Chromatin Profiles Are Prognostic of Clinical Response to Bortezomib-Containing Chemotherapy in Pediatric Acute Myeloid Leukemia: Results from the COG AAML1031 Trial.

The addition of the proteasome inhibitor bortezomib to standard chemotherapy did not improve survival in pediatric acute myeloid leukemia (AML) when all patients were analyzed as a group in the Children's Oncology Group phase 3 trial AAML1031 (NCT01371981). Proteasome inhibition influences the chromatin landscape and proteostasis, and we hypothesized that baseline proteomic analysis of histone- and chromatin-modifying enzymes (HMEs) would identify AML subgroups that benefitted from bortezomib addition. A proteomic profile of 483 patients treated with AAML1031 chemotherapy was generated using a reverse-phase protein array. A relatively high expression of 16 HME was associated with lower EFS and higher 3-year relapse risk after AML standard treatment compared to low expressions (52% vs. 29%, p = 0.005). The high-HME profile correlated with more transposase-accessible chromatin, as demonstrated via ATAC-sequencing, and the bortezomib addition improved the 3-year overall survival compared with standard therapy (62% vs. 75%, p = 0.033). These data suggest that there are pediatric AML populations that respond well to bortezomib-containing chemotherapy.

MRD at the End of Induction and EFS in T-cell Lymphoblastic Lymphoma: Children's Oncology Group Trial AALL1231.

Defining prognostic variables in T-lymphoblastic lymphoma (T-LL) remains a challenge. AALL1231 was a COG phase 3 clinical trial for newly diagnosed with T Acute Lymphoblastic leukemia or T-LL patients randomizing children and young adults to a modified augmented BFM backbone to receive standard therapy (Arm A) or with addition of bortezomib (Arm B). Optional bone marrow (BM) samples to assess minimal residual disease (MRD) at the end of induction (EOI) were collected in T-LL analyzed to assess the correlation of MRD at the EOI to event-free survival (EFS). Eighty-six (41%) of the 209 T-LL patients accrued to this trial submitted samples for MRD assessment. Patients with MRD <0.1% (n= 75) at EOI had a superior 4-year EFS versus those with MRD >0.1% (n= 11), (89.0±4.4% versus 63.6±17.2%, p= 0.025). Overall survival did not significantly differ between the two groups. Cox regression for EFS using Arm A as a reference demonstrated that MRD EOI ≥0.1% was associated with a greater risk of inferior outcome (Hazard Ratio, HR= 3.73 (1.12-12.40, p= 0.032), which was independent of treatment arm assignment. Consideration to incorporate MRD at EOI into future trials will help establish its value in defining risk groups. CT# NCT02112916.

Integrin signaling is critical for myeloid-mediated support of T-cell acute lymphoblastic leukemia.

We previously found that T-cell acute lymphoblastic leukemia (T-ALL) requires support from tumor-associated myeloid cells, which activate Insulin Like Growth Factor 1 Receptor (IGF1R) signaling in leukemic blasts. However, IGF1 is not sufficient to sustain T-ALL in vitro, implicating additional myeloid-mediated signals in leukemia progression. Here, we find that T-ALL cells require close contact with myeloid cells to survive. Transcriptional profiling and in vitro assays demonstrate that integrin-mediated cell adhesion activates downstream focal adhesion kinase (FAK)/ proline-rich tyrosine kinase 2 (PYK2), which are required for myeloid-mediated T-ALL support, partly through activation of IGF1R. Blocking integrin ligands or inhibiting FAK/PYK2 signaling diminishes leukemia burden in multiple organs and confers a survival advantage in a mouse model of T-ALL. Inhibiting integrin-mediated adhesion or FAK/PYK2 also reduces survival of primary patient T-ALL cells co-cultured with myeloid cells. Furthermore, elevated integrin pathway gene signatures correlate with higher FAK signaling and myeloid gene signatures and are associated with an inferior prognosis in pediatric T-ALL patients. Together, these findings demonstrate that integrin activation and downstream FAK/PYK2 signaling are important mechanisms underlying myeloid-mediated support of T-ALL progression.

Feasibility of pevonedistat combined with azacitidine, fludarabine, cytarabine in pediatric relapsed/refractory AML: Results from COG ADVL1712.

