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Glucocorticoids (GCs) are a mainstay of contemporary, multidrug chemotherapy in the treatment of childhood acute lymphoblastic leukemia (ALL), and resistance to GCs remains a major clinical concern. Resistance to GCs is predictive of ALL relapse and poor clinical outcome, and therefore represents a major hurdle limiting further improvements in survival rates. While advances have been made in identifying genes implicated in GC resistance, there remains an insufficient understanding of the impact of cis-regulatory disruptions in resistance. To address this, we mapped the gene regulatory response to GCs in two ALL cell lines using functional genomics and high-throughput reporter assays and identified thousands of GC-responsive changes to chromatin state, including the formation of over 250 GC-responsive super-enhancers and a depletion of AP-1 bound cis-regulatory elements implicated in cell proliferation and anti-apoptotic processes. By integrating our GC response maps with genetic and epigenetic datasets in primary ALL cells from patients, we further uncovered cis-regulatory disruptions at GC-responsive genes that impact GC resistance in childhood ALL. Overall, these data indicate that GCs initiate pervasive effects on the leukemia epigenome, and that alterations to the GC gene regulatory network contribute to GC resistance.

Understanding the genomic and epigenetic mechanisms of drug resistance in pediatric acute lymphoblastic leukemia (ALL) is critical for further improvements in treatment outcomes. The role of transcriptomic response in conferring resistance to l-asparaginase (LASP) is poorly understood beyond asparagine synthetase (ASNS). We defined reproducible LASP response genes in LASP-resistant and LASP-sensitive ALL cell lines as well as primary leukemia samples from newly diagnosed patients. Defining target genes of the amino acid stress response-related transcription factor activating transcription factor 4 (ATF4) in ALL cell lines using chromatin immunoprecipitation sequencing (ChIP-seq) revealed 45% of genes that changed expression after LASP treatment were direct targets of the ATF4 transcription factor, and 34% of these genes harbored LASP-responsive ATF4 promoter binding events. SLC7A11 was found to be a response gene in cell lines and patient samples as well as a direct target of ATF4. SLC7A11 was also one of only 2.4% of LASP response genes with basal level gene expression that also correlated with LASP ex vivo resistance in primary leukemia cells. Experiments using chemical inhibition of SLC7A11 with sulfasalazine, gene overexpression, and partial gene knockout recapitulated LASP resistance or sensitivity in ALL cell lines. These findings show the importance of assessing changes in gene expression following treatment with an antileukemic agent for its association with drug resistance and highlight that many response genes may not differ in their basal expression in drug-resistant leukemia cells.

Although acute lymphoblastic leukemia (ALL) is the most common childhood cancer, there is limited understanding of the contribution of inherited genetic variation on inter-individual differences in chemotherapy response. Defining genetic factors impacting therapy failure can help better predict response and identify drug resistance mechanisms. We therefore mapped inherited noncoding variants associated with chemotherapeutic drug resistance and/or treatment outcome to ALLcis-regulatory elements and investigated their gene regulatory potential and genomic connectivity using massively parallel reporter assays and promoter capture Hi-C, respectively. We identified 53 variants with reproducible allele-specific effects on transcription and high-confidence gene targets. Subsequent functional interrogation of the top variant (rs1247117) determined that it disrupted a PU.1 consensus motif and PU.1 binding affinity. Importantly, deletion of the genomic interval containing rs1247117 sensitized ALL cells to vincristine. Together, these data demonstrate that noncoding regulatory variation associated with diverse pharmacological traits harbor significant effects on allele-specific transcriptional activity and impact sensitivity to chemotherapeutic agents in ALL.

FcRn mediates recycling and transcytosis of IgG and albumin in various cell types. The MHC-class-I-like protein of the FcRn heterodimer is encoded by FCGRT. Few determinants of variable FCGRT expression in humans have been identified so far. In this study, we investigated the presence of DNA methylation in regulatory regions of FCGRT in samples of human liver and myocardium tissue, and we examined the impact of FCGRT methylation on FcRn expression in model cell lines. Quantitative DNA methylation analysis of the FCGRT locus revealed differentially methylated regions in DNA from liver and myocardium. Methylation status in individual CpG sites correlated with FCGRT mRNA expression. Data from model cell lines suggest that differential methylation in the −1058 to −587 bp regulatory region of FCGRT contributes to FcRn expression. Chromatin immunoprecipitation assays indicate that CpG site methylation impacts the binding of the methylation sensitive transcription factors Zbtb7a and Sp1. This study provides a foundation to further define the contribution of epigenetic factors during the control of FcRn expression and IgG traffic in human tissues.

