植化素引發之細胞自噬及新穎鐵依賴型細胞死亡在癌症治療的角色

The tautomeric pair of garcinielliptone FC (GFC) is isolated from the pericarps of Garcinia subelliptica Merr., and saponin formosanin C (FC) is isolated from Paris formosana Hayata (Liliaceae). Here, cDNA microarray data indicated GFC-induced autophagy, which was confirmed in colorectal cancer HT-29 cells by observing the formation of acidic vesicular organelles, LC3 puncta, and double-membrane autophagic vesicles using flow cytometry, confocal microscopy, and transmission electron microscopy, respectively. Administration of autophagy inhibitor (3-methyladenine and shRNA Atg5) and apoptosis inhibitor Z-VAD showed that the GFC-induced autophagy was cytotoxic form and GFC-induced apoptosis enhanced GFC-induced autophagy. In breast cancer cells, ferroptosis specific inhibitor (ferrostatin-1) and iron chelator (deferoxamine) significantly reversed FC-induced growth inhibition of chemoresistant non-metastatic MCF-7 and highly metastatic cancer MDA-MB-231 cells. Iron overload with ferric ammonium citrate further significantly enhanced the growth inhibition. Flow cytometric analysis showed that FC increased total and lipid reactive oxygen species as well as intracellular labile iron pool, which was paralleled by a decrease in glutathione and glutathione peroxidase 4 levels using ELISA, and expression of Nrf2, Keap1, and Xc- using immunoblotting. Electron microscopy analysis further observed the morphological changes of mitochondria and colocalization of ferritin and NCOA4. Furthermore, addition of FC synergistic enhanced growth inhibition to anticancer drug cisplatin, which was significantly reversed by the presence of ferrostatin-1. In hepatocellular carcinoma cells, FC induced autophagic flux, evidenced by preventing autophagic marker LC3-II degradation and increasing yellow LC3 puncta in ptfLC3 plasmid transfected cells when combined with autophagic flux inhibitor. It is noteworthy that FC-induced ferroptosis and autophagic flux were stronger in HepG2 cells expressing higher NCOA4 and lower FTH1 levels, agreeing with the results of gene expression analysis using CTRP and PRISM, indicating that FTH1 expression level exhibited a significant negative correlation with the sensitivity of the cells to a ferroptosis inducer. Confocal and electron microscopy confirmed the pronounced involvement of ferritinophagy in FC-induced ferroptosis in the cells with elevated NCOA4. Overall, our data suggest the involvement of autophagy and apoptosis in GFC-induced anticancer mechanisms of human colorectal cancer, and FC has chemotherapeutic potential against breast cancer cells and apoptosis-resistant HCC with a higher NCOA4 expression via ferritinophagy.