before expenses, will be $             .

Sole Book-Running Manager

H.C. Wainwright & Co.

The date of this prospectus is               , 2019

TABLE OF CONTENTS

about this prospectus

We have not authorized anyone to provide you with information other than that contained or incorporated by reference in this prospectus or in any free writing prospectus prepared by or on behalf of us or to which we have referred you. We take no responsibility for and can provide no assurance as to the reliability of, any other information that others may give to you. We are not offering to sell, and the Selling Stockholder is not offeringseeking offers to sell,buy, securities only in any jurisdictions where offers and sales are not permitted. The information contained or incorporated by reference in this prospectus or any free writing prospectus is accurate only as of its date, regardless of its time of delivery or any sale of our securities. Our business, financial condition, results of operations, and prospects may have changed since that date.

We urge youThis prospectus contains or incorporates by reference summaries of certain provisions contained in some of the documents described herein, but reference is made to carefully read this prospectus and any prospectus supplement, together with the informationactual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed or have been incorporated herein by reference as exhibits to the registration statement of which this prospectus forms a part, and you may obtain copies of those documents as described in this prospectus under the heading “Where You Can Find Additional Information” andheadings “Incorporation of Certain Information by Reference.Reference” and “Where You Can Find More Information.”

No action is being taken in any jurisdiction outside the United States to permit an offering of our securities or possession or distribution of this prospectus in that jurisdiction. Persons who come into possession of this prospectus in jurisdictions outside the United States are required to inform themselves about and to observe any restrictions as to this offering and the distribution of this prospectus applicable to that jurisdiction.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTSCautionary Note Regarding Forward-Looking Statements

This prospectus contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Forward-looking statements can be identified by words such as “intends,” “believes,” “anticipates,” “indicates,” “plans,” “expects,” “suggests,” “may,” “should,” “potential,” “designed to,” “will” and similar references, although not all forward-looking statements contain these words. Forward-looking statements are neither historical facts nor assurances of future performance. These statements are based only on our current beliefs, expectations and assumptions regarding the future of our business, future plans and strategies, projections, anticipated events and trends, the economy and other future conditions. Because forward-looking statements relate to the future, they are subject to inherent uncertainties, risks and changes in circumstances that are difficult to predict and many of which are outside of our control. Risks that could cause actual results to vary from expected results expressed in our forward-looking statements include, but are not limited to:

Our actual results and financial condition may differ materially from those indicated in the forward-looking statements as a result of the foregoing factors, as well as those identified in this prospectus under the heading “Risk Factors” and in other filings the Company periodically makes with the Securities and Exchange Commission. Therefore, you should not rely unduly on any of these forward-looking statements. Forward-looking statements contained in this prospectus speak as of the date hereof and the Company does not undertake to update any of these forward-looking statements to reflect a change in its views or events or circumstances that occur after the date of this report.

RISK FACTORS

Investing in our securities involves a high degree of risk. Before investing in our securities, you should carefully consider the risks, uncertainties and assumptions described below, and discussed under the heading “Risk Factors” included in our most recent Annual Report on Form 10-K for the year ended December 31, 2018, as revised or supplemented by subsequent filings, which are on file with the Securities and Exchange Commission and are incorporated herein by reference, and which may be amended, supplemented or superseded from time to time by other reports we file with the Securities and Exchange Commission in the future.

Our business, financial condition, results of operations and future growth prospects could be materially and adversely affected by any of these risks. In these circumstances, the market price of our common stock could decline, and you may lose all or part of your investment. The risks and uncertainties incorporated by reference into this prospectus are not the only ones we face. Additional risks and uncertainties not presently known or which we consider immaterial as of the date hereof may also have an adverse effect on our business.

Risks Related to Thisthis Offering

We have broad discretion in how we use the net proceeds of this offering, and we may not use these proceeds effectively or in ways with which you agree.

Our management will have broad discretion as to the application of the net proceeds of this offering and could use them for purposes other than those contemplated at the time of the offering. Our stockholders may not agree with the manner in which our management chooses to allocate and spend the net proceeds. Moreover, our management may use the net proceeds for corporate purposes that may not increase the market price of our common stock.

The saleoffering price was set by our Board of Directors and does not necessarily indicate the actual or issuancemarket value of our common stock.

Our Board of Directors approved the offering price and other terms of this offering after considering, among other things: the number of shares authorized in our certificate of incorporation; the current market price of our common stock; trading prices of our common stock to Lincoln Park may cause dilutionover time; the volatility of our common stock; our current financial condition and the saleprospects for our future cash flows; the availability of and likely cost of capital of other potential sources of capital; and market and economic conditions at the time of the sharesoffering. The offering price is not intended to bear any relationship to the book value of our assets or our past operations, cash flows, losses, financial condition, net worth or any other established criteria used to value securities. The offering price may not be indicative of the fair value of the common stock acquired by Lincoln Park, orstock.

Because the perception that such sales may occur, could cause thepublic offering price of our common stock to fall.included in the units or issuable upon exercise of the warrants or pre-funded warrants will be substantially higher than the net tangible book value per share of our outstanding common stock following this offering, new investors will experience immediate and substantial dilution.

On August 7, 2019, we entered into the Purchase Agreement with Lincoln Park, pursuant to which Lincoln Park has committed to purchase up to $10,000,000The public offering price of our common stock. Uponstock included in the executionunits or issuable upon exercise of the Purchase Agreement, we issued 500,000 Commitment Shares to Lincoln Park as a fee for its commitment towarrants or pre-funded warrants will be substantially higher than the net tangible book value per share of our common stock immediately following this offering based on the total value of our tangible assets less our total liabilities. Therefore, if you purchase shares of our common stock, underincluded in the Purchase Agreement. The remainingunits or issuable upon exercise of the warrants or pre-funded warrants in this offering, you will experience immediate and substantial dilution. See the section entitled “Dilution” beginning on page 9 of this prospectus for a more detailed discussion of the dilution you will incur if you purchase common stock in this offering.

There is no public market for the pre-funded warrants and warrants.

There is no established public trading market for the pre-funded warrants or the warrants in this offering, and we do not expect a market to develop. In addition, the pre-funded warrants and the warrants are not listed, and we do not intend to apply for listing of the pre-funded warrants and the warrants on any securities exchange or trading system. Without an active market, the liquidity of the pre-funded warrants and the warrants is limited, and investors may be unable to liquidate their investments in the pre-funded warrants and the warrants.

A pre-funded warrant or warrant does not entitle the holder to any rights as common stockholders until the holder exercises the pre-funded warrant or warrant for shares of our common stock.

Until you acquire shares of our common stock that mayupon exercise of your pre-funded warrants or warrants, the pre-funded warrants or warrants will not provide you any rights as a common stockholder. Upon exercise of your pre-funded warrants or warrants, you will be issued underentitled to exercise the Purchase Agreement may be sold by usrights of a common stockholder only as to Lincoln Park at our discretion from time to time over a 30-month period commencingmatters for which the record date occurs on or after the satisfaction of certain conditions set forth in the Purchase Agreement, including that the SEC has declared effective the registration statement that includes this prospectus, and subject to applicable Nasdaq limits on the number of shares that we can sell to Lincoln Park, absent stockholder approval. The purchase price for the shares that we may sell to Lincoln Park under the Purchase Agreement will fluctuate based on the price of our common stock. Depending on market liquidity at the time, sales of such shares may cause the trading price of our common stock to fall.

We generally have the right to control the timing and amount of any future sales of our shares to Lincoln Park. Additional sales of our common stock, if any, to Lincoln Park will depend upon market conditions and other factors to be determined by us. We may ultimately decide to sell to Lincoln Park all, some, or none of the additional shares of our common stock that may be available for us to sell pursuant to the Purchase Agreement. If and when we do sell shares to Lincoln Park, after Lincoln Park has acquired the shares, Lincoln Park may resell all, some or none of those shares at any time or from time to time in its discretion. Therefore, sales to Lincoln Park by us could result in substantial dilution to the interests of other holders of our common stock. Additionally, the sale of a substantial number of shares of our common stock to Lincoln Park, or the anticipation of such sales, could make it more difficult for us to sell equity or equity-related securities in the future at a time and at a price that we might otherwise wish to effect sales.

