Combined CDK4/6 and pan-mTOR inhibition is synergistic against intrahepatic cholangiocarcinoma

Purpose: Intrahepatic cholangiocarcinoma (ICC) is an aggressive cancer type, lacking effective therapies and associated with a dismal prognosis. Palbociclib is a selective CDK4/6 inhibitor, which has been shown to suppress cell proliferation in many experimental cancer models. Recently, we demonstrated that pan-mTOR inhibitors, such as MLN0128, effectively induce apoptosis, although have limited efficacy in restraining proliferation of ICC cells. Here, we tested the hypothesis that palbociclib, due to its antproliferative properties in many cancer types, might synergize with MLN0128 to impair ICC growth. Experimental Design: Human ICC cell lines and the AKT/YapS127A ICC mouse model were used to test the therapeutic efficacy of palbociclib and MLN0128, either alone or in combination. Results: Administration of palbociclib suppressed in vitro ICC cell growth by inhibiting cell-cycle progression. Concomitant administration of palbociclib and MLN0128 led to a pronounced, synergistic growth constraint of ICC cell lines. Furthermore, while treatment with palbociclib or MLN0128 alone resulted in tumor growth reduction in AKT/YapS127A mice, a remarkable tumor regression was achieved when the two drugs were administered simultaneously. Mechanistically, palbociclib was found to poten-tiate MLN0128 mTOR inhibition activity, whereas MLN0128 prevented the upregulation of cyclin D1 induced by palbociclib treatment. Conclusions: Our study indicates the synergistic activity of palbociclib and MLN0128 in inhibiting ICC cell proliferation. Thus, combination of CDK4/6 and mTOR inhibitors might represent a novel, promising, and effective therapeutic approach against human ICC.