Note 5 - Equity 

In August 2020, the Company entered into the Capital on Demand™ Sales Agreement with JonesTrading Institutional Services LLC, “JonesTrading”, pursuant to which the Company may sell, from time to time, through or to JonesTrading, up to an aggregate of $200 million of its common stock. On June 28, 2022, the Company entered into an Amended and Restated Capital on Demand™ Sales Agreement (the “A&R Sales Agreement”) with JonesTrading and B. Riley Securities, Inc. (“B. Riley”). The A&R Sales Agreement modifies the original Capital on Demand™ Sales Agreement to include B. Riley Securities as an additional sales agent thereunder. Shares of common stock are offered pursuant to a shelf registration statement on Form S-3 (File No. 333-242322) filed with the SEC on August 7, 2020 (the “Prior Shelf Registration Statement”). On August 11, 2023, the Company filed a new registration statement on Form S-3 (File No. 333-273911), which registration statement was amended on February 2, 2024, and declared effective on February 5, 2024, to replace the Prior Shelf Registration Statement, including a base prospectus which covers the offering, issuance and sale of up to $500 million of common stock, preferred stock, warrants, units and/or subscription rights; and a sales agreement prospectus covering the offering, issuance and sale of up to a maximum aggregate offering price of $200 million of common stock that may be issued and sold under the Amended Sales Agreement. On March 31, 2025, upon filing of the Company’s Annual Report on Form 10-K for the year ended December 31, 2024, the Company became subject to General Instruction I.B.6 of Form S-3, pursuant to which in no event will the Company sell its common stock in a registered primary offering using Form S-3 with a value exceeding more than one-third of its public float in any 12 calendar month period so long as its public float remains below $75 million.

The Company did not sell any shares of common stock during the three months ended March 31, 2025. During the three months ended March 31, 2024, the Company sold 1.8 million shares of common stock, resulting in gross proceeds of $15.0 million and net proceeds of $14.7 million.

Stock Options

The following is a summary of stock option activity for the three months ended March 31, 2025:

During the three months ended March 31, 2025, the Company granted new employees options to purchase 25 thousand shares of common stock with an exercise price ranging from $1.06 to $1.43 per share, a term of 10 years, and a vesting period of 4 years. The options had an aggregated fair value of $28 thousand that was calculated using the Black-Scholes option-pricing model. Variables used in the Black-Scholes option-pricing model include: (1) discount rate range from 4.0% to 4.5% (2) expected life of 6 years, (3) expected volatility range from 90.6% to 90.7%, and (4) zero expected dividends. During the three months ended March 31, 2024, the Company did not grant any stock options.

On March 31, 2025, the Board of Directors approved of the cancellation of stock options to purchase an aggregate of 4.9 million shares of common stock held by certain current employees and directors that were initially granted under the Amended and Restated 2013 Stock Plan and the 2019 Amended and Restated Stock Plan. Such cancellations were subject to the consent of the applicable holders of the stock options, which the Company received. The cancellation of these stock options resulted in the recording of $8.7 million in stock compensation expense. During the three months ended March 31, 2024, the Company recorded compensation expense related to stock options of $1.2 million.

The fair values of all options issued and outstanding are being amortized over their respective vesting periods. The unrecognized compensation expense at March 31, 2025 was $0.4 million related to unvested options, which is expected to be expensed over a weighted average of 2.3 years.

Restricted Stock Units

The following is a summary of restricted stock unit (“RSU”) activity for the three months ended March 31, 2025:

The RSUs vest at the earliest of a change of control event, the termination of the recipient’s continuous service status for any reason other than by the Company for cause and the third anniversary of the date of the grant. The fair value of the RSUs, $1.8 million, was determined based on the stock price on the dates of the grant and is being recognized over three years. The unrecognized compensation expense at March 31, 2025 of $0.2 million is expected to be expensed over 0.4 years. During the three months ended March 31, 2025 and 2024, the Company recorded compensation expense related to RSUs of $0.1 million and $0.1 million, respectively.

Warrants

Following is a summary of warrant activity for the three months ended March 31, 2025: