Abstract 5850: Salicylate sensitizes prostate cancer (PrCa) to radiotherapy; activation of AMPK and suppression of lipogenesis

Abstract Radiotherapy (RT) is a key therapeutic modality for PrCa that achieves reasonable disease control rates in localized disease. However, this requires dose-escalated RT, which is associated with increased toxicity to surrounding tissues and leads to deterioration of patient quality of life. Improving the therapeutic ratio in PrCa RT is of high clinical importance. Aspirin has an established role in cancer prevention and studies suggested association with improved PrCa outcomes. It was shown that its metabolite salicylate (SAL) binds directly and activates the metabolic stress sensor AMP-activated kinase (AMPK). This is likely achieved through direct binding to the AMPK β1 subunit, leading to enhanced AMPK activity through suppression of AMPK α-subunit T172 de-phosphorylation. In this study we examined the ability of SAL to sensitize PrCa to RT. Hormone insensitive (PC3) and sensitive (LnCap) human PrCa cells, as well as PC3 xenografts grown in immunocompromised nude mice were subjected to SAL and RT treatments. SAL mediated a dose-dependent inhibition of proliferation and clonogenic survival in both PrCa cell lines and suppressed de novo lipogenesis (DNL). This was detected at μM concentrations of the drug, which can be safely achieved in human circulation. SAL (100-500 μM) radio-sensitized PC3 and LnCap cells, and enhanced the ability of SAL to inhibit DNL. In animals treated with conformal RT (10Gy) to the tumor xenografts, Salsalate feeding (chow diet containing 2.5gr/kg) enhanced the cytotoxicity of RT detected as reduced tumor growth kinetics and weight and volume at sacrifice. Salicylate treatment of cells or salsalate feeding of mice led to increased AMPK activity in cells and tumors, inhibitory phosphorylation of Acetyl-CoA Carboxylase and reduction of AktThr308 phosphorylation. These results indicate that SAL could improve radiation response in PrCa through a mechanism involving the suppression of DNL. This is achieved at clinically attainable doses of SAL. This work supports prospective investigation of SAL as a radio-sensitizer in early phase clinical trials of localized PrCa. Note: This abstract was not presented at the meeting. Citation Format: Theodoros Tsakiridis, Katarina Marcinko, Linsday Broadfield, Linda Villani, Carrie Gerdes, Danitra Maharaj, Tom Farell, James Wright, Gregory Steinberg. Salicylate sensitizes prostate cancer (PrCa) to radiotherapy; activation of AMPK and suppression of lipogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5850. doi:10.1158/1538-7445.AM2017-5850