Single-cell imaging analysis, therapeutic modeling and a Phase Ib trial validate BCL-2 as a target across heterogeneous castration-resistant prostate cancer

Abstract BCL-2 has been implicated in prostate cancer (PCa) progression and development of castration-resistant disease (CRPC); however, it remains unclear how the BCL-2- and AR-expressing PCa cell populations evolve across the PCa continuum, how AR molecularly regulates BCL-2 and whether BCL-2 represents a common therapeutic target in heterogeneous CRPC. Here we first show the selective induction of BCL-2 by AR pathway inhibitors (ARPIs). Vectra-based quantitative multiplex immunofluorescence (qmIF) and image mass cytometry (IMC) analyses with single-cell resolution in patient PCa and xenograft models reveal markedly increased BCL-2+ (AR+ or AR-) PCa cells in CRPC. Mechanistically, AR represses BCL-2 transcription through several AR binding sites and ARPIs relieve this repression. Therapeutic studies in cells, organoids and xenografts support BCL-2 as a shared vulnerability across diverse CRPC subtypes. A Phase Ib clinical trial (NCT03751436) combining enzalutamide and BCL-2 inhibitor venetoclax demonstrated reduced circulating tumor cells in responding patients. In summary, by integrating high-content single-cell level imaging analyses with mechanistic studies, extensive preclinical therapeutic experiments and a Phase Ib clinical trial, our studies herein elucidate the AR+/-BCL-2+/- PCa cell subpopulation dynamics and credentials BCL-2 as a vital therapeutic target in heterogeneous CRPC.