SPIN1 (Spindlin 1) is a methyllysine reader protein, which interacts with trimethylated histone H3 lysine 4 (H3K4me3). It was found to be overexpressed in several types of malignant tumors, including ovarian cancer, certain types of liver carcinomas, non-small-cell lung cancers and liposarcoma. Upregulation of SPIN1 has been shown to increase cellular proliferation, abnormal mitosis and chromosomal instability. Therefore, small molecules that selectively disrupt the protein–protein interactions between SPIN1 and its respective binding partners (such as H3K4me3) are valuable chemical tools for investigating biological functions of SPIN1 and assessing the potential of SPIN1 as a therapeutic target.<br/>By screening our quinazoline compound library, UNC0638, a highly potent inhibitor of the histone methyltransferases G9a and GLP, was identified as a weak inhibitor of SPIN1. Further optimization of this weak hit resulted in the discovery of a potent, selective and cell-active SPIN1 inhibitor, MS31, which is the first potent, selective and cell-active fragment-like inhibitor of any methyllysine reader proteins. MS31 displayed high potency in orthogonal SPIN1 biochemical assays (IC50 = 77 nM (AlphaLISA) and 243 nM (FP)). And This activity was further confirmed by ITC assay with high binding affinity to SPIN1 (KD = 91 nM). MS31 was highly selective for SPIN1 over a panel of epigenetic targets including G9a and GLP. A crystal structure of the SPIN1–MS31 complex was also obtained, which indicated that MS31 selectively binds Tudor domain II of SPIN1. A structurally similar but inactive compound (MS31N) as a negative control based on the cocrystal structure was designed and synthesized. Furthermore, MS31 directly engaged SPIN1 in cells and was not toxic to non-tumorigenic cells. These results have demonstrated that it is feasible to generate potent, selective and cell-active inhibitors by targeting a single Tudor domain and paved the way for discovering improved inhibitors of methyllysine reader proteins.

Discovery of a potent and selective fragment-like inhibitor of SPIN1

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.