A potent therapeutics for gallbladder cancer by combinatorial inhibition of the MAPK and mTOR signaling networks

Gallbladder cancer (GBC) is the most common type of cancer with the worst prognosis among the bile duct cancers. There still remains a clear need for effective mechanism-based novel therapeutic approaches. A crosstalk between mitogen-activated protein kinase (MAPK) and the mammalian target of Rapamycin (mTOR) signaling pathways has been reported in several cancers. We hypothesized that targeting both pathways in combination will be a potent therapeutic for GBC. Expression of phospho-ERK and phospho-S6rp protein were evaluated by immunostaining in surgically resected GBC specimens (n = 30). GBC cell lines and a xenograft model were treated with CI-1040, an inhibitor of MEK (mitogen-activated protein kinase kinase) and RAD001, an inhibitor of mTOR, alone or in combination, and then, we examined the cell proliferation and tumor growth, cell cycle status, and apoptosis. Analysis of human GBC tissues demonstrated that MAPK and mTOR signaling pathways were frequently coordinately dysregulated in one third of them. The combination therapy inhibited both signaling pathways and subsequently inhibited human GBC cell proliferation in vitro and xenograft tumor growth in vivo. Compared to the single treatment, the combination therapy significantly induced cell cycle arrest and apoptosis with decreased cyclin D1 expression. The double blockade of MAPK and mTOR signaling pathways inhibits the signal crosstalk and shows anti-tumor activity, which can be a potent therapeutic for GBC, especially for the patients with hyperactivated signaling of both pathways.