The Company has authorized 150,000,000 shares of common stock, $0.0001 par value per share, of which 57,139,892 shares and 55,603,427 shares were issued and outstanding as of March 31, 2018 and December 31, 2017, respectively.

During the three months ended March 31, 2018 and 2017, the Company issued 36,465 and 160,549 shares of common stock upon the exercise of stock options to purchase common stock and the Company received proceeds of $156,655 and $80,248 from these exercises, respectively.

On January 5, 2018, the Company entered into a sales agreement with Cantor Fitzgerald under which the Company may direct Cantor Fitzgerald as its sales agent to sell common stock up to an aggregate offering of up to $50 million under an “At the Market Offering” (“January 2018 Sales Agreement”). Sales of common stock under the January 2018 Sales Agreement were made pursuant to an effective registration statement for an aggregate offering of up to $50 million. In the first quarter of 2018, the Company sold 1,500,000 shares of its common stock to an institutional investor under the January 2018 Sales Agreement for which the Company received net proceeds of approximately $11.2 million. In the first quarter of 2017, the Company sold 1,413,633 shares of its common stock under a sales agreement that the Company entered into in November 2016 with Cantor Fitzgerald (“Sales Agreement”) for net proceeds of $13,268,208. The Sales Agreement was terminated in October 2017.

On February 28, 2017, the Company entered in a securities purchase agreement providing for the issuance and sale by the Company of 3,887,815 shares of its common stock in a registered direct offering to institutional and accredited investors at a purchase price of $7.00 per share with gross proceeds to the Company totaling $27,214,705 less issuance costs of $36,291.