Exhibit 4.21

April 25, 2024

Jeffrey Bonacorda

[***]

Dear Jeff,

Offer of Employment with Kazia Therapeutics

On behalf of Kazia Therapeutics, Inc, I am pleased to offer you the position of Vice President Finance and Controller. We look forward to welcoming you as a colleague.

The terms of the position are as set forth below.

Position

Particulars. Your position, place of work, and commencement date will be as described in Attachment 1 of this letter.

Employer. Your employer will be Kazia Therapeutics, Inc (the “Company”), a Delaware company. Kazia reserves the right to assign your employment to other corporate entities within its group at its sole discretion.

Obligation to Best Efforts. You agree that you will, at all times, loyally and conscientiously perform all the duties and obligations associated with this role to the best of your ability and experience, and to the reasonable satisfaction of the Company.

No Interference. During the term of your employment, you further agree that you will devote all of your business time and attention to the business of the Company, the Company will be entitled to all of the benefits and profits arising from or incident to all such work services and advice, you will not render commercial or professional services of any nature to any person or organization, whether or not for compensation, without the prior consent of the Company’s Chief Executive Officer, and you will not directly or indirectly engage or participate in any business that is competitive in any manner with the business of the Company. Nothing in this letter agreement will prevent you from accepting speaking or presentation engagements in exchange for honoraria or from serving on boards of charitable organizations, or from owning no more than one percent (1%) of the outstanding equity securities of a corporation whose stock is listed on a national stock exchange.

Travel and Expenses. You acknowledge that the nature of the position may require travel within and outside of the United States from time to time. The Company will make reasonable efforts to accommodate your circumstances and preferences in directing such travel. You will be entitled to reimbursement of reasonable and customary expenses incurred in carrying out the position, in accordance with the Company’s policies, on submission of an expense report and valid receipts.

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Compensation

Salary. Your compensation will be as itemised in Attachment 1 of this letter and paid to you once per month pursuant to the Company’s regular payroll policy.

Performance and Salary Review. Your performance and compensation package will be reviewed no less than once annually. Any pay adjustments will be made in accordance with your performance and in reference to industry compensation benchmarks for comparable positions. Adjustments to compensation will be at Kazia’s sole discretion and are not guaranteed.

Sole Consideration. You acknowledge that the compensation described in Attachment 1 of this letter will be your only remuneration for your employment with the company. Kazia may require you to provide services and / or to hold offices within the Company or on behalf of the Company without additional remuneration. You will be required to work such hours as are reasonably required for the position, without additional payment for overtime or travel.

Equity Participation. Following your commencement, Kazia will recommend to the Board of Directors that you be granted options over the company’s stock, to an amount as specified in Attachment 1 of this letter. This grant is at the discretion of the Board of Directors and will be subject to the company’s Employee Stock Option Plan. At the discretion of the Board of Directors, you may be eligible for further grants of stock options during the term of your employment.

Benefits

Benefits. Your benefits will be as itemised in Attachment 1 of this letter.

Insurance Benefits. The Company will provide a welfare benefits package which includes medical, dental, vision and other coverages, the benefits of which are equivalent for other employees of similar position and may require an employee monthly co-payment depending upon coverage options selected.

Vacation and Holidays. You will be eligible for paid time off (PTO) as itemised in Attachment 1 of this letter. You will also receive paid time off for US holidays observed by Kazia. Kazia’s policies regarding vacation and holidays will be provided to you separately on commencement.

Terms of Employment

At-Will Employment. Notwithstanding any other obligation in this letter, your employment with the Company will be on an “at will” basis, meaning that either you or the Company may terminate your employment at any time for any reason or no reason.

Debarment and Suspension. You agree, assert, and affirm that you are in compliance with United States Federal Executive Order 12549 “Debarment and Suspension” and in further compliance with Executive Order 12689, and with Section 2455 of the Federal Acquisition Regulation as provided in 45 CFR 76 “Government-Wide Debarment and Suspension (Non-procurement) and Government-Wide Requirements for Drug-Free Workplace (Grants)”, and in further compliance with Office of Management and Budget Memorandum M-87-32, “Certification of Non-delinquency by Applicants for Federal Assistance,” that I, to the best of my knowledge and belief:

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(a) Am not presently debarred, suspended, proposed for debarment, declared ineligible, or voluntarily excluded by any Federal department or agency;

