The RNA polymerase I transcription inhibitor CX-5461 cooperates with topoisomerase 1 inhibition by enhancing the DNA damage response in homologous recombination-proficient high-grade serous ovarian cancer

Shunfei Yan,Natalie Brajanovski,Madeleine R C Tancock,Ross D Hannan,Elaine Sanij,Kaylene J Simpson,Katherine M Hannan,Sarah Ellis,Jian Kang,Jiachen Xuan,Richard B Pearson,Carleen Cullinane,Karen E Sheppard,Piyush B Madhamshettiwar,Keefe T Chan

doi:10.1038/s41416-020-01158-z

Abstract

BackgroundIntrinsic and acquired drug resistance represent fundamental barriers to the cure of high-grade serous ovarian carcinoma (HGSC), the most common histological subtype accounting for the majority of ovarian cancer deaths. Defects in homologous recombination (HR) DNA repair are key determinants of sensitivity to chemotherapy and poly-ADP ribose polymerase inhibitors. Restoration of HR is a common mechanism of acquired resistance that results in patient mortality, highlighting the need to identify new therapies targeting HR-proficient disease. We have shown promise for CX-5461, a cancer therapeutic in early phase clinical trials, in treating HR-deficient HGSC.MethodsHerein, we screen the whole protein-coding genome to identify potential targets whose depletion cooperates with CX-5461 in HR-proficient HGSC.ResultsWe demonstrate robust proliferation inhibition in cells depleted of DNA topoisomerase 1 (TOP1). Combining the clinically used TOP1 inhibitor topotecan with CX-5461 potentiates a G2/M cell cycle checkpoint arrest in multiple HR-proficient HGSC cell lines. The combination enhances a nucleolar DNA damage response and global replication stress without increasing DNA strand breakage, significantly reducing clonogenic survival and tumour growth in vivo.ConclusionsOur findings highlight the possibility of exploiting TOP1 inhibition to be combined with CX-5461 as a non-genotoxic approach in targeting HR-proficient HGSC.

Highlights

Intrinsic and acquired drug resistance represent fundamental barriers to the cure of high-grade serous ovarian carcinoma (HGSC), the most common histological subtype accounting for the majority of ovarian cancer deaths
We demonstrate the CX-5461 exhibits a unique sensitivity pattern distinct to those reported for G-quadruplex stabilisers and topoisomerase 2 (TOP2) poisons previously thought to function in an equivalent mechanism to CX-5461.16 Importantly, we find that DNA topoisomerase I (TOP1) inhibition can be combined with CX-5461 to target homologous recombination (HR)-proficient HGSC cells
We show that the combination of CX-5461 and topotecan inhibits proliferation of HR-proficient HGSC by enhancing G2/M checkpoint arrest induced by replication stress and activation of the ATR pathway without further generating DNA strand breaks compared to single-agent treatment

Summary

Introduction

Intrinsic and acquired drug resistance represent fundamental barriers to the cure of high-grade serous ovarian carcinoma (HGSC), the most common histological subtype accounting for the majority of ovarian cancer deaths. HGSC is characterised by nearly universal TP53 mutations (>96%), and 50% of HGSC harbour defects in homologous recombination (HR) DNA repair genes, the most common alterations occurring in breast cancer-related antigen 1 (BRCA1) and BRCA2, which are necessary for maintaining genomic integrity.[1] Defects in HR confer exquisite sensitivity of HGSC to standard DNA-damaging chemotherapies (carboplatin/cisplatin and paclitaxel) as well as the recently Food Drug Administrationapproved poly-ADP ribose polymerase (PARP) inhibitors (olaparib, rucaparib, niraparib, talazoparib), which are synthetic lethal by generating catastrophic DNA damage and cell death in cells lacking HR.[2] resistance to these therapies frequently develops via multiple mechanisms, including stabilisation of stalled DNA replication forks, increased drug efflux, decreased PARP trapping and restoration of HR, a common form of resistance observed in the clinic that inevitably results in patient mortality.[3,4,5,6,7] Of the 50% primary HGSC tumours that are HRproficient, 20% harbour CCNE1 amplifications, which are associated with intrinsic platinum-based chemotherapy, PARPinhibitor resistance and poor clinical outcome.[8] new therapies targeting HR-proficient HGSCs arising from both intrinsic and acquired resistance are urgently needed to improve patient outcomes

Methods

Results

Conclusion