BACKGROUND: Outcomes for children with relapsed/refractory (R/R) acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) are poor, and new therapies are needed. Pevonedistat is an inhibitor of the NEDD-8 activating enzyme, a key regulator of the ubiquitin proteasome system that is responsible for protein turnover, with protein degradation regulating cell growth and survival. PROCEDURE: We evaluated the feasibility, toxicity, and pharmacokinetics (PK) of pevonedistat (20 mg/m2 days 1, 3, 5) in combination with azacitidine, fludarabine, cytarabine (aza-FLA) in children with R/R AML and MDS (NCT03813147). Twelve patients were enrolled, median age was 13 years (range 1-21). Median number of prior chemotherapeutic regimens was two (range one to five), and two (25%) patients had prior hematopoietic cell transplantation. Diagnoses were AML NOS (n = 10, 83%), acute monocytic leukemia (n = 1), and therapy-related AML (n = 1). RESULTS: Overall, three of 12 (25%) patients experienced DLTs. The day 1 mean ± SD (n = 12) Cmax , VSS , T1/2 , and CL were 223 ± 91 ng/mL, 104 ± 53.8 L/m2 , 4.3 ± 1.2 hours, and 23.2 ± 6.9 L/h/m2 , respectively. T1/2 , VSS , and Cmax , but not CL, were significantly different between age groups. The overall response rate was 25%, with n = 3 patients achieving a complete remission with incomplete hematologic recovery (CRi). CONCLUSIONS: Pevonedistat 20 mg/m2 combined with Aza-FLA was tolerable in children with R/R AML with similar toxicity profile to other intensive AML regimens. However, within the confines of a phase 1 study, we did not observe that the pevonedistat + Aza-FLA combination demonstrated significant anti-leukemic activity.

Valosin-containing protein (VCP/p97) is prognostically unfavorable in pediatric AML, and negatively correlates with unfolded protein response proteins IRE1 and GRP78: A report from the Children's Oncology Group.

PURPOSE: The endoplasmic reticulum (ER) is the major site of protein synthesis and folding in the cell. ER-associated degradation (ERAD) and unfolded protein response (UPR) are the main mechanisms of ER-mediated cell stress adaptation. Targeting the cell stress response is a promising therapeutic approach in acute myeloid leukemia (AML). EXPERIMENTAL DESIGN: Protein expression levels of valosin-containing protein (VCP), a chief element of ERAD, were measured in peripheral blood samples from in 483 pediatric AML patients using reverse phase protein array methodology. Patients participated in the Children's Oncology Group AAML1031 phase 3 clinical trial that randomized patients to standard chemotherapy (cytarabine (Ara-C), daunorubicin, and etoposide [ADE]) versus ADE plus bortezomib (ADE+BTZ). RESULTS: Low-VCP expression was significantly associated with favorable 5-year overall survival (OS) rate compared to middle-high-VCP expression (81% versus 63%, p < 0.001), independent of additional bortezomib treatment. Multivariable Cox regression analysis identified VCP as independent predictor of clinical outcome. UPR proteins IRE1 and GRP78 had significant negative correlation with VCP. Five-year OS in patients characterized by low-VCP, moderately high-IRE1 and high-GRP78 improved after treatment with ADE+BTZ versus ADE (66% versus 88%, p = 0.026). CONCLUSION AND CLINICAL RELEVANCE: Our findings suggest the potential of the protein VCP as biomarker in prognostication prediction in pediatric AML.

Reverse Phase Protein Array Profiling Identifies Recurrent Protein Expression Patterns of DNA Damage-Related Proteins across Acute and Chronic Leukemia: Samples from Adults and the Children's Oncology Group.

