Search

Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) is an intractable disease and most cases harbor genetic alterations that activate JAK or ABL signaling. The commonest subtype of Ph-like ALL exhibits a CRLF2 gene rearrangement that brings about JAK1/2-STAT5 pathway activation. However, JAK1/2 inhibition alone is insufficient as a treatment, so combinatorial therapies targeting multiple signals are needed. To better understand the mechanisms underlying the insufficient efficacy of JAK inhibition, we explored gene expression changes upon treatment with a JAK1/2 inhibitor (ruxolitinib) and found that elevated BCL6 expression was one such mechanism. Upregulated BCL6 suppressed the expression of TP53 along with its downstream cell cycle inhibitor p21 (CDKN2A) and pro-apoptotic molecules, such as FAS, TNFRSF10B, BID, BAX, BAK, PUMA, and NOXA, conferring cells some degree of resistance to therapy. BCL6 inhibition (with FX1) alone was able to upregulate TP53 and restore the TP53 expression that ruxolitinib had diminished. In addition, ruxolitinib and FX1 concertedly downregulated MYC. As a result, FX1 treatment alone had growth-inhibitory and apoptosis- sensitizing effects, but the combination of ruxolitinib and FX1 more potently inhibited leukemia cell growth, enhanced apoptosis sensitivity, and prolonged the survival of xenografted mice. These findings provide one mechanism for the insufficiency of JAK inhibition for the treatment of CRLF2-rearranged ALL and indicate BCL6 inhibition as a potentially helpful adjunctive therapy combined with JAK inhibition.

B-cell acute lymphoblastic leukemia (B-ALL), a genetically heterogeneous disease, is classified into different molecular subtypes that are defined by recurrent gene rearrangements, gross chromosomal abnormalities, or specific gene mutations. Cells with these genetic alterations acquire a leukemia-initiating ability and show unique expression profiles. The distribution of B-ALL molecular subtypes is greatly dependent on age, which also affects treatment responsiveness and long-term survival, partly accounting for the inferior outcome in adolescents and young adults (AYA) and (older) adults with B-ALL. Recent advances in sequencing technology, especially RNA sequencing and the application of these technologies in large B-ALL cohorts have uncovered B-ALL molecular subtypes prevalent in AYA and adults. These new insights supply more precise estimations of prognoses and targeted therapies informed by sequencing results, as well as a deeper understanding of the genetic basis of AYA/adult B-ALL. This article provides an account of these technological advances and an overview of the recent major findings of B-ALL molecular subtypes in adults., (© 2022 The Authors. Cancer Science published by John Wiley & Sons Australia, Ltd on behalf of Japanese Cancer Association.)

The genetic basis of leukemogenesis in adults with B-cell acute lymphoblastic leukemia (B-ALL) is largely unclear, and its clinical outcome remains unsatisfactory. This study aimed to advance the understanding of biological characteristics, improve disease stratification, and identify molecular targets of adult B-ALL. Adolescents and young adults (AYA) (15 to 39 years old, n = 193) and adults (40 to 64 years old, n = 161) with Philadelphia chromosome-negative (Ph-) B-ALL were included in this study. Integrated transcriptomic and genetic analyses were used to classify the cohort into defined subtypes. Of the 323 cases included in the RNA sequencing analysis, 278 (86.1%) were classified into 18 subtypes. The ZNF384 subtype (22.6%) was the most prevalent, with 2 novel subtypes (CDX2-high and IDH1/2-mut) identified among cases not assigned to the established subtypes. The CDX2-high subtype (3.4%) was characterized by high expression of CDX2 and recurrent gain of chromosome 1q. The IDH1/2-mut subtype (1.9%) was defined by IDH1 R132C or IDH2 R140Q mutations with specific transcriptional and high-methylation profiles. Both subtypes showed poor prognosis and were considered inferior prognostic factors independent of clinical parameters. Comparison with a previously reported pediatric B-ALL cohort (n = 1003) showed that the frequencies of these subtypes were significantly higher in AYA/adults than in children. We delineated the genetic and transcriptomic landscape of adult B-ALL and identified 2 novel subtypes that predict poor disease outcomes. Our findings highlight the age-dependent distribution of subtypes, which partially accounts for the prognostic differences between adult and pediatric B-ALL., (© 2022 by The American Society of Hematology.)

