E-Poster Presentation 34th Lorne Cancer Conference 2022

When drug resistance becomes a vulnerability: exploiting the NRF2-MRP1-GSH axis to improve treatment response of lung cancer (#303)

Kimberley Hanssen 1 2 , Madeleine Wheatley 1 , Christine Gana 1 2 , Nisitha Jayatilleke 1 , Gavin Wright 3 , Richard Young 3 , Ben Solomon 3 , Michelle Haber 1 2 , Jamie Fletcher 1 2
  1. Children's Cancer Institute, Randwick, NSW, Australia
  2. School of Women's and Children's Health, Faculty of Medicine, UNSW Sydney, Kensington, NSW, Australia
  3. Peter MacCallum Cancer Centre, Melbourne, VIC, Australia

Background and Aims: The antioxidant glutathione (GSH) and drug efflux pump MRP1 are often elevated in cancers and work together to detoxify and efflux chemotherapeutics, leading to treatment failure. GSH and MRP1 levels can be promoted by the transcription factor NRF2, which is aberrantly activated in non-small cell lung cancer (NSCLC) and associated with poor outcome. We hypothesised that GSH and MRP1 could be therapeutic targets for NRF2-activated NSCLC. We previously developed compounds that modulate MRP1 activity such that GSH is exported from the cancer cell, lowering its levels, while chemotherapeutics are retained and accumulate. Our aim was to investigate MRP1 modulation as a strategy to improve the chemotherapy response of NRF2-activated NSCLC.

Methods: To validate NRF2-driven MRP1 expression in NSCLC, MRP1 expression was correlated with a NRF2-active gene signature in TCGA datasets and examined following NRF2 knockdown in NSCLC cell lines. The ability of our MRP1 modulators to inhibit MRP1-mediated drug transport, deplete GSH, and chemosensitise NRF2-active NSCLC was measured by [3H]substrate uptake, GSH recycling assays, and cell viability assays, respectively.

Results: MRP1 expression was significantly elevated in tumours with a high NRF2-active signature compared to either normal tissue or low NRF2-active tumours and decreased following NRF2 knockdown in cell lines. Our MRP1 modulator (5 μM) inhibited transport of canonical MRP1 substrates by >80% and enhanced the in vitro efficacy of MRP1-substrate chemotherapeutics up to 7-fold in NRF2-activated NSCLC cell lines. Although the modulator alone was not sufficient to deplete GSH, striking synergy was observed with the GSH synthesis inhibitor BSO, driving near complete GSH depletion, diminishing clonogenic capacity, and further enhancing the efficacy of chemotherapy preferentially in the NRF2-activated NSCLC cell lines.

Conclusions and Significance/Impact: This study is the first to demonstrate that high MRP1 expression in NRF2-activated NSCLC can be exploited to expand the therapeutic window available to treat these resistant cancers. This strategy could be beneficial for other NRF2-activated cancers and warrants further preclinical investigation.