Isogarcinol inhibits nasopharyngeal carcinoma growth through mitochondria-mediated autophagic cell death

Isogarcinol, a natural compound extracted from the fruits of Garcinia oblongifolia, has potential chemopreventive activity. This study aimed to elucidate the anti-tumor effects and mechanism of action of isogarcinol on nasopharyngeal carcinoma (NPC). Isogarcinol was isolated from Garcinia oblongifolia using chromatographic separation. The anti-tumor effects of isogarcinol in NPC cells were tested by MTT assay, flow cytometry, wound healing assay, western blotting, transwell assay, colony formation assay, immunofluorescence, and transmission electron microscopy (TEM). The anti-tumor efficacy in vivo was evaluated in NPC xenograft models. Functional studies revealed that isogarcinol inhibited the proliferation, colony formation, migration and invasion abilities of NPC cells in vitro. Isogarcinol caused mitochondrial damage to overproduce reactive oxygen species through reducing the mitochondrial membrane potential and ΔΨm. Isogarcinol also substantially inhibited NPC cell growth in a xenograft tumor model without any obvious toxicity when compared with PTX. Mechanistic studies have illustrated that isogarcinol increased the Bax/Bcl-2 ratio, cleaved caspase-3, and cytoplasmic cytochrome C levels to induce mitochondrial apoptosis. The ROS overproduction by isogarcinol could suppress EMT pathway via decreasing the levels of p-Akt and Snail. Furthermore, isogarcinol promoted the conversion of LC3Ⅰ to LC3Ⅱ, but increased p62 level to block autophagic flux, resulting in the accumulation of damaged mitochondria to promote autophagic cell death in NPC cells. This study provides a new theoretical foundation for the anti-tumor application of Garcinia oblongifolia and confirms that isogarcinol could be developed as a candidate drug for NPC treatment with low toxicity.