Functional inhibition of MEF2 by C/EBP is a possible mechanism of leukemia development by CEBP-IGH fusion gene.

CEBPA-IGH, a fusion gene of the immunoglobulin heavy-chain locus (IGH) and the CCAAT enhancer-binding protein α (C/EBPα) gene, is recurrently found in B-ALL cases and causes aberrant expression of C/EBPα, a master regulator of granulocyte differentiation, in B cells. Forced expression of C/EBPα in B cells was reported to cause loss of B-cell identity due to the inhibition of Pax5, a master regulator of B-cell differentiation; however, it is not known whether the same mechanism is applicable for B-ALL development by CEBPA-IGH. It is known that a full-length isoform of C/EBPα, p42, promotes myeloid differentiation, whereas its N-terminal truncated isoform, p30, inhibits myeloid differentiation through the inhibition of p42; however, the differential role between p42 and p30 in ALL development has not been clarified. In the present study, we examined the effect of the expression of p42 and p30 in B cells by performing RNA-seq of mRNA from LCL stably transfected with p42 or p30. Unexpectedly, suppression of PAX5 target genes was barely observed. Instead, both isoforms suppressed the target genes of MEF2 family members (MEF2s), other regulators of B-cell differentiation. Similarly, MEF2s target genes rather than PAX5 target genes were suppressed in CEBP-IGH-positive ALL (n = 8) compared with other B-ALL (n = 315). Furthermore, binding of both isoforms to MEF2s target genes and the reduction of surrounding histone acetylation were observed in ChIP-qPCR. Our data suggest that the inhibition of MEF2s by C/EBPα plays a role in the development of CEBPA-IGH-positive ALL and that both isoforms work co-operatively to achieve it.

Albendazole induces the terminal differentiation of acute myeloid leukaemia cells to monocytes by stimulating the Krüppel-like factor 4-dihydropyrimidinase-like 2A (KLF4-DPYSL2A) axis.

Differentiation therapy is a less toxic but still a very effective treatment for a subset of acute myeloid leukaemia (AML) cases. With the goal to identify novel compounds that can effectively and safely induce the terminal differentiation of non-acute promyelocytic leukaemia (APL) AML cells, we performed a chemical screening and identified albendazole (ABZ), a widely used anti-helminthic drug, as a promising lead compound that can differentiate non-APL AML cells by stimulating the Krüppel-like factor 4-dihydropyrimidinase-like 2A (KLF4-DPYSL2A) differentiation axis to the monocytes. Our in vitro and in vivo findings demonstrate that ABZ is an attractive candidate drug as a novel differentiation chemotherapy for patients with non-APL AML.

Suppression of malignant rhabdoid tumors through Chb-M'-mediated RUNX1 inhibition.

Malignant rhabdoid tumor (MRT) is a rare and highly aggressive pediatric malignancy primarily affecting infants and young children. Intensive multimodal therapies currently given to MRT patients are not sufficiently potent to control this highly malignant tumor. Therefore, additive or alternative therapy for these patients with a poor prognosis is necessary. We herein demonstrated that the inhibition of runt-related transcription factor 1 (RUNX1) by novel alkylating conjugated pyrrole-imidazole (PI) polyamides, which specifically recognize and bind to RUNX-binding DNA sequences, was highly effective in the treatment of rhabdoid tumor cell lines in vitro as well as in an in vivo mouse model. Therefore, suppression of RUNX1 activity may be a novel strategy for MRT therapy.

NUP98-BPTF promotes oncogenic transformation through PIM1 upregulation.

