Drivers of AR indifferent anti-androgen resistance in prostate cancer cells

Florian Handle,Stefan Prekovic,Roy Eerlings,Steven Joniau,Sarah El Kharraz,Alfonso Urbanucci,Ian G Mills,Frank Claessens,Thomas Van Den Broeck,Christine Helsen,Lisa Moris,Gerhardt Attard,Elien Smeets

doi:10.1038/s41598-019-50220-1

Abstract

Inhibition of the androgen receptor (AR) by second-generation anti-androgens is a standard treatment for metastatic castration resistant prostate cancer (mCRPC), but it inevitably leads to the development of resistance. Since the introduction of highly efficient AR signalling inhibitors, approximately 20% of mCRPC patients develop disease with AR independent resistance mechanisms. In this study, we generated two anti-androgen and castration resistant prostate cancer cell models that do not rely on AR activity for growth despite robust AR expression (AR indifferent). They are thus resistant against all modern AR signalling inhibitors. Both cell lines display cross-resistance against the chemotherapeutic drug docetaxel due to MCL1 upregulation but remain sensitive to the PARP inhibitor olaparib and the pan-BCL inhibitor obatoclax. RNA-seq analysis of the anti-androgen resistant cell lines identified hyper-activation of the E2F cell-cycle master regulator as driver of AR indifferent growth, which was caused by deregulation of cyclin D/E, E2F1, RB1, and increased Myc activity. Importantly, mCRPC tissue samples with low AR activity displayed the same alterations and increased E2F activity. In conclusion, we describe two cellular models that faithfully mimic the acquisition of a treatment induced AR independent phenotype that is cross-resistant against chemotherapy and driven by E2F hyper-activation.

Highlights

Androgen deprivation therapy is part of the first-line treatment for advanced prostate cancer, but it inevitably leads to the development of castration resistant prostate cancer (CRPC)[1,2]
We describe the independent generation of two distinct multi anti-androgen, castration, and chemotherapy resistant cell lines derived from LNCaP that show an androgen responsive, androgen receptor (AR) indifferent non-neuroendocrine phenotype that is driven by hyper-activation of the cell-cycle master regulator E2F due to multiple alterations in cyclin D/E, E2F1, RB1 and Myc signalling
SiRNA mediated MYC knockdown led to a reduction in the proliferation of all cell lines, but the effect was significantly stronger in ResB cells compared to LNCaP (Fig. 6d, Supplementary Fig. 4c). These findings suggest that deregulation of the MYC/E2F1/RB1 cell-cycle regulator axis by various means is a ubiquitous event in AR indifferent prostate cancer that is necessary to overcome the G1 arrest caused by low AR activity

Summary

Introduction

Androgen deprivation therapy is part of the first-line treatment for advanced prostate cancer, but it inevitably leads to the development of castration resistant prostate cancer (CRPC)[1,2]. The efficacy of enzalutamide and other anti-androgens is limited by the rapid development of acquired resistance and numerous in vitro and in vivo models have been developed[10,11,12,13,14,15,16] These model systems together with corroborating clinical data from patients have led to the identification of a large variety of anti-androgen resistance mechanisms[17,18,19]. We describe the independent generation of two distinct multi anti-androgen, castration, and chemotherapy resistant cell lines derived from LNCaP that show an androgen responsive, AR indifferent non-neuroendocrine phenotype that is driven by hyper-activation of the cell-cycle master regulator E2F due to multiple alterations in cyclin D/E, E2F1, RB1 and Myc signalling

Methods

Results

Conclusion