Acute lymphoblastic leukemia (ALL) is a hematopoietic malignancy comprised of molecular subtypes largely characterized by aneuploidy or recurring chromosomal rearrangements. Despite extensive information on the ALL transcriptome and methylome, there is limited understanding of the ALL chromatin landscape. We therefore mapped accessible chromatin in 24 primary ALL cell biospecimens comprising three common molecular subtypes (DUX4/ERG, ETV6-RUNX1 and hyperdiploid) from patients treated at St. Jude Children's Research Hospital. Our findings highlight extensive chromatin reprogramming in ALL, including the identification ALL subtype-specific chromatin landscapes that are additionally modulated by genetic variation. Chromatin accessibility differences between ALL and normal B-cells implicate the activation of B-cell repressed chromatin domains and detail the disruption of normal B-cell development in ALL. Among ALL subtypes, we uncovered roles for basic helix-loop-helix, homeodomain and activator protein 1 transcription factors in promoting subtype-specific chromatin accessibility and distinct gene regulatory networks. In addition to chromatin subtype-specificity, we further identified over 3500 DNA sequence variants that alter the ALL chromatin landscape and contribute to inter-individual variability in chromatin accessibility. Collectively, our data suggest that subtype-specific chromatin landscapes and gene regulatory networks impact ALL biology and contribute to transcriptomic differences among ALL subtypes.

Acute lymphoblastic leukemia (ALL) is the most prevalent childhood cancer and despite improved survival rates, relapsed ALL is still among the most common causes of cancer death in children. Although changes in the expression of specific genes have been linked to chemotherapeutic resistance, relatively little is understood of the pharmacogenomic impact of the noncoding, cis-regulatory landscape governing gene regulation. Glucocorticoids (GCs; i.e. steroids) are a mainstay of contemporary, multi-drug chemotherapy in ALL, and GC resistance is predictive of both relapse and poor clinical outcome in ALL. Because GCs function through activation of glucocorticoid receptor (GR), a nuclear receptor transcription factor that interacts directly with cis-regulatory elements, unveiling the glucocorticoid gene regulatory network (GC-GRN) in leukemia cells is crucial to understanding not only the biological mechanism of apoptosis, but also illuminating gene regulatory mechanisms contributing to GC resistance. To test the hypothesis that alterations to the GC-GRN are important contributors to steroid resistance in ALL, we comprehensively mapped cellular responses to GCs in human ALL cell lines using >100 independent functional genomic datasets. This comprehensive approach uncovered thousands of genes and cis-regulatory elements that were responsive to GCs, and further identified >38,000 high-confidence glucocorticoid response elements (GREs) in the ALL genome. A closer examination of these data revealed GR binding profiles that were consistent with the long-range flexible billboard model of gene regulation. By further integrating our results with genetic and epigenetic data in primary ALL cells from patients enrolled on St. Jude clinical trials, we identified 45 DNA sequence variants associated with ex vivo GC resistance that map to GREs and functionally validated an associated variant within the TLE1 gene locus. We also uncovered 1929 accessible chromatin sites (FDR10,000 sgRNAs targeting >1000 GR binding events at putative GC-resistance accessible chromatin sites identified a subset of GR binding sites implicated in GC resistance. Overall, these data indicate that GCs initiate pervasive, genome-wide effects on the leukemia epigenome and transcriptome, and that genetic and epigenetic alterations to GREs are mechanisms contributing to GC resistance in childhood ALL. Disclosures Pui: Adaptive Biotechnologies: Membership on an entity's Board of Directors or advisory committees; Novartis: Other: Data Monitoring Committee. Evans: Princess Máxima Center for Pediatric Oncology, Scientific Advisory Board, Chair: Membership on an entity's Board of Directors or advisory committees; BioSkryb, Inc.: Membership on an entity's Board of Directors or advisory committees; St. Jude Children's Research Hospital, Emeritus Member (began Jan 2021): Ended employment in the past 24 months.

Understanding the genomic and epigenetic mechanisms of drug resistance in pediatric acute lymphoblastic leukemia (ALL) is critical for further improvements in treatment outcome. The role of transcriptomic response in conferring resistance to l-asparaginase (LASP) is poorly understood, beyond asparagine synthetase (ASNS). We defined reproducible LASP response genes in LASP resistant and sensitive ALL cell lines (n = 7) as well as primary leukemia samples from newly diagnosed patients. We identified 2219 response genes (absolute log 2FC > 1.5, FDR p-value Disclosures Stock: Pfizer: Consultancy, Honoraria, Research Funding; amgen: Honoraria; agios: Honoraria; jazz: Honoraria; kura: Honoraria; kite: Honoraria; morphosys: Honoraria; servier: Honoraria; syndax: Consultancy, Honoraria; Pluristeem: Consultancy, Honoraria. Mullighan: Amgen: Current equity holder in publicly-traded company; Illumina: Membership on an entity's Board of Directors or advisory committees; AbbVie: Research Funding; Pfizer: Research Funding. Pui: Adaptive Biotechnologies: Membership on an entity's Board of Directors or advisory committees; Novartis: Other: Data Monitoring Committee. Evans: Princess Máxima Center for Pediatric Oncology, Scientific Advisory Board, Chair: Membership on an entity's Board of Directors or advisory committees; BioSkryb, Inc.: Membership on an entity's Board of Directors or advisory committees; St. Jude Children's Research Hospital, Emeritus Member (began Jan 2021): Ended employment in the past 24 months.

