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

Abstract

Prostate cancer regression by hormonal vitamin D₃(calcitriol) is clinicallyuntenable despite its well-documented anticancer effects in experimental models, sincesupraphysiologic dosing of calcitriolrequiredin 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) ata physiologic level, evidentfrom G1/S cell cycle arrest, induction of p21/Cip1, blockade of clonal cell growth, retardation of proliferation, migration and invasion of cellsinvitro, and xenograft growth suppressioninvivo. AKR1D1, an androgen-inactivating 5β-reductase, was upregulated >30-fold upon calcitriol/DHT co-treatment, while each hormone individually didnot 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 reducedHSD3β1 wouldlower 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 encodingNCOA4, ALOX-5 and PTGS2which arecore participants in ferroptosis.The combination treatment caused lipid peroxidation, evident from thefluorescence 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 isunderclinical 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 alternativefor arresting CRPC.