Over the past two decades, marked progress has been made in treating non-small cell lung cancer (NSCLC) patients with EGFR-, ALK-, ROS1- and KRAS^G12C-targeted inhibitors. NSCLC patients very often develop brain metastases. Despite the continuous development of newer and better inhibitors, the survival outcomes of NSCLC patients with brain metastases remain significantly worse than those of patients without. The main challenges in these pharmacotherapies are the development of resistance mutations, and, potentially, the presence of the blood-brain barrier (BBB). The outcomes of clinical studies show the improved efficacy of later-generation targeted inhibitors. The increase in progression free survival (PFS) in patients treated with these later-generation inhibitors is largely attributed to their efficacy against multiple resistance mutations, and possibly due to enhanced brain penetration. This review explores the different aspects hindering the targeted treatment of NSCLC and especially of brain metastases, focusing on recent clinical trials and emerging resistance mutations and the influence of the BBB on the efficacy of EGFR, ALK, ROS1 and KRAS^G12C inhibitors. The role of the ABCB1 and ABCG2 drug transporters in differential efflux of the targeted drugs at the BBB is also discussed, since preclinical studies indicate that they may reduce the efficacy of transported inhibitors.

The mammalian carboxylesterase 1 (Ces1/CES1) family comprises several enzymes that hydrolyze many xenobiotic chemicals and endogenous lipids. To investigate the pharmacological and physiological roles of Ces1/CES1, we generated Ces1 cluster knockout (Ces1 ^-/- ) mice, and a hepatic human CES1 transgenic model in the Ces1 ^-/- background (TgCES1). Ces1 ^-/- mice displayed profoundly decreased conversion of the anticancer prodrug irinotecan to SN-38 in plasma and tissues. TgCES1 mice exhibited enhanced metabolism of irinotecan to SN-38 in liver and kidney. Ces1 and hCES1 activity increased irinotecan toxicity, likely by enhancing the formation of pharmacodynamically active SN-38. Ces1 ^-/- mice also showed markedly increased capecitabine plasma exposure, which was moderately decreased in TgCES1 mice. Ces1 ^-/- mice were overweight with increased adipose tissue, white adipose tissue inflammation (in males), a higher lipid load in brown adipose tissue, and impaired blood glucose tolerance (in males). These phenotypes were mostly reversed in TgCES1 mice. TgCES1 mice displayed increased triglyceride secretion from liver to plasma, together with higher triglyceride levels in the male liver. These results indicate that the carboxylesterase 1 family plays essential roles in drug and lipid metabolism and detoxification. Ces1 ^-/- and TgCES1 mice will provide excellent tools for further study of the in vivo functions of Ces1/CES1 enzymes.