CD74 is expressed in a subset of pediatric acute myeloid leukemia patients and is a promising target for therapy: a report from the Children's Oncology Group

As curative therapies for pediatric AML remain elusive, identifying potential new treatment targets is vital. We assessed the cell surface expression of CD74, also known as the MHC-II invariant chain, by multidimensional flow cytometry in 973 patients enrolled in the Children's Oncology Group AAML1031 clinical trial. 38% of pediatric AML patients expressed CD74 at any level and a comparison to normal hematopoietic cells revealed a subset with increased expression relative to normal myeloid progenitor cells. Pediatric AML patients expressing high intensity CD74 typically had an immature immunophenotype and an increased frequency of lymphoid antigen expression. Increased CD74 expression was associated with older patients with lower WBC and peripheral blood blast counts, and was enriched for t(8;21), trisomy 8, and CEBPA mutations. Overall, high CD74 expression was associated with low-risk status, however 26% of patients were allocated to high-risk protocol status and 5-year event free survival was 53%, indicating that a significant number of high expressing patients had poor outcomes. In vitro pre-clinical studies indicate that anti-CD74 therapy demonstrates efficacy against AML cells but has little impact on normal CD34+ cells. Together, we demonstrate that CD74 is expressed on a subset of pediatric AMLs at increased levels compared to normal hematopoietic cells and is a promising target for therapy in expressing patients. Given that nearly half of patients expressing CD74 at high levels experience an adverse event within 5 years, and the availability of CD74 targeting drugs, this represents a promising line of therapy worthy of additional investigation.

Prognostic Impact of Co-occurring Mutations in FLT3-ITD Pediatric Acute Myeloid Leukemia

We sought to define the co-occurring mutational profile of FLT3-ITD positive (ITDpos) acute myeloid leukemia (AML) in pediatric and young adult patients and to define the prognostic impact of cooperating mutations. We identified 464 patients with FLT3-ITD mutations treated on Children's Oncology Group trials with available sequencing and outcome data. Overall survival (OS), event-free survival (EFS), and relapse risk (RR) were determined according to the presence of co-occurring risk stratifying mutations. Among the cohort, 79% of patients had co-occurring alterations across 239 different genes that were altered through mutations or fusions. Evaluation of the prognostic impact of the co-occurring mutations demonstrated that ITDpos patients experienced significantly different outcomes according to the co-occurring mutational profile. ITDpos patients harboring a co-occurring favorable risk mutation (ITDFR) of NPM1, CEBPA, t(8;21), or inv(16) experienced a 5-year EFS of 64%, which was significantly superior to patients with ITDpos and poor risk mutations (ITDPR) of WT1, UBTF or NUP98::NSD1 of 22.2% as well as those that lacked either FR or PR mutation (ITDINT) of 40.9% (p<0.001 for both). Multivariable analysis demonstrated co-occurring mutations had significant prognostic impact, while allelic ratio had no impact. Therapy intensification, specifically consolidation transplant in remission resulted in significant improvements in survival for ITDpos AML. However, ITDpos/NUP98::NSD1 patients continued to have poor outcomes with intensified therapy, including sorafenib. Co-occurring mutational profile in ITDpos AML has significant prognostic impacts is critical to determining risk stratification and therapeutic allocation for ITDpos patients.

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.

Characteristics and prognostic impact of IDH mutations in AML: a COG, SWOG, and ECOG analysis

Somatic mutations in isocitrate dehydrogenase (IDH) genes occur frequently in adult acute myeloid leukemia (AML) and less commonly in pediatric AML. The objective of this study was to describe the prevalence, mutational profile, and prognostic significance of IDH mutations in AML across age. Our cohort included 3141 patients aged between <1 month and 88 years treated on Children's Cancer Group/Children's Oncology Group (n = 1872), Southwest Oncology Group (n = 359), Eastern Cooperative Oncology Group (n = 397) trials, and in Beat AML (n = 333) and The Cancer Genome Atlas (n = 180) genomic characterization cohorts. We retrospectively analyzed patients in 4 age groups (age range, n): pediatric (0-17, 1744), adolescent/young adult (18-39, 444), intermediate-age (40-59, 640), older (≥60, 309). IDH mutations (IDHmut) were identified in 9.2% of the total cohort (n = 288; IDH1 [n = 123, 42.7%]; IDH2 [n = 165, 57.3%]) and were strongly correlated with increased age: 3.4% pediatric vs 21% older, P < .001. Outcomes were similar in IDHmut and IDH-wildtype (IDHWT) AML (event-free survival [EFS]: 35.6% vs 40.0%, P = .368; overall survival [OS]: 50.3% vs 55.4%, P = .196). IDH mutations frequently occurred with NPM1 (47.2%), DNMT3A (29.3%), and FLT3-internal tandem duplication (ITD) (22.4%) mutations. Patients with IDHmut AML with NPM1 mutation (IDHmut/NPM1mut) had significantly improved survival compared with the poor outcomes experienced by patients without (IDHmut/NPM1WT) (EFS: 55.1% vs 17.0%, P < .001; OS: 66.5% vs 35.2%, P < .001). DNTM3A or FLT3-ITD mutations in otherwise favorable IDHmut/NPM1mut AML led to inferior outcomes. Age group analysis demonstrated that IDH mutations did not abrogate the favorable prognostic impact of NPM1mut in patients aged <60 years; older patients had poor outcomes regardless of NPM1 status. These trials were registered at www.clinicaltrials.gov as #NCT00070174, #NCT00372593, #NCT01371981, #NCT00049517, and #NCT00085709.

