Combined TP53 and RB1 Loss Promotes Prostate Cancer Resistance to a Broad Spectrum of Cancer Therapeutics and Confers Vulnerability to Replication Stress

Prostate cancers (PC) with loss of the potent tumor suppressors TP53 and RB1 exhibit poor outcomes that include resistance to androgen receptor (AR) pathway antagonists. TP53 and RB1 also influence cell plasticity and are frequently lost in PCs with neuroendocrine (NE) differentiation. Therapeutic strategies that address these aggressive variant PCs are urgently needed. Using deep genomic profiling of 410 metastatic biopsies, we determined the relationships between combined TP53 and RB1 loss and PC phenotypes. Notably, 40% of TP53/RB1 deficient tumors were classified as AR-active adenocarcinomas indicating that NE differentiation is not an obligate consequence of TP53/RB1 inactivation. A gene expression signature reflecting TP53/RB1 loss was associated with diminished responses to AR antagonists and reduced survival. These tumors exhibit high proliferation rates and evidence of elevated DNA repair processes. While tumor cells lacking TP53/RB1 were highly resistant to all single agent therapeutics, the combination of pharmacological PARP and ATR inhibition produced significant responses, reflecting a clinically-exploitable vulnerability resulting from replication stress. Overall design: RNA sequencing of human prostate tumor cell lines and metastatic castration-resistant prostate cancer (mCRPC) tumors using Illumina TruSeq Stranded mRNA Library prep and sequenced on Illumina HiSeq 2500.