In September 2021, we completed an underwritten follow-on public offering of 10,781,250 shares of our common stock, including the full exercise of the underwriters’ option to purchase additional shares, at a price to the public of $8.00 per share. The total net proceeds from the offering were approximately $80.6 million after deducting underwriting discounts, commissions and offering expenses payable by us.

In March 2021, we entered into a Capital on DemandTM Sales Agreement with JonesTrading Institutional Services LLC (JonesTrading) for an at-the-market offering program (the Prior ATM Offering Program), pursuant to which we were entitled to sell from time to time, at our option, up to an aggregate of $25.0 million of shares of our common stock through JonesTrading, as sales agent or principal. JonesTrading was entitled to a commission at a fixed rate of up to 3.0% of the gross proceeds. During 2021, we sold an aggregate of 986,267 shares of common stock at a weighted-average price of $4.75 per share for net proceeds of $4.4 million under the Prior ATM Offering Program. During the six months ended June 30, 2022, we sold an aggregate of 260,455 shares of common stock at a weighted-average price of $6.07 per share for net proceeds of approximately $1.5 million under the Prior ATM Offering Program. In April 2022, we terminated the Prior ATM Offering Program.

In April 2022, we entered into an Open Market Sale AgreementSM with Jefferies LLC (Jefferies) implementing an “at-the-market” offering program (the ATM Offering Program), pursuant to which we may offer and sell, from time to time and at our option, up to an aggregate of $65.0 million of shares of our common stock through Jefferies, acting as sales agent. Jefferies is entitled to a fixed commission rate of up to 3.0% of the gross sales proceeds of shares sold under the ATM Offering Program. During the six months ended June 30, 2022, we sold an aggregate of 69,251 shares of common stock at a weighted-average price of $2.80 per share for gross proceeds of approximately $0.2 million under the ATM Offering Program.

In September 2020, we entered into a common stock purchase agreement (the Purchase Agreement) with Aspire Capital Fund, LLC (Aspire Capital), which provides that, upon the terms and subject to the conditions and limitations set forth therein, Aspire Capital is committed to purchase up to an aggregate of $20.0 million of shares of our common stock at our request from time to time during the 30 month term of the Purchase Agreement. Concurrently with entering into the Purchase Agreement, we also entered into a registration rights agreement with Aspire Capital, in which we agreed to file one or more registration statements, as permissible and necessary to register under the Securities Act of 1933, as amended, for the resale of the shares of our common stock that have been and may be issued to Aspire Capital under the Purchase Agreement. During the six months ended June 30, 2021, we sold an aggregate of 3,000,000 shares of common stock at a weighted-average price of $5.09 per share for net proceeds of $15.2 million under the Purchase Agreement. During the six months ended June 30, 2022, there were no issuances or sales under the Purchase Agreement.

In March 2022, we adopted and our board of directors approved our 2022 Inducement Plan (our Inducement Plan). Awards granted under our Inducement Plan are in accordance with Nasdaq Listing Rule 5635(c)(4). A total of 300,000 shares of our common stock were initially reserved for the issuance under our Inducement Plan.

The maximum term of options granted under our Inducement Plan is ten years. Each option vests over a period of four years, with 25% of the shares vesting on the one-year anniversary of the applicable vesting commencement date and the remaining 75% vesting in equal monthly installments over three years, subject to continuous employment.

In March 2022, we granted nonstatutory stock options under our Inducement Plan to purchase an aggregate of 58,400 shares of our common stock, each with an exercise price of $5.24 per share as inducement awards to 10 new employees. In May 2022, we granted nonstatutory stock options under our Inducement Plan to purchase an aggregate of 113,400 shares of our common stock, each with an exercise price of $3.48 per share as inducement awards to four new employees.

Common stock reserved for future issuance was as follows:


	June 30, 2022
Common stock warrants		13,760
Common stock options and restricted stock units		3,048,636
Shares available under the 2015 equity incentive plan		961,351
Shares available under the 2022 inducement plan		128,200
Shares available under the employee stock purchase plan		819,975
		4,971,922

The following table summarizes our stock option activity under all equity incentive plans for the six months ended June 30, 2022:


	Number of Outstanding Stock Options			Weighted- Average Exercise Price
Outstanding as of December 31, 2021		1,412,550		$	12.01
Granted		1,528,444		$	3.44
Exercises		(259	)	$	3.77
Canceled/forfeited/expired		(13,537	)	$	18.17
Outstanding as of June 30, 2022		2,927,198		$	7.51

The assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows:


	Three Months Ended June 30,						Six Months Ended June 30,
	2022			2021			2022			2021
Expected term (in years)	6.02 – 6.06			5.50 – 6.08			6.02 – 6.08			5.50 – 6.08
Risk-free interest rate	2.8%-3.0%			1.07% – 1.09%			1.7% – 3.0%			0.6% – 1.09%
Expected volatility	84.7% – 84.9%			87.4% – 88.29%			84.7% – 86.5%			88.3% – 104.8%
Expected dividend yield		0.0	%		0.0	%		0.0	%		0.0	%

The following table summarizes our restricted stock unit activity under all equity incentive plans for the six months ended June 30, 2022:


	Number of Outstanding Restricted Stock Units			Weighted-Average Grant Date Fair Value
Balance as of December 31, 2021		7,500		$	4.08
Granted		116,438		$	5.13
Released		(2,500	)	$	4.13
Balance as of June 30, 2022		121,438		$	5.09

The allocation of stock-based compensation for all options and restricted stock units and stock issued pursuant to our employee stock purchase plan is as follows (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Research and development	$	131	$	64	$	238	$	128
General and administrative		386		334		696		630
Total stock-based compensation expense	$	517	$	398	$	934	$	758