Although runt-related transcription factor 2 (RUNX2) is well known for its bone-specific transcriptional regulator in highly metastatic prostate cancer, there is little knowledge about its role of RUNX2 in castration-resistant neuroendocrine prostate cancer (it is named CRPC-NE). It is well known that expression of Androgen Receptor (AR) in CRPC-NE cases is lower than other types and AR suppresses RUNX2 expression by binding it and abrogating its recruitment to DNA. This fact suggests that in CRPC-NE, low expression of AR, the addiction of RUNX2 is relatively higher than that of other prostate cancer types. Extensive analysis of the clinical datasets revealed that RUNX2 is one of the most consistently up-regulated genes in CRPC-NE and the overexpression of SOX2 confers an accelerated disease progression and shortened overall survival periods to CRPC-NE patients. We also found that the silencing RUNX2 induced apoptotic cell death in CRPC-NE cells independent on p53, but through transcriptionally down-regulating SOX2 expressions. Mechanistically, ChIP-qPCR assay and luciferase reporter experiments confirmed that RUNX2 positively regulates SOX2 expression by binding to the consensus RUNX2 binding sequence (5'-TGTGGT-3') located in the proximal promoter region of SOX2. Short hairpin RNA (shRNA)-mediated knockdown of RUNX2 in the CRPC-NE cell line PC-3 induced the decreased expression of SOX2 and the increased expression of cleaved form of caspase-3 and PARP in a p53 independent manner. Silencing of SOX2 in PC-3 cells suppressed the proliferation of these cancer cells and induced apoptosis, which phenotypes were rescued by restoring SOX2 in the cells. These data indicates that inhibition of SOX2-apoptosis axis via RUNX2 could be a better therapeutic choice in CRPC-NE. Lastly, we examined the efficacy of our novel molecule Chlorambucil-conjugated Pyrrole Imidazole Polyamide (we named it as Chb-M'), which specifically binds to the consensus RUNX2 binding sequence and inhibits RUNX2 target gene. Surprisingly, Chb-M' had tremendous inhibitory effect on PC-3 cells (IC50 value at 620 nM) through effective SOX2 inhibition. Additionally, it was exceptionally well-tolerated in mice and exerted excellent efficacy against xenograft mice models of CRPC-NE. Taken together, our work identified a novel interaction of RUNX2 and SOX2-apoptosis axis, offering a new strategy for the management of poor-prognostic advanced stage CRPC-NE cancer patients.
Citation Format: Yuki Noguchi, Natsuki Wariishi, Shiina Iwai, Gengo Kashiwazaki, Junichi Taniguchi, Toshikazu Bando, Masaya Baba, Souichi Adachi, Hiroshi Sugiyama, Yasuhiko Kamikubo. Genetic regulation of RUNX2 induce apoptotic cell death through regulating the expression of SOX2 in CRPC-NE cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3357.