Stockholders' Equity And Stock-Based Compensation | 6. Stockholders’ Equity and Stock-Based Compensation At-the-Market Equity Offering On February 4, 2021, the Company entered into a sales agreement (Sales Agreement) with Stifel, Nicolaus & Company, Inc. (Stifel) as sales agent, pursuant to which the Company may offer and sell, from time to time, through Stifel, up to $ 60.0 million in shares of common stock, by any method permitted by law deemed to be an “at-the-market” offering as defined in Rule 415 promulgated under the Securities Act of 1933, as amended. The Company has no obligation to make any sales of its common stock pursuant to such Sales Agreement. During the three-month period ended March 31, 2021, the Company issued and sold 157,742 shares of common stock under the Sales Agreement. The shares were sold at a weighted average price of $ 34.29 per share for aggregate net proceeds of approximately $ 5.0 million, after deducting sales commissions and offering costs payable by the Company. At March 31, 2021, the Company had received $ 4.9 million of the net proceeds, which are included in cash and cash equivalents on the balance sheet, and has recorded $ 0.1 million as other receivable due to timing of receipt of funds. Rights Offering During June 2020, the Company completed a rights offering to purchase up to $ 30 million of units, each unit consisting of one share of the Company’s common stock, par value $ 0.001 per share, and 0.15 warrants to purchase shares of common stock (the Units) at a price of $ 7.01 per Unit (the Rights Offering). The common stock and warrants comprising the Units separated upon the closing of the Rights Offering and were issued separately. A total of 4,279,600 shares of common stock and 641,571 warrants (Rights Offering Warrants) were issued and sold in the Rights Offering for net proceeds of approximately $ 29.4 million. Each warrant was exercisable for one share of the Company’s common stock at an exercise price equal to $ 7.01 , the subscription price for the Units. The Rights Offering Warrants were exercisable immediately and expired on the fifth anniversary of the completion of the Rights Offering, or June 16, 2025, subject to certain redemption rights by the Company. The Rights Offering Warrants were subject to redemption by the Company, on or after December 16, 2020, six months after the issue date, for $ 0.01 per warrant, with not less than 30 days written notice, if the volume weighted average price of our common stock equaled or exceeded 200 % of the exercise price for the Rights Offering Warrants for 10 consecutive trading days. Robert W. Duggan, principal stockholder and Chairman of the board of directors, who was the beneficial owner of approximately 43 % of the Company’s outstanding common stock prior to the Rights Offering, participated in the Rights Offering and purchased an aggregate of 2,561,873 Units. After giving effect to the Rights Offering, including exercise of the Rights Offering Warrants, Mr. Duggan is the beneficial owner of approximately 47 % of the Company’s outstanding common stock as of March 31, 2021. Common Stock Warrants In connection with a private placement in 2014 of the Company’s common stock, par value $ 0.001 per share, the Company issued warrants as compensation to the placement agent to purchase a total of 299,625 shares of its common stock at an exercise price of $ 2.67 per share (Private Placement Warrants). The Private Placement Warrants are exercisable for period of seven years from issuance. In March 2021, warrants to purchase 45,638 shares of common stock were net exercised, resulting in the issuance of 40,563 shares of common stock. As of March 31, 2021, there were a total of 600 of Private Placement Warrants outstanding. In connection with the closing of the Company’s initial public offering in 2016, the Company issued warrants as compensation to its underwriters, to purchase a total of 574,985 shares of its common stock at an exercise price of $ 5.00 per share (IPO Warrants). The IPO Warrants were exercisable for a period of five years from issuance. In March 2021, warrants to purchase 85,385 shares of common stock were net exercised, resulting in the issuance of 68,958 shares of common stock. As of March 31, 2021, there were no IPO Warrants outstanding. In connection with the Rights Offering , the Company issued warrants to purchase a total of 641,571 shares of it s common stock at an exercise price of $ 7.01 . On December 31, 2020 the Company met the requirements for redemption of these warrants and delivered a notice of redemption to redeem all of the outstanding warrants that remained unexercised at February 5, 2021, for the redemption price of $ 0.01 per warrant. Pursuant to the redemption, the Company redeemed 5,139 warrants. Prior to the February 5, 2021 redemption date, 636,432 warrants were exercised, generating approximately $ 4.5 million of total gross proceeds to the Company. As of March 31, 2021, there were no Rights Offering Warrants outstanding . Equity Plans 2017 Equity Incentive Plan and 2017 Inducement Equity Incentive Plan The Board of Directors of the Company (Board) previously adopted, and the Company’s stockholders approved, the Company’s 2017 Equity Incentive Plan (2017 Plan). The 2017 Plan has a 10 -year term, and provides for the grant of stock options, stock appreciation rights, restricted stock, restricted stock units, performance units, and performance shares to employees, directors and consultants of the Company and any parent or subsidiary of the Company, as the Compensation Committee of the Board may determine. Subject to an annual evergreen increase and adjustment in the case of certain capitalization events, the Company initially reserved 1,500,000 shares of the Company’s common stock for issuance pursuant to awards under the 2017 Plan. In addition, shares remaining available under the Company’s 2015 Equity Incentive Plan, as amended (2015 Plan), and shares reserved but not issued pursuant to outstanding equity awards that expire or terminate without being exercised or that are forfeited or repurchased by the Company will be added to the shares of common stock available for issuance under the 2017 Plan. The 2017 Plan is administered by the Board’s Compensation Committee. Effective January 1, 2021, the Company’s Board authorized an increase in the number of shares of common stock available under