(b) Have not within a three-year period preceding the Start Date been convicted of or had a civil judgment rendered against me for commission of fraud or a criminal offense in connection with obtaining, attempting to obtain, or performing a public (Federal, State, or local) transaction or contract under a public transaction; violation of Federal or State antitrust statutes or commission of embezzlement, theft, forgery, bribery, falsification or destruction of records, making false statements, or receiving stolen property;

(c) Am not presently indicted for or otherwise criminally or civilly charged by a governmental entity (Federal, State, or local) with commission of any of the offenses enumerated in paragraph (1)(b) of this certification;

(d) Have not within a three-year period preceding the Start Date had one or more public transactions (Federal, State, or local) terminated for cause or default; and

(e) Am not currently delinquent on the repayment of any federal debt.

Confidentiality. You agree that, by executing this letter, you enter into a Confidentiality Agreement with the company, which is provided in Attachment 2 of this letter.

Work Product Agreement. You agree that, by executing this letter, you enter into a Proprietary Information and Inventions Agreement with the company, which is provided in Attachment 3 of this letter.

Notification of Material Changes. You agree to promptly notify Kazia of any material changes in your circumstances, including without limitation your residential address, your qualifications, professional memberships or certifications, or any of the representations and warranties contained in this letter.

Adherence to Policies. You acknowledge that you are expected act as a role model for the company and to uphold and champion its policies including, but not limited to, its policies relating to work health and safety, equal employment opportunities, anti-discrimination, harassment and bullying. You must also comply with any policies issued by the company, including policies relating to corporate governance.

Surveillance and Data Privacy. The company undertakes continuous and ongoing surveillance in relation to activities carried out on its premises, or using its property, in order to ensure that its workplaces are safe, and free of risk of harm to all employees and visitors, and also to protect the company’s business interests. In accepting employment with the company, you acknowledge the surveillance set out in this clause, and consent to such use.

Ownership of Physical Property. All document, apparatus, equipment and other physical property in any form furnished to you by the Company or produced by you or others in connection with your employment shall be and remain the sole property of the Company. You shall return to the Company all such documents, materials and property as and when requested by the Company, except only (i) personal copies of records relating to my compensation; (ii) if applicable, personal copies of any materials evidencing shares of the Company’s capital stock purchased by you and/or options to purchase shares of the Company’s capital stock granted to you; (iii) your copy of this Agreement and (iv) your personal property and personal documents that you bring with you to the Company and any

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personal correspondence and personal materials that you accumulate and keep at the Company’s office during your employment. Even if the Company does not so request, you shall return all such documents, materials and property upon termination of your employment, and, except for your personal documents, you will not take with you any such documents, material or property or any reproduction thereof upon such termination.

Obligations at Termination. Upon termination of your employment for any reason, you must, at the Company’s request, cooperate with the company and render all reasonable assistance in the prosecution or defence of legal claims and proceedings. You must execute all documents and give all reasonable assistance required to relinquish offices held on behalf of the Company, and to allow the Company to protect intellectual property and confidential information.

Non-Solicitation. During your employment, and for a period of twelve (12) months after termination, you may not directly or indirectly solicit, induce, recruit or encourage any of the Company’s employees or consultants to terminate their relationship with the Company, or attempt any of the foregoing, either for yourself or any other person or entity.

Conditions of Employment

Proof of Right to Work. For purposes of federal immigration law, you will be required to provide to the Company documentary evidence of your identity and eligibility for employment in the United States. Such documentation must be provided to us within three (3) business days of your date of hire, or our employment relationship with you may be terminated.

Background and Credit Review. You agree to and will promptly complete any necessary documentation to allow a personal background and credit review. All information will be held strictly confidential but will be used to finally qualify you for this position. Satisfactory passage of this check must be completed within seven (7) business days of your date of hire, or our employment relationship with you may be terminated.

Warranties. In accepting this offer of employment, you warrant that:-

(a) You will not be in breach of any agreement with, or obligation owed to, any third party; and

(b) You have disclosed all material information to Kazia which may be relevant to the company’s decision to offer you employment; and

(c) Any representations you have made as to your qualifications, skills, experience, industry knowledge, business influence, contacts, and employment history are true and correct and complete.