INTRODUCTION: Nucleoporin 98 (NUP98) fusion proteins are recurrently found in leukemia and are associated with unfavorable clinical outcomes. They are distributed to the nucleus and contribute to leukemogenesis via aberrant transcriptional regulation. We previously identified NUP98-BPTF (NB) fusion in patients with T-cell acute lymphoblastic leukemia (T-ALL) using next-generation sequencing. The FG-repeat of NUP98 and the PHD finger and bromodomain of bromodomain PHD finger transcription factor (BPTF) are retained in the fusion. Like other NUP98 fusion proteins, NB is considered to regulate genes that are essential for leukemogenesis. However, its target genes or pathways remain unknown. MATERIALS AND METHODS: To investigate the potential oncogenic properties of the NB fusion protein, we lentivirally transduced a doxycycline-inducible NB expression vector into mouse NIH3T3 fibroblasts and human Jurkat T-ALL cells. RESULTS: NB promoted the transformation of mouse NIH3T3 fibroblasts by upregulating the proto-oncogene Pim1, which encodes a serine/threonine kinase. NB transcriptionally regulated Pim1 expression by binding to its promoter and activated MYC and mTORC1 signaling. PIM1 knockdown or pharmacological inhibition of mTORC1 signaling suppressed NB-induced NIH3T3 cell transformation. Furthermore, NB enhanced the survival of human Jurkat T-ALL cells by inactivating the pro-apoptotic protein BCL2-associated agonist of cell death (BAD). CONCLUSION: We demonstrated the pivotal role of NB in cell transformation and survival and identified PIM1as a key downstream target of NB. These findings propose a promising therapeutic strategy for patients with NB fusion-positive leukemia.

Suppression of super-enhancer-driven TAL1 expression by KLF4 in T-cell acute lymphoblastic leukemia.

TAL1 is one of the most frequently dysregulated genes in T-ALL and is overexpressed in about 50% of T-ALL cases. One of the molecular mechanisms of TAL1 overexpression is abnormal mutations in the upstream region of the TAL1 promoter that introduce binding motifs for the MYB transcription factor. MYB binding at this location creates a 5' TAL1 super-enhancer (SE), which leads to aberrant expression of TAL1 and is associated with unfavorable clinical outcomes. Although targeting TAL1 is considered to be an attractive therapeutic strategy for patients with T-ALL, direct inhibition of transcription factors is challenging. Here, we show that KLF4, a known tumor suppressor in leukemic cells, suppresses SE-driven TAL1 expression in T-ALL cells. Mechanistically, KLF4 downregulates MYB expression by directly binding to its promoter and inhibits the formation of 5' TAL1 SE. In addition, we found that APTO-253, a small molecule inducer of KLF4, exerts an anti-leukemic effect by targeting SE-driven TAL1 expression in T-ALL cells. Taken together, our results suggest that the induction of KLF4 is a promising strategy to control TAL1 expression and could be a novel treatment for T-ALL patients with a poor prognosis.

Parbendazole as a promising drug for inducing differentiation of acute myeloid leukemia cells with various subtypes.

Acute myeloid leukemia (AML) is a malignancy characterized by differentiation arrest of hematopoietic precursor cells. Differentiation therapy is effective for patients with acute promyelocytic leukemia; however, only a few effective differentiation therapies have been established for patients with other AML subtypes. In this study, seven benzimidazole anthelmintics were examined to determine the effects of differentiation on AML cells. The expression of monocyte markers (CD11b and CD14) was elevated after treatment with most benzimidazole anthelmintics. Among these drugs, parbendazole (PBZ) induced AML cell differentiation at low concentration. PBZ induced the monocyte marker expression, KLF4/DPYSL2A gene expression, and apoptosis for 21 AML cell lines with various subtypes and a primary AML sample. Finally, an in vivo analysis using an AML patient-derived xenograft mouse model showed a significant decrease in the chimerism level and prolonged survival in PBZ-treated mice. These findings could lead to a more effective differentiation therapy for AML.

EBF1-JAK2 inhibits the PAX5 function through physical interaction with PAX5 and kinase activity.

