ALBERT

Description: An acquired JAK2 V617F mutation has been detected in up to 90% of patients with polycythemia vera (PV) and in a sizeable proportion of patients with other myeloproliferative disorders such as essential thrombocythemia (ET) and idiopathic myelofibrosis (IMF). However, how a single mutation may be responsible for such different clinical phenotypes is unknown. Mice transplanted with bone marrow cells in which V617F JAK2 was retrovirally expressed developed PV-like features, but not ET or IMF. To address the contribution of this mutation to the pathogenesis of these three MPDs, we generated transgenic mice expressing V617F JAK2 driven by the murine H2Kb promoter. We established two lines. The expression of V617F JAK2 mRNA in bone marrow cells was 0.45 and 1.35 that of endogenous wild-type JAK2 in the two lines. One line showed leukocytosis after 4 months of age, with a predominance of granulocytes. Among 43 mice, examined after 3 months of age, 8 (19%) showed polycythemia and 14 (33%) showed thrombocythemia. Two polycythemia cases also showed thromobocytosis. The other line showed extreme leukocytosis and thromobocytosis at one month of age. The leukocytosis progressed as the animals aged, but the thrombocytosis tended to resolve at 8 months. They showed anemia that means Hb value from 9 to 10 g/dL at one month old. Myeloid cells and megakaryocytes were predominant in the bone marrow of these animals, and splenomegaly with myeloid cell and megakaryocyte invasion was observed. We conclude that in vivo expression of V617F JAK2 results in ET-like, IMF-like, and PV-like disease.

Description: Abstract 1901 Poster Board I-924 Leukocyte alkaline phosphatase (LAP) is considered as a neutrophil activation marker. The level of LAP is quantitated as the LAP score. It is well known that patients with chronic myelogenous leukemia (CML) usually have low LAP scores, whereas those with BCR-ABL negative chronic myeloproliferative disorders (MPD) have elevated LAP scores. In CML patients, the premature release of granulocytes from the bone marrow into the peripheral blood is considered as the cause of low LAP scores. However, the reason for elevated LAP scores in BCR-ABL negative MPD patients has been unclear. An acquired JAK2V617F mutation is observed in most patients with BCR-ABL negative MPD. It has been shown that the JAK2V617F mutation induces constitutive activation of its downstream signaling pathways such as STAT3/STAT5, Ras/MAPK and PI3K pathways. We speculated that an elevated LAP score might be due to the activation of Jak2 downstream pathways through the JAK2V617F mutation. We analyzed LAP expression in BCR-ABL negative MPD patients. JAK2V617F homozygous patients had higher LAP expression than JAK2V617F heterozygous or negative patients. AG490, the Jak2 inhibitor, was shown to significantly decrease the LAP expression in neutrophils of JAK2V617F positive patients. The myeloid cell line NB4 was transfected with the JAK2V617F mutation and a wild-type Jak2 using lentivirus vectors. It was observed that the JAK2V617F mutation, but not wild-type Jak2, enhanced cell proliferation. Then the LAP expression in NB4 cells was evaluated after these cells were differentiated by all-trans retinoic acid and granulocyte colony-stimulating factor. It was observed that the JAK2V617F mutation, but not wild-type Jak2, increased LAP expression. Next, we examined which of the Jak2 downstream pathways played a major role in increasing LAP expression and prompting cell proliferation. By using MEK1/2 inhibitor U0126, PI3K inhibitor LY294002, STAT3 siRNA and STAT5 siRNA, we demonstrated that the JAK2V617F mutation primarily used the STAT3 pathway to increase LAP expression. On the other hand, the JAK2V617F mutation used the STAT5, the Ras/MAPK and the PI3K pathways, but not the STAT3 pathway, to prompt proliferation of NB4 cells. In conclusion, we obtained direct evidence that the JAK2V617F mutation induced elevation of LAP scores via the STAT3 pathway, and prompted proliferation of NB4 cells via the STAT5, the Ras/MAPK and the PI3K pathways. Our findings showed the possibility that the JAK2V617F mutation might use specific downstream pathways depending on various phenotypic manifestations of BCR-ABL negative MPD. Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 1921 Poster Board I-944 Background: Janus kinase 1 (JAK1) plays a critical role in lymphocyte proliferation and differentiation. Somatic JAK1 mutations are found in 18% of adult precursor T acute lymphoblastic leukemias (T-ALL). Some of the mutations were shown to induce the phosphorylation of JAK1 and STAT5 and lead to cytokine-independent proliferation. These data suggest that dysregulation of JAK1 can be involved in the development or progression of T-ALL (Flex et al. J Exp Med. 2008;205:751-758). Adult T-cell leukemia/lymphoma (ATLL) is a type of T-cell neoplasm, and the activation of JAK/STAT is sometimes observed in the tumor cells. Therefore, we investigated JAK1 mutations in ATLL patients. Patients and methods: Twenty Japanese ATLL patients whose percentage of peripheral abnormal lymphocytes was greater than 30% total cell count were sequentially enrolled into the study from 2000 to 2007. Diagnosis of ATLL was made on the basis of clinical features and laboratory characteristics. All cases tested positive for the serum anti-HTLV-1 antibody. The diagnosis was confirmed by observing monoclonal insertion of the HTLV-1 viral genome into leukemia cells by Southern blot hybridization. Peripheral blood mononuclear cells (PBMCs) were isolated and cryopreserved at -80°C. These PBMCs were thawed and genomic DNA was isolated using standard protocol. The entire coding sequence of the JAK1 gene (exons 2 through 25) was amplified by the polymerase chain reaction (PCR) method. The sequence of PCR primers were kindly provided by Dr. Marco Tartaglia (Istituto Superiore di Sanità, Roma, PhD). The nucleotide sequences were determined by fluorescent dye chemistry sequencing and analyzed by sequencing analysis software. By referencing the assembled sequence in the Ensembl genome database, the presence of homozygous mutations was first checked and then candidates for heterozygous mutations or single nucleotide polypeptides (SNPs) on each allele were screened by comparing the ratio of different bases calculated with the height of the peaks seen from sequencing to the reference genome when the ratio was between 0.15 and 1.0. Result: The percentage of abnormal lymphocytes ranged from 30-90%, and the mean value was 55.4%. The mean value of WBC and lymphocyte number was 40.5×109/L and 33.4×109/L, respectively. The mean value of LDH, Ca2+ or sIL-2R was 609 IU/L, 11.4 mg/dL, or 54748 U/mL, respectively. According to Shimoyama criteria (Shimoyama et al. Br J Haematol. 1991;79:428-437), 19 cases were diagnosed as acute-type ATLL, and one case was diagnosed as chronic-type ATLL. The surface markers of all but one abnormal PBMC were CD3+CD4+CD8-CD25+. In that one exception, loss of CD4 expression was observed. We examined the entire coding sequence of the JAK1 gene in 20 ATLL patients and identified no nonsynonymous or nonsense mutations and five types of silent substitutions in 12 cases. All silent substitutions were synonymous SNPs, as determined from referencing the base sequence in the Ensembl genome database. In the ATLL patients examined, the genotype frequency (%) is c546-AA/AG/GG, 97.5/2.5/0; c1590-CC/CT/TT, 97.5/2.5/0; c2049-CC/CT/TT, 50/50/0; c2097-CC/CG/GG, 95/5/0; c2199-AA/AG/GG, 60/40/0. There is no statistical difference in genotype frequency pattern of these SNPs, between the Japanese ATLL patients examined and the general Asian population on the Ensembl database. Conclusion: Mutations in the coding region of JAK1 do not associate with either activation of the JAK/STAT pathway or leukemogenesis in ATLL. We only examined the coding region of JAK1, and the regulatory region of JAK1 remains to be investigated. Further investigation including downstream signaling molecules and inhibitory molecules in the JAK/STAT signaling pathway is necessary to clarify the mechanism contributing to the leukemogenesis of ATLL. Disclosures: No relevant conflicts of interest to declare.

Description: In primary myelofibrosis patients, somatic mutations such as JAK2V617F(JAKVF) and MPLW515 that activate JAK-STAT signaling are often seen. Small-molecule JAK2 inhibitors are effective for organomegaly and constitutional symptoms, but the drugs have little effect on BM fibrosis. To clarify the mechanism by which MPN cells with JAK2 mutations cause BM fibrosis, we compared the gene expression patterns of Lin−Sca1+ BM cells in JAK2VF transgenic mice (JAK2VF-TG), which develop myelofibrosis (MF), with that in WT mice. We found that TGFb1 and HOXB4, the target genes of transcription factor USF1 were highly expressed. TGFβ1, which is secreted by hematopoietic cells, is essential for fibrotic development in a murine model of MF (Chagraoui et al. Blood 2002), and increased expression of HOXB4 enhances human megakaryocytic development (Zhong et al. BBRC 2010). To investigate the mechanism of the high expression of these genes downstream of JAK2 signaling, USF1 and a cytokine receptor gene (MPL, EPOR or CSF3R) were co-transfected into 293T cells along with either a TGF-β1/HOXB4 promoter-driven or a STAT5 response element-driven luciferase reporter. Stimulation of MPL with TPO enhanced USF1 transcriptional activity about 3 fold, but stimulation of EPOR with EPO or of CSF3R with G-CSF did not change this activity. However, stimulation with any of the 3 types of cytokines enhanced STAT5 transcriptional activity. JAK2VF upregulated USF1 and STAT5 much more highly than JAK2WT without TPO stimulation. This USF1 upregulation specifically to TPO/MPL signaling was suppressed by a dominant negative mutant of USF1, JAK2 inhibitors (AG490, NS-018) or MEK inhibitors (U0126, PD325901). Inhibition of PI3K or p38MAPK did not affect the USF1 activation. Co-treatment with JAK2 and MEK inhibitors showed a synergistic effect in blocking both USF1 upregulation and STAT5 activation induced by JAK2VF. Next, we tested the MEK inhibitor, PD325901, in combination with the JAK2 inhibitor, NS-018, in the JAK2VF-TG mice. After disease was established 12 weeks after birth, JAK2VF-TG mice were divided into the following 4 groups: vehicle control; PD325901 monotherapy; NS-018 monotherapy; and combined therapy. PD325901 (5 mg/kg) and NS-018 (50 mg/kg) were orally administered once and twice daily, respectively. After 12 weeks of treatment, we evaluated the effect on BM fibrosis. The grading of MF in each group (n = 5-6) was as follows: vehicle control (MF-0: 0/6, MF-1 or 2: 6/6); PD325901 monotherapy (MF-0: 4/5, MF-1 or 2: 1/5); NS-018 monotherapy (MF-0: 0/6, MF-1 or 2: 6/6); and combined therapy (MF-0: 3/6, MF-1 or 2: 3/6). In the 2 groups treated with PD325901, 50~80% of mice showed MF-0. In contrast, in vehicle-treated or NS-018 monotherapy groups, all mice showed MF-1 or 2. Consistent with the MF grading, BM cellularity was significantly increased in the PD325901 monotherapy or combined therapy groups compared with the vehicle-treated group. A significant reduction was seen in the plasma TGFβ1 concentration in the PD325901 monotherapy and combined therapy groups compared with the vehicle-treated group (9.7 ng/ml, 8.1 ng/ml vs. 18.2 ng/ml, respectively). The TGFβ1 concentration in the extracellular fluid of BM (Wagner et al blood 2007) was also significantly reduced (5.6 ng/ml, 6.8 ng/ml vs. 9.1 ng/ml, respectively). BM cellularity and the TGFβ1 concentration in the NS-018 monotherapy group were comparable to those in the vehicle-treated group. Interestingly, megakaryocytes in the PD325901 monotherapy and combined therapy groups were decreased in number and were smaller than those in the vehicle-treated or NS-018 monotherapy groups. Regarding the effect on splenomegaly, spleen weight was significantly reduced in the NS-018 monotherapy and combined therapy groups compared with the vehicle-treated group (0.83 g, 0.69 g vs. 1.18 g, respectively). PD325901 monotherapy had little effect on splenomegaly. It is known that MEK-ERK1/2 pathway is critical in normal megakaryocyte development. In vitro data suggest that JAK2VF activates this pathway downstream of MPL and may contribute to TGFβ1 overproduction and dysmegakaryopoiesis, causing BM fibrosis via transcriptional enhancement of USF1. In vivo data suggest that MEK inhibition has the potential to improve dysmegakaryopoiesis and BM fibrosis. The combined therapy of JAK2 inhibitors with MEK inhibitors might be a promising therapy for improving both splenomegaly and BM fibrosis. Disclosures No relevant conflicts of interest to declare.

Description: Key Points Loss of TET2 accelerates the degree of malignancy of MPNs in combination with JAK2V617F. Loss of TET2 sustains MPNs in combination with JAK2V617F.

Description: Abstract 2585 Several lines of reports have suggested that mature magakaryocytes (MKs) form long cytoplasmic processes containing platelets (PLT) organelles from which PLT break off due to blood flow pressures in bone marrow (BM). These cytoplasmic processes were termed ‘proplatelet'. MKs differentiated from hematopoietic stem cells by in vitro culture also develop similar processes, referred to as ‘proplatelet-like formation (PPF)'. It has been already reported that fibronectin (FN) and phorbol 12-myristate 13-acetate (PMA) are essential for inducing PPF in MKs using CHRF-288 human megakaryoblastic cell line (Jiang F et al. Blood 99, 2002). FN plays important roles in megakaryocytopoiesis through the FN-receptors. The role of adhesive interactions with FN in BM stroma and FN-receptor beta1-integrins has been reported in proliferation, differentiation and maintenance of megakaryocytic lineage cells. However, the substantial role of these FN-receptors and their functional assignment in PPF are not yet fully understood. We first investigated the effects of beta1-integrins on PPF using CHRF-288 cells, which express alpha4beta1-integrin (VLA-4) and alpha5beta1-integrin (VLA-5) as FN-receptors. When the cells were cultured on FN for 3 days, PMA prompted PPF in a dose-dependent manner. While nearly 15% of the cells displayed PPF with PMA (100 ng/mL), no cells cultured with FN alone or PMA alone exhibited PPF. PPF induced by FN plus PMA combination (FN/PMA) was abrogated by addition of anti-alpha4-integrin monoclonal antibodies (mAb) plus anti-alpha5-integrin mAb combination, but not by the addition of anti-alpha4-integrin mAb alone or anti-alpha5-integrin mAb alone. Thus, the adhesive interaction with FN via VLA-4 and VLA-5 were responsible for PPF. We next investigated the effect of TNIIIA2, which enhances the adhesive interaction between FN and beta1-integrins, in PPF induced by FN/PMA. TNIIIA2 (RSTDLPGLKAATHYTITIRGVC) is a 22-mer peptide derived from the 14th FN type III-like (FNIII) repeat in tenascin (TN)-C molecule which we found recently, and it induces the conformational change necessary for functional activation of beta1-integrins (Fukai F et al. J Biol Chem 282, 2007; J Biol Chem 284, 2009). The PPF induced by FN/PMA was highly accelerated when CHRF-288 cells were enforced adhering to FN by treatment with TNIIIA2 (25 microg/mL). More than 45% of the cells displayed PPF with FN/PMA plus TNIIIA2 combination (FN/PMA/TNIIIA2). Blocking experiments using anti-beta1-integrin mAbs indicated that adhesive interaction with FN via VLA-4 and VLA-5 was also responsible for acceleration of PPF induced by FN/PMA/TNIIIA2. On the other hand, control peptide, TNIIIA2mutant (RSTDLPGLKAATHYTATARGVC) did not accelerate PPF induced by PMA/FN. The calculated yield of the cells with PPF induced by FN/PMA/TNIIIA2 was 2.5-fold more than that induced by FN/PMA. We have previously established ‘a three-phase serum-free culture system' to generate large amount of PLT from human cord blood CD34+ cells (Matsunaga T et al. Stem cells 24, 2006). A study on the effect of TNIIIA2 on our ‘three-phase serum-free culture system' is now underway. Finally, we investigated signal transduction pathways responsible for PPF induced by FN/PMA. While FN/PMA induced activation of extracellular signal-regulated protein kinase 1 (ERK1/2), FN alone or PMA alone did not induce ERK1/2 activation. The results was in accordance with the data previously reported by Jiang et at (Blood 99, 2002). TNIIIA2 strongly enhanced activation of ERK1/2 by FN/PMA. However, c-Jun amino-terminal kinase 1 (JNK1), p38 and phosphoinositide-3 kinase (PI3K)/Akt were not stimulated by FN/PMA even in the presence of TNIIIA2. Thus, enhanced activation of ERK1/2 by FN/PMA/TNIIIA2 was responsible for acceleration of PPF by FN/PMA. Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 3897 Poster Board III-833 The V617F mutation of JAK2 (JAK2-V617F) occurs at a high frequency in Philadelphia chromosome-negative myeloproliferative diseases (MPDs). JAK2-V617F leads to constitutive activation of the JAK2 kinase, causing cytokine independent growth in cell lines and development of MPD in mice. These data suggest that aberrant activation of JAK2 plays a pivotal role in the pathophysiology of MPDs and targeting JAK2-V617F may be therapeutically useful. Some orally bioavailable inhibitors of JAK2 are already in clinical trials. R723 is a potent and highly selective (in vitro kinase assay: JAK2 IC50=2nM, JAK1 IC50 〉1μM, JAK3 IC50 =24nM) small molecule inhibitor of JAK2. We tested R723 in a murine model of MPD induced by JAK2-V617F. H2Kb promoter-controlled JAK2-V617F expressing mice (V617F-TG) show extreme leukocytosis, thrombocytosis and progressive anemia. They also show hepato-splenomegaly with extramedullary hematopoiesis. Megakaryocytes are predominant in bone marrow and new formation of bony trabeculae and accumulation of fibers are seen. In vitro analysis of bone marrow cells shows constitutive activation of STAT5 and formation of cytokine-independent growth of erythroid colony-forming units (CFU-E). They exhibit high mortality compared to wild-type controls. At first, we assessed the effect of R723 on wild-type (WT) and V617F-TG bone marrow cells in vitro. R723 inhibited cytokine-independent CFU-E growth and constitutive activation of STAT5 of V617F-TG cells. R723 also inhibited cytokine-dependent colony growth and cytokine-induced STAT5 activation in both WT and V617F-TG cells at the same level. Next, we assessed the effect of R723 in vivo. On development of MPD, V617F-TG mice were divided into treatment or vehicle control groups. R723 was administered by oral gavage at 35mg/kg or 70mg/kg bid for 16 weeks, whereas the control groups received vehicle only. Mice were followed by blood counts and a subset of mice was euthanized for detailed histopathology and FACS analysis. In treated mice, there was a significant reduction in leukocyte count in both groups, and a reduction in platelet count in the high dose group. There was no improvement in anemia. They showed a dose-dependent-reduction of hepato-splenomegaly. Histopathology and FACS analysis revealed a reduction of myeloid cells, with partially restored architecture in spleen. In bone marrow, R723 had little effect on progression of fibrosis and megakaryocyte hyperplasia. During the time course of study, 6 out of 23 mice died in the vehicle group, whereas 1 out of 26 mice died in the 70mg/kg group. There was a statistically significant prolongation of survival in the 70mg/kg group (p

Description: Abstract 4106 An activating mutation in the Janus kinase 2 gene (JAK2) (G1849T, which produces JAK2 V617F) occurs at a high frequency in Bcr-Abl-negative myeloproliferative neoplasms (MPNs). JAK2 V617F induces cytokine-independent growth in cell lines and, in murine models, recapitulates much of the pathobiology observed in MPN patients, suggesting that small-molecule inhibitors targeting JAK2 may be therapeutically useful. Some orally bioavailable inhibitors of JAK2 are already in clinical trials. NS-018 is a novel JAK2 inhibitor that inhibits JAK2 enzyme activity with an IC50 value of less than 1 nM. NS-018 shows 30–50-fold selectivity for JAK2 over other JAK-family kinases such as JAK1, JAK3 and TYK2. We tested NS-018 in a murine model of MPN induced by JAK2 V617F. Mice expressing JAK2 V617F controlled by the H2Kb promoter (V617F-TG mice) show an MPN phenotype: leukocytosis, thrombocytosis, progressive anemia, hepatosplenomegaly with extramedullary hematopoiesis, megakaryocyte hyperplasia and bone marrow fibrosis. They also exhibit body weight loss and high mortality compared to wild-type controls. Bone-marrow cells show constitutive activation of STAT5 and cytokine-independent growth of erythroid colony-forming units (CFU-E). NS-018 inhibited cytokine-independent CFU-E growth and constitutive activation of STAT5 in V617F-TG cells in vitro. For in vivo experiments, V617F-TG mice were divided into treatment and vehicle control groups after disease was established at 12 weeks after birth. NS-018 was administered for 24 weeks by oral gavage at doses of 25 mg/kg or 50 mg/kg bid, and the control groups received vehicle only. Mice were monitored by blood counts, and a subset of mice was euthanized for detailed histopathology and fluorescence activated cell sorting analysis. During the study, 12 of 34 mice died in the vehicle group, whereas 1 of 36 mice died in the 50 mg/kg group. There was a statistically significant prolongation of survival in the 50 mg/kg group (p