Common Stock and Stock Warrants

3 Months Ended

Mar. 31, 2016

Equity [Abstract]

Common Stock and Stock Warrants

Common Stock and Stock Warrants

Shelf Registration Statement

We currently have an effective shelf registration statement on Form S-3 on file. Upon the effective date, the shelf registration statement permitted: (i) the offering, issuance and sale by us of up to a maximum aggregate offering price of $200.0 million of common stock, preferred stock, warrants, debt securities, and/or units in one or more offerings and in any combination; (ii) sales of up to 2.5 million shares of common stock by certain selling stockholders; and (iii) the offering, issuance and sale by us of up to a maximum aggregate offering price of $75.0 million of our common stock that may be issued and sold under an “at-the-market” sales agreement, or ATM, with Cantor Fitzgerald & Co.

In October 2015, we completed an additional follow-on public offering raising gross proceeds of $34.5 million leaving $165.5 million available under the shelf registration statement, $75.0 million of which could be offered, issued and sold under the ATM. Under this follow-on public offering we sold 6,272,727 shares of our common stock, which includes an additional 818,181 shares of our common stock sold upon full exercise of the underwriter's option to purchase additional shares of common stock, at a price to the public of $5.50 per share. The net proceeds to us from the follow-on offering were $32.1 million after deducting underwriting discounts and commissions of $2.1 million and estimated offering expenses of $280,000.

Through March 2016, we raised gross proceeds of $4.5 million pursuant to the ATM, leaving $161.0 million available under the shelf registration statement, of which $70.5 million may be offered, issued and sold at a future date under the ATM. As of March 31, 2016, we had sold 499,000 shares of our common stock at a weighted average price of $8.95 per share under the ATM. The net proceeds to us from these follow-on offerings was $4.3 million, after deducting underwriter commissions of $134,000 and estimated offering expenses of $75,000.

Stock Reserved for Future Issuance

Shares reserved for future issuance at March 31, 2016 are as follows:

	Number of Shares
Common stock options outstanding	3,733,711
Common stock options available for future grant	345,486
Common stock warrants	250,539
Total common shares reserved for future issuance	4,329,736

Stock Warrants

We issued warrants to purchase redeemable convertible preferred stock in connection with financing activities or for consulting services. In connection with the junior preferred stock financing in February 2012, all warrants to purchase Series B, Series C, and Series D preferred stock converted to common stock warrants. We had warrants outstanding and exercisable for 250,539 and 250,646 shares of common stock as of March 31, 2016 and December 31, 2015, respectively, as all 107 of the Series B warrants expired during the quarter ended March 31, 2016.

The following table summarizes the outstanding warrants as of March 31, 2016:

	Warrants Outstanding	Exercise Price		Expiration Date
Series C	9,919	$	147.91	11/20/2016
Series D	240,620	$	92.99	9/25/2019
Total warrants outstanding	250,539