Systematic chemical and molecular profiling of MLL-rearranged infant acute lymphoblastic leukemia reveals efficacy of romidepsin

Histone deacetylase inhibition sensitizes p53-deficient B-cell precursor acute lymphoblastic leukemia to chemotherapy

In pediatric acute lymphoblastic leukemia (ALL), mutations/deletions affecting the TP53 gene are rare at diagnosis. However, at relapse about 12% of patients show TP53 aberrations, which are predictive of a very poor outcome. Since p53-mediated apoptosis is an endpoint for many cytotoxic drugs, loss of p53 function frequently leads to therapy failure. In this study we show that CRISPR/Cas9-induced loss of TP53 drives resistance to a large majority of drugs used to treat relapsed ALL, including novel agents such as inotuzumab ozogamicin. Using a high-throughput drug screen, we identified the histone deacetylase inhibitor romidepsin as a potent sensitizer of drug responsiveness, improving sensitivity to all chemotherapies tested. In addition, romidepsin improved the response to cytarabine in TP53-deleted ALL cells in vivo. Together, these results indicate that the histone deacetylase inhibitor romidepsin can improve the efficacy of salvage therapies for relapsed TP53-mutated leukemia. Since romidepsin has been approved for clinical use in some adult malignancies, these findings may be rapidly translated to clinical practice.

Charting a path through resistance: histone deacetylase inhibitors for TP53-mutated B-cell acute lymphoblastic leukemia

Not available.

SET-PP2A complex as a new therapeutic target in KMT2A (MLL) rearranged AML

KMT2A-rearranged (KMT2A-R) is an aggressive and chemo-refractory acute leukemia which mostly affects children. Transcriptomics-based characterization and chemical interrogation identified kinases as key drivers of survival and drug resistance in KMT2A-R leukemia. In contrast, the contribution and regulation of phosphatases is unknown. In this study we uncover the essential role and underlying mechanisms of SET, the endogenous inhibitor of Ser/Thr phosphatase PP2A, in KMT2A-R-leukemia. Investigation of SET expression in acute myeloid leukemia (AML) samples demonstrated that SET is overexpressed, and elevated expression of SET is correlated with poor prognosis and with the expression of MEIS and HOXA genes in AML patients. Silencing SET specifically abolished the clonogenic ability of KMT2A-R leukemic cells and the transcription of KMT2A targets genes HOXA9 and HOXA10. Subsequent mechanistic investigations showed that SET interacts with both KMT2A wild type and fusion proteins, and it is recruited to the HOXA10 promoter. Pharmacological inhibition of SET by FTY720 disrupted SET-PP2A interaction leading to cell cycle arrest and increased sensitivity to chemotherapy in KMT2A-R-leukemic models. Phospho-proteomic analyses revealed that FTY720 reduced the activity of kinases regulated by PP2A, including ERK1, GSK3β, AURB and PLK1 and led to suppression of MYC, supporting the hypothesis of a feedback loop among PP2A, AURB, PLK1, MYC, and SET. Our findings illustrate that SET is a novel player in KMT2A-R leukemia and they provide evidence that SET antagonism could serve as a novel strategy to treat this aggressive leukemia.

Preclinical efficacy of azacitidine and venetoclax for infant KMT2A-rearranged acute lymphoblastic leukemia reveals a new therapeutic strategy

Infants with KMT2A-rearranged B-cell acute lymphoblastic leukemia (ALL) have a dismal prognosis. Survival outcomes have remained static in recent decades despite treatment intensification and novel therapies are urgently required. KMT2A-rearranged infant ALL cells are characterized by an abundance of promoter hypermethylation and exhibit high BCL-2 expression, highlighting potential for therapeutic targeting. Here, we show that hypomethylating agents exhibit in vitro additivity when combined with most conventional chemotherapeutic agents. However, in a subset of samples an antagonistic effect was seen between several agents. This was most evident when hypomethylating agents were combined with methotrexate, with upregulation of ATP-binding cassette transporters identified as a potential mechanism. Single agent treatment with azacitidine and decitabine significantly prolonged in vivo survival in KMT2A-rearranged infant ALL xenografts. Treatment of KMT2A-rearranged infant ALL cell lines with azacitidine and decitabine led to differential genome-wide DNA methylation, changes in gene expression and thermal proteome profiling revealed the target protein-binding landscape of these agents. The selective BCL-2 inhibitor, venetoclax, exhibited in vitro additivity in combination with hypomethylating or conventional chemotherapeutic agents. The addition of venetoclax to azacitidine resulted in a significant in vivo survival advantage indicating the therapeutic potential of this combination to improve outcome for infants with KMT2A-rearranged ALL.

A Comprehensive Overview of Recent Advances in Epigenetics in Pediatric Acute Lymphoblastic Leukemia

Recent years have brought a novel insight into our understanding of childhood acute lymphoblastic leukemia (ALL), along with several breakthrough treatment methods. However, multiple aspects of mechanisms behind this disease remain to be elucidated. Evidence suggests that leukemogenesis in ALL is widely influenced by epigenetic modifications. These changes include: DNA hypermethylation, histone modification and miRNA alteration. DNA hypermethylation in promoter regions, which leads to silencing of tumor suppressor genes, is a common epigenetic alteration in ALL. Histone modifications are mainly caused by an increased expression of histone deacetylases. A dysregulation of miRNA results in changes in the expression of their target genes. To date, several hundred genes were identified as suppressed by epigenetic mechanisms in ALL. What is promising is that epigenetic alterations in ALL may be used as potential biomarkers for classification of subtypes, predicting relapse and disease progression and assessing minimal residual disease. Furthermore, since epigenetic lesions are potentially reversible, an activation of epigenetically silenced genes with the use of hypomethylating agents or histone deacetylase inhibitors may be utilized as a therapeutic strategy for ALL. The following review summarizes our current knowledge about epigenetic modifications in ALL and describes potential uses of epigenetics in the clinical management of this disease.

Multi-omics analysis defines highly refractory RAS burdened immature subgroup of infant acute lymphoblastic leukemia

KMT2A-rearranged infant acute lymphoblastic leukemia (ALL) represents the most refractory type of childhood leukemia. To uncover the molecular heterogeneity of this disease, we perform RNA sequencing, methylation array analysis, whole exome and targeted deep sequencing on 84 infants with KMT2A-rearranged leukemia. Our multi-omics clustering followed by single-sample and single-cell inference of hematopoietic differentiation establishes five robust integrative clusters (ICs) with different master transcription factors, fusion partners and corresponding stages of B-lymphopoietic and early hemato-endothelial development: IRX-type differentiated (IC1), IRX-type undifferentiated (IC2), HOXA-type MLLT1 (IC3), HOXA-type MLLT3 (IC4), and HOXA-type AFF1 (IC5). Importantly, our deep mutational analysis reveals that the number of RAS pathway mutations predicts prognosis and that the most refractory subgroup of IC2 possesses 100% frequency and the heaviest burden of RAS pathway mutations. Our findings highlight the previously under-appreciated intra- and inter-patient heterogeneity of KMT2A-rearranged infant ALL and provide a rationale for the future development of genomics-guided risk stratification and individualized therapy.

The Combination of Curaxin CBL0137 and Histone Deacetylase Inhibitor Panobinostat Delays KMT2A-Rearranged Leukemia Progression

Rearrangements of the Mixed Lineage Leukemia (MLL/KMT2A) gene are present in approximately 10% of acute leukemias and characteristically define disease with poor outcome. Driven by the unmet need to develop better therapies for KMT2A-rearranged leukemia, we previously discovered that the novel anti-cancer agent, curaxin CBL0137, induces decondensation of chromatin in cancer cells, delays leukemia progression and potentiates standard of care chemotherapies in preclinical KMT2A-rearranged leukemia models. Based on the promising potential of histone deacetylase (HDAC) inhibitors as targeted anti-cancer agents for KMT2A-rearranged leukemia and the fact that HDAC inhibitors also decondense chromatin via an alternate mechanism, we investigated whether CBL0137 could potentiate the efficacy of the HDAC inhibitor panobinostat in KMT2A-rearranged leukemia models. The combination of CBL0137 and panobinostat rapidly killed KMT2A-rearranged leukemia cells by apoptosis and significantly delayed leukemia progression and extended survival in an aggressive model of MLL-AF9 (KMT2A:MLLT3) driven murine acute myeloid leukemia. The drug combination also exerted a strong anti-leukemia response in a rapidly progressing xenograft model derived from an infant with KMT2A-rearranged acute lymphoblastic leukemia, significantly extending survival compared to either monotherapy. The therapeutic enhancement between CBL0137 and panobinostat in KMT2A-r leukemia cells does not appear to be mediated through cooperative effects of the drugs on KMT2A rearrangement-associated histone modifications. Our data has identified the CBL0137/panobinostat combination as a potential novel targeted therapeutic approach to improve outcome for KMT2A-rearranged leukemia.

