Combined targeting of histone deacetylases and hedgehog signaling enhances cytoxicity in pancreatic cancer

Abstract

Combined targeting of distinct cellular signaling mechanisms may improve the efficacy

and reduce the toxicity of therapy in pancreatic cancer. Histone deacetylases (HDACs) control

cellular functions through epigenetic modulation, and HDACs inhibitors suppress cell growth in

pancreatic adenocarcinoma. The Hedgehog (Hh) pathway regulates the development of the

pancreas, and aberrant Hh signaling promotes the initiation and progression of pancreatic

neoplasia. We hypothesize that HDACs and the Hh pathway cooperatively interact to regulate

cellular proliferation of the exocrine pancreas. A combination of the HDAC inhibitor SAHA and

the Smoothened antagonist SANT-1 was evaluated for their ability to suppress growth of the

Gemcitabine-resistant pancreatic adenocarcinoma cell lines Panc-1 and BxPC-3. The

combination of SAHA and SANT-1 supra-additively suppressed cellular proliferation and colony

formation. Flow cytometric and immunohistochemical analyses indicated that enhanced

induction of apoptotic cell death, cell cycle arrest in G0/G1 phase, and ductal epithelial

differentiation are involved. Cell death was associated with nuclear localization of survivin,

increased bax expression, and activation of caspases 3 and 7. Consistent with the cell cycle arrest

and cytodifferentiation, the cyclin-dependent kinase inhibitors p21waf and p27kip1 were upregulated,

and cyclin D1 down-regulated. The potentiated anti-proliferative effect by the

combination of SAHA and SANT-1 may involve cooperative suppression of the Hh pathway

activity, as shown by the up-regulation of HHIP by SAHA, and enhanced repression of of Ptc-1

mRNA expression. In summary, we have developed a molecular target-based therapeutic

approach that overcomes chemoresistance in pancreatic cancer cells by chemically inhibiting

HDACs and Hh signaling in combination.