Targeting Hsp90 using EC154, a novel synthetic Hsp90 inhibitor, impairs multiple oncogenic signaling pathways in human gastric and pancreatic cancer cells and reduces tumor growth in vivo

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Background: Hsp90 has been identified to be crucial for stability and functionality of oncogenic signaling molecules, including EGFR, Her-2, Akt, Erk, and various transcription factors. We recently demonstrated that gastric and pancreatic cancer harbors multiple such targets, which can effectively be inhibited by geldanamycin derivates, and leading to significant growth inhibition. We now followed-up on this aspect by investigating effects of a novel synthetic Hsp90 inhibitor (EC154) ingastrointestinal cancers. Methods: Human pancreatic cancer cells, gastric cancer cells, and endothelial cells were employed. Cytotoxic effects were assessed by MTT analyses. Effects of Hsp90 blockade on signaling pathways were investigated by Western blotting. The impact of EC154 on cell migration was evaluated in modified Boyden chambers. Effects of EC154 tumor growth and vascularization were investigated in subcutaneous xenograft models. Mice received either EC154 (25 mg/kg, 50 mg/kg; 2x/week) or vehicle by intraperitoneal injections. Tumor volumes were measured every other day. Tissue was harvested for immunohistochemical analyses and Western blotting. Results: The drug dose-dependently reduced proliferation of gastric and pancreatic cancer cells in vitro and Western blot analyses showed that EC154 effectively blocked STAT3, Akt and Erk activation in cancer cells, in addition to down-regulating EGFR and IGF-IR. Furthermore, EC154 led to marked inhibition of tumor cell migration in vitro (P<0.05). Interestingly, in endothelial cells (EC), EC154 not only significantly reduced cell survival/proliferation in MTT analyses, but also markedly deceased VEGFR2 activation and STAT3 phosphorylation. In addition, EC154 significantly reduced VEGF-A mediated EC migration in vitro, suggesting a potential antiangiogenic effect of this compound. In vivo, treatment with EC154 significantly reduced tumor growth rates of both pancreatic and gastric cancer cells. Analyses of tumor tissues showed that blocking Hsp90 reduced COX-2 expression in gastric cancer and diminished IGF-IR expression in pancreatic cancer. Moreover, the anti-metastatic transcription factor ATF3 is up-regulated by EC154 therapy. Conclusion: EC154 is a novel potent inhibitor of Hsp90 that effectively disrupts multiple oncogenic signaling cascades in gastric and pancreatic cancer cells, and significantly reduces tumor growth in vivo. Moreover, direct effects of EC154 on endothelial cells suggested that EC154 could be used for antineoplastic and antiangiogenic therapy in gastric and pancreatic cancer.