We may require additional financing to sustain our operations and without it we may not be able to continue operations.

The Company believes that its existing cash, and the potential proceeds available under the Purchase Agreement with Lincoln Park (assuming the Company is able to access the full amount), should be sufficient to fund the Company’s operations for at least the next twelve months. We have generated significant losses to date and expect to continue to incur significant operating losses as we advance our product candidates through drug development and the regulatory process. In the future, we will be dependent on obtaining funding from third parties, such as proceeds from the issuance of debt, sale of equity, funded research and development programs and payments under partnership and collaborative agreements, in order to maintain our operations and meet our obligations to licensors. There is no guarantee that debt, additional equity or other funding will be available to us on acceptable terms, or at all.

The extent we rely on Lincoln Park as a source of funding will depend on a number of factors including, the prevailing market price of our common stock and the extent to which we are able to secure working capital from other sources. If obtaining sufficient funding from Lincoln Park were to prove unavailable or prohibitively dilutive, we will need to secure another source of funding in order to satisfy our working capital needs. Even if we sell all $10,000,000 under the Purchase Agreement to Lincoln Park, we may still need additional capital to fully implement our business, operating and development plans. Should the financing we require to sustain our working capital needs be unavailable or prohibitively expensive when we require it, the consequences could be a material adverse effect on our business, operating results, financial condition and prospects.exercise date.

USE OF PROCEEDSThe pre-funded warrants and the warrants in this offering are speculative in nature.

This prospectus relates to sharesNeither the pre-funded warrants nor the warrants in this offering confer any rights of our common stock that may be offered and sold from timeownership on its holders, such as voting rights or the right to time by Lincoln Park. We will receive no proceeds fromdividends, but rather merely represent the sale ofright to acquire shares of common stock by Lincoln Park in this offering. Weat a fixed price, as the case may receive upbe, and, with respect to $10,000,000 in aggregate gross proceeds from any salesthe warrants, during a fixed period of our common stock to Lincoln Park under the Purchase Agreement aftertime. Specifically, commencing on the date of this prospectus. We will pay the expenses relating to the registration under the Securities Actissuance, holders of the offerpre-funded warrants may exercise their right to acquire common stock and sale by Lincoln Parkpay an exercise price of $0.01 per share at any time until the pre-funded warrants are exercised in full. Commencing on the date of issuance, holders of the shares covered by this prospectus, including legalwarrants may exercise their right to acquire common stock and accounting fees.pay an exercise price of $           per share of common stock. The warrants will be exercisable beginning on the date of issuance and expire on thefifth anniversary of the date of issuance.

Moreover, following this offering, the market value of the pre-funded warrants and the warrants, if any, is uncertain and there can be no assurance that the market value of the pre-funded warrants or the warrants will equal or exceed their imputed offering price. There can also be no assurance that the market price of the common stock will ever equal or exceed the exercise price of the warrants, and consequently, whether it will ever be profitable for holders of the warrants to exercise the warrants.

DIVIDEND POLICYUse of Proceeds

We estimate that the net proceeds to us from this offering will be approximately $            , based on an assumed public offering price per unit of $          , the last reported sale price of our common stock on The Nasdaq Capital Market on October           , 2019, assuming the sale of          units and no sale of any pre-funded units in this offering, after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us, and excluding the proceeds, if any, from the exercise of warrants issued pursuant to this offering. If the underwriter exercises its option to purchase the additional securities in full, we estimate that the net proceeds will be approximately $           million, based on an assumed public offering price per unit of $           , the last reported sale price of our common stock on The Nasdaq Capital Market on October           , 2019, assuming the sale of           units and no sale of any pre-funded units in this offering, after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us, and excluding the proceeds, if any, from the exercise of the warrants issued pursuant to this offering.

The actual offering price per unit and pre-funded unit, as applicable, will be as determined between us and the underwriter at the time of pricing, and may be at a discount to the current market price of our common stock. These estimates exclude the proceeds, if any, from the exercise of warrants in this offering. If all of the warrants sold in this offering were to be exercised in cash at an assumed exercise price of $           per unit, we would receive additional net proceeds of approximately $           million. However, the warrants contain a cashless exercise provision that permit exercise of the warrants on a cashless basis at any time where there is no effective registration statement under the Securities Act covering the issuance of the underlying shares. We cannot predict when or if these warrants will be exercised or whether they will be exercised for cash. It is possible that these warrants may be exercised solely on a cashless basis.

A $            increase or decrease in the assumed public offering price of $              per unit, which was the last reported sale price of our common stock on The Nasdaq Capital Market on October        , 2019, would increase or decrease the net proceeds to us from this offering by $                   million or $                   million, respectively, assuming that the number of units offered by us, as set forth on the cover page of this prospectus, remains the same, after deducting the estimated underwriter discounts and commissions and estimated offering expenses payable by us, assuming no sale of any pre-funded units and excluding the proceeds, if any, from the exercise of the warrants issued pursuant to this offering.

Similarly, each increase or decrease of               units offered by us would increase or decrease the net proceeds to us by approximately $                   million or $                   million, respectively, assuming the assumed public offering price of $          per unit remains the same, after deducting the underwriting discounts and commissions and estimated offering expenses payable by us, assuming no sale of any pre-funded units and excluding the proceeds, if any, from the exercise of the warrants issued pursuant to this offering.

We intend to use the net proceeds from this offering to fund the development of the Company’s immuno-oncology program, for other research and development activities and for general working capital needs. We may also use a portion of the net proceeds to acquire or invest in complementary businesses, products and technologies or to fund the development of any such complementary businesses, products or technologies that we may acquire in a stock-based acquisition. We have no current plans for any such acquisitions.

MARKET FOR Common Stock

Our common stock is listed on The Nasdaq Capital Market under the symbol “PHIO.”

As of September 27, 2019, there were approximately 64 holders of record of our common stock. Because many of our shares are held by brokers and other institutions on behalf of stockholders, we are unable to estimate the total number of individual stockholders represented by these holders of record.

dividend policy

We have never declared or paid any cash dividends and do not anticipate paying any cash dividends on our common stock in the foreseeable future. We expect to retain future earnings, if any, for use in our development activities and the operation of our business. The payment of any future dividends will be subject to the discretion of our Board of Directors and will depend, among other things, upon our results of operations, financial condition, cash requirements, prospects and other factors that our Board of Directors may deem relevant.

Dilution

Our net tangible book value as of June 30, 2019, was $9.7 million, or $0.39 per share of common stock. Net tangible book value per share represents total tangible assets less total liabilities, divided by the number of shares of common stock outstanding. Assuming that we issue only units (and no pre-funded units) at a per share public offering price of $           , the last reported sale price of our common stock on The Nasdaq Capital Market on October        , 2019, and after deducting the underwriting fees and estimated offering expenses payable by us, and excluding any proceeds received upon exercise of warrants issued pursuant to this offering, our net tangible book value as of June 30, 2019, would have been $           , or $           per share. This represents an immediate increase in net tangible book value of $           per share to existing stockholders and an immediate dilution in net tangible book value of $           per share to purchasers of common stock in this offering.

The following table illustrates this per-share dilution:

Each $           increase or decrease in the assumed public offering price of $           per unit, the last reported sale price of our common stock on The Nasdaq Capital Market on October            , 2019, would increase (decrease) our as adjusted net tangible book value per share after this offering by approximately $           or $           , respectively, and the dilution per share to new investors purchasing units in this offering by $           or $           , respectively, assuming the number of units offered by us, as set forth on the cover page of this prospectus, remains the same and after deducting underwriting fees and estimated offering expenses payable by us. We may also increase or decrease the number of units to be offered in this offering. Each increase or decrease of units offered by us would increase (decrease) our as adjusted net tangible book value per share by $          or $          , respectively, and the dilution per share to new investors purchasing units in this offering by $         or $         , respectively, assuming that the assumed public offering price remains the same, and after deducting underwriting fees and estimated offering expenses payable by us, and excluding any proceeds from the exercise of the warrants issued pursuant to this offering. The information discussed above is illustrative only and will be adjusted based on the actual public offering price and other terms of this offering as determined between us and the underwriter at pricing.