Comprehensive molecular and clinical characterization of NUP98 fusions in pediatric acute myeloid leukemia

NUP98 fusions c omprise a family o f rare r ecurrent a lterations i n A ML, associated w ith adverse outcomes. To define the underlying biology and clinical implications of this family of fusions, we performed comprehensive transcriptome, epigenome, and immunophenotypic profiling of 2,235 children and young adults with AML and identified 160 NUP98 rearrangements (7.2%), including 108 NUP98-NSD1 (4.8%), 32 NUP98-KDM5A (1.4%) and 20 NUP98-X cases (0.9%) with 13 different fusion partners. Fusion partners defined disease characteristics and biology; patients with NUP98-NSD1 or NUP98-KDM5A had distinct immunophenotypic, transcriptomic, and epigenomic profiles. Unlike the two most prevalent NUP98 fusions, NUP98-X variants are typically not cryptic. Furthermore, NUP98-X cases are associated with WT1 mutations, and have epigenomic profiles that resemble either NUP98- NSD1 or NUP98-KDM5A. Cooperating FLT3-ITD and WT1 mutations define NUP98-NSD1, and chromosome 13 aberrations are highly enriched in NUP98-KDM5A. Importantly, we demonstrate that NUP98 fusions portend dismal overall survival, with the noteworthy exception of patients bearing abnormal chr13.

CBFA2T3-GLIS2 model of pediatric acute megakaryoblastic leukemia identifies FOLR1 as a CAR T cell target

Fusion oncoproteins are the initiating event in the pathogenesis of many pediatric AML. The CBFA2T3-GLIS2 (C/G) fusion is a product of a cryptic translocation primarily seen in infants and early childhood and is associated with dismal outcome. Here, we demonstrate that the expression of the C/G oncogenic fusion protein promotes the transformation of human cord blood hematopoietic stem/progenitor cells (CB HSPCs) in an endothelial cell (EC) co-culture system, that recapitulates the transcriptome, morphology and immunophenotype of C/G AML and induces highly aggressive leukemia in xenograft models. Interrogating the transcriptome of C/G-CB cells and primary C/G AML identified a library of C/G fusion-specific genes that are potential targets for therapy. We developed chimeric antigen receptor (CAR) T cells directed against one of the targets, FOLR1, and demonstrated their pre-clinical efficacy against C/G AML using in vitro and xenograft models. FOLR1 is also expressed in renal and pulmonary epithelium, raising concerns for toxicity that must be addressed for the clinical application of this therapy. Our findings underscore the role of the endothelial niche in promoting leukemic transformation of C/G-transduced CB HSPCs. Furthermore, this work has broad implications for studies of leukemogenesis applicable to a variety of oncogenic fusion-driven pediatric leukemias, providing a robust and tractable model system to characterize the molecular mechanisms of leukemogenesis and identify biomarkers for disease diagnosis and targets for therapy.

Integrated stem cell signature and cytomolecular risk determination in pediatric acute myeloid leukemia

Relapsed or refractory pediatric acute myeloid leukemia (AML) is associated with poor outcomes and relapse risk prediction approaches have not changed significantly in decades. To build a robust transcriptional risk prediction model for pediatric AML, we perform RNA-sequencing on 1503 primary diagnostic samples. While a 17 gene leukemia stem cell signature (LSC17) is predictive in our aggregated pediatric study population, LSC17 is no longer predictive within established cytogenetic and molecular (cytomolecular) risk groups. Therefore, we identify distinct LSC signatures on the basis of AML cytomolecular subtypes (LSC47) that were more predictive than LSC17. Based on these findings, we build a robust relapse prediction model within a training cohort and then validate it within independent cohorts. Here, we show that LSC47 increases the predictive power of conventional risk stratification and that applying biomarkers in a manner that is informed by cytomolecular profiling outperforms a uniform biomarker approach.

Relapsed pediatric acute myeloid leukemia is associated with poor prognosis. Here, the authors use RNA-seq data from 1503 primary samples to create a combined transcriptional and cytomolecular signature to improve relapse risk prediction.

Case Report: The First Case Report of Visceral Leishmaniasis in Cambodia

Leishmaniasis is considered a neglected tropical disease that is commonly found in Asia, Africa, South America, and Mediterranean countries. Visceral leishmaniasis (VL) is the most severe form of the disease and is almost universally fatal if left untreated. The symptoms of VL overlap with many infectious diseases, malignancies, and other blood disorders. The most common findings include fever, cytopenias, and splenomegaly. Given the nonspecific symptoms, the diagnosis requires detailed laboratory investigations, including bone marrow examination, that can be challenging in low- and middle-income countries. Diagnostic limitations likely lead to the underdiagnosis or delay in diagnosis of VL. We describe, to our knowledge, the first case report of VL in Cambodia in a child presenting with fever, anemia, and thrombocytopenia. The diagnosis required a liver biopsy and multiple bone marrow biopsies to visualize intracellular Leishmania spp. Our case illustrates the diagnostic challenges and the importance of timely diagnosis. This case also highlights the need for heightened awareness of the diagnostic findings of VL and improved reporting of tropical diseases.