FCGRT encodes the alpha-chain component of the neonatal Fc receptor (FcRn). FcRn is critical for the trafficking of endogenous and exogenous IgG molecules and albumin in various tissues. Few regulators of FcRn expression have been identified. We investigated the epigenetic regulation of FcRn by two microRNAs (hsa-miR-3181 and hsa-miR-3136-3p) acting on FCGRT. The binding of candidate microRNAs to the 3′-untranslated region of FCGRT was evaluated using luciferase reporter constructs in CHO cells. The effect of microRNAs on FCGRT mRNA and FcRn protein expression was evaluated using specific microRNA mimics and inhibitor transfections in A549, HEK293 and HepG2 cells. Hsa-miR-3181 mimic reduced luciferase reporter activity by 70.1% (10 nM, P

The intracardiac synthesis of anthracycline alcohol metabolites (e.g., daunorubicinol) contributes to the pathogenesis of anthracycline-related cardiotoxicity. Cancer patients with Down syndrome (DS) are at increased risk for anthracycline-related cardiotoxicity. We profiled the expression of anthracycline metabolizing enzymes in hearts from donors with- and without- DS.Cardiac expression of CBR1, CBR3, AKR1A1, AKR1C3 and AKR7A2 was examined by quantitative real time PCR, quantitative immunoblotting, and enzyme activity assays using daunorubicin. The CBR1 polymorphism rs9024 was investigated by allelic discrimination with fluorescent probes. The contribution of CBRs/AKRs proteins to daunorubicin reductase activity was examined by multiple linear regression.CBR1 was the most abundant transcript (average relative expression; DS: 81%, non-DS: 58%), and AKR7A2 was the most abundant protein (average relative expression; DS: 38%, non-DS: 35%). Positive associations between cardiac CBR1 protein levels and daunorubicin reductase activity were found for samples from donors with- and without- DS. Regression analysis suggests that sex, CBR1, AKR1A1, and AKR7A2 protein levels were significant contributors to cardiac daunorubicin reductase activity. CBR1 rs9024 genotype status impacts on cardiac CBR1 expression in non-DS hearts.CBR1, AKR1A1, and AKR7A2 protein levels point to be important determinants for predicting the synthesis of cardiotoxic daunorubicinol in heart.

The clinical use of anthracyclines to treat various canine cancers is limited by the development of cardiotoxicity. The intra-cardiac synthesis of anthracycline C-13 alcohol metabolites (e.g. daunorubicinol) contributes to the development of cardiotoxicity. Canine carbonyl reductase 1 (cbr1) catalyzes the reduction of daunorubicin into daunorubicinol. Recent mapping of the cbr1 locus by sequencing DNA samples from dogs from various breeds revealed a cluster of conserved motifs for the transcription factor Sp1 in the putative promoter region of cbr1. We hypothesized that the variable number of Sp1 motifs could impact the transcription of canine cbr1. In this study, we report the functional characterization of the canine cbr1 promoter. Experiments with reporter constructs and chromatin immunoprecipitation show that cbr1 transcription depends on the binding of Sp1 to the proximal promoter. Site-directed mutagenesis experiments suggest that the variable number of Sp1 motifs impacts the transcription of canine cbr1. Inhibition of Sp1-DNA binding decreased canine cbr1 mRNA levels by 54% in comparison to controls, and also decreased enzymatic carbonyl reductase activity for the substrates daunorubicin (16%) and menadione (23%). The transactivation of Sp1 increased the expression of cbr1 mRNA (67%), and increased carbonyl reductase activity for daunorubicin (35%) and menadione (27%). These data suggest that the variable number of Sp1 motifs in the canine cbr1 promoter may impact the pharmacodynamics of anthracyclines in canine cancer patients.