DNA damage response (DNADR) recognition and repair (DDR) pathways affect carcinogenesis and therapy responsiveness in cancers, including leukemia. We measured protein expression levels of 16 DNADR and DDR proteins using the Reverse Phase Protein Array methodology in acute myeloid (AML) (n = 1310), T-cell acute lymphoblastic leukemia (T-ALL) (n = 361) and chronic lymphocytic leukemia (CLL) (n = 795) cases. Clustering analysis identified five protein expression clusters; three were unique compared to normal CD34+ cells. Individual protein expression differed by disease for 14/16 proteins, with five highest in CLL and nine in T-ALL, and by age in T-ALL and AML (six and eleven proteins, respectively), but not CLL (n = 0). Most (96%) of the CLL cases clustered in one cluster; the other 4% were characterized by higher frequencies of deletion 13q and 17p, and fared poorly (p < 0.001). T-ALL predominated in C1 and AML in C5, but both occurred in all four acute-dominated clusters. Protein clusters showed similar implications for survival and remission duration in pediatric and adult T-ALL and AML populations, with C5 doing best in all. In summary, DNADR and DDR protein expression was abnormal in leukemia and formed recurrent clusters that were shared across the leukemias with shared prognostic implications across diseases, and individual proteins showed age- and disease-related differences.

DNA Damage Response-Related Proteins Are Prognostic for Outcome in Both Adult and Pediatric Acute Myelogenous Leukemia Patients: Samples from Adults and from Children Enrolled in a Children's Oncology Group Study.

The survival of malignant leukemic cells is dependent on DNA damage repair (DDR) signaling. Reverse Phase Protein Array (RPPA) data sets were assembled using diagnostic samples from 810 adult and 500 pediatric acute myelogenous leukemia (AML) patients and were probed with 412 and 296 strictly validated antibodies, respectively, including those detecting the expression of proteins directly involved in DDR. Unbiased hierarchical clustering identified strong recurrent DDR protein expression patterns in both adult and pediatric AML. Globally, DDR expression was associated with gene mutational statuses and was prognostic for outcomes including overall survival (OS), relapse rate, and remission duration (RD). In adult patients, seven DDR proteins were individually prognostic for either RD or OS. When DDR proteins were analyzed together with DDR-related proteins operating in diverse cellular signaling pathways, these expanded groupings were also highly prognostic for OS. Analysis of patients treated with either conventional chemotherapy or venetoclax combined with a hypomethylating agent revealed protein clusters that differentially predicted favorable from unfavorable prognoses within each therapy cohort. Collectively, this investigation provides insight into variable DDR pathway activation in AML and may help direct future individualized DDR-targeted therapies in AML patients.

Molecular Evolution of Classic Hodgkin Lymphoma Revealed Through Whole-Genome Sequencing of Hodgkin and Reed Sternberg Cells.

The rarity of malignant Hodgkin and Reed Sternberg (HRS) cells in classic Hodgkin lymphoma (cHL) limits the ability to study the genomics of cHL. To circumvent this, our group has previously optimized fluorescence-activated cell sorting to purify HRS cells. Using this approach, we now report the whole-genome sequencing landscape of HRS cells and reconstruct the chronology and likely etiology of pathogenic events leading to cHL. We identified alterations in driver genes not previously described in cHL, APOBEC mutational activity, and the presence of complex structural variants including chromothripsis. We found that high ploidy in cHL is often acquired through multiple, independent chromosomal gains events including whole-genome duplication. Evolutionary timing analyses revealed that structural variants enriched for RAG motifs, driver mutations in B2M, BCL7A, GNA13, and PTPN1, and the onset of AID-driven mutagenesis usually preceded large chromosomal gains. This study provides a temporal reconstruction of cHL pathogenesis. SIGNIFICANCE: Previous studies in cHL were limited to coding sequences and therefore not able to comprehensively decipher the tumor complexity. Here, leveraging cHL whole-genome characterization, we identify driver events and reconstruct the tumor evolution, finding that structural variants, driver mutations, and AID mutagenesis precede chromosomal gains. This article is highlighted in the In This Issue feature, p. 171.

IL-10 and TNFα are associated with decreased survival in low-risk pediatric acute myeloid leukemia; a children's oncology group report.

