Targeted therapy of the AKT kinase inhibits esophageal squamous cell carcinoma growth in vitro and in vivo

Esophageal cancer, a leading cause of cancer death worldwide, is associated with abnormal activation of the AKT signaling pathway. Xanthohumol, a prenylated flavonoid tested in clinical trials, is reported to exert anti-diabetes, anti-inflammation and anticancer activities. However, the mechanisms underlying its chemopreventive or chemotherapeutic effects remain elusive. In the present study, we found that xanthohumol directly targeted AKT1/2 in esophageal squamous cell carcinoma (ESCC). Xanthohumol significantly inhibited the AKT kinase activity in an ATP competitive manner, which was confirmed in binding and computational docking models. KYSE70, 450 and 510 ESCC cell lines highly express AKT and knockdown of AKT1/2 suppressed proliferation of these cells. Treatment with xanthohumol inhibited ESCC cell growth and induced apoptosis and cell cycle arrest at the G1 phase. Xanthohumol also decreased expression of cyclin D1 and increased the levels of cleaved caspase-3, -7 and -PARP as well as Bax, Bim(s) and cytochrome c in ESCC cells by downregulating AKT signaling targets, including glycogen synthase kinase 3 beta (GSK3 beta), mammalian target of rapamycin, and ribosomal protein S6 (S6K). Furthermore, xanthohumol decreased tumor volume and weight in patient-derived xenografts (PDXs) that highly expressed AKT, but had no effect on PDXs that exhibited low expression of AKT in vivo. Kinase array results showed that xanthohumol treatment decreased phosphorylated p27 expression in both ESCC cell lines and PDX models. Taken together, our data suggest that the inhibition of ESCC tumor growth with xanthohumol is caused by targeting AKT. These results provide good evidence for translation toward clinical trials with xanthohumol.