9h-purine-9-propanamine--6-amino-8-((6-iodo-1-3-benzodioxol-5-yl)thio)-n-(1-methylethyl)- and Myeloproliferative-Disorders

Patients with myeloproliferative neoplasms (MPNs) are at significant, cumulative risk of leukemic transformation to acute myeloid leukemia (AML), which is associated with adverse clinical outcome and resistance to standard AML therapies. We performed genomic profiling of post-MPN AML samples; these studies demonstrate somatic tumor protein 53 (TP53) mutations are common in JAK2V617F-mutant, post-MPN AML but not in chronic-phase MPN and lead to clonal dominance of JAK2V617F/TP53-mutant leukemic cells. Consistent with these data, expression of JAK2V617F combined with Tp53 loss led to fully penetrant AML in vivo. JAK2V617F-mutant, Tp53-deficient AML was characterized by an expanded megakaryocyte erythroid progenitor population that was able to propagate the disease in secondary recipients. In vitro studies revealed that post-MPN AML cells were sensitive to decitabine, the JAK1/2 inhibitor ruxolitinib, or the heat shock protein 90 inhibitor 8-(6-iodobenzo[d][1.3]dioxol-5-ylthio)-9-(3-(isopropylamino)propyl)-9H-purine-6-amine (PU-H71). Treatment with ruxolitinib or PU-H71 improved survival of mice engrafted with JAK2V617F-mutant, Tp53-deficient AML, demonstrating therapeutic efficacy for these targeted therapies and providing a rationale for testing these therapies in post-MPN AML.

Topics: Animals; Azacitidine; Benzodioxoles; Blotting, Western; Colony-Forming Units Assay; Decitabine; Exome; Flow Cytometry; Hematologic Neoplasms; High-Throughput Nucleotide Sequencing; Humans; Janus Kinase 2; Leukemia, Myeloid, Acute; Mice; Mutation, Missense; Myeloproliferative Disorders; Nitriles; Purines; Pyrazoles; Pyrimidines; Tumor Suppressor Protein p53

JAK2 kinase inhibitors were developed for the treatment of myeloproliferative neoplasms (MPNs), following the discovery of activating JAK2 mutations in the majority of patients with MPN. However, to date JAK2 inhibitor treatment has shown limited efficacy and apparent toxicities in clinical trials. We report here that an HSP90 inhibitor, PU-H71, demonstrated efficacy in cell line and mouse models of the MPN polycythemia vera (PV) and essential thrombocytosis (ET) by disrupting JAK2 protein stability. JAK2 physically associated with both HSP90 and PU-H71 and was degraded by PU-H71 treatment in vitro and in vivo, demonstrating that JAK2 is an HSP90 chaperone client. PU-H71 treatment caused potent, dose-dependent inhibition of cell growth and signaling in JAK2 mutant cell lines and in primary MPN patient samples. PU-H71 treatment of mice resulted in JAK2 degradation, inhibition of JAK-STAT signaling, normalization of peripheral blood counts, and improved survival in MPN models at doses that did not degrade JAK2 in normal tissues or cause substantial toxicity. Importantly, PU-H71 treatment also reduced the mutant allele burden in mice. These data establish what we believe to be a novel therapeutic rationale for HSP90 inhibition in the treatment of JAK2-dependent MPN.

Topics: Animals; Benzodioxoles; Bone Marrow Transplantation; Cell Line; Erythropoiesis; Female; HSP90 Heat-Shock Proteins; Humans; Janus Kinase 2; Mice; Mice, Inbred BALB C; Myeloproliferative Disorders; Polycythemia Vera; Primary Myelofibrosis; Purines; Signal Transduction; Thrombocythemia, Essential; Thrombopoiesis