AC699 Fast-Tracked for ESR1-Mutant Breast Cancer

The FDA will speed up the review of AC699, a novel treatment for patients with ER-positive, HER2-negative ESR1-mutant advanced or metastatic breast cancer.

The Food and Drug Administration (FDA) granted a fast track designation to the novel drug, AC699, for the treatment of patients with ER-positive, HER2-negative ESR1-mutant advanced or metastatic breast cancer that has progressed on one or more prior endocrine-based therapies, according to Accutar Biotechnology, the manufacturer of the agent.

According to the FDA, fast track designations are given to speed up the review of drugs that can improve outcomes for serious conditions and diseases. To be fast-tracked — which includes more frequent communication between the FDA and the pharmaceutical company — clinical trials must show that the drug is safe and promising, especially compared to other available treatments.

"Receiving Fast Track designation for AC699 from the FDA highlights their recognition of the serious and life-threatening nature of this malignancy, the critical unmet medical needs not fully addressed by existing therapies, and the potential of AC699 to fill in the gap," Jie Fan, chief executive officer of Accutar Biotechnology, Inc, said in the company-issued press release.

ER-positive, HER2-negative is the most common subtype of breast cancer, and approximately 20-40% of patients with this disease and have been treated with endocrine (hormone-based) therapy have a mutant ESR1 gene, according to the release.

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The ER-positive, HER2-negative ESR1-mutant breast cancer is typically treated with Orserdu (elacestrant), a drug that gained FDA approval in February 2023.

This fast track designation for AC699 was based on findings from an ongoing phase 1 trial presented at the 2024 American Society of Clinical Oncology (ASCO) Annual Conference. Findings showed that the overall response rate (ORR; percentage of patients whose disease shrinks or disappears) was 50% for patients with breast cancer who harbored an ESR1 mutation.

AC699 is a drug that is taken orally. Similar to Orserdu, it works by breaking down a specific type of estrogen receptor that is involved in the growth of breast cancer. In preclinical studies — meaning those that were not conducted on humans — AC699 showed “promising anti-tumor activities in ER-positive animal tumor models.”

Researchers are still recruiting patients to participate in the phase 1 trial of AC699. The main goal of the study is to determine the recommended dose, safety profile and efficacy of the drug, as well as the pharmacokinetics, which describes how the body interacts with a drug, according to the National Institutes of Health.

According to the trial’s listing on ClinicalTrials.gov, researchers plan on completing the study in December 2024.

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