PI3K/Akt/mTOR and CDK4 Combined Inhibition Enhanced Apoptosis of Thyroid Cancer Cell Lines

Introduction: Thyroid cancer is a malignant disease which could hardly be prognosticated. The PI3K/Akt/mTOR and Cyclin-DependentKinase 4 (CDK4) pathways are vital regulators of tumor cell proliferation and survival. The present study was accordingly designed to use dual inhibition of such pathways to kill thyroid cancer cells. Methods and materials: The effects of each inhibitors on human ATC and BCPAP cell lines wereevaluated by MTT assay. The right concentrations of inhibitors were determined and synergistic effects of such inhibitors were evaluated by bax/bcl-2 mRNA ratio, Caspase- 3,and Caspase-9 activity assay as well as Akt, mTOR,and CDK4. Results:Our finding showed thatboth ATC and BCPAP cell proliferation is significantly inhibited by PD-332991(PD) and NVP-BEZ235 (NVP) in a time and concentration- dependent manner (P 0.05), however, the BCPAP cells were more sensitive than ATC cells. Our data also revealed that NVP treatment significantly decreasedthe phosphorylation state of both AKT and mTOR. Nonetheless, PD treatment alone increased activation of both AKT and mTORwhereascombination treatment of NVP and PD1 significantly decreased AKT and mTOR phosphorylation (P 0.001). NVP and PD treatment either alone or in a combination also decreased Retinoblastoma phosphorylation. Combination of NVP and PD similarly decreased Cyclin D1 expression.In addition, our data of Caspase 8 and Caspase 3 as well as Bax/Bcl-2 ratio indicated that the combinationof NVP and PD induced cell apoptosis significantly (P 0.05). Conclusion: The present study suggests thatinhibition ofPI3K and CDK4 is the effective treatment for bothresistant and sensitivethyroid cancer cell line.