If the underwriter exercises its option to purchase additional securities in full, and assuming no sale of any pre-funded units in this offering, the as adjusted net tangible book value per share after this offering would be $         per share, the increase in net tangible book value per share to existing stockholders would be $         per share and the dilution to new investors purchasing units in this offering would be $         per share.

The number of shares of common stock outstanding used in the calculations above is based on 25,091,197 shares outstanding as of June 30, 2019, and excludes:

Except as otherwise indicated, the number of shares of common stock presented in this prospectus excludes: (i) no exercises by the underwriter of its option to purchase additional securities, (ii) no sale of any pre-funded units; (iii) no exercises of the warrants issued in this offering; and (iv) no exercise of the warrants issued to the underwriter in connection with this offering.

Furthermore, we may choose to raise additional capital through the sale of equity or convertible debt securities due to market conditions or strategic considerations even if we believe we have sufficient funds for our current or future operating plans. New investors will experience further dilution if any of our outstanding options or warrants are exercised, new options are issued and exercised under our equity incentive plans or we issue additional shares of common stock, other equity securities or convertible debt securities in the future.

Description of SECURITIES we are offering

Capital Stock

The following summary description of our capital stock is based on the provisions of our amended and restated certificate of incorporation and amended and restated bylaws and the applicable provisions of the Delaware General Corporation Law (“DGCL”). This information is qualified entirely by reference to the applicable provisions of our amended and restated certificate of incorporation, bylaws and the DGCL. For information on how to obtain copies of our amended and restated certificate of incorporation and bylaws, which are exhibits to the registration statement of which this prospectus is a part, see the sections titled "Where You Can Find More Information" and "Incorporation of Certain Information by Reference" in this prospectus.

General

Our authorized capital stock consists of 100,000,000 shares of common stock, par value $0.0001 per share and 10,000,000 shares of preferred stock, par value $0.0001 per share.

Common Stock

Holders of our common stock are entitled to one vote per share for the election of members of our board of directors and on all other matters that require stockholder approval. Holders of our common stock may not cumulate votes for the election of directors. Subject to any preferential rights of any outstanding preferred stock, in the event of our liquidation, dissolution or winding up, holders of our common stock are entitled to share ratably in the assets remaining after payment of liabilities and the liquidation preferences of any outstanding preferred stock. Holders of common stock have the right to receive dividends when, as and if, declared by the board of directors. The Company’s common stock does not carry any preemptive rights enabling a holder to subscribe for, or receive shares of, any class of our common stock or any other securities convertible into shares of any class of our common stock. There are no redemption or sinking-fund provisions applicable to the common stock.

Preferred Stock

The shares of preferred stock have such rights and preferences as our board of directors shall determine, from time to time, the board of directors may divide the preferred stock into any number of series and shall fix the designation and number of shares of each such series. Our board of directors may determine and alter the rights, powers, preferences and privileges, and qualifications, restrictions and limitations thereof, including, but not limited to, voting rights (if any), granted to and imposed upon any wholly unissued series of preferred stock. Our board of directors (within the limits and restrictions of any resolutions adopted originally fixing the number of shares of any series) may increase or decrease the number of shares of that series; provided, that no such decrease shall reduce the number of shares of such series to a number less than the number of shares of such series then outstanding, plus the number of shares reserved for issuance upon the exercise of outstanding options, rights or warrants or upon the conversion of any outstanding securities issued by the Corporation convertible into shares of such series.

Our common stock is subject to the express terms of our preferred stock and any series thereof. Our board of directors may issue preferred stock with voting, dividend, liquidation and other rights that could adversely affect the relative rights of the holders of the common stock.

Anti-Takeover Effects of Provisions of the Certificate of Incorporation and Bylaws

Certificate of Incorporation and Bylaw Provisions.Certain provisions of our certificate of incorporation and bylaws, which provisions are summarized in the following paragraphs, may have an anti-takeover effect and may delay, defer or prevent a takeover attempt that a stockholder might consider in its best interest, including those attempts that might result in a premium over the market price for the shares held by stockholders.

Filling Vacancies.Any vacancy on our board of directors, however occurring, including a vacancy resulting from an increase in the size of the board of directors, may only be filled by the affirmative vote of a majority of our directors then in office even if less than a quorum.

No Written Consent of Stockholders.Our certificate of incorporation provides that all stockholder actions are required to be taken by a vote of the stockholders at an annual or special meeting, and that stockholders may not take any action by written consent in lieu of a meeting.

Advance Notice Requirements.Our bylaws include advance notice procedures with regard to stockholder proposals relating to the nomination of candidates for election as directors or new business to be brought before meetings of our stockholders. These procedures provide that notice of stockholder proposals must be timely given in writing to our corporate secretary prior to the meeting at which the action is to be taken. Generally, to be timely, notice must be received at our principal executive offices not less than 90 days nor more than 120 days prior to the first anniversary date of the annual meeting for the preceding year. The notice must contain certain information specified in the amended and restated bylaws.

Amendment to Bylaws and Certificate of Incorporation.As required by the DGCL any amendment to our certificate of incorporation must first be approved by a majority of our board of directors and, if required by law or our certificate of incorporation, thereafter be approved by a majority of the outstanding shares entitled to vote on the amendment, and a majority of the outstanding shares of each class entitled to vote thereon as a class. Our bylaws may be amended by the affirmative vote of a majority vote of the directors then in office, subject to any limitations set forth in the bylaws.

Blank Check Preferred Stock.Our amended and restated certificate of incorporation provides for 10,000,000 authorized shares of preferred stock. The existence of authorized but unissued shares of preferred stock may enable our board of directors to render more difficult or to discourage an attempt to obtain control of the Company by means of a merger, tender offer, proxy contest, or otherwise. In this regard, the amended and restated certificate of incorporation grants the board of directors broad power to establish the rights and preferences of authorized and unissued shares of preferred stock. The issuance of shares of preferred stock could decrease the amount of earnings and assets available for distribution to holders of shares of common stock. The issuance may also adversely affect the relative rights and powers, including voting rights, of these holders and may have the effect of delaying, deterring, or preventing a change of control of the Company.

Exclusive Forum Provision in Certificate of Incorporation.Our certificate of incorporation provides that the Court of Chancery of the State of Delaware is the exclusive forum for the following types of actions or proceedings: any derivative action or proceeding brought on behalf of the Company, any action asserting a claim of breach of a fiduciary duty owed by any director, officer or other employee of the Company to the Company or the Company’s stockholders, any action asserting a claim against the Company arising pursuant to any provision of the DGCL or the Company’s certificate of incorporation or bylaws, or any action asserting a claim against the Company governed by the internal affairs doctrine. Despite the fact that the certificate of incorporation provides for this exclusive forum provision to be applicable to the fullest extent permitted by applicable law, Section 27 of the Securities and Exchange Act of 1934, as amended (the “Exchange Act”), creates exclusive federal jurisdiction over all suits brought to enforce any duty or liability created by the Exchange Act or the rules and regulations thereunder and Section 22 of the Securities Act of 1933, as amended (the “Securities Act”), creates concurrent jurisdiction for federal and state courts over all suits brought to enforce any duty or liability created by the Securities Act or the rules and regulations thereunder. As a result, this provision of the Company’s certificate of incorporation would not apply to claims brought to enforce a duty or liability created by the Securities Act, Exchange Act, or any other claim for which the federal courts have exclusive jurisdiction.

