Abstract 4267: mTORC1-dependent tumors have innate vulnerability to autophagic cell death by HDAC inhibitors

mTORC1 plays a significant role in the development and progression of many different types of cancers. Although mTORC1 inhibitors, such as Rapamycin, have anti-tumor effects on some specific cancers, their efficacy is still largely limited to anti-proliferative effects. Histone deacetylase (HDAC) inhibitors have been proven to be effective in cancer treatment including some solid cancers. We have previously established a vascular tumor cell line, Tsc1Δ EC, which was derived from Tsc1 deletion in mouse endothelial cells leading to constitutive activation of mTORC1. Here, we found that a pan-HDAC inhibitor, SAHA, caused Tsc1Δ EC cell death and growth arrest in vitro and in vivo. Our data showed that a selective Class I HDAC inhibitor CI994 treatment also caused Tsc1Δ EC cell death. Unlike mTORC1 inhibitors, the anti-tumor activity of SAHA was dependent on mTORC1 activation but it had little effect on mTORC1 activity in mTORC1 activated tumor cells. We found that Z-VAD-FMK, a pan-caspase inhibitor, had no inhibitory effect on SAHA treatment. Cell death pathway array analysis revealed that SAHA treatment in Tsc1ΔEC upregulated autophagy-related genes. Further experiments revealed that both autophagy gene Fip200 deletion and autophagy inhibition by spautin-1 in Tsc1Δ EC impaired tumor cell death by SAHA treatment. We further found that SAHA could play a role by increasing reactive oxygen species (ROS) via autophagy. Fip200 deletion caused Nrf2 activation through p62 accumulation, which can lead to antioxidation effect through p62-Keap1-Nrf2 pathway. We showed that inhibition of p62 expression re-sensitized Fip200 deleted Tsc1Δ EC to SAHA treatment. Taken together, HDAC inhibitors treatment provides an alternative promising therapeutic strategy for mTORC1-dependent cancers. Note: This abstract was not presented at the meeting. Citation Format: Fuchun Yang, Chenran Wang, Shaogang Sun, Michael Haas, Syn Yeo, Jun-Lin Guan. mTORC1-dependent tumors have innate vulnerability to autophagic cell death by HDAC inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4267.