BTK, a nonreceptor tyrosine kinase member of the Tec kinase family, plays a significant role in B-cell development. BTK is a unique therapeutic target in B-cell malignancies. XMU-MP-3, a noncovalent inhibitor with potent BTK inhibitory. XMU-MP-3 suppresses BTK kinase activity both in vitro and in vivo. In addition, XMU-MP-3 also successfully overrides Ibrutinib-resistant BtkC481S mutation. As a result, XMU-MP-3 is a lead for developing targeted therapeutics.

XMU-MP-3 exerts its pharmacological activity by inhibiting BTK-mediated signaling pathways in B-cell lymphoma. In particular, XMU-MP-3 inhibits BTK-transformed Ba/F3 cell proliferation with an IC50 of 11.4 nM and potently inhibits BTK with an IC50 of 10.7 nM. XMU-MP-3 is less potent (IC50 of 2815 nM) against the proliferation of BTK (T474M)-transformed Ba/F3 cells, as compared with wild type BTK-transformed Ba/F3 cells. Moreover, XMU-MP-3 inhibits the proliferation of JeKo-1, Ramos, and NALM-6 with IC50 values of 326.6 nM, 685.6 nM and 1065 nM, respectively. Furthermore, XMU-MP-3 also significantly inhibits colony formation as shown for NALM-6 cells.

In JeKo-1 cells, XMU-MP-3 arrests cell cycle progression at the G2 phase and also induces significant cell apoptosis. XMU-MP-3 selectively inhibits the proliferation of malignant B cells and inhibits both the auto- and trans-phosphorylation of BTK at the site of Y223 and Y551 in a dose-dependent manner in BTK-transformed Ba/F3 cells. XMU-MP-3 blocks phosphorylation of PLCγ2 at the sites of Y759 and Y1217. Furthermore, XMU-MP-3 also blocks phosphorylation of STAT3Y705, STAT5Y694, NF-κBS536 and TFⅡ-1Y248. Interestingly, XMU-MP-3 also affects the phosphorylation of the mTOR signaling pathway mediator, S6K. In a 24 -hour end point assay, XMU-MP-3 significantly induces apoptosis.

Taken together, XMU-MP-3 is a potent and selective inhibitor of BTK.

Fu Gui, et al. A Non-Covalent Inhibitor XMU-MP-3 Overrides Ibrutinib-Resistant Btk C481S Mutation in B-cell Malignancies. Br J Pharmacol. 2019 Dec;176(23):4491-4509.