An HLA-matched relative is the first-choice donor for patients with Philadelphia chromosome (Ph)-negative acute lymphoblastic leukemia (ALL) in first complete remission (CR1). The most promising alternative donor is thought to be an HLA-matched unrelated donor (MUD) in patients who do not have an HLA-matched related donor. Cord blood transplantation (CBT) is an alternative option. Higher rates of engraftment failure and nonrelapse mortality (NRM) are significant problems, but the ready availability of cord blood can be an advantage, because patients can immediately undergo transplantation before progression. This study was conducted to identify an appropriate alternative donor in patients with Ph-negative ALL in CR1 who do not have an HLA-matched related donor (MRD). Decision analyses using a Markov model were performed to compare immediate CBT, in which CBT was performed at 1 month after the achievement of CR1, with elective unrelated bone marrow transplantation (uBMT) from an 8/8 MUD (8/8 uBMT) or uBMT from a 7/8 MUD (7/8 uBMT), in which uBMT was performed at 4 months, in patients age 16 to 55 years with Ph-negative ALL in CR1 who did not have an MRD. We constructed a decision tree. The cycle length was set at 3 months, and analyses were performed for 19 cycles for uBMT and 20 cycles for CBT, resulting in evaluation of the 5-year life expectancy after both decisions. Transition probabilities (TPs) and utilities were estimated from prospective and retrospective Japanese studies and the registry database of Japan. Subgroup analyses were performed according to risk stratification based on WBC count and cytogenetics at diagnosis and according to age stratification, with a cutoff of 25 years. One-way sensitivity analyses for TPs and utilities were performed as well. The baseline analyses showed that 8/8 uBMT or 7/8 uBMT had superior results to CBT, with quality-adjusted life years (QALYs) of 2.86 in 8/8 uBMT, 2.84 in 7/8 uBMT, and 2.75 in CBT. One-way sensitivity analyses showed that the results of the baseline analyses were reversed if the probability of NRM in CBT improved. Subgroup analyses showed similar results in younger, older, and high-risk patients. However, QALY was worse in 8/8 uBMT compared with CBT in standard-risk patients. In one-way sensitivity analyses, the probabilities of NRM in uBMT and CBT affected the baseline results in all analyses except for comparisons between 8/8 uBMT and CBT in younger and high-risk patients. In these 2 populations, the superiority of 8/8 uBMT was consistently demonstrated throughout the one-way sensitivity analyses. For patients with Ph-negative ALL in CR1 who decide to undergo transplantation from an alternative donor, elective uBMT from either an 8/8 MUD or a 7/8 MUD is expected to yield a better outcome than immediate CBT. Nonetheless, CBT is a viable option, and improvements to reduce the risk of NRM in CBT may change these results., (Copyright © 2021 The American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc. All rights reserved.)

The standard treatment for adults with Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) in Japan is imatinib-based chemotherapy followed by allogeneic hematopoietic stem cell transplantation (HSCT). However, ∼40% of patients cannot undergo HSCT in their first complete remission (CR1) because of chemotherapy-related toxicities or relapse before HSCT or older age. In this study, we evaluated dasatinib-based 2-step induction with the primary end point of 3-year event-free survival (EFS). The first induction (IND1) was dasatinib plus prednisolone to achieve CR, and IND2 was dasatinib plus intensive chemotherapy to achieve minimal residual disease (MRD) negativity. For patients who achieved CR and had an appropriate donor, HSCT during a consolidation phase later than the first consolidation, which included high-dose methotrexate, was recommended. Patients with pretransplantation MRD positivity were assigned to receive prophylactic dasatinib after HSCT. All 78 eligible patients achieved CR or incomplete CR after IND1, and 52.6% achieved MRD negativity after IND2. Nonrelapse mortality (NRM) was not reported. T315I mutation was detected in all 4 hematological relapses before HSCT. Fifty-eight patients (74.4%) underwent HSCT in CR1, and 44 (75.9%) had negative pretransplantation MRD. At a median follow-up of 4.0 years, 3-year EFS and overall survival were 66.2% (95% confidence interval [CI], 54.4-75.5) and 80.5% (95% CI, 69.7-87.7), respectively. The cumulative incidence of relapse and NRM at 3 years from enrollment were 26.1% and 7.8%, respectively. Dasatinib-based 2-step induction was demonstrated to improve 3-year EFS in Ph+ ALL. This study was registered in the UMIN Clinical Trial Registry as #UMIN000012173., (© 2022 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

