TG101348, a potent, highly selective JAK2 inhibitor, inhibits colony formation in stem cells from polycythemia vera patients and prevents JAK2V617F-mediated splenomegaly and death in a mouse model

Abstract

7031 Background: The molecular pathogenesis of the myeloproliferative disorders (MPDs) polycythemia vera, essential thrombocythemia, and myelofibrosis with myeloid metaplasia has been strongly linked to an activating mutation of JAK2 (Janus Associated Kinase 2). A G-T transversion event in exon 14 that translates into a substitution of phenylalanine for valine at amino acid residue 617 leads to constitutive activation of JAK2V617F in a majority of these MPD cases. Methods: In order to address this unmet clinical need we designed, synthesized and performed preclinical evaluations on a series of structurally novel compounds optimized for JAK2 inhibition. Results: TG101348, a compound which potently inhibits JAK2V617F enzymatically and in human cells, was selected as a clinical development candidate from this medicinal chemistry campaign. TG101348 displays remarkable kinase specificity as shown by 83X selectivity versus JAK3 and potent inhibition of <2% of the kinases evaluated in a commercial, phylogenetically diverse panel of 212 kinases. TG101348 potently inhibits erythroid colony formation in patient-derived cells from polycythemia patients at doses 2–3X lower than in normal control patients. Consistent with this observation TG101348 inhibits JAK2-driven STAT5 phosphorylation, cell proliferation and cell survival in JAK2V617F-expressing cell lines. In vivo, TG101348 exhibits promising pharmacokinetic profiles in species ranging from mouse to monkey including oral availabilities >20%, and half-lives consistent with once or twice daily dosing. TG101348 reduces the number of circulating mutant JAK2 cells, inhibited splenomegaly and improved survival without significantly impacting normal hematocrit in an aggressive JAK2-driven circulating cell model of disease in rodents. Conclusion: TG101348 has considerable potential for the treatment of JAK2- driven myeloproliferative disorders based on its promising preclinical potency, selectivity and pharmaceutical properties. [Table: see text]