operational, commercial, financial and management personnel, and external research and development expenses, such as clinical trials and preclinical activity related to our product candidates.
As of June 30, 2021, we had cash, cash equivalents and marketable securities totaling $323.8 million compared to $284.1 million as of December 31, 2020, with the increase attributable to net proceeds of $130.2 million (reflecting $2.4 million in commissions plus other transaction expenses) raised from the sale of 1,087,126 shares under our
sales agreement, partially offset by funding of operations. Our cash and investment balances are held in a variety of interest bearing instruments, including obligations of U.S. government agencies, U.S. Treasury debt securities, corporate debt securities and money market funds. Cash in excess of immediate requirements is invested in accordance with our investment policy with a view toward capital preservation and liquidity.
We anticipate continuing to incur operating losses for the foreseeable future. While our rate of cash usage will likely increase in the future, in particular to support our product development and clinical trial efforts, we believe our available cash resources as of June 30, 2021 will be sufficient to fund our operations past one year from the issuance of the financial statements contained herein, and this outlook takes into account circumstances that are currently reasonably foreseeable in connection with the
COVID-19
pandemic. For a description of
COVID-19
pandemic risks, including risks and uncertainties beyond our control, see Part I, Item 1A, “Risk Factors” on Form
10-K
for the year ended December 31, 2020, filed with the SEC on February 25, 2021. Our future long-term liquidity requirements will be substantial and will depend on many factors. To meet future long-term liquidity requirements, we will need to and intend to raise additional capital to fund our operations, primarily through equity or debt financings. We regularly consider fundraising opportunities and may decide, from time to time, to raise capital based on various factors, including market conditions and our plans of operation. This includes, but is not limited to, the use of the $200 million
sales agreement. Additional capital may not be available on terms acceptable to us, or at all. If adequate funds are not available, or if the terms of potential funding sources are unfavorable, our business and our ability to develop our product candidates would be harmed. Furthermore, any sales of additional equity securities may result in dilution to our stockholders, and any debt financing may include covenants that restrict our business.
The following table provides a summary of our net cash flow activity (in thousands):
| | | | | | | | |
| | Six Months Ended June 30, | |
| | | | | | |
|
Net cash used in operating activities | | $ | (90,310 | ) | | $ | (54,764 | ) |
Net cash (used in) provided by investing activities | | | (60,789 | ) | | | 69,825 | |
Net cash provided by financing activities | | | 130,635 | | | | 109 | |
| | | | | | | | |
Net (decrease) increase in cash and cash equivalents | | $ | (20,464 | ) | | $ | 15,170 | |
Net cash used in operating activities was $90.3 million for the six months ended June 30, 2021, compared to $54.8 million for the corresponding period in 2020. The use of cash in these periods resulted primarily from our losses from operations, as adjusted for
non-cash
charges for stock-based compensation, and changes in our working capital accounts.
Net cash used in investing activities was $60.8 million for the six months ended June 30, 2021, compared to $69.8 million provided for the corresponding period in 2020. Net cash used in investing activities for the six months ended June 30, 2021 consisted of $224.1 million of purchases of marketable securities for our investment portfolio, partially offset by $163.3 million from sales and maturities of marketable securities. Net cash provided by investing activities for the six months ended June 30, 2020 consisted of $224.0 million from sales and maturities of marketable securities, partially offset by $153.9 million of purchases of marketable securities for our investment portfolio and $0.3 million of purchases of property and equipment.
Net cash provided by financing activities was $130.6 million for the six months ended June 30, 2021, which consisted of $130.2 million from net proceeds from issuances of stock under our ATM and proceeds from the exercise of stock options. Financing activities for the corresponding period in 2020 consisted of proceeds from the exercise of stock options.