MS31 is a potent, highly affinity and selective fragment-like methyllysine reader protein spindlin 1 (SPIN1) inhibitor. MS31 potently inhibits the interactions between SPIN1 and H3K4me3 ( IC 50 =77 nM, AlphaLISA; 243 nM, FP). MS31 selectively binds Tudor domain II of SPIN1 ( K d =91 nM). MS31 potently inhibits binding of trimethyllysine-containing peptides to SPIN1. MS31 is not toxic to nontumorigenic cells In Vitro MS31 potently inhibits binding of trimethyllysine-containing peptides to SPIN1, displays high binding affinity, is highly selective for SPIN1 over other epigenetic readers and writers, directly engages SPIN1 in cells, and is not toxic to nontumorigenic cells. MS31 selectively binds tudor domain II of SPIN1. MCE has not independently confirmed the accuracy of these methods. They are for reference only. IC50& Target:IC50: 77 nM (SPIN1 by AlphaLISA), 243 nM (SPIN1 by FP), Kd: 91 nM (SPIN1)