Aptose Biosciences Inc. — Proxy Solicitation & Information Statement 2023

Apr 26, 2023

Aptose Biosciences Inc. Suite 120, 12770 High Bluff Drive, San Diego, California, 92130 Notice of 2023 Annual and Special Meeting of Shareholders

NOTICE IS HEREBY GIVEN that the annual and special meeting (the “Meeting”) of shareholders of Aptose Biosciences Inc. (the “Corporation”) will be held on May 23, 2023 at 9:00 a.m. (Pacific time). The Meeting will be conducted in a hybrid format. Therefore shareholders are invited to attend in person at Highlands Corporate Center - Conference Room, 12730 High Bluff Drive, Cantina Ste, San Diego, 92130 or by live webcast accessible directly online at web.lumiagm.com/472428776, where they will be able to listen, vote, and submit questions during the Meeting.

What the Meeting is About

The following items of business will be covered at the Meeting:

1. receiving the financial statements of the Corporation for the fiscal year ended December 31, 2022, including the auditor’s report thereon;

2. Proposal No. 1 – electing seven directors to serve until the 2024 Annual Meeting of Shareholders;

3. Proposal No. 2 – appointing KPMG LLP as the independent registered public accounting firm of the Corporation for the fiscal year ending December 31, 2023;

4. Proposal No. 3 – passing an ordinary resolution, the full text of which is set forth in the accompanying proxy statement (the “Proxy Statement”), approving an amendment to the Corporation’s 2021 stock incentive plan to increase the number of common shares (the “Shares”) reserved for issuance thereunder by 1,027,758 Shares;

5. Proposal No. 4 – passing a special resolution, the full text of which is set forth in the Proxy Statement, approving the adoption of an amendment to the Corporation’s articles to effect a reverse stock split of the Corporation’s outstanding Shares at a ratio in the range of 1-for-10 to 1-for-20 (the “Reverse Stock Split”), such amendment to become effective at an exact ratio and a date to be determined by the board of directors of the Corporation (the “Board”) if the Board considers it to be in the best interests of the Corporation to implement such Reverse Stock Split, all as more particularly described in the Proxy Statement;

6. Proposal No. 5 – passing a resolution, the full text of which is set forth in the Proxy Statement, approving one or more adjournments of the Meeting, if necessary or appropriate, if a quorum is present, to permit further solicitation of proxies if there are not sufficient votes at the time of the Meeting to approve Proposals No. 3 and 4;

7. Proposal No. 6 – passing an advisory (non-binding) resolution on the compensation of the Corporation’s named executive officers, as more particularly described in the Proxy Statement; and

8. transacting such other business as may be properly brought before the Meeting.

The shareholders may also consider other business that properly comes before the Meeting or any adjournment of the Meeting. The Proxy Statement provides additional information relating to the matters to be dealt with at the Meeting and forms part of this notice.

You have the right to vote.

You are entitled to receive notice of and vote at the Meeting, or any adjournment, if you are a holder of Shares at the close of business on April 3, 2023.

You have the right to vote your shares on items 2 through 7 listed above and any other items that may properly come before the Meeting or any adjournment.

The Notice of Meeting, Proxy Statement and the form of proxy will be mailed to you on or around April 26, 2023. Detailed instructions regarding shareholders’ voting process are also available on our website at https://www.aptose.com/investors/news-events/ir-calendar.

Your vote is important.

If you are not able to attend the Meeting, please exercise your right to vote by signing and returning the enclosed form of proxy to Computershare Investor Services Inc., 100 University Avenue, 8[th] Floor, Toronto, Canada M5J 2Y1, so as to arrive not later than 5:00 p.m. (Toronto time) on May 18, 2023 or, if the Meeting is adjourned, 48 hours (excluding Saturdays, Sundays and holidays) before any adjournment of the Meeting.

BY ORDER OF THE BOARD OF DIRECTORS

William G. Rice, Ph.D. Chairman, President and Chief Executive Officer April 18, 2023