Hybridization strategy is an effective strategy to obtain multi-target inhibitors in drug design. In this study, we assembled the pharmacophores of momelotinib and tandutinib to get a series of 4-piperazinyl-2-aminopyrimidine derivatives. All compounds were tested for the inhibition of JAK2 and FLT3 enzymes, of which, compounds with potent enzyme activities were assayed for antiproliferative activities against three cancer cell lines (HEL, MV4-11, and HL60). The structure-activity relationship studies were conducted through variations in two regions, the "A" phenyl ring and "B" phenyl ring. Compound 14j showed the most balanced in vitro inhibitory activity against JAK2 and FLT3 (JAK2 IC₅₀ = 27 nM, FLT3 IC₅₀ = 30 nM), and it also showed potent inhibition against the above tested cell lines. In the cellular context, 14j strongly induced apoptosis by arresting cell cycle in the G₁/S phase, and was selected as a promising JAK2/FLT3 dual inhibitor.

We report a case of a chronic myeloid leukemia patient showing progressive bone marrow fibrosis and anemia during imatinib therapy. Given the loss of major molecular response, we switched treatment to dasatinib 100 mg daily, observing a reduction in BCR-ABL transcript, a significant improvement of anemia, and a gradual disappearance of fibrosis. After 7 years of dasatinib therapy the patient maintains a complete cytogenetic response and a deep molecular response; the last bone biopsy confirmed the absence of fibrosis.

Pacritinib, potent inhibitor of Janus kinase 2 (JAK2), JAK2V617F, and fms-like receptor tyrosine kinase 3, is in Phase III development in myelofibrosis. Among type 1 inhibitors, pacritinib shows a lack of myelosuppression at doses that both inhibit JAK2/signal transducer and activator of transcription 3 pathway and demonstrate clinical efficacy. To elucidate these mechanisms and identify other disease targets, a kinome analysis screened 439 recombinant kinases at 100 nM pacritinib concentration. For kinases with >50% inhibition, pacritinib was titrated from 1 to 100 nM. JAK2, JAK2V617F, FLT3, colony-stimulating factor 1 receptor, and interleukin-1 receptor-associated kinase 1 achieved half-maximal inhibitory concentrations <50 nM. Pacritinib did not inhibit JAK1 (82% control at 100 nM). Lack of myelosuppression may stem from inhibiting JAK2 without affecting JAK1 and reducing hematopoietic inhibitory cytokines by suppressing interleukin-1 receptor-associated kinase 1 or colony-stimulating factor 1 receptor. The pacritinib kinome suggests therapeutic utility in acute myeloid leukemia, myelodysplastic syndrome, chronic myelomonocytic leukemia, solid tumors, and inflammatory conditions.

Myelofibrosis (MF) is a chronic myeloproliferative neoplasm characterized by bone marrow fibrosis, ineffective hematopoiesis, splenomegaly, constitutional symptoms, and shortened survival. Patients often experience multiple disease-associated, as well as treatment-emergent, cytopenias, including thrombocytopenia. However, patients with MF with thrombocytopenia have few therapeutic options, and there is little information on the management of these patients. Several Janus kinase (JAK) inhibitors have been developed for the treatment of MF, with one (ruxolitinib) having been approved. However, given their mechanism of action, JAK inhibitors are associated with high rates of thrombocytopenia. Patients can be successfully managed with dose modifications, but little is known about the safety and efficacy of these agents in patients with thrombocytopenia. Recent studies of JAK inhibitors in patients with MF who have low platelet counts have had mixed results. This review discusses the prevalence, prognostic implications, and management of thrombocytopenia in MF and the different therapeutic options available for this patient population, with an emphasis on current clinical experience with targeted therapies, as well as recent findings from several clinical studies currently underway.

Despite the emergence of JAK inhibitors, there is a need for disease-modifying treatments for Philadelphia-negative myeloproliferative neoplasms (MPNs). JAK inhibitors ameliorate symptoms and address splenomegaly, but because of the heterogeneous contributors to the disease process, JAK inhibitor monotherapy incompletely addresses the burden of disease. The ever-growing understanding of MPN pathogenesis has provided the rationale for testing novel and targeted therapeutic agents, as monotherapies or in combination, in preclinical and clinical settings. A number of intriguing options have emerged, and it is hoped that further progress will lead to significant changes in the natural history of MPNs.

The clinical phenotype of patients with myeloproliferative neoplasms (MPNs) including primary myelofibrosis (PMF), polycythemia vera (PV), and essential thrombocytosis (ET) whom manifest WHO grade 1 marrow fibrosis is poorly defined. Current IWG-MRT criteria require 2+ marrow fibrosis for diagnosis of post PV/ET myelofibrosis (MF). In contrast, the 2008 WHO definition of PMF does not require a minimum fibrosis threshold.

We retrospectively analyzed the clinical characteristics of 91 MPN patients with 1+ marrow fibrosis. We compared the clinical phenotype of sub threshold fibrosis PV/ET with that manifested by PMF. We applied the IWG-MRT criteria for post-PV/ET MF with the fibrosis component omitted and evaluated for percentage of criteria fulfillment.

When IWG-MRT criteria were applied to the PV/ET group, 38/58 (66%) of patients fulfilled criteria for diagnosis of post-PV/ET myelofibrosis except for the 2+ fibrosis requirement. Comparison of sub threshold fibrotic PV/ET clinical phenotype to PMF revealed similar characteristics including heavy symptomatic burden (57% and 52%), presence of splenomegaly (43% and 55%), leukoerythroblastic blood smear (38% and 45%), and median hemoglobin (12.8g/dL and 11.1g/dL).

MPN progression represents a biological spectrum and definitions of progression in ET/PV may benefit from criteria not restricted by degree of fibrosis.