Pediatric acute myeloid leukemia (AML) is a devastating disease with a high risk of relapse. Current risk classification designates patients as high or low risk (LR) based on molecular features and therapy response. However, 30% of LR patients still suffer relapse, indicating a need for improvement in risk stratification. Cytokine levels, such as IL-6 and IL-10, have been shown to be prognostic in adult AML but have not been well studied in children. Previously, we reported elevated IL-6 levels in pediatric AML bone marrow to be associated with inferior prognosis. Here, we expanded our investigation to assess cytokine levels in diagnostic peripheral blood plasma (PBP) of pediatric AML patients and determined correlation with outcome. Diagnostic PBP was obtained from 80 patients with LR AML enrolled on the Children's Oncology Group AAML1031 study and normal PBP from 11 controls. Cytokine levels were measured and correlation with clinical outcome was assessed. IL-6, TNFα, MIP-3a, and IL-1ß were significantly higher in AML patients versus controls when corrected by the Bonferroni method. Furthermore, elevated TNFα and IL-10 were significantly associated with inferior outcomes. Our data demonstrate that in diagnostic PBP of LR pediatric AML patients, certain cytokine levels are elevated as compared to healthy controls and that elevated TNFα and IL-10 are associated with inferior outcomes, supporting the idea that an abnormal inflammatory state may predict poor outcomes. Studies are needed to determine the mechanisms by which these cytokines impact survival, and to further evaluate their use as prognostic biomarkers in pediatric AML.

Inhibition of mitochondrial complex I reverses NOTCH1-driven metabolic reprogramming in T-cell acute lymphoblastic leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) is commonly driven by activating mutations in NOTCH1 that facilitate glutamine oxidation. Here we identify oxidative phosphorylation (OxPhos) as a critical pathway for leukemia cell survival and demonstrate a direct relationship between NOTCH1, elevated OxPhos gene expression, and acquired chemoresistance in pre-leukemic and leukemic models. Disrupting OxPhos with IACS-010759, an inhibitor of mitochondrial complex I, causes potent growth inhibition through induction of metabolic shut-down and redox imbalance in NOTCH1-mutated and less so in NOTCH1-wt T-ALL cells. Mechanistically, inhibition of OxPhos induces a metabolic reprogramming into glutaminolysis. We show that pharmacological blockade of OxPhos combined with inducible knock-down of glutaminase, the key glutamine enzyme, confers synthetic lethality in mice harboring NOTCH1-mutated T-ALL. We leverage on this synthetic lethal interaction to demonstrate that IACS-010759 in combination with chemotherapy containing L-asparaginase, an enzyme that uncovers the glutamine dependency of leukemic cells, causes reduced glutaminolysis and profound tumor reduction in pre-clinical models of human T-ALL. In summary, this metabolic dependency of T-ALL on OxPhos provides a rational therapeutic target.

Inhibition of the Sec61 translocon overcomes cytokine-induced glucocorticoid resistance in T-cell acute lymphoblastic leukaemia.

Glucocorticoid (GC) resistance is a poor prognostic factor in T-cell acute lymphoblastic leukaemia (T-ALL). Interleukin-7 (IL-7) mediates GC resistance via GC-induced upregulation of IL-7 receptor (IL-7R) expression, leading to increased pro-survival signalling. IL-7R reaches the cell surface via the secretory pathway, so we hypothesized that inhibiting the translocation of IL-7R into the secretory pathway would overcome GC resistance. Sec61 is an endoplasmic reticulum (ER) channel that is required for insertion of polypeptides into the ER. Here, we demonstrate that KZR-445, a novel inhibitor of Sec61, potently attenuates the dexamethasone (DEX)-induced increase in cell surface IL-7R and overcomes IL-7-induced DEX resistance.

Children's Oncology Group Trial AALL1231: A Phase III Clinical Trial Testing Bortezomib in Newly Diagnosed T-Cell Acute Lymphoblastic Leukemia and Lymphoma.

