foreseeable future. We currently expect to retain all future earnings, if any, for use in the development, operation and expansion of our business. Any determination to pay cash dividends in the future will depend upon, among other things, our results of operations, plans for expansion, tax considerations, available net profits and reserves, limitations under law, financial condition, capital requirements and other factors that our board of directors considers to be relevant.
Preferred Stock
Under the terms of our certificate of incorporation, our board of directors is authorized to direct us to issue shares of preferred stock in one or more series without stockholder approval. Our board of directors has the discretion to determine the rights, preferences, privileges and restrictions, including voting rights, dividend rights, conversion rights, redemption privileges and liquidation preferences, of each series of preferred stock.
The purpose of authorizing our board of directors to issue preferred stock and determine its rights and preferences is to eliminate delays associated with a stockholder vote on specific issuances. The issuance of preferred stock, while providing flexibility in connection with possible acquisitions, future financings and other corporate purposes, could have the effect of making it more difficult for a third party to acquire, or could discourage a third party from seeking to acquire, a majority of our outstanding voting stock. There are no shares of preferred stock outstanding, and we have no present plans to issue any shares of preferred stock.
Options
As of May 1, 2022, options to purchase an aggregate of 124,729 shares of our common stock were outstanding under our 2005 Equity Incentive Plan, or our 2005 Plan (all of which were vested and exercisable as of such date), options to purchase 549,486 shares of common stock were outstanding under our 2016 Equity Incentive Plan, or our 2016 Plan (of which 456,050 shares were vested and exercisable as of such date), options to purchase 1,769,584 shares of common stock were outstanding under our 2020 Incentive Award Plan, or our 2020 Plan (of which 419,100 shares were vested and exercisable as of such date), restricted stock units covering 41,051 shares of common stock were outstanding under our 2020 Plan and options to purchase 520,000 shares of common stock were outstanding under our 2022 Employment Inducement Plan (none of which were vested or exercisable as of such date).
Warrants
On April 7, 2022, we entered into a securities purchase agreement with certain purchasers named therein, pursuant to which we agreed to sell securities to such purchasers in a private placement. In the private placement, the purchasers had the option to purchase either shares of our common stock or, in lieu thereof, pre-funded warrants to purchase shares of our common stock, each with an exercise price of $0.001 per share. Accordingly, we issued pre-funded warrants to purchase 5,000,000 shares of our common stock upon the closing of the private placement.
As of May 1, 2022, warrants to purchase an aggregate of 5,000,000 shares of our common stock were outstanding.
The warrants are exercisable until 5:00 p.m., New York time, on April 12, 2027. The exercise price and number of shares of common stock issuable upon exercise of the warrants may be adjusted in certain circumstances, including in the event of a stock dividend, a forward or reverse split of our shares of common stock, and certain other events. However, the warrants will not be adjusted for issuances of common stock at prices below their respective exercise prices.
We issued the warrants in certificated form. A holder of a warrant certificate may exercise such warrant upon surrender of the applicable warrant certificate on or prior to the applicable expiration date at our principal office, with the exercise form on the reverse side of the warrant certificate completed and executed as indicated, accompanied by full payment of the exercise price for the number of warrants being exercised.
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