Selective Inhibitors of Nuclear Export Block Pancreatic Cancer Cell Proliferation and Reduce Tumor Growth in Mice

Abstract

Tumor-suppressor proteins are inactivated by many different mechanisms, including nuclear exclusion by chromosome region maintenance (CRM)-1. Increased tumor levels of CRM-1 have been correlated with poor prognosis of patients with pancreatic cancer, making it a therapeutic target. Selective inhibitors of nuclear export (SINEs) bind to CRM-1 to irreversibly inhibit its ability to export proteins; we investigated a new class of SINEs in pancreatic cancer cells. We studied the effects of SINE analogs in a panel of pancreatic cancer cell lines and nontransformed human pancreatic ductal epithelial cells using proliferation, apoptosis, immunoblot, co-immunoprecipitation, small inhibitor RNA, and fluorescence microscopy analyses. The effects of the SINEs also were investigated in mice with subcutaneous and orthotopic tumors. SINEs (KPT-185, KPT-127, KPT-205, and KPT-227) inhibited proliferation and promoted apoptosis of pancreatic cancer cells, but did not affect human pancreatic ductal epithelial cells. The nuclei of cells incubated with KPT-185 accumulated tumor-suppressor proteins (p27, FOXO, p73, and prostate apoptosis response-4 [PAR-4]) and inhibited interactions between CRM-1 and these proteins. Mutations in the region of CRM-1 that bind to SINEs (Cys-528), or small inhibitor RNA knockdown of PAR-4, prevented the ability of KPT-185 to block proliferation and induce apoptosis of pancreatic cancer cells. Oral administration of KPT-330 to mice reduced growth of subcutaneous and orthotopic xenograft tumors without major toxicity. Analysis of tumor remnants showed that KPT-330 disrupted the interaction between CRM-1 and PAR-4, activated PAR-4 signaling, and reduced proliferation of tumor cells. We identified SINEs that inhibit CRM-1 and promote nuclear accumulation of tumor-suppressor proteins in pancreatic cancer cells. Oral administration of the drug to mice reduces growth of xenograft tumors.