Adcentrx Therapeutics, a clinical-stage biotechnology company developing antibody-drug conjugate (ADC) therapies for cancer treatments and other life-threatening diseases, announced on July 8, 2025, that FDA has granted orphan drug designation to ADRX-0405, Adcentrx’s treatment of patients with gastric cancer.

"Receiving orphan drug designation from FDA is a notable milestone for Adcentrx and reinforces the potential for ADRX-0405 to improve the lives of patients with gastric cancer," said Hui Li, Ph.D., founder and chief executive officer of Adcentrx. "We are encouraged by the progress of our Phase 1a trial and look forward to further evaluating the safety, tolerability and anti-tumor activity of ADRX-0405 in gastric and other cancer.”1

ADRX-0405 is currently under evaluation in Phase 1a of Phase 1a/b clinical trials for treatment of select advanced solid tumors such as metastatic castration resistant prostate cancer, gastric cancer, and non-small cell lung cancer.

This is a 2-part study. Phase 1a will consist of a dose escalation of ADRX-0405 to evaluate initial safety and tolerability in patients with select advanced solid tumors, including metastatic castration resistant prostate cancer (mCRPC), gastric cancer (GC), and non-small cell lung cancer (NSCLC) and to identify the recommended dose to be used in the Phase 1b. Phase 1b will further evaluate the safety and tolerability, as well as preliminary efficacy, and identify the optimal dose of ADRX-0405 in subjects with previously treated metastatic castration resistant prostate cancer (mCRPC).2

ADRX-0405 is uniquely being tested during its 1a/b clinical trials. ADRX-0405 is labeled as a STEAP1 ADC (primarily associated with forms of prostate cancer) but is instead targeting gastric cancer during this round of clinical trials.

ADRX-0405 is a clinical-stage next-generation ADC targeting six-transmembrane epithelial antigen of the prostate 1 (STEAP1), a cell surface protein that is upregulated in prostate cancer and certain other cancers with limited expression in normal healthy tissue. The ADC is composed of a humanized IgG1 antibody coupled with a novel topoisomerase inhibitor linker-payload through Adcentrx's innovative i-Conjugation® technology platform––a core component in the design of the company's ADCs. The platform utilizes a cleavable linker and stable conjugation chemistry to enhance payload delivery. This novel technology enables a highly stable ADC with a drug-antibody ratio of eight (DAR 8) to maximize payload delivery to solid tumors. ADRX-0405 preclinical studies have demonstrated its favorable pharmacokinetics, safety profile, and significant efficacy across multiple animal tumor models. ADRX-0405 is currently being evaluated in a Phase 1a/b clinical trial.1

The American Cancer Society estimates that there are roughly 30,300 new cases of gastric cancer in the U.S. in 2025, meeting FDA requirements to be labeled as a rare disease. This streamlined the FDA’s decision to designate ADRX-0405 as an Orphan Drug.

The orphan drug designation is a program designed to stimulate the development of treatments for rare diseases, defined as conditions affecting fewer than 200,000 people in the U.S. Benefits of this designation include access to grant funding and scientific assistance, tax credits for qualified clinical trials, waiver of Prescription Drug User Fee Act (PDUFA) application fees, and the potential for seven years of market exclusivity following regulatory approval.1

Sources
U.S. FDA Grants Orphan Drug Designation to Adcentrx Therapeutics' ADRX-0405 STEAP1 ADC for Gastric Cancer. Adcentrx Therapeutics.July 8, 2025.
https://www.prnewswire.com/news-releases/us-fda-grants-orphan-drug-designation-to-adcentrx-therapeutics-adrx0405-steap1-adc-for-gastric-cancer-302499372.html
A Study of ADRX-0405 in Subjects With Select Advanced Solid Tumors Clinical Trials Gov. April 9, 2025. Accessed July 9, 2025. https://clinicaltrials.gov/study/NCT06710379