Active Motif's NSC-663284 is a potent and selective inhibitor of the protein lysine methyltransferase SETD8 (IC50 = 0.21 uM) which efficiently suppresses cellular H4K20me1 at doses lower than 5 uM. NSC-663284 also inhibits CDC25 phosphatases. It arrests cells at G1 and G2/M, inhibits cdk1 and 2 activation, and it inhibits the growth of a variety of human tumor cell lines.