Gene aberrations of B-cell regulators and growth signal components such as the JAK-STAT pathway are frequently found in B-cell acute lymphoblastic leukemia (B-ALL). EBF1 is a B-cell regulator that regulates the expression of PAX5 and co-operates with PAX5 to regulate B-cell differentiation. Here, we analyzed the function of the fusion protein of EBF1 and JAK2, EBF1-JAK2 (E-J). E-J caused constitutive activation of JAK-STAT and MAPK pathways and induced autonomous cell growth in a cytokine-dependent cell line. E-J did not affect the transcriptional activity of EBF1 but inhibited that of PAX5. Both the physical interaction of E-J with PAX5 and kinase activity of E-J were required for E-J to inhibit PAX5 function, although the detailed mechanism of inhibition remains unclear. Importantly, gene set enrichment analysis using the results of our previous RNA-seq data of 323 primary BCR-ABL1-negative ALL samples demonstrated repression of the transcriptional target genes of PAX5 in E-J-positive ALL cells, which suggests that E-J also inhibited PAX5 function in ALL cells. Our results shed new light on the mechanisms of differentiation block by kinase fusion proteins.

RUNX1-Survivin Axis Is a Novel Therapeutic Target for Malignant Rhabdoid Tumors.

Malignant rhabdoid tumor (MRT) is a highly aggressive pediatric malignancy with no effective therapy. Therefore, it is necessary to identify a target for the development of novel molecule-targeting therapeutic agents. In this study, we report the importance of the runt-related transcription factor 1 (RUNX1) and RUNX1-Baculoviral IAP (inhibitor of apoptosis) Repeat-Containing 5 (BIRC5/survivin) axis in the proliferation of MRT cells, as it can be used as an ideal target for anti-tumor strategies. The mechanism of this reaction can be explained by the interaction of RUNX1 with the RUNX1-binding DNA sequence located in the survivin promoter and its positive regulation. Specific knockdown of RUNX1 led to decreased expression of survivin, which subsequently suppressed the proliferation of MRT cells in vitro and in vivo. We also found that our novel RUNX inhibitor, Chb-M, which switches off RUNX1 using alkylating agent-conjugated pyrrole-imidazole polyamides designed to specifically bind to consensus RUNX-binding sequences (5'-TGTGGT-3'), inhibited survivin expression in vivo. Taken together, we identified a novel interaction between RUNX1 and survivin in MRT. Therefore the negative regulation of RUNX1 activity may be a novel strategy for MRT treatment.

Efficacy of a combination therapy targeting CDK4/6 and autophagy in a mouse xenograft model of t(8;21) acute myeloid leukemia.

One of the most frequent cytogenetic abnormalities in acute myeloid leukemia (AML) is t(8;21). Although patients with t(8;21) AML have a more favorable prognosis than other cytogenetic subgroups, relapse is still common and novel therapeutic approaches are needed. A recent study showed that t(8;21) AML is characterized by CCND2 deregulation and that co-inhibition of CDK4/6 and autophagy induces apoptosis in t(8;21) AML cells. In this study, we examined the in vivo effects of co-inhibiting CDK4/6 and autophagy. We used a mouse model in which t(8;21)-positive Kasumi-1 cells were subcutaneously inoculated into NOD/Shi-scid IL2Rgnull mice. The mice were treated with the autophagy inhibitor chloroquine (CQ), a CDK4/6 inhibitor (either abemaciclib or palbociclib), or a CDK4/6 inhibitor plus CQ. After 20 days of treatment, tumor volume was measured, and immunostaining and transmission electron microscopy observations were performed. There was no change in tumor growth in CQ-treated mice. However, mice treated with a CDK4/6 inhibitor plus CQ had significantly less tumor growth than mice treated with a CDK4/6 inhibitor alone. CDK4/6 inhibitor treatment increased the formation of autophagosomes. The number of single-strand DNA-positive (apoptotic) cells was significantly higher in the tumors of mice treated with a CDK4/6 inhibitor plus CQ than in mice treated with either CQ or a CDK4/6 inhibitor. These results show that CDK4/6 inhibition induces autophagy, and that co-inhibition of CDK4/6 and autophagy induces apoptosis in t(8;21) AML cells in vivo. The results suggest that inhibiting CDK4/6 and autophagy could be a novel and promising therapeutic strategy in t(8;21) AML.