The optimal treatment for Philadelphia chromosome (Ph)-negative acute lymphoblastic leukemia (ALL) in first complete remission (CR1) has not been established in the high-intensity chemotherapy era. The outcomes of patients with Ph-negative ALL who underwent allogeneic hematopoietic stem cell transplantation (HSCT) from a human leukocyte antigen-matched related or unrelated donor in CR1 (HSCT-MRD group and HSCT-MUD group) were obtained from a Japanese registry database. Patients aged 16-24 years and 25-65 years were analyzed separately, and their outcomes were compared to those of patients who continued high-intensity chemotherapy in CR1 in studies (202U group and 202O group) by the Japan Adult Leukemia Study Group (JALSG). In the HSCT-MRD group, patients younger than 25 years had lower overall survival (OS) than the 202U group, presumably due to the higher non-relapse mortality (NRM) in the HSCT-MRD group. Patients 25 years and older had similar OS to the 202O group. The lower relapse rate was counterbalanced by higher NRM in the HSCT-MRD group. In the HSCT-MUD group, patients in both age groups had similar OS to their corresponding groups in the JALSG studies. In conclusion, high-intensity chemotherapy may change the role of HSCT for Ph-negative ALL., (© 2021. Japanese Society of Hematology.)

This phase 1/2 study aimed to identify the maximum tolerated dose, the recommended phase 2 dose (RP2D), and efficacy of the clofarabine, etoposide, and cyclophosphamide combination regimen in adult patients with relapsed/refractory acute lymphoblastic leukemia (ALL). Patients aged ≥ 15 years with relapsed/refractory ALL were enrolled. Escalating doses of clofarabine (20-30 mg/m 2 /day × 5 days), etoposide (50-100 mg/m 2 /day × 5 days), and cyclophosphamide (200-440 mg/m 2 /day × 5 days) were administered. Dose-limiting toxicity was defined as Grade 3 or more non-hematological toxicities and others. A total of 18 patients (B-ALL; n = 13, T-ALL; n = 5) were recruited in phase 1; however, the protocol was amended to close study without proceeding to phase 2. Three patients were enrolled in cohort 1, three in cohort 2, six in cohort 3, and six in cohort 4. The RP2D of clofarabine, etoposide, and cyclophosphamide was 30, 100, and 440 mg/m 2 daily, respectively. Complete remission (CR) was achieved in four patients (22%) and CR without platelet recovery in four patients (22%), with an overall response rate of 44%. The RP2D of the combination therapy was successfully determined in this study.

It is over two decades since the first retrospective analysis indicated the superiority of pediatric-like therapy for adolescent and young adult (AYA) patients in 2000. To date, many prospective studies confirmed the efficacy and safety of pediatric-like therapy for AYA and older adult ALL, while therapy for pediatric ALL also made progress by innovating a new technology such as stratification of therapy by minimal residual disease (MRD). Furthermore, it is expected that further improvements will be achieved by applying newly approved anti-cancer drugs such as inotuzumab ozogamicin and blinatumomab. In this review, I will introduce these front line studies and discuss about the perspective of adult B-ALL treatment.