Exploiting the reactive oxygen species imbalance in high-risk paediatric acute lymphoblastic leukaemia through auranofin

BACKGROUND

The prognosis for high-risk childhood acute leukaemias remains dismal and established treatment protocols often cause long-term side effects in survivors. This study aims to identify more effective and safer therapeutics for these patients.

METHODS

A high-throughput phenotypic screen of a library of 3707 approved drugs and pharmacologically active compounds was performed to identify compounds with selective cytotoxicity against leukaemia cells followed by further preclinical evaluation in patient-derived xenograft models.

RESULTS

Auranofin, an FDA-approved agent for the treatment of rheumatoid arthritis, was identified as exerting selective anti-cancer activity against leukaemia cells, including patient-derived xenograft cells from children with high-risk ALL, versus solid tumour and non-cancerous cells. It induced apoptosis in leukaemia cells by increasing reactive oxygen species (ROS) and potentiated the activity of the chemotherapeutic cytarabine against highly aggressive models of infant MLL-rearranged ALL by enhancing DNA damage accumulation. The enhanced sensitivity of leukaemia cells towards auranofin was associated with lower basal levels of the antioxidant glutathione and higher baseline ROS levels compared to solid tumour cells.

CONCLUSIONS

Our study highlights auranofin as a well-tolerated drug candidate for high-risk paediatric leukaemias that warrants further preclinical investigation for application in high-risk paediatric and adult acute leukaemias.

Preclinical Evaluation of Carfilzomib for Infant KMT2A-Rearranged Acute Lymphoblastic Leukemia

BACKGROUND

Infants with KMT2A-rearranged B-cell precursor acute lymphoblastic leukemia (ALL) have poor outcomes. There is an urgent need to identify novel agents to improve survival. Proteasome inhibition has emerged as a promising therapeutic strategy for several hematological malignancies. The aim of this study was to determine the preclinical efficacy of the selective proteasome inhibitor carfilzomib, for infants with KMT2A-rearranged ALL.

METHODS

Eight infant ALL cell lines were extensively characterized for immunophenotypic and cytogenetic features. In vitro cytotoxicity to carfilzomib was assessed using a modified Alamar Blue assay with cells in logarithmic growth. The Bliss Independence model was applied to determine synergy between carfilzomib and the nine conventional chemotherapeutic agents used to treat infants with ALL. Established xenograft models were used to identify the maximal tolerated dose of carfilzomib and determine in vivo efficacy.

RESULTS

Carfilzomib demonstrated low IC50 concentrations within the nanomolar range (6.0-15.8 nm) across the panel of cell lines. Combination drug testing indicated in vitro synergy between carfilzomib and several conventional chemotherapeutic agents including vincristine, daunorubicin, dexamethasone, L-asparaginase, and 4-hydroperoxycyclophosphamide. In vivo assessment did not lead to a survival advantage for either carfilzomib monotherapy, when used to treat both low or high disease burden, or for carfilzomib in combination with multi-agent induction chemotherapy comprising of vincristine, dexamethasone, and L-asparaginase.

CONCLUSIONS

Our study highlights that in vitro efficacy does not necessarily translate to benefit in vivo and emphasizes the importance of in vivo validation prior to suggesting an agent for clinical use. Whilst proteasome inhibitors have an important role to play in several hematological malignancies, our findings guard against prioritization of carfilzomib for treatment of KMT2A-rearranged infant ALL in the clinical setting.