Sorafenib in Combination With Standard Chemotherapy for Children With High Allelic Ratio FLT3/ITD+ Acute Myeloid Leukemia: A Report From the Children's Oncology Group Protocol AAML1031

PURPOSE

High allelic ratio (HAR) FLT3/ITD (AR > 0.4) mutations confer poor prognosis in pediatric acute myeloid leukemia (AML). COG AAML1031 studied the feasibility and efficacy of adding sorafenib, a multikinase tyrosine kinase inhibitor to standard chemotherapy and as single-agent maintenance therapy in this population.

MATERIALS AND METHODS

Patients were treated in three cohorts. The initial safety phase defined the maximum tolerated dose of sorafenib starting in induction 2. Cohorts 2 and 3 added sorafenib in induction and as single-agent maintenance. Clinical outcome analysis was limited to n = 72 patients in cohorts 2/3 and compared with n = 76 HAR FLT3/ITD+ AML patients who received identical chemotherapy without sorafenib. Sorafenib pharmacokinetics and plasma inhibitory activity were measured in a subset of patients.

RESULTS

The maximum tolerated dose of sorafenib was 200 mg/m2 once daily; dose-limiting toxicities included rash (n = 2; 1 grade 3 and 1 grade 2), grade 2 hand-foot syndrome, and grade 3 fever. Pharmacokinetics/plasma inhibitory activity data demonstrated that measured plasma concentrations were sufficient to inhibit phosphorylated FLT3. Although outcomes were superior with sorafenib in cohorts 2 and 3, patients treated with sorafenib also underwent hematopoietic stem-cell transplant more frequently than the comparator population. Multivariable analysis that accounted for both hematopoietic stem-cell transplant and favorable co-occurring mutations confirmed sorafenib's benefit. Specifically, risk of an event was approximately two-fold higher in HAR FLT3/ITD+ patients who did not receive sorafenib (event-free survival from study entry: hazard ratio [HR] 2.37, 95% CI, 1.45 to 3.88, P < .001, disease-free survival from complete remission: HR 2.28, 95% CI, 1.08 to 4.82, P = .032, relapse risk from complete remission: HR 3.03, 95% CI 1.31 to 7.04, P = .010).

CONCLUSION

Sorafenib can be safely added to conventional AML chemotherapy and may improve outcomes in pediatric HAR FLT3/ITD+ AML.

Abstract 3479: UBTF tandem duplications (UBTF-TD) in childhood AML: Enrichment in FLT3-ITD and association with clinical outcome

Childhood AML is an aggressive disease with high rates of failures and poor survival. We have demonstrated that the molecular landscape of AML in children is distinct, and co-occurrence of variants modulate outcomes. Recent discovery of tandem duplication (TD) of the UBTF gene in AML, with enrichment in FLT3-ITD has implicated yet another mutation whose cooperation with FLT3-ITD may modify outcome. Here, we provide a comprehensive evaluation of UBTF-TD in de novo AML and define its clinical implications within FLT3-ITD patients. Initial interrogation of transcriptome data from 1,158 children enrolled on COG AAML1031 identified 50 cases of UBTF-TD (4.3%). Overwhelming majority of UBTF-TD cases were observed in FLT3-ITD cases (77%), vs. that of 1.2% in those without FLT3-ITD (p&lt;0.001). Given extreme enrichment of UBTF-TD in FLT3-ITD, we inquired whether cooperation of UBTF-TD and FLT3-ITD creates a distinct clinical entity. To this end we screened diagnostic DNA from 400 FLT3-ITD patients treated on three consecutive CCG/COG trials (COG AAML1031, COG AAML0531, and CCG-2961) by PCR and fragment analysis. UBTF-TD was identified in 61 FLT3-ITD cases (15.3%).

The data presented here forth focuses on evaluation of implications of UBTF-TD in FLT3-ITD positive patients only. Within the FLT3-ITD patients, initial correlation of UBTF-TD with demographics, disease characteristics, and associated genomic variants was conducted. Patients with and without UBTF-TD had a similar median age at diagnosis (p=0.322), lower diagnostic WBC (p=0.010) and higher marrow blast % (p&lt;0.001). There was a stark paucity of cooperating variants that commonly co-occur with FLT3-ITD, with a single NPM1 mutation (1.6% vs. 29%, p&lt;0.001) and no NUP98 fusions (0% vs. 23%, p&lt;0.001). There was a significant enrichment of WT1 mutations, with 45% UBTF-TD patients with a WT1 mutation (FLT3-ITD/UBTF-TD/WT1), vs. 11% in UBTF-WT (p&lt;0.001). Trisomy 8 (Tri8) was seen in 15% of UBTF-TD. Patients with UBTF-TD had a lower CR rate (44% vs. 60%, p = 0.018), and Higher MRD rate (38% vs. 21%, p&lt;0.001). Patients with and without UBTF-TD had an EFS of 28% vs. 42% (p=0.047) with a corresponding OS of 40% and 57% (p=0.019). Given enrichment of WT1 mutations and Tri8 in patients with UBTF-TD, we studied the outcome UBTF-TD patients in the context of these two variants. FLT3-ITD/UBTF-TD/WT1 patients had a 5-year EFS of 17% vs. 38% for similar patients without WT1 mutations (p=0.0062). Patients with UBTF-TD with additional Tri8 had a similarly poor outcome with an EFS of 23% with a corresponding OS of 33%, providing a distinct high risk UBTF-TD cohort (+WT1 or Tri8), whereas the remaining UBTF-TD patients had a more favorable outcome with EFS and OS of 64% and 86%, respectively (p&lt;0.0001, and p&lt;0.0001). UBTF-TD is a novel genomic entity with high enrichment in patients with FLT3-ITD and a distinct clinical outcome driven by cooperating WT1 mutation and Tri8.