PURPOSE: To improve the outcomes of patients with T-cell acute lymphoblastic leukemia (T-ALL) and lymphoblastic lymphoma (T-LL), the proteasome inhibitor bortezomib was examined in the Children's Oncology Group phase III clinical trial AALL1231, which also attempted to reduce the use of prophylactic cranial radiation (CRT) in newly diagnosed T-ALL. PATIENTS AND METHODS: Children and young adults with T-ALL/T-LL were randomly assigned to a modified augmented Berlin-Frankfurt-Münster chemotherapy regimen with/without bortezomib during induction and delayed intensification. Multiple modifications were made to the augmented Berlin-Frankfurt-Münster backbone used in the predecessor trial, AALL0434, including using dexamethasone instead of prednisone and adding two extra doses of pegaspargase in an attempt to eliminate CRT in most patients. RESULTS: AALL1231 accrued 824 eligible and evaluable patients from 2014 to 2017. The 4-year event-free survival (EFS) and overall survival (OS) for arm A (no bortezomib) versus arm B (bortezomib) were 80.1% ± 2.3% versus 83.8% ± 2.1% (EFS, P = .131) and 85.7% ± 2.0% versus 88.3% ± 1.8% (OS, P = .085). Patients with T-LL had improved EFS and OS with bortezomib: 4-year EFS (76.5% ± 5.1% v 86.4% ± 4.0%; P = .041); and 4-year OS (78.3% ± 4.9% v 89.5% ± 3.6%; P = .009). No excess toxicity was seen with bortezomib. In AALL0434, 90.8% of patients with T-ALL received CRT. In AALL1231, 9.5% of patients were scheduled to receive CRT. Evaluation of comparable AALL0434 patients who received CRT and AALL1231 patients who did not receive CRT demonstrated no statistical differences in EFS (P = .412) and OS (P = .600). CONCLUSION: Patients with T-LL had significantly improved EFS and OS with bortezomib on the AALL1231 backbone. Systemic therapy intensification allowed elimination of CRT in more than 90% of patients with T-ALL without excess relapse.

Clinical relevance of proteomic profiling in de novo pediatric acute myeloid leukemia: a Children's Oncology Group study.

Pediatric acute myeloid leukemia (AML) remains a fatal disease for at least 30% of patients, stressing the need for improved therapies and better risk stratification. As proteins are the unifying feature of (epi)genetic and environmental alterations, and are often targeted by novel chemotherapeutic agents, we studied the proteomic landscape of pediatric AML. Protein expression and activation levels were measured in 500 bulk leukemic patients' samples and 30 control CD34+ cell samples, using reverse phase protein arrays with 296 strictly validated antibodies. The multistep MetaGalaxy analysis methodology was applied and identified nine protein expression signatures (PrSIG), based on strong recurrent protein expression patterns. PrSIG were associated with cytogenetics and mutational state, and with favorable or unfavorable prognosis. Analysis based on treatment (i.e., ADE vs. ADE plus bortezomib) identified three PrSIG that did better with ADE plus bortezomib than with ADE alone. When PrSIG were studied in the context of cytogenetic risk groups, PrSIG were independently prognostic after multivariate analysis, suggesting a potential value for proteomics in combination with current classification systems. Proteins with universally increased (n=7) or decreased (n=17) expression were observed across PrSIG. Certain proteins significantly differentially expressed from normal could be identified, forming a hypothetical platform for personalized medicine.

Bortezomib is significantly beneficial for de novo pediatric AML patients with low phosphorylation of the NF-κB subunit RelA.

PURPOSE: The addition of the proteasome inhibitor (PI) bortezomib to standard chemotherapy (ADE: cytarabine [Ara-C], daunorubicin, and etoposide) did not improve overall outcome of pediatric AML patients in the Children's Oncology Group AAML1031 phase 3 randomized clinical trial (AAML1031) . Bortezomib prevents protein degradation, including RelA via the intracellular NF-kB pathway. In this study, we hypothesized that subgroups of pediatric AML patients benefitting from standard therapy plus bortezomib (ADEB) could be identified based on pre-treatment RelA expression and phosphorylation status. EXPERIMENTAL DESIGN: RelA-total and phosphorylation at serine 536 (RelA-pSer536 ) were measured in 483 patient samples using reverse phase protein array technology. RESULTS: In ADEB-treated patients, low-RelA-pSer536 was favorably prognostic when compared to high-RelA-pSer536 (3-yr overall survival (OS): 81% vs. 68%, p = 0.032; relapse risk (RR): 30% vs. 49%, p = 0.004). Among low-RelA-pSer536 patients, RR significantly decreased with ADEB compared to ADE (RR: 30% vs. 44%, p = 0.035). Correlation between RelA-pSer536 and 295 other assayed proteins identified a strong correlation with HSF1-pSer326 , another protein previously identified as modifying ADEB response. The combination of low-RelA-pSer536 and low-HSF1-pSer326 was a significant predictor of ADEB response (3-yr OS: 86% vs. 67%, p = 0.013). CONCLUSION AND CLINICAL RELEVANCE: Bortezomib may improve clinical outcome in a subgroup of AML patients identified by low-RelA-pSer536 and low-HSF1-pSer326 .

