Faculty Bibliography

PEGylated asparaginase (pegaspargase) can be administered via intramuscular (IM) injection or intravenous (IV) infusion with a hypersensitivity reaction (HSR) incidence ranging 3-41%. We evaluated grade >/=3 HSRs when given IM vs. IV on six Children's Oncology Group (COG) leukemia trials (2003-2015) to determine differences in HSR rates. 54,280 doses were administered to 16,534 patients. Considering all doses of pegaspargase during induction, consolidation, and delayed intensification, grade >/=3 HSR rate with IM injection was 5.4% (n = 482/8981) compared to 3.2% for IV (n = 245/7553) (p < .0001). If only the second and third doses of pegaspargase were analyzed, where the majority of grade >/=3 HSRs occur, the rate following IM injection was 10.1% (n = 459/4534) compared to 5.0% (n = 222/4443) for IV (p < .0001). On standardized treatment protocols conducted by the COG during 2003-2015, grade >/=3 HSR rates to pegaspargase occurred less frequently with IV infusion than IM injection.

Minimal residual disease (MRD) after initial therapy is integral to risk stratification in B-precursor and T-precursor acute lymphoblastic leukemia (B-ALL, T-ALL). Although MRD determines depth of remission, remission remains defined by morphology. We determined the outcomes of children with discordant assessments of remission by morphology vs. flow cytometry using patients age 1-30.99 years enrolled on Children's Oncology Group ALL trials who underwent bone marrow assessment at the end of induction (N = 9350). Morphologic response was assessed locally as M1 (<5% lymphoblasts; remission), M2 (5-25%), or M3 (>25%). MRD was centrally measured by flow cytometry. Overall, 19.8% of patients with M2/M3 morphology had MRD < 5%. M1 with MRD ≥ 5% was less common in B-ALL (0.9%) than T-ALL (6.9%; p < 0.0001). In B-ALL, M1/MRD ≥ 5% was associated with superior 5-year event-free survival (EFS) than M2/MRD ≥ 5% (59.1% ± 6.5% vs. 39.1% ± 7.9%; p = 0.009), but was inferior to M1/MRD < 5% (87.1% ± 0.4%; p < 0.0001). MRD levels were higher in M2/MRD ≥ 5% than M1/MRD ≥ 5% patients. In T-ALL, EFS was not significantly different between M1/MRD ≥ 5% and M2/MRD ≥ 5%. Patients with morphologic remission but MRD ≥ 5% have outcomes similar to those who fail to achieve morphological remission, and significantly inferior to those with M1 marrows and concordant MRD, suggesting that flow cytometry should augment the definition of remission in ALL.

Activating mutations in NT5C2, a gene encoding cytosolic purine 5'-nucleotidase (cN-II), confer chemoresistance in relapsed acute lymphoblastic leukemia. Here we show that all mutants became independent of allosteric effects of ATP and thus constitutively active. Structural mapping of mutations described in patients demonstrates that 90% of leukemia-specific allelles directly affect two regulatory hotspots within the cN-II molecule-the helix A region: residues 355-365, and the intersubunit interface: helix B (232-242) and flexible interhelical loop L (400-418). Furthermore, analysis of hetero-oligomeric complexes combining wild-type (WT) and mutant subunits showed that the activation is transmitted from the mutated to the WT subunit. This intersubunit interaction forms structural basis of hyperactive NT5C2 in drug-resistant leukemia in which heterozygous NT5C2 mutation gave rise to hetero-tetramer mutant and WT proteins. This enabled us to define criteria to aid the prediction of NT5C2 drug resistance mutations in leukemia.

Survival of children with relapsed acute lymphoblastic leukemia is poor and understanding mechanisms underlying resistance is essential in developing new therapy. Relapse-specific heterozygous deletions in MSH6, a crucial part of DNA Mismatch Repair, are frequently detected. Our aim was to determine whether MSH6 deletion results in a hypermutator phenotype associated with generation of secondary mutations involved in drug resistance or leads to a failure to initiate apoptosis directly in response to chemotherapeutic agents. We knocked down MSH6 in mismatch repair proficient cell lines (697 and UOCB1) and showed significant increases in IC50s to 6-Thioguanine & 6-Mercaptopurine (697: 26- and 9-fold; UOCB1: 5- and 8-fold) in vitro, as well as increased resistance to 6-Mercaptopurine treatment in vivo. No shift in IC50 was observed in deficient cells (Reh & RS4;11). 697 MSH6 knockdown resulted in increased DNA thioguanine nucleotide levels compared to non-targeted cells (3,070 versus 1,722 fmol/mg DNA) with no difference observed in mismatch repair deficient cells. Loss of MSH6 did not give rise to microsatellite instability in cells lines or clinical samples nor did it significantly increase mutation rate, but rather resulted in a defect in cell cycle arrest upon thiopurine exposure. MSH6 knockdown cells showed minimal activation of checkpoint regulator CHK1, ɣH2AX (DNA damage marker) and p53 levels upon treatment with thiopurines, consistent with intrinsic chemoresistance due to failure to recognize thioguanine nucleotide mismatching and initiate mismatch repair. Aberrant MSH6 adds to the list of alterations/mutations associated with acquired resistance to purine analogues emphasizing the importance of thiopurine therapy.

