Abstract 1599: Inhibition of COX-2 with apricoxib enhances the efficacy of standard therapy in preclinical models of human pancreatic cancer

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Cyclo-oxygenase-2 (COX-2) is expressed at a high level in pancreatic cancer and is implicated in pancreatic tumor progression. Inhibition of COX-2 can decrease tumor growth and augment cytotoxicity induced by either gemcitabine or EGFR inhibition. COX-2 while poorly understood has been implicated in tumor angiogenesis, tumor cell apoptosis and epithelial to mesenchymal transition (EMT). We investigated apricoxib, a novel COX-2 inhibitor, to further define the function of COX-2 in pancreatic cancer. Baseline expression and functional response of EGFR and COX-2 was determined in seven human pancreatic cancer cell lines. The level of phosphorylated EGFR (p-EGFR) and prostaglandin E2 (PGE2) production was determined by ELISA. Cytotoxicity was determined for gemcitabine, erlotinib, and apricoxib independently and in combination by MTS assay. The effect of standard therapy alone and in combination with apricoxib on AsPC-1 and Colo357 tumor growth in vivo was determined in SCID mice bearing orthotopic pancreatic xenografts. Microenvironmental parameters including apoptosis, proliferation, vessel density, and EMT were analyzed by IHC and VEGF levels were determined by ELISA. All cell lines expressed EGFR and COX-2; however expression was not predictive of p-EGFR level, PGE2 production or response to drug. AsPC-1 cells had negligible baseline COX-2 activity in vitro, whereas Colo357 cells expressed relatively high levels COX-2 and PGE2. Apricoxib decreased cell growth and COX-2 activity in all cell lines and addition of apricoxib improved response to chemotherapy in vitro. In vivo, addition of apricoxib to standard therapy significantly reduced tumor growth and, strikingly, almost eradicated metastases in mice bearing Colo357 but not AsPC-1 xenografts. COX-2 expression decreased in a dose-dependent fashion in apricoxib-treated animals. Plasma VEGF levels were unaffected by apricoxib in ASPC-1 -bearing animals, but were suppressed to undetectable levels in Colo357-bearing animals. Microvessel density was unaltered between groups but tumors from animals treated with combination therapy displayed increased pericyte coverage of vessels. Apoptosis was increased by addition of apricoxib, while markers of proliferation were decreased. In addition, combination of standard therapy with apricoxib reduced EMT, evidenced by elevation of epithelial markers and reduction of Zeb1 and vimentin, markers of a mesenchymal phenotype. We conclude that apricoxib significantly enhances the activity of gemcitabine and erlotinib, specifically in tumors with elevated COX-2 activity. Inhibition of COX-2 by apricoxib results in increased apoptosis, decreased proliferation, vascular normalization and a decrease in the mesenchymal phenotype in COX-2-dependent models. We believe clinical evaluation of apricoxib is warranted in pancreatic cancer patients. A Phase 2 study is ongoing. 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 1599. doi:10.1158/1538-7445.AM2011-1599