PAX5-KIDINS220 (PAX5-K220) is a novel chimeric fusion gene identified in a pediatric Philadelphia chromosome (Ph)-like acute lymphoblastic leukemia (ALL) patient, but the function of the encoded fusion protein has not yet been analyzed. Here, we report the functional analysis of PAX5-K220 in vitro. We successfully generated PAX5-K220 expressing cells and demonstrate that PAX5-K220 is a nuclear protein. Luciferase reporter assay reveals that PAX5-K220 inhibits wild-type PAX5 transcriptional activity in a dominant-negative fashion like other PAX5-related fusion proteins, and may contribute to lymphocyte differentiation block. However, although identified in Ph-like ALL, PAX5-K220 does not induce IL-3-independent proliferation when transduced in the IL-3-dependent Ba/F3 murine leukemia cells, but rather attenuates growth. These results reveal that PAX5-K220 certainly shares the character with other PAX5-related fusion proteins rather than other fusion proteins with tyrosine kinase activity identified in Ph-like ALL, and did not contribute to proliferation activity. Precise functional analysis of each differently partnered PAX5 fusion protein is warranted in the future for better understanding of PAX5-related translocations and their effects.

MEF2D-fusion (M-fusion) genes are newly discovered recurrent gene abnormalities that are detected in approximately 5 % of acute lymphoblastic leukemia (ALL) cases. Their introduction to cells has been reported to transform cell lines or increase the colony formation of bone marrow cells, suggesting their survival-supporting ability, which prompted us to examine M-fusion-targeting drugs. To identify compounds that reduce the protein expression level of MEF2D, we developed a high-throughput screening system using 293T cells stably expressing a fusion protein of MEF2D and luciferase, in which the protein expression level of MEF2D was easily measured by a luciferase assay. We screened 3766 compounds with known pharmaceutical activities using this system and selected staurosporine as a potential inducer of the proteolysis of MEF2D. Staurosporine induced the proteolysis of M-fusion proteins in M-fusion (+) ALL cell lines. Proteolysis was inhibited by caspase inhibitors, not proteasome inhibitors, suggesting caspase dependency. Consistent with this result, the growth inhibitory effects of staurosporine were stronger in M-fusion (+) ALL cell lines than in negative cell lines, and caspase inhibitors blocked apoptosis induced by staurosporine. We identified the cleavage site of MEF2D-HNRNPUL1 by caspases and confirmed that its caspase cleavage-resistant mutant was resistant to staurosporine-induced proteolysis. Based on these results, we investigated another Food and Drug Administration-approved caspase activator, venetoclax, and found that it exerted similar effects to staurosporine, namely, the proteolysis of M-fusion proteins and strong growth inhibitory effects in M-fusion (+) ALL cell lines. The present study provides novel insights into drug screening strategies and the clinical indications of venetoclax., Competing Interests: Declaration of Competing Interest H.K. received research funding from Astellas Pharma Inc., Bristol-Myers Squibb, Chugai Pharmaceutical Co., Ltd., Daiichi Sankyo Co., Ltd, Eisai Co., Ltd., FUJIFILM Corporation, Kyowa-Hakko Kirin Co., Ltd, Nippon Shinyaku Co., Ltd., Otsuka Pharmaceutical Co., Ltd., Perseus Proteomics Inc., Takeda Pharmaceutical Co., Ltd., Sumitomo Dainippon Parma Co., Ltd., and Zenyaku Kogyo Co., Ltd., and honoraria from Astellas Pharma Inc., Bristol-Myers Squibb, and Pfizer Japan Inc. The other authors have no potential conflicts of interest., (Copyright © 2020 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

