Janus kinases (JAK), a group of proteins in the nonreceptor
tyrosine
kinase (NRTKs) family, play a crucial role in growth, survival, and
angiogenesis. They are activated by cytokines through the Janus kinase–signal
transducer and activator of a transcription (JAK-STAT) signaling pathway.
JAK-STAT signaling pathways have significant roles in the regulation
of cell division, apoptosis, and immunity. Identification of the V617F
mutation in the Janus homology 2 (JH2) domain of JAK2 leading to myeloproliferative
disorders has stimulated great interest in the drug discovery community
to develop JAK2-specific inhibitors. However, such inhibitors should
be selective toward JAK2 over other JAKs and display an extended residence
time. Recently, novel JAK2/STAT5 axis inhibitors (N-(1H-pyrazol-3-yl)pyrimidin-2-amino
derivatives) have displayed extended residence times (hours or longer)
on target and adequate selectivity excluding JAK3. To facilitate a
deeper understanding of the kinase–inhibitor interactions and
advance the development of such inhibitors, we utilize a multiscale
Markovian milestoning with Voronoi tessellations (MMVT) approach within
the Simulation-Enabled Estimation of Kinetic Rates v.2 (SEEKR2) program
to rank order these inhibitors based on their kinetic properties and
further explain the selectivity of JAK2 inhibitors over JAK3. Our
approach investigates the kinetic and thermodynamic properties of
JAK–inhibitor complexes in a user-friendly, fast, efficient,
and accurate manner compared to other brute force and hybrid-enhanced
sampling approaches.