Abstract B060: Small molecule inhibitor of pre-mRNA splicing evokes antitumor activity via MDM4-p53 pathway

Proper control of gene expression at the level of transcription and RNA processing is a fundamental process of tumor cell growth. Here we showed that a novel pre-mRNA splicing modulator, Cdc2-like kinase (CLK) inhibitor T-025, suppressed tumor cell growth in vitro and in vivo. To reveal the mechanisms linking aberrant splicing and tumor growth suppression by T-025, we combined transcriptomic RNA-seq and proteomic p-SILAC data. We identified MDM4 as a mediator for triggering p53-dependent apoptosis in response to T-025. CLK inhibition led to exon 6 skipping of MDM4 mRNA, a potential target for nonsense-mediated decay, decreasing MDM4 protein. Consistent with these results, overexpression of MDM4 or knockdown of p53 attenuated growth-suppressive effects of T-025. We then investigated the relationship between genomic features and sensitivity to T-025 by evaluating the antiproliferative effect of T-025 against 240 cancer cell lines. Strikingly, expression of MDM4 was correlated with that of CLK2 and cell sensitivity to T-025. In addition, we found that copy number variation and mRNA expression of MYC were correlated with cell sensitivity to T-025. T-025 exhibited greater sensitivity in MYC-expressing cells and MYC-driven spontaneous breast cancer models. Together, we demonstrated that MDM4-p53 signaling and MYC-activation have key roles in antitumor activity of CLK inhibitor. Citation Format: Kazuho Nishimura, Masahiro Yaguchi, Yukiko Yamamoto, Shunsuke Ebara, Kawakita Yoichi, Ryo Mizojiri, Yusuke Nakayama, Kozo Hayashi, Shuichi Miyakawa, Kenichi Iwai, Toshiyuki Nomura. Small molecule inhibitor of pre-mRNA splicing evokes antitumor activity via MDM4-p53 pathway [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B060.