The cellular context that integrates gene expression, signaling, and metabolism dictates the oncogenic behavior and shapes the treatment responses in distinct cancer types. Although chimeric fusion proteins involving transcription factors (TF) are hallmarks of many types of acute lymphoblastic leukemia (ALL), therapeutically targeting the fusion proteins is a challenge. In this work, we characterize the core regulatory circuitry (CRC; interconnected autoregulatory loops of TFs) of B-ALL involving MEF2D-fusions and identify MEF2D-fusion and SREBF1 TFs as crucial CRC components. By gene silencing and pharmacologic perturbation, we reveal that the CRC integrates the pre-B-cell receptor (BCR) and lipid metabolism to maintain itself and govern malignant phenotypes. Small-molecule inhibitors of pre-BCR signaling and lipid biosynthesis disrupt the CRC and silence the MEF2D fusion in cell culture and show therapeutic efficacy in xenografted mice. Therefore, pharmacologic disruption of CRC presents a potential therapeutic strategy to target fusion protein-driven leukemia., Significance: Cancer type-specific gene expression is governed by transcription factors involved in a highly interconnected autoregulatory loop called CRC. Here, we characterized fusion protein-driven CRC and identified its pharmacologic vulnerabilities, opening therapeutic avenues to indirectly target fusion-driven leukemia by disrupting its CRC. See related commentary by Sadras and Müschen, p. 18 . This article is highlighted in the In This Issue feature, p. 5 ., Competing Interests: A. Ota reports receiving a commercial research grant from Celgene. H. Mano has ownership interest in a patent. No potential conflicts of interest were disclosed by the other authors., (©2020 American Association for Cancer Research.)

Zinc-finger protein 384 (ZNF384) fusion (Z-fusion) genes have recently been identified as recurrent fusion genes in B-cell precursor acute lymphoblastic leukaemia (BCP-ALL) and have been detected in 7-17% of Philadelphia chromosome-negative BCP-ALL cases. We selected SALL4 and ID2 as potential Z-fusion-specific transcriptional targets that might lead to the differentiation disorder of Z-fusion-positive ALL. The introduction of EP300-ZNF384 and SYNRG-ZNF384 induced the expression of these genes. Z-fusion proteins exhibited stronger transcriptional activities on the promoter or enhancer region of these genes than Wild-Z. Furthermore, GST pull-down assay revealed that Z-fusion proteins associated more strongly with EP300 than Wild-Z. Coexpression of EP300 specifically enhanced the transcriptional activities of Z-fusion proteins. We propose the increased EP300 binding of Z-fusion proteins as a mechanism for their increased transcriptional activities., (© 2019 Federation of European Biochemical Societies.)

MEF2D fusion genes are newly discovered recurrent gene abnormalities that are detected in approximately 5% of acute lymphoblastic leukemia cases. We previously demonstrated that the vector-driven expression of MEF2D fusion proteins was markedly stronger than that of wild-type MEF2D; however, the underlying mechanisms and significance of this expression have yet to be clarified. We herein showed that the strong expression of MEF2D fusion proteins was caused by the loss of the target site of miRNA due to gene translocation. We identified the target region of miRNA located in the coding region and selected miR-122 as a candidate of the responsible miRNA. Mutations at a putative binding site of miR-122 increased MEF2D expression, while the transfection of its miRNA mimic reduced the expression of wild-type MEF2D, but not MEF2D fusion proteins. We also found that MEF2D fusion proteins inhibited the transcriptional activity of PAX5, a B-cell differentiation regulator in a manner that depended on fusion-specific strong expression and an association with histone deacetylase 4, which may lead to the differentiation disorders of B cells. Our results provide novel insights into the mechanisms underlying leukemia development by MEF2D fusion genes and the involvement of the deregulation of miRNA-mediated repression in cancer development.

For a long time, treatment for adult acute lymphoblastic leukemia (ALL) lacked significant improvements. Since 2000, new approaches, such as the treatments of adolescent and young adult ALL using pediatric-like protocols and Ph+ ALL treatments using tyrosine kinase inhibitor-combined chemotherapies. Further improvements are expected from the use of pediatric-like protocols to whole adults, and the use of newly approved anti-cancer drugs, such as inotuzumab ozogamicin and blinatumomab. Furthermore, comprehensive genetic analyses using next generation sequencing technology have recently discovered new recurrent fusion genes of ALL, such as DUX4 fusion genes, ZNF384 fusion genes, and MEF2D fusion genes. In this review, I will introduce these frontline studies and discuss about the treatment of patients with adult ALL.

