A novel microRNA-based treatment approach for malignant pleural mesothelioma.

Abstract

7586 Background: Malignant pleural mesothelioma (MPM) is recalcitrant to treatment and new approaches are needed. The microRNA miR-16 has been implicated as a tumor suppressor in a range of cancer types, and restoration of miR-16 expression has been shown to inhibit tumor cell proliferation. The miR-16 status in MPM is largely unknown. Methods: MicroRNA expression was analysed by TaqMan-based RT-qPCR in 10 MPM cell lines and 60 tumour specimens consisting of archival blocks from patients undergoing surgery. MicroRNA expression was restored in vitro using mimics corresponding to the sequence of the mature microRNA, and effects on proliferation and target genes were assessed with standard methods. Human xenograft-bearing mice were treated with miR-16 mimics packaged in minicells targeted with EGFR-specific antibodies. Results: Expression of miR-16 was consistently down-regulated in MPM cell lines and MPM tumor specimens as were the co-expressed miR-15a and miR-15b. A decrease of 2- to 5-fold in miR-16 expression was found when MPM cell lines were compared with the normal mesothelial cell line MeT-5A. When tumor specimens were compared with normal pleura, the down-regulation of miR-16 was in the order of 10-fold. Using synthetic miR-16 mimics to restore miR-16 expression in MPM cell lines led to time- and dose-dependent growth inhibition in a panel of MPM cell lines but did not affect growth of MeT-5A. Growth inhibition correlated with cell cycle arrest and concordant down-regulation of miR-16 target genes including Bcl-2 and CCND1. In a series of experiments with nude mice bearing MPM (MSTO-H211) xenografts, intravenous administration of miR-16 mimics packaged in minicells led to consistent and dose-dependent inhibition of tumor growth. Conclusions: Restoring miR-16 expression represents a novel approach to treatment for MPM. Preparations are being made to test miR-16 packaged in minicells as a new treatment approach for patients with recurrent MPM and NSCLC.