Ferroptosis induction, androgen biosynthesis disruption and prostate cancer suppression by androgen and vitamin D combination

Prostate cancer regression by hormonal vitamin D₃(calcitriol) is clinically untenable despite its well-documented anticancer effects in experimental models, since supraphysiologic dosing of calcitriol required in clinical settings causes hypercalcemia and other toxicities. We show that subnanomolar/low-nanomolar calcitriol, while non-inhibitory on its own, inhibited CRPC cells upon co-treatment with androgen (5α-DHT) at a physiologic level, evident from G1/S cell cycle arrest, induction of p21/Cip1, blockade of clonal cell growth, retardation of proliferation, migration and invasion of cells in vitro, and xenograft growth suppression in vivo. AKR1D1, an androgen-inactivating 5β-reductase, was upregulated >30-fold upon calcitriol/DHT co-treatment, while each hormone individually did not induce AKR1D1. In contrast, HSD3β1, a key enzyme for androgen biosynthesis, was upregulated >12-fold by calcitriol, which was blocked by DHT co-treatment. Elevated AKR1D1 and reduced HSD3β1 would lower intracellular androgens and contribute to CRPC repression. Autophagy mediated ferroptosis (ferritinophagy) paralleled CRPC growth inhibition by the hormone combination –indicated by LC3B induction, ferritin reduction, and upregulation of mRNAs encoding NCOA4, ALOX-5 and PTGS2 which are core participants in ferroptosis. The combination treatment caused lipid peroxidation, evident from the fluorescence shift of C11-BODIPY(581/591)-labeled cells from red to green, and from elevated malondialdehyde. GPX4 - an antioxidant peroxidase and ferroptosis regulator – was downregulated. Bipolar androgen therapy employing supraphysiologic testosterone is under clinical evaluation for efficacy against treatment-resistant metastatic CRPC, although the high androgen dose raises safety concerns. Vitamin D and androgen administered concurrently at physiologic levels may offer a superior alternative for arresting CRPC.