Fusion genes found in cases of acute lymphoblastic leukemia (ALL) are reported to be associated with age, such as MLL rearrangements in neonates and BCR-ABL1 in adults. However, the pathogenesis of ALL in adolescents and young adults (AYA) remains largely unknown. To investigate the potential role of fusion genes, we performed RNA-sequencing on 73 BCR-ABL1-negative ALL patients who were all AYA. Interestingly, DUX4-IGH was the most frequent fusion gene detected in B-ALL (18.5%) and was preferentially detected in the AYA generation. ZNF384 and MEF2D genes were also recurrently identified as functionally relevant fusion genes in 16.7% and 9.3% of AYA with B-ALL, respectively. Patients with DUX4 and ZNF384 fusion genes displayed better prognosis, while those with the MEF2D fusion gene displayed a worse outcome. To improve treatment outcome, the fusion genes detected in this study will be useful for risk stratification and target therapy.

Cell lines have been used for drug discovery as useful models of cancers; however, they do not recapitulate cancers faithfully, particularly from the viewpoints of microenvironmental independence. Patient-derived xenografts (PDX) are established by the transfer of primary tumor cells directly from patients into immunodeficient mice and can provide primary-like tumor cells of the amount needed at the desired time. We developed a high-throughput drug screening system using PDX cells and performed drug screening using the PDX cells of Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL). We established four Ph+ ALL PDX mice and performed high-throughput screening of 3440 compounds using leukemia cells from the PDX mice (PDX-cell screening). The profiles of drugs selected by PDX-cell screening were markedly different from those by screening using the Ph+ ALL cell line. We found that verteporfin, an FDA-approved drug, exhibited strong PDX cell-specific cytotoxicity. In the validation assay, its GI50 was 228 nM, 395 nM, and 538 nM in three PDX cells and 3.93 µM, 2.11 µM, and 5.61 µM in three cell lines. Although verteporfin is a photosensitizer activated by photoirradiation, its cytotoxic effects were mediated by the light-independent production of reactive oxygen species; therefore, its anti-leukemic effects were also exerted in vivo without photoirradiation. Furthermore, it exhibited synergistic effects with dasatinib, an ABL kinase inhibitor. These results indicated the potential of verteporfin as a new anti-leukemic reagent., Competing Interests: K.S. is an employee of Otsuka Pharmaceutical Co. Ltd., T.N. received research funding from Fujifilm Corporation. H.K. received research funding from Chugai Pharmaceutical Co. LTD., Bristol-Myers Squibb, Kyowa-Hakko Kirin Co. LTD., Zenyaku Kogyo Company LTD., and Fujifilm Corporation. The other authors have no potential conflicts of interest.

The oncogenic mechanisms underlying acute lymphoblastic leukemia (ALL) in adolescents and young adults (AYA; 15-39 years old) remain largely elusive. Here we have searched for new oncogenes in AYA-ALL by performing RNA-seq analysis of Philadelphia chromosome (Ph)-negative AYA-ALL specimens (n = 73) with the use of a next-generation sequencer. Interestingly, insertion of D4Z4 repeats containing the DUX4 gene into the IGH locus was frequently identified in B cell AYA-ALL, leading to a high level of expression of DUX4 protein with an aberrant C terminus. A transplantation assay in mice demonstrated that expression of DUX4-IGH in pro-B cells was capable of generating B cell leukemia in vivo. DUX4 fusions were preferentially detected in the AYA generation. Our data thus show that DUX4 can become an oncogenic driver as a result of somatic chromosomal rearrangements and that AYA-ALL may be a clinical entity distinct from ALL at other ages.