Citation Format: Leila Robinson, Amanda Leonti, Todd A. Alonzo, Yi-Cheng Wang, Michele S. Redell, Rhonda E. Ries, Jenny L. Smith, Tiffany A. Hylkema, Quy Le, E Anders Kolb, Richard Aplenc, Xiaotu Ma, Jeffrey Klco, Katherine Tarlock, Soheil Meshinchi. UBTF tandem duplications (UBTF-TD) in childhood AML: Enrichment in FLT3-ITD and association with clinical outcome [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3479.

Therapeutic Targeting of Mesothelin with Chimeric Antigen Receptor T Cells in Acute Myeloid Leukemia

PURPOSE

We previously identified mesothelin (MSLN) as highly expressed in a significant fraction of acute myeloid leukemia (AML) but entirely silent in normal hematopoiesis, providing a promising antigen for immunotherapeutic targeting that avoids hematopoietic toxicity. Given that T cells genetically modified to express chimeric antigen receptors (CAR) are effective at eradicating relapsed/refractory acute lymphocytic leukemia, we developed MSLN-directed CAR T cells for preclinical evaluation in AML.

EXPERIMENTAL DESIGN

The variable light (VL) and heavy (VH) sequences from the MSLN-targeting SS1P immunotoxin were used to construct the single-chain variable fragment of the standard CAR containing 41-BB costimulatory and CD3Zeta stimulatory domains. The preclinical efficacy of MSLN CAR T cells was evaluated against AML cell lines and patient samples expressing various levels of MSLN in vitro and in vivo.

RESULTS

We demonstrate that MSLN is expressed on the cell surface of AML blasts and leukemic stem cell-enriched CD34⁺CD38^- subset, but not on normal hematopoietic stem and progenitor cells (HSPC). We further establish that MSLN CAR T cells are highly effective in eliminating MSLN-positive AML cells in cell line- and patient-derived xenograft models. Importantly, MSLN CAR T cells can target and eradicate CD34⁺CD38^- cells without impacting the viability of normal HSPCs. Finally, we show that CAR T-cell functionality can be improved by inhibition of the ADAM17 metalloprotease that promotes shedding of MSLN.

CONCLUSIONS

These findings demonstrate that MSLN is a viable target for CAR T-cell therapy in AML and that inhibiting MSLN shedding is a promising approach to improve CAR T-cell efficacy.

CEBPA-bZip mutations are associated with favorable prognosis in de novo AML: a report from the Children's Oncology Group

Biallelic CEBPA mutations are associated with favorable outcomes in acute myeloid leukemia (AML). We evaluated the clinical and biologic implications of CEBPA-basic leucine zipper (CEBPA-bZip) mutations in children and young adults with newly diagnosed AML. CEBPA-bZip mutation status was determined in 2958 patients with AML enrolled on Children's Oncology Group trials (NCT00003790, NCT0007174, NCT00372593, NCT01379181). Next-generation sequencing (NGS) was performed in 1863 patients (107 with CEBPA mutations) to characterize the co-occurring mutations. CEBPA mutational status was correlated with disease characteristics and clinical outcomes. CEBPA-bZip mutations were identified in 160 (5.4%) of 2958 patients, with 132 (82.5%) harboring a second CEBPA mutation (CEBPA-double-mutated [CEBPA-dm]) and 28 (17.5%) had a single CEBPA-bZip only mutation. The clinical and laboratory features of the 2 CEBPA cohorts were very similar. Patients with CEBPA-dm and CEBPA-bZip experienced identical event-free survival (EFS) of 64% and similar overall survival (OS) of 81% and 89%, respectively (P = .259); this compared favorably to EFS of 46% and OS of 61% in patients with CEBPA-wild-type (CEBPA-WT) (both P < .001). Transcriptome analysis demonstrated similar expression profiles for patients with CEBPA-bZip and CEBPA-dm. Comprehensive NGS of patients with CEBPA mutations identified co-occurring CSF3R mutations in 13.1% of patients and GATA2 mutations in 21.5% of patients. Patients with dual CEBPA and CSF3R mutations had an EFS of 17% vs 63% for patients with CEBPA-mutant or CSF3R-WT (P < .001) with a corresponding relapse rate (RR) of 83% vs 22%, respectively (P < .001); GATA2 co-occurrence did not have an impact on outcome. CEBPA-bZip domain mutations are associated with favorable clinical outcomes, regardless of monoallelic or biallelic status. Co-occurring CSF3R and CEBPA mutations are associated with a high RR that nullifies the favorable prognostic impact of CEBPA mutations.

