Abstract
Background:
Uterine leiomyosarcoma (uLMS) has a poor prognosis owing to its high recurrence rate and resistance to chemotherapy. Therefore, novel therapeutic targets for uLMS need to be discovered.
SUV39H2 is a histone methyltransferase that promotes the repair of double-stranded DNA breaks by recruiting phosphorylated H2AX (γH2AX). In this study, we investigated the potential therapeutic targets of SUV39H2 in uLMS and the mechanism of synthetic lethality between PARP inhibitors and SUV39H2 inhibitors, OTS186935.
Methods:
First, we analyzed the mRNA and protein expression of SUV39H2 in clinical tissues of uLMS, normal myometrium, and leiomyomas using real-time polymerase chain reaction and immunohistochemistry, respectively. Next, we conducted drug sensitivity assays for OTS186935 alone and in combination with olaparib, a poly (ADP-ribose) polymerase inhibitor, using uLMS cell lines, SK-LMS-1 and SK-UT-1. We conducted an annexin assay to investigate the mechanisms of cellular death. We performed Western blotting, immunofluorescence, and chromatin immunoprecipitation sequencing (ChIP-seq) to investigate γH2AX following OTS186935 treatment in addition to in vivo experiments using nude mice with subcutaneously implanted uLMS.
Results:
SUV39H2 expression was significantly increased in uLMS compared to that in normal myometrium and leiomyomas. OTS186935 decreased cell viability in both cell lines, and its combination with olaparib resulted in synthetic lethality in SK-UT-1 cells (combination index = 0.87). Annexin assay revealed that the combination therapy induced apoptosis. After treatment with OTS186935, γH2AX accumulation decreased. ChIP-seq also showed downregulated γH2AX following OTS186935 treatment. Notably, the combination with OTS186935 and PARP inhibitor was significantly more effective in vivo.
Conclusion:
OTS186935 inhibits double-stranded DNA break repair as evidenced by γH2AX downregulation through ChIP-seq and other assays. OTS186935 combined with olaparib induces synthetic lethality in patients with uLMS.