A validated pediatric disease risk index for allogeneic hematopoietic cell transplantation

A disease risk index (DRI) that was developed for adults with hematologic malignancy who were undergoing hematopoietic cell transplantation is also being used to stratify children and adolescents by disease risk. Therefore, to develop and validate a DRI that can be used to stratify those with AML and ALL by their disease risk, we analyzed 2569 patients aged <18 years with acute myeloid (AML; n = 1224) or lymphoblastic (ALL; n = 1345) leukemia who underwent hematopoietic cell transplantation. Training and validation subsets for each disease were generated randomly with 1:1 assignment to the subsets, and separate prognostic models were derived for each disease. For AML, 4 risk groups were identified based on age, cytogenetic risk, and disease status, including minimal residual disease status at transplantation. The 5-year leukemia-free survival for low (0 points), intermediate (2, 3, 5), high (7, 8), and very high (>8) risk groups was 78%, 53%, 40%, and 25%, respectively (P < .0001). For ALL, 3 risk groups were identified based on age and disease status, including minimal residual disease status at transplantation. The 5-year leukemia-free survival for low (0 points), intermediate (2-4), and high (≥5) risk groups was 68%, 51%, and 33%, respectively (P < .0001). We confirmed that the risk groups could be applied to overall survival, with 5-year survival ranging from 80% to 33% and 73% to 42% for AML and ALL, respectively (P < .0001). This validated pediatric DRI, which includes age and residual disease status, can be used to facilitate prognostication and stratification of children with AML and ALL for allogeneic transplantation.

The expression and clinical significance of murine double minute 2, lysosome-associated membrane protein 1, and P-glycoprotein in pediatric acute lymphoblastic leukemia

BACKGROUND

To analyze the expression and clinical significance of murine double minute 2 (MDM2), lysosome-associated membrane protein (LAMP1) and P-glycoprotein (P-gp) in children with acute lymphoblastic leukemia (ALL).

METHODS

Thirty-three children with ALL who were admitted to our hospital between January 2017 and January 2018 were enrolled as the ALL group. The expression of MDM2, LAMP1 and P-gp was compared between the two groups, as well as between ALL patients with different clinical characteristics. Logistic regression was used to analyze the risk factors that affect the prognosis and survival of ALL patients. Kaplan-Meier survival curves were used to analyze the correlations of MDM2, LAMP1 and P-gp on the prognosis and survival of ALL patients.

RESULTS

The expression levels of MDM2, LAMP1 and P-gp in the ALL group were higher than those in the control group (P<0.05). The average survival time of the group with low expression of MDM2 was (34.92±0.56) months, the average survival time of the group with high expression of MDM2 was (31.32±0.42) months, and the difference was statistically significant (P<0.05). The average survival time of the group with low expression of LAMP1 was (36.71±0.55) months, the average survival time of the group with high expression of LAMP1 was (29.87±0.40) months, the difference was statistically significant (P<0.05). The average survival time of the group with low expression of P-gp was (36.29±0.41) months, the average survival time of the group with high expression of P-gp was (26.46±0.37) months, and the difference was statistically significant (P<0.05).

CONCLUSIONS

Abnormal expression levels of MDM2, LAMP1 and P-gp protein are related to the occurrence and development of ALL, and are closely related to patient prognosis and survival. Therefore, MDM2, LAMP1and P-gp can serve as molecular markers for predicting the prognosis of children with ALL.

MLL-rearranged infant leukaemia: A 'thorn in the side' of a remarkable success story

Advances in treatment of childhood leukaemia has led to vastly improved survival rates, however some subtypes such as those characterised by MLL gene rearrangement (MLL-r), especially in infants, continue to have high relapse rates and poor survival. Natural history and molecular studies indicate that infant acute lymphoblastic leukaemia (ALL) originates in utero, is distinct from childhood ALL, and most cases are caused by MLL-r resulting in an oncogenic MLL fusion protein. Unlike childhood ALL, only a very small number of additional mutations are present in infant ALL, indicating that MLL-r alone may be sufficient to give rise to this rapid onset, aggressive leukaemia in an appropriate fetal cell context. Despite modifications in treatment approaches, the outcome of MLL-r infant ALL has remained dismal and a clear understanding of the underlying biology of the disease is required in order to develop appropriate disease models and more effective therapeutic strategies.

