Poster Presentation 35th Lorne Cancer Conference 2023

Identifying A Novel Class of DNA Damage Response Therapy to Target relapsed Ovarian Cancer (#331)

Shalini Sundramurthi Chelliah 1 2 3 , Anthony Xuan 3 , Henry Beetham 3 4 , Kaylene Simpson 3 4 , Richard B Pearson 2 3 , Elaine Sanij 1 2 3
  1. St Vincent's Institute of Medical Research, Fitzroy, VIC, Australia
  2. Department of Biochemistry and Molecular Biology, Monash University, Clayton, VIC, Australia
  3. Research Division, Peter MacCallum Cancer Centre, Parkville, VIC, Australia
  4. Victorian Centre for Functional Genomics, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia

High-grade serous ovarian cancer (HGSOC) is the most prevalent subtype (70-80%) of ovarian cancer with a 45% 5-year survival rate. Despite the introduction of poly-ADP ribose polymerase inhibitors (PARPi), acquired resistance to PARPi and chemotherapy remains a challenge. The first-in-class inhibitor of RNA polymerase I (Pol I) transcription of ribosomal RNA (rRNA) genes, CX-5461 (Pidnarulex) has shown significant efficacy in PARPi-resistant HGSOC models [1-5] and promising activity in Phase I clinical trials [6]. In addition to inhibiting Pol I transcription in the nucleoli, CX-5461 induces localised activation of ATR-mediated DNA Damage response (DDR) at the rRNA genes within the nucleoli, leading to global stalling of DNA replication and cell cycle arrest. CX-5461 has a unique sensitivity profile with low genome-wide DNA damage compared to chemotherapeutics and therefore activation of nucleolar DDR and nucleolar stress is an exciting new therapeutic approach.  

Hence, we aim to characterise modulators of nucleolar DDR to identify and validate novel therapeutic DDR targets whose inhibition enhances nucleolar DDR and cooperates with CX-5461 in inhibiting the growth of resistant ovarian cancer cells. We have assessed the role of topoisomerase 2A/B (top2a/top2b), RPA, ATR and DNA-PK in mediating response to CX-5461 in HGSOC cells in vitro. We have also assessed optimal drug combinations of CX-5461 with DDR inhibitors (ATMi, ATRi, DNA-PKi) in PARPi-resistant ovarian cancer models in vitro. Future work will assess the therapeutic benefit of combining CX-5461 with DDR inhibition in vivo.

To characterize nucleolar stress response, we have recently performed an unbiased arrayed whole-genome CRISPR-Cas9 screen to identify modulators of nucleolar stress based on altered nucleolar morphology in response to gene deletion alone or in combination with CX-5461. Our screen utilises a high-throughput, high-content immunofluorescence (IF) imaging at 40X magnification to deep phenotype nucleolar dynamics of nucleolar proteins, nucleophosmin and fibrillarin. We plan to identify and validate mediators of nucleolar stress as novel cancer therapeutic targets in chemo-resistant ovarian cancer.

  1. Sanij, E., et al., CX-5461 activates the DNA damage response and demonstrates therapeutic efficacy in high-grade serous ovarian cancer. Nat Commun, 2020. 11(1): p. 2641.
  2. Xuan, J., et al., Harnessing the Nucleolar DNA Damage Response in Cancer Therapy. Genes (Basel), 2021. 12(8).
  3. Hein, N., et al., The nucleolus: an emerging target for cancer therapy. Trends Mol Med, 2013. 19(11): p. 643-54.
  4. Yan, S., et al., The Potential of Targeting Ribosome Biogenesis in High-Grade Serous Ovarian Cancer. Int J Mol Sci, 2017. 18(1).
  5. Drygin, D., et al., Targeting RNA polymerase I with an oral small molecule CX-5461 inhibits ribosomal RNA synthesis and solid tumor growth. Cancer Res, 2011. 71(4): p. 1418-30.
  6. Khot, A., et al., First-in-Human RNA Polymerase I Transcription Inhibitor CX-5461 in Patients with Advanced Hematologic Cancers: Results of a Phase I Dose-Escalation Study. Cancer Discov, 2019. 9(8): p. 1036-1049.