Evaluation of selective inhibitors of nuclear export (SINE) CRM1 inhibitors for the treatment of renal cell carcinoma (RCC).

Abstract

4634 Background: For the ~30% of patients who present with RCC at the metastatic stage, multi-kinase inhibitors have been used with moderate success: progression-free survival remains at only one to two years, and thus it is imperative to discover novel therapeutic approaches for metastatic disease. We asked whether (1) SINE inhibitors of chromosome region maintenance protein 1 (CRM1) attenuate key cell cycle regulatory and apoptotic molecules and whether these compounds exert salutary effects in a human RCC xenograft mouse model. Methods: Four RCC cell lines (ACHN, Caki-1, 786-O, and A498) with distinct genotypes, and primary normal human kidney (NHK) cell lines, were used in this study. The cells were treated with the chemically related SINE CRM1 inhibitors KPT-185 or 251 and MTT assays were performed. In addition, cell cycle analyses, immunofluorescence for p53 and p21, and immunoblotting for CRM1, p53, p21, p27, and p-MDM2 were performed for all cell lines. RCC mice with Caki-1 xenografts were treated with vehicle, the orally-available CRM1 inhibitor KPT-251, or sorafenib for 26 days. Tumor volume was measured over several days. Results: Both KPT185 and 251 specifically reduced CRM1 protein levels in RCC cells. KPT-185 caused dose-dependent cytotoxicity in RCC cells, which was greater than sorafenib in RCC cell lines but less in NHK cells, suggesting a possible clinical advantage of KPT-185 over sorafenib. By FACS analysis, we showed that KPT-185 arrests the cell cycle in both G2/M and G1, and increased the sub-G0 cell population. KPT-185 and 251 both increased p53 and p21 in RCC cells, and KPT-185 confined these proteins to the nucleus. In vivo, KPT-251 inhibited Caki-1 xenografts in mice compared to both vehicle and sorafenib without obvious systemic adverse effects. Conclusions: We introduce a completely novel therapeutic approach to the treatment of RCC based on inhibition of the nuclear export of key cell cycle regulatory proteins. Inhibition of CRM1 leads to forced nuclear retention, and thereby activation, of several key p53-pathway proteins, leading to cell cycle arrest and apoptosis in RCC cell lines in vitro and tumor growth inhibition in vivo.