A gene expression-based model predicts outcome in children with intermediate-risk classical Hodgkin lymphoma.

Classical Hodgkin lymphoma (cHL) is a common malignancy in children and adolescents. Although cHL is highly curable, treatment with chemotherapy and radiation often come at the cost of long-term toxicity and morbidity. Effective risk-stratification tools are needed to tailor therapy. Here, we used gene expression profiling (GEP) to investigate tumor microenvironment (TME) biology, to determine molecular correlates of treatment failure, and to develop an outcome model prognostic for pediatric cHL. A total of 246 formalin-fixed, paraffin-embedded tissue biopsies from patients enrolled in the Children's Oncology Group trial AHOD0031 were used for GEP and compared with adult cHL data. Eosinophil, B-cell, and mast cell signatures were enriched in children, whereas macrophage and stromal signatures were more prominent in adults. Concordantly, a previously published model for overall survival prediction in adult cHL did not validate in pediatric cHL. Therefore, we developed a 9-cellular component model reflecting TME composition to predict event-free survival (EFS). In an independent validation cohort, we observed a significant difference in weighted 5-year EFS between high-risk and low-risk groups (75.2% vs 90.3%; log-rank P = .0138) independent of interim response, stage, fever, and albumin. We demonstrate unique disease biology in children and adolescents that can be harnessed for risk-stratification at diagnosis. This trial was registered at www.clinicaltrials.gov as #NCT00025259.

Reverse phase protein arrays in acute leukemia: investigative and methodological challenges.

INTRODUCTION: Acute leukemia results from a series of mutational events that alter cell growth and proliferation. Mutations result in protein changes that orchestrate growth alterations characteristic of leukemia. Proteomics is a methodology appropriate for study of protein changes found in leukemia. The high-throughput reverse phase protein array (RPPA) technology is particularly well-suited for the assessment of protein changes in samples derived from clinical trials. AREAS COVERED: This review discusses the technical, methodological, and analytical issues related to the successful development of acute leukemia RPPAs. EXPERT COMMENTARY: To obtain representative protein sample lysates, samples should be prepared from freshly collected blood or bone marrow material. Variables such as sample shipment, transit time, and holding temperature only have minimal effects on protein expression. CellSave preservation tubes are preferred for cells collected after exposure to chemotherapy, and incorporation of standardized guidelines for antibody validation is recommended. A more systematic biological approach to analyze protein expression is desired, searching for recurrent patterns of protein expression that allow classification of patients into risk groups, or groups of patients that may be treated similarly. Comparing RPPA protein analysis between cell lines and primary samples shows that cell lines are not representative of patient proteomic patterns.

Comparison of the blood, bone marrow, and cerebrospinal fluid metabolomes in children with b-cell acute lymphoblastic leukemia.

Metabolomics may shed light on treatment response in childhood acute lymphoblastic leukemia (ALL), however, most assessments have analyzed bone marrow or cerebrospinal fluid (CSF), which are not collected during all phases of therapy. Blood is collected frequently and with fewer risks, but it is unclear whether findings from marrow or CSF biomarker studies may translate. We profiled end-induction plasma, marrow, and CSF from N = 10 children with B-ALL using liquid chromatography-mass spectrometry. We estimated correlations between plasma and marrow/CSF metabolite abundances detected in ≥ 3 patients using Spearman rank correlation coefficients (rs). Most marrow metabolites were detected in plasma (N = 661; 81%), and we observed moderate-to-strong correlations (median rs 0.62, interquartile range [IQR] 0.29-0.83). We detected 328 CSF metabolites in plasma (90%); plasma-CSF correlations were weaker (median rs 0.37, IQR 0.07-0.70). We observed plasma-marrow correlations for metabolites in pathways associated with end-induction residual disease (pyruvate, asparagine) and plasma-CSF correlations for a biomarker of fatigue (gamma-glutamylglutamine). There is considerable overlap between the plasma, marrow, and CSF metabolomes, and we observed strong correlations for biomarkers of clinically relevant phenotypes. Plasma may be suitable for biomarker studies in B-ALL.

