16746 Afuresertib stimulates p16 and apoptotic pathway activation to suppress Merkel cell carcinoma growth

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine skin cancer caused by the Merkel cell polyomavirus in 80% of cases. In particular, T antigens encoded by polyomaviruses have been implicated in malignant transformation and unregulated cell growth through activation of the AKT/mTOR pathway, although the possibility of targeting this pathway for the treatment of MCCs has not been fully explored. In the current study, we identify the novel AKT inhibitor, Afuresertib, as a potent agent capable of stimulating pro-apoptotic pathways in MCCs. Our data revealed that treatment of virus-positive MCC cells (MKL-1 cell line) with afuresertib resulted in marked dephosphorylation (and thus increased activation) of the Bcl-2 associated death promoter and caspase-9. In addition to activation of the intrinsic apoptotic pathway, afuresertib treatment also led to the up-regulation of p16, a key molecule that preferentially associates with cyclin dependent kinase 4 to halt cell cycle progression. Subsequently, we show that treatment of MCC cells with afuresertib led to robust inhibition of cell growth, with 45% reduction at 5 μmol/L and 80% reduction at 10 μmol/L. Overall, our findings demonstrate that the AKT inhibitor afuresertib induces activation of pro-apoptotic signaling pathways that culminate in increased p16 activity and marked reduction of MCC cell proliferation. As AKT inhibitors have shown promising results in the treatment of other solid organ tumors, our findings raise intriguing new considerations for the use of afuresertib in the future management of MCC and suggest a further need to delineate the effect and mechanism of AKT inhibition in this cancer.