228P SMARCA4 inactivation drives aggressiveness in STK11/KEAP1 co-mutant lung adenocarcinomas through the induction of TGFβ signaling

Even if the development of targeted therapies in lung adenocarcinomas (LUADs) has improved outcomes in patient subsets, intra-driver genetic heterogeneity underlies the diversity of patient responses to such therapies, dramatically impacting patient survival. Co-occurring alterations in the genes SMARCA4, STK11, and KEAP1 predict exceptionally poor prognosis in patients with LUAD. Here, we characterize the effects of SMARCA4 loss in the context of STK11/KEAP1-mutated LUADs by performing multi-omic analyses on clinical specimens and isogenic preclinical models, followed by functional validation in vitro and in vivo. Clinical analyses of the MSK-LUAD cohort (N=5049) confirmed strikingly poorer outcomes and increased metastasis in patients with SSK tumors. Transcriptomic profiling in a subset of tumors from this cohort (N=49) revealed upregulation of genes involved in epithelial-to-mesenchymal transition (EMT) and metastasis, as well as in TGFβ signaling, specifically in SSK tumors. To further interrogate these differences, we engineered isogenic LUAD cell line models with SMARCA4-knock out (KO), SK double KO, and SSK triple KO. Multi-omic characterization of these revealed upregulation in metastasis- and stemness-related pathways in the SSK-KO models, as well as in the TGFβ signaling pathway, consistent with our clinical transcriptomic data. In line with these results, functional studies revealed increased EMT marker expression, migration/invasion and colony formation abilities in the SSK models in vitro, which were reverted by treatment with the TGFβ inhibitor SB-431542. Remarkably, pharmacological inhibition of TGFβ signaling sensitized SSK cells to different therapies used in the treatment of LUAD, such as the KRAS inhibitor sotorasib and cisplatin. SMARCA4 inactivation upregulates TGFβ signaling in LUAD tumors with inactivated STK11/KEAP1, inducing an aggressive phenotype. Pharmacological inhibition does not only suppress this phenotype, but also sensitizes to cytotoxic or targeted therapy. These results provide mechanistic insight into the aggressiveness of SSK-mutant LUADs and nominates TGFβ signaling as a therapeutic vulnerability in these.