Rational biomarker development for the early and minimally invasive monitoring of AML.

Recurrent disease remains the principal cause for treatment failure in acute myeloid leukemia (AML) across age groups. Reliable biomarkers of AML relapse risk and disease burden have been problematic, as symptoms appear late and current monitoring relies on invasive and cost-ineffective serial bone marrow (BM) surveillance. In this report, we discover a set of unique microRNA (miRNA) that circulates in AML-derived vesicles in the peripheral blood ahead of the general dissemination of leukemic blasts and symptomatic BM failure. Next-generation sequencing of extracellular vesicle-contained small RNA in 12 AML patients and 12 controls allowed us to identify a panel of differentially incorporated miRNA. Proof-of-concept studies using a murine model and patient-derived xenografts demonstrate the feasibility of developing miR-1246, as a potential minimally invasive AML biomarker.

Defining the transcriptional control of pediatric AML highlights RARA as a superenhancer-regulated druggable dependency.

Somatic mutations are rare in pediatric acute myeloid leukemia (pAML), indicating that alternate strategies are needed to identify targetable dependencies. We performed the first enhancer mapping of pAML in 22 patient samples. Generally, pAML samples were distinct from adult AML samples, and MLL (KMT2A)-rearranged samples were also distinct from non-KMT2A-rearranged samples. Focusing specifically on superenhancers (SEs), we identified SEs associated with many known leukemia regulators. The retinoic acid receptor alpha (RARA) gene was differentially regulated in our cohort, and a RARA-associated SE was detected in 64% of the study cohort across all cytogenetic and molecular subtypes tested. RARA SE+ pAML cell lines and samples exhibited high RARA messenger RNA levels. These samples were specifically sensitive to the synthetic RARA agonist tamibarotene in vitro, with slowed proliferation, apoptosis induction, differentiation, and upregulated retinoid target gene expression, compared with RARA SE- samples. Tamibarotene prolonged survival and suppressed the leukemia burden of an RARA SE+ pAML patient-derived xenograft mouse model compared with a RARA SE- patient-derived xenograft. Our work shows that examining chromatin regulation can identify new, druggable dependencies in pAML and provides a rationale for a pediatric tamibarotene trial in children with RARA-high AML.

The Anti-Tumor Activity of the NEDD8 Inhibitor Pevonedistat in Neuroblastoma.

Pevonedistat is a neddylation inhibitor that blocks proteasomal degradation of cullin-RING ligase (CRL) proteins involved in the degradation of short-lived regulatory proteins, including those involved with cell-cycle regulation. We determined the sensitivity and mechanism of action of pevonedistat cytotoxicity in neuroblastoma. Pevonedistat cytotoxicity was assessed using cell viability assays and apoptosis. We examined mechanisms of action using flow cytometry, bromodeoxyuridine (BrDU) and immunoblots. Orthotopic mouse xenografts of human neuroblastoma were generated to assess in vivo anti-tumor activity. Neuroblastoma cell lines were very sensitive to pevonedistat (IC50 136-400 nM). The mechanism of pevonedistat cytotoxicity depended on p53 status. Neuroblastoma cells with mutant (p53MUT) or reduced levels of wild-type p53 (p53si-p53) underwent G2-M cell-cycle arrest with rereplication, whereas p53 wild-type (p53WT) cell lines underwent G0-G1 cell-cycle arrest and apoptosis. In orthotopic neuroblastoma models, pevonedistat decreased tumor weight independent of p53 status. Control mice had an average tumor weight of 1.6 mg + 0.8 mg versus 0.5 mg + 0.4 mg (p < 0.05) in mice treated with pevonedistat. The mechanism of action of pevonedistat in neuroblastoma cell lines in vitro appears p53 dependent. However, in vivo studies using mouse neuroblastoma orthotopic models showed a significant decrease in tumor weight following pevonedistat treatment independent of the p53 status. Novel chemotherapy agents, such as the NEDD8-activating enzyme (NAE) inhibitor pevonedistat, deserve further study in the treatment of neuroblastoma.