Early response to induction chemotherapy is an important prognostic factor in B lymphoblastic leukemia (B-ALL). Here, we compare high throughput sequencing (HTS) of IGH and TRG genes versus flow cytometry (FC) for measurable residual disease (MRD) detection at the end of induction chemotherapy in pediatric patients with newly diagnosed B-ALL. 619 paired pretreatment and end of induction bone marrow samples from Children's Oncology Group (COG) studies AALL0331 (clinicaltrials.gov NCT00103285) (standard-risk; SR with MRD by FC at any level) and AALL0232 (clinicaltrials.gov NCT00075725) (high-risk; HR with day 29 MRD <0.1% by FC) were evaluated by HTS and FC for Event-free (EFS) and Overall Survival (OS). HTS and FC showed similar 5-year EFS and OS for MRD positive and negative patients using an MRD threshold of 0.01%. However, there was a high discordant rate with HTS identifying 55 (38.7%) more patients MRD positive at this threshold. These discrepant patients have worse outcomes than FC MRD negative patients. Additionally, the increased analytic sensitivity of HTS permitted identification of 19.9% of SR patients without MRD at any detectable level who had excellent 5-year EFS (98.1%) and OS (100%). The higher analytic sensitivity and lower false negative rate of HTS improves upon FC for measurable residual disease detection in pediatric B lymphoblastic leukemia by identifying a novel subset of patients at end of induction who are essentially cured using current chemotherapy and identifying MRD at 0.01% in up to one-third of patients who are missed at the same threshold by FC.

BACKGROUND:Children, adolescents, and young adults with very high-risk (VHR) B acute lymphoblastic leukemia (B-ALL) have poor outcomes, and novel therapies are needed for this subgroup. The AALL1131 study evaluated postinduction therapy using cyclophosphamide (CPM), etoposide (ETOP), and clofarabine (CLOF) for patients with VHR B-ALL. METHODS:Patients who were 1 to 30 years old and had VHR B-ALL received modified Berlin-Frankfurt-Münster therapy after induction and were randomized to 1) CPM, cytarabine, mercaptopurine, vincristine (VCR), and pegaspargase (control arm), 2) CPM, ETOP, VCR, and pegaspargase (experimental arm 1), or 3) CPM, ETOP, CLOF (30 mg/m2 /d × 5), VCR, and pegaspargase (experimental arm 2) during the second half of consolidation and delayed intensification. RESULTS:The rates of grade 4/5 infections and grade 3/4 pancreatitis were significantly increased in experimental arm 2. The dose of CLOF was, therefore, reduced to 20 mg/m2 /d × 5, and myeloid growth factor was required after CLOF administration. Despite these changes, 4 of 39 patients (10.3%) developed grade 4 infections, with 1 of these patients developing a grade 5 acute kidney injury attributed to CLOF, whereas only 1 of 46 patients (2.2%) in experimental arm 1 developed grade 4 infections, and there were no grade 4/5 infections in the control arm (n = 20). Four patients in experimental arm 2 had prolonged cytopenias for >60 days, whereas none did in the control arm or experimental arm 1. Counts failed to recover for 2 of these patients, one having a grade 5 acute kidney injury and the other removed from protocol therapy; both events occurred 92 days after the start of consolidation part 2. CONCLUSIONS:In AALL1131, CLOF, administered with CPM and ETOP, was associated with unacceptable toxicity. Cancer 2017. © 2017 American Cancer Society.

