A. Gooding, and K. Wood; Duke University, Durham, NC
Purpose/Objective(s): Osimertinib (OSI) is a third-generation EGFR-tyrosine kinase inhibitor (TKI) with marked clinical efficacy in early- and late-stage non-small cell lung cancer (NSCLC) patients harboring EGFR mutant tumors. Despite the efficacy of OSI monotherapy, most late-stage patients will develop progressive, OSI-resistant disease that is only marginally responsive to salvage therapies. Mounting evidence suggests that the evolutionary pressures exerted on malignant cells during their acquired resistance to molecularly targeted therapies often lead to the positive selection of common and exploitable cellular traits, so-called ‘collateral sensitivities,’ which arise irrespective of the genomic changes that engender resistance. We hypothesize that OSI-resistant NSCLCs are functionally dependent upon convergent, actionable, and EGFR-independent cellular processes which can be therapeutically targeted to overcome the diversity of OSI-resistant cellular populations present in EGFR-mutant NSCLC patients. Materials/
Methods: We generated models of OSI resistance in a diverse series of EGFR-mutant NSCLCs, including several cell lines derived from the tumors of patients who were either EGFR TKI-naïve or who had disease progression while on EGFR TKI therapy, as well as in multiple prototypic EGFR-mutant NSCLC cell lines. These cell lines were rendered OSI-resistant via long-term propagation in escalating concentrations of OSI until a durable >10-fold increase in GI50 was obtained. We then performed whole-genome CRISPR-Cas9 loss-of-function screens on a subset of these parental and OSI-resistant NSCLC derivatives. Deconvolution of enriched or depleted sgRNAs via deep sequencing allowed for derivation of gene-level ‘essentiality scores’ to identify differentially essential genes in parental and OSI-resistant populations. Results: Of the top 500 differentially essential genes within each individual patient-derived cell line (e.g., genes most essential to the outgrowth of OSI-resistant cells but most dispensable to drug-sensitive cells), 23 genes were commonly represented among the 4 cell lines screened to date, a quantity significantly exceeding that which would be expected by chance. Interestingly, these overlapping essential genes were highly enriched for members of the heme biosynthesis pathway. Accordingly, genetic and pharmacologic inhibition of heme synthesis reduced the clonogenic survival of OSI-resistant NSCLC derivatives to a significantly greater extent than in their respective parental derivatives. Conclusion: Our findings suggest that diverse populations of OSI-resistant NSCLCs are uniquely and convergently vulnerable to perturbations in heme synthesis and homeostasis, a candidate collateral sensitivity which is known to impact cellular metabolism, ROS production, apoptosis, and sensitivity to ionizing radiation, thereby warranting further investigation into modulating heme homeostasis as a means to overcome 76 simertinib resistance.