Inhibition of CDK4/6 and autophagy synergistically induces apoptosis in t(8;21) acute myeloid leukemia cells.

The t(8;21) translocation is the most common cytogenetic abnormality in acute myeloid leukemia (AML). Although t(8;21) AML patients have a relatively favorable prognosis, relapse is a frequent occurrence, underscoring the need to develop novel therapeutic approaches. Here, we showed that t(8;21) AML is characterized by frequent mutation and overexpression of CCND2. Analysis of 19 AML cell lines showed that t(8;21) AML cells had lower IC50 values for the selective CDK4/6 inhibitors palbociclib and abemaciclib than non-t(8;21) AML cells. CDK4/6 inhibitors caused cell cycle arrest at G1 phase and impaired cell proliferation in t(8;21) AML cells. CDK4/6 inhibition decreased MAP-ERK and PI3K-AKT-mTOR signaling pathway activity, induced LC3B-I to LC3B-II conversion, and enhanced autophagosome formation, suggesting autophagy induction. Treatment of t(8;21) AML cells with the autophagy inhibitors chloroquine (CQ) or LY294002 in combination with the CDK4/6 inhibitor abemaciclib significantly increased the percentage of apoptotic (Annexin V positive) cells, whereas CQ or LY294002 single treatment had no significant effects. The effectiveness of co-inhibiting CDK4/6 and autophagy was confirmed in primary t(8;21) AML cells. The results suggest that the combination of CDK4/6 and autophagy inhibitors had a synergistic effect on inducing apoptosis, suggesting a novel therapeutic approach for the treatment of t(8;21) AML.

RUNX inhibitor suppresses graft-versus-host disease through targeting RUNX-NFATC2 axis.

Patients with refractory graft-versus-host disease (GVHD) have a dismal prognosis. Therefore, novel therapeutic targets are still needed to be identified. Runt-related transcriptional factor (RUNX) family transcription factors are essential transcription factors that mediate the essential roles in effector T cells. However, whether RUNX targeting can suppress, and GVHD is yet unknown. Here, we showed that RUNX family members have a redundant role in directly transactivating NFATC2 expression in T cells. We also found that our novel RUNX inhibitor, Chb-M', which is the inhibitor that switches off the entire RUNX family by alkylating agent-conjugated pyrrole-imidazole (PI) polyamides, inhibited T-cell receptor mediated T cell proliferation and allogenic T cell response. These were designed to specifically bind to consensus RUNX-binding sequences (TGTGGT). Chb-M' also suppressed the expression of NFATC2 and pro-inflammatory cytokine genes in vitro. Using xenogeneic GVHD model, mice injected by Chb-M' showed almost no sign of GVHD. Especially, the CD4 T cell was decreased and GVHD-associated cytokines including tissue necrosis factor-α and granulocyte-macrophage colony-stimulating factor were reduced in the peripheral blood of Chb-M' injected mice. Taken together, our data demonstrates that RUNX family transcriptionally upregulates NFATC2 in T cells, and RUNX-NFATC2 axis can be a novel therapeutic target against GVHD.

TXNIP induces growth arrest and enhances ABT263-induced apoptosis in mixed-lineage leukemia-rearranged acute myeloid leukemia cells.

Thioredoxin-interacting protein (TXNIP) has been widely recognized as a tumor suppressor in various cancers, including liver, breast, and thyroid cancers. Although TXNIP is epigenetically silenced in acute myeloid leukemia (AML) cells, as in many cancer cells, its role in leukemogenesis remains elusive. Mixed-lineage leukemia (MLL) gene rearrangements in AML are associated with poor prognosis, and the development of a new treatment method is eagerly anticipated. In this study, we first reveal that lower expression of TXNIP is correlated with shortened overall survival periods in AML patients. Moreover, we demonstrated that TXNIP overexpression significantly suppresses proliferation in AML cells harboring MLL fusion genes. TXNIP promotes autophagy by increasing expression of the autophagy protein, Beclin 1, and lipidation of LC3B. We also show that TXNIP overexpression combined with ABT263, a potent inhibitor of Bcl-2 and Bcl-xL, is highly effective at inducing cell death in MLL-rearranged (MLL-r) AML cells. In summary, this study provides insights into the molecular mechanism of TXNIP-mediated tumor suppression and furthermore underscores the potential of TXNIP as a promising therapeutic target for MLL-r AML.

Pivotal role of DPYSL2A in KLF4-mediated monocytic differentiation of acute myeloid leukemia cells.

Although the biological importance of Krüppel-like factor 4 (KLF4) transcription factor in the terminal differentiation of hematopoietic cells to the monocytes has been well established, the underlying mechanisms remain elusive. To clarify the molecular basis of KLF4-mediated monocytic differentiation, we performed detailed genetic studies in acute myeloid leukemia (AML) cells. Here, we report that dihydropyrimidinase like 2 (DPYSL2), also known as CRMP2, is a novel key differentiation mediator downstream of KLF4 in AML cells. Interestingly, we discovered that KLF4-mediated monocytic differentiation is selectively dependent on one specific isoform, DPYSL2A, but not on other DPYSL family genes. Terminal differentiation to the monocytes and proliferation arrest in AML cells induced by genetic or pharmacological upregulation of KLF4 were significantly reversed by short hairpin RNA (shRNA)-mediated selective depletion of DPYSL2A. Chromatin immunoprecipitation assay revealed that KLF4 associates with the proximal gene promoter of DPYSL2A and directly transactivates its expression. Together with the unique expression patterns of KLF4 and DPYSL2 limited to the differentiated monocytes in the hematopoietic system both in human and mouse, the identified KLF4-DPYSL2 axis in leukemia cells may serve as a potential therapeutic target for the development of novel differentiation therapies for patients with AML.

RUNX transcription factors potentially control E-selectin expression in the bone marrow vascular niche in mice.

Although the function of Runt-related (RUNX) transcription factors has been well characterized in leukemogenesis and regarded as an ideal target in antileukemia strategies, the effect of RUNX-inhibition therapy on bone marrow niche cells andr its impact on the engraftment of acute myeloid leukemia (AML) cells have largely been unknown. Here, we provide evidence suggesting the possible involvement of RUNX transcription factors in the transactivation of E-selectin, a member of selectin family of cell adhesion molecules, on the vascular endothelial cells of the mice bone marrow niche. In our experiments, gene switch-mediated silencing of RUNX downregulated E-selectin expression in the vascular niche and negatively controlled the engraftment of AML cells in the bone marrow, extending the overall survival of leukemic mice. Our work identified the novel role of RUNX family genes in the vascular niche and showed that the vascular niche, a home for AML cells, could be strategically targeted with RUNX-silencing antileukemia therapies. Considering the excellent efficacy of RUNX-inhibition therapy on AML cells themselves as we have previously reported, this strategy potentially targets AML cells both directly and indirectly, thus providing a better chance of cure for poor-prognostic AML patients.

Recurrent CCND3 mutations in MLL-rearranged acute myeloid leukemia.

