SAN DIEGO - Ambrx Biopharma, Inc., or Ambrx, (NASDAQ: AMAM), today announced that in biomarker unselected patients ARX517 monotherapy demonstrated a strong antibody-drug conjugate (ADC) safety profile at all doses tested with promising early efficacy signals that included PSA50 declines, ctDNA reductions, and RECIST v1.1 tumor response.
The ESMO clinical posters present updated safety, efficacy and PK data from Ambrx's on-going trial, APEX-01 (NCT04662580).
APEX-01 is a Phase 1 / 2, first-in-human, open label dose escalation and dose expansion trial enrolling patients with metastatic castration-resistant prostate cancer (mCRPC). To be eligible for APEX-01, patients with mCRPC had to satisfy certain criteria, including receiving at least two prior FDA-approved therapies for metastatic disease, with at least one being a 2nd generation androgen receptor pathway inhibitor (ARPI), and who have met at least one of the following three criteria: PSA progression defined by a minimum of two rising PSA values, radiographic progression by RECIST v1.1, and/or disease progression by the presence of new bone lesions.
APEX-01 opened for enrollment in July 2021 and is the only on-going clinical trial in the United States targeting PSMA with an ADC. The two primary objectives of APEX-01 are to analyze the safety and tolerability of ARX517 and establish a recommended Phase 2 dose.
Dr. John Shen, a medical oncologist at UCLA and an investigator on APEX-01, stated that, 'The PSA results are very encouraging especially in this heavily pre-treated patient population where eligible patients would have exhausted all available and appropriate treatment options prior to enrolling in this study.'
About ARX517
ARX517 is an investigational antibody-drug conjugate composed of a humanized anti-PSMA mAb linked to AS269, an Ambrx proprietary potent microtubule inhibitor. ARX517 is designed to target the prostate-specific membrane antigen (PSMA). PSMA is highly expressed in metastatic castration-resistant prostate cancer (mCRPC) and has been validated as a therapeutic target.
In preclinical studies, the cancer cell killing payload of ARX517, pAF-AS269, is highly cytotoxic when delivered by a mAb into cancer cells. ARX517's site-specific linkage, stable conjugation chemistry, and non-cleavable linker result in an ADC with a homogenous drug-antibody-ratio, mAb-like biophysical properties, and exceptional stability. Therefore, Ambrx believes ARX517 can promote highly specific tumor cell killing with minimal off-target toxicity.
ARX517 has the potential to be a first- and best-in-class anti-PSMA ADC addressing the high unmet medical need in mCRPC.
About APEX-01
Ambrx is currently investigating ARX517 in the APEX-01 (NCT04662580) first-in-human Phase 1 / 2, multicenter, dose escalation and dose expansion clinical study to evaluate the safety, pharmacokinetics, and preliminary anti-tumor activity of ARX517 in adult subjects and is currently enrolling patients with advanced prostate cancer (mCRPC) whose tumors have progressed following at least two FDA approved treatments for prostate cancer, including at least one second-generation androgen receptor pathway inhibitor, and have met one of the following three criteria: PSA progression defined by a minimum of 2 rising PSA values or radiographic progression by RECIST v 1.1 or disease progression by the presence of new bone lesions.
About Ambrx Biopharma, Inc.
Ambrx is a clinical-stage biopharmaceutical company using an expanded genetic code technology platform to discover and develop 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 ARX517, its proprietary ADC targeting the prostate-specific membrane antigen (PSMA) and ARX788, its proprietary ADC targeting HER2. In addition, Ambrx has preclinical and clinical collaborations with multiple partners on drug candidates generated using Ambrx technology. Ambrx was spun out of The Scripps Research Institute in 2003 and has several other product candidates involving ADCs and other aspects of Ambrx's protein engineering technology.
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 'intend,' 'plan,' and similar expressions. 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: 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 and marketing approval of novel therapeutics, including potential delays in clinical trials and regulatory submissions and the fact that future clinical trial results/data may not be consistent with interim, initial or preliminary results/data or results/data 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 Current Report on Form 8-K filed with the SEC on October 12, 2023, 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.
Contact:
Mike Moyer
Tel: 617-308-4306
Email: mmoyer@lifesciadvisors.com
AMBRX BIOPHARMA INC. 
