ABSTRACT: Translocation-related sarcomas (TRSs) harbor an oncogenic fusion gene generated by chromosome translocation and account for approximately one-third of all sarcomas; however, effective targeted therapies have not yet been established. We previously reported that a pan-PI3K inhibitor, ZSTK474, was suggested to be effective for sarcomas in a phase I clinical trial, and demonstrated its efficacy in preclinical model, particularly in cell lines from synovial sarcomas (SS), Ewing’s sarcomas (ES) and alveolar rhabdomyosarcomas (ARMS), all of which harbor chromosomal translocation. Actually, ZSTK474 selectively induced apoptosis in these types of sarcoma cell lines, but the precise mechanism of apoptosis induction remained unclear. Here, we performed transcriptional analyses in SS cell lines including Aska-SS, SYO-1, Yamato-SS and Fuji treated with or without ZSTK474. Gene set enrichment analyses (GSEA) and Gene ontology (GO) analysis revealed that SS cell lines treated with ZSTK474 significantly reduced signatures of PI3K signaling. In addition, upon treatment with ZSTK474, the expression of apoptosis and cell cycle related genes was significantly changed. Importantly, PI3K inhibitors triggered induction of PUMA and BIM, resulting in loss of mitochondrial membrane potential, and the expression knockdown of these genes by RNA interference efficiently suppressed the apoptosis, suggesting their functional involvement in the apoptosis progression. In contrast, TRS-derived cell lines/patient-derived cells from alveolar soft part sarcoma (ASPS), CIC-DUX4 sarcoma and dermatofibrosarcoma protuberans failed to undergo apoptosis nor induce PUMA and BIM expression, as well as cell lines derived from non-TRSs and carcinomas. These results indicate that PI3K inhibitors selectively induce apoptosis in selective TRSs such as ES and SS via the induction of PUMA and BIM and subsequent loss of mitochondrial membrane potential, which would be a proof of concept for PI3K-targeted therapy especially for such TRS patients.
