Molecular Genetics of Myelofibrosis and its associated Disease Phenotypes

In 2005, the discovery of Janus kinase 2 (JAK2) V617F mutation in approximately half of patients with myelofibrosis (MF) marked an important milestone in our understanding of the pathophysiology of MF. This has broadened our understanding of the disease pathogenesis and became the foundation for the development and subsequent clinical use of JAK inhibitors for MF. However, it is clear that other pathogenetic modifiers contribute to the disease diversity and phenotypic variability of MF. Novel genome scanning technologies were useful in the identification of recurrent molecular mutations in other genes including MPL, TET2, IDH1/2, DNMT3A, SH3B2 (LNK) and CBL in MF pointing out that other pathways might be important in addition to the JAK/STAT pathway. The biologic role and clinical implications of these molecular mutations in MF is currently under investigation. The main challenge is to understand the mechanisms whereby molecular mutations whether alone or in combination with other genetic and non-genetic events contribute to the pathogenesis of MF and eventually can explain the phenotypic variability among the MF patients. In the present review we will provide an overview of the molecular pathogenesis of MF describing past and recent discoveries in molecular markers and their possible relevance in disease phenotype

Molecular Pathogenesis of Myelodysplastic Syndromes

Myelodysplastic syndromes (MDS) are a group of clonal hematologic disorders characterized by inefficient hematopoiesis, hypercellular bone marrow, dysplasia of blood cells and cytopenias. Most patients are diagnosed in their late 60s to early 70s. MDS is a risk factor for the development of acute myeloid leukemia which can occur in 10-15% of patients with MDS. A variety of pathophysiologic mechanisms contributes to the genesis and persistence of MDS including immunologic, epigenetic, cytogenetic and genetic factors. The only potential curative option for MDS is hematopoietic cell transplantation which is suitable for only a few patients. Currently approved therapeutic options for MDS, including lenalidomide, decitabine, and 5-azacytidine, are targeted to improve transfusion requirements and quality of life. Moreover, 5-azacytidine has also been demonstrated to improve survival in some patients with higher risk MDS. New ways to predict which patients will better gain benefit from currently available therapeutic agents are the primary challenges in MDS. In the last 10 years, chromosome scanning and high throughput technologies (single nucleotide polymorphism array genotyping, comparative genomic hybridization, and whole genome/ exome sequencing) have tremendously increased our knowledge of MDS pathogenesis. Indeed, the molecular heterogeneity of MDS supports the idea of different therapeutic approaches which will take into account the diverse morphologic and clinical presentations of MDS patients rather than a restricted therapeutic strategy. This review will summarize the molecular abnormalities in key relevant components of the biology and pathogenesis of MDS and will provide an update on the clinical impact and therapeutic response in MDS patients

Regulation of Stat5 by FAK and PAK1 in Oncogenic FLT3 and KIT driven Leukemogenesis

Oncogenic mutations of FLT3 and KIT receptors are associated with poor survival in patients with acute myeloid leukemia (AML) and myeloproliferative neoplasms (MPN) and currently available drugs are largely ineffective. Although Stat5 has been implicated in regulating several myeloid and lymphoid malignancies, how precisely Stat5 regulates leukemogenesis, including its nuclear translocation to induce gene transcription is poorly understood. In leukemic cells, we show constitutive activation of focal adhesion kinase (FAK), whose inhibition represses leukemogenesis. Downstream of FAK, activation of Rac1 is regulated by RacGEF Tiam1, whose inhibition prolongs the survival of leukemic mice. Inhibition of the Rac1 effector PAK1 prolongs the survival of leukemic mice in part by inhibiting the nuclear translocation of Stat5. These results reveal a leukemic pathway involving FAK/Tiam1/Rac1/PAK1 and demonstrate an essential role for these signaling molecules in regulating the nuclear translocation of Stat5 in leukemogenesis

ERK inhibitor LY3214996-based treatment strategies for RAS-driven lung cancer

RAS gene mutations are the most frequent oncogenic event in lung cancer. They activate multiple RAS-centric signaling networks among them the MAPK, PI3K and RB pathways. Within the MAPK pathway ERK1/2 proteins exert a bottleneck function for transmitting mitogenic signals and activating cytoplasmic and nuclear targets. In view of disappointing anti-tumor activity and toxicity of continuously applied MEK inhibitors in patients with KRAS mutant lung cancer, research has recently focused on ERK1/2 proteins as therapeutic targets and on ERK inhibitors for their ability to prevent bypass and feedback pathway activation. Here we show that intermittent application of the novel and selective ATP-competitive ERK1/2 inhibitor LY3214996 exerts single-agent activity in patient-derived xenograft (PDX) models of RAS mutant lung cancer. Combination treatments were well tolerated and resulted in synergistic (ERKi plus PI3K/mTORi LY3023414) and additive (ERKi plus CDK4/6i abemaciclib) tumor growth inhibition in PDX models. Future clinical trials are required to investigate if intermittent ERK inhibitor-based treatment schedules can overcome toxicities observed with continuous MEK inhibition and - equally important - to identify biomarkers for patient stratification

The role of AMG-531 in the treatment of thrombocytopenia in idiopathic thrombocytopenic purpura and myelodysplastic syndromes

Thrombocytopenia can be seen in a variety of disease states, including immune mediated thrombocytopenic purpura (ITP) and myelodysplastic syndromes (MDS). The most concerning complication is the development of hemorrhagic complications that may contribute to patient morbidity and mortality. The ligand thrombopoeitin (TPO) and its interaction with its receptor (c-mpl) are important in platelet production. Thrombopoietic agonists can help in the management of thrombocytopenia related to these conditions. Amgen Megakaryopoiesis Protein 531 (AMG-531) (Romiplostim) is a recombinant TPO with a peptide fragment that shares no sequence homology with endogenous TPO, preventing the production of neutralizing antibodies. Recent studies have shown that it is effective in raising platelet counts, and is well tolerated in ITP and MDS patients. In this review, we discuss thrombopoiesis regulation by TPO; the chemistry, pharmacokinetics and pharmacodynamics of AMG-531 in animals and humans; the pathophysiological mechanisms leading to thrombocytopenia in ITP and MDS; and clinical trials demonstrating its efficacy in treating thrombocytopenia

Clofarabine for myelodysplastic syndromes

Areas covered: A PubMed search for articles pertaining to clofarabine was conducted and streamlined to only include data on MDS or AML that evolved from MDS. Also included were clofarabine-related response and safety data from presentations at the 52(nd) Annual American Society of Hematology Meeting in Orlando, Florida, USA. Expert opinion: Clinical trials using clofarabine in MDS and MDS/myeloproliferative neoplasms have produced overall response rates of 31 - 43% including complete responders. Although myelosuppression is an important side effect, clofarabine is generally well tolerated in MDS. Clofarabine is currently available in an intravenous form with an oral formulation presently under investigation, either as a single agent or in combination therapy in MDS. Larger studies may help clarify the viability of clofarabine in the treatment of MDS patients