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

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Background: Outcomes for children with relapsed/refractory (R/R) AML and 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, cell growth and survival. In preclinical models, pevonedistat was synergistic with cytarabine (AraC) and azacitidine (aza). The combination of pevonedistat + aza in adults with AML demonstrated improved responses compared to either single agent. We evaluated the feasibility, toxicity and pharmacokinetics (PK) of pevonedistat in combination with aza, fludarabine, AraC (Aza-FLA) in children with R/R AML and MDS. Methods: Pevonedistat 20 mg/m2, IV days 1, 3, 5, the recommended adult dose, was administered in combination with aza (75 mg/m2, days 1-5), fludarabine (30 mg/m2, days 6-10), and AraC (2000 mg/m2, days 6-10). Intrathecal AraC was administered at the start of therapy and additional doses given to patients with CNS leukemia. If < 33% of the initial 6 enrolled patients experienced dose limiting toxicity (DLT) during cycle 1 the regimen would be considered tolerable and 6 additional patients could enroll to further assess tolerability and PK. Pevonedistat PK was determined during cycle 1 following doses 1 and 5. Response was evaluated after cycle 1. Results: A total of 12 patients were enrolled, median age was 13 years (range 1-21). All patients received prior chemotherapy, median number of prior regimens was 2 (range 1-5) and 3 (25%) patients had prior hematopoietic stem cell transplant. Diagnoses were AML NOS (n = 10, 83%), acute monocytic leukemia (n = 1), and therapy related AML (n = 1). One of the initial 6 patients had DLTs (hypertension, GGT elevation, and proteinuria); pevonedistat 20 mg/m2 + Aza-FLA was considered tolerable. Six additional patients were enrolled, two had DLTs (weight loss, hypoxia). Overall, 3/12 (25%) of patients experienced DLTs. As expected, using the intensive Aza-FLA backbone, myelosuppression, electrolyte abnormalities, and hepatic transaminase elevation were common. Day 1 PK parameters (n = 12, mean±SD) were: Cmax= 223±91 ng/mL, AUC0-24h= 892±216 ng/hr/mL, T1/2=4.3±1.2 hours, CL = 23.2±6.9 L/hr/m2. PK parameters were similar following doses 1 and 5, for patients < 12 (n = 6) and ≥ 12 (n = 6) years, and to adult PK profiles. Ten patients were evaluable for response. The overall response rate was 30% (95% CI: 7,75) with 3 patients achieving a CR with incomplete hematologic recovery (CRi). Conclusions: Pevonedistat 20 mg/m2 combinedwith Aza-FLA was tolerable in children with R/R AML. The toxicity of the regimen was similar to other intensive AML regimens. PK parameters were similar among the two age groups and were comparable to adults. Within the confines of a phase I study, there was limited anti-leukemic activity of the combination of pevonedistat +Aza-FLA in R/R AML. Clinical trial information: NCT03813147.

Matched Targeted Therapy for Pediatric Patients with Relapsed, Refractory, or High-Risk Leukemias: A Report from the LEAP Consortium

Despite a remarkable increase in the genomic profiling of cancer, integration of genomic discoveries into clinical care has lagged behind. We report the feasibility of rapid identification of targetable mutations in 153 pediatric patients with relapsed/refractory or high-risk leukemias enrolled on a prospective clinical trial conducted by the LEAP Consortium. Eighteen percent of patients had a high confidence Tier 1 or 2 recommendation. We describe clinical responses in the 14% of patients with relapsed/refractory leukemia who received the matched targeted therapy. Further, in order to inform future targeted therapy for patients, we validated variants of uncertain significance, performed ex vivo drug-sensitivity testing in patient leukemia samples, and identified new combinations of targeted therapies in cell lines and patient-derived xenograft models. These data and our collaborative approach should inform the design of future precision medicine trials. SIGNIFICANCE: Patients with relapsed/refractory leukemias face limited treatment options. Systematic integration of precision medicine efforts can inform therapy. We report the feasibility of identifying targetable mutations in children with leukemia and describe correlative biology studies validating therapeutic hypotheses and novel mutations.See related commentary by Bornhauser and Bourquin, p. 1322.This article is highlighted in the In This Issue feature, p. 1307.

Preemptive mitigation of CD19 CAR T-cell cytokine release syndrome without attenuation of antileukemic efficacy

Immunotherapy with the adoptive transfer of T cells redirected with CD19-specific chimeric antigen receptors (CARs) for B-lineage acute lymphoblastic leukemia (ALL) can salvage >80% of patients having relapsed/refractory disease. The therapeutic index of this emerging modality is attenuated by the occurrence of immunologic toxicity syndromes that occur upon CAR T-cell engraftment. Here, we report on the low incidence of severe cytokine release syndrome (CRS) in a subject treated with a CAR T-cell product composed of a defined ratio CD4:CD8 T-cell composition with a 4-1BB:zeta CAR targeting CD19 who also recieved early intervention treatment. We report that early intervention with tocilizumab and/or corticosteroids may reduce the frequency at which subjects transition from mild CRS to severe CRS. Although early intervention doubled the numbers of subjects dosed with tocilizumab and/or corticosteroids, there was no apparent detrimental effect on minimal residual disease-negative complete remission rates or subsequent persistence of functional CAR T cells compared with subjects who did not receive intervention. Moreover, early intervention therapy did not increase the proportion of subjects who experience neurotoxicity or place subjects at risk for infectious sequelae. These data support the contention that early intervention with tocilizumab and/or corticosteroids in subjects with early signs of CRS is without negative impact on the antitumor potency of CD19 CAR T cells. This intervention serves to enhance the therapeutic index in relapsed/refractory patients and provides the rationale to apply CAR T-cell therapy more broadly in ALL therapy. This trial was registered at www.clinicaltrials.gov as #NCT020284.

Functional Properties of KIT Mutations Are Associated with Differential Clinical Outcomes and Response to Targeted Therapeutics in CBF Acute Myeloid Leukemia

PURPOSE

KIT mutations (KIT ⁺) are common in core binding factor (CBF) AML and have been associated with varying prognostic significance. We sought to define the functional and clinical significance of distinct KIT mutations in CBF pediatric AML.