Effective targeting of NAMPT in patient-derived xenograft models of high-risk pediatric acute lymphoblastic leukemia

The prognosis for children diagnosed with high-risk acute lymphoblastic leukemia (ALL) remains suboptimal, and more potent and less toxic treatments are urgently needed. We investigated the efficacy of a novel nicotinamide phosphoribosyltransferase inhibitor, OT-82, against a panel of patient-derived xenografts (PDXs) established from high-risk and poor outcome pediatric ALL cases. OT-82 was well-tolerated and demonstrated impressive single agent in vivo efficacy, achieving significant leukemia growth delay in 95% (20/21) and disease regression in 86% (18/21) of PDXs. In addition, OT-82 enhanced the efficacy of the established drugs cytarabine and dasatinib and, as a single agent, showed similar efficacy as an induction-type regimen combining three drugs used to treat pediatric ALL. OT-82 exerted its antileukemic action by depleting NAD⁺ and ATP, inhibiting the NAD⁺-requiring DNA damage repair enzyme PARP-1, increasing mitochondrial ROS levels and inducing DNA damage, culminating in apoptosis induction. OT-82 sensitivity was associated with the occurrence of mutations in major DNA damage response genes, while OT-82 resistance was characterized by high expression levels of CD38. In conclusion, our study provides evidence that OT-82, as a single agent, and in combination with established drugs, is a promising new therapeutic strategy for a broad spectrum of high-risk pediatric ALL for which improved therapies are urgently needed.

Outcome of Infants Younger Than 1 Year With Acute Lymphoblastic Leukemia Treated With the Interfant-06 Protocol: Results From an International Phase III Randomized Study

PURPOSE

Infant acute lymphoblastic leukemia (ALL) is characterized by KMT2A (MLL) gene rearrangements and coexpression of myeloid markers. The Interfant-06 study, comprising 18 national and international study groups, tested whether myeloid-style consolidation chemotherapy is superior to lymphoid style, the role of stem-cell transplantation (SCT), and which factors had independent prognostic value.

MATERIALS AND METHODS

Three risk groups were defined: low risk (LR): KMT2A germline; high risk (HR): KMT2A-rearranged and older than 6 months with WBC count 300 × 10⁹/L or more or a poor prednisone response; and medium risk (MR): all other KMT2A-rearranged cases. Patients in the MR and HR groups were randomly assigned to receive the lymphoid course low-dose cytosine arabinoside [araC], 6-mercaptopurine, cyclophosphamide (IB) or experimental myeloid courses, namely araC, daunorubicin, etoposide (ADE) and mitoxantrone, araC, etoposide (MAE).

RESULTS

A total of 651 infants were included, with 6-year event-free survival (EFS) and overall survival of 46.1% (SE, 2.1) and 58.2% (SE, 2.0). In West European/North American groups, 6-year EFS and overall survival were 49.4% (SE, 2.5) and 62.1% (SE, 2.4), which were 10% to 12% higher than in other countries. The 6-year probability of disease-free survival was comparable for the randomized arms (ADE+MAE 39.3% [SE 4.0; n = 169] v IB 36.8% [SE, 3.9; n = 161]; log-rank P = .47). The 6-year EFS rate of patients in the HR group was 20.9% (SE, 3.4) with the intention to undergo SCT; only 46% of them received SCT, because many had early events. KMT2A rearrangement was the strongest prognostic factor for EFS, followed by age, WBC count, and prednisone response.

CONCLUSION

Early intensification with postinduction myeloid-type chemotherapy courses did not significantly improve outcome for infant ALL compared with the lymphoid-type course IB. Outcome for infant ALL in Interfant-06 did not improve compared with that in Interfant-99.

The histone deacetylase inhibitor Romidepsin induces as a cascade of differential gene expression and altered histone H3K9 marks in myeloid leukaemia cells

Myelodysplastic syndromes (MDS) are a heterogeneous, clonal haematopoietic disorder, with ~1/3 of patients progressing to acute myeloid leukaemia (AML). Many elderly MDS patients do not tolerate intensive therapeutic regimens, and therefore have an unmet need for better tolerated therapies.

