Ambrx Announces NovoCodex's Dosing of First Patient with ARX305, Ambrx's Investigational Antibody Drug Conjugate Targeting CD70

- ARX305 is being evaluated by Ambrx's partner, NovoCodex, in a Phase 1 clinical trial in various advanced tumors -

- First patient dosing triggers milestone payment to Ambrx -

- NovoCodex responsible for funding Ambrx's Phase 1 development of ARX305 -

Ambrx Biopharma Inc., or Ambrx, (NYSE: AMAM), a clinical stage biopharmaceutical company using its proprietary Engineered Precision Biologics (EPBs) platform to create antibody drug conjugates (ADCs), today announced the first patient has been dosed by Ambrx's partner, NovoCodex Biopharmaceuticals, Inc. (NovoCodex) in its Phase 1 trial of ARX305 in patients with advanced solid tumors. ARX305 is the only anti-CD70 ADC in active development that targets CD70, a protein that is overexpressed in a broad range of solid and hematologic tumors, giving it the potential to treat a range of liquid and solid tumor cancers, where CD70 is overexpressed.

According to their development agreement, NovoCodex and Ambrx will collaborate in the development of ARX305 up until the completion of Phase 1 clinical trials. Under the terms of the development agreement, Ambrx is eligible to receive up to $4.0 million in clinical milestones, as well as tiered royalties in the low teens percentage range of aggregate net sales of ARX305 in China from NovoCodex. As a result of the first patient being dosed in NovaCodex's Phase 1 clinical trial in China, Ambrx will now receive a significant portion of the $4.0 million milestones payments.

Ambrx plans to leverage the safety data from NovoCodex's Phase 1 dose escalation clinical trial to inform its own Phase 1a trial, thereby efficiently using the company's cash and resources. Specifically, using the data gained from NovoCodex's dose escalation trial, Ambrx can reduce the expense of conducting its own initial dose escalation clinical trial. Building on the NovoCodex Phase 1 data, Ambrx plans to expedite its Phase 1a trial of ARX305 by starting at higher doses (i.e., doses closer to a recommended Phase 2 dose). Following the completion of NovoCodex's Phase 1 clinical trial, Ambrx's Phase 1a clinical trial for ARX305 is expected to initiate in the second half of 2023. NovoCodex is also responsible for funding a majority of Ambrx's development of ARX305 through the end of Phase 1 clinical trials, up to a certain cap, and will be able to leverage Ambrx's data in its own development of ARX305.

"The dosing of the first patient with ARX305 by NovoCodex represents an important strategic benchmark that will not only advance another Ambrx-generated ADC asset into the clinic, but also will allow us to leverage findings from the study to inform our own clinical trial," said Daniel O'Connor, Chief Executive Officer of Ambrx. "Leveraging partner data will both expedite internal development and cut costs, establishing a strong foundation from which to begin our own Phase 1 trial."

Mr. O'Connor added, "CD70 is highly expressed on the surface of a variety of hematological and solid tumor cells, and I believe the stability of ARX305 conferred by our proprietary EBP platform uniquely positions it as a potential best-in-class treatment for CD70 expressing tumors. I want to thank NovoCodex for continuing our strong partnership and look forward to continued progress as they advance ARX305 through the clinic."

About Ambrx Biopharma Inc. (Ambrx)

Ambrx is a clinical stage biopharmaceutical company using an expanded genetic code technology platform to discover and develop Engineered Precision Biologics. These include next generation antibody drug conjugates (ADCs) and other engineered therapies to modulate the immune system. Ambrx is advancing a focused portfolio of clinical and preclinical programs designed to optimize efficacy and safety in multiple cancer indications, including its lead product candidate ARX517, a prostate-specific membrane antigen (PSMA) targeting ADC. In addition, Ambrx has clinical collaborations with multiple partners on drug candidates generated using Ambrx technology. For more information, please visit www.ambrx.com .

Forward-Looking Statements

This press release includes certain "forward-looking statements" intended to qualify for the "safe harbor" from liability established by the Private Securities Litigation Reform Act of 1995, as amended. Forward-looking statements may be identified by the words "anticipate," believe," "estimate," "expect," "intend," "plan," "project," "may," "will," "could," "should," "seek," "potential" and similar expressions, and include, without limitation, express or implied statements regarding Ambrx's beliefs and expectations regarding the advancement and potential benefits of its product candidates, clinical development and strategic plans, and the timing of program updates and milestones related to its product candidates. Forward-looking statements are based on Ambrx's current expectations and are subject to inherent uncertainties, risks and assumptions that are difficult to predict. Factors that could cause actual results to differ include, but are not limited to, those risks and uncertainties associated with: the continuing impact of the COVID-19 pandemic and other public health-related risks and events on Ambrx's business, operations, strategy, goals and anticipated milestones; Ambrx's ability to execute on its strategy including with respect to the timing of its R&D efforts, initiation of clinical trials and other anticipated milestones; risks associated with development of novel therapeutics, including potential delays in clinical trials and regulatory submissions and the fact that future clinical trial results may not be consistent with preliminary results or results from prior preclinical studies or clinical trials; Ambrx's ability to fund operations as anticipated; and the additional risks and uncertainties set forth more fully under the caption "Risk Factors" in Ambrx's Annual Report on Form 20-F filed with the United States Securities and Exchange Commission (SEC) on April 26, 2022, and elsewhere in Ambrx's filings and reports with the SEC. Forward-looking statements contained in this press release are made as of this date, and Ambrx undertakes no duty to publicly update or revise any forward looking statements, whether as a result of new information, future events or otherwise, except as may be required under applicable law.

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