We are all delighted to be able to extend you this offer and look forward to working with you. To indicate your acceptance of the Company’s offer, please sign and date this letter in the space provided below, and separately on Attachment 2 and Attachment 3. Please return the signed documents to the company. This letter, together with its Attachments, set forth the terms of your employment with the Company and supersede any prior representations or agreements, whether written or oral. This letter may not be modified or amended except by a written agreement, signed by the Company and by you.

Yours sincerely,

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For and on behalf of Kazia Therapeutics:-

/s/ John Friend

Dr John Friend

Chief Executive Officer

Accepted and agreed by:-

/s/ Jeffrey Bonacorda

Jeffrey Bonacorda

Date: April 24, 2024

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ATTACHMENT 1

PARTICULARS OF EMPLOYMENT

Position	Vice President Finance and Controller
Position Overview	As VP Finance and Controller, your specific responsibilities include the following: •  Providing key technical accounting judgments and policies, including oversight, implementation, and execution of new accounting guidance. •  Manage other finance-related activities, including general accounting, treasury, and interactions with transfer agent, banks and investment managers •  Oversee the company’s HR-related activities (third party vendor), equity plans, including the stock option and ESPP programs •  Leading preparation and review of SEC filings, including quarterly and annual reporting. •  Financial reports including monthly, quarterly, and annual financial statements and management report in accordance with IFRS or GAAP. •  Evaluating all financial systems and procedures and implements changes and improvements to increase accuracy, control, and timely reporting. Ensures the integrity of financial reporting systems with books of original records. •  Supporting Admin in the development of the annual budget and the monthly rolling forecast, budget to actual analysis and other management financial reporting. •  Participating in Audit Committee reporting, and meetings as needed while coordinate external and internal auditors on an ongoing basis regarding Financial Reporting and Sox compliance. •  Leading all aspects of the financial sections of public offering documents, proxy, and statutory reporting. You may be asked to work on other projects as required.
Manager	Chief Executive Officer
Place of Work	Home-based [***]
Commencement Date	May 13, 2024
Base Salary	US$ 150,000 per annum (paid as $12,500 per calendar month)

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Target Bonus	20% of your annual base salary Your bonus for 2024 will be calculated based on the first year base salary and will not be pro-rated.
LTI Options Grant (subject to Board approval)	250,000 (two hundred fifty thousand) options over Kazia’s NASDAQ-listed ADS, to vest in four equal annual instalments, beginning on the first anniversary of joining
Health Insurance	Health, Dental, and Vision 100% of premium for employees and a proportion of premium, not less than 50%, for dependents
401(k) Plan	Company sponsored Safe Harbor 401k Plan with Company Match (100% for first 4% and 50% for next 2%). Employees are eligible to participate after one pay cycle. Matching is immediate with no vesting period.
Paid Time Off (PTO)	20 days per calendar year

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ATTACHMENT 2

CONFIDENTIALITY AGREEMENT

For the purposes of this Agreement, Confidential Information means information which came to the employee’s knowledge in the course of, or as a result of, their employment including, but not limited to:

(a) the business or affairs, financial information, intellectual property, business plans, research and development, and sales and marketing information of the Company;

(b) unpatented molecular structures, manufacturing processes, assay methodologies, preclinical or clinical data;

(c) information which would reasonably be considered to be of a business sensitive nature;

(d) trade secrets and confidential information and know-how of the Company;

(e) information regarding investments, investment opportunities, investment strategies and investment research of the Company; and

(f) confidential information of a third party that has been shared with Company.

Confidential Information will not include information which is or becomes readily available in the public domain otherwise than as a result of the breach of this Agreement.

The employee must not use or disclose this Confidential Information during and after their employment, and must take all reasonable steps to prevent the unauthorised disclosure of the Confidential Information, except in the following circumstances:

(a) the Company has given its prior written consent; or

(b) in the proper course of performing their duties and for the benefit of the Company; or

(c) to the extent required by law.

Without limiting the generality of the above, the employee must not disclose Confidential Information to other employees of the Company unless these employees are authorised by the Company to receive this information and need to know this information to perform their duties to the Company.

The employee must immediately notify the Company if the employee suspects or becomes aware that Confidential Information has been improperly used, copied or disclosed.

The employee must not copy or remove from the Company’s premises any document which contains Confidential Information except for the purpose of properly performing the duties of the position and for the benefit of the Company.

The employee must provide assistance reasonably requested by the Company in relation to proceedings against any person for unauthorised use, copying or disclosure of Confidential Information.

