JAK and MPL mutations in myeloid malignancies

Phenylaminopyrimidines as inhibitors of Janus kinases (JAKs)

A series of phenylaminopyrimidines has been identified as inhibitors of Janus kinases (JAKs). Development of this initial series led to the potent JAK2/JAK1 inhibitor CYT387 (N-(cyanomethyl)-4-[2-[[4-(4-morpholinyl)phenyl]amino]-4-pyrimidinyl]-benzamide). Details of synthesis and SAR studies of these compounds are reported.

Thrombocytopenia in myelodysplastic syndromes and myelofibrosis

Myelodysplastic syndromes (MDS) are a group of hematopoietic stem cell disorders characterized by ineffective hematopoeisis and an increased risk of transforming to acute myelogenous leukemia (AML). Determining the molecular basis of the disease has been hampered by its heterogeneity. Thrombocytopenia is often a manifestation of MDS and needs to be monitored and treated accordingly. Treating the underlying disorder with a variety of differentiation and immunosuppressive agents alleviates the problem in a small percentage of patients but more often complicates the issue. Several treatments used for primary immune thrombocytopenic purpura (ITP) have been tried in MDS patients, though with only modest success rates. Preliminary studies suggest that the use of a thrombopoietic growth factor may afford substantial increases in platelet levels without excessive deleterious side effects. Primary myelofibrosis (MF) is a chronic myeloproliferative disorder associated with hepatosplenomegaly and refractory cytopenias. Immunomodulatory agents have shown promise in treating the anemia associated with this MF. However, there are currently no standard therapies to treat the thrombocytopenia that is often found in patients with this disease.

Detection of JAK2 exon 12 mutations in 15 patients with JAK2V617F negative polycythemia vera

To further characterize JAK2 exon 12 mutations, we performed molecular screening in 409 patients with polycythemia vera or unclear erythrocytosis with unmutated JAK2V617. The frequency of JAK2exon12 mutations was 10/63 (15.9%) in PV but only 5/346 (1.4%) in the erythrocytosis cases. Nine different mutations including four new types (D544-L545del, H538DK539LI540S, H538-K539del, V536-F547dup) were detected. In 2 cases we found evidence for the presence of cells homozygous for mutated JAK2exon12. As this was the case in only 2/15 cases with JAK2exon12 mutations (13%) homozygosity seemed to be less frequent than in V617F-mutated polycythemia vera (69%) (p<0.001). There were more females than males in the group of patients with a JAK2exon12 mutation (10 vs. 5) compared to the group with wildtype JAK2 (132 vs. 262; p=0.012). Median age of onset was lower than in the V617Fmut controls (58.5 vs. 67.8 years, p<0.001). In conclusion, JAK2 exon 12 mutation analysis contributes to diagnostics in polycythemia vera or erythrocytosis.

Response criteria for essential thrombocythemia and polycythemia vera: result of a European LeukemiaNet consensus conference

European experts were convened to develop a definition of response to treatment in polycythemia vera (PV) and essential thrombocythemia (ET). Clinicohematologic (CH), molecular, and histologic response categories were selected. In ET, CH complete response (CR) was: platelet count less than or equal to 400 x 10(9)/L, no disease-related symptoms, normal spleen size, and white blood cell count less than or equal to 10 x 10(9)/L. Platelet count less than or equal to 600 x 10(9)/L or a decrease greater than 50% was partial response (PR). In PV, CH-CR was: hematocrit less than 45% without phlebotomy, platelet count less than or equal to 400 x 10(9)/L, white blood cell count less than or equal to 10 x 10(9)/L, and no disease-related symptoms. A hematocrit less than 45% without phlebotomy or response in 3 or more of the other criteria was defined as PR. In both ET and in PV, molecular CR was a reduction of any molecular abnormality to undetectable levels. Molecular PR was defined as a reduction more than or equal to 50% in patients with less than 50% mutant allele burden, or a reduction more than or equal to 25% in patients with more than 50% mutant allele burden. Bone marrow histologic response in ET was judged on megakaryocyte hyperplasia while on cellularity and reticulin fibrosis in PV. The combined use of these response definitions should help standardize the design and reporting of clinical studies.

Validation of the revised 2008 WHO diagnostic criteria in 75 suspected cases of myeloproliferative neoplasm

The objective of this study was to validate the recently revised 2008 WHO diagnostic criteria of myeloproliferative neoplasms (MPN) together with the analysis of correlation of JAK2 (Janus kinase 2)-V617F mutant allele burden with clinical/laboratory findings on each patient. We made a diagnosis of 75 suspected MPN patients based on both diagnostic criteria of the 2001 WHO classification and the revised 2008 WHO classification, and found that both criteria show a quite similar diagnostic power except for two patients (idiopathic erythrocytosis (IE) and thrombocytosis) who were diagnosed as essential thrombocythemia by the 2008 WHO criteria. From JAK2-V617F analysis, hemoglobin and hematocrit values were significantly higher and platelet count was lower in JAK2-V617F high allele burden group than JAK2-V617F middle allele burden group. Mutant allele burden of polycythemia vera (PV) group was higher than that of essential thrombocythemia group. Therefore, the amount of mutant allele seemed to define the disease phenotypes. We further found a PV case presenting a rare type of JAK2-exon12 mutation. In contrast, IE presented a good prognosis unlike MPN. Hereafter, the 2008 WHO criteria with JAK2 gene analysis are useful for precise diagnosis of MPN and the patients with erythrocytosis.

Inteferons pen the JAK-STAT pathway

Characterization of how interferons (IFNs) mediate their biological response led to identification of the JAK-STAT signaling cascade, where JAKs are receptor-associated kinases and STATs the transcription factors they activate. Today, 4 JAKs and 7 STATs are known to transduce pivotal signals for the over 50 members of the four-helix bundle family of cytokines. This review will provide an overview and historical perspective of the JAK-STAT paradigm.