SOS2 modulates the threshold of EGFR signaling to regulate osimertinib efficacy and resistance in lung adenocarcinoma

Son of sevenless 1 and 2 (SOS1 and SOS2) are RAS guanine nucleotide exchange factors (RasGEFs) that mediate physiologic and pathologic receptor tyrosine kinase (RTK)‐dependent RAS activation. Here, we show that SOS2 modulates the threshold of epidermal growth factor receptor (EGFR) signaling to regulate the efficacy of and resistance to the EGFR tyrosine kinase inhibitor (EGFR‐TKI) osimertinib in lung adenocarcinoma (LUAD). SOS2 deletion (SOS2KO) sensitized EGFR‐mutated cells to perturbations in EGFR signaling caused by reduced serum and/or osimertinib treatment to inhibit phosphatidylinositol 3‐kinase (PI3K)/AKT pathway activation, oncogenic transformation, and survival. Bypassing RTK reactivation of PI3K/AKT signaling represents a common resistance mechanism to EGFR‐TKIs; SOS2KO reduced PI3K/AKT reactivation to limit osimertinib resistance. In a forced HGF/MET‐driven bypass model, SOS2KO inhibited hepatocyte growth factor (HGF)‐stimulated PI3K signaling to block HGF‐driven osimertinib resistance. Using a long‐term in situ resistance assay, most osimertinib‐resistant cultures exhibited a hybrid epithelial/mesenchymal phenotype associated with reactivated RTK/AKT signaling. In contrast, RTK/AKT‐dependent osimertinib resistance was markedly reduced by SOS2 deletion; the few SOS2KO cultures that became osimertinib resistant primarily underwent non‐RTK‐dependent epithelial–mesenchymal transition (EMT). Since bypassing RTK reactivation and/or tertiary EGFR mutations represent most osimertinib‐resistant cancers, these data suggest that targeting proximal RTK signaling, here exemplified by SOS2 deletion, has the potential to delay the development osimertinib resistance and enhance overall clinical responses for patients with EGFR‐mutated LUAD

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

Summary: Intrinsic and acquired resistance limit the window of effectiveness for oncogene-targeted cancer therapies. Here, we describe an in situ resistance assay (ISRA) that reliably models acquired resistance to RTK/RAS-pathway-targeted therapies across cell lines. Using osimertinib resistance in EGFR-mutated lung adenocarcinoma (LUAD) as a model system, we show that acquired osimertinib resistance can be significantly delayed by inhibition of proximal RTK signaling using SHP2 inhibitors. Isolated osimertinib-resistant populations required SHP2 inhibition to resensitize cells to osimertinib and reduce MAPK signaling to block the effects of enhanced activation of multiple parallel RTKs. We additionally modeled resistance to targeted therapies including the KRASG12C 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