Abstract A121: Suppression of orthotopic pancreatic cancer growth by sulforaphane is associated with activation of FOXO transcription factors

Abstract

Abstract FoxO (forkhead box O) transcription factors are crucial regulators of cell fate. This function of FoxO proteins relies on their ability to control diverse functions such as proliferation, differentiation, DNA repair and apoptosis. Constitutively active AKT and ERK in cancer cells have been shown to phosphorylate FoxO transcription factors (FKHR, FKHRL1 and AFX), which bind to protein 14-3-3 and sequester in the cytoplasm. In the absence of survival signals, FoxO proteins dephosphorylate, translocate to the nucleus and upregulate a series of target genes, thereby promoting cell cycle arrest and apoptosis. Sulforaphane a naturally occurring isothiocyanate, exerts anti cancer effects through diverse mechanisms. In this study we have shown that sulforaphane acts both by suppressing cell proliferation and inducing apoptosis in pancreatic tumors orthotopically implanted in nude mice. Sulforaphane regulates cell survival and cell death by modulating the expression of two interacting survival signaling pathways. The inhibition of PI3K/AKT and MEK/ERK pathways by sulforaphane resulted in the inhibition of cytoplasmic phosphorylation of FOXOs, and enhanced their nuclear translocation and transcriptional activities leading to apoptosis. Furthermore, deletion of FOXO1, FOXO3 and FOXO4 genes by shRNA abrogated sulforaphane-induced cell cycle arrest and apoptosis whereas the phosphorylation deficient triple mutants of FOXOs enhanced sulforaphane-induced FOXO transcriptional activity and apoptosis by nuclear translocation of FOXO. Sulforaphane-treated mice showed significant inhibition in tumor growth which was associated with reduced phosphorylation of ERK, PI3K, AKT, FOXO1 and FOXO3a, cyclin D1 and induction of FOXO’s target genes Bim, p21/CIP1, and p27/KIP1. These data suggest that inhibition of ERK and AKT pathways act together to activate FOXO transcription factors which are involved in sulforaphane-mediated pancreatic tumor growth suppression, thus supporting the use of sulforaphane as a chemopreventive agent for the treatment of pancreatic cancer. Citation Format: Wei Yu, Rakesh Srivastava, Sharmila Shankar. Suppression of orthotopic pancreatic cancer growth by sulforaphane is associated with activation of FOXO transcription factors. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr A121.