Epigenetics is important in the pathogenesis of MDS/AML with DNA methylation, and histone acetylation the most widely studied modifications. Epigenetic therapeutic agents have targeted the reversible nature of these modifications with some clinical success. The aim of this study was to characterise the molecular consequences of treatment of MDS and AML cells with the histone deacetylase inhibitor (HDACi) Romidepsin.

Romidepsin as a single agent induced cell death with an increasing dose and time profile associated with increased acetylation of histone H3 lysine 9 (H3K9) and decreased HDAC activity. Gene expression profiling, qPCR, network and pathway analysis recognised that oxidation-reduction was involved in response to Romidepsin. ROS was implicated as being involved post-treatment with the involvement of TSPO and MPO.

Genomic analysis uncoupled the differences in protein-DNA interactions and gene regulation. The spatial and temporal transcriptional differences associated with acetylated, mono- and tri-methylated H3K9, representative of two activation and a repression mark respectively, were identified. Bioinformatic analysis uncovered positional enrichment and transcriptional differences between these marks; a degree of overlap with increased/decreased gene expression that correlates to increased/decreased histone modification. Overall, this study has unveiled a number of underlying mechanisms of the HDACi Romidepsin that could identify potential drug combinations for use in the clinic.

How I treat infant leukemia

Leukemia in infants is rare but generates tremendous interest due to its aggressive clinical presentation in a uniquely vulnerable host, its poor response to current therapies, and its fascinating biology. Increasingly, these biological insights are pointing the way toward novel therapeutic approaches. Using representative clinical case presentations, we review the key clinical, pathologic, and epidemiologic features of infant leukemia, including the high frequency of KMT2A gene rearrangements. We describe the current approach to risk-stratified treatment of infant leukemia in the major international cooperative groups. We highlight recent discoveries that elucidate the molecular biology of infant leukemia and suggest novel targeted therapeutic strategies, including modulation of aberrant epigenetic programs, inhibition of signaling pathways, and immunotherapeutics. Finally, we underscore the need for increased global collaboration to translate these discoveries into improved outcomes.

New Approaches to the Management of Adult Acute Lymphoblastic Leukemia

Traditional treatment regimens for adult acute lymphoblastic leukemia, including allogeneic hematopoietic cell transplantation, result in an overall survival of approximately 40%, a figure hardly comparable with the extraordinary 80% to 90% cure rate currently reported in children. When translated to the adult setting, modern pediatric-type regimens improve the survival to approximately 60% in young adults. The addition of tyrosine kinase inhibitors for patients with Philadelphia chromosome-positive disease and the measurement of minimal residual disease to guide risk stratification and postremission approaches has led to additional improvements in outcomes. Relapsed disease and treatment toxicity-sparing no patient but representing a major concern especially in the elderly-are the most critical current issues awaiting further therapeutic advancement. Recently, there has been considerable progress in understanding the disease biology, specifically the Philadelphia-like signature, as well as other high-risk subgroups. In addition, there are several new agents that will undoubtedly contribute to additional improvement in the current outcomes. The most promising agents are monoclonal antibodies, immunomodulators, and chimeric antigen receptor T cells, and, to a lesser extent, several new drugs targeting key molecular pathways involved in leukemic cell growth and proliferation. This review examines the evidence supporting the increasing role of the new therapeutic tools and treatment options in different disease subgroups, including frontline and relapsed or refractory disease. It is now possible to define the best individual approach on the basis of the emerging concepts of precision medicine.

Selective DOT1L, LSD1, and HDAC Class I Inhibitors Reduce HOXA9 Expression in MLL-AF9 Rearranged Leukemia Cells, But Dysregulate the Expression of Many Histone-Modifying Enzymes

Mixed lineage leukemia results from chromosomal rearrangements of the gene mixed lineage leukemia (MLL). MLL-AF9 is one such rearrangement that recruits the lysine methyltransferase, human disruptor of telomere silencing 1-like (DOT1L) and lysine specific demethylase 1 (LSD1), resulting in elevated expression of the Homeobox protein A9 (HOXA9), and leukemia. Inhibitors of LSD1 or DOT1L reduce HOXA9 expression, kill MLL-rearranged cells, and may treat leukemia. To quantify their effects on histone modifying enzyme activity and expression in MLL-rearranged leukemia, we tested inhibitors of DOT1L (EPZ-5676), LSD1 (GSK2879552), and HDAC (mocetinostat), in the MLL-AF9 cell line MOLM-13. All inhibitors reduced MOLM-13 viability but only mocetinostat induced apoptosis. EPZ-5676 increased total histone lysine dimethylation, which was attributed to a reduction in LSD1 expression, and was indistinguishable from direct LSD1 inhibition by GSK2879552. All compounds directly inhibit, or reduce the expression of, HOXA9, DOT1L and LSD1 by qPCR, increase total histone lysine methylation and acetylation by LC-MS/MS, and specifically reduce H3K79Me2 and increase H3K14Ac. Each inhibitor altered the expression of many histone modifying enzymes which may precipitate additional changes in expression. To the extent that this decreases HOXA9 expression it benefits mixed lineage leukemia treatment, all other expression changes are off-target effects.

Antileukemic Efficacy of BET Inhibitor in a Preclinical Mouse Model of MLL-AF4+ Infant ALL

MLL-rearranged acute lymphoblastic leukemia (ALL) occurring in infants is a rare but very aggressive leukemia, typically associated with a dismal prognosis. Despite the development of specific therapeutic protocols, infant patients with MLL-rearranged ALL still suffer from a low cure rate. At present, novel therapeutic approaches are urgently needed. Recently, the use of small molecule inhibitors targeting the epigenetic regulators of the MLL complex emerged as a promising strategy for the development of a targeted therapy. Herein, we have investigated the effects of bromodomain and extra-terminal (BET) function abrogation in a preclinical mouse model of MLL-AF4⁺ infant ALL using the BET inhibitor I-BET151. We reported that I-BET151 is able to arrest the growth of MLL-AF4⁺ leukemic cells in vitro, by blocking cell division and rapidly inducing apoptosis. Treatment with I-BET151 in vivo impairs the leukemic engraftment of patient-derived primary samples and lower the disease burden in mice. I-BET151 affects the transcriptional profile of MLL-rearranged ALL through the deregulation of BRD4, HOXA7/HOXA9, and RUNX1 gene networks. Moreover, I-BET151 treatment sensitizes glucocorticoid-resistant MLL-rearranged cells to prednisolone in vitro and is more efficient when used in combination with HDAC inhibitors, both in vitro and in vivo Given the aggressiveness of the disease, the failure of the current therapies and the lack of an ultimate cure, this study paves the way for the use of BET inhibitors to treat MLL-rearranged infant ALL for future clinical applications. Mol Cancer Ther; 17(8); 1705-16. ©2018 AACR.

MLL-Rearranged Leukemias-An Update on Science and Clinical Approaches

The mixed-lineage leukemia 1 (MLL1) gene (now renamed Lysine [K]-specific MethylTransferase 2A or KMT2A) on chromosome 11q23 is disrupted in a unique group of acute leukemias. More than 80 different partner genes in these fusions have been described, although the majority of leukemias result from MLL1 fusions with one of about six common partner genes. Approximately 10% of all leukemias harbor MLL1 translocations. Of these, two patient populations comprise the majority of cases: patients younger than 1 year of age at diagnosis (primarily acute lymphoblastic leukemias) and young- to-middle-aged adults (primarily acute myeloid leukemias). A much rarer subgroup of patients with MLL1 rearrangements develop leukemia that is attributable to prior treatment with certain chemotherapeutic agents-so-called therapy-related leukemias. In general, outcomes for all of these patients remain poor when compared to patients with non-MLL1 rearranged leukemias. In this review, we will discuss the normal biological roles of MLL1 and its fusion partners, how these roles are hypothesized to be dysregulated in the context of MLL1 rearrangements, and the clinical manifestations of this group of leukemias. We will go on to discuss the progress in clinical management and promising new avenues of research, which may lead to more effective targeted therapies for affected patients.