Abstract 2882: CREB inhibition attenuates MM tumor growth and drug resistance

Abstract

Abstract Malignant mesothelioma (MM) has a poor prognosis because of its difficult diagnosis and chemoresistance. We have shown previously that cyclic AMP response element binding protein (CREB) is constitutively activated (phosphorylated) in MM cells and tissue arrays as compared to mesothelial cells or benign lesions. Moreover, inhibition of CREB results in increased Doxorubicin (Dox)-induced apoptosis by attenuation of prosurvival genes, Bcl2 and BclxL. Using intraperitoneal and subcutaneous SCID xenograft mice models injected with shCREB (CREB inhibited) human MM cells (Hmeso), we show that CREB inhibition significantly attenuates tumor growth in both models. In addition, CREB inhibition also results in additional decreases in tumor size after treatment with Dox (0.5mg/kg, ip, 3 times a wk for 6 wks), suggesting a role of CREB in drug resistance. TUNEL staining on tumor sections showed increased cell death in CREB-inhibited tumors. Assessment of human cytokine levels by Bioplex analysis in peritoneal lavage fluid (PLF) of tumor-bearing mice showed that CREB inhibition significantly attenuated levels of IL-6, IL-8, VEGF, MCP1, IFN-gamma, IP-10 and RANTES. Dox treatment per se increased levels of several cytokines (IL-6, IL-8, G-CSF, IP-10, MIP-1B, RANTES), however, in the presence of shCREB, these levels were significantly decreased after Dox treatment. Other cytokine levels like bFGF, IFN-gamma, MCP1 and VEGF were reduced following Dox treatment, and further decreases were observed in CREB inhibited (shCREB) tumors. Microarray analysis performed on shCREB-Hmeso cells in vitro showed several fold decreases in various tumorigenesis- related genes including PAK7, Calbindin 1, TIE-2, MCAM, CD24, CCL-5, c-Met, v-kit, MMP2, IL-6, and snail homolog 2 as compared to shControl-Hmeso cells. In addition, increases in mRNA levels of phosphatases, Dachund homolog, and Caspase-1 were also observed following CREB inhibition. The patterns of gene expression and cytokine release by shCREB suggest that CREB affects tumor growth by regulating proliferation/survival, angiogenesis, migration and apoptosis. In addition, we also show that inhibition of CREB expression renders MM tumors more susceptible to Dox. This study is supported by National Cancer Institute grant PO1CA114047 and a grant from the Vermont Genetics Network (VGN). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2882. doi:10.1158/1538-7445.AM2011-2882