For men whose metastatic prostate cancer has stopped responding to standard androgen-pathway blockade, treatment options narrow quickly and outcomes worsen. A new class of molecular tools — PROTAC degraders — has raised the possibility of dismantling the androgen receptor entirely rather than merely blocking it, potentially circumventing the resistance mutations that render conventional inhibitors ineffective. This trial represents an early but meaningful clinical test of that concept.
The Phase 1b study enrolled 45 patients with metastatic prostate cancer experiencing PSA progression on abiraterone, adding bavdegalutamide (ARV-110) — an oral PROTAC that tags the androgen receptor for proteasomal destruction — at 420 mg daily atop continued abiraterone. No dose-limiting toxicities were recorded. The most prevalent treatment-emergent adverse events were fatigue and nausea, each affecting roughly half of participants, with 17.8% experiencing grade 3 events. Critically, bavdegalutamide did not meaningfully alter abiraterone's pharmacokinetic profile, supporting co-administration. A PSA control rate of approximately 49% was observed, and 13 patients remained on therapy at data cutoff. Seven patients harbored androgen receptor ligand-binding domain mutations — a subgroup of particular mechanistic interest given PROTAC's mechanism-of-action advantage over competitive inhibitors in this setting.
PROTAC technology has generated sustained preclinical excitement precisely because degrader molecules can eliminate mutant receptor protein regardless of whether the ligand-binding pocket is altered — the Achilles' heel of enzalutamide and apalutamide. This trial's safety and tolerability data are encouraging for a first-in-combination context, though the 48.9% dose-modification rate warrants attention in longer treatment courses. The cohort is small and uncontrolled, so efficacy signals like PSA50 rates are hypothesis-generating rather than practice-changing. The field will need randomized data to determine whether PROTAC-based AR degradation meaningfully extends radiographic progression-free survival beyond what sequential ARPI switching achieves. Still, establishing the recommended Phase 2 dose without pharmacokinetic interference is an important procedural milestone for this mechanistically novel combination.