Genetic resistance to JAK2 enzymatic inhibitors is overcome by HSP90 inhibition

Enzymatic inhibitors of Janus kinase 2 (JAK2) are in clinical development for the treatment of myeloproliferative neoplasms (MPNs), B cell acute lymphoblastic leukemia (B-ALL) with rearrangements of the cytokine receptor subunit cytokine receptor–like factor 2 (CRLF2), and other tumors with constitutive JAK2 signaling. In this study, we identify G935R, Y931C, and E864K mutations within the JAK2 kinase domain that confer resistance across a panel of JAK inhibitors, whether present in cis with JAK2 V617F (observed in MPNs) or JAK2 R683G (observed in B-ALL). G935R, Y931C, and E864K do not reduce the sensitivity of JAK2-dependent cells to inhibitors of heat shock protein 90 (HSP90), which promote the degradation of both wild-type and mutant JAK2. HSP90 inhibitors were 100–1,000-fold more potent against CRLF2-rearranged B-ALL cells, which correlated with JAK2 degradation and more extensive blockade of JAK2/STAT5, MAP kinase, and AKT signaling. In addition, the HSP90 inhibitor AUY922 prolonged survival of mice xenografted with primary human CRLF2-rearranged B-ALL further than an enzymatic JAK2 inhibitor. Thus, HSP90 is a promising therapeutic target in JAK2-driven cancers, including those with genetic resistance to JAK enzymatic inhibitors

JAK1/2 and pan-deacetylase inhibitor combination therapy yields improved efficacy in preclinical mouse models of JAK2V617F-driven disease

JAK inhibitors have demonstrated rapid and durable reductions in splenomegaly, as well as improvement in symptoms and quality of life in patients with myelofibrosis. However, the impact on the mutant allele burden and bone marrow fibrosis has been modest, indicating that combinations with other agents may further improve outcomes. Histone deacetylase inhibition has emerged as a promising combination modality based on in vitro studies using JAK2V617F mutant models that suggested a synergistic effect upon combination with a JAK2 inhibitor, and encouraging single-agent activity of the pan-deacetylase inhibitor panobinostat in phase I/II myelofibrosis trials. Here, we investigated the combination of the JAK1/2 inhibitor ruxolitinib and panobinostat in mouse models of JAK2V617F-driven disease. The combination was found to have a more profound effect on efficacy readouts as compared to either agent alone, and the analysis of pharmacodynamic readouts demonstrated that ruxolitinib and panobinostat have non-overlapping and complementary effects on biological pathways

JAK1/2 and pan-deacetylase inhibitor combination therapy yields improved efficacy in preclinical mouse models of JAK2V617F-driven disease”

JAK inhibitors have demonstrated rapid and durable reductions in splenomegaly, as well as improvement in symptoms and quality of life in patients with myelofibrosis. However, the impact on the mutant allele burden and bone marrow fibrosis has been modest, indicating that combinations with other agents may further improve outcomes. Histone deacetylase inhibition has emerged as a promising combination modality based on in vitro studies using JAK2V617F mutant models that suggested a synergistic effect upon combination with a JAK2 inhibitor, and encouraging single-agent activity of the pan-deacetylase inhibitor panobinostat in phase I/II myelofibrosis trials. Here, we investigated the combination of the JAK1/2 inhibitor ruxolitinib and panobinostat in mouse models of JAK2V617F-driven disease. The combination was found to have a more profound effect on efficacy readouts as compared to either agent alone, and the analysis of pharmacodynamic readouts demonstrated that ruxolitinib and panobinostat have non-overlapping and complementary effects on biological pathways

JAK1/2 and pan-deacetylase inhibitor combination therapy yields improved efficacy in preclinical mouse models of JAK2V617F-driven disease

JAK inhibitors have demonstrated rapid and durable reductions in splenomegaly, as well as improvement in symptoms and quality of life in patients with myelofibrosis. However, the impact on the mutant allele burden and bone marrow fibrosis has been modest, indicating that combinations with other agents may further improve outcomes. Histone deacetylase inhibition has emerged as a promising combination modality based on in vitro studies using JAK2V617F mutant models that suggested a synergistic effect upon combination with a JAK2 inhibitor, and encouraging single-agent activity of the pan-deacetylase inhibitor panobinostat in phase I/II myelofibrosis trials. Here, we investigated the combination of the JAK1/2 inhibitor ruxolitinib and panobinostat in mouse models of JAK2V617F-driven disease. The combination was found to have a more profound effect on efficacy readouts as compared to either agent alone, and the analysis of pharmacodynamic readouts demonstrated that ruxolitinib and panobinostat have non-overlapping and complementary effects on biological pathways

Genetic resistance to JAK2 enzymatic inhibitors is overcome by HSP90 inhibition

Enzymatic inhibitors of Janus kinase 2 (JAK2) are in clinical development for the treatment of myelproliferative neoplasms (MPNs) and other diseases with dependence on JAK2. We and others recently identified rearrangements of the CRLF2 cytokine receptor, which signals through JAK2, in a subset of B-cell acute lymphoblastic leukemias (B-ALL) 1-4. Here we show that B-ALL cells with CRLF2-rearrangements maintain JAK2 signaling in the presence of therapeutic concentrations of enzymatic JAK2 inhibitors. In contrast, destabilization and degradation of JAK2 through inhibition of heat shock protein 90 (HSP90) effectively blocks CRLF2 signaling and prolongs survival in mice xenografted with primary human B-ALL. We identify G935R, Y931C and E864K mutations within the JAK2 kinase domain that confer resistance to a panel of JAK2 inhibitors, whether involving JAK2 V617F (observed in MPNs) signaling through the erythropoietin receptor or JAK2 R683G (observed in B-ALL) signaling through CRLF2. None of the mutations affect sensitivity to HSP90 inhibitors. Thus, resistance to JAK2 enzymatic inhibitors can either result from persistent JAK2 signaling or kinase domain mutations and is overcome by inhibition of HSP90

Genetic resistance to JAK2 enzymatic inhibitors is overcome by HSP90 inhibition

Enzymatic inhibitors of Janus kinase 2 (JAK2) are in clinical development for the treatment of myeloproliferative neoplasms (MPNs), B cell acute lymphoblastic leukemia (B-ALL) with rearrangements of the cytokine receptor subunit cytokine receptor–like factor 2 (CRLF2), and other tumors with constitutive JAK2 signaling. In this study, we identify G935R, Y931C, and E864K mutations within the JAK2 kinase domain that confer resistance across a panel of JAK inhibitors, whether present in cis with JAK2 V617F (observed in MPNs) or JAK2 R683G (observed in B-ALL). G935R, Y931C, and E864K do not reduce the sensitivity of JAK2-dependent cells to inhibitors of heat shock protein 90 (HSP90), which promote the degradation of both wild-type and mutant JAK2. HSP90 inhibitors were 100–1,000-fold more potent against CRLF2-rearranged B-ALL cells, which correlated with JAK2 degradation and more extensive blockade of JAK2/STAT5, MAP kinase, and AKT signaling. In addition, the HSP90 inhibitor AUY922 prolonged survival of mice xenografted with primary human CRLF2-rearranged B-ALL further than an enzymatic JAK2 inhibitor. Thus, HSP90 is a promising therapeutic target in JAK2-driven cancers, including those with genetic resistance to JAK enzymatic inhibitors