The mTOR Kinase Inhibitor CZ415 Inhibits Human Papillary Thyroid Carcinoma Cell Growth

Abstract

Background/Aim: Mammalian target of rapamycin (mTOR) plays an important role in papillary thyroid carcinoma (PTC) cell progression. CZ415 is a novel, highly-efficient and specific mTOR kinase inhibitor. The current study tested the potential anti-tumor activity of CZ415 in human PTC cells. Methods: The established (TPC-1 cell line) and primary human PTC cells were treated with CZ415. Cell survival and growth were tested by Cell Counting Kit-8 assay and BrdU ELISA assay, respectively. Cell apoptosis was tested by caspase-3/-9 activity assay, Hoechst-33342 staining assay and single-stranded DNA ELISA assay. Cell cycle progression was tested by propidium iodide-FACS assay. The mTOR signaling was tested by Western blotting assay and co-immunoprecipitation assay. The mouse xenograft tumor model was applied to study the effect of CZ415 in vivo. Results: In cultured human PTC cells, treatment with CZ415 at nM concentrations significantly inhibited cell survival and growth. CZ415 induced apoptosis activation and cell cycle arrest in human PTC cells. CZ415 disrupted assembling of mTORC1 (mTOR-Raptor association) and mTORC2 (mTOR-Rictor-GβL association) in TPC-1 cells, which led to de-phosphorylation of the mTORC1 substrates (S6K1 and 4E-BP1) and the mTORC2 substrate AKT (Ser-473). Further studies show that the autophagy inhibitor 3-methyladenine (3-MA) or Beclin-1 shRNA aggravated CZ415-induced cytotoxicity against PTC cells. In vivo, CZ415 oral administration inhibited TPC-1 xenograft tumor growth in mice. Conclusion: Our results show that mTOR blockage by CZ415 inhibits PTC cell growth in vitro and in vivo.