Crucial Role of c-Myc/Monocarboxylate Transporter 4 Signaling in Capsaicin Induced Apoptotic and Anti-Warburg Effects in Hepatocellular Carcinoma.

Though Capsaicin from chili peppers was known to have antitumor effects in several cancers, the underlying antitumor pathogenesis of Capsaicin is not clear to date. Thus, the antitumor mechanism of Capsaicin was explored in Hep3B and Huh7 hepatocellular carcinoma (HCC) cells in relation to c-Myc/monocarboxylate transporter 4 (MCT4) signaling. To elucidate the antitumor mechanism of capsaicin, cytotoxicity assay, cell cycle analysis, Western blotting, RT-qPCR, RNA interference, ELISA, immunoprecipitation, and mouse xenograft model were used in this work. Capsaicin increased the cytotoxicity, subG1 population, and the number of TUNEL-positive bodies in Huh7 and Hep3B cells. Consistently, Capsaicin diminished the expression of pro-PARP, HK2, PKM2, LDHA, glucose transporter type 1 (Glut1), c-Myc, and monocarboxylate transporter 4 (MCT4) in Huh7 and Hep3B cells, along with decreased production of glucose, lactate, and ATP. However, a glycolysis end product pyruvate treatment reversed the capacity of Capsaicin to attenuate the expression of pro-PARP, HK2, c-Myc, and MCT4 in Hep3B cells. Furthermore, Capsaicin reduced c-Myc stability in the presence of cycloheximide and induced c-Myc ubiquitination in Hep3B cells, while c-Myc directly binds to MCT4 as a lactate transporter and downstream of c-Myc in Hep3B cells by immunoprecipitation and correlation factor (Spearman efficient = 0.0027). Furthermore, a preliminary analysis of an animal study reveals that Capsaicin significantly suppressed the growth of Hep3B cells inoculated in BALB/c nude mice without hurting body weight, liver, and spleen. Our findings provide novel evidence that Capsaicin exerts apoptotic and anti-Warburg effect via c-Myc/MCT4 signaling axis as a potent anticancer candidate for liver cancer therapy.