In situ modeling of acquired resistance to RTK/RAS pathway targeted therapies

Intrinsic and acquired resistance limit the window of effectiveness for oncogene-targeted cancer therapies. Preclinical studies that identify synergistic combinations enhance therapeutic efficacy to target intrinsic resistance, however, methods to study acquired resistance in cell culture are lacking. Here, we describe an in situ resistance assay (ISRA), performed in a 96-well culture format, that models acquired resistance to RTK/RAS pathway targeted therapies. Using osimertinib resistance in EGFR -mutated lung adenocarcinoma (LUAD) as a model system, we show acquired resistance can be reliably modeled across cell lines with objectively defined osimertinib doses. We further show that acquired osimertinib resistance can be significantly delayed by inhibition of proximal RTK signaling using two distinct SHP2 inhibitors. Similar to patient populations, isolated osimertinib-resistant populations showed resistance via enhanced activation of multiple parallel RTKs so that individual RTK inhibitors did not re-sensitize cells to osimertinib. In contrast, inhibition of proximal RTK signaling using the SHP2 inhibitor RMC-4550 both re-sensitized resistant populations to osimertinib. Similar, objectively defined drug doses were used to model resistance to additional RTK/RAS pathway targeted therapies including the KRAS G12C inhibitors adagrasib and sotorasib, the MEK inhibitor trametinib, and the farnesyl transferase inhibitor tipifarnib. These studies highlight the tractability of in situ resistance assays to model acquired resistance to targeted therapies and provide a framework for assessing the extent to which synergistic drug combinations can target acquired drug resistance. Highlights Acquired resistance to RTK/RAS pathway members can be modeled in situ SHP2 inhibitors reduce the development of acquired osimertinib resistance Isolated osimertinib-resistant populations show hyperactivation of multiple RTKs SHP2 inhibitors re-sensitize resistant populations to osimertinib treatment