EXPERIMENTAL DESIGN

Following transfection of exon 17 (E17) and exon 8 (E8) mutations into HEK293 and Ba/F3 cells, KIT phosphorylation, cytokine-independent growth, and response to tyrosine kinase inhibitors (TKI) were evaluated. Clinical outcomes of patients treated on COG AAML0531 (NCT01407757), a phase III study of gemtuzumab ozogamicin (GO), were analyzed according to mutation status [KIT ⁺ vs. wild-type KIT (KIT ^-)] and mutation location (E8 vs. E17).

RESULTS

KIT mutations were detected in 63 of 205 patients (31%); 22 (35%) involved only E8, 32 (51%) only E17, 6 (10%) both exons, and 3 (5%) alternative exons. Functional studies demonstrated that E17, but not E8, mutations result in aberrant KIT phosphorylation and growth. TKI exposure significantly affected growth of E17, but not E8, transfected cells. Patients with KIT ⁺ CBF AML had overall survival similar to those with KIT ^- (78% vs. 81%, P = 0.905) but higher relapse rates (RR = 43% vs. 21%; P = 0.005). E17 KIT ⁺ outcomes were inferior to KIT ^- patients [disease-free survival (DFS), 51% vs. 73%, P = 0.027; RR = 21% vs. 46%, P = 0.007)], although gemtuzumab ozogamicin abrogated this negative prognostic impact. E8 mutations lacked significant prognostic effect, and GO failed to significantly improve outcome.

CONCLUSIONS

E17 mutations affect prognosis in CBF AML, as well as response to GO and TKIs; thus, clinical trials using both agents should be considered for KIT ⁺ patients.

Distinct age-associated molecular profiles in acute myeloid leukemia defined by comprehensive clinical genomic profiling

Large scale comprehensive genomic profiling (CGP) has led to an improved understanding of oncogenic mutations in acute myeloid leukemia (AML), as well as identification of alterations that can serve as targets for potential therapeutic intervention. We sought to gain insight into age-associated variants in AML through comparison of extensive DNA and RNA-based GP results from pediatric and adult AML. Sequencing of 932 AML specimens (179 pediatric (age 0-18), 753 adult (age ≥ 19)) from diagnostic, relapsed, and refractory times points was performed. Comprehensive DNA (405 genes) and RNA (265) sequencing to identify a variety of structural and short variants was performed. We found that structural variants were highly prevalent in the pediatric cohort compared to the adult cohort (57% vs. 30%; p < 0.001), with certain structural variants detected only in the pediatric cohort. Fusions were the most common structural variant and were highly prevalent in AML in very young children occurring in 68% of children < 2 years of age. We observed an inverse trend in the prevalence of fusions compared to the average number of mutations per patient. In contrast to pediatric AML, adult AML was marked by short variants and multiple mutations per patient. Mutations that were common in adult AML were much less common in the adolescent and young adult cohort and were rare or absent in the pediatric cohort. Clinical CGP demonstrates the biologic differences in pediatric vs. adult AML that have significant therapeutic impacts on prognosis, therapeutic allocation, disease monitoring, and the use of more targeted therapies.

Rapidly Progressive, Isolated Subretinal Leukemic Relapse: A Case Report

Purpose

The aim of this paper is to describe a case of relapsed pediatric acute lymphoblastic leukemia (ALL) presenting as a rapidly progressive subretinal infiltrate, as diagnosed by ultrasound-guided fine needle aspiration (FNA).

Methods

We conducted a clinical pathological retrospective chart review.

Results

Eleven months after documented remission of T-cell ALL while on maintenance therapy, this 17-year-old patient presented with acute open angle glaucoma in the right eye. B-scan ultrasonography suggested total retinal detachment. Eight weeks later, based on routine cerebrospinal fluid analysis, the patient was diagnosed with central nervous system relapse of T-cell ALL. Repeat B-scan 1 week later showed a new hyperechoic subretinal mass. FNA of the mass confirmed leukemic infiltrate. The involved eye was enucleated, demonstrating leukemic cells throughout the subretinal space, choroid, and the optic nerve. Following hematopoietic stem cell transplant, the patient continues to maintain bone marrow remission 5 months after enucleation without involvement in the opposite eye.

Conclusion

Retinal detachment in any patient with a history of leukemia should raise the possibility of relapse and may warrant aspiration/biopsy if other means of diagnosing relapse are inconclusive. Subretinal infiltrate may progress rapidly and prompt diagnosis is paramount to tailoring therapy and preserving vision.

Disease Characteristics and Prognostic Implications of Cell-Surface FLT3 Receptor (CD135) Expression in Pediatric Acute Myeloid Leukemia: A Report from the Children's Oncology Group

Purpose: The FLT3 cell-surface receptor tyrosine kinase (CD135) is expressed in a majority of both acute lymphoid leukemia (ALL) and myeloid leukemia (AML). However, the prognostic significance of CD135 expression in AML remains unclear. We therefore evaluated the association between FLT3 surface expression and disease characteristics and outcomes in pediatric patients with AML.Experimental Design: We analyzed FLT3 receptor expression on AML blasts by multi-dimensional flow cytometry and its association with disease characteristics, clinical outcomes, and FLT3 transcript level in 367 children with AML treated on the Children's Oncology Group trial AAML0531.Results: There was high variability in blast CD135 cell-surface expression across specimens. CD135 expression measured by flow cytometry was not correlated with FLT3 transcript expression determined by quantitative RT-PCR. Overall, CD135 expression was not significantly different for patients with FLT3/WT, FLT3/ITD, or FLT3/ALM (P = 0.25). High cell-surface CD135 expression was associated with FAB M5 subtype (P < 0.001), KMT2A rearrangements (P = 0.009), and inversely associated with inv(16)/t(16;16) (P < 0.001). Complete remission rate, overall survival, disease-free survival, and relapse rates were not significantly different between patients with low and high CD135 expression.Conclusions: FLT3 cell-surface expression did not vary by FLT3 mutational status, but high FLT3 expression was strongly associated with KMT2A rearrangements. Our study found that there was no prognostic significance of FLT3 cell surface expression in pediatric AML. Clin Cancer Res; 23(14); 3649-56. ©2017 AACR.

