Synthesis of Pyrazole-Based Macrocycles Leads to a Highly Selective Inhibitor for MST3

MST1, MST2, MST3, MST4, and YSK1 are conserved members
of the mammalian
sterile 20-like serine/threonine (MST) family that regulate cellular
functions such as proliferation and migration. The MST3 isozyme plays
a role in regulating cell growth and apoptosis, and its dysregulation
has been linked to high-grade tumors. To date, there are no isoform-selective
inhibitors that could be used for validating the role of MST3 in tumorigenesis.
We designed a series of 3-aminopyrazole-based macrocycles based on
the structure of a promiscuous inhibitor. By varying the moieties
targeting the solvent-exposed region and optimizing the linker, macrocycle
JA310 (21c) was synthesized. JA310 exhibited high cellular
potency for MST3 (EC50 = 106 nM) and excellent kinome-wide
selectivity. The crystal structure of the MST3–JA310 complex
provided intriguing insights into the binding mode, which is associated
with large-scale structural rearrangements. In summary, JA310 demonstrates
the utility of macrocyclization for the design of highly selective
inhibitors and presents the first chemical probe for MST3.