Stockholders' Equity

12 Months Ended

Dec. 31, 2020

Stockholders' Equity Note [Abstract]

Stockholders’ Equity

Preferred Stock


			Shares Outstanding as of December 31,
	Shares Authorized	Shares Issued	2020	2019


Series C Preferred Stock, par $0.001	1,091	1,091	9	23

In June 2020, 14 shares of the Company’s Series C preferred stock were converted into an aggregate of 5,147 shares of the Company’s common stock.

The holder of any share or shares of Series C Preferred Stock has the right at any time, at such holder’s option, to convert all or any lesser portion of such holder’s shares of the Preferred Stock into fully paid and non-assessable shares of Common Stock. As of December 31, 2020, the Conversion Value was $27.20 per share, such that the outstanding shares of Series C Preferred Stock were convertible into an aggregate of 3,309 shares of common stock.

Common Stock

In May 2018, the Company entered into the Sales Agreement with an outside placement agent (the “Placement Agent”) to sell shares of its common stock with aggregate gross proceeds of up to $100.0 million, from time to time, through an “at-the-market” equity offering program under which the Placement Agent will act as sales agent. During the first quarter of 2020, the Company and the Placement Agent entered into a first and second amendment to the Sales Agreement (the "Prior Sales Agreement") to increase the amount of common stock that may be sold under the Sales Agreement from $100.0 million to $250.0 million. As of March 31, 2020, there was no remaining capacity under the Prior Sales Agreement. On April 3, 2020, the Company and the Placement Agent entered into a new Sales Agreement (the "New Sales Agreement") to sell shares of its common stock. On April 3, 2020 and May 12, 2020, the Company filed prospectus supplements pursuant to the New Sales Agreement for the offer and sale of its Common Stock for aggregate gross proceeds of up to an aggregate of $250.0 million. Under the New Sales Agreement, the Company will set the parameters for the sale of shares, including the number of shares to be issued, the time period during which sales are requested to be made, limitation on the number of shares that may be sold in any one trading day and any minimum price below which sales may not be made. The New Sales Agreement provides that the Placement Agent will be entitled to compensation for its services in an amount equal to up to 3.0% of the gross proceeds from the sales of shares sold through the Placement Agent under the New Sales Agreement. The Company has no obligation to sell any shares under the New Sales Agreement, and could at any time suspend solicitation and offers under the New Sales Agreement.

During the three months ended March 31, 2020, the Company sold 43,148,952 shares of its common stock under the Prior Sales Agreement. The sales were made at a weighted average price of $4.92 per share, resulting in aggregate net proceeds of $208.2 million. As of March 31, 2020, there was no remaining capacity under the Prior Sales Agreement.

During the year ended December 31, 2020, the Company sold a total of 22,915,934 shares of common stock under the New Sales Agreement. The sales were made at a weighted average price of $10.91 per share resulting in aggregate net proceeds of $246.2 million. As of December 31, 2020, there was no remaining capacity under the New Sales Agreement.

Stock Options and Restricted Stock Units

The Company has a stock-based incentive plan, the 2016 Omnibus Incentive Plan (as amended to date, the "2016 Incentive Plan"), pursuant to which the Company may grant stock options, restricted stock awards, restricted stock units and other stock-based awards or short-term cash incentive awards to employees, directors and consultants.

The 2016 Incentive Plan was originally approved by the Company's stockholders on May 13, 2016, and an amendment to the plan to increase the number of shares available for issuance was approved by the stockholders on May 8, 2019. The maximum number of shares of the Company’s common stock available for issuance over the term of the 2016 Incentive Plan

may not exceed 18,000,000 shares, provided that commencing with the first business day of each calendar year beginning January 1, 2020, such maximum number of shares shall be increased by 2,000,000 shares of common stock unless the Board determines, prior to January 1 for any such calendar year, to increase such maximum amount by a fewer number of shares or not to increase the maximum amount at all for such year. On January 1, 2021, the maximum number of shares to be issued increased by 2,000,000. At December 31, 2020, there were 18,000,000 shares of common stock reserved for issuance upon exercise of incentive awards granted and to be granted at future dates under the 2016 Incentive Plan. At December 31, 2020, the Company had 6,739,577 shares of common stock available for future grant under the 2016 Incentive Plan, 2,558,052 shares underlying outstanding but unvested restricted stock units and options outstanding to purchase 5,742,109 shares of common stock under the 2016 Incentive Plan. The awards granted and available for future grant under the 2016 Incentive Plan generally vest over three years and have a maximum contractual term of ten years. The 2016 Incentive Plan terminates by its terms on March 9, 2026.

The Amended and Restated 2007 Omnibus Incentive Plan (the "2007 Incentive Plan") was adopted on March 31, 2007 and terminated by its terms on March 31, 2017. At December 31, 2020, the Company had options outstanding to purchase 3,164,515 shares of common stock under the 2007 Incentive Plan. The awards granted under the 2007 Incentive Plan generally vest over three years and have a maximum contractual term of ten years.