Gemtuzumab Ozogamicin Reduces Relapse Risk in FLT3/ITD Acute Myeloid Leukemia: A Report from the Children's Oncology Group

PURPOSE

Gemtuzumab ozogamicin (GO), a calicheamicin-conjugated mAb against CD33, has been used in the treatment of acute myeloid leukemia (AML). We evaluated the impact of the addition of GO to standard chemotherapy and hematopoietic stem cell transplant (HCT) in patients withFLT3/ITD.

EXPERIMENTAL DESIGN

We analyzed children withFLT3/ITD-positive AML (n= 183) treated on two consecutive Children's Oncology Group AML trials (NCT00070174andNCT00372593). Outcomes were assessed forFLT3/ITD patients receiving standard chemotherapy with or without GO (GO vs. No-GO, respectively), and the impact of consolidation HCT for high-riskFLT3/ITD patients [highFLT3/ITD allelic ratio (ITD-AR)].

RESULTS

For allFLT3/ITD patients, complete remission (CR) rates for the GO versus No-GO cohorts were identical (64% vs. 64%;P= 0.98). Relapse rate (RR) after initial CR was 37% for GO recipients versus 59% for No-GO recipients (P= 0.02), disease-free survival (DFS) was similar (47% vs. 41%;P= 0.45), with higher treatment-related mortality (TRM) in GO recipients (16% vs. 0%;P= 0.008). Among high-riskFLT3/ITD patients with high ITD-AR, those who received HCT in first CR with prior exposure to GO had a significant reduction in RR (15% vs. 53%;P= 0.007), with a corresponding DFS of 65% versus 40% (P= 0.08), and higher TRM (19% vs. 7%;P= 0.08).

CONCLUSIONS

CD33 targeting with HCT consolidation may be an important therapeutic strategy in high-riskFLT3/ITD AML and its efficacy and associated toxicity warrant further investigation.

Sorafenib treatment following hematopoietic stem cell transplant in pediatric FLT3/ITD acute myeloid leukemia

BACKGROUND

FLT3/ITD is associated with poor outcomes in adult and pediatric acute myeloid leukemia (AML). Allogeneic hematopoietic stem cell transplantation (HSCT) can improve cure rates, however relapse is still common. Recent studies demonstrate the activity of FLT3 inhibitors, including sorafenib, in targeting the underlying mutation.

PROCEDURE

We conducted a retrospective study of 15 pediatric patients with FLT3/ITD+ AML treated with sorafenib within 18 months after receiving HSCT. Sorafenib was administered either as prophylaxis in patients considered at very high risk for relapse (n = 6) or at the time of disease recurrence (n = 9).

RESULTS

Sorafenib was initiated at a median of 100 days post HSCT. Overall, 11/15 (73%) of patients experienced medically significant toxicities. Among patients who experienced toxicity, 6/11 (55%) received treatment at doses above what was later determined to be the maximum tolerated dose of sorafenib for pediatric leukemia. Importantly, sorafenib did not appear to exacerbate graft versus host disease. Our findings suggest that sorafenib may be of particular efficacy in patients with minimal residual disease (MRD); all patients who received sorafenib for MRD immediately prior to transplant or with emergence post-HSCT are alive and remain in complete remission at a median of 48 months post HSCT.

CONCLUSIONS

Our case series suggests that sorafenib administration is feasible and tolerable in pediatric FLT3/ITD+ AML patients early post HSCT. Ongoing prospective controlled studies are needed to further define the dosing of sorafenib in the post-HSCT period and to determine the optimal context for this treatment approach.

Elevated fluoride levels and periostitis in pediatric hematopoietic stem cell transplant recipients receiving long-term voriconazole

Azole therapy is widely utilized in hematopoietic stem cell transplant (HCT) recipients for the treatment of aspergillus. Complications of voriconazole treatment related to its elevated fluoride content have been described in adults, including reports of symptomatic skeletal fluorosis. We review fluoride levels, clinical, and laboratory data in five pediatric HCT recipients on long-term voriconazole therapy, all found to have elevated serum fluoride levels. Two patients had toxic fluoride levels, one infant had symptoms of significant pain with movement and radiographs confirmed skeletal fluorosis. Monitoring fluoride levels in children, especially with skeletal symptoms, should be considered in patients on long-term voriconazole.

Pediatric acute myeloid leukemia: biology and therapeutic implications of genomic variants

Acute myeloid leukemia (AML) is a molecularly heterogeneous disease and age-associated molecular alterations result in younger children harboring a distinct signature from older children and adolescents. Pediatric AML has a genetic and epigenetic profile with significant differences compared to adult AML. Somatic and epigenetic alterations contribute to myeloid leukemogenesis and can evolve from diagnosis to relapse. Cytogenetic alterations, somatic mutations and response to induction therapy are important in informing risk stratification and appropriate therapy allocation. Next-generation sequencing technologies are providing novel insights into the biology of AML and have the ability to identify potential targets for therapeutic intervention.

