Abstract 1245: Delaying resistance to Gefitinib in EGFR+ NSCLC through optimized treatment scheduling: an integrated experimental-theoretical approach

Abstract Tyrosine kinase inhibitors (TKI) have revolutionized treatment of oncogene-driven non-small cell lung cancer (NSCLC). However, almost all patients with advanced disease eventually acquire resistance and the disease remains largely incurable. Much research is dedicated to identifying and targeting the molecular mechanisms of resistance. But even when challenged by our most advanced treatments, cancers display a remarkable ability to adapt. We seek to complement the development of new agents by investigating treatment scheduling - the dose and frequency at which drugs are administered - as a means to slow the emergence of therapy resistance. Work by us and others on so-called adaptive therapy has demonstrated that well-timed treatment breaks in prostate can maintain sensitive cells which slow the growth of resistant cells through competition, and they can also induce phenotypic switching of some resistant cells to more sensitive states in melanoma. In this study, we use an integrated experimental-theoretical approach to investigate how treatment scheduling impacts the evolution of resistance to Gefitinib in EGFR+ NSCLC, and we lay the foundation for an adaptive therapy protocol to delay resistance. Using fluorescent, time-lapse microscopy we characterize the evolutionary dynamics of co-cultures of Gefitinib-sensitive and paired resistant cell lines (PC9; PC9+BRAF knock-in; PC9 with evolved resistance to Gefitinib) across four different treatment schedules: i) continuous therapy, ii) intermittent therapy (on/off), iii) intermittent therapy (off/on), iv) continuous therapy at half the full dose. Our results clearly demonstrate that both the dose and the frequency of treatment influence evolutionary dynamics. Intermittent therapy minimizes the final resistant cell and total cell count after six treatment changes (18 days total), across all four dose levels examined (2uM, 200nM, 100nM, 20nM Gefitinib). Moreover, the off/on intermittent schedule outperforms the on/off schedule, suggesting a role for spatial competition in suppressing the outgrowth of resistant cells. Leveraging our in vitro data, we develop a mathematical model of the treatment response dynamics, which reveals an additional subpopulation of drug-tolerant persister cells in the “sensitive” population. Using a step-wise model selection approach we characterize their contribution to the evolution of drug-resistance and investigate how to optimally schedule treatment to balance the three populations. Overall, we provide novel insights into how treatment scheduling impacts resistance evolution in EGFR+ NSCLC and we demonstrate the power of an integrated experimental-theoretical approach for developing more effective treatment schedules. Citation Format: Maximilian Strobl, Jinling Wu, Dagim Tadele, Mina Dinh, Jacob Scott. Delaying resistance to Gefitinib in EGFR+ NSCLC through optimized treatment scheduling: an integrated experimental-theoretical approach [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 1245.