Inhibition of the menin-mixed lineage leukemia (MLL) protein?protein interaction is a promising new therapeutic strategy for the treatment of acute leukemia carrying MLL fusion (MLL leukemia). We describe herein our structure-based design, synthesis, and evaluation of a new class of small-molecule inhibitors of the menin-MLL interaction (hereafter called menin inhibitors). Our efforts have resulted in the discovery of highly potent menin inhibitors, as exemplified by compound 42 (M-89). M-89 binds to menin with a K<
sub>
d<
/sub>
value of 1.4 nM and effectively engages cellular menin protein at low nanomolar concentrations. M-89 inhibits cell growth in the MV4
11 and MOLM-13 leukemia cell lines carrying MLL fusion with IC<
sub>
50<
/sub>
values of 25 and 55 nM, respectively, and demonstrates >
100-fold selectivity over the HL-60 leukemia cell line lacking MLL fusion. The determination of a co-crystal structure of M-89 in a complex with menin provides the structural basis for their high-affinity interaction. Overall, we conclude that further optimization of M-89 may lead to a new class of therapy for the treatment of MLL leukemia.