Abstract 2112: FoxO3a activation by HDAC class IIa inhibition induces cell cycle arrest in pancreatic cancer cells

Pancreatic cancer is highly chemo-resistant associated with oncogenic mutations such as KRAS and/or p53. The effect of conventional chemotherapy is not sufficient and new target and strategy is urgently needed. The forkhead box (Fox) proteins are multidirectional transcriptional factors strongly implicated in malignancies. Although Fox O (FoxO) protein, and particularly FoxO3a, works as negative regulator of cell proliferation by repressing cyclin proteins and inducing cell cycle inhibitors such as p21Waf1/Cip1, its expression is consistently suppressed by several oncogenic pathways including phosphatidylinositol-3 kinase (PI3K) / AKT pathway, constitutively activated in pancreatic cancer. Thus, upregulating FoxO3a activity could be a promising target of pancreatic cancer treatment without impact of underlying oncogenic mutations. Class IIa Histone deacetylase (HDAC) is a subgroup of HDAC. Though HDAC inhibitors (HDACi) have been extensively investigated as a cancer target, its action mechanism is considered due to histone modification by class I. Biological significance of class IIa HDACs which have minimal histone deacetylation activity have not been elucidated yet. Recent studies show class IIa HDACs act as a transcriptional regulator including FoxO3a. In this study, we investigate the biologic impact of HDAC class IIa inhibition on FoxO3a and anti-tumor effect against pancreatic cancer cell line using selective class IIa HDACi TMP269. TMP269 treatment showed increased FoxO3a expression in a dose dependent manner with immunoblotting and modest cell growth inhibition effect at 57.5 μM of IC50 dose for 48-hour treatment against AsPC-1 in MTT. G1/S arrest was observed with cell cycle assay. Upregulated p21Waf1/Cip1 and downregulated CDK2 and 4/6 and cyclin D1 and D2 expressions were further observed, consistent with inducing G1/S arrest and transcriptionally activated FoxO3a. Importantly, upregulated p21Waf1/Cip1 was observed in AsPC-1 p53 null cell line, suggesting independent with p53 pathway. These findings suggest upregulated FoxO3a induced by HDAC class IIa inhibition activated its transcription and resulted in cell growth inhibition. Because PI3K/AKT leads FoxO3a to the ubiquitylation-mediated proteasome degradation, we examined irreversible proteasome inhibitor carfilzomib (CFZ) combined with TMP269, aiming synergistic FoxO3a upregulating. As expected, FoxO3a expression was further increased in TMP269 combined with CFZ compared with TMP269 or CFZ alone. Following the activated FoxO3a, p21Waf1/Cip1 expression was upregulated and cell growth inhibition was dramatically enhanced. In conclusion, HDAC class IIa inhibition modified FoxO3a transcriptional activation and upregulating FoxO3 by dual inhibition of HDAC class IIa and proteasome is promising target against pancreas cancer. Citation Format: Makoto Usami, Shohei Kikuchi, Kohichi Takada, Yusuke Sugama, Yohei Arihara, Naotaka Hayasaka, Hajime Nakamura, Yuki Ikeda, Yusuke Kamihara, Masahiro Hirakawa, Makoto Yoshida, Masayoshi Kobune, Koji Miyanishi, Junji Kato. FoxO3a activation by HDAC class IIa inhibition induces cell cycle arrest in pancreatic cancer cells [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 2112. doi:10.1158/1538-7445.AM2017-2112