Selective inhibition of nuclear export function for cancer therapy

Background and Aims: Tumor suppressor proteins (TSPs) are inactivated by many different mechanisms, including nuclear exclusion by the chromosome region maintenance protein (CRM-1). Increased tumor levels of CRM-1 have been correlated with poor prognosis of patients with different cancers, making it a therapeutic target. We have developed selective inhibitors of nuclear export (SINEs) that bind to CRM-1 to irreversibly inhibit its ability to export proteins. Here we investigated our new class of SINEs in multiple tumor models. Methods: We studied the effects of SINE analogs in a panel of pancreatic, colon, triple-negative breast cancer (TNBC), prostate, non Hodgkin's lymphoma (NHL) cell lines and non-transformed/normal cells using proliferation, apoptosis, immunoblot, co-immunoprecipitation, small inhibitor (Si)-RNA, and fluorescence microscopy analyses. The effects of the SINEs were also investigated in mice with subcutaneous, orthotopic tumors and in disseminated liquid tumor models. Results: SINEs (KPT-185, KPT-127, KPT-205, and KPT-227) inhibited proliferation and promoted apoptosis of both solid liquid cancer cells, but did not affect normal lymphocytes or immortalized non-transformed cells. The nuclei of cells incubated with KPT-185 accumulated major TSPs such as p53, p73, 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 binds to SINEs (Cys-528), or siRNA knockdown of TSPs, prevented the ability of KPT-185 to block proliferation and induce apoptosis of cancer cells. Oral administration of the KPT SINEs to mice reduced growth of subcutaneous, orthotopic and disseminated xenograft tumors without major toxicity. Analysis of tumor remnants showed that KPT-SINE disrupted the interaction between CRM-1 and TSP, activated TSP function, and reduced proliferation of tumor cells. Conclusion: We identified SINEs that inhibit CRM-1 and promote nuclear accumulation of tumor suppressor proteins in multiple tumor models. Oral administration of the drug to mice reduces growth of xenograft tumors. Based on our solid preliminary studies a phase I clinical trial has been initiated for both solid tumors and hematological malignancies. Our results provide conclusive evidence in support of a global therapy for different cancers that involves targeted inhibition of nuclear export protein function and warrants advanced clinical investigations.