There was no significant improvement in the treatment of adult acute lymphoblastic leukemia (ALL) in the 1ast two decades of the 20th century. However, remarkable improvements in survival have been achieved since the beginning of the 21st century, employing new treatments such as those for AYA ALL based on pediatric protocols and Ph+ ALL chemotherapies combining imatinib with other treatments. This review introduces the frontline therapies for adult ALL and discusses the current perspectives on the treatment of this malignancy.

PAX5 is a transcription factor that is required for the development and maintenance of B cells. Promyelocytic leukemia (PML) is a tumor suppressor and proapoptotic factor. The fusion gene PAX5-PML has been identified in acute lymphoblastic leukemia with chromosomal translocation t(9;15)(p13;q24). We have reported previously that PAX5-PML dominant-negatively inhibited PAX5 transcriptional activity and impaired PML function by disrupting PML nuclear bodies (NBs). Here we demonstrated the leukemogenicity of PAX5-PML by introducing it into normal mouse pro-B cells. Arrest of differentiation was observed in PAX5-PML-introduced pro-B cells, resulting in the development of acute lymphoblastic leukemia after a long latency in mice. Among the transactivation targets of PAX5, B cell linker protein (BLNK) was repressed selectively in leukemia cells, and enforced BLNK expression abrogated the differentiation block and survival induced by PAX5-PML, indicating the importance of BLNK repression for the formation of preleukemic state. We also showed that PML NBs were intact in leukemia cells and attributed this to the low expression of PAX5-PML, indicating that the disruption of PML NBs was not required for the PAX5-PML-induced onset of leukemia. These results provide novel insights into the molecular mechanisms underlying the onset of leukemia by PAX5 mutations., (© 2016 by The American Society for Biochemistry and Molecular Biology, Inc.)

Treatments for acute lymphoblastic leukemia (ALL) have been developed, independently, by both pediatric and adult study groups. Adolescents and young adults (AYA) represent a minority of patients enrolled in either pediatric or adult clinical studies and have not been the focus of trials. However, it has become evident that intensified pediatric chemotherapy regimens might be associated with better outcomes for not only AYA but also adult patients. During the last decade, the survival of AYA ALL patients has been greatly improved with the use of pediatric or pediatric-inspired protocols. The 5-year overall survival rate is now expected to exceed 70% when AYA ALL is treated employing pediatric-type protocols. In this new context, the risk factors and the application of stem cell transplantation need to be reassessed.

Objective: We investigated the mechanism responsible for imatinib (IM) resistance in Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph(+) ALL) cell lines., Methods: We established cell lines from a patient with Ph(+) ALL at the time of first diagnosis and relapsed phase and designated as NPhA1 and NPhA2, respectively. We also derived IM-resistant cells, NPhA2/STIR, from NPhA2 under gradually increasing IM concentrations., Results: NPhA1 was sensitive to IM (IC(50) 0.05 microm) and NPhA2 showed mild IM resistance (IC(50) 0.3 microm). NPhA2/STIR could be maintained in the presence of 10 microm IM. Phosphorylation of MEK and ERK was slightly elevated in NPhA2 and significantly elevated in NPhA2/STIR compared to NPhA1 cells. After treatment with IM, phosphorylation of MEK and ERK was not suppressed but rather increased in NPhA2 and NPhA2/STIR. Active RAS was also increased markedly in NPhA2/STIR after IM treatment. The expression of BCL-2 was increased in NPhA2 compared to NPhA1, but no further increase in NPhA2/STIR. Proliferation of NPhA2/STIR was significantly inhibited by a combination of MEK inhibitor and IM. Analysis of tyrosine phosphorylation status with a protein tyrosine kinase array showed increased phosphorylation of EphB4 in NPhA2/STIR after IM treatment. Although transcription of EphB4 was suppressed in NPhA1 and NPhA2 after IM treatment, it was not suppressed and its ligand, ephrinB2, was increased in NPhA2/STIR. Suppression of EphB4 transcripts by introducing short hairpin RNA into NPhA2/STIR partially restored their sensitivity to IM., Conclusions: These results suggest a new mechanism of IM resistance mediated by the activation of RAS/MAPK pathway and EphB4.