Phase I multi-center clinical and biomarker study of the dual-action androgen receptor inhibitor ONCT-534

ONCT-534 is a dual-action androgen receptor inhibitor (DAARI) that combines AR antagonism and degradation via N-terminal domain binding, additionally targeting AR splice variants. In this study patients received ONCT-534 daily ranging from 40 to 1200 mg. The primary objectives were safety and dose-limiting toxicities (DLTs). Additional objectives included antitumor activity and AR signaling biomarkers. Adverse events (AEs) were assessed within the first 28 days for DLTs. Clinical activity was evaluated by PSA and radiographic progression per PCWG3 and RECIST v1.1. The trial was stopped early and not all patients were evaluated per protocol. Twenty-one patients received ONCT-534 across six doses. The most common AEs were anemia, back pain, and fatigue. While no DLTs were observed within 28 days, Grade 3/4 AEs occurred later in 9 patients (anemia most frequently). One patient discontinued due to treatment-related AE. No radiographic or PSA-based responses were observed; however, three patients showed PSA declines at week 4, with one achieving a PSA50 at time of study closure. Of 10 patients with baseline AR protein data, the median change was - 40.59% in AR protein levels at week 4. In the 300 mg cohort, 3 patients showed concordant decreases in AR protein and AR gene expression. Here, PSA levels correlated positively with AR target gene and AR gene expression. ONCT-534 had acceptable safety and demonstrated biological activity through AR protein degradation and AR signaling suppression in mCRPC patients. Although clinical responses weren't observed, these findings provide proof-of-concept for examining AR protein changes in patients receiving DAARIs.