Lestaurtinib is a potent inhibitor of the wild-type and the V617F mutant JAK2. (A) In in vitro kinase assay lestaurtinib inhibited activity of the WT JAK2 with an average (n = 10) IC50 of 0.9 nM (± 0.2 nM). Lestaurtinib suppressed JAK2/STAT signaling (B), proliferation in cultures (C) and growth in vivo (D) of HEL92.1.7 human erythroleukemia cells, which are homozygous for the V617F mutation. (B) HEL92.1.7 cells were incubated with increasing concentrations of lestaurtinib, as indicated, and effects on JAK2, STAT5 and STAT3 activation were evaluated by Western blot using phospho-specific antibodies. (C) HEL92.1.7 cultures were incubated with increasing concentrations of lestaurtinib for 72 hours and cell proliferation was assessed by MTS assay. All samples were done in triplicate. (D) Lestaurtinib (30 mg/kg, subcutaneous delivery twice a day) suppressed growth of HEL92.1.7 tumor xenografts in nude mice. Nude mice were injected with HEL92.1.7 cells; when tumors reached approximately 150 mm3, animals (10/group) were divided into treated and control groups, which were dosed with lestaurtinib or vehicle, respectively. Tumor volumes were measured every 3 to 4 days. Results were statistically significant (***) with P < .01. Error bars represent SD.