Accepted and agreed by:-

/s/ Jeffrey Bonacorda

Name: Jeffrey Bonacorda

Date: April 24, 2024

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ATTACHMENT 3

PROPRIETARY INFORMATION AND INVENTIONS AGREEMENT

In exchange for my becoming employed (or my employment being continued), or retained as a consultant (or my consulting relationship being continued), by Kazia Therapeutics, or any of its current or future subsidiaries, affiliates, successors or assigns (collectively, the “Company”), and for any cash and equity compensation for my services, I hereby agree as follows:

Assignment of Inventions.

(a) Without further compensation, I hereby agree promptly to disclose to the Company, all Inventions (as defined below) which I may solely or jointly develop or reduce to practice during the period of my employment or consulting relationship with the Company which (i) pertain to any line of business activity of the Company, (ii) are aided by the use of time, material or facilities of the Company, whether or not during working hours or (iii) relate to any of my work during the period of my employment or consulting relationship with the Company, whether or not during normal working hours (“Company Inventions”). During the term of my employment or consultancy, all Company Inventions that I conceive, reduce to practice, develop or have developed (in whole or in part, either alone or jointly with others) shall be the sole property of the Company and its assigns to the maximum extent permitted by law (and to the fullest extent permitted by law shall be deemed “works made for hire”), and the Company and its assigns shall be the sole owner of all patents, copyrights, trademarks, trade secrets and other rights in connection therewith. I hereby assign to the Company any rights that I may have or acquire in such Company Inventions.

(b) I have provided to the Company, prior to my engagement, a complete list of all Inventions, if any, made by me prior to my employment or consulting relationship with the Company that are relevant to the Company’s business, and I represent and warrant that such list is complete. If no such list is provided, I represent that I have no such Inventions at the time of signing this Agreement. If in the course of my employment or consultancy (as the case may be) with the Company, I use or incorporate any Invention in which I have an interest into a product or process of the Company, the Company is hereby granted a nonexclusive, fully paid-up, royalty-free, perpetual, irrevocable worldwide license of my interest to use and sublicense such Invention without restriction of any kind.

NOTICE REQUIRED BY REVISED CODE OF WASHINGTON 49.44.140:

Any assignment of Inventions required by this Agreement does not apply to an Invention for which no equipment, supplies, facility or trade secret information of the Company was used and which was developed entirely on the employee’s own time, unless (a) the Invention relates (i) directly to the business of the Company or (ii) to the Company’s actual or demonstrably anticipated research or development or (b) the Invention results from any work performed by the employee for the Company.

Further Assistance and Power of Attorney. I agree to perform, during and after my employment or consulting relationship, all acts deemed necessary or desirable by the Company to permit and assist it, at its expense, in obtaining and enforcing the full benefits, enjoyment, rights and title throughout the world in the Inventions assigned to the Company as set forth in Section 4 above. Such acts may include, but are not limited to, execution of documents and assistance or cooperation in legal proceedings. I

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hereby irrevocably designate the Company and its duly authorized officers and agents as my agent and attorney-in fact, to execute and file on my behalf any such applications and to do all other lawful acts to further the prosecution and issuance of patents, copyright and mask work registrations related to such Inventions. This power of attorney shall not be affected by my subsequent incapacity.

Inventions. As used in this Agreement, the term “Inventions” means discoveries, developments, concepts, designs, ideas, know how, improvements, inventions, trade secrets and/or original works of authorship, whether or not patentable, copyrightable or otherwise legally protectable. This includes, but is not limited to, any new product, machine, article of manufacture, biological material, method, procedure, process, technique, use, equipment, device, apparatus, system, compound, formulation, composition of matter, design or configuration of any kind, or any improvement thereon.

Survival. This Agreement (a) shall survive for a period of five years beyond the termination of my employment by or consulting relationship with the Company, (b) inures to the benefit of successors and assigns of the Company and (c) is binding upon my heirs and legal representatives.

Injunctive Relief. I acknowledge that violation of this Agreement by me may cause irreparable injury to the Company, and I agree that the Company will be entitled to seek extraordinary relief in court, including, but not limited to, temporary restraining orders, preliminary injunctions and permanent injunctions without the necessity of posting a bond or other security and without prejudice to any other rights and remedies that the Company may have for a breach of this Agreement.

Accepted and agreed by:-

/s/ Jeffrey Bonacorda

Name: Jeffrey Bonacorda

Date: April 24, 2024

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