The anticancer anthracyclines doxorubicin and daunorubicin are used to treat a variety of cancers in dogs. The therapeutic utility of anthracyclines is limited by cardiotoxicity in some cases. Synthesis of anthracycline alcohol metabolites by carbonyl reductase 1 (CBR1) is crucial for the pathogenesis of cardiotoxicity. We hypothesize that genetic polymorphisms in canine cbr1 contribute to the variable pharmacodynamics of anthracyclines in dogs. DNA sequence variants in canine cbr1 were investigated in DNA samples from dogs of seven breeds. Thirteen SNPs were detected in canine cbr1. A 10-bp deletion in the 5'-untranslated region (5'-UTR) was found in specimens from the Labrador Retriever, Beagle, Siberian Husky, and Boxer breeds. The 5'-UTR also included a polymorphic "hot spot" region immediately downstream of the 10-bp deletion. DNA sequence variants in the "hot spot region" ranged from 1 to 21 bp in length. Bioinformatics searches identified a cluster of three to six potential binding sites for the transcription factor Sp1 in the DNA segment containing both the "hot spot" region and the 10-bp deletion. This information provides a foundation to allow us to investigate whether DNA sequence variants in the 5'-UTR of canine cbr1 impact the pharmacodynamics of anticancer anthracyclines in dogs.

The anthracyclines doxorubicin and daunorubicin are used in the treatment of various human and canine cancers, but anthracycline-related cardiotoxicity limits their clinical utility. The formation of anthracycline C-13 alcohol metabolites (e.g., doxorubicinol and daunorubicinol) contributes to the development of anthracycline-related cardiotoxicity. The enzymes responsible for the synthesis of anthracycline C-13 alcohol metabolites in canines remain to be elucidated. We hypothesized that canine carbonyl reductase 1 (cbr1), the homolog of the prominent anthracycline reductase human CBR1, would have anthracycline reductase activity. Recombinant canine cbr1 (molecular weight: 32.8 kDa) was purified from Escherichia coli. The enzyme kinetics of "wild-type" canine cbr1 (cbr1 D218) and a variant isoform (cbr1 V218) were characterized with the substrates daunorubicin and menadione, as well as the flavonoid inhibitor rutin. Canine cbr1 catalyzes the reduction of daunorubicin to daunorubicinol, with cbr1 D218 and cbr1 V218 displaying different kinetic parameters (cbr1 D218 Km: 188 ± 144 μM versus cbr1 V218 Km: 527 ± 136 μM, P < 0.05, and cbr1 D218 Vmax: 6446 ± 3615 nmol/min per milligram versus cbr1 V218 Vmax: 15539 ± 2623 nmol/min per milligram, P < 0.01). Canine cbr1 also metabolized menadione (cbr1 D218 Km: 104 ± 50 μM, Vmax: 2034 ± 307 nmol/min per milligram). Rutin acted as a competitive inhibitor for the reduction of daunorubicin (cbr1 D218 Ki: 1.84 ± 1.02 μM, cbr1 V218 Ki: 1.38 ± 0.47 μM). These studies show that canine cbr1 metabolizes daunorubicin and provide the necessary foundation to characterize the role of cbr1 in the variable pharmacodynamics of anthracyclines in canine cancer patients.

2594 Background: The anthracycline doxorubicin (DOX) is widely used to treat breast cancer. Doxorubicin is associated with pharmacokinetic and pharmacodynamic variability and despite its use for several years there is limited understanding behind it. Hepatic carbonyl reductases (CBR1 and CBR3) catalyze the reduction of DOX into its main circulating C-13 metabolite doxorubicinol (DOXOL). Polymorphisms in CBR1 and CBR3 influence synthesis of DOXOL, and could potentially play a role in the pharmacokinetic (PK) variability seen with doxorubicin treatment. In this study, we examined the influence of genetic polymorphisms in CBR1 and CBR3 on DOX and DOXOL PK. Methods: DOX was administered IV to 79 breast cancer patients at 60 mg/m2. Population PK modeling was performed on the parent concentration-time profiles with the following patient factors: [BSA (1.4-2.6 m2), weight (40-140 kg), age (25-75), race (78% white), CBR1 rs9024 (78% wild-type), CBR3 V244M (47% wild-type), CBR3 C4Y (20.5% wild-type); followed by model validation. Noncompartmental analysis (NCA) was performed for both DOX and DOXOL and the metabolic ratio was calculated as AUCDOXOL0-24:AUCDOX0-24. Results: A two-compartment model was used to describe DOX PK. Mean predicted (%SEM) clearance (CL), plasma volume (Vp), tissue volume and distribution clearance were 28.1 L/hr (7.72), 22.5 L (3.80), 257 L (13.8) and 13.6L (21.8), respectively. Interpatient variability on CL and Vp were 22.1% and 12.6%, respectively. BSA was found to be a significant predictor of the interpatient variability on CL. No other patient factors were found to be significant on parent drug PK. The metabolic ratio, assessing the conversion of DOX to DOXOL, was stratified by different polymorphisms of CBR1 and CBR3. There were no significant differences in metabolic ratio due to CBR1 and CBR3 genotypes. Conclusions: A PK model was developed that was able to characterize DOX pharmacokinetics. CBR1 and CBR3 polymorphisms were tested as covariates but were not found to be significant contributors to the variable pharmacokinetic profiles of DOX and DOXOL.