Inhibition of MIF with an Allosteric Inhibitor Triggers Cell Cycle Arrest in Acute Myeloid Leukemia.

Macrophage migration inhibitory factor (MIF) is a key modulator of innate and adaptive immunity that has been extensively reported to promote tumor cell survival, proliferation, and metastasis. A recent study focusing on the microenvironment of acute myeloid leukemia (AML) showed that pharmacological inhibition of MIF signaling, in vitro as well as in vivo, reduces AML cell survival. Such data highlights the crucial role of MIF in AML pathogenesis and support the efforts for developing selective MIF modulators. Here, we report the identification and crystallographic characterization of a MIF inhibitor (compound 1) with an allosteric binding motif. Single point screening of 1 against a panel of National Cancer Institute (NCI) 60 human tumor cell lines revealed a selective antitumor activity for the AML cell line HL-60. After confirming the protein's expression in multiple AML cell lines, we utilized 1 to extract mechanistic insights into MIF action. Our findings demonstrate that AML cells utilize an MIF-dependent proliferation mechanism, which upon inhibition triggers a G0/G1 cell cycle arrest of the malignant cells. Complementary analysis of the MIF receptors utilizing neutralizing antibodies and selective small molecule antagonists associates this effect with inhibition of CD74 activation. The collection of data presented herein highlights the important role of MIF in proliferation of AML cells and points to the need of developing small molecule anticancer therapeutics that target MIF signaling.