Garcioligantone J and K, a pair of epimeric caged-polyprenylated xanthonoids from Garcinia Oligantha, inhibit the growth of lung cancer cells through ER stress-mediated apoptosis

Garcioligantone J and K (GLJ and GLK) are a pair of isomers isolated from <i>Garcinia Oligantha</i> Merr. Herein, we described the structure elucidation including the absolute configurations of GLJ and GLK, explored and compared their anti-cancerous effects and underlying mechanism in A549 and NCI-H292 ​cells. The results indicated that GLJ and GLK are two isomers with different configuration at C-12, they inhibited cell proliferation and induced apoptosis in two lung cancer cell lines with almost the same extent. The induction of apoptosis by GLJ and GLK was demonstrated by DAPI and annexin-V-FITC/PI staining. Further investigation revealed increased Bax/Bcl-2 ratio, cleaved caspase-3, caspase-9 and PARP, loss of mitochondrial membrane potential (MMP) in cells, indicating that GLJ and GLK induced mitochondrial apoptosis. Increased GRP78, p-eIF2α and GADD153 manifested that endoplasmic reticulum (ER) stress was induced by GLJ and GLK. Meanwhile, upregulated reactive oxygen species (ROS) level was found and GLJ and GLK-induced ER stress and apoptosis could be attenuated by ROS scavenger NAC. Apoptosis induced by GLJ and GLK also could be alleviated by ER stress inhibitor 4-PBA. These showed that GLJ and GLK-induced apoptosis was mediated by ER stress relied on ROS generation. The efficacy of GLJ and GLK on lung cancer cell proliferation was further demonstrated in a zebrafish xenograft model. Collectively, the absolute configurations of GLJ and GLK were identified and they exerted lethal effects on lung cancer cells to the same extent via ROS-ER stress-mitochondrial apoptosis signaling, suggesting that GLJ and GLK might be used as potential modulating agents in lung cancer treatments.