In acute myeloid leukemia (AML), MLL (KMT2A) rearrangements are among the most frequent chromosomal abnormalities; however, knowledge of the genetic landscape of MLL-rearranged AML is limited. In this study, we performed whole-exome sequencing (n = 9) and targeted sequencing (n = 56) of samples from pediatric MLL-rearranged AML patients enrolled in the Japanese Pediatric Leukemia/Lymphoma Study Group AML-05 study. Additionally, we analyzed 105 pediatric t(8;21) AML samples and 30 adult MLL-rearranged AML samples. RNA-sequencing data from 31 patients published in a previous study were also reanalyzed. As a result, we identified 115 mutations in pediatric MLL-rearranged AML patients (2.1 mutations/patient), with mutations in signaling pathway genes being the most frequently detected (60.7%). Mutations in genes associated with epigenetic regulation (21.4%), transcription factors (16.1%), and the cohesin complex (8.9%) were also commonly detected. Novel CCND3 mutations were identified in 5 pediatric MLL-rearranged AML patients (8.9%) and 2 adult MLL-rearranged AML patients (3.3%). Recurrent mutations of CCND1 (n = 3, 2.9%) and CCND2 (n = 8, 7.6%) were found in pediatric t(8;21) AML patients, whereas no CCND3 mutations were found, suggesting that D-type cyclins exhibit a subtype-specific mutation pattern in AML. Treatment of MLL-rearranged AML cell lines with CDK4/6 inhibitors (abemaciclib and palbociclib) blocked G1 to S phase cell-cycle progression and impaired proliferation. Pediatric MLL-MLLT3-rearranged AML patients with coexisting mutations (n = 16) had significantly reduced relapse-free survival and overall survival compared with those without coexisting mutations (n = 9) (P = .048 and .046, respectively). These data provide insights into the genetics of MLL-rearranged AML and suggest therapeutic strategies.

Autonomous feedback loop of RUNX1-p53-CBFB in acute myeloid leukemia cells.

Although runt-related transcription factor 1 (RUNX1) and its associating core binding factor-ß (CBFB) play pivotal roles in leukemogenesis, and inhibition of RUNX1 has now been widely recognized as a novel strategy for anti-leukemic therapies, it has been elusive how leukemic cells could acquire the serious resistance against RUNX1-inhibition therapies and also whether CBFB could participate in this process. Here, we show evidence that p53 (TP53) and CBFB are sequentially up-regulated in response to RUNX1 depletion, and their mutual interaction causes the physiological resistance against chemotherapy for acute myeloid leukemia (AML) cells. Mechanistically, p53 induced by RUNX1 gene silencing directly binds to CBFB promoter and stimulates its transcription as well as its translation, which in turn acts as a platform for the stabilization of RUNX1, thereby creating a compensative RUNX1-p53-CBFB feedback loop. Indeed, AML cells derived from relapsed cases exhibited higher CBFB expression levels compared to those from primary AML cells at diagnosis, and these CBFB expressions were positively correlated to those of p53. Our present results underscore the importance of RUNX1-p53-CBFB regulatory loop in the development and/or maintenance of AML cells, which could be targeted at any sides of this triangle in strategizing anti-leukemia therapies.

Genetic regulation of the RUNX transcription factor family has antitumor effects.

Runt-related transcription factor 1 (RUNX1) is generally considered to function as a tumor suppressor in the development of leukemia, but a growing body of evidence suggests that it has pro-oncogenic properties in acute myeloid leukemia (AML). Here we have demonstrated that the antileukemic effect mediated by RUNX1 depletion is highly dependent on a functional p53-mediated cell death pathway. Increased expression of other RUNX family members, including RUNX2 and RUNX3, compensated for the antitumor effect elicited by RUNX1 silencing, and simultaneous attenuation of all RUNX family members as a cluster led to a much stronger antitumor effect relative to suppression of individual RUNX members. Switching off the RUNX cluster using alkylating agent-conjugated pyrrole-imidazole (PI) polyamides, which were designed to specifically bind to consensus RUNX-binding sequences, was highly effective against AML cells and against several poor-prognosis solid tumors in a xenograft mouse model of AML without notable adverse events. Taken together, these results identify a crucial role for the RUNX cluster in the maintenance and progression of cancer cells and suggest that modulation of the RUNX cluster using the PI polyamide gene-switch technology is a potential strategy to control malignancies.