Cross-talk between oncogene-driven signaling pathways and thyroid cancer metabolism

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Objective: Lenvatinib is an FDA-approved tyrosine kinase inhibitor (TKI) used for the treatment of metastatic radioactive iodine (RAI) non-responsive progressive thyroid cancer (TC). The objective response rate to Lenvatinib of 65% is non-durable, and most patients develop resistance to therapy with Lenvatinib. Given a well-established clinical phenomenon of RAI-non-responsive thyroid cancer being characterized by a higher glucose uptake evidenced by fluorodeoxyglucose positron emission tomography imaging, we hypothesized that glucose metabolism might play a role in resistance to TKIs. Methods: We used two human Lenvatinib sensitive (LS) TC cell lines THJ29T and TPC1 and induced Lenvatinib resistance (LR) through continuous exposure to increasing concentrations of the drug. A resistance factor of 2 (what is this, definition?) was attained in the LR cells. The LR cells phenotype was assessed through analysis of the cell cycle and apoptosis rate, that were quantified with flow cytometry. Immunoblot was performed to analyze the expression of the components of the mitochondrial respiratory chain. Aerobic glycolysis was measured via Seahorse XF Cell Mito Stress Kit, that quantifies mitochondrial oxidative phosphorylation (OXPHOS) in glucose-rich conditions. A p-value of 0.05 was considered statistically significant. Results: LR TC cells are characterized by either a similar cell cycle pattern or enhanced G2-M phase of cell cycle as compared with LS cells, revealing a pattern promoting mitosis and proliferation. There was a lower early apoptosis rate in LR vs LS cells (THJ29T: 0.41 0.03 vs 0.8 0.1, p=0.001, TPC1: 0.40 0.02 vs 0.81 0.12, p=0.003). There was a significant upregulation of the protein expression of mitochondrial respiration markers: complex I NDUFB8, complex II SDHB, complex III UQCRC2, complex IV COX II, and complex V ATP5A in LR cells as compared with LS-TC. Consistently, LR cells were characterized by a significantly increased maximal mitochondrial oxygen consumption rate as compared with LS cells (THJ29T-LR 4013 306 vs THJ29T-LS 2293 334, p<0.001; TPC1-LR 3999 358 vs TPC1-LS 1774 208, p<0.0001). Conclusions: Enhanced mitochondrial respiration is one of the contributing factors towards resistance to Lenvatinib. Combination therapies including OXPHOS inhibitors should be tested as potential avenues to overcome metabolic resistance mechanisms.