Macropinocytosis and Vascularization Determine Response to mTOR Inhibitors in Lung Squamous Cell Carcinoma

Abstract The capacity of cancer cells to rewire their cellular metabolism in response to therapeutic pressure confers resistance to treatments targeting key metabolic pathways, which represents a significant challenge in personalized cancer therapy for lung tumors. In this study, we investigated the mechanisms of resistance to the small molecule mTOR inhibitor TAK228 across lung squamous cell carcinoma (LUSC) models, including cell lines, xenografts, and patient-derived xenografts (PDXs). LUSC cells adapted to mTOR inhibition by engaging macropinocytosis, a form of endocytosis that facilitates enhanced uptake of extracellular nutrients, thereby increasing amino acid availability. Co-inhibition of both mTOR and macropinocytosis using small molecule inhibitors effectively reduced tumor growth. Additionally, angiogenesis limited the efficacy of inhibition of mTOR and macropinocytosis by ensuring a sufficient nutrient supply. Notably, inhibiting angiogenesis in combination with inhibitors of mTOR and macropinocytosis reduced tumor growth in xenografts and PDXs. Moreover, prolonged treatment of LUSC PDXs with TAK228 and the glutaminase inhibitor CB-839 led to upregulation of vascularization, which coincided with a rebound in tumor growth despite continued therapeutic administration. These findings highlight adaptive resistance mechanisms to small molecule inhibitors that target key metabolic pathways, lending insight into potential future clinical strategies for the treatment of LUSC.