WP1066 Inhibits Growth of Human Cells Carrying the JAK2 V617F Mutation.

Myeloproliferative disorders (MPDs) are characterized by proliferation of one or more myeloid cell lineages in bone marrow and peripheral blood, with relatively preserved differentiation. Recent discovery of a dominant gain-of-function mutation in the Janus kinase 2 (JAK2) gene in patients with MPDs, involving the substitution of valine for phenylalanine at position 617 of the JAK2 protein (JAK2 V617F), represents the first acquired somatic mutation in hematopoietic stem cells described in these disorders. This discovery has opened new avenues for the development of targeted therapies for MPDs. WP1066 is a small molecule, a member of a novel class of anticancer agents whose development was based upon the backbone of AG490, a tyrphostin with activity against JAK2 V617F-expressing cell lines but limited in vivo activity. We investigated the inhibitory activity of the WP1066 against the JAK2 V617F-mutant expressing erythroid leukemia HEL cell line and peripheral blood mononuclear cells from patients with polycythemia vera (PV). WP1066 significantly inhibited the phosphorylation of JAK2 and downstream signal transduction proteins STAT3, STAT5, and ERK1/2 in a dose- and time-dependent manner. It induced a time- and dose-dependent antiproliferative and pro-apoptotic effects (activation of caspase 3, release of cytochrome c, and cleavage of PARP) in the JAK2 V617F-bearing HEL cell line in the low micromolar range. Pretreatment of cells with pan-caspase inhibitor Z-VAD abolished WP1066-induced apoptosis. The expression of apoptosis related proteins bcl-2, bax, and XIAP, however, was not changed. More important, WP1066 was effective in inhibiting cell growth in clonogenic assays of mononuclear cells harboring the JAK2 V617F mutation obtained from peripheral blood of patients with PV. We conclude that WP1066 is active both in vitro and ex vivo against cells carrying the JAK2 V617F mutation and represents a solid candidate for the treatment of JAK2 V617V-expressing MPDs.