Abstract B53: Dynamic evolution of resistance to EGFR blockade from drug tolerant cancer cells

Abstract

Abstract Despite the success of targeted cancer therapies, acquired drug resistance remains a significant clinical challenge, as in the case of EGFR mutant non-small cell lung cancers (NSCLC) treated with EGFR inhibitor therapy. Although molecular mechanisms of acquired resistance to EGFR inhibitors have been identified, little is known about how resistant clones evolve during drug therapy. In some cases, clones with clinically validated genetic resistance mechanisms may exist prior to drug exposure and are simply selected by treatment. Alternatively, it has been hypothesized that drug tolerant (or “persister”) cells without bona fide resistance mechanisms may survive initial drug treatment by epigenetic adaptations, and undergo further evolution over time to acquire validated genetic resistance mechanisms. Although this would have immediate implications for new therapeutic strategies to prevent resistance, there has not been any direct evidence that drug tolerant cells can undergo such evolution. Using EGFR mutant NSCLC models, we observe that acquired resistance caused by the T790M gatekeeper mutation, which is observed in 50% of patients with acquired resistance to EGFR inhibitor therapy, can occur by either selection of pre-existing T790M clones or via evolution of T790M-negative drug tolerant cells that develop the mutation during months of drug treatment. Additionally, the path to resistance impacts the biology of the resistant clone, as those that evolved from drug tolerant cells have a diminished apoptotic response to third generation EGFR inhibitors that target T790M EGFR and can be sensitized by BCL-XL inhibitors. In total, these findings provide evidence that clinically relevant drug resistant cancer cells can both pre-exist and evolve from drug tolerant cells, and point to new therapeutic opportunities to prevent or overcome resistance in the clinic. Citation Format: Aaron N. Hata, Matthew Niederst, Maria Gomez-Caraballo, Hannah Archibald, Faria Siddiqui, Hillary Mulvey, Haichuan Hu, Lecia Sequist, Jeffrey Engelman. Dynamic evolution of resistance to EGFR blockade from drug tolerant cancer cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B53.