As a consequence of acquired or intrinsic disease resistance, the prognosis for patients with relapsed or refractory T-cell acute lymphoblastic leukemia (T-ALL) is dismal. Novel, less toxic drugs are clearly needed. One of the most promising emerging therapeutic strategies for cancer treatment is targeted immunotherapy. Immune therapies have improved outcomes for patients with other hematologic malignancies including B-ALL, however no immune therapy has been successfully developed for T-ALL. We hypothesize targeting CD38 will be effective against T-ALL. We demonstrate that blasts from patients with T-ALL have robust surface CD38 surface expression and that this expression remains stable after exposure to multi-agent chemotherapy. CD38 is expressed at very low levels on normal lymphoid and myeloid cells and on a few tissues of non-hematopoietic origin, suggesting that CD38 may be an ideal target. Daratumumab is a human IgG1κ monoclonal antibody that binds CD38, and has been demonstrated to be safe and effective in patients with refractory multiple myeloma (MM). We tested daratumumab in a large panel of T-ALL patient-derived xenografts (PDX) and found striking efficacy in 14 of 15 different PDX. These data suggest that daratumumab is a promising novel therapy for pediatric T-ALL patients.

Purpose Germline TP53 variation is the genetic basis of Li-Fraumeni syndrome, a highly penetrant cancer predisposition condition. Recent reports of germline TP53 variants in childhood hypodiploid acute lymphoblastic leukemia (ALL) suggest that this type of leukemia is another manifestation of Li-Fraumeni syndrome; however, the pattern, prevalence, and clinical relevance of TP53 variants in childhood ALL remain unknown. Patients and Methods Targeted sequencing of TP53 coding regions was performed in 3,801 children from the Children's Oncology Group frontline ALL clinical trials, AALL0232 and P9900. TP53 variant pathogenicity was evaluated according to experimentally determined transcriptional activity, in silico prediction of damaging effects, and prevalence in non-ALL control populations. TP53 variants were analyzed for their association with ALL presenting features and treatment outcomes. Results We identified 49 unique nonsilent rare TP53 coding variants in 77 (2.0%) of 3,801 patients sequenced, of which 22 variants were classified as pathogenic. TP53 pathogenic variants were significantly over-represented in ALL compared with non-ALL controls (odds ratio, 5.2; P < .001). Children with TP53 pathogenic variants were significantly older at ALL diagnosis (median age, 15.5 years v 7.3 years; P < .001) and were more likely to have hypodiploid ALL (65.4% v 1.2%; P < .001). Carrying germline TP53 pathogenic variants was associated with inferior event-free survival and overall survival (hazard ratio, 4.2 and 3.9; P < .001 and .001, respectively). In particular, children with TP53 pathogenic variants were at a dramatically higher risk of second cancers than those without pathogenic variants, with 5-year cumulative incidence of 25.1% and 0.7% ( P < .001), respectively. Conclusion Loss-of-function germline TP53 variants predispose children to ALL and to adverse treatment outcomes with ALL therapy, particularly the risk of second malignant neoplasms.

BACKGROUND: Children with average-risk acute lymphoblastic leukemia (AR-ALL) face many challenges that can adversely affect their quality of life (QOL). However, to the authors' knowledge, patterns and predictors of QOL impairment during therapy have not been well characterized to date. METHODS: Patients with AR-ALL who were enrolled on the Children's Oncology Group AALL0932 trial were offered participation in this prospective cohort study if they were aged >/=4 years at the time of diagnosis and had an English-speaking parent. At approximately 2 months, 8 months, 17 months, 26 months, and 38 months (boys only) after diagnosis, parents completed the Pediatric Quality of Life Inventory Generic Core Scales Version 4.0 (PedsQL4.0) and McMaster Family Assessment Device instruments for QOL (physical, emotional, and social functioning) and family functioning, respectively. The proportions of individuals scoring in the impaired range (2 standard deviations below the population mean) were calculated at each time point. Longitudinal impairment patterns and predictors were examined. RESULTS: A total of 594 participants with AR-ALL were diagnosed at a mean age of 6.0 years (standard deviation, 1.6 years). At 2 months, a substantial proportion of participants had impaired scores for physical (36.5%; 95% confidence interval [95% CI], 32.3%-40.8%) and emotional (26.2%; 95% CI, 22.5%-30.2%) functioning compared with population norms of 2.3%. These elevations persisted at 26 months. Emotional impairment at 2 months (odds ratio, 3.4; 95% CI, 1.5-7.7) was found to significantly predict emotional impairment at 26 months. In repeated measures analysis with multivariate modeling, unhealthy family functioning (odds ratio, 1.5; 95% CI, 1.1-2.1) significantly predicted emotional impairment controlling for age and sex. QOL outcomes were similar between sexes at the end of therapy (26 months for girls and 38 months for boys). CONCLUSIONS: Many children with AR-ALL experience physical and emotional functioning impairment that begins early in treatment and persists. Early screening may identify high-risk patients who might benefit from family-based interventions. Cancer 2017. (c) 2017 American Cancer Society.