On December 28, 2018, the Company entered into an At-the-Market Equity Offering Sales Agreement (the “2018 Sales Agreement”) with Stifel, as sales agent, pursuant to which the Company can sell through Stifel, from time to time, up to $75.0 million in shares of common stock in an at-the-market offering. The Company pays Stifel a commission of approximately 3% of the aggregate gross proceeds received from all sales of common stock under the 2018 Sales Agreement. Unless otherwise terminated earlier, the 2018 Sales Agreement continues until all shares available under the Sales Agreement have been sold or termination of the 2018 Sales Agreement by the Company or by Stifel. As of December 31, 2018, there were no sales of common stock under the 2018 Sales Agreement.

On April 28, 2017, the Company sold 24.9 million units, each consisting of one share of the Company’s common stock, a Series A warrant to purchase one share of common stock, and a Series B warrant to purchase 0.75 shares of common stock, at a public offering price of $1.00 per unit for aggregate gross proceeds of $24.9 million in an underwritten firm commitment public offering. Net proceeds after issuance costs were $23.2 million, assuming no exercise of the warrants. The closing of the public offering occurred on May 3, 2017.

On December 16, 2016, the Company entered into a purchase agreement (the “LPC Purchase Agreement”) with Lincoln Park Capital Fund, LLC, (“Lincoln Park”), pursuant to which the Company had the right to sell to Lincoln Park up to an aggregate of $25.0 million in shares of the Company’s common stock, (the “Common Stock”), subject to certain limitations and conditions set forth in the LPC Purchase Agreement. The Company issued to Lincoln Park 345,421 shares of Common Stock as commitment shares in consideration for the LPC Purchase Agreement through April 27, 2017. Sales under the LPC Purchase Agreement for the year ended December 31, 2016 were 300,000 shares, with gross proceeds of $412,500 and net proceeds of $392,500. Sales under the LPC Purchase Agreement for the year ended December 31, 2017 were 3,972,741 shares, with gross and net proceeds of $5,304,000. Effective April 27, 2017, the Company terminated the LPC Purchase Agreement. The LPC Purchase Agreement provided the Company with an election to terminate the Purchase Agreement for any reason or for no reason by delivering a notice to Lincoln Park, and the Company did not incur any early termination penalties in connection with the termination of the LPC Purchase Agreement.

On February 20, 2015, the Company entered into a Controlled Equity Offering SM Sales Agreement (the “2015 Sales Agreement”) with Cantor Fitzgerald & Co. (“Cantor”), as sales agent, pursuant to which the Company sold through Cantor, from time to time, up to $25.0 million in shares of common stock in an at-the-market offering. The Company paid Cantor a commission of approximately 3% of the aggregate gross proceeds received from all sales of common stock under the 2015 Sales Agreement.

On February 9, 2016, the Company entered into a Controlled Equity Offering SM Sales Agreement (the “2016 Sales Agreement”) with Cantor, as sales agent, pursuant to which the Company can sell through Cantor, from time to time, up to $43.6 million in shares of common stock in an at-the-market offering. The Company paid Cantor a commission of approximately 3% of the aggregate gross proceeds received from all sales of common stock under the 2016 Sales Agreement.

On August 31, 2017, the Company entered into an At-the-Market Equity Offering Sales Agreement (the “2017 Sales Agreement”) with Stifel, Nicolaus & Company, Incorporated (“Stifel”), as sales agent, pursuant to which the Company sold through Stifel, up to $50.0 million in shares of common stock in an at-the-market offering. The Company paid Stifel a commission of approximately 3% of the aggregate gross proceeds received from all sales of common stock under the 2017 Sales Agreement.

The amounts offered and sold under the 2015 Sales Agreement, 2016 Sales Agreement and the 2017 Sales Agreement are as set forth below (in thousands, except per share amounts):

	2017 Sales Agreement		2016 Sales Agreement		2015 Sales Agreement
	Year Ended December 31, 2017		Year Ended December 31, 2016		Year Ended December 31, 2016		Year Ended December 31, 2015
Total shares of common stock sold		15,998.5		8,763.4		5,710.2		2,014.3
Average price per share	$	3.13	$	4.70	$	3.23	$	3.25
Gross proceeds	$	50,000	$	41,156	$	18,454	$	6,546
Commissions earned by Cantor	$	1,500	$	1,235	$	553	$	197
Other issuance costs	$	97	$	185	$	—	$	259