(P 324) BENZIMIDAZOLE DERIVATIVES AS NOVEL THERAPEUTIC AGENTS FOR INI1-DEFICIENT EPITHELIOID SARCOMA

Objective: Epithelioid sarcoma (EpS) is a high-grade soft tissue sarcoma characterized by loss of integrase interactor 1 (INI1). Effective chemotherapies for EpS have not yet been established, and thus, novel therapeutic approaches are urgently required. We performed high-throughput screening for EpS treatment, finding that benzimidazole derivatives were potentially effective therapeutic drugs against EpS.

Methods: We used two benzimidazole derivatives, flubendazole (FLU) and mebendazole (MBZ) in this study. The effects of FLU and MBZ on cell proliferation of two INI1-deficient EpS cell lines, VA-ES-BJ and Asra-EPS, and normal human dermal fibroblasts (NHDF) were investigated using WST-8 assay. To determine whether the antiproliferative effects were dependent on INI1 deficiency in EpS, we generated VA-INI1 and VA-GFP clones by reintroducing INI1 and GFP into VA-ES-BJ, respectively. The cell cycle activity and apoptosis were evaluated by flow cytometry. Western blotting was used to evaluate the expression of cell cycle and senescence markers. An in vivo tumor xenograft model using VA-ES-BJ was performed.

Results: FLU and MBZ significantly inhibited the cell proliferation of EpS cell lines in a dose-dependent manner compared with that of NHDF. The reintroduction of INI1 into VA-ES-BJ cells significantly reduced proliferation, mitigated tumorigenicity, and attenuated antiproliferative efficacies of FLU and MBZ. FLU and MBZ induced G2/M cell cycle arrest and apoptosis in both EpS cell lines. FLU and MBZ strongly decreased the phosphorylation of STAT3 and the expressions of HIF1A and cyclin B1. STAT3 was highly and constitutively phosphorylated in VA-ES-BJ and Asra-EPS. Treatment with MBZ markedly abrogated VA-ES-BJ xenograft tumor growth.

Conclusion: Taken together, our findings revealed that benzimidazole derivatives exerted significant antiproliferative effects on INI1-deficient EpS by inducing G2/M cell cycle arrest and apoptosis. These effects were dependent on INI1 deficiency. Therefore, benzimidazole derivatives should be novel therapeutic agents for this devastating disease.