Stockholders' Equity (Tables)

9 Months Ended

Sep. 30, 2018

Summary of the Company's Outstanding Common Stock Warrants

The following is a summary of the Company’s outstanding common stock warrants:


	Exercise Price	September 30, 2018		December 31, 2017
Expiration Date	Exercise Price	(in thousands)
04/16/18	$ 3.40		—		1,460
09/23/18	$ 2.80		—		147
02/11/19	$ 2.56		293		293
02/18/19	$ 2.75		1,872		1,872
08/28/19	$ 2.90		2,700		2,700
03/20/20	$ 2.13		234		234
03/25/20	$ 1.71		2,920		2,920
04/12/20	$ 0.40		7,437		—
06/20/20	$ 0.40		7,437		—
04/30/23	$ 0.20		1,488		—

Total Warrants Outstanding			24,381		9,626

Summary of the Company's Stock Option Activity under Equity Incentive Plans

The following is a summary of the Company’s stock option activity under its equity incentive plans:


	Options Available for Grant			Options Outstanding			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life		Aggregate Intrinsic Value
	(in thousands)								(years)		(in thousands)
Balance at December 31, 2017		1,846			4,880		$	1.05		7.6	$	—
Options authorized		2,524			—
Options granted		(3,033	)		3,033		$	0.22
Options forfeited		1,127			(1,127	)	$	0.61

Balance at September 30, 2018		2,464			6,786		$	0.75		7.3	$	—

Vested and exercisable at September 30, 2018					3,080		$	0.88		6.8	$	—
Vested and expected to vest at September 30, 2018					6,099		$	0.61		7.3	$	—
Unvested at September 30, 2018					3,706		$	0.64

Weighted-Average Assumptions

The fair value for stock options granted is estimated at the date of grant using the Black-Scholes option pricing model. The Company used the following weighted average assumptions to estimate the fair value of the stock options.


	Nine months ended September 30,
	2018			2017
Risk-free interest rate		2.8	%		2.0	%
Expected life (years)		5.2			6.0
Expected volatility		88	%		88	%
Dividend yield		0	%		0	%

- Definition

Tabular disclosure of warrants or rights issued. Warrants and rights outstanding are derivative securities that give the holder the right to purchase securities (usually equity) from the issuer at a specific price within a certain time frame. Warrants are often included in a new debt issue to entice investors by a higher return potential. The main difference between warrants and call options is that warrants are issued and guaranteed by the company, whereas options are exchange instruments and are not issued by the company. Also, the lifetime of a warrant is often measured in years, while the lifetime of a typical option is measured in months. Disclose the title of issue of securities called for by warrants and rights outstanding, the aggregate amount of securities called for by warrants and rights outstanding, the date from which the warrants or rights are exercisable, and the price at which the warrant or right is exercisable.

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