PARP Inhibition Suppresses GR-MYCN-CDK5-RB1-E2F1 Signaling and Neuroendocrine Differentiation in Castration-Resistant Prostate Cancer


In this study we addressed the underlying mechanisms for the association between enzalutamide treatment and NEPC, and the critical involvement of MYCN, and loss of RB1 function in NED of prostatic epithelial cells, and the development of NEPC. We further sought to determine whether PARP inhibition could suppress NEPC, and to identify molecular determinants of this therapeutic activity.


We utilized a novel prostate cancer PDX treatment model, prostatic adenocarcinoma and NEPC cell lines, an NEPC organoid line, and NEPC xenograft models to address the mechanistic basis of enzalutamide (ENZ)-induced NED, and to analyze suppression of NED and NEPC growth by PARP inhibition.


We identified an ENZ treatment-associated glucocorticoid receptor (GR)-MYCN-CDK5-RB1-E2F1 signaling pathway that drives NED in prostatic adenocarcinoma patient-derived xenograft (PDX) and cell line models. Mechanistically, long-term ENZ treatment transcriptionally upregulates signaling of the GR-MYCN axis, leading to CDK5R1 and CDK5R2 upregulation, Rb1 phosphorylation, and N-Myc- and E2F1-mediated NED gene expression. Importantly, olaparib (OLA) or talazoparib (TALA) suppressed these activities, and the combination of OLA and dinaciclib (DINA), an inhibitor of CDK2 and CDK5, which also inhibits Rb1 phosphorylation, suppressed NED, and significantly improved therapeutic efficiency in neuroendocrine prostate cancer (NEPC) cells in vitro and in NEPC tumors in vivo.


The results of our study indicate an important role of GR-MYCN-CDK5R1/2-RB1-NED signaling in ENZ-induced, and PARP inhibitor-suppressed NEPC. We also demonstrated efficacy for OLA+DINA combination therapy in NEPC xenograft models.

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S1060 Olaparib (AZD2281) Olaparib (AZD2281, KU0059436) is a selective inhibitor of PARP1/2 with IC50 of 5 nM/1 nM in cell-free assays, 300-times less effective against tankyrase-1. Olaparib induces significant autophagy that is associated with mitophagy in cells with BRCA mutations.

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