Acute myeloid leukaemia (AML) with t(6;9)(p23;q34) is associated with poor outcome in childhood AML regardless of FLT3-ITD status: a report from the Children's Oncology Group

Acute myeloid leukaemia (AML) with t(6;9)(p23;q34) is a rare subtype associated with FLT3-internal tandem duplication (ITD) and poor outcomes. The clinical outcomes of paediatric patients with t(6;9) with and without FLT3-ITD treated on six consecutive cooperative trails were evaluated. In contrast to patients without t(6;9), those with t(6;9) had a significantly lower complete remission rate, higher relapse rate (RR), and poor overall survival (OS). Within t(6;9) patients, those with and without FLT3-ITD had an OS of 40% and 27% respectively (P > 0·9), demonstrating that t(6;9) is a high-risk cytogenetic feature in paediatric AML and its clinical impact is independent of the presence of FLT3-ITD.

Immunogene therapy as a treatment for malignant brain tumors in young mice

OBJECT

New and innovative forms of effective treatments for malignant brain tumors in children are urgently needed. The authors have previously shown that intracerebral injection into the tumor bed of allogeneic fibroblasts genetically engineered to secrete interleukin-2 (IL-2) results in prolongation of survival and an antitumor immunocytotoxic response in adult mice that harbor intracerebral gliomas. The first goal of this study was to determine if malignant gliomas (GI261) could be treated in mice (C57BL/6) in the pediatric age group (weanlings [2-3 weeks old] and adolescents [3-4 weeks old]). The second goal was to determine the effectiveness of using IL-2-secreting allogeneic fibroblasts as a protective vaccine to prevent the development of intracerebral gliomas in these young mice.

METHODS

Using GI261 glioma cells derived from a spontaneously arising glioma in C57BL/6 immunocompetent mice, animals 2 to 4 weeks of age received an intracranial injection of 5 x 10(4) tumor cells into the right frontal lobe through a bur hole. The treatment vaccine consisted of 10(6) allogeneic IL-2-secreting fibroblasts, given at the time of tumor injection (treatment experiments) or at three weekly intervals prior to tumor injection (protection experiments). Control groups received either medium or nonsecreting allogeneic fibroblasts. The effects of this treatment on survival and long-term immunity were investigated. The results demonstrate a significant prolongation of survival in animals harboring intracerebral gliomas that were treated with intracerebral injections of IL-2-secreting allogeneic fibroblasts (p < 0.05). Morbidity and mortality rates did not increase as a result of intracerebral immunization. Compared with naive controls, long-term survivors demonstrated immune memory, as evidenced by prolongation of survival when they were rechallenged with tumor cells. The results of the protection experiment demonstrate a significant delay (p < 0.005) in the development of gliomas in the animals pretreated with either allogeneic nonsecreting or allogeneic IL-2-secreting fibroblasts prior to the introduction of tumor cells. In addition, in 78% of these animals a tumor did not develop when rechallenged.

CONCLUSIONS

These results demonstrate the efficacy and safety of using intratumoral injection of IL-2-secreting allogeneic fibroblasts as a treatment or protective vaccine in young mice. It is hoped that these preclinical studies will lead to a clinical trial for the treatment of malignant brain tumors in children.

Application of interleukin-2-secreting syngeneic/allogeneic fibroblasts in the treatment of primary and metastatic brain tumors

We found previously that mice injected intracerebrally (i.c.) with a mixture of malignant cells and allogeneic fibroblasts genetically engineered to secrete interleukin-2 (IL-2) survived longer than mice in various control groups. The primary goal of this study was to determine if an established i.c. glioma (Gl261) or breast carcinoma (SB-5b) could be treated by injection of IL-2-secreting allogeneic fibroblasts into the tumor region. As an additional objective, these results were compared with the effectiveness of injecting IL-2-secreting allogeneic fibroblasts prior to the introduction of the tumor cells as a means of preventing the development of an i.c. glioma or breast carcinoma. The results demonstrated that treatment of mice bearing an established i.c. glioma or breast carcinoma with IL-2-secreting allogeneic fibroblasts resulted in a prolonged survival. Furthermore, the results demonstrate a significant delay (P<.005) in the development of glioma in the animals treated with either allogeneic nonsecreting or IL-2-secreting fibroblasts prior to introduction of tumor cells. In addition, 50% of the animals pretreated with IL-2-secreting allogeneic fibroblasts injected subsequently with Gl261 glioma cells did not develop a tumor, whereas all of the animals injected with glioma cells alone and 92% of those treated with nonsecreting fibroblasts eventually died. Evidence also exists that long-term immunity was established in the treated animals because there was a significant prolongation of survival in comparison to naïve controls (P<.01) for those animals without evidence of glioma that previously had been immunized with treatment cells when challenged again with tumor cells. In a parallel experiment, 62% of the animals pretreated with nonsecreting allogeneic fibroblasts and 75% of the animals pretreated with allogeneic IL-2-secreting fibroblasts subsequently injected with SB-5b breast carcinoma cells did not develop tumors. The results indicate that IL-2-secreting allogeneic fibroblasts can be effective in the treatment of an established brain tumor. These data also suggest that i.c. injection of allogeneic IL-2-secreting fibroblasts is effective in prevention of the development of a brain tumor when the fibroblasts are introduced into the same site where the tumor is subsequently injected.