Chromosomal Region Maintenance 1 (CRM1) overexpression has been associated with cancer progression and mortality in several human cancers, suggesting that activation of nuclear export may play a role in human neoplasia and may serve as a novel target for the treatment of cancers. This overexpression of CRM1 may be related to the export of most tumor suppressor and growth regulatory proteins out of the nucleus, thereby functionally inactivating them. Mantle cell lymphoma (MCL) is an aggressive histotype of B-cell non-Hodgkin lymphoma that is not yet curable. The objective of our study was to investigate the status of CRM1 in MCL, both in MCL cell lines and primary MCL cells, in comparison to normal B cells, and to evaluate the therapeutic efficiency of CRM1 inhibition in MCL in vitro and in vivo, and to elucidate the mechanism of CRM1 inhibitor-mediated MCL cell apoptosis. We used 8 established MCL cell lines and primary cells from 4 patients with relapsed/refractory MCL. KPT185 and KPT276 are novel, highly selective, drug-like small molecular CRM1 inhibitors. Western Blot analysis showed that CRM1 was expressed in both the cytoplasm and nuclei of 8 MCL cell lines. CRM1 was mainly detected in nuclei of normal resting B cells; In contrast, CRM1 was primarily detected in the cytoplasm of freshly isolated primary MCL cells from patients with relapsed/refractory MCL. In 3H-thymidine incorporation assays, inhibition of CRM1 by KPT185 resulted in a significant dose-dependent growth inhibition of 8 MCL cells, with IC50 values range between 10 nM to 120 nM. The blastoid-variant MCL cell lines (Z-138 and Rec-1) were significantly more sensitive to KPT185 than the non-blastoid variant MCL cell lines. Flow cytometry analysis with fluorescence-labeled Annexin V and propidium iodide showed that KPT185 induced MCL cells apoptosis in both time- and dose-dependent manners, but had no effect on cell cycle arrest. MCL cells treated with KPT185 for 12 hours showed caspase 3 activation and PARP cleavage. As shown in Western blot and confocal microscopy, blocking CRM1 activity by KPT185 in MCL cells up-regulated the protein expression of p53, a known CRM1-mediated export protein, and also induced CRM1 translocation to the nucleus and decreased CRM1 expression. In severe combined immunodeficient (SCID) mice bearing palpable Z-138 tumors, treatment with KPT-276 (similar structure to KPT-185 but improved animal pharmacokinetics), 50mg/kg or 150 mg/kg PO QDx5 each week, or cyclophosphamide 100 mg/kg on days 1–3, was initiated. Tumor growth was significantly inhibited (>75%) in all of treatment groups compared with vehicle control. Neutropenia and other cytotoxic-agent specific effects have not been observed in treated animals. In conclusion, CRM1 inhibitors inhibited growth of MCL cells in vitro and in vivo, and induced apoptosis of MCL cells via inhibition of CRM1 expression and blockage of its translocation with functional nuclear proteins. Our data suggest that novel CRM1 inhibitors provide a potential therapy for patients with relapsed/refractory MCL.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.