Total employee and director stock-based compensation expense recognized in the consolidated statements of operations for the years ended December 31, 2020, 2019 and 2018 was $14.5 million, $9.8 million and $10.2 million, respectively, of which $8.0 million, $5.9 million and $5.9 million was included in research and development expenses and $6.5 million, $3.9 million and $4.3 million was included in general and administrative expenses, respectively.

At December 31, 2020 and 2019, there was $4.4 million and $3.4 million, respectively, of total unrecognized compensation expense related to unvested stock options, which is expected to be recognized over a weighted-average period of 1.4 years and 1.7 years, respectively.

At December 31, 2020 and 2019, there was $10.9 million and $4.3 million, respectively, of total unrecognized compensation expense related to unvested restricted stock units, which is expected to be recognized over a weighted-average period of 1.9 years and 1.6 years, respectively.

The fair value of stock options granted to non-employees was estimated using the Black-Scholes pricing model. Total stock-based compensation expense for stock options and restricted stock units granted to non-employees for the years ended December 31, 2020, 2019 and 2018 was $1.2 million, $970,000 and $302,000, respectively. As of December 31, 2020, options to purchase 845,375 shares of common stock granted to non-employees remained outstanding.

The following table summarizes total stock options outstanding at December 31, 2020:


	Options Outstanding				Options Exercisable
Exercise Price	Shares Underlying Options Outstanding	Weighted-Average Remaining Contractual Life (in Years)	Weighted Average Exercise Price		Shares Underlying Options Exercisable	Weighted Average Exercise Price
$1.48-$3.00	452,749	2.5	$	2.24	428,231	$	2.23
$3.01-$6.00	3,261,410	7.4	$	3.85	1,975,426	$	3.98
$6.01-$9.00	3,879,209	6.5	$	7.59	2,864,794	$	7.33
$9.01-$12.00	365,223	7.2	$	10.42	233,282	$	10.08
$12.01-$15.00	833,282	5.9	$	13.46	546,723	$	13.14
$15.01-$25.62	114,751	9.6	$	20.57	31,041	$	20.59
	8,906,624	6.6	$	6.78	6,079,497	$	6.58

At December 31, 2020, the aggregate intrinsic value of options outstanding was $24.2 million, the aggregate intrinsic value of options exercisable was $16.8 million, and the weighted average remaining contractual term of options exercisable was 5.7 years.

At December 31, 2020, the aggregate intrinsic value of unvested restricted stock units was $22.6 million and the aggregate intrinsic value of restricted stock units which vested during the year ended December 31, 2020 was $13.5 million.

At December 31, 2020, options to purchase 8,906,624 shares of common stock and 2,558,052 restricted stock units were expected to vest.

Stock option activity under the Company’s equity incentive plans during the year ended December 31, 2020 was as follows:


	Number of Shares	Weighted-Average Exercise Price








Balance, December 31, 2019	9,265,390	$	5.72
Granted	2,126,182	10.17
Exercised	(2,178,252)	5.63
Cancelled	(306,696)	6.40
Balance, December 31, 2020	8,906,624	$	6.78

Restricted stock unit activity under the Company’s equity incentive plans during the year ended December 31, 2020 was as follows:


			Number of Shares








Balance, December 31, 2019			2,069,936
Granted			1,586,280
Vested			(1,040,628)
Cancelled			(57,536)
Balance, December 31, 2020			2,558,052

The weighted average exercise price per share was $4.44 for the 78,750 options which expired during the year ended December 31, 2020, $6.27 for the 324,502 options which expired during the year ended December 31, 2019 and $5.17 for the 119,091 options which expired during the year ended December 31, 2018.

The weighted average grant date fair value per share was $6.87, $2.19 and $2.86 for options granted during the years ended December 31, 2020, 2019 and 2018, respectively.

The weighted average grant date fair value was $9.12, $3.09 and $4.31 per share for restricted stock units granted during the years ended December 31, 2020, 2019 and 2018, respectively.

The Company received $12.3 million, $113,000 and $1.5 million in proceeds from the exercise of stock options during the years ended December 31, 2020, 2019 and 2018, respectively. The aggregate intrinsic value of options exercised was $14.2 million, $25,000 and $910,000 during the years ended December 31, 2020, 2019 and 2018, respectively.

On August 28, 2020, the Company granted 663,353 performance-based RSUs to key employees under the 2016 Incentive Plan. The RSUs will vest in two tranches as follows: 50% of the shares in each tranche will vest upon achievement of the predetermined performance milestones and the remaining 50% of the shares in each tranche will vest upon subsequent completion of a one-year service period. The grant date fair value of the performance-based RSUs was $8.0 million based on the grant date closing price per share of $12.06. As of December 31, 2020, the underlying performance milestones of the RSUs were not probable of achievement, and no stock-based compensation expense was recognized for the performance-based RSUs for the year then ended.