Abstract 813: <i>In vitro</i> and <i>in vivo</i> modelling of drug tolerance and minimal residual disease to discover effective therapeutic combination strategies for EGFR-mutated lung cancer

Abstract Resistance to EGFR-targeted therapy is a major barrier to improving survival rates for non-small cell lung cancer (NSCLC) patients whose tumors have activating EGFR mutations. Resistance to EGFR tyrosine kinase inhibitors (TKIs) emerges from drug-tolerant persister cells (DTPs) that survive TKI therapy and manifest in patients as minimal residual disease, which inevitably drives fatal tumor recurrences. DTPs are a rare population of cancer cells in a reversible, slowly proliferating state that survives targeted therapy. Upon TKI withdrawal, they exit the DTP state to recommence rapid proliferation and aggressive tumor growth. Since DTPs provide a reservoir of surviving cells from which outright resistance driven by acquired genetic alterations arises, we hypothesize that discovering DTP survival mechanisms will inform vulnerabilities whose inhibition could enhance the efficacy of EGFR TKIs. However, such mechanisms are poorly understood in EGFR-mutant lung adenocarcinoma (LUAD). To address this knowledge gap, this study aims to generate robust in vitro and in vivo LUAD models of Osimertinib (Osi)-induced drug tolerance. Genetic and functional characterization of these models has the potential to identify mechanisms enabling drug tolerance that could be targeted to prevent TKI resistance from developing. To date, the response of 3 EGFR-mutant LUAD models to Osi treatment has been characterized both in vitro and in vivo [PC9, HCC4006, and 1 patient-derived xenograft (PDX)-derived cell line, X137CL]. Osi treatment of these cells increased apoptosis, but also arrested treated cells in G0-G1 phases of the cell cycle, consistent with the slow cycling nature of DTPs. Osi treatment of the xenografts formed by these lines induced strong tumor regressions and tumor replicates relapsed upon drug cessation, indicating these models are appropriate for studying DTPs in vivo. These models will be leveraged for molecular, functional, and pharmacological studies to identify shared and distinct mechanisms driving drug tolerance, in in vitro and in vivo conditions, including comparative single-cell transcriptomic profiling and pathway analysis. Candidate genes and pathways discovered will be functionally validated using CRISPR screens. Our comparative analyses of DTP versus untreated tumors will reveal novel interventions for preventing tumor relapse following TKI therapy in EGFR-mutant lung cancers. Citation Format: Kristyna A. Gorospe, Ming Li, Arundhathi Arivajiagane, Nhu-An Pham, Roya Navab, Kelsie L. Thu, Ming-Sound Tsao. In vitro and in vivo modelling of drug tolerance and minimal residual disease to discover effective therapeutic combination strategies for EGFR-mutated lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 813.