9. Equity Incentive Plans

Stock options

The Company had granted stock options under an amended and restated 1997 Equity Incentive Plan (the “1997 Plan”) and a 2008 Equity Incentive Plan (the “2008 Plan”). The plans provided for the granting of incentive and non-statutory options and stock awards to consultants, directors, officers and employees. Such options are exercisable for a period of ten years and generally vest over a four-year period. In conjunction with the adoption of the 2008 Plan in April 2008, no additional grants were made from the 1997 Plan and issued options from the 1997 Plan remain outstanding. In 2014, the Board approved the 2014 Equity Incentive Plan (the “2014 Plan”). The 2014 Plan is the successor to the Company’s 2008 Plan and 1997 Plan. In conjunction with the adoption of the 2014 Plan in 2014, no additional grants were made from the 2008 Plan and options from the 1997 Plan and the 2008 Plan remain outstanding. In June 2018, the 2014 Plan was amended and restated and the Amended and Restated 2014 Incentive Compensation is now referred to as the Amended 2014 Plan. As of December 31, 2018, there were 1,988,069 shares available for future grant under the Amended 2014 Plan.

Through December 31, 2018, the Company granted options to certain employees and nonemployees to purchase shares of common stock at exercise prices ranging from $0.58 to $285.71 per share. The Company recorded noncash stock-based compensation expense for the years ended December 31, 2018, 2017 and 2016 based on the fair market value of the options and shares granted at the grant date. Stock‑based compensation expense was as follows:


	Year Ended December 31,
	2018		2017		2016
Research and development	$	1,274	$	1,184	$	1,063
General and administrative		2,356		2,467		2,362
Total	$	3,630	$	3,651	$	3,425

The following assumptions were used to compute employee stock‑based compensation under the Black‑Scholes option pricing model:


	2018		2017		2016
Risk-free interest rate	2.57	%	2.27	%	1.48	%
Expective volatility	70.0	%	73.9	%	75.0	%
Expected dividend yield	0	%	0	%	0	%
Expected life (in years)	6.25		6.25		6.25

Risk‑free interest rate. The Company bases the risk‑free interest rate assumption on observed interest rates appropriate for the expected term of the stock option grants.

Expected dividend yield. The Company bases the expected dividend yield assumption on the fact that it has never paid cash dividends and has no present intention to pay cash dividends.

Expected volatility. The expected volatility assumption is based on volatilities of a peer group of similar companies whose share prices are publicly available. The peer group was developed based on comparable companies in the biotechnology and pharmaceutical industries.

Expected term. The expected term represents the period of time that options are expected to be outstanding. Because the Company does not have historic exercise behavior, management determined the expected life assumption using the simplified method, which is an average of the contractual term of the option and its ordinary vesting period.

Forfeitures. The Company has elected to record forfeitures as they occur.

As of December 31, 2018, the unrecorded deferred stock‑based compensation balance related to stock options was approximately $3.1 million and will be recognized over an estimated weighted‑average amortization period of 1.7 years. The weighted average grant date fair value of options granted during the year ended December 31, 2018 was $1.27.

The following table summarizes the options outstanding, options vested and the options exercisable as of December 31, 2018, 2017 and 2016:


		Weighted		Weighted Average
		Average		Remaining	Aggregate
		Exercise		Contractual	Intrinsic
	Options	Price		Life (Years)	Value
Options outstanding at December 31, 2016	2,844,970	$	6.97	7.5
Options granted	1,145,750		2.64
Options exercised	(76,610)		1.98
Options cancelled/forfeited	(108,805)		7.62
Options outstanding at December 31, 2017	3,805,305		5.74	7.4
Options granted	2,230,000		1.96
Options exercised	—		—
Options cancelled/forfeited	(347,404)		4.19
Options outstanding at December 31, 2018	5,687,901		4.34	7.4	$	—
Options exercisable at December 31, 2018	3,430,512		5.48	6.4	$	—
Vested and expected to vest at December 31, 2018	5,687,901				$	—

Intrinsic value in the tables was calculated as the difference between the Company's stock price at December 31, 2018, of $0.58, and the exercise price, multiplied by the number of options.

Restricted Stock

During the year ended December 31, 2016, the Company granted 50,000 RSUs to an employee of the Company, 16,666 RSUs vested on the grant date, 16,667 RSUs vested in February 2017 and the remaining 16,667 RSUs vested in February 2018.

During the year ended December 31, 2017, the Company granted a total of 247,694 RSUs to executive officers and directors of the Company. These RSUs vest ratably over a two-year period for the executive officers and on the one-year anniversary of the grant date for the directors.

During the year ended December 31, 2018, the Company granted a total of 108,254 RSUs to executive officers of the Company representing payment for 2017 target bonuses. These RSUs vest on the one-year anniversary of the grant date.

The following table shows the Company's restricted stock activity during the years ended December 31, 2018, 2017 and 2016:


		Weighted Average
		Grant Date Fair		Aggregate
	Shares	Value		Intrinsic Value
Restricted stock outstanding at December 31, 2016	33,334	$	5.93
Granted	247,694		2.97
Vested	(16,667)		5.93	$	38
Cancelled/forfeited	—		—
Restricted stock outstanding at December 31, 2017	264,361		3.16
Granted	108,254		3.46
Vested	(225,061)		3.39	$	370
Cancelled/forfeited	—		—
Restricted stock outstanding at December 31, 2018	147,554		3.03

Performance Based Restricted Stock Awards

In addition to the RSUs detailed in the table above, during 2017 the Company granted up to 260,000 shares of performance-based restricted stock units (“Performance Units”) under the Company’s Amended 2014 Incentive Compensation Plan, to executive officers which are primarily contingent upon achievement of performance goals during the performance period beginning on the date of grant and ending on December 31, 2018 as set forth in each officer’s performance unit agreement. For awards with a performance condition which affects the vesting of the Performance Units, cost is recognized only if the performance condition is probable of being satisfied. Given the uncertainty of the achievement of the performance goals during the performance period, the Company has not recorded compensation expense related to these awards for the year ended December 31, 2017. These performance-based restricted stock units expired and were subsequently replaced with new awards in January 2018 (see below).

In January 2018, the Company granted up to 365,000 shares of performance-based restricted stock units ("Performance Units") under the Company's 2014 Incentive Compensation Plan primarily to executive officers, which are largely contingent upon the achievement of performance goals during the performance period beginning on the date of grant and ending on December 31, 2019 as set forth in each individual's Performance Unit agreement. Performance Units granted in January 2018 replaced Performance Units granted in April 2017 which expired. During 2018, 50,000 Performance Units were cancelled and as of December 31, 2018 315,000 Performance Units remain outstanding. Given the uncertainty of the achievement of the performance goals during the performance period, the Company has not recorded compensation expense related to these awards for the year ended December 31, 2018.