Physical Poster + E-Poster Presentation 34th Lorne Cancer Conference 2022

Understanding and overcoming resistance to ribosome-targeting therapy in human acute myeloid leukaemia (#144)

Xinran Huang 1 2 , Keefe T Chan 1 2 , Elaine Sanij 1 3 , Jian Kang 1 2 , Richard B Pearson 1 2
  1. Division of Cancer Research, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia
  2. Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, VIC, Australia
  3. St Vincent's Institute, Melbourne, Victoria, Australia

Background and Aims: Targeting elevated ribosome biogenesis is a novel treatment option for oncogene-driven cancers. We developed a “first-in-class” selective inhibitor of ribosomal RNA gene transcription, CX-5461, which causes cancer cell apoptosis, cell cycle arrest, and/or senescence by inducing a p53-dependent nucleolar stress response (NSR) or a p53-independent DNA damage response (DDR), as well as causing defects in mRNA translation and energy metabolism. CX-5461 demonstrated remarkable potency in mouse models of solid and blood cancers 1-3 and showed safety and single-agent efficacy in phase 1 clinical trial 4. However, diseases still progressed after varying periods of time on treatment. Therefore, understanding and overcoming drug resistance is an important step in improving the clinical efficacy of CX-5461.  

Methods: We have generated CX-5461 resistant human acute myeloid leukemia (AML) cell lines by exposure to escalating concentrations of CX-5461. We characterize the molecular changes associated with CX-5461 resistance using qRT-PCR, Western blotting, RNA-seq, proteomics, and CRISPR-Cas9 gene editing to determine the mechanisms of resistance to ribosome-targeting therapy in AML cells. 

Results: CX-5461 resistance was confirmed in vitro by measuring cell death/proliferation and cell cycle progression. The CX-5461 resistant MV4-11 cells lost the p53-mediated NSR and expression of p53 targets (e.g. p21) upon CX-5461 treatment, but CRISPR-mediated knockdown of p21 did not change CX-5461 sensitivity in MV4-11 cells. The p53-independent DDR signalling pathway was impaired in CX-5461 resistant cells. The RNA-seq and proteomics data revealed novel genes and signalling pathways that are altered in the sensitive cells upon CX-5461 treatment but were not responsive in the resistant cells.  

Conclusions and Significance/Impact: The initial results revealed that multiple mechanisms underpinning the CX-5461 resistance in AML cells. Further investigation of the candidate genes/signalling pathways identified through RNA-seq and proteomics will help us to uncover new therapeutic vulnerabilities that can be targeted with combination therapies to improve the clinical efficacy of CX-5461 in treating AML. 

 

  1. Bywater, M. J. et al. Inhibition of RNA Polymerase I as a Therapeutic Strategy to Promote Cancer-Specific Activation of p53. Cancer Cell 22, 51–65 (2012).
  2. Sanij, E. et al. CX-5461 activates the DNA damage response and demonstrates therapeutic efficacy in high-grade serous ovarian cancer. Nature Communications 11, (2020).
  3. Kusnadi, E. P. et al. Reprogrammed mRNA translation drives resistance to therapeutic targeting of ribosome biogenesis. The EMBO Journal (2020) doi:10.15252/embj.2020105111.
  4. 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 Discovery 9, 1036–1049 (2019).