Targeting NOX4 Disrupts the Resistance of Papillary Thyroid Carcinoma to Chemotherapeutic Drugs and Lenvatinib

Abstract Background: Advanced differentiated thyroid cancer cells are subjected to extreme nutritional starvation which contributes to develop resistance to treatments; however, the underlying mechanism remains unclear. Methods: We used 0.5% serum to mimic starvation during cell culture. A CCK8 assay, cell death Detection ELISAPLUS kit, PI staining were measured to determine cell viability, cell apoptosis and cell cycle respectively in BCPAP cells and TPC-1 cells expressing shRNA against NOX4. The cells were then treated with etoposide and doxorubicin, two chemotherapeutic drugs, as well as lenvatinib to determine the role of NOX4 in resistance. Lenvatinib-resistant BCPAP cells (LRBCs) were also established to confirm the role. Finally, GLX351322, a chemical inhibitor targeting NOX4, was used to inhibit NOX4-derived ROS and detect the the contribution of NOX4 to resistance in vitro and in vivo. Results: NADPH oxidase 4 (NOX4) is highly expressed under serum starvation in BCPAP or TPC-1 cells. NOX4 knockdown impairs cell viability, increases cell apoptosis, extends G1 phase in cell cycle and modulates the level of energy-associated metabolites in starved cells. When these starved cells or Lenvatinib-resistant BCPAP cells (LRBCs) are treated with chemotherapeutic drugs or Lenvatinib, NOX4 knockdown inhibits cell viability and aggravates cell apoptosis depending on NOX4-derived ROS production. GLX351322, a NOX4-derived ROS inhibitor, has a significantly inhibitory effect on cell growth in vitro and the growth of BPCPA-derived even LRBCs-derived xenografts in vivo. Conclusions: These findings highlight NOX4 and NOX4-derived ROS as a potential therapeutic target in resistance of PTC patients.