Targeting the JAK2 Kinase in Hematological Malignancies.

JAK2 is an intracellular protein tyrosine kinase whose dysregulation has been implicated in leukemia, lymphoma, and myeloproliferative disorders (MPD). Increased kinase activity of JAK2, caused by point mutation of the JH2 autoinhibitory region or formation of JAK2 fusion proteins, causes increased activation of downstream signaling pathways affecting cell differentiation, proliferation, migration, and apoptosis. Through the use of CLIMB™, our proprietary drug discovery process, the published JAK2 crystal structure was used to build several models that were then used as a substrate for in silico docking of 2.3 million virtual small molecule compounds to generate a subset of leads based on calculated binding energies. These leads were further screened using a number of in silico physicochemical and ADMET prediction algorithms to determine “druggable” leads which were most likely to be successful in a biological context. Lead JAK2 inhibitor candidates exhibit low nanomolar IC₅₀ activity against the JAK2 and JAK2 V617F mutant enzymes. Cancer cell lines expressing either the wild-type or mutant JAK2 enzyme demonstrate sensitivity to these inhibitors resulting in IC₅₀ values in low micromolar to nanomolar range. Consistent with the inhibition of the JAK2 enzyme, activity of downstream signaling partners are severely decreased. The phosphorylation level of STAT5, a downstream modulator of JAK2 signaling, in treated HEL cell lysates was analyzed by western blot analysis. These results showed that lead JAK2 candidates caused an inhibition of STAT5 phosphorylation at a low nanomolar EC₅₀. This series of compounds are currently being tested in in vivo xenograft models. Evaluation of lead candidates in biochemical assays against the hERG and CYP450 enzymes showed that these compounds have little inhibitory activity against these enzymes. SuperGen’s lead selective JAK2 inhibitors exhibit potent inhibition of wild-type and mutant JAK2 kinase activity translating into potent inhibition of cellular signaling pathways and cancer cell proliferation.