Poster Presentation 25th Annual Lorne Proteomics Symposium 2020

Quantitative proteomic analyses of molecular response to the RNA polymerase I transcription inhibitor CX-5461 in olaparib-resistant ID8 mouse ovarian cancer cells   (#107)

Jian Kang 1 , Huy Nguyen 2 , Michael Hendley 2 , Natalie Brajanovski 1 , Ching-Seng Ang 3 , Richard Pearson 1 , Elaine Sanij 1
  1. Division of Research, Peter Maccullum Cancer Centre, East Melbourne, VIC, Australia
  2. Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, VIC, Australia
  3. Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Melbourne, VIC, Australia

The poly (ADP-ribose) polymerase inhibitor (PARPi) olaparib have been approved by FDA for the treatment of homologous recombination (HR) DNA repair–deficient ovarian cancer. However, acquired resistance to PARPi is common and develops through multiple mechanisms including restoration of homologous recombination status. We have developed a selective inhibitor of ribosome biogenesis, CX-5461, which targets RNA Polymerase I (Pol I) transcription of ribosomal RNA (rRNA) synthesis. We have recently demonstrated that CX-5461 activate DNA damage response at rRNA genes, is synthetic lethal with HR deficiency and enhances synthetic lethal interactions of PARPi with HR deficiency in high-grade serous ovarian cancer (HGSOC) patient-derived xenograft (PDX) model. Importantly, CX-5461 has single-agent efficacy in PARPi-resistant HGSOC-PDX. To investigate the mechanisms of PARPi resistance and the mechanisms of efficacy of CX-5461 in PARPi-resistant ovarian cancer cells, we generated olaparib resistant-ID8 mouse ovarian cancer cell lines. Using this cell model, we performed quantitative global proteomic and phosphoproteomic analyses and identified altered metabolism to be associated with olaparib resistance in ID8 cells. We also identified key biological processes to be implicated in cellular response to CX-5461 including ribosome biogenesis, mRNA translation and mRNA processing and mitotic cell cycle progression. Further biochemical investigations will elucidate the molecular mechanisms of PARPi resistance and define the signalling pathways that mediate the actions of CX-5461, which will facilitate the rational design of more effective regimens for ovarian cancer patients.