Poster Presentation 32nd Lorne Cancer 2020

Characterisation of molecular response to the RNA polymerase I transcription inhibitor CX-5461 in olaparib-resistant ID8 mouse ovarian cancer cells (#126)

Natalie Brajanovski 1 , Michael Hendley 1 , Huy Nguyen 1 , Jian Kang 1 2 , Ching-Seng Ang 3 , Rick Pearson 1 2 4 5 , Elaine Sanij 1 2 6
  1. Division of Cancer Research, Peter MacCallum Cancer Centre, Parkville, VIC, Australia
  2. Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria, Australia
  3. Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia
  4. Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
  5. Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria, Australia
  6. Department of Pathology, University of Melbourne, Parkville, Victoria, Australia

The Poly-(ADP-ribose) Polymerase inhibitor (PARPi) olaparib has been approved by the FDA for the treatment of recurrent homologous recombination (HR) DNA repair–deficient ovarian cancer. Despite showing great promise in the clinic, however, rates of acquired resistance are high and can arise through multiple mechanisms including the restoration of the homologous recombination pathway. As such, the identification and development of novel treatment strategies that overcome PARPi resistance and improve therapeutic outcomes in HR-proficient disease is of critical importance.

Pre-clinical work performed by our group has demonstrated that CX-5461, a first-in-class inhibitor of RNA polymerase I (Pol I) transcription of ribosomal RNA (rRNA) genes (rDNA), activates a targeted DNA damage response at rRNA genes and exhibits synthetic lethality with HR deficiency. Furthermore, CX-5461 has also been found to enhance synthetic lethal interactions of PARPi with HR deficiency, in a high-grade serous ovarian cancer (HGSOC) patient-derived xenograft (PDX) in vivo, and more importantly exhibit single-agent efficacy in PARPi-resistant HGSOC-PDX.

In order to investigate the mechanisms of efficacy of CX-5461 in PARPi-resistant ovarian cancer cells and to identify pathways involved in mediating resistance to PARPi, culture adapted olaparib resistant-ID8 mouse ovarian cancer cell lines were generated. Using this cell model, we performed quantitative global proteomic and phosphoproteomic analyses and identified altered metabolism and restoration of the G2M checkpoint to be associated with olaparib resistance in ID8 cells. We also identified key biological processes to be implicated in the cellular response to CX-5461, including ribosome biogenesis, mRNA translation and G2M cell cycle checkpoint.

Additional biochemical investigations will further elucidate the molecular mechanisms promoting PARPi resistance in this model and define the signalling pathways that mediate the actions of CX-5461. This will facilitate the rational design of more effective treatment regimens for ovarian cancer patients.