Delaware Business Combination Statute

Section 203 of the DGCL provides that, subject to exceptions set forth therein, an “interested stockholder” of a Delaware corporation shall not engage in any business combination, including mergers or consolidations or acquisitions of additional shares of the corporation, with the corporation for a three-year period following the date that such stockholder becomes an interested stockholder unless:

Except as otherwise set forth in Section 203, an “interested stockholder” is defined to include:

Section 203 may make it more difficult for a person who would be an interested stockholder to effect various business combinations with a corporation for a three-year period. We have not elected to be exempt from the restrictions imposed under Section 203. The provisions of Section 203 may encourage persons interested in acquiring us to negotiate in advance with our board of directors, since the stockholder approval requirement would be avoided if a majority of the directors then in office approves either the business combination or the transaction which results in any such person becoming an interested stockholder. Such provisions also may have the effect of preventing changes in our management. It is possible that such provisions could make it more difficult to accomplish transactions, which our stockholders may otherwise deem to be in their best interests.

Units

We are offering up to           units, with each unit consisting of one share of common stock and one warrant to purchase one share of our common stock. We are also offering to those purchasers, whose purchase of units in this offering would result in the purchaser, together with its affiliates and certain related parties, beneficially owning more than 4.99% of our outstanding common stock following the consummation of this offering, the opportunity to purchase, in lieu of units that would result in ownership in excess of 4.99% of our outstanding common stock, pre-funded units. Each pre-funded unit consists of one pre-funded warrant to purchase one share of common stock and one warrant to purchase one share of our common stock. For each pre-funded unit we sell, the number of units we are offering will be decreased on a one-for-one basis. The shares of common stock accompanying warrants included in each unit will be issued separately, and the pre-funded warrants to purchase one share of common stock and the accompanying warrants included in each pre-funded unit will be issued separately. Units or pre-funded units will not be issued or certificated. We are registering the shares of common stock included in the units and the shares of common stock issuable from time to time upon exercise of the pre-funded warrants included in the pre-funded units and the warrants included in the units and the pre-funded units offered hereby.

Description of Warrants

The material terms and provisions of the warrants being issued in this offering are summarized below. The following description is subject to, and qualified in its entirety by, the form of warrant, which has been filed as an exhibit to the registration statement of which this prospectus is a part. Prospective investors should carefully review the terms and provisions set forth in the form of warrant.

Exercise Price.The initial exercise price is $           per share of common stock. The exercise price is subject to appropriate adjustment in the event of certain stock dividends and distributions, stock splits, stock combinations, reclassifications or similar events affecting our common stock.

Exercisability.The warrants are exercisable at any time after the date of issuance, and at any time up to the date that is five years from the date of issuance, at which time any unexercised warrants will expire and cease to be exercisable. The warrants will be exercisable, at the option of each holder, in whole or in part by delivering to us a duly executed exercise notice and by payment in full in immediately available funds for the number of shares of common stock purchased upon such exercise. If a registration statement registering the issuance of the shares of common stock underlying the warrants under the Securities Act of 1933, as amended, is not then effective or available, the holder may only exercise the warrant through a cashless exercise, in whole or in part, in which case the holder would receive upon such exercise the net number of shares of common stock determined according to the formula set forth in the warrant. No fractional shares of common stock will be issued in connection with the exercise of a warrant. In lieu of fractional shares, we will either pay the holder an amount in cash equal to the fractional amount multiplied by the exercise price or round up to the next whole share.

Exercise Limitation.A holder will not have the right to exercise any portion of the warrant if the holder (together with its affiliates) would beneficially own in excess of 4.99% of the number of shares of our common stock outstanding immediately after giving effect to the exercise, as such percentage ownership is determined in accordance with the terms of the warrant. However, any holder may increase or decrease such percentage to any other percentage not in excess of 9.99%, provided that any increase in such percentage shall not be effective until 61 days after such notice to us.

Transferability.Subject to applicable laws, the warrants may not be offered for sale, sold, transferred or assigned without our consent. There is currently no trading market for the warrants and a trading market is not expected to develop.

Fundamental Transactions.In the event of a fundamental transaction, as described in the warrants and generally including any reorganization, recapitalization or reclassification of our common stock, the sale, transfer or other disposition of all or substantially all of our properties or assets, or our consolidation or merger with or into another person, the holders of the warrants will instead be entitled to receive upon exercise of the warrants the kind and amount of securities, cash or other property that the holders would have received had they exercised the warrants immediately prior to such fundamental transaction.

Exchange Listing.We do not plan to apply to list the warrants on The Nasdaq Capital Market, any other national securities exchange or any other nationally recognized trading system.

Rights as a Stockholder.Except as otherwise provided in the warrants or by virtue of such holder’s ownership of shares of our common stock, the holder of a warrant does not have the rights or privileges of a holder of our common stock, including any voting rights, until the holder exercises the warrant.

Description of Pre-Funded Warrants

The material terms and provisions of the pre-funded warrants being issued in this offering are summarized below. The following description is subject to, and qualified in its entirety by, the form of pre-funded warrant, which has been filed as an exhibit to the registration statement of which this prospectus is a part. Prospective investors should carefully review the terms and provisions set forth in the form of pre-funded warrant.

Purchasers whose purchase of units in this offering would result in the purchase, together with its affiliates and certain related parties, beneficially owning more than 4.99% of our outstanding common stock following the consummation of this offering, may purchase, in lieu of the number of units that would result in ownership in excess of 4.99% of our outstanding common stock, pre-funded units (each pre-funded unit consisting of one pre-funded warrant to purchase one share of our common stock and one warrant to purchase one share of our common stock) at a public offering price equal to the price per unit being sold to the public in this offering minus $0.01. Each pre-funded warrant included in the pre-funded units will have a per share exercise price of $0.01. Thus, the purchaser is essentially paying the purchase price for a unit at closing of the offering, but is not deemed to beneficially own the shares of common stock included in the units until the purchaser exercises the pre-funded warrant. Once purchased, the purchase price of the pre-funded warrants is not refundable. While the pre-funded warrants permit waiver of provisions by us and the holder of the pre-funded warrants, this would not affect the pre-funding as that is the purchase price of the instrument which is paid at the time of closing and becomes part of our proceeds received from this offering. In addition, the pre-funded warrants are perpetual and do not have an expiration date.

Exercise Price.The initial exercise price is $0.01 per share of common stock. The exercise price is subject to appropriate adjustment in the event of certain stock dividends and distributions, stock splits, stock combinations, reclassifications or similar events affecting our common stock.

Exercisability.The pre-funded warrants will be immediately exercisable and may be exercised at any time until the pre-funded warrants are exercised in full. The pre-funded warrants will be exercisable, at the option of each holder, in whole or in part by delivering to us a duly executed exercise notice and by payment in full in immediately available funds for the number of shares of common stock purchased upon such exercise. If a registration statement registering the issuance of the shares of common stock underlying the pre-funded warrants under the Securities Act of 1933, as amended, is not then effective or available, the holder may only exercise the pre-funded warrant through a cashless exercise, in whole or in part, in which case the holder would receive upon such exercise the net number of shares of common stock determined according to the formula set forth in the pre-funded warrant. No fractional shares of common stock will be issued in connection with the exercise of a pre-funded warrant. In lieu of fractional shares, we will either pay the holder an amount in cash equal to the fractional amount multiplied by the exercise price or round up to the next whole share.

Exercise Limitation.A holder will not have the right to exercise any portion of the pre-funded warrant if the holder (together with its affiliates) would beneficially own in excess of 4.99% of the number of shares of our common stock outstanding immediately after giving effect to the exercise, as such percentage ownership is determined in accordance with the terms of the pre-funded warrants. However, any holder may increase or decrease such percentage to any other percentage not in excess of 9.99%, provided that any increase in such percentage shall not be effective until 61 days after such notice to us.

Transferability.Subject to applicable laws, the pre-funded warrants may not be offered for sale, sold, transferred or assigned without our consent. There is currently no trading market for the pre-funded warrants and a trading market is not expected to develop.

Fundamental Transactions.In the event of a fundamental transaction, as described in the pre-funded warrants and generally including any reorganization, recapitalization or reclassification of our common stock, the sale, transfer or other disposition of all or substantially all of our properties or assets, or our consolidation or merger with or into another person, the holders of the pre-funded warrants will instead be entitled to receive upon exercise of the pre-funded warrants the kind and amount of securities, cash or other property that the holders would have received had they exercised the pre-funded warrants immediately prior to such fundamental transaction.

Exchange Listing.We do not plan to apply to list the pre-funded warrants on The Nasdaq Capital Market, any other national securities exchange or any other nationally recognized trading system.

Rights as a Stockholder.Except as otherwise provided in the pre-funded warrants or by virtue of such holder’s ownership of shares of our common stock, the holder of a pre-funded warrant does not have the rights or privileges of a holder of our common stock, including any voting rights, until the holder exercises the pre-funded warrant.

lincoln park TransactionUnderwriting

General

On August 7, 2019, weWe have entered into a purchasean underwriting agreement dated           , 2019, with Lincoln Park, which, as amended on August 20, 2019, we refer to in this prospectusH.C. Wainwright & Co., LLC as the “Purchase Agreement,” pursuantunderwriter of this offering. Subject to which Lincoln Parkthe terms and conditions of the underwriting agreement, we have agreed to sell to the underwriter and the underwriter has agreed to purchase from us, upat the public offering price less the underwriting discounts and commissions set forth on the cover page of this prospectus,           units and           pre-funded units. The public offering price shown on the cover page of this prospectus was determined by negotiation between us and the underwriter at the time of pricing and may be at a discount to an aggregate of $10,000,000 of our common stock (subject to certain limitations) from time to time over the termcurrent market price.

A copy of the Purchase Agreement. Also on August 7, 2019, we entered into a registration rightsunderwriting agreement with Lincoln Park, which we referhas been filed as an exhibit to in this prospectus as the “Registration Rights Agreement,” pursuant to which we have filed with the SEC the registration statement that includes this prospectus to register for resale under the Securities Act of 1933, as amended, or the “Securities Act,” the shares of common stock that have been or may be issued to Lincoln Park under the Purchase Agreement.

Following the execution of the Purchase Agreement, we issued 500,000 shares of common stock to Lincoln Park as consideration for its commitment to purchase shares of our common stock under the Purchase Agreement, which we refer to in this prospectus as the “Commitment Shares.” We do not have the right to commence any sales of our common stock to Lincoln Park under the Purchase Agreement until certain conditions set forth in the Purchase Agreement, all of which are outside of Lincoln Park’s control, have been satisfied, including that the registration statement of which this prospectus is a part is declared effectivepart. The securities we are offering are being offered by the Securities and Exchange Commission.underwriter subject to certain conditions specified in the underwriting agreement.

Thereafter, underWe have been advised by the terms andunderwriter that it proposes to offer the securities directly to the public at the public offering price set forth on the cover page of this prospectus. Any securities sold by the underwriter to securities dealers will be sold at the public offering price less a selling concession not in excess of $           per unit or pre-funded unit.

The underwriting agreement provides that the underwriter’s obligation to purchase the securities we are offering is subject to conditions contained in the conditions of the Purchase Agreement, we have the right to sell to Lincoln Park, and Lincoln Parkunderwriting agreement. The underwriter is obligated to purchase up to $10,000,000 of shares of our common stock, subject to certain limitations set forth in the Purchase Agreement, from time to time, over a 30-month period.

Under the Purchase Agreement, on any business day selected by the Company, the Company may direct Lincoln Park to purchase shares of our common stock in amounts up to 200,000 shares (or up to $50,000 in shares of common stock, whichever is greater) in a “regular purchase,” which amounts may be increased to up to 500,000 shares provided the market price of our common stock at the time of sale exceeds is not below certain threshold prices, as set forth in the Purchase Agreement, subject in each case to $1,000,000 in total purchase proceeds per purchase date. In addition to regular purchases, the Company may also direct Lincoln Park to purchase additional amounts as accelerated purchases or as additional purchases if the Company has utilized the Regular Purchase Amount in full and if the closing sale price of the Common Stock exceeds certain threshold prices, as set forth in the Purchase Agreement. The purchase price of the shares that may be sold to Lincoln Park under the Purchase Agreement will be based on the market price of our common stock preceding the time of sale as computed under the Purchase Agreement.

In accordance with applicable rules of The Nasdaq Capital Market, the Purchase Agreement also limits the Company’s issuance of shares of Common Stock to Lincoln Park thereunder to 5,015,730 shares of Common Stock, representing 19.99% of the shares of Common Stock outstanding on the date of the Purchase Agreement (the “Exchange Cap”) unless (a) stockholder approval is obtained to issue more than such amount or (b) the average price ofpay for all applicable sales of our common stock to Lincoln Park under the Purchase Agreement equals or exceeds the lower of (i) the closing price of our common stock on the Nasdaq Capital Market immediately preceding August 7, 2019 plus an incremental amount or (ii) the average of the closing price of our common stock on the Nasdaq Capital Market for the five Business Days immediately preceding August 7, 2019 plus an incremental amount, such that issuances and sales of our common stock to Lincoln Park under the Purchase Agreement would be exempt from the Exchange Cap limitation under applicable Nasdaq rules.

The Purchase Agreement also prohibits us from directing Lincoln Park to purchase any shares of common stock if those shares, when aggregated with all other shares of our common stock then beneficially owned by Lincoln Park and its affiliates, would result in Lincoln Park and its affiliates having beneficial ownership, at any single point in time, of more than 9.99% of the then total outstanding shares of our common stock, as calculated pursuant to Section 13(d) of the Securities Exchange Act of 1934, as amended, or the “Exchange Act,” and Rule 13d-3 thereunder, which limitation we refer to as the “Beneficial Ownership Cap”.

There are no trading volume requirements or restrictions under the Purchase Agreement, and we will control the timing and amount of any sales of our common stock to Lincoln Park. We may at any time in our sole discretion terminate the Purchase Agreement without fee, penalty or cost upon one business days’ notice. There are no restrictions on future financings, rights of first refusal, participation rights, penalties or liquidated damages in the Purchase Agreement or Registration Rights Agreement, other than a prohibition on entering into any “Variable Rate Transaction,” as defined in the Purchase Agreement. Lincoln Park may not assign or transfer its rights and obligations under the Purchase Agreement.

A total of 8,125,946 shares of our common stock are being offered under this prospectus, which may be less than the amount of shares issuable under the Purchase Agreement. As of August 23, 2019, there were 25,591,197 shares of our common stock outstanding, of which 25,124,081 shares were held by non-affiliates. If all of the 8,125,946 shares offered by Lincoln Park under this prospectus were issued and outstanding as of August 23, 2019, such shares would represent 24% of the total number of shares of our common stock outstanding and 25% of the total number of outstanding shares held by non-affiliates, in each case as of the date hereof; however, these percentages do not give effect to the prohibition contained in the Purchase Agreement that prevents us from selling and issuing to Lincoln Park shares of our common stock that would cause us to exceed the Exchange Cap or that would cause Lincoln Park and its affiliates to exceed the Beneficial Ownership Cap.

If we elect to issue and sell more than the 8,125,946 shares offered under this prospectus to Lincoln Park, which we have the right, but not the obligation, to do, we must first register for resale under the Securities Act any such additional shares, which could cause additional substantial dilution to our stockholders. The number of shares ultimately offered for resale by Lincoln Park is dependent upon the number of shares we sell to Lincoln Park under the Purchase Agreement.

Issuances of our common stock in this offering will not affect the rights or privileges of our existing stockholders, except that the economic and voting interests of each of our existing stockholders will be diluted as a result of any such issuance. Although the number of shares of common stock that our existing stockholders own will not decrease, the shares owned by our existing stockholders will represent a smaller percentage of our total outstanding shares after any such issuance to Lincoln Park.

Purchase of Shares Under the Purchase Agreement

Under the Purchase Agreement, on any business day selected by us, we may direct Lincoln Park to purchase up to 200,000 shares of our common stock on any such business day, which we refer to as a “Regular Purchase,” provided, however, that (i) the Regular Purchase may be increased to up to 300,000 shares, provided that the closing sale price is not below $0.60 on the purchase date, (ii) the Regular Purchase may be increased to up to 400,000 shares, provided that the closing sale price is not below $0.80 on the purchase date, and (iii) the Regular Purchase may be increased to up to 500,000 shares, provided that the closing sale price is not below $1.00 on the purchase date. In each case, the maximum amount of any single Regular Purchase may not exceed $1,000,000 per purchase. The purchase price per share for each such Regular Purchase will be equal to the lower of:

In addition to Regular Purchases described above, we may also direct Lincoln Park, on any business day on which we have properly submitted a Regular Purchase for the full amount of our common stock permitted on such business day, to purchase an additional amount of our common stock, which we refer to as an “Accelerated Purchase,” not to exceed the lesser of:

The purchase price per share for each such Accelerated Purchase will be equal to the lower of:

We may also direct Lincoln Park, not later than 1:00 p.m., Eastern time, on a business day on which an Accelerated Purchase has been completed and all of the shares to be purchased thereunder have been delivered to Lincoln Park in accordance with the Purchase Agreement prior to such time on such business day to purchase an additional amount of our common stock, which we refer to as an Additional Accelerated Purchase, of up to the lesser of:

The purchase price per share for each such Additional Accelerated Purchase will be equal to the lower of:

The Company has the right, in its sole discretion, to set a minimum price threshold for each Accelerated Purchase and Additional Accelerated Purchase in the notice provided with respect to such Accelerated Purchase and Additional Accelerated Purchase, and the Company may direct multiple Regular, Accelerated and Additional Accelerated Purchases in a day provided that delivery of shares has been completed with respect to any prior Regular, Accelerated and Additional Accelerated Purchases that Lincoln Park has purchased.

In the case of the Regular Purchases, Accelerated Purchases and Additional Accelerated Purchases, the purchase price per share will be equitably adjusted for any reorganization, recapitalization, non-cash dividend, stock split, reverse stock split or other similar transaction occurring during the business days used to compute the purchase price.

Other than as described above, there are no trading volume requirements or restrictions under the Purchase Agreement, and we will control the timing and amount of any sales of our common stock to Lincoln Park.

Events of Default

Events of default under the Purchase Agreement include the following:

Lincoln Park does not have the right to terminate the Purchase Agreement upon any of the events of default set forth above. During an event of default, all of which are outside of Lincoln Park’s control, we may not direct Lincoln Park to purchase any shares of our common stock under the Purchase Agreement.

Our Termination Rights

We have the unconditional right, at any time, for any reason and without any payment or liability to us, to give notice to Lincoln Park to terminate the Purchase Agreement. In the event of bankruptcy proceedings by or against us, the Purchase Agreement will automatically terminate without action of any party.

No Short-Selling or Hedging by Lincoln Park

Lincoln Park has agreed that neither it nor any of its affiliates shall engage in any direct or indirect short-selling or hedging of our common stock during any time prior to the termination of the Purchase Agreement.

Prohibitions on Variable Rate Transactions

There are no restrictions on future financings, rights of first refusal, participation rights, penalties or liquidated damages in the Purchase Agreement or Registration Rights Agreement other than a prohibition on entering into a “Variable Rate Transaction,” as defined in the Purchase Agreement.

Effect of Performance of the Purchase Agreement on Our Stockholders

All 8,125,946 shares registered in this offering which have been or may be issued or sold by us to Lincoln Park under the Purchase Agreement are expected to be freely tradable. It is anticipated that shares registered in this offering will be sold over a period of up to 30 months commencing on the date that the registration statement including this prospectus becomes effective. The sale by Lincoln Park of a significant amount of shares registered in this offering at any given time could cause the market price of our common stock to decline and to be highly volatile. Sales of our common stock to Lincoln Park, if any, will depend upon market conditions and other factors to be determined by us. We may ultimately decide to sell to Lincoln Park all, some or none of the additional shares of our common stock that may be available for us to sell pursuant to the Purchase Agreement. If and when we do sell shares to Lincoln Park, after Lincoln Park has acquired the shares, Lincoln Park may resell all, some or none of those shares at any time or from time to time in its discretion. Therefore, sales to Lincoln Park by us under the Purchase Agreement may result in substantial dilution to the interests of other holders of our common stock. In addition, if we sell a substantial number of shares to Lincoln Park under the Purchase Agreement, or if investors expect that we will do so, the actual sales of shares or the mere existence of our arrangement with Lincoln Park may make it more difficult for us to sell equity or equity-related securities in the future at a time and at a price that we might otherwise wish to effect such sales. However, we have the right to control the timing and amount of any additional sales of our shares to Lincoln Park and the Purchase Agreement may be terminated by us at any time at our discretion without any cost to us.

Pursuant to the terms of the Purchase Agreement, we have the right, but not the obligation, to direct Lincoln Park to purchase up to $10,000,000 of our common stock, exclusive of the 500,000 shares issued to Lincoln Park on such date as a commitment fee. Depending on the price per share at which we sell our common stock to Lincoln Park pursuant to the Purchase Agreement, we may need to sell to Lincoln Park under the Purchase Agreement more shares of our common stock than are offered under this prospectus in order to receive aggregate gross proceeds equal to the $10,000,000 total commitment available to us under the Purchase Agreement. If we choose to do so, we must first register for resale under the Securities Act such additional shares of our common stock, which could cause additional substantial dilution to our stockholders. The number of shares ultimately offered for resale by Lincoln Park under this prospectus is dependent upon the number of shares we direct Lincoln Park to purchase under the Purchase Agreement.

The Purchase Agreement prohibits us from issuing or selling to Lincoln Park under the Purchase Agreement (i) any shares of our common stock if those shares, when aggregated with all other shares of our common stock then beneficially owned by Lincoln Park and its affiliates, would exceed the Beneficial Ownership Cap and (ii) shares of our common stock in excess of the Exchange Cap, unless we obtain stockholder approval to issue shares in excess of the Exchange Cap or the average price of all applicable sales of our common stock to Lincoln Park under the Purchase Agreement equals or exceeds the lower of (a) the closing price of our common stock on the Nasdaq Capital Market immediately preceding August 7, 2019 plus an incremental amount or (b) the average of the closing price of our common stock on the Nasdaq Capital Market for the five Business Days immediately preceding August 7, 2019 plus an incremental amount, such that the transactions contemplated by the Purchase Agreement are exempt from the Exchange Cap limitation under applicable NASDAQ rules.

The following table sets forth the amount of gross proceeds we would receive from Lincoln Park from our sale of shares to Lincoln Park under the Purchase Agreement at varying purchase prices:

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DETERMINATION OF OFFERING PRICE

The prices at which the Shares covered by this prospectus may actually be sold will be determined by the prevailing public market price for shares of our common stock, by negotiations between the Selling Stockholder and buyers of our Common Stock in private transactions or as otherwise described in “Plan of Distribution.”

SELLING STOCKHOLDER

This prospectus relates to the possible resale by the Selling Stockholder, Lincoln Park, of shares of our common stock that have been or may be issued to Lincoln Park pursuant to the Purchase Agreement. We are filing the registration statement of which this prospectus forms a part pursuant to the provisions of the Registration Rights Agreement, which we entered into with Lincoln Park on August 7, 2019 concurrently with our execution of the Purchase Agreement, in which we agreed to provide certain registration rights with respect to sales by Lincoln Park of the shares of our common stock that have been or may be issued to Lincoln Park under the Purchase Agreement.

Lincoln Park, as the Selling Stockholder, may, from time to time, offer and sell pursuant to this prospectus any or all of the shares that we have issued or may issue to Lincoln Park under the Purchase Agreement. The Selling Stockholder may sell some, all or none of its shares. We do not know how long the Selling Stockholder will hold the shares before selling them, and we currently have no agreements, arrangements or understandings with the Selling Stockholder regarding the sale of any of the shares.

The following table presents information regarding the Selling Stockholder and the shares that it may offer and sell from time to time under this prospectus. The table is prepared based on information supplied to us by the Selling Stockholder, and reflects its holdings as of August 7, 2019. Neither Lincoln Park nor any of its affiliates has held a position or office, or had any other material relationship, with us or any of our predecessors or affiliates. Beneficial ownership is determined in accordance with Section 13(d) of the Exchange Act and Rule 13d-3 thereunder. The percentage of shares beneficially owned prior to the offering is based on 25,591,197 shares of our common stock actually outstanding as of August 23, 2019.

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PLAN OF DISTRIBUTION

The common stock offered by this prospectus is being offered by the Selling Stockholder, Lincoln Park. The common stock may be sold or distributed from time to time by the Selling Stockholder directly to one or more purchasers or through brokers, dealers, or underwriters who may act solely as agents at market prices prevailing at the time of sale, at prices related to the prevailing market prices, at negotiated prices, or at fixed prices, which may be changed. The sale of the common stock offered by this prospectus could be effected in one or more of the following methods:

In order to comply with the securities laws of certain states, if applicable, the shares may be sold only through registered or licensed brokers or dealers. In addition, in certain states, the shares may not be sold unless they have been registered or qualified for sale in the state or an exemption from the state’s registration or qualification requirement is available and complied with.

Lincoln Park is an “underwriter” within the meaning of Section 2(a)(11) of the Securities Act.

Lincoln Park has informed us that it intends to use an unaffiliated broker-dealer to effectuate all sales, if any, of the common stock that it may purchase from us pursuant to the Purchase Agreement. Such sales will be made at prices and at terms then prevailing or at prices related to the then current market price. Each such unaffiliated broker-dealer will be an underwriter within the meaning of Section 2(a)(11) of the Securities Act. Lincoln Park has informed us that each such broker-dealer will receive commissions from Lincoln Park that will not exceed customary brokerage commissions.

Brokers, dealers, underwriters or agents participating in the distribution of the shares as agents may receive compensation in the form of commissions, discounts, or concessions from the Selling Stockholder and/or purchasers of the common stock for whom the broker-dealers may act as agent. The compensation paid to a particular broker-dealer may be less than or in excess of customary commissions. Neither we nor Lincoln Park can presently estimate the amount of compensation that any agent will receive.

We know of no existing arrangements between Lincoln Park or any other stockholder, broker, dealer, underwriter or agent relating to the sale or distribution of the shares offered by this prospectus. At the time a particular offer of shares is made, a prospectus supplement, if required, will be distributed that will set forth the names of any agents, underwriters or dealers and any compensation from the Selling Stockholder, and any other required information.

We will pay the expenses incident to the registration, offering, and sale of the shares to Lincoln Park. We have agreed to indemnify Lincoln Park and certain other persons against certain liabilities in connection with the offering of shares of common stock offered hereby, including liabilities arising under the Securities Act or, if such indemnity is unavailable, to contribute amounts required to be paid in respect of such liabilities. Lincoln Park has agreed to indemnify us against liabilities under the Securities Act that may arise from certain written information furnished to us by Lincoln Park specifically for use in this prospectus or, if such indemnity is unavailable, to contribute amounts required to be paid in respect of such liabilities.

Lincoln Park has represented to us that at no time prior to the Purchase Agreement has Lincoln Park or its agents, representatives or affiliates engaged in or effected, in any manner whatsoever, directly or indirectly, any short sale (as such term is defined in Rule 200 of Regulation SHO of the Exchange Act) of our common stock or any hedging transaction, which establishes a net short position with respect to our common stock. Lincoln Park agreed that during the term of the Purchase Agreement, it, its agents, representatives or affiliates will not enter into or effect, directly or indirectly, any of the foregoing transactions.

We have advised Lincoln Park that it is required to comply with Regulation M promulgated under the Exchange Act. With certain exceptions, Regulation M precludes the selling stockholder, any affiliated purchasers, and any broker-dealer or other person who participates in the distribution from bidding for or purchasing, or attempting to induce any person to bid for or purchase any security which is the subject of the distribution until the entire distribution is complete. Regulation M also prohibits any bids or purchases made in order to stabilize the price of a security in connection with the distribution of that security. All of the foregoing may affect the marketability of the securities offered by this prospectus.

No action has been taken by us or the underwriter that would permit a public offering of our securities in any jurisdiction where action for that purpose is required. None of our securities included in this offering may be offered or sold, directly or indirectly, nor may this prospectus or any other offering material or advertisements in connection with the offer and sales of any of the securities be distributed or published in any jurisdiction, except under circumstances that will result in compliance with the applicable rules and regulations of that jurisdiction. Persons who receive this prospectus are advised to inform themselves about and to observe any restrictions relating to this offering of the securities and the distribution of this prospectus. This prospectus is neither an offer to sell nor a solicitation of any offer to buy the securities in any jurisdiction where that would not be permitted or legal.

The underwriter has advised us that it does not intend to confirm sales to any accounts over which it exercises discretionary authority.

Underwriting Discount, Commissions and Expenses

We have agreed to pay an underwriter discount of 7.5% of the aggregate gross proceeds raised in this offering.

The following table summarizes the public offering price, underwriting discounts and commissions and proceeds, before expenses to us. These amounts are shown assuming both no exercise and full exercise of the underwriter’s option to purchase additional securities.

We estimate the total expenses payable by us for this offering to be approximately $           , which amount includes (i) the underwriting discounts and commissions of $           ($           if the underwriter’s option to purchase additional securities is exercised in full), (ii) an assumed management fee in the amount of $           which represents 1.0% of the assumed aggregate offering price,(iii) a $40,000 non-accountable expense allowance payable to the underwriter, (iv) reimbursement of the accountable expenses of the underwriter equal to $100,000, including the legal fees of the underwriter being paid by us, and (v) other estimated expenses of approximately $           which includes legal, accounting, printing costs and various fees associated with the registration and listing of our shares.

Underwriter Warrants

We have agreed to issue to the underwriter warrants to purchase           shares of our common stock (equal to 7.5% of the aggregate number of shares underlying the units and pre-funded units sold in this offering). The underwriter warrants will have substantially the same terms as the terms of the warrants offered pursuant to this prospectus, except that the exercise price per share will be $           (equal to 125% of the public offering price for the shares sold in this offering). Pursuant to FINRA Rule 5110(g), the underwriter warrants and any shares issued upon exercise of the underwriter warrants shall not be sold, transferred, assigned, pledged, or hypothecated, or be the subject of any hedging, short sale, derivative, put or call transaction that would result in the effective economic disposition of the securities by any person for a period of 180 days immediately following the date of effectiveness or commencement of sales of this offering, except the transfer of any security: (i) by operation of law or by reason of our reorganization; (ii) to any FINRA member firm participating in the offering and the officers or partners thereof, if all securities so transferred remain subject to the lock-up restriction set forth above for the remainder of the time period; (iii) if the aggregate amount of our securities held by the underwriter or related persons do not exceed 1% of the securities being offered; (iv) that is beneficially owned on a pro rata basis by all equity owners of an investment fund, provided that no participating member manages or otherwise directs investments by the fund and the participating members in the aggregate do not own more than 10% of the equity in the fund; or (v) the exercise or conversion of any security, if all securities remain subject to the lock-up restriction set forth above for the remainder of the time period.

Right of First Refusal

We have also agreed, subject to certain conditions, to give the underwriter a twelve-month right of first refusal from the closing date of any securities offering consummated during the term of our engagement with the underwriter, to act as a lead book-running manager, lead underwriter or lead placement agent in any financing involving an underwriter or placement agent following the closing date of this offering. In addition, we will pay the underwriter a cash fee as provided under our engagement agreement with them equal to the underwriting discount percentage in this offering in the event that the offering contemplated hereby does not close and any investor contacted by the underwriter in connection with this offering (other than certain insider investors) purchases securities from us at any time between the termination of the offering and nine months after the date of termination or expiration of the offering.

Option to Purchase Additional Securities

We have granted the underwriter the option to purchase up to           additional shares of common stock at a purchase price of $           per share and/or warrants to purchase           shares of common stock at a purchase price of $0.01 per warrant with an exercise price of $           per share of common stock, less the underwriting discounts and commissions. The underwriter may exercise the option at any time and from time to time within 30 days from the date of this prospectus. If any additional shares of common stock and/or warrants are purchased pursuant to the option, the underwriter will offer these shares of common stock and warrants on the same terms as those on which the other units are being offered hereby.

Determination of Offering Price

The actual offering price of the securities we are offering will terminatebe negotiated between us and the underwriter based on the trading of our common stock prior to the offering, among other things, and may be at a discount to the current market price.

Lock-up Agreements

Pursuant to certain “lock-up” agreements, our executive officers and directors have agreed, subject to certain exceptions, not to offer, pledge, sell, contract to sell or otherwise transfer or dispose of, directly or indirectly, any shares or any securities convertible into or exercisable or exchangeable for shares, whether currently owned or subsequently acquired, without the prior written consent of the underwriter, for a period of 90 days from the date of effectiveness of the underwriting agreement. Pursuant to the underwriting agreement, we and our subsidiaries have agreed, subject to certain exceptions, not to issue, enter into any agreement to issue or announce the issuance or proposed issuance of any shares of common stock or common stock equivalents for a period of 90 days from the purchase and sale of securities by the underwriters and the Company, respectively, under the underwriting agreement.

Stabilization, Short Positions and Penalty Bids

The underwriter may engage in syndicate covering transactions, stabilizing transactions and penalty bids or purchases for the purpose of pegging, fixing or maintaining the price of our common stock:

•Syndicate covering transactions involve purchases of shares of common stock in the open market after the distribution has been completed in order to cover syndicate short positions. Such a naked short position would be closed out only by buying shares in the open market. A naked short position is more likely to be created if the underwriter is concerned that allafter pricing there could be downward pressure on the price of the shares offered byin the open market that could adversely affect investors who purchase in this prospectus have beenoffering.

• Stabilizing transactions permit bids to purchase shares of common stock so long as the stabilizing bids do not exceed a specified maximum and are engaged in for the purpose of preventing or retarding a decline in the market price of the shares of common stock while this offering is in progress.

•Penalty bids permit the underwriter to reclaim a selling concession from a syndicate member when the securities originally sold by Lincoln Park.the syndicate member are purchased in a stabilizing or syndicate covering transaction to cover syndicate short positions.

These syndicate covering transactions, stabilizing transactions and penalty bids may have the effect of raising or maintaining the market prices of our securities or preventing or retarding a decline in the market prices of our securities. As a result, the price of our common stock may be higher than the price that might otherwise exist in the open market. Neither we nor the underwriter make any representation or prediction as to the effect that the transactions described above may have on the price of our common stock. These transactions may be effected on The Nasdaq Capital Market, in the over-the-counter market or on any other trading market and, if commenced, may be discontinued at any time.

In connection with this offering, the underwriter also may engage in passive market making transactions in our common stock in accordance with Regulation M during a period before the commencement of offers or sales of shares of our common stock in this offering and extending through the completion of the distribution. In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for that security. However, if all independent bids are lowered below the passive market maker’s bid, that bid must then be lowered when specific purchase limits are exceeded. Passive market making may stabilize the market price of the securities at a level above that which might otherwise prevail in the open market and, if commenced, may be discontinued at any time.

Neither we nor the underwriter make any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the prices of our securities. In addition, neither we nor the underwriter make any representation that the underwriter will engage in these transactions or that any transactions, once commenced, will not be discontinued without notice.

Indemnification

We have agreed to indemnify the underwriter against certain liabilities, including certain liabilities arising under the Securities Act, or to contribute to payments that the underwriter may be required to make for these liabilities.

Other Relationships

The underwriter and its affiliates have engaged in, and may in the future engage in, investment banking and other commercial dealings in the ordinary course of business with us or our affiliates. They have received, or may in the future receive, customary fees and commissions for these transactions.

Listing

Our common stock is quotedlisted on The NASDAQNasdaq Capital Market under the symbol “PHIO”. We do not intend to apply for listing of the pre-funded warrants or the warrants on any securities exchange or other trading system.

Legal Matters

Certain legal matters relating to the issuance of the securities offered by this prospectus will be passed upon for us by Gibson, Dunn & Crutcher LLP, San Francisco, California. Certain legal matters in connection with this offering will be passed upon for the underwriter by Zysman, Aharoni, Gayer and Sullivan & Worcester LLP, New York, New York.

Experts

The consolidated financial statements as of December 31, 2018 and 2017 and for each of the two years in the period ended December 31, 2018 incorporated by reference in this prospectus have been so incorporated in reliance on the report of BDO USA, LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

Where You Can Find More Information

We are required to file annual, quarterly and current reports, proxy statements and other information with the Securities and Exchange Commission (“SEC”(the “SEC”). You may read and copy any document filed by us at the SEC’s Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549. Our filings with the SEC filings are also available to the public over the Internet at the SEC’s websiteInternet web site at http://www.sec.gov.www.sec.gov. Copies of certain information filed by us with the SEC are also available on our website at www.phiopharma.com.www.phiopharma.com. Our website is not a part of this prospectus and is not incorporated by reference in this prospectus, and you should not consider the contents of our website in making an investment decision with respect to our common stock.

This prospectus is part ofWe have filed a registration statement, that we filed withof which this prospectus is a part, covering the SEC. Thissecurities offered hereby. As allowed by SEC rules, this prospectus omits somedoes not include all of the information contained in the registration statement in accordance with SEC rules and regulations. the included exhibits, financial statements and schedules. You are referred to the registration statement, the included exhibits, financial statements and schedules for further information.You should review the information and exhibits in the registration statement for further information about us and our subsidiaries and the securities we are offering. Statements in this prospectus concerning any document we filed as an exhibit to the registration statement or that we otherwise filed with the SEC are not intended to be comprehensive and are qualified by reference to these filings. You should review the complete document to evaluate these statements.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCEincorporation of certain information by reference

The SEC allows us to “incorporate by reference” the information we have filed with them, which means that we can disclose important information to you by referring you to those documents. The information we incorporate by reference is an important part of this prospectus, and information that we file later with the SEC will automatically update and supersede this information. The documents we are incorporating by reference are:

All documents we file with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, except as to any portion of any report or document that is not deemed filed under such provisions, (1) on or after the date of filing of the registration statement containing this prospectus and prior to the effectiveness of the registration statement and (2) on or after the date of this prospectus until the earlier of the date on which all of the securities registered hereunder have been sold or the registration statement of which this prospectus is a part has been withdrawn, shall be deemed incorporated by reference in this prospectus and to be a part of this prospectus from the date of filing of those documents and will be automatically updated and, to the extent described above, supersede information contained or incorporated by reference in this prospectus and previously filed documents that are incorporated by reference in this prospectus.

Nothing in this prospectus shall be deemed to incorporate information furnished but not filed with the SEC pursuant to Item 2.02, 7.01 or 9.01 of Form 8-K.

Upon written or oral request, we will provide without charge to each person, including any beneficial owner, to whom a copy of the prospectus is delivered a copy of any or all of the reports or documents incorporated by reference herein (other than exhibits to such documents, unless such exhibits are specifically incorporated by reference herein). You may request a copy of these filings, at no cost, by writing or telephoning us at the following address: Phio Pharmaceuticals Corp., 257 Simarano Drive, Suite 101, Marlborough, Massachusetts 01752 Attention: Investor Relations, telephone: (508) 767-3861. We maintain a website at www.phiopharma.com. You may access our definitive proxy statements on Schedule 14A, annual reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K and periodic amendments to those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Exchange Act with the SEC free of charge at our website as soon as reasonably practicable after such material is electronically filed with, or furnished to, the SEC. The information contained in, or that can be accessed through, our website is not incorporated by reference in, and is not part of, this prospectus. We have not authorized any one to provide you with any information that differs from that contained in this prospectus. Accordingly, you should not rely on any information that is not contained in this prospectus. You should not assume that the information in this prospectus is accurate as of any date other than the date of the front cover of this prospectus.

Phio Pharmaceuticals Corp.

Up to             8,125,946 Units (each Unit consisting of one share of Common Stock and one Warrant to

purchase one share of Common Stock)

Up to            Pre-funded Units (each Pre-funded Unit consisting of one Pre-funded Warrant to

Purchase one share of Common Stock and one Warrant to purchase one share of Common Stock)

Shares of Common Stock Underlying the Pre-funded Warrants and

Shares of Common Stock Underlying the Warrants

PROSPECTUS

, 2019