Description of securities

EXHIBIT 4.15

DESCRIPTION OF SECURITIES

The foregoing description is intended as a summary and is qualified in its entirety by reference to our certificate of incorporation, as amended (the “Certificate of Incorporation”) and our amended and restated by-laws, as amended (the “By-laws”) as currently in effect, copies of which are filed as exhibits to this Annual Report on Form 10-K and are incorporated by reference herein.

Authorized Capital Stock

As of December 31, 2020, we have authorized 1,050,000,000 shares of capital stock, par value $0.001 per share, of which 1,000,000,000 are shares of common stock and 50,000,000 are shares of “blank check” preferred stock. As of December 31, 2020, there were 17,532,893 shares of common stock issued and outstanding. The authorized and unissued shares of common stock and the authorized and undesignated shares of preferred stock are available for issuance without further action by our stockholders, unless such action is required by applicable law or the rules of any stock exchange on which our securities may be listed.

On August 10, 2020, we filed an amendment of our Certificate of Incorporation to effect a 1-for-30 reverse stock split of our common stock (the “Reverse Stock Split”). The Reverse Stock Split became effective as of 5:00 p.m. Eastern Time on August 10, 2020 (the “Effective Time”) and our common stock began trading on a split-adjusted basis when the market opened on August 11, 2020. As a result of the Reverse Stock Split, every 30 shares of our pre-Reverse Stock Split common stock were combined and reclassified into one share of our common stock. No fractional shares were issued in connection with the Reverse Stock Split, and cash paid to stockholders for potential fractional shares was insignificant. As of the Effective Time, we adjusted and proportionately decreased the number of shares of our common stock reserved for issuance upon exercise of, and adjusted and proportionately increased the exercise price of, all options and warrants and other rights to acquire our common stock. In addition, as of the Effective Time, we adjusted and proportionately decreased the total number of shares of our common stock that may be the subject of the future grants under our stock plans.

Common Stock

The holders of our common stock are entitled to one vote per share. Our Certificate of Incorporation does not provide for cumulative voting. Our directors are divided into three classes. At each annual meeting of stockholders, directors elected to succeed those directors whose terms expire are elected for a term of office to expire at the third succeeding annual meeting of stockholders after their election. The holders of our common stock are entitled to receive ratably such dividends, if any, as may be declared by our board of directors out of legally available funds. Upon liquidation, dissolution or winding-up, the holders of our common stock are entitled to share ratably in all assets that are legally available for distribution. There are no preemptive, subscription, conversion rights, redemption or sinking fund provisions regarding the common stock. The rights, preferences and privileges of holders of our common stock are subject to, and may be adversely affected by, the rights of the holders of any series of preferred stock, which may be designated solely by action of our board of directors and issued in the future.

The transfer agent and registrar for our common stock is Action Stock Transfer Corporation. The transfer agent’s address is 2469 East Fort Union Blvd., Suite 214, Salt Lake City, UT 84121. Our common stock is listed on the NYSE American under the symbol “ATNM.”

Preferred Stock

The board of directors is authorized, subject to any limitations prescribed by law, without further vote or action by the stockholders, to issue from time to time up to 50,000,000 shares of preferred stock in one or more series. Each such series of preferred stock shall have such number of shares, designations, preferences, voting powers, qualifications, and special or relative rights or privileges as shall be determined by the board of directors, which may include, among others, dividend rights, voting rights, liquidation preferences, conversion rights and preemptive rights. Issuance of preferred stock by our board of directors may result in such shares having dividend and/or liquidation preferences senior to the rights of the holders of our common stock and could dilute the voting rights of the holders of our common stock.

Prior to the issuance of shares of each series of preferred stock, the board of directors is required by the Delaware General Corporation Law and our Certificate of Incorporation to adopt resolutions and file a certificate of designation with the Secretary of State of the State of Delaware. The certificate of designation fixes for each class or series the designations, powers, preferences, rights, qualifications, limitations and restrictions, including, but not limited to, some or all of the following:

Once designated by our board of directors, each series of preferred stock may have specific financial and other terms.

Anti-Takeover Law and Provisions of our Certificate of Incorporation and By-laws

Provisions of our Certificate of Incorporation and By-laws may delay or discourage transactions involving an actual or potential change in our control or change in our management, including transactions in which stockholders might otherwise receive a premium for their shares, or transactions that our stockholders might otherwise deem to be in their best interests. Therefore, these provisions could adversely affect the price of our common stock. Among other things, our Certificate of Incorporation and By-laws: