Jak2 inhibitors: Rationale and role as therapeutic agents in hematologic malignancies

Although the Jak2-V617F mutation has generated strong awareness because of its causative role in myeloproliferative disorders, reports of Jak2 gene aberrations linked to hematologic malignancies have preceded those of V617F by nearly a decade. These malignant mutations include Jak2 amino acid substitutions, deletions, insertions, and chromosomal translocations. As a consequence, researchers are increasingly focused on identifying Jak2 inhibitors that suppress aberrant Jak2 kinase activity. Some of these inhibitors may one day become therapeutically beneficial for individuals with Jak2-related hematologic malignancies. This review summarizes various Jak2 mutations associated with hematologic malignancies and assesses some of the Jak2 inhibitors in the preclinical phase or in clinical trials. By reviewing these specific areas, we hope to have a better understanding of Jak2’s role in hematologic malignancies and to shed light on the utility of Jak2 inhibitors.     

Suppression of multiple anti‐apoptotic BCL2 family proteins recapitulates the effects of JAK2 inhibitors in JAK2V617F driven myeloproliferative neoplasms

Several lines of research suggest that Bcl‐xL‐mediated anti‐apoptotic effects may contribute to the pathogenesis of myeloproliferative neoplasms driven by JAK2V617F and serve as therapeutic target. Here, we used a knock‐in JAK2V617F mouse model and confirmed that Bcl‐xL was overexpressed in erythroid progenitors. The myeloproliferative neoplasm (MPN)‐induced phenotype in the peripheral blood by conditional knock‐in of JAK2V617F was abrogated by conditional knockout of Bcl2l1, which presented anemia and thrombocytopenia independently of JAK2 mutation status. Mx1‐Cre Jak2V617^W/VF/Bcl2l1^f/f mice presented persistent splenomegaly as a result of extramedullary hematopoiesis and pro‐apoptotic stimuli in terminally differentiated erythroid progenitors. The pan‐BH3 mimetic inhibitor obatoclax showed superior cytotoxicity in JAK2V617F cell models, and reduced clonogenic capacity in ex vivo assay using Vav‐Cre Jak2V617F bone marrow cells. Both ruxolitinib and obatoclax significantly reduced spleen weights in a murine Jak2V617F MPN model but did not show additive effect. The tumor burden reduction was observed with either ruxolitinib or obatoclax in terminal differentiation stage neoplastic cells but not in myeloid‐erythroid precursors. Therefore, disrupting the BCL2 balance is not sufficient to treat MPN at the stem cell level, but it is certainly an additional option for controlling the critical myeloid expansion of the disease.     

原发性血小板增多症骨髓病理及JAK2-V617F突变分析

目的:分析原发性血小板增多症（essential thrombocythemia,ET）患者的骨髓病理及JAK2-V617F突变特点。方法:回顾109例ET患者的临床资料,并与继发性血小板增多症(secondary thrombocythemia,ST)进行比较。结果:ET骨髓病理巨核细胞体积明显增大,核多分叶、多核易见,成簇、成片状分布,ST巨核细胞体积未见明显增大及异常分布。ET患者JAK2-V617F突变阳性率为 57.83%,ST患者JAK2-V617F突变均为阴性。JAK2-V617F突变阳性组WBC、Hb、骨髓纤维化、初诊血栓事件高于阴性组,差异有统计学意义（P<0.05)。JAK2-V617F突变阳性组年龄、Plt、骨髓粒系、红系百分比及巨核细胞计数与阴性组比较,无显著性差异（P>0.05）;JAK2-V617F突变阳性组无血栓生存率较阴性组低,差异有统计学意义（P<0.05）。结论:ET的骨髓病理特征明显,骨髓活检与JAK2-V617F基因检查相结合对ET诊断及治疗具有重要意义。     

Bone marrow stroma-secreted cytokines protect JAK2(V617F)-mutated cells from the effects of a JAK2 inhibitor

Signals emanating from the bone marrow microenvironment, such as stromal cells, are thought to support the survival and proliferation of the malignant cells in patients with myeloproliferative neoplasms (MPN). To examine this hypothesis, we established a coculture platform [cells cocultured directly (cell-on-cell) or indirectly (separated by micropore membrane)] designed to interrogate the interplay between Janus activated kinase 2-V617F (JAK2(V617F))-positive cells and the stromal cells. Treatment with atiprimod, a potent JAK2 inhibitor, caused marked growth inhibition and apoptosis of human (SET-2) and mouse (FDCP-EpoR) JAK2(V617F)-positive cells as well as primary blood or bone marrow mononuclear cells from patients with polycythemia vera; however, these effects were attenuated when any of these cell types were cocultured (cell-on-cell) with human marrow stromal cell lines (e.g., HS5, NK.tert, TM-R1). Coculture with stromal cells hampered the ability of atiprimod to inhibit phosphorylation of JAK2 and the downstream STAT3 and STAT5 pathways. This protective effect was maintained in noncontact coculture assays (JAK2(V617F)-positive cells separated by 0.4-μm-thick micropore membranes from stromal cells), indicating a paracrine effect. Cytokine profiling of supernatants from noncontact coculture assays detected distinctly high levels of interleukin 6 (IL-6), fibroblast growth factor (FGF), and chemokine C-X-C-motif ligand 10 (CXCL-10)/IFN-γ-inducible 10-kD protein (IP-10). Anti-IL-6, -FGF, or -CXCL-10/IP-10 neutralizing antibodies ablated the protective effect of stromal cells and restored atiprimod-induced apoptosis of JAK2(V617F)-positive cells. Therefore, our results indicate that humoral factors secreted by stromal cells protect MPN clones from JAK2 inhibitor therapy, thus underscoring the importance of targeting the marrow niche in MPN for therapeutic purposes.     

Preclinical studies of Flonoltinib Maleate,a novel JAK2/FLT3 inhibitor,in treatment of JAK2V617F-induced myeloproliferative neoplasms

Janus kinase 2 (JAK2) hyperactivation by JAK2^V617F mutation leads to myeloproliferative neoplasms (MPNs) and targeting JAK2 could serve as a promising therapeutic strategy for MPNs. Here, we report that Flonoltinib Maleate (FM), a selective JAK2/FLT3 inhibitor, shows high selectivity for JAK2 over the JAK family. Surface plasmon resonance assays verified that FM had a stronger affinity for the pseudokinase domain JH2 than JH1 of JAK2 and had an inhibitory effect on JAK2 JH2V617F. The cocrystal structure confirmed that FM could stably bind to JAK2 JH2, and FM suppressed endogenous colony formation of primary erythroid progenitor cells from patients with MPNs. In several JAK2^V617F-induced MPN murine models, FM could dose-dependently reduce hepatosplenomegaly and prolong survival. Similar results were observed in JAK2^V617F bone marrow transplantation mice. FM exhibited strong inhibitory effects on fibrosis of the spleen and bone marrow. Long-term FM treatment showed good pharmacokinetic/pharmacodynamic characteristics with high drug exposure in tumor-bearing tissues and low toxicity. Currently, FM has been approved by the National Medical Products Administration of China (CXHL2000628), and this study will guide clinical trials for patients with MPNs.Subject terms: Myeloproliferative disease, Targeted therapies     

急性淋巴细胞白血病患者 ASB2和 Jak3基因mRNA 表达的研究

目的：研究急性淋巴细胞白血病（ALL）患者骨髓中锚蛋白重复序列和抑制细胞因子信号盒蛋白2（ASB2）和 Janus 激酶3（Jak3）mRNA 的表达及其两者的相关性。方法收集初诊的48例 ALL患者（37例 B 细胞 ALL,11例 T 细胞 ALL）和34例非白血病患者（对照组）骨髓,采用实时荧光定量 PCR检测骨髓中 ASB2和 Jak3 mRNA 表达情况。结果B 细胞 ALL 和 T 细胞 ALL 患者骨髓中 ASB2 mRNA表达量相对于对照组分别升高了32．7倍和68．5倍,差异均有统计学意义（t ＝20．1,P ＜0．01;t ＝23．1, P ＜0．01）,Jak3 mRNA 表达量较对照组分别升高了2336．3和7131．5倍（t ＝70．2,P ＜0．01;t ＝90．4, P ＜0．01）。ASB2和 Jak3 mRNA 表达量具有相关性（r ＝0．523,P ＜0．001）。结论ASB2和 Jak3在 ALL患者骨髓中异常表达,且具有正相关性,两者可能共同参与白血病细胞的恶性增殖和异常分化。     

80例急性髓性白血病M2型患者JAK2V617F基因突变的检测及临床意义

目的 探讨JAK2V617F基因突变在急性髓性白血病M2型(AML-M2)患者中的发牛率和临床预后意义.方法 采用等位基因特异性聚合酶链反应(AS-PCR)技术,检测80例AML-M2患者的JAK2V617F基因突变情况.结果 80例AML-M2患者中,初诊时JAK2V617F基因突变6例,复发时JAK2V617F基因突变1例,JAK2V617F基因的突变率为8.8%.7例JAK2V617F基因突变者的血象和骨髓象均呈现出白血病改变特征,而无骨髓增殖性疾病(MPD)征象;免疫分型显示为髓系表达.接受治疗的5例JAK2V617F基因突变者中,有4例患者在治疗后达到完全缓解,1例未缓解;除1例失访外,其余4例患者的中位生存期为18.5个月.结论 JAK2V617F基因突变作为AML发病机制中的Ⅰ类突变,可能并不是AML发病的初始事件;初诊AML患者出现JAK2V617F基因突变也并不意味着疾病顸后较差.     

