Ambrx Announces Positive Data on ARX788 for the Treatment of HER2+ Gastric Cancer Presented at CSCO

­- ARX788 demonstrated an ORR of 44.4% in ongoing ACE-Gastric-01 Phase 1 clinical study in China -

- Ambrx and NovoCodex recently dosed the first patient in the ACE-Gastic-02 global Phase 2/3 study -

Ambrx (NYSE: AMAM), a clinical stage biopharmaceutical company using an expanded genetic code technology platform to create Engineered Precision Biologics, today announced that NovoCodex Pharmaceuticals Ltd. (NovoCodex), Ambrx’s partner in China, presented positive interim data from the ACE-Gastric-01 Phase 1 clinical study of ARX788 for the treatment of HER2+ metastatic gastric / gastroesophageal junction (GEJ) cancer at The Chinese Society of Clinical Oncology (CSCO). The newly presented data suggests that ARX788 at a 1.7 mg/kg dose has a tolerable safety profile. The data presented here adds to and updates trial data that Ambrx presented at the 2021 American Society of Clinical Oncology (ASCO) Annual Meeting in June 2021. Ambrx received Orphan Drug designation from the FDA for the treatment of gastric cancer, including cancer at the GEJ, in early 2021.

Updated ACE-Gastric-01 Phase 1 Interim Data Highlights

(Data as of June 30, 2021)

• 7 patients dosed at 1.7 mg/kg every three weeks.
• Demonstrated overall response rate (ORR) of 44.4% (12/27) in the response-evaluable patients across all three cohorts (1.3 mg/kg, 1.5 mg/kg, 1.7 mg/kg every three weeks).
• Low drug-related severe adverse events (SAE) occurred in 6.7% (2/30) of all treated patients across all three cohorts (1.3 mg/kg, 1.5 mg/kg, 1.7 mg/kg every three weeks). Drug-related grade 3 and above adverse events (AEs) comprised only 10% (3/30).
  • As expected, the most common AEs observed were ocular-related and dose-dependent.
• Median overall survival (mOS) of 10.7 months across all three cohorts (1.3 mg/kg, 1.5 mg/kg, 1.7 mg/kg every three weeks) and mOS for the 1.7 mg/kg cohort has not been reached.
• Enrollment in ACE-Gastric-01 is completed with ongoing follow-up.

“We are thrilled with the progress from the NovoCodex sponsored study of our lead clinical asset, ARX788, and look forward to continuing our collaboration as we explore the capabilities of our antibody drug conjugate in treating HER2 positive cancers and solid tumors,” said Feng Tian, Ph.D., Chairman of the Board, President and CEO of Ambrx. “We are encouraged by the continued positive data from the ACE-Gastric-01 study and we look forward to enrolling more patients in our ongoing global co-sponsored ACE-Gastric-02 Phase 2/3 trial.”

ACE-Gastric-01 is a Phase 1 clinical study of ARX788 for the treatment of HER2+ metastatic gastric/GEJ cancer that is being conducted in China by Ambrx’s partner, NovoCodex. The ongoing clinical study recently completed enrollment of 30 patients and is designed to be a dose escalation and expansion study with patients receiving treatment doses of 1.3 mg/kg, 1.5 mg/kg, or 1.7 mg/kg every 3 weeks. Ambrx previously presented data from two Phase 1 studies of ARX788 at ASCO where patients received a dose of ARX788 up to 1.5 mg/kg every three weeks or every four weeks.

In August 2021, NovoCodex also announced the dosing of the first patient in the Ambrx and NovoCodex co-sponsored global Phase 2/3 trial of ARX788 in HER2+ gastric cancer. ACE-Gastric-02 is a multicenter, randomized, controlled clinical trial to evaluate the efficacy and safety of ARX788 in patients with HER2+ advanced gastric or gastroesophageal junction adenocarcinoma.

About 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), bispecifics, targeted immuno-oncology therapies, novel cytokines to modulate the immune system, and long-acting therapeutic peptides for metabolic and cardiovascular disease. Ambrx is advancing a robust portfolio of clinical and preclinical programs designed to optimize efficacy, safety and ease of use, in multiple therapeutic areas, including its lead product candidate ARX788. In addition, the company has clinical collaborations with multiple partners, for 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, the timing of future events, and anticipated upcoming milestones. 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 impact of the COVID-19 pandemic 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 studies 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 registration statement on Form F-1 filed with the United States Securities and Exchange Commission (SEC) on June 14, 2021, and elsewhere in Ambrx’s filings and reports with the SEC. Forward-looking statements contained in this announcement 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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