In vivo activity of the second-generation proteasome inhibitor ixazomib against pediatric T-cell acute lymphoblastic leukemia xenografts

The overall survival rate of patients with T-cell acute lymphoblastic leukemia (T-ALL) is now 90%, although patients with relapsed T-ALL face poor prognosis. The ubiquitin-proteasome system maintains normal protein homeostasis, and aberrations in this pathway are associated with T-ALL. Here we demonstrate the in vitro and in vivo activity of ixazomib, a second-generation orally available, reversible, and selective proteasome inhibitor against pediatric T-ALL cell lines and patient-derived xenografts (PDXs) grown orthotopically in immunodeficient NOD.Cg-PrkdcscidIL2rgtm1Wjl/SzJAusb (NSG) mice. Ixazomib was highly potent in vitro, with half-maximal inhibitory concentration (IC50) values in the low nanomolar range. As a monotherapy, ixazomib significantly extended mouse event-free survival of five out of eight T-ALL PDXs in vivo.

A proteogenomic surfaceome study identifies DLK1 as an immunotherapeutic target in neuroblastoma

Cancer immunotherapies have produced remarkable results in B-cell malignancies; however, optimal cell surface targets for many solid cancers remain elusive. Here, we present an integrative proteomic, transcriptomic, and epigenomic analysis of tumor specimens along with normal tissues to identify biologically relevant cell surface proteins that can serve as immunotherapeutic targets for neuroblastoma, an often-fatal childhood cancer of the developing nervous system. We apply this approach to human-derived cell lines (N=9) and cell/patient-derived xenograft (N=12) models of neuroblastoma. Plasma membrane-enriched mass spectrometry identified 1,461 cell surface proteins in cell lines and 1,401 in xenograft models, respectively. Additional proteogenomic analyses revealed 60 high-confidence candidate immunotherapeutic targets and we prioritized Delta-like canonical notch ligand 1 (DLK1) for further study. High expression of DLK1 directly correlated with the presence of a super-enhancer spanning the DLK1 locus. Robust cell surface expression of DLK1 was validated by immunofluorescence, flow cytometry, and immunohistochemistry. Short hairpin RNA mediated silencing of DLK1 in neuroblastoma cells resulted in increased cellular differentiation. ADCT-701, a DLK1-targeting antibody-drug conjugate (ADC), showed potent and specific cytotoxicity in DLK1-expressing neuroblastoma xenograft models. Moreover, DLK1 is highly expressed in several adult cancer types, including adrenocortical carcinoma (ACC), pheochromocytoma/paraganglioma (PCPG), hepatoblastoma, and small cell lung cancer (SCLC), suggesting potential clinical benefit beyond neuroblastoma. Taken together, our study demonstrates the utility of comprehensive cancer surfaceome characterization and credentials DLK1 as an immunotherapeutic target.

Highlights

Plasma membrane enriched proteomics defines surfaceome of neuroblastomaMulti-omic data integration prioritizes DLK1 as a candidate immunotherapeutic target in neuroblastoma and other cancersDLK1 expression is driven by a super-enhancer DLK1 silencing in neuroblastoma cells results in cellular differentiation ADCT-701, a DLK1-targeting antibody-drug conjugate, shows potent and specific cytotoxicity in DLK1-expressing neuroblastoma preclinical models.

In vivo activity of the dual SYK/FLT3 inhibitor TAK-659 against pediatric acute lymphoblastic leukemia xenografts

BACKGROUND

While children with acute lymphoblastic leukemia (ALL) experience close to a 90% likelihood of cure, the outcome for certain high-risk pediatric ALL subtypes remains dismal. Spleen tyrosine kinase (SYK) is a prominent cytosolic nonreceptor tyrosine kinase in pediatric B-lineage ALL (B-ALL). Activating mutations or overexpression of Fms-related receptor tyrosine kinase 3 (FLT3) are associated with poor outcome in hematological malignancies. TAK-659 (mivavotinib) is a dual SYK/FLT3 reversible inhibitor, which has been clinically evaluated in several other hematological malignancies. Here, we investigate the in vivo efficacy of TAK-659 against pediatric ALL patient-derived xenografts (PDXs).

METHODS

SYK and FLT3 mRNA expression was quantified by RNA-seq. PDX engraftment and drug responses in NSG mice were evaluated by enumerating the proportion of human CD45+ cells (%huCD45+ ) in the peripheral blood. TAK-659 was administered per oral at 60 mg/kg daily for 21 days. Events were defined as %huCD45+ ≥ 25%. In addition, mice were humanely killed to assess leukemia infiltration in the spleen and bone marrow (BM). Drug efficacy was assessed by event-free survival and stringent objective response measures.

RESULTS

FLT3 and SYK mRNA expression was significantly higher in B-lineage compared with T-lineage PDXs. TAK-659 was well tolerated and significantly prolonged the time to event in six out of eight PDXs tested. However, only one PDX achieved an objective response. The minimum mean %huCD45+ was significantly reduced in five out of eight PDXs in TAK-659-treated mice compared with vehicle controls.

CONCLUSIONS

TAK-659 exhibited low to moderate single-agent in vivo activity against pediatric ALL PDXs representative of diverse subtypes.

In vivo activity of the dual PI3Kδ and PI3Kγ inhibitor duvelisib against pediatric acute lymphoblastic leukemia xenografts

BACKGROUND

Acute lymphoblastic leukemia (ALL) remains one of the most common causes of cancer-related mortality in children. Phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases, and aberrations in the PI3K pathway are associated with several hematological malignancies, including ALL. Duvelisib (Copiktra) is an orally available, small molecule dual inhibitor of PI3Kδ and PI3Kγ, that is Food and Drug Administration (FDA) approved for the treatment of relapsed/refractory chronic lymphocytic leukemia and small lymphocytic lymphoma. Here, we report the efficacy of duvelisib against a panel of pediatric ALL patient-derived xenografts (PDXs).

PROCEDURES

Thirty PDXs were selected for a single mouse trial based on PI3Kδ (PIK3CD) and PI3Kγ (PIK3CG) expression and mutational status. PDXs were grown orthotopically in NSG (NOD.Cg-Prkdc^scid IL2rg^tm1Wjl /SzJAusb) mice, and engraftment was evaluated by enumerating the proportion of human versus mouse CD45⁺ cells (%huCD45⁺ ) in the peripheral blood. Treatment commenced when the %huCD45⁺ reached greater than or equal to 1%, and events were predefined as %huCD45⁺ greater than or equal to 25% or leukemia-related morbidity. Duvelisib was administered per oral (50 mg/kg, twice daily for 28 days). Drug efficacy was assessed by event-free survival and stringent objective response measures.

RESULTS

PI3Kδ and PI3Kγ mRNA expression was significantly higher in B-lineage than T-lineage ALL PDXs (p-values <.0001). Duvelisib was well-tolerated and reduced leukemia cells in the peripheral blood in four PDXs, but with only one objective response. There was no obvious relationship between duvelisib efficacy and PI3Kδ or PI3Kγ expression or mutation status, nor was the in vivo response to duvelisib subtype dependent.

CONCLUSIONS

Duvelisib demonstrated limited in vivo activity against ALL PDXs.

Sources of variation in estimates of Duchenne and Becker muscular dystrophy prevalence in the United States

BACKGROUND

Direct estimates of rare disease prevalence from public health surveillance may only be available in a few catchment areas. Understanding variation among observed prevalence can inform estimates of prevalence in other locations. The Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) conducts population-based surveillance of major muscular dystrophies in selected areas of the United States. We identified sources of variation in prevalence estimates of Duchenne and Becker muscular dystrophy (DBMD) within MD STARnet from published literature and a survey of MD STARnet investigators, then developed a logic model of the relationships between the sources of variation and estimated prevalence.

RESULTS

The 17 identified sources of variability fell into four categories: (1) inherent in surveillance systems, (2) particular to rare diseases, (3) particular to medical-records-based surveillance, and (4) resulting from extrapolation. For the sources of uncertainty measured by MD STARnet, we estimated each source's contribution to the total variance in DBMD prevalence. Based on the logic model we fit a multivariable Poisson regression model to 96 age-site-race/ethnicity strata. Age accounted for 74% of the variation between strata, surveillance site for 6%, race/ethnicity for 3%, and 17% remained unexplained.

CONCLUSION

Variation in estimates derived from a non-random sample of states or counties may not be explained by demographic differences alone. Applying these estimates to other populations requires caution.

Gene-Folic Acid Interactions and Risk of Conotruncal Heart Defects: Results from the National Birth Defects Prevention Study

Conotruncal heart defects (CTDs) are heart malformations that affect the cardiac outflow tract and typically cause significant morbidity and mortality. Evidence from epidemiological studies suggests that maternal folate intake is associated with a reduced risk of heart defects, including CTD. However, it is unclear if folate-related gene variants and maternal folate intake have an interactive effect on the risk of CTDs. In this study, we performed targeted sequencing of folate-related genes on DNA from 436 case families with CTDs who are enrolled in the National Birth Defects Prevention Study and then tested for common and rare variants associated with CTD. We identified risk alleles in maternal MTHFS (OR_meta = 1.34; 95% CI 1.07 to 1.67), maternal NOS2 (OR_meta = 1.34; 95% CI 1.05 to 1.72), fetal MTHFS (OR_meta = 1.35; 95% CI 1.09 to 1.66), and fetal TCN2 (OR_meta = 1.38; 95% CI 1.12 to 1.70) that are associated with an increased risk of CTD among cases without folic acid supplementation. We detected putative de novo mutations in genes from the folate, homocysteine, and transsulfuration pathways and identified a significant association between rare variants in MGST1 and CTD risk. Results suggest that periconceptional folic acid supplementation is associated with decreased risk of CTD among individuals with susceptible genotypes.

Identifying Datasets for Cross-Study Analysis in dbGaP using PhenX

Identifying relevant studies and harmonizing datasets are major hurdles for data reuse. Common Data Elements (CDEs) can help identify comparable study datasets and reduce the burden of retrospective data harmonization, but they have not been required, historically. The collaborative team at PhenX and dbGaP developed an approach to use PhenX variables as a set of CDEs to link phenotypic data and identify comparable studies in dbGaP. Variables were identified as either comparable or related, based on the data collection mode used to harmonize data across mapped datasets. We further added a CDE data field in the dbGaP data submission packet to indicate use of PhenX and annotate linkages in the future. Some 13,653 dbGaP variables from 521 studies were linked through PhenX variable mapping. These variable linkages have been made accessible for browsing and searching in the repository through dbGaP CDE-faceted search filter and the PhenX variable search tool. New features in dbGaP and PhenX enable investigators to identify variable linkages among dbGaP studies and reveal opportunities for cross-study analysis.