Involvement of Jak2 tyrosine phosphorylation in Bcr-Abl transformation

We have previously reported that the Jak2 tyrosine kinase but not Jak1 is tyrosine phosphorylated in the absence of IL-3 in Bcr-Abl positive M3.16 cells, which are rendered IL-3 independent by BCR-ABL gene expression. We have explored the involvement of Jak2 tyrosine phosphorylation in Bcr-Abl oncogenic effects. Our results indicate that Jak2 became tyrosine-phosphorylated in a number of cell lines expressing Bcr-Abl, when maintained in medium lacking IL-3, whereas Bcr-Abl negative cells lacked Jak2 tyrosine phosphorylation. Jak2 was poorly tyrosine-phosphorylated in cells expressing the SH2 deletion mutant of Bcr-Abl compared to either wild-type Bcr-Abl or its SH3 deletion mutant. Moreover, tyrosine phosphorylation of Jak2 by Bcr-Abl was inhibited by the Abl tyrosine kinase inhibitor, STI 571, in a dose-dependent manner. This inhibition of Bcr-Abl kinase by the drug did not interfere with the ability of Jak2 and Bcr-Abl to form a complex. Studies with deletion mutants of Bcr-Abl indicated that the C-terminal domain of Abl within Bcr-Abl was involved in complex formation with Jak2. Similarly, GST-Abl pull-down assays confirmed the strong binding to Jak2 by the C-terminus of Abl. Jak2 peptide substrate studies indicated that the Bcr-Abl and Abl tyrosine kinases specifically phosphorylated Y1007 of Jak2 but only poorly phosphorylated Y1008. Phosphorylation of Y1007 of Jak2 is known to be critical for its tyrosine kinase activation. Tyrosine residue 1007 of Jak2 was phosphorylated in 32Dp210 cells as measured by Western blotting with a phosphotyrosine 1007 sequence-specific antibody. A kinase-inactive Jak2 mutant blocked the colony forming ability of K562 cells. Tumor formation of K562 cells in nude mice was similarly inhibited by this kinase-inactive Jak2 mutant. This inhibition was independent of Stat5 tyrosine phosphorylation. Furthermore, tyrosine-phosphorylated Jak2 was detected in blood cells from CML patients in blast crisis but not in a normal marrow sample. In summary, these findings provide strong evidence that the Jak2 tyrosine kinase is a critical factor in Bcr-Abl malignant transformation.     

Characterization of murine JAK2V617F-positive myeloproliferative disease

The JAK2(V617F) mutation is present in almost all patients with polycythemia vera (PV), large proportions of patients with essential thrombocythemia and idiopathic myelofibrosis, and less frequently in atypical myeloproliferative disorders (MPD). We show that transplantation of JAK2(V617F)-transduced bone marrow into BALB/c mice induces MPD reminiscent of human PV, characterized by erythrocytosis, granulocytosis, extramedullary hematopoiesis, and bone marrow fibrosis, but not thrombocytosis. Fluorescence-activated cell sorting of bone marrow and spleen showed proportional expansion of common myeloid progenitors, granulocyte-monocyte and megakaryocyte-erythrocyte progenitors. Megakaryocyte and late erythroid progenitors were dramatically increased, with only modest expansion of early erythroid progenitors. Erythropoietin (Epo) receptor expression was reduced on early, but normal on late erythroblasts. Serum levels of Epo and granulocyte colony-stimulating factor, but not granulocyte macrophage colony-stimulating factor, were reduced, whereas tumor necrosis factor-alpha was increased, possibly exerting a negative effect on JAK2(V617F)-negative hematopoiesis. These data suggest that erythrocytosis and granulocytosis in JAK2(V617F) mice are the net result of a complex interplay between cell intrinsic and extrinsic factors. There were no thromboembolic events and no animals succumbed to their disease, implicating additional factors in the manifestation of human disease. The disease was not transplantable and prolonged observation showed normalization of blood counts in most JAK2(V617F) mice, suggesting that the mutation may not confer self-renewal capacity.     

骨髓增殖性肿瘤120例JAK2 V617F基因突变的临床分析

目的 探讨JAK2 V617F基因突变在骨髓增殖性肿瘤(MPN)患者中的发生率及临床意义.方法 采用骨髓细胞学和活组织检查方法分析120例患者的骨髓病理状况,监测费城染色体(Ph染色体)和bcr-abl融合基因.从患者骨髓抽提DNA,采用荧光定量PCR技术检测JAK2 V617F基因突变.结果 所有患者均呈现出MPN各自类型的典型特征.Ph染色体和bcr-abl融合基因检测均为阴性.120例MPN患者中JAK2 V617F基因突变的阳性率为66.7％(80/120),其中真性红细胞增多症(PV)为72.7％(16/22),原发性血小板增多症(ET)为66.0％(62/94),4例原发性骨髓纤维化(PMF)患者中2例阳性.JAK2 V617F突变阳性PV患者的外周血白细胞计数(P=0.001)和血小板计数(P=0.010)均高于阴性患者;JAK2 V617F突变阳性ET患者的白细胞计数高于阴性患者(P=0.006);PMF中JAK2V617F突变阳性和阴性患者间各项指标差异均无统计学意义(均P＞0.05).结论 JAK2 V617F基因突变检测有助于bcr-abl阴性MPN的诊断和鉴别诊断,使患者能够在早期被发现和治疗.     

骨髓增殖性疾病的研究进展:后JAK2突变时代的几个临床问题

 细胞死亡与细胞增殖是对立面,是机体的基本细胞生物学机制之一。近年来报道的越来越多的细胞死亡方式令人困惑。最近细胞死亡命名委员会（NCCD）的细胞死亡分类建议书梳理了相关的研究进展,使概念更清晰。文章概述其主要精神,补充一些文献资料,并探讨细胞死亡研究的意义。     

Atypical chronic myeloid leukemia as defined in the WHO classification is a JAK2 V617F negative neoplasm

Atypical chronic myeloid leukemia (aCML) as defined by the WHO classification is a rare hematopoietic stem cell disorder, which shows both myeloproliferative as well as myelodysplastic features. Because of the presence of neutrophilic leukocytosis, aCML may resemble chronic myelogenous leukemia. However, in contrast with the latter, aCML lacks a Philadelphia chromosome or the BCR/ABL fusion gene. The molecular pathogenesis of aCML and its relationship to other myeloproliferative neoplasms is unknown. To clarify these points, the presence of JAK2 V617F was examined by a retrospective analysis of archival specimens obtained from two large medical institutions.Paraffin-embedded bone marrow (BM) trephines and clot sections were examined by an allele-specific TaqMan PCR suitable for use with decalcified tissue. Fifty-nine cases of Philadelphia (Ph) chromosome negative chronic myeloproliferative neoplasms (CMPN) and normal bone marrows (BM) served as controls. None of the nine amplifiable cases of aCML and none of the normal BM controls showed a JAK2 V617F mutation, in contrast to 45/59 (76%) of the Ph chromosome negative CMPN cases. Atypical CML should therefore be considered as a JAK2 negative chronic myeloid neoplasm that remains properly categorized, alongside chronic myelomonocytic leukemia and juvenile myelomonocytic leukemia, within the WHO group of myelodysplastic/myeloproliferative neoplasms.     

Elimination of clonogenic breast cancer cells from human bone marrow. A comparison of immunotoxin treatment with chemoimmunoseparation using 4-hydroperoxycyclophosphamide, monoclonal antibodies, and magnetic microspheres

Autologous bone marrow transplantation (ABMT) may aid in the management of breast cancer, but is currently limited to patients without bone marrow metastases. In earlier studies, 5 logs of malignant clonogenic breast cancer cells could be eliminated from human bone marrow using a combination of chemoseparation with 4-hydroperoxycyclophosphamide (4-HC) and immunoseparation with monoclonal antibodies and magnetic microspheres. In this report the authors compare chemoimmunoseparation to treatment with immunotoxins for elimination of tumor cells from human bone marrow and for the preservation of normal precursors. Breast cancer cells from each of five cell lines were mixed with a tenfold excess of irradiated human bone marrow cells. Treatment with a combination of five immunotoxins reduced clonogenic tumor cell growth by 1.8 to 5.5 logs depending upon the cell line. With two of the five cell lines, clonogenic tumor cells were eliminated quantitatively. Using the CAMA-1 breast cancer cell line, treatment with multiple immunotoxins was compared with chemoimmunoseparation with 4-HC, a panel of five unconjugated monoclonal antibodies and magnetic microspheres. Chemoimmunoseparation eliminated 3.5 to 5.4 logs of malignant cells, while preserving 21% of Colony-forming unit-granulocyte-macrophage (CFU-GM) and 37% of burst-forming unit-erythrocyte (BFU-E). No clonogenic breast cancer cells could be detected. Immunotoxin treatment eliminated 2.2 to 5.4 logs of clonogenic breast cancer cells, but had no effect on the bone marrow precursors. In seven of ten experiments, however, clonogenic breast cancer cells remained after immunotoxin treatment. Consequently, treatment with 4-HC, multiple murine monoclonal antibodies and magnetic microspheres provided more consistent elimination of tumor cells than separation with immunotoxins, but was significantly more toxic for marrow precursors.     

The Development of Gastric Cancer in a Patient with Polycythemia Vera, 3P Deletion, and JAK2 V617F Mutation

3p deletion which is frequently associated with solitary tumors and hematological malignancies is a chromosomal abnormality. Recently, Janus kinase-2 (JAK2) V617F mutation has an important role in the diagnosis of myeloproliferative disorders, especially in polycythemia vera (PV). We reported the development of gastric cancer in a 75-year-old patient with PV, 3p 12-14 deletion and JAK2 V617F mutation. PV was diagnosed according to the classification of World Health Organization. JAK2 V617F mutation with polymerase chain reaction and 3p12-14 deletion with cytogenetic examination of the bone marrow were detected. We investigated solitary tumors in the patient using computed tomographies of thorax, neck, ear, nose, and throat. However, they were normal. After 2 years, gastric cancer appeared in the patient. In conclusion, cytogenetic examination may be important in both the development and the diagnosis of hematological malignancies and solitary tumors. So the patients should be followed closely.     

干扰素对JAK2 V617F阳性骨髓增殖性肿瘤PD-1/PD-L1及Treg表达的影响

 目的 探讨干扰素-alpha-2b（IFN-α2b）对JAK2 V617F阳性骨髓增殖性肿瘤（MPN）患者中程序性死亡受体-1（PD-1）、程序性死亡配体-1 （PD-L1）及CD4+ CD25+ Foxp3+调节性T细胞（Treg）表达的影响及临床意义。方法 收集JAK2 V617F阳性MPN患者61例，包括初治组41例、IFN-α2b治疗组20例，健康对照组20例。应用荧光定量PCR检测JAK2 V617F/JAK2突变率，流式细胞术检测PD-1、PD-L1、Treg的表达情况。选取15例患者骨髓及外周血标本进行体外细胞培养，应用1×106 U/L IFN-α2b作用48 h后检测PD-1、PD-L1及Treg表达情况。结果 初治组的JAK2 V617F、PD-1、PD-L1及Treg表达明显高于IFN-α2b治疗组及对照组（均P<0.05）。JAK2 V617F突变量≥50%患者骨髓髓系细胞PD-1、PD-L1及外周血Treg细胞均明显高于突变量<50%患者（均P<0.05）。相关性分析结果显示JAK2 V617F突变量与骨髓髓系细胞PD-1、PD-L1和淋巴细胞PD-1呈正相关，与Treg表达无相关性。1×106 U/L IFN-α2b作用48 h后能够体外抑制MPN原代细胞PD-1、PD-L1及Treg的表达（P<0.05）。结论 PD-1、PD-L1及Treg共同参与了MPN的发病过程，干扰素能够不同程度抑制MPNJAK2 V617F、PD-1、PD-L1及Treg表达，进而抑制MPN的进展。     

Efficacy of TG101348, a selective JAK2 inhibitor, in treatment of a murine model of JAK2V617F-induced polycythemia vera

We report that TG101348, a selective small-molecule inhibitor of JAK2 with an in vitro IC50 of approximately 3 nM, shows therapeutic efficacy in a murine model of myeloproliferative disease induced by the JAK2V617F mutation. In treated animals, there was a statistically significant reduction in hematocrit and leukocyte count, a dose-dependent reduction/elimination of extramedullary hematopoiesis, and, at least in some instances, evidence for attenuation of myelofibrosis. There were no apparent toxicities and no effect on T cell number. In vivo responses were correlated with surrogate endpoints, including reduction/elimination of JAK2V617F disease burden assessed by quantitative genomic PCR, suppression of endogenous erythroid colony formation, and in vivo inhibition of JAK-STAT signal transduction as assessed by flow cytometric measurement of phosphorylated Stat5.