the 2017 Plan by 1,022,002 shares pursuant to the evergreen provision of the 2017 Plan. Pursuant to the 2017 Plan, the 2021 share increase is determined based on the least of (i) 1,200,000 shares, (ii) 4 % of the Company’s common stock outstanding at December 31 of the immediately preceding year, or (iii) such number of shares as determined by the Board. As of March 31, 2021, 998,290 shares of common stock remained available for issuance under the 2017 Plan. During November 2017, the Board adopted the 2017 Inducement Equity Incentive Plan (Inducement Plan) and reserved 1,000,000 shares of the Company’s common stock for issuance pursuant to equity awards granted under the Inducement Plan. The Inducement Plan was adopted without stockholder approval. The Inducement Plan has a 10 -year term, and provides for the grant of equity-based awards, including nonstatutory stock options, restricted stock units, restricted stock, stock appreciation rights, performance shares and performance units, and its terms are substantially similar to the 2017 Plan, including with respect to treatment of equity awards in the event of a “merger” or “change in control” as defined under the Inducement Plan. Options issued under the Inducement Plan may have a term up to ten years and have variable vesting provisions. New hire grants generally vest 25 % annual starting upon the first anniversary of the grant. Equity-based awards issued under the Inducement Plan are only issuable to individuals not previously engaged as employees or non-employee directors of the Company prior to the Inducement Plan’s adoption date. As of March 31, 2021, 23,346 shares of common stock remained available for issuance under the Inducement Plan. Certain stock options awarded to the Company’s executives and other key employees contain performance conditions related to certain financial measures and achievements of strategic/operational milestones (performance options). As of March 31, 2021, not all of the performance conditions are probable to be achieved. Compensation expense has only been recognized for those conditions that are assumed to be probable. During February 2021, Management and the Compensation Committee approved of a modification to certain vesting conditions of outstanding performance options. The Company had no t recognized any compensation expense in relation to these performance options as the performance condition was previously deemed to be improbable. However, upon modification those specific performance conditions are now deemed probable and fully vested. As such, during the three-month period ended March 31, 2021, the full expense in relation to the amended performance conditions was recognized resulting in $ 4.2 million of additional stock-compensation expense. 2017 Employee Stock Purchase Plan The Board previously adopted and the stockholders approved the Company’s 2017 Employee Stock Purchase Plan (2017 ESPP). The 2017 ESPP is a broad-based plan that provides employees of the Company and its designated affiliates with the opportunity to become stockholders through periodic payroll deductions that are applied towards the purchase of Company common shares at a discount from the then-current market price. Subject to adjustment in the case of certain capitalization events, a total of 250,000 common shares of the Company were available for purchase at adoption of the 2017 ESPP. Pursuant to the 2017 ESPP, the annual share increase pursuant to the evergreen provision is determined based on the least of (i) 450,000 shares, (ii) 1.5 % of the Company’s common stock outstanding at December 31 of the immediately preceding year, or (iii) such number of shares as determined by the Board. Effective January 1, 2021, pursuant to the evergreen provision of the 2017 ESPP, the number of shares of common stock available under the 2017 ESPP was increased by 383,250 shares. During the three-month period ended March 31, 2021, the Company issued 68,057 shares of common stock under the 2017 ESPP. As of March 31, 2021, 672,417 shares of common stock remained available for issuance under the 2017 ESPP. A summary of stock option activity under the 2015 Plan, 2017 Plan and Inducement Plan for the three-months ended March 31 , 2021 is presented below: Stock Options Outstanding Weighted Number average of shares exercise price Balances — December 31, 2020 5,039,194 $ 14.26 Options granted 608,815 Options exercised ( 39,981 ) Options canceled ( 68,654 ) Options expired ( 62,738 ) Balances — March 31, 2021 5,476,636 $ 15.47 Exercisable — March 31, 2021 2,905,929 $ 16.13 Stock-based Compensation Total stock-based compensation expense consisted of the following (in thousands): Three-Month Periods Ended March 31, 2021 2020 Research and development $ 3,166 $ 877 Sales and marketing 1,761 310 General and administrative 2,038 1,439 Total stock-based compensation expense $ 6,965 $ 2,626 The Company estimated the fair value of employee stock options on the grant date using the Black-Scholes option pricing model . The estimated fair value of employee stock options is amortized on a straight-line basis over the requisite service period of the awards. The Company reviews, and when deemed appropriate, updates the assumptions used on a periodic basis. Due to the limited trading history of the Company’s common stock, the Company utilizes a portfolio of comparable companies to estimate volatility. The fair value of employee stock options was estimated using the following weighted-average assumptions: Three-Month Periods Ended March 31, 2021 2020 Expected term in years 6.1 6.1 Expected volatility 78 % 70 % Risk-free interest rate 1.0 - 1.1 % 0.4 - 1.7 % Dividend yield — — The Company estimated the fair value of ESPP on the grant date using the Black-Scholes option pricing model . The estimated fair value of ESPP is amortized on a straight-line basis over the requisite service period of the awards. The Company reviews, and when deemed appropriate, updates the assumptions used on a periodic basis. The Company utilizes its estimated volatility in the Black-Scholes option pricing model to determine the fair value of ESPP. The fair value of ESPP was estimated using the following weighted-average assumptions: Three-Month Periods Ended March 31, 2021 2020 Expected term in years 0.5 - 1.0 0.5 - 1.0 Expected volatility 91 % 70 % Risk-free interest rate 0.07 - 0.08 % 0.9 - 1.0 % Dividend yield — — |