Trastuzumab Deruxtecan, Antibody-Drug Conjugate Targeting HER2, Is Effective in Pediatric Malignancies: A Report by the Pediatric Preclinical Testing Consortium

HER2 is expressed in many pediatric solid tumors and is a target for innovative immune therapies including CAR-T cells and antibody-drug conjugates (ADC). We evaluated the preclinical efficacy of trastuzumab deruxtecan (T-DXd, DS-8201a), a humanized monoclonal HER2-targeting antibody conjugated to a topoisomerase 1 inhibitor, DXd, in patient- and cell line-derived xenograft (PDX/CDX) models. HER2 mRNA expression was determined using RNA-seq and protein expression via IHC across multiple pediatric tumor PDX models. Osteosarcoma (OS), malignant rhabdoid tumor (MRT), and Wilms tumor (WT) models with varying HER2 expression were tested using 10 mice per group. Additional histologies such as Ewing sarcoma (EWS), rhabdomyosarcoma (RMS), neuroblastoma (NB), and brain tumors were evaluated using single mouse testing (SMT) experiments. T-DXd or vehicle control was administered intravenously to mice harboring established flank tumors at a dose of 5 mg/kg on day 1. Event-free survival (EFS) and objective response were compared between treatment and control groups. HER2 mRNA expression was observed across histologies, with the highest expression in WT (median = 22 FPKM), followed by MRT, OS, and EWS. The relationship between HER2 protein and mRNA expression was inconsistent. T-DXd significantly prolonged EFS in 6/7 OS, 2/2 MRT, and 3/3 WT PDX models. Complete response (CR) or maintained CR (MCR) were observed for 4/5 WT and MRT models, whereas stable disease was the best response among OS models. SMT experiments also demonstrated activity across multiple solid tumors. Clinical trials assessing the efficacy of a HER2-directed ADC in pediatric patients with HER2-expressing tumors should be considered.

Evaluation of the DLL3-targeting antibody-drug conjugate rovalpituzumab tesirine in preclinical models of neuroblastoma

Neuroblastomas have neuroendocrine features and often show similar gene expression patterns to small cell lung cancer including high expression of delta-like ligand 3 (DLL3). Here we determine the efficacy of rovalpituzumab tesirine (Rova-T), an antibody drug conjugated (ADC) with a pyrrolobenzodiazepine (PBD) dimer toxin targeting DLL3, in preclinical models of human neuroblastoma. We evaluated DLL3 expression in RNA sequencing data sets and performed immunohistochemistry (IHC) on neuroblastoma patient derived xenograft (PDX), human neuroblastoma primary tumor and normal childhood tissue microarrays (TMAs). We then evaluated the activity of Rova-T against 11 neuroblastoma PDX models using varying doses and schedules and compared anti-tumor activity to expression levels. DLL3 mRNA was differentially overexpressed in neuroblastoma at comparable levels to small cell lung cancer, as well as Wilms and rhabdoid tumors. DLL3 protein was robustly expressed across the neuroblastoma PDX array, but membranous staining was variable. The human neuroblastoma array, however, showed staining in only 44% of cases, whereas no significant staining was observed in the normal childhood tissue array. Rova-T showed a clear dose response effect across the 11 models tested, with a single dose inducing a complete or partial response in 3/11 and stable disease in another 3/11 models. No overt signs of toxicity were observed, and there was no treatment-related mortality. Strong membranous staining was necessary, but not sufficient, for anti-tumor activity. Rova-T has activity in a subset of neuroblastoma preclinical models, but heterogeneous expression in these models and the near absence of expression seen in human tumors suggests that any DLL3-targeting clinical trial should be only performed with a robust companion diagnostic to evaluate DLL3 expression for patient selection.

Comprehensive surfaceome profiling to identify and validate novel cell-surface targets in osteosarcoma

Immunoconjugates targeting cell-surface antigens have demonstrated clinical activity to enable regulatory approval in several solid and hematologic malignancies. We hypothesize that a rigorous and comprehensive surfaceome profiling approach to identify osteosarcoma-specific cell-surface antigens can similarly enable development of effective therapeutics in this disease. Herein, we describe an integrated proteomic and transcriptomic surfaceome profiling approach to identify cell-surface proteins that are highly expressed in osteosarcoma but minimally expressed on normal tissues. Using this approach, we identified targets that are highly expressed in osteosarcoma. Three targets, MT1-MMP, CD276, and MRC2, were validated as overexpressed in osteosarcoma. Further, we tested BT1769, an MT1-MMP-targeted Bicycle toxin conjugate, in osteosarcoma PDX models. The results showed BT1769 had encouraging anti-tumor activity, high affinity for its target and a favorable pharmacokinetic profile. This confirms the hypothesis that our approach identifies novel targets with significant therapeutic potential in osteosarcoma.

Evaluation of an EZH2 inhibitor in patient-derived orthotopic xenograft models of pediatric brain tumors alone and in combination with chemo- and radiation therapies

Brain tumors are the leading cause of cancer-related death in children. Tazemetostat is an FDA-approved enhancer of zeste homolog (EZH2) inhibitor. To determine its role in difficult-to-treat pediatric brain tumors, we examined EZH2 levels in a panel of 22 PDOX models and confirmed EZH2 mRNA over-expression in 9 GBM (34.6 ± 12.7-fold) and 11 medulloblastoma models (6.2 ± 1.7 in group 3, 6.0 ± 2.4 in group 4) accompanied by elevated H3K27me3 expression. Therapeutic efficacy was evaluated in 4 models (1 GBM, 2 medulloblastomas and 1 ATRT) via systematically administered tazemetostat (250 and 400 mg/kg, gavaged, twice daily) alone and in combination with cisplatin (5 mg/kg, i.p., twice) and/or radiation (2 Gy/day × 5 days). Compared with the untreated controls, tazemetostat significantly (Pcorrected < 0.05) prolonged survival times in IC-L1115ATRT (101% at 400 mg/kg) and IC-2305GBM (32% at 250 mg/kg, 45% at 400 mg/kg) in a dose-dependent manner. The addition of tazemetostat with radiation was evaluated in 3 models, with only one [IC-1078MB (group 4)] showing a substantial, though not statistically significant, prolongation in survival compared to radiation treatment alone. Combining tazemetostat (250 mg/kg) with cisplatin was not superior to cisplatin alone in any model. Analysis of in vivo drug resistance detected predominance of EZH2-negative cells in the remnant PDOX tumors accompanied by decreased H3K27me2 and H3K27me3 expressions. These data supported the use of tazemetostat in a subset of pediatric brain tumors and suggests that EZH2-negative tumor cells may have caused therapy resistance and should be prioritized for the search of new therapeutic targets.

Role Attainment in Emerging Adulthood: Subjective Evaluation by Male Adolescents and Adults with Duchenne and Becker Muscular Dystrophy

BACKGROUND

Youth with Duchenne and Becker muscular dystrophy (DBMD) experience challenges in attaining adult roles, which may impact quality of life. New interventions and treatments may facilitate adult role attainment through improved function. Historical data on adult role attainment is important to assess the impact of new interventions on teens and young adults with DBMD. This study assesses medical knowledge, independence and employment, and relationships among adolescents and young adults with DBMD.

METHODS

This study uses data from a 2013 Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) survey on adult transition. Males with DBMD aged 16-30 years were included.

RESULTS

Sixty-five of 258 eligible males participated; we report results on 60 participants with an MD STARnet case definition of DMD or BMD. Individuals with BMD reported higher rates than those with DMD of frequently staying home without supervision (50% BMD; 14% DMD), independently performing daily physical needs (93% BMD; 7% DMD) and being employed full or part time (33% BMD; 4% DMD). Most participants understood medication and physical therapy goals; less than half indicated being often or always responsible for scheduling DMBD-related management and refilling medications. Most had not been in a romantic relationship but reported desiring such relationships.

CONCLUSIONS

Our data reinforce the impact of DMD (and to a lesser extent, BMD) on transition to adult roles. These results provide an important historical comparator for teen and adult patients who are trying new interventions and therapies. Such data are important for assessing the quality-of-life impact of new treatments and to inform support and training programs for people with DBMD as they transition to new adult roles and responsibilities.

In vivo evaluation of the lysine-specific demethylase (KDM1A/LSD1) inhibitor SP-2577 (Seclidemstat) against pediatric sarcoma preclinical models: A report from the Pediatric Preclinical Testing Consortium (PPTC)

SP-2577(Seclidemstat), an inhibitor of lysine-specific demthylase KDM1A (LSD1) that is overexpressed in pediatric sarcomas, was evaluated against pediatric sarcoma xenografts. SP-2577 (100 mg/kg/day × 28 days) statistically significantly (p < .05) inhibited growth of three of eight Ewing sarcoma (EwS), four of five rhabdomyosarcoma (RMS), and four of six osteosarcoma (OS) xenografts. The increase in EFS T/C was modest (<1.5) for all models except RMS Rh10 (EFS T/C = 2.8). There were no tumor regressions or consistent changes in dimethyl histone H3(K4), HOXM1, DAX1, c-MYC and N-MYC, or tumor histology/differentiation. SP-2577 has limited activity against these pediatric sarcoma models at the dose and schedule evaluated.

Abstract 3039: Pediatric preclinical testing consortium evaluation of the dual SYK/FLT3 inhibitor TAK-659 in xenograft models of pediatric acute lymphoblastic leukemia

Introduction: While children with acute lymphoblastic leukemia (ALL) experience close to a 90% likelihood of cure, the outcome for certain high-risk pediatric ALL subtypes remains poor. Spleen Tyrosine Kinase (SYK), a cytosolic nonreceptor tyrosine kinase, is primarily expressed in the hematopoietic lineage and is essential for B-cell receptor signaling. It is associated with malignant transformation, cancer cell proliferation, and is a prominent tyrosine-phosphorylated protein in B-lineage pediatric ALL (Dolai et al, Cancer Res 76:2766-77, 2016). Fms Related Receptor Tyrosine Kinase 3 (FLT3) is a Class III receptor tyrosine kinase that regulates hematopoiesis. While uncommon in ALL, activating FLT3 mutations and internal tandem duplications are associated with poor outcome. TAK-659 is a dual SYK/FLT3 reversible inhibitor currently undergoing clinical trials against B-cell lymphoma, acute myeloid leukemia and solid tumors. Therefore, it was of interest for the Pediatric Preclinical Testing Consortium to test TAK-659 in vivo against its patient-derived xenograft (PDX) models of pediatric ALL.

Methods: SYK and FLT3 mRNA expression in ALL PDXs was quantified by RNAseq (https://pedcbioportal.org) and 8 B-lineage pediatric ALL PDXs (3 B-cell precursor, BCP; 4 mixed-lineage leukemia-rearranged, MLLr; one Philadelphia Chromosome-like, Ph-like) were selected for testing. Engraftment was evaluated by enumerating the proportion of human CD45+ cells (%huCD45+) in the peripheral (PB) blood at weekly intervals. TAK-659 was tested at 60 mg/kg by oral gavage daily for 21 days. Events were defined as %huCD45+ ≥ 25%. At Day 28 post-treatment initiation or event (whichever occurred first), 4 mice/group were humanely killed to assess leukemia infiltration in the spleen and bone marrow (BM). Drug efficacy was assessed by event-free survival (EFS) of treated (T) and control (C) groups by T-C, T/C and stringent objective response measures (Houghton et al, Pediatr Blood Cancer 49:928-40, 2007).

Results: The in vivo efficacy of TAK-659 was evaluated against B-lineage PDXs as FLT3 and SYK mRNA expression was higher in the PDXs from this lineage compared with PDXs from T-ALL. TAK-659 was well tolerated and significantly prolonged the time to event in 6/8 PDXs (T-C 0-25.5 days, T/C 1.0-2.2). Only one MLLr-ALL obtained an objective response (partial response) with all other models exhibiting progressive disease. The minimum mean %huCD45+ was significantly reduced in 5/8 PDXs in TAK-659 treated mice compared to control. Despite significant reductions in %huCD45+ in the PB for 5/8 PDXs, TAK-659 did not significantly reduce the spleen or BM infiltration of any PDXs.

Conclusion: TAK-659 exhibited low to moderate single-agent in vivo activity against pediatric B-ALL PDXs representative of diverse disease subtypes. (Supported by NCI Grants CA199000 and CA199922)

Citation Format: Richard B. Lock, Kathryn Evans, Narimanne El-Zein, Eric J. Earley, Stephen W. Erickson, Beverly A. Teicher, Malcolm A. Smith. Pediatric preclinical testing consortium evaluation of the dual SYK/FLT3 inhibitor TAK-659 in xenograft models of pediatric acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3039.

Abstract 3038: Evaluation of ROR1-targeted antibody-drug conjugates against ROR1-expressing pediatric preclinical models - a report from the pediatric preclinical testing consortium (PPTC)

Introduction: ROR1 is an orphan-receptor tyrosine kinase-like surface antigen that is expressed primarily during development but is not expressed on normal adult tissues. ROR1 is expressed on multiple adult hematologic and solid cancers, making it a target for antibody-based therapies. UC-961 (cirmtuzumab), a humanized IgG1 monoclonal antibody, binds with high affinity to a specific extracellular epitope of human ROR1 and rapidly internalizes and traffics to lysosomes. VLS-101 is an ADC developed by conjugating UC-961 to a cleavable linker with an MMAE payload. VLS-211 was generated by conjugating UC-961 with a PNU payload. VLS-101 is in clinical development for adults with hematologic and solid cancers and has received FDA Fast Track and Orphan Drug designation for the treatment of patients with mantle cell lymphoma. To better define the utility of ROR1 as an immuno-oncology target for pediatric cancers, we evaluated VLS-101 and VLS-211 against pediatric preclinical models selected based on ROR1 expression.

Methods: Models were selected based on RNA-seq transcript levels for ROR1 with subsequent confirmation by flow cytometry for acute lymphoblastic leukemia (ALL) models. For the ALL models, UC-961 (5 mg/kg), VLS-101 (2.5 and 5.0 mg/kg), and VLS-211 (0.25 and 0.5 mg/kg) were each administered weekly x 3. For the Ewing sarcoma (EWS) models, the dose of VLS-211 was 0.5 and 1 mg/kg. Four models were treated using a twice-weekly or every 4-day treatment schedule while 2 models were treated weekly.

Results: Elevated ROR1 gene expression among PPTC models was most notable among the ALL and EWS panels. Leukemia cell surface expression of ROR1 correlated with transcript levels. ALL models with elevated ROR1 expression [TCF3-HLF (1), TCF3-PBX1 (2), ETV6-RUNX1 (2), and BCR-ABL1 (1)] as well as a non-expressing model were tested against the ROR1 ADCs. Activity of each ADC was ROR1 expression-level dependent, and for VLS-211 dose-dependency was noted. At the highest doses of each ADC studied, 2 of 6 (VLS-101) and 3 of 6 (VLS-211) ROR1-expressing models showed objective responses. For most models, median time to event was longer for VLS-211 versus VLS-101. Five EWS models were studied, and expression-level dependent activity was observed for both ADCs. VLS-101 induced tumor regressions in 2 of 5 models, while VLS211 induced regressions in 3 of 5 models. Time to event was generally longer for VLS-211 compared to VLS-101. No objective responses were observed to UC-961 for the ALL and EWS models.

Conclusions: VLS-101 and VLS-211 showed expression-level dependent activity against ALL and EWS models. These results support ROR1 as a relevant immuno-oncology target for the subset of B-ALL and Ewing sarcoma cases with elevated ROR1 expression. Further research is required to identify the optimal payload for ROR1 ADCs for use against pediatric cancers.

Citation Format: Richard B. Lock, Kathryn Evans, Narimanne El-Zein, Brian J. Lannutti, Katti A. Jessen, Eric J. Earley, Stephen W. Erickson, Malcolm A. Smith, Raushan Kurmasheva, Peter J. Houghton. Evaluation of ROR1-targeted antibody-drug conjugates against ROR1-expressing pediatric preclinical models - a report from the pediatric preclinical testing consortium (PPTC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3038.

Abstract LB171: The differentiated CD47 monoclonal antibody AO-176 exhibits significant in vivo activity against xenograft models of pediatric acute lymphoblastic leukemia (ALL)

Introduction: CD47 is a cell surface marker that interacts with signal regulatory protein alpha (SIRPα) on macrophages and dendritic cells to negatively regulate phagocytosis. This interaction elicits a “don't eat me” signal preventing phagocytosis by immune cells, enabling cell survival. CD47 is expressed on tumor cells, including acute leukemia cells. AO-176 is a highly differentiated monoclonal antibody that targets CD47, exerts potent in vivo activity in mouse xenograft models, has an established safety profile in cynomolgus monkeys, and is being evaluated in clinical trials. Given the broad expression of CD47 in malignant hematopoietic cells, it was of interest for the Pediatric Preclinical Testing Consortium to evaluate AO-176 in vivo against patient-derived xenograft (PDX) models of pediatric ALL. Methods: CD47 mRNA and protein expression were quantified by RNAseq (https://pedcbioportal.org) and flow cytometry (relative fluorescence intensity, RFI), respectively. AO-176 was tested in vivo against 3 T-ALL (ALL-8, ALL-30, ALL-121) and one early T-cell precursor (ETP) ALL (ETP-2) PDXs in NSG mice at 25 mg/kg intraperitoneally once per week for 4 weeks. Engraftment was evaluated by enumerating the proportion of human CD45+ cells in the peripheral blood (%huCD45+) at weekly intervals. Events were defined as the %huCD45+ ≥ 25%. At Day 28 post-treatment initiation or event (whichever occurred first), 3 mice/group were humanely killed to assess leukemia infiltration of hematolymphoid organs. Drug efficacy was assessed by event-free survival (EFS) of treated (T) and control (C) groups by T-C, T/C, and stringent objective response measures (Houghton et al, Pediatr Blood Cancer 49:928-40, 2007). Results: CD47 mRNA expression was significantly higher in a panel of T-lineage ALL PDXs (n=25; mean + SD FPKM, 149 + 57.9) compared with B-ALL PDXs (n=65; 65.3 + 18.7 FPKM) (P&lt;0.0001, unpaired t-test). Cell surface CD47 expression in a subset of 8 PDXs (6 T-ALL, 2 ETP-ALL) was a median of 40.2 (RFI range 17.9-81.9). AO-176 was well tolerated in NSG mice and significantly (P&lt;0.006) delayed the progression of 3/4 PDXs tested (3 T-ALL, one ETP-ALL) (T-C, 12.7-56.9 days; T/C 3.4-4.9) and one PDX elicited an objective response (Partial Response). AO-176 was least effective against the lowest CD47 expressing PDX. AO-176 significantly (P&lt;0.005) decreased human leukemia infiltration of murine spleens, but not bone marrow, in 3/4 PDXs. Conclusion: Despite being tested in highly immune-deficient mice, the naked antibody AO-176 exhibited significant single-agent in vivo anti-leukemic activity against pediatric T-lineage ALL PDXs. The significant decrease in spleen infiltration elicited by AO-176 in 3/4 PDXs suggests on-target activity consistent with the known mechanism of action of CD47 targeting agents. (Supported by NCI Grants CA199000 and CA199922)

Citation Format: Richard B. Lock, Kathryn Evans, Narimanne El-Zein, Eric J. Earley, Stephen W. Erickson, Beverly A. Teicher, Victoria Sung, Malcolm A. Smith. The differentiated CD47 monoclonal antibody AO-176 exhibits significant in vivo activity against xenograft models of pediatric acute lymphoblastic leukemia (ALL) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB171.

Abstract LB252: Evaluation of the pan-class I phosphoinositide 3-kinase (PI3K) inhibitor copanlisib in the Pediatric Preclinical Testing Consortium osteosarcoma in vivo models

Background. Copanlisib is a pan-class I phosphoinositide 3-kinase (PI3K) inhibitor with activity against all four PI3K class I isoforms (PI3Kα, PI3Kβ, PI3Kγ, and PI3Kδ). Copanlisib was approved for use by the FDA in the treatment of refractory follicular lymphoma in 2017. Preclinical data have suggested that deregulation of the PI3K pathway is a key driver of multiple malignancies. The relevance of this pathway in osteosarcoma tumorigenesis remains a subject of debate, however, whole genome and RNA sequencing data have revealed several PI3K aberrations in osteosarcoma tumor samples. The in vivo effects of copanlisib were studied in the Pediatric Preclinical Testing Consortium osteosarcoma xenograft models. Methods. The in vivo anticancer effects of copanlisib were assessed in a panel of 6 osteosarcoma models (OS-2, OS-9, OS-31, OS-33, OS-36, and OS-60). Copanlisib was administered by oral gavage at a dose of 10 mg/kg/day, two days on and five days off, repeated weekly for 4 weeks. Time to event and tumor volume responses were defined and analyzed utilizing standard PPTC statistical methods. Results. Copanlisib was well tolerated in the models with minimal weight loss and no treatment related mortality as compared to controls. Copanlisib induced prolonged event-free survival (EFS) in 5/6 osteosarcoma models (p&lt;0.05, Gehan-Wilcoxon). Tumor regression (mean minimum attained relative tumor volume (minRTV) &lt; 1.0) was not observed for any of the tested models. 3/6 models exhibited lower min RTV compared to untreated controls (p &lt; 0.05, Wilcoxon rank sum). All osteosarcoma models showed progressive disease as their objective response measure. Conclusions. While copanlisib induced prolonged EFS in 5/6 osteosarcoma models, no tumor regression was seen, with all models developing progressive disease suggesting minimal activity. While copanlisib did not result in tumor regression, further study is needed to fully explore the role of the PI3K pathway in the pathogenesis of osteosarcoma.

Citation Format: Douglas Harrison, Jonathan Gill, Pooja Hingorani, Michael Roth, Wendong Zhang, Beverly Teicher, Eric J. Earley, Stephen W. Erickson, Gregory Gatto, Raushan T. Kurmasheva, Peter J. Houghton, Malcolm A. Smith, Edward A. Kolb, Richard Gorlick. Evaluation of the pan-class I phosphoinositide 3-kinase (PI3K) inhibitor copanlisib in the Pediatric Preclinical Testing Consortium osteosarcoma in vivo models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB252.

Testing of B7-H3 targeting antibody-drug conjugate (ADC) MGC018 in models of pediatric solid tumors by the Pediatric Preclinical Testing Consortium (PPTC)

10037

Background: B7-H3 (encoded by the CD276 gene) is an immunoregulatory molecule that is widely expressed in pediatric embryonal tumors and sarcomas, while expression is limited for normal tissues. Among PPTC models, osteosarcoma models showed highest CD276 transcript levels followed by Wilms tumor, neuroblastoma, rhabdomyosarcoma, and Ewing sarcoma. Protein expression by IHC generally followed expression at the RNA level, with high expression by IHC observed across a range of models. MGC018 is a duocarmycin-based humanized ADC targeting B7-H3 that shows selective cytotoxicity for B7-H3 expressing cancer cells, robust in vivo activity against a range of adult cancer preclinical models, a favorable pharmacokinetic and safety profile in cynomolgus monkeys, and has entered clinical testing for adults with cancer. Herein we report the in vivo antitumor activity of MGC018 against preclinical models of pediatric solid tumors. Methods: MGC018 was tested at 6 mg/kg administered intraperitoneally (IP) on Day 1. SYD988, an anti-CD20 ADC with the same linker and payload as MGC018, was used as a control arm at 6 mg/kg IP on Day 1. Osteosarcoma models, due to their slower growth kinetics and lower rates of tumor regression, were tested with n = 10 mice per arm, while the sarcoma and neuroblastoma models were tested with n of 1 or n of 2 designs, respectively. Activity was evaluated using response criteria mirroring clinical criteria (progressive disease (PD), stable disease (SD), partial response (PR), complete response (CR), and maintained CR (MCR)], by minimum relative tumor volume across all models, and by event-free survival (EFS) comparisons between treatment groups. Results: For neuroblastoma models (n = 9), 3 and 2 neuroblastoma models showed objective responses (PR/CR/MCR) or SD, respectively, to MGC018, while none showed an objective response or SD to SYD988. For osteosarcoma, results are mature for 1 of 5 models, with this model showing an MCR response to MGC018 and a PD response to SYD988. For Ewing sarcoma (n = 5), a PR and MCR were observed to MGC018 with the remaining models showing PD; for SYD988 a single CR was observed with the remaining 4 models showing PD. For rhabdomyosarcoma (n = 3) 2 MCR and 1 PD were noted for MGC018, while only PD was noted for SYD988. EFS duration exceeding 100 days to a single dose of MGC018 was observed for 2 rhabdomyosarcoma, 1 Ewing sarcoma, and 1 neuroblastoma model. Evaluation of the relationship between B7-H3 expression and response to MGC018 will be performed when results from all studies are completed. Conclusions: B7-H3 is an important target for immuno-oncology agents for childhood cancers. Our results provide proof-of-principle for the ability of MGC018 to produce profound antitumor activity in select pediatric solid tumor models in a B7-H3 specific manner.

Combination efficacy of ruxolitinib with standard-of-care drugs in CRLF2-rearranged Ph-like acute lymphoblastic leukemia

Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) is a high-risk ALL subtype with high rates of relapse and poor patient outcome. Activating mutations affecting components of the JAK-STAT signaling pathway occur in the majority of Ph-like ALL cases. The use of JAK inhibitors represents a potential treatment option for Ph-like ALL, although we and others have shown that CRLF2-rearranged Ph-like ALL responds poorly to single-agent JAK inhibitors in the preclinical setting. Therefore, the aim of this study was to identify effective combination treatments against CRLF2-rearranged Ph-like ALL, and to elucidate the underlying mechanisms of synergy. We carried out a series of high-throughput combination drug screenings and found that ruxolitinib exerted synergy with standard-of-care drugs used in the treatment of ALL. In addition, we investigated the molecular effects of ruxolitinib on Ph-like ALL by combining mass spectrometry phosphoproteomics with gene expression analysis. Based on these findings, we conducted preclinical in vivo drug testing and demonstrated that ruxolitinib enhanced the in vivo efficacy of an induction-type regimen consisting of vincristine, dexamethasone, and L-asparaginase in 2/3 CRLF2-rearranged Ph-like ALL xenografts. Overall, our findings support evaluating the addition of ruxolitinib to conventional induction regimens for the treatment of CRLF2-rearranged Ph-like ALL.

The B7-H3-Targeting Antibody-Drug Conjugate m276-SL-PBD Is Potently Effective Against Pediatric Cancer Preclinical Solid Tumor Models

PURPOSE

Patients with relapsed pediatric solid malignancies have few therapeutic options, and many of these patients die of their disease. B7-H3 is an immune checkpoint protein encoded by the CD276 gene that is overexpressed in many pediatric cancers. Here, we investigate the activity of the B7-H3-targeting antibody-drug conjugate (ADC) m276-SL-PBD in pediatric solid malignancy patient-derived (PDX) and cell line-derived xenograft (CDX) models.

EXPERIMENTAL DESIGN

B7-H3 expression was quantified by RNA sequencing and by IHC on pediatric PDX microarrays. We tested the safety and efficacy of m276-SL-PBD in two stages. Randomized trials of m276-SL-PBD of 0.5 mg/kg on days 1, 8, and 15 compared with vehicle were performed in PDX or CDX models of Ewing sarcoma (N = 3), rhabdomyosarcoma (N = 4), Wilms tumors (N = 2), osteosarcoma (N = 5), and neuroblastoma (N = 12). We then performed a single mouse trial in 47 PDX or CDX models using a single 0.5 m/kg dose of m276-SL-PBD.

RESULTS

The vast majority of PDX and CDX samples studied showed intense membranous B7-H3 expression (median H-score 177, SD 52). In the randomized trials, m276-SL-PBD showed a 92.3% response rate, with 61.5% of models showing a maintained complete response (MCR). These data were confirmed in the single mouse trial with an overall response rate of 91.5% and MCR rate of 64.4%. Treatment-related mortality rate was 5.5% with late weight loss observed in a subset of models dosed once a week for 3 weeks.

CONCLUSIONS

m276-SL-PBD has significant antitumor activity across a broad panel of pediatric solid tumor PDX models.

In vivo evaluation of the EZH2 inhibitor (EPZ011989) alone or in combination with standard of care cytotoxic agents against pediatric malignant rhabdoid tumor preclinical models-A report from the Pediatric Preclinical Testing Consortium

The Pediatric Preclinical Testing Program (PPTP) previously reported the activity of the EZH2 inhibitor tazemetostat (EPZ6438) against xenograft models of rhabdoid tumors. Here, we determined whether an inhibitor of EZH2 enhanced the effect of standard of care chemotherapeutic agents: irinotecan, vincristine, and cyclophosphamide. EPZ011989 significantly prolonged time to event in all the six rhabdoid models studied but did not induce tumor regression. The addition of EPZ011989 to standard of care agents significantly improved time to event in at least one model for each of the agents studied, although this effect was observed in only a minority of the combination testing experiments.

Initial in vivo testing of TPO-receptor agonist eltrombopag in osteosarcoma patient-derived xenograft models by the pediatric preclinical testing consortium

Eltrombopag is a small molecule, thrombopoietin receptor agonist approved for the treatment of patients with aplastic anemia and chronic immune thrombocytopenia. It is also a polyvalent cation chelator and inhibits leukemia cell proliferation via reduction of intracellular iron. The in vivo efficacy of eltrombopag was tested against a panel of six Pediatric Preclinical Testing Consortium osteosarcoma xenografts at doses of 5 mg/kg/day (moderate dose) and 50 mg/kg/day (high dose). Eltrombopag, at moderate doses, failed to significantly improve event-free survival (EFS) in 6/6 models. At high doses, eltrombopag significantly prolonged EFS in 2/2 models, though the effect size was small. All models tested demonstrated progressive disease. While eltrombopag did not meaningfully inhibit osteosarcoma growth, it also did not stimulate tumor growth, suggesting it may be safely investigated as a supportive care agent to enhance platelet recovery post chemotherapy.

Abstract 4181: The XPO1 inhibitior, eltanexor, exhibits potent in vivo activity against a broad range of pediatric acute lymphoblastic leukemia subtypes

Introduction: Exportin 1 (XPO1/CRM1) plays a central role in the export of proteins from the nucleus including those with tumor suppressor and growth regulatory activity. Eltanexor (KPT-8602) is a second-generation Selective Inhibitor of Nuclear Export (SINE) that specifically blocks XPO1 cargo interactions and is under clinical evaluation for adults with cancer (NCT02649790). In previous Pediatric Preclinical Testing Consortium (PPTC) studies, eltanexor showed potent in vivo activity against acute lymphoblastic leukemia (ALL) patient-derived xenografts (PDXs). In an effort to understand whether eltanexor exhibited subtype-specific activity in pediatric ALL we carried out a single-mouse trial (SMT) against an intended 90 pediatric ALL PDXs.

Methods: Pediatric ALL PDXs, an orthotopic model of the disease, were inoculated into NSG mice in an SMT format (a single mouse inoculated with a single PDX was treated with a single drug). Engraftment and drug responses were assessed by weekly enumeration of the % human leukemic blasts in the peripheral blood (%huCD45+/HLA-ABC+). Treatment commenced when the median %huCD45+/HLA-ABC+ exceeded 1%, and mice received eltanexor at 12.5 mg/kg per oral daily x 5 for 4 weeks. The baseline level of the %huCD45+/HLA-ABC+ in each mouse served as its own control. PDX responses to treatment were assessed by time to event, the maximum decrease in %huCD45+/ABC+ at any point after treatment initiation, and by stringent Objective Response Measures (ORMs) modeled after the clinical setting (Houghton et al, Pediatr Blood Cancer, 2007, 49:928-40).

Results: Eltanexor was well tolerated with a mean maximum weight loss of 5.5% across all mice. SMT testing was successful in all 90 pediatric ALL PDXs representative of B-ALL (typical B-ALL, Philadelphia chromosome-positive ALL [Ph+-ALL] and Ph-like ALL), T-ALL (typical T-ALL and early T-cell precursor ALL [ETP-ALL]), and MLL-rearranged ALL (MLLr-ALL). Event-free survival (EFS) of mice ranged from 2.6-137 days, and 61 (68%) of mice experienced EFS that extended beyond the treatment window. Regressions of ≥50% from baseline were observed in 56 (62%) of mice, and these were most pronounced in T-ALL (14/18, 78%) and Ph-like ALL (11/19, 58%). ORMs classified as Complete Response (CR) or Maintained CR (MCR) were elicited in 43 (48%) of PDXs, and again these were more common in T-ALL (12/18, 67%). The ALL subtypes that exhibited the poorest responses to eltanexor were Ph+-ALL and ETP-ALL, although with relatively small sample size (n=3 and 6, respectively). ORMs in the SMT correlated highly with historical conventional drug testing (R=0.94, P&lt;0.001, n=12).

Conclusions: Eltanexor exhibits potent single-agent in vivo activity against PDXs derived from a broad range of ALL subtypes including T-ALL and Ph-like ALL and warrants further investigation in pediatric ALL. (Supported by NCI Grants CA199222 & CA199000)

Citation Format: Richard B. Lock, Kathryn Evans, Connor D. Jones, Stephen W. Erickson, Beverly A. Teicher, TJ Unger, Yosef Landesman, Malcolm A. Smith. The XPO1 inhibitior, eltanexor, exhibits potent in vivo activity against a broad range of pediatric acute lymphoblastic leukemia subtypes [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4181.

Evaluation of VTP-50469, a menin-MLL1 inhibitor, against Ewing sarcoma xenograft models by the pediatric preclinical testing consortium

BACKGROUND

VTP-50469 is a potent inhibitor of the menin-MLL1 interaction and is implicated in signaling downstream of EWSR1-FLI1.

PROCEDURE

VTP-50469 was evaluated against seven Ewing sarcoma (EwS) xenograft models and in vitro against EwS cell lines.

RESULTS

VTP-50469 showed limited antitumor activity, statistically significantly slowing tumor progression in four tumor models but with no evidence of tumor regression. In vitro, the IC₅₀ concentration was 10 nM for the mixed lineage leukemia (MLL)-rearranged leukemia cell line MV4;11, but > 3 μM for EwS cell lines.

CONCLUSIONS

In contrast to its high level of activity against MLL1-rearranged leukemia xenografts, VTP-50469 shows little activity against EwS models.

Evaluation of Eribulin Combined with Irinotecan for Treatment of Pediatric Cancer Xenografts

PURPOSE

Vincristine combined with camptothecin derivatives showed synergy in preclinical pediatric cancer models, and the combinations are effective in treatment of childhood solid tumors. We determined whether the synergy between vincristine and irinotecan extends to eribulin, another microtubule inhibitor.

EXPERIMENTAL DESIGN

Vincristine or eribulin, alone or combined with irinotecan, was studied in 12 xenograft models. Tumor regression and time to event were used to assess antitumor activity. Pharmacodynamic studies and RNA sequencing (RNA-seq) were conducted 24 and 144 hours after single-agent or combination treatment. Effects on vascular development were studied in Matrigel plugs implanted in mice. The interaction between binary combinations was examined in vitro.

RESULTS

Eribulin combined with irinotecan was more effective than vincristine-irinotecan in 6 of 12 models. Pharmacodynamic markers induced by eribulin (phospho-histone H3) and irinotecan (γ-H2A.X) were abrogated in combination-treated tumors. The predominant RNA-seq signature in combination-treated tumors was activation of the TP53 pathway with increased nuclear TP53. Massive apoptosis was observed 24 hours only after treatment with the eribulin combination. In vitro, neither combination showed interaction using combination index analysis. Eribulin alone and the combination caused alterations in developing vasculature.

CONCLUSIONS

The eribulin combination is very active in these xenograft models, but not synergistic in vitro. The combination reduced pharmacodynamic markers indicative of single-agent mechanisms but in tumors, dramatically activated the TP53 pathway. Although a mechanism for in vivo synergy requires further study, it is possible that eribulin-induced inhibition of microtubule dynamics enhances irinotecan-induced nuclear accumulation of TP53, leading to rapid cell death.

Preclinical evaluation of the combination of AZD1775 and irinotecan against selected pediatric solid tumors: A Pediatric Preclinical Testing Consortium report

INTRODUCTION

WEE1 is a serine kinase central to the G₂ checkpoint. Inhibition of WEE1 can lead to cell death by permitting cell-cycle progression despite unrepaired DNA damage. AZD1775 is a WEE1 inhibitor that is in clinical development for children and adults with cancer.

METHODS

AZD1775 was tested using a dose of 120 mg/kg administered orally for days 1 to 5. Irinotecan was administered intraperitoneally at a dose of 2.5 mg/kg for days 1 to 5 (one hour after AZD1775 when used in combination). AZD1775 and irinotecan were studied alone and in combination in neuroblastoma (n = 3), osteosarcoma (n = 4), and Wilms tumor (n = 3) xenografts.

RESULTS

AZD1775 as a single agent showed little activity. Irinotecan induced objective responses in two neuroblastoma lines (PRs), and two Wilms tumor models (CR and PR). The combination of AZD1775 + irinotecan-induced objective responses in two neuroblastoma lines (PR and CR) and all three Wilms tumor lines (CR and 2 PRs). The objective response measure improved compared with single-agent treatment for one neuroblastoma (PR to CR), two osteosarcoma (PD1 to PD2), and one Wilms tumor (PD2 to PR) xenograft lines. Of note, the combination yielded CR (n = 1) and PR (n = 2) in all the Wilms tumor lines. The event-free survival was significantly longer for the combination compared with single-agent irinotecan in all models tested. The magnitude of the increase was greatest in osteosarcoma and Wilms tumor xenografts.

CONCLUSIONS

AZD1775 potentiates the effects of irinotecan across most of the xenograft lines tested, with effect size appearing to vary across tumor panels.

From Clinical Phenotype to Genotypic Modelling: Incidence and Prevalence of Recessive Dystrophic Epidermolysis Bullosa (RDEB)

Background

Recessive dystrophic epidermolysis bullosa (RDEB) is an inherited genetic disorder characterized by recurrent and chronic open wounds with significant morbidity, impaired quality of life, and early mortality. RDEB patients demonstrate reduction or structural alteration type VII collagen (C7) owing to mutations in the gene COL7A1, the main component of anchoring fibrils (AF) necessary to maintain epidermal-dermal cohesion. While over 700 alterations in COL7A1 have been reported to cause dystrophic epidermolysis bullosa (DEB), which may be inherited in an autosomal dominant (DDEB) or autosomal recessive pattern (RDEB), the incidence and prevalence of RDEB is not well defined. To date, the widely estimated incidence (0.2–6.65 per million births) and prevalence (3.5–20.4 per million people) of RDEB has been primarily characterized by limited analyses of clinical databases or registries.

Methods

Using a genetic modelling approach, we use whole exome and genome sequencing data to estimate the allele frequency of pathogenic variants. Through the ClinVar and NCBI database of human genome variants and phenotypes, DEB Register, and analyzing premature COL7A1 termination variants we built a model to predict the pathogenicity of previously unclassified variants. We applied the model to publicly available sequences from the Exome Aggregation Consortium (ExAC) and Genome Aggregation Database (gnomAD) and identified variants which were classified as pathogenic for RDEB from which we estimate disease incidence and prevalence.

Results

Genetic modelling applied to the whole exome and genome sequencing data resulted in the identification of predicted RDEB pathogenic alleles, from which our estimate of the incidence of RDEB is 95 per million live births, 30 times the 3.05 per million live birth incidence estimated by the National Epidermolysis Bullosa Registry (NEBR). Using a simulation approach, we estimate a mean of approximately 3,850 patients in the US who may benefit from COL7A1-mediated treatments in the US.

Conclusion

We conclude that genetic allele frequency estimation may enhance the underdiagnosis of rare genetic diseases generally, and RDEB specifically, which may improve incidence and prevalence estimates of patients who may benefit from treatment.

Abstract C003: Initial testing of m276-PBD CD276 antibody-drug conjugate in preclinical models of pediatric cancers by the Pediatric Preclinical Testing Consortium (PPTC)

Purpose: CD276 (B7-H3) is an immunoregulatory molecule that is reported to be widely expressed in pediatric embryonal tumors, pediatric sarcomas, and tumor infiltrating blood vessels. CD276 protein is expressed at low levels on several normal tissues, including cerebral cortex, liver and germinal lymph node. m276 is a fully-human IgG1 that binds with similar affinity to both mouse CD276 (24 nM kD) and human CD276 (29 nM kD) (Seaman et al., Cancer Cell, 2017). To generate an antibody-drug conjugate, m276 was site-specifically conjugated to the DNA damaging agent pyrrolobenzodiazepine (PBD) via a cleavable valine-alanine linker, providing m276-PBD with a Drug-to-Antibody Ratio (DAR) of 2. Here we examined the antitumor activity of m276-PBD against preclinical xenograft models of pediatric solid tumors. Experimental Procedures: Expression of CD276 across PPTC xenograft models (&gt;200) representing leukemias, brain tumors and solid tumors was determined by RNA seq, and additionally in neuroblastoma models by IHC. Xenograft experiments were undertaken in heterotopic models using standard methods of the PPTC. Response criteria were tumor regression (PR, CR, maintained CR [at 6 weeks]) and Event-Free Survival (EFS). m276-PBD was administered by intraperitoneal injection at a dose of 0.5 mg/kg, once weekly x 3 consecutive weeks. Results: CD276 expression was high in most solid tumors (median 41 FPKM) with highest expression in osteosarcoma. Neuroblastoma, rhabdomyosarcoma, Wilms tumor and embryonal brain tumor models had similar levels of expression, whereas ALL models showed low expression. In vivo efficacy studies are ongoing, but data to date are available for 5 osteosarcoma, 4 rhabdomyosarcoma, 2 Ewing sarcoma and 2 Wilms tumors. Maintained Complete Response (MCR) at 6 weeks was attained in 2/5 osteosarcoma, 3/4 rhabdomyosarcoma and 1/2 Ewing sarcoma. CR was achieved in 1/2 Wilms tumor, 1/2 rhabdomyosarcoma, and 2/5 osteosarcoma models. Body weight loss (&lt;3%) was noted in only one study. Conclusions: Expression of CD276 was high in most PPTC solid tumor models. mCD276-PBD was highly active against most models tested inducing long-lasting CR’s. There was no toxicity, suggesting that this agent has an effective therapeutic window in these models. Mature results (100 days observation) and additional results for neuroblastoma models will be presented.

Citation Format: Raushan Kurmasheva, E. Anders Kolb, Malcolm A. Smith, Beverly A. Teicher, Stephen W. Erickson, John M. Maris, Yael P. Mosse, Kateryna Krytska, David Groff, Matthew Tang, Yifei Wang, Brad St. Croix, Richard Gorlick, Peter J. Houghton. Initial testing of m276-PBD CD276 antibody-drug conjugate in preclinical models of pediatric cancers by the Pediatric Preclinical Testing Consortium (PPTC) [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C003. doi:10.1158/1535-7163.TARG-19-C003

Abstract C004: The CXCR4 inhibitor X4-136 enhances the in vivo efficacy of established drugs against preclinical models of aggressive pediatric acute lymphoblastic leukemia

Introduction: While overall survival for pediatric acute lymphoblastic leukemia (ALL) now approaches 90%, new treatment options are urgently required for certain high-risk subtypes including BCR-ABL1 or TCF3-HLF ALL, and relapsed T-cell ALL (T-ALL). CXCR4 (CD184) is the most frequently over-expressed chemokine receptor in hematological malignancies, including ALL. Binding of CXCL12 to its cognate receptor CXCR4 promotes tumor progression, metastasis and cell survival through multiple signaling pathways, including ERK1/2, RAS, p38 MAPK, PLC/MAPK, SAPK/JNK and cancer stem cell regulation. X4-136 (X4 Pharmaceuticals) is a second-generation potent, orally available, allosteric CXCR4 inhibitor under clinical evaluation. Therefore, it was of interest for the Pediatric Preclinical Testing Consortium to evaluate the in vivo activity of X4-136 in combination with established drugs against patient-derived xenograft (PDX) models of aggressive pediatric ALL. Methods: CXCR4 expression was quantified by RNAseq (https://pedcbioportal.org). Specific antibody binding capacity (sABC) was assessed using the CELLQUANT Calibrator. X4-136 was tested in vivo in NSG mice against 3 ALL PDXs (ALL-4, BCR-ABL1; ALL-7, TCF3-HLF; ALL-31, relapsed T-ALL) at 100 mg/kg/day PO for 4 weeks either as a single agent or in combination with an induction-type regimen of vincristine, dexamethasone and L-asparaginase (VXL). Events were defined as the proportion of human CD45+cells in the peripheral blood (%huCD45+) ≥25%. Drug efficacy was assessed by event-free survival (EFS) of treated (T) and control (C) groups by T-C, T/C and stringent objective response criteria (Houghton PJ, et al. Pediatr Blood Cancer, 2007) and leukemia infiltration into the femoral bone marrow on Day 28 post treatment initiation. Results: RNAseq showed significantly higher (P&lt;0.0001) CXCR4 expression in ALL PDXs (n=90) compared with 154 PDXs derived from 9 other pediatric cancer histotypes. Median CXCR4 sABC on 29 ALL PDXs ranged from 0 to 3,796 (median 476). ALL-4 (median sABC 901), ALL-7 (3,796) and ALL-31 (1,483) were selected for in vivo efficacy studies. X4-136 was generally well tolerated, with maximum average animal weight loss of 4.5 to 8.8% for the 3 PDXs. Single-agent X4-136 significantly (P&lt;0.05) delayed the progression of all 3 PDXs (T-C 1.8-16 days, T/C 1.4-2.2) but elicited no objective responses of the disease. In contrast, X4-136 combined with VXL delayed disease progression by 28.4-35.7 days (T/C 3.8-7.9) and elicited objective responses in all 3 PDXs (2 Complete Responses, 1 Maintained Complete Response). Moreover, the X4-136/VXL combination was significantly more effective than X4-136 and VXL alone against ALL-4 (P&lt;0.05) and ALL-31 (P&lt;0.01) but not ALL-7. Finally, the X4-136/VXL combination significantly decreased leukemia bone marrow infiltration compared with X4-136 and VXL alone in ALL-7 and ALL-31 (P&lt;0.0001). Conclusions: The addition of X4-136 to an established anti-leukemia regimen significantly prolongs time to event in preclinical models of aggressive childhood ALL. Our results support further evaluation of X4-136 in combination with established drugs for pediatric ALL. (Supported by NCI Grants CA199000 and CA199922)

Citation Format: Richard B Lock, Kathryn Evans, Connor D Jones, Narimanne El-Zein, Stephen W Erickson, Sarah Beaussant-Cohen, E. Lynne Kelley, Beverly A Teicher, Malcolm A Smith. The CXCR4 inhibitor X4-136 enhances the in vivo efficacy of established drugs against preclinical models of aggressive pediatric acute lymphoblastic leukemia [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C004. doi:10.1158/1535-7163.TARG-19-C004

Abstract LB-B04: A multi-omic surfaceome study identifies DLK1 as an epigenetically regulated protein and immunotherapeutic target in neuroblastoma

Background: Neuroblastoma (NB) is an embryonal tumor of the sympathetic nervous system that accounts for 12% of childhood cancer deaths. While the introduction of GD2 immunotherapy provides an improvement in time to progression, the therapy is toxic and impact on overall survival is minimal, supporting an urgent need for novel immunotherapies. To date, the cell surface landscape (surfaceome) of NB remains undefined, hindering the identification of immunotherapeutic targets. Methods: To identify NB surfaceome proteins, we performed plasma membrane protein extraction using sucrose gradient ultracentrifugation coupled to mass spectrometry (nLC-MS/MS) in NB cell lines (n=12) and patient derived xenografts (PDX; n=10). These data were integrated with existing RNA-sequencing (NB=153; Normal=7859) and H3K27ac chromatin immunoprecipitation (ChIP)-sequencing data (from overlapping NB cell lines) to evaluate extracellular proteins differentially expressed in NB compared to normal tissues. Candidate targets were validated by immunohistochemistry on NB tumor and normal tissue microarrays (TMAs), flow cytometry and immunofluorescence. In-vitro functional studies were performed following genetic manipulation of candidate targets to assess cell proliferation, differentiation and viability. Finally, we tested ADCT-701 (a DLK1-directed antibody drug conjugate [ADC] with a pyrrolobenzodiazepine [PBD] warhead) in eight PDX models (study ongoing, total of 12 models initiated) with varying levels of DLK1 expression. At enrollment, two mice were each treated with a single dose of saline or 1mg/kg of B12-PL1601 (non-targeting PBD-conjugated ADC) or 1mg/kg ADCT-701 and mice were evaluated for 100 days or until tumor reached 2.0cm3. Results: We yielded on average 66% (range:60-68%) membrane protein enrichment with high reproducibility between biological replicates (80%; range:78-84%) and identified 4826 unique membrane proteins. Our approach confirmed known cell surface proteins in development as immunotherapeutic targets in NB (ALK, GPC2, NCAM1, DLL3 and CD276). Here, we prioritized DLK1 for further evaluation due to it being the only candidate with expression directly associated with a super enhancer element (P=6.09X10-5). RNA-sequencing and tissue microarray analysis of NB and normal tissues showed DLK1 to be overexpressed in a large subset of high-risk NB with minimal expression in normal tissues, excepting adrenal medulla and pituitary. Flow cytometry and immunofluorescence confirmed cell surface expression of DLK1 in a panel of NB cell lines. Genetic depletion of DLK1 using shRNA resulted in neurite outgrowth (P=7.26X10-5) and terminal differentiation. Full proteome analysis of DLK1 knockdown and control cell lines using MS showed regulation of proteins that control outgrowth of neurites (P=3.37X10-3) and development of neurons (P=3.76X10-3). To date, ADCT-701 treatment resulted in maintained complete response (N=2), complete response (N=3) and stable disease (N=1) in models with high DLK1 expression, while those with low/no expression showed disease progression (N=2). Conclusion: DLK1 is an epigenetically regulated immunotherapeutic target in neuroblastoma. ADCT-701 shows potent activity in preclinical models of NB and should be prioritized for clinical development.

Citation Format: Amber K. Weiner, Alexander B. Radaoui, Matthew Tsang, Dan Martinez, Simone Sidoli, Karina L. Conkrite, Alberto Delaidelli, Jo Lynne Rokita, Maria V. Lane, Zalman Vaksman, Komal S. Rathi, Pichai Raman, Jennifer Pogoriler, Tricia Bhatti, Bruce Pawel, Beverly Teicher, Stephen W. Erickson, Poul Sorensen, Yael P. Mosse, Kateryna Krytska, Francesca Zammarchi, Patrick H. van Berkel, Malcolm A. Smith, Benjamin A. Garcia, John M. Maris, Sharon J. Diskin. A multi-omic surfaceome study identifies DLK1 as an epigenetically regulated protein and immunotherapeutic target in neuroblastoma [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr LB-B04. doi:10.1158/1535-7163.TARG-19-LB-B04

Evaluation of entinostat alone and in combination with standard-of-care cytotoxic agents against rhabdomyosarcoma xenograft models

BACKGROUND

Entinostat, a selective class I histone deacetylase inhibitor, has been reported to enhance the activity of cytotoxic agents and suppress expression of PAX3-FOXO1 in alveolar rhabdomyosarcoma (ARMS).

PROCEDURES

Entinostat was tested against three rhabdomyosarcoma cell lines using 96-hour drug exposure. Entinostat alone or in binary combination with vincristine, actinomycin D or cyclophosphamide was tested in ARMS and two embryonal rhabdomyosarcoma (ERMS) xenograft models. Tumor growth was measured at weekly intervals. Drug-induced changes in acetylated histone H3(K9) and entinostat pharmacokinetics were determined.

RESULTS

In vitro, the IC₅₀ concentration of entinostat ranged from 280 to 1300 nM. In vivo, entinostat significantly inhibited the growth of only Rh10 xenografts. For most studies, entinostat did not potentiate the activity of the cytotoxic agent. Exceptions included the vincristine and entinostat combination for Rh10 and the entinostat and actinomycin D combination for Rh10 and Rh18, although the effects were modest. For Rh18, the combination of entinostat with vincristine showed evidence of an antagonistic interaction compared with single-agent vincristine. Pharmacokinetic studies showed the average C_max was 569.4 ng/mL (1.51 μM) with T_max at 15 minutes, and total exposure (AUC_{0-12 h} ) was 435.6 h × ng/mL. Entinostat treatment increased acetylated histone H3.

CONCLUSIONS

Entinostat demonstrated modest antitumor activity in only one of four models at dose and shedule that gave drug exposures relevant to human treatment. The addition of entinostat to standard-of-care cytotoxic agents was in most instances no more effective than the cytotoxic agents used alone. Entinostat demonstrated target inhibition with increased histone 2A acetylation.

Abstract LB-321: Re-evaluating sample sizes in preclinical testing of patient-derived xenografts

The NCI Pediatric Preclinical Testing Consortium (PPTC) has established panels of patient-derived xenografts (PDXs) and cell lines of pediatric cancers for preclinical testing. We performed a systematic analysis of in vivo testing results from 2015-2018 to re-evaluate the number of mice needed for testing. Data were compiled from experiments performed on 30 anti-cancer agents; each agent was tested against 1 to 31 PDXs (median, 9) from a consortium-wide panel of 112 PDXs.

We evaluated time-to-event across control mice, with “event” defined as quadrupling of tumor volume in solid tumors, mice becoming moribund or severely neurologically deficient in brain tumors, and hCD45+ &gt; 25% or other leukemic event for leukemia. Observed median time-to-event and coefficient of variation (CV, standard deviation/mean) varied between PDXs. Overall, the median CV was 0.257 with an interquartile range of 0.172 to 0.363.

We estimated the power to detect differential time-to-event across a range of parameters observed historically. We modeled time-to-event under two scenarios: a right-skewed, heavy-tailed log-normal distribution, and a more symmetric and light-tailed gamma distribution. We also varied CV and treatment effect size (T/C, ratio of median time-to-event between treated and controls). The PPTC defines a median T/C of 2 or greater as growth delay; progressive disease with growth delay is the lowest objective response measure beyond that of controls. Differential time-to-event was evaluated using the Gehan-Wilcoxon test.

The PPTC has generally used sample sizes of 8 or 10 mice per group. Under both the log-normal and gamma models, a sample size of 5 mice per group yielded ≥87% power to detect a T/C of 2 assuming a CV of 0.3; over 60% of tested PDXs have a CV lower than this. Table 1 summarizes our results across a subset of parameters used in our calculations. Our results suggest that for most PPTC PDXs, power for detecting major growth delay effects can be maintained while employing fewer mice than used previously.

Table 1Summary of Power Analysis for α = 0.05CoefficientTime-to-eventPower (α = 0.05)Distributionof VariationMedian T/Cn = 3n = 5n = 8n = 10Log-normal0.202.095.8%99.6%100.0%100.0%3.0100.0100.0100.0100.00.302.075.390.598.799.93.097.299.7100.0100.00.402.056.868.790.595.73.085.896.0100.0100.00.502.044.051.975.984.53.073.187.197.799.8Gamma0.202.094.499.1100.0100.03.0100.0100.0100.0100.00.302.072.587.098.0100.03.095.099.5100.0100.00.402.051.164.985.692.93.082.894.199.699.90.502.038.246.369.380.23.066.079.496.698.9

Citation Format: Eric Earley, Richard Gorlick, Peter J. Houghton, John M. Maris, Xiao-Nan Li, Richard B. Lock, Beverly Teicher, Malcolm A. Smith, Stephen W. Erickson. Re-evaluating sample sizes in preclinical testing of patient-derived xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-321.

Evaluation of the TPO-receptor agonist Eltrombopag in the Pediatric Preclinical Testing Consortium osteosarcoma in vivo models

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Background: Eltrombopag (EP) is a small molecule, thrombopoietin receptor (TPO-R) agonist indicated for the treatment of patients with chronic immune thrombocytopenia and severe aplastic anemia. EP is a polyvalent cation chelator and inhibits leukemia cell proliferation via depletion of intracellular iron. Recent studies show EP inhibits the proliferation of osteosarcoma cells lines via depletion of polyvalent cations. The in vivo effects of EP were studied in osteosarcoma patient derived xenograft models by the Pediatric Preclinical Testing Consortium (PPTC). Methods: The in vivo anticancer effects of EP were assessed in a panel of six osteosarcoma PPTC PDX models with limited MPL mRNA expression (OS2, OS9, OS31, OS33, OS36, OS60). EP was administered at an oral dose of 5 mg/kg/day given for 5 days each week with planned treatment period of 4 weeks. High dose EP (50mg/kg/day) was also tested in 2 PDX models (OS2, OS9) on the same schedule. A control cohort that received vehicle was included for each PDX model. Tumor volumes were measured and responses defined utilizing the PPTC statistical analyses. Results: EP at 5 mg/kg failed to inhibit tumor growth or induce significant differences in event-free survival (EFS) in any of the 6 osteosarcoma PDX models. At the higher dose of 50 mg/kg a significant prolongation in time to event in the EP-treated group was observed, but the effect was small with the ratio of the median time to event for treated versus control animals (EFS T/C) being only 1.2 in the 2 OS PDX models tested. No objective responses were observed with EP at either dose, with all models demonstrating progressive disease. Conclusions: EP did not exhibit significant antitumor activity against the PPTC osteosarcoma PDX panel. However, EP also did not enhance tumor growth. EP’s lack of anti-tumor activity against the OS PDX models suggests leukemia and osteosarcoma cells likely have different dependencies on intracellular polyvalent cations. Given EPs effect on stimulating platelet production, and the demonstration that EP does not stimulate in vivo growth of osteosarcoma, EP may be considered in patients with osteosarcoma as a supportive care agent in supporting platelet recovery.

Evaluation of the multi-kinase inhibitor regorafenib in the Pediatric Preclinical Testing Consortium osteosarcoma, rhabdomyosarcoma, and Ewing sarcoma in vivo models

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Background: Regorafenib is a multi-kinase inhibitor, developed by adding a fluorine atom to the phenyl ring of sorafenib. Regorafenib inhibits multiple kinases including BRAF, FGFR1, KIT, PDGFRB, RAF, RET, and VEGFR1-3, many at a higher potency than sorafenib. Prior studies within the Pediatric Preclinical Testing Consortium (PPTC) demonstrated sorafenib exhibited intermediate activity for tumor growth inhibition in more than 50% of the sarcoma models tested at a dose of 60mg/kg by oral gavage daily (5 days/wk for 6 consecutive weeks). The in vivo effects of regorafenib were studied in the PPTC osteosarcoma (OS), rhabdomyosarcoma (Rh) and Ewing (EW) sarcoma xenograft models. Methods: The in vivo anticancer effects of regorafenib were assessed in a panel of 6 osteosarcoma models (OS2, OS9, OS31, OS33, OS36, OS60), two rhabdomyosarcoma models (Rh30, Rh41), and one Ewing sarcoma model (EW5). Regorafenib was administered by oral gavage at a dose of 30 mg/kg/day given daily for 21 consecutive days. Time to event and tumor volume responses were defined and analyzed utilizing standard PPTC statistical methods. Results: Regorafenib induced significant improvements in event-free survival (EFS) compared to control in 100% (9/9) of sarcoma models tested. Most models showed pronounced slowing of tumor growth compared to control during the 21 days of regorafenib treatment, with tumor growth generally approximating control rates soon after completion of regorafenib treatment. Three out of 8 sarcoma models demonstrated EFS T/C values > 2 (1/6 OS, 2/2 Rh, 0/1 EW). Minimum relative tumor volumes ranged from 0.74 to 1.60, with no models meeting criteria for objective response. Conclusions: Regorafenib induced modest inhibition of tumor growth in the PPTC sarcoma models evaluated. The overall pattern of response to the multi-kinase inhibitor regorafenib against the PPTC sarcoma models appears similar to that of the kinase inhibitor sorafenib, with pronounced slowing of tumor growth in some models that is limited to the period of agent administration being the primary treatment effect.

OBI-3424, a Novel AKR1C3-Activated Prodrug, Exhibits Potent Efficacy against Preclinical Models of T-ALL

PURPOSE

OBI-3424 is a highly selective prodrug that is converted by aldo-keto reductase family 1 member C3 (AKR1C3) to a potent DNA-alkylating agent. OBI-3424 has entered clinical testing for hepatocellular carcinoma and castrate-resistant prostate cancer, and it represents a potentially novel treatment for acute lymphoblastic leukemia (ALL).

EXPERIMENTAL DESIGN

We assessed AKR1C3 expression by RNA-Seq and immunoblotting, and evaluated the in vitro cytotoxicity of OBI-3424. We investigated the pharmacokinetics of OBI-3424 in mice and nonhuman primates, and assessed the in vivo efficacy of OBI-3424 against a large panel of patient-derived xenografts (PDX).

RESULTS

AKR1C3 mRNA expression was significantly higher in primary T-lineage ALL (T-ALL; n = 264) than B-lineage ALL (B-ALL; n = 1,740; P < 0.0001), and OBI-3424 exerted potent cytotoxicity against T-ALL cell lines and PDXs. In vivo, OBI-3424 significantly prolonged the event-free survival (EFS) of nine of nine ALL PDXs by 17.1-77.8 days (treated/control values 2.5-14.0), and disease regression was observed in eight of nine PDXs. A significant reduction (P < 0.0001) in bone marrow infiltration at day 28 was observed in four of six evaluable T-ALL PDXs. The importance of AKR1C3 in the in vivo response to OBI-3424 was verified using a B-ALL PDX that had been lentivirally transduced to stably overexpress AKR1C3. OBI-3424 combined with nelarabine resulted in prolongation of mouse EFS compared with each single agent alone in two T-ALL PDXs.

CONCLUSIONS

OBI-3424 exerted profound in vivo efficacy against T-ALL PDXs derived predominantly from aggressive and fatal disease, and therefore may represent a novel treatment for aggressive and chemoresistant T-ALL in an AKR1C3 biomarker-driven clinical trial.

Broad Spectrum Activity of the Checkpoint Kinase 1 Inhibitor Prexasertib as a Single Agent or Chemopotentiator Across a Range of Preclinical Pediatric Tumor Models

PURPOSE

Checkpoint kinase 1 (CHK1) inhibitors potentiate the DNA-damaging effects of cytotoxic therapies and/or promote elevated levels of replication stress, leading to tumor cell death. Prexasertib (LY2606368) is a CHK1 small-molecule inhibitor under clinical evaluation in multiple adult and pediatric cancers. In this study, prexasertib was tested in a large panel of preclinical models of pediatric solid malignancies alone or in combination with chemotherapy.

EXPERIMENTAL DESIGN

DNA damage and changes in cell signaling following in vitro prexasertib treatment in pediatric sarcoma cell lines were analyzed by Western blot and high content imaging. Antitumor activity of prexasertib as a single agent or in combination with different chemotherapies was explored in cell line-derived (CDX) and patient-derived xenograft (PDX) mouse models representing nine different pediatric cancer histologies.

RESULTS

Pediatric sarcoma cell lines were highly sensitive to prexasertib treatment in vitro, resulting in activation of the DNA damage response. Two PDX models of desmoplastic small round cell tumor and one malignant rhabdoid tumor CDX model responded to prexasertib with complete regression. Prexasertib monotherapy also elicited robust responses in mouse models of rhabdomyosarcoma. Concurrent administration with chemotherapy was sufficient to overcome innate resistance or prevent acquired resistance to prexasertib in preclinical models of neuroblastoma, osteosarcoma, and Ewing sarcoma, or alveolar rhabdomyosarcoma, respectively.

CONCLUSIONS

Prexasertib has significant antitumor effects as a monotherapy or in combination with chemotherapy in multiple preclinical models of pediatric cancer. These findings support further investigation of prexasertib in pediatric malignancies.

Abstract LB-136: Pediatric Preclinical Testing Consortium evaluation of a DLL3-targeted antibody drug conjugate rovalpituzumab tesirine, in neuroblastoma

Introduction: Rova-T (SC16LD6.5) is an ADC targeting delta-like protein 3 (DLL3), a member of the delta-notch signaling pathway, composed of the monoclonal antibody SC16 conjugated to the DNA-damaging D6.5 pyrrolobenzodiazepine (PBD) dimer toxin. In clinical trials, Rova-T demonstrated anti-tumor activity in patients with small cell lung cancer with high DLL3 protein expression. We have identified DLL3 as highly expressed in NBs, especially the MYCN-amplified subset. Here, we characterize the expression of DLL3 in NB patient derived xenografts (PDX), and define the efficacy of Rova-T in these models ex vivo and in vivo.

Methods: To assess DLL3 protein expression, we performed immunohistochemistry (IHC) on 32 PDXs from high-risk human primary tumors in tissue microarrays. We quantified cell surface DLL3 from dissociated PDX tumors using immunoblotting and flow-cytometry with a PE-conjugated DLL3 antibody. The cytotoxic activity of Rova-T against 8 dissociated PDXs placed in short term culture was evaluated using cell viability assays and a testing range of 10 fm to 10 nM. The in vivo activity of Rova-T was tested against 3 NB PDX models (Felix-PDX, COG-N-452x and COG-N-415x) using single intraperitoneal injection on day 0. Treatment groups included: vehicle control, IgGADC6.5 at 0.6 mg/kg, and Rova-T at 0.1 mg/kg, 0.3 mg/kg or 0.6 mg/kg. Events were defined as quadrupling of tumor volume from day 0.

Results:

DLL3 protein was expressed in 27 of 32 NB PDXs. The median percentage of tumor cells with a ≥ 2+ intensity was 25%-55% in 12/27 samples, 55%-85% in 8/27 samples and 85%-100% in 7/27 samples. The relative IHC scores in the tested samples correlated with levels of cell surface DLL3 and with DLL3 protein and RNA expression levels assessed by immunoblotting and RNAseq. Rova-T showed IC50 values from 0.026-47.25 nM, whereas PBD alone showed IC50 values from 0.003-0.345 nM. Tumors that expressed high DLL3 levels did not necessarily show a higher sensitivity to Rova-T ex vivo. In vivo, Rova-T induced significant differences in EFS distribution compared to control in 3 of 3 PDX models treated with 0.6 mg/kg and in 1 of 2 PDX models dosed at 0.1 and 0.3 mg/kg. All 3 PDX models showed a &gt;2-fold extension in median EFS for treated compared to control animals at 0.6 mg/kg. Two PDXs, COG-N-452x and Felix-PDX, had a minimum relative tumor volume &lt;0.2 to 0.6 mg/kg, and achieved complete and partial responses, respectively. Among the PDXs tested, DLL3 expression was lowest in COG-N-452x; this model showed superior in vivo sensitivity to Rova-T compared with the other 2 models which had higher DLL3 expression and also higher IC50 values for PBD.

Conclusions: These data suggest that targeting DLL3 using an ADC approach in NB could be an active therapeutic strategy. Studies are ongoing to further explore biomarkers of response as DLL3 expression alone may be insufficient for NB.

Citation Format: Renata Sano, Kateryna Krytska, Matthew Tsang, Stephen W. Erickson, Beverly A. Teicher, Laura Saunders, Ryan T. Jones, Malcom A. Smith, John M. Maris, Yael P. Mosse. Pediatric Preclinical Testing Consortium evaluation of a DLL3-targeted antibody drug conjugate rovalpituzumab tesirine, in neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-136.

Abstract 3187: Pediatric Preclinical Testing Consortium evaluation of the menin inhibitor, VTP-50469, against xenograft models of MLL-rearranged infant acute lymphoblastic leukemia

Introduction: Rearrangements involving the MLL (mixed lineage leukemia, KMT2A) gene (MLLr) occur broadly in acute leukemia, in ~80% of infant acute lymphoblastic leukemia (ALL) cases, and are associated with poor outcome. Menin is a ubiquitously expressed nuclear protein, and the MLLr-menin interaction is the key impetus for transformation of MLLr-expressing cells. VTP-50469 is a potent, orally available, small molecule inhibitor of the MLL-menin interaction with pM binding affinity for menin. Therefore, it was of interest to test the in vivo efficacy of VTP-50469 against preclinical models of infant MLLr-ALL.

Methods: Infant MLLr-ALL patient-derived xenografts (PDXs) grew in an orthotopic manner in NSG mice. Engraftment and response to treatment were assessed by enumeration of the % human leukemic blasts in the murine peripheral blood (%huCD45+). Treatment commenced when the median %huCD45+ exceeded 1%, and mice received VTP-50469 (120 mg/kg by oral gavage twice daily x 28) or vehicle. An event was defined as the %huCD45+ &gt;25% or leukemia-related morbidity. The Kaplan-Meier method was used to compare event-free survival (EFS) between treated (T) and control (C) groups. Stringent objective response measures were assigned to each mouse and reported as group medians (Houghton et al, Pediatr. Blood Cancer, 2007;49:928-40). Leukemia infiltration into the femoral bone marrow was also assessed at Day 28 following treatment initiation. VTP-50469 was provided by Vitae Pharmaceuticals.

Results: VTP-50469 was well tolerated, with maximum average weight losses of 1.6-6.4% across treatment groups compared to 0-2.0% in vehicle control treated groups. VTP-50469 induced significant differences in EFS distribution compared to control in 6 of 6 (100%) of the evaluable MLLr-ALL PDXs. VTP-50469 T-C values in MLLr-ALL PDXs ranged from 1.2 to 100 days (T/C 1.3-21.1), and Maintained Complete Responses (MCRs) were observed in 5 of 6 PDXs. Two of 8 mice engrafted with an MLLr-ALL harboring the MLL-AFF1 (t4;11) translocation had not reached event &gt;230 days following treatment initiation. A significant reduction (P&lt;0.001) in bone marrow infiltration at Day 28 was observed in 2 of 4 evaluable MLLr-ALL PDXs. VTP-50469 at 30 mg/kg (4-fold lower than its maximum tolerated dose) also elicited MCRs in 8 of 8 mice engrafted with an MLL-AFF1 PDX. The on-target activity of VTP-50469 was verified by its lack of efficacy against an ALL PDX harboring the BCR-ABL1 translocation.

Conclusions: VTP-50469 exerted profound in vivo efficacy against ALL PDXs derived from infants harboring MLL-AFF1, MLL-GAS7, and MLL-ENL translocations, and significantly reduced leukemia infiltration in the bone marrow. VTP-50469 was also effective across a broad dose range, indicating that it may represent a novel treatment for MLLr leukemia. (Supported by NCI Grants CA199222 & CA199000)

Citation Format: Richard B. Lock, Kathryn Evans, Tara Pritchard, Stephen W. Erickson, Yuelong Guo, David A. Claremon, Gerard M. McGeehan, Beverly A. Teicher, Malcolm A. Smith. Pediatric Preclinical Testing Consortium evaluation of the menin inhibitor, VTP-50469, against xenograft models of MLL-rearranged infant acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3187.

Bone Health and Endocrine Care of Boys with Duchenne Muscular Dystrophy: Data from the MD STARnet

BACKGROUND

Patients with Duchenne muscular dystrophy (DMD) are at high risk of endocrine and bone health complications resulting from the high glucocorticoid (GC) doses used to treat this condition. There are limited data characterizing the clinical management of these complications.

OBJECTIVE

To determine the frequency of bone health screening, endocrinologist evaluation, and use of endocrine and bone health pharmacotherapy in the clinical care of males with DMD.

METHODS

A population based cohort study using data from the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) was conducted. Clinical data was abstracted from the medical records of 683 males with DMD at five surveillance sites across the US.

RESULTS

A DXA scan had been documented in 24% of cases; the percentage of cases with DXA varied across surveillance sites from 13% to 43%, p < 0.001. History of fracture and greater disease duration were associated with greater odds of having a DXA. Only 4.7% of cases had documentation of an endocrinologist evaluation. The frequency of documented endocrine and bone health pharmacotherapy use included calcium (42.8%), vitamin D (36.6%), bisphosphonates (13.3%), growth hormone (1.9%), testosterone (1.7%), insulin (1.2%), and metformin (0.3%)Conclusions:A low percentage of DMD males had record of DXA scan, endocrinologist evaluation, or treatment with endocrine or bone health pharmacotherapy. Endocrine and bone health care may represent an unmet need in the DMD population.

Abstract LB-B14: Pediatric Preclinical Testing Consortium evaluation of the second-generation selective inhibitor of nuclear export (SINE) compound KPT-8602

Introduction: KPT-8602 is a second-generation SINE compound that specifically blocks exportin-1 (XPO1) cargo interactions. XPO1 is a nuclear export receptor, a critical regulator of cell proliferation and survival, that is characterized as the sole transporter of several tumor suppressor and growth regulatory proteins, including p53, p21, p27, BCR-ABL, FOXO and STAT3. Overexpression of XPO1 has been correlated with high-risk disease and poor survival in multiple pediatric cancers, including leukemia and neuroblastoma (NB). Our prior work demonstrated that selinexor, a closely-related SINE compound, induced complete remission (CR) or maintained CR (MCR) in 2 of 8 ALL patient-derived xenografts (PDXs) tested while it did not induce tumor regressions in 6 neuroblastoma models (Attiyeh EF, et al. Pediatr Blood Cancer. 2016;63:276-86). While selinexor has shown activity in a variety of adult malignancies and is being tested in pediatric phase 1 trials, KPT-8602 shows similar pharmacokinetic properties to selinexor and improved tolerability in preclinical models, and thus it was tested against ALL and NB models by the PPTC. Methods: KPT-8602 was tested against 6 NB and 12 ALL pediatric PDX models using 10 and 8 mice/arm, respectively. Based on tolerability, a dose of 12.5 mg/kg was selected and administered once daily via oral gavage 5 days per week for 4 weeks. Events were defined as quadrupling of tumor volume from day 0 (for NB) or as the proportion of human CD45+ cells in the peripheral blood (%huCD45+) ≥25% (for ALL). The Kaplan-Meier method was used to compare time-to-event between treated and control groups. Objective response categories were assigned as progressive disease (PD, which is subdivided into progressive disease without or with growth delay, PD1 or PD2, respectively), stable disease (SD), partial response (PR), CR, and MCR [Houghton PJ, et al. Pediatr Blood Cancer, 2007]. KPT-8602 was developed and provided for testing by Karyopharm Therapeutics, Inc. Results: KPT-8602 was generally well tolerated, but with weight loss during treatment of approximately 15% and 2% for the neuroblastoma and ALL models, respectively. KPT-8602 induced significant differences in event free survival (EFS) distribution compared to control in 16 of the 18 (88.9%) evaluable xenograft lines studied. Four NB and 10 ALL PDX models showed a &gt;2-fold extension in median EFS for treated compared to control animals. For the 6 NB PDX models, 3 had a minimum relative tumor volume (minRTV) of &lt;1, and 2 achieved PR while 1 was PD2. For the ALL panel, 3 achieved a CR and 3 more achieved a MCR. Among the ALL PDXs achieving CR/MCR were 4 B-cell ALL (including 2 Ph-like ALL) and 2 T-ALL. The neuroblastoma PDX showing the most favorable response to selinexor showed a PR to KPT-8602, and the 2 ALL PDXs with CR/MCR responses to selinexor showed MCR responses to KPT-8602. Conclusions: These data indicate that KPT-8602 demonstrates significant anti-cancer efficacy and tolerability in preclinical models of childhood ALL and NB. Our results support further preclinical testing of KPT-8602 in combination with other targeted therapies for ALL and NB, as well as testing against additional pediatric cancer models in the PPTC. (Supported by NCI Grants: CA199222; CA199000; CA199287)

Citation Format: Kateryna Krytska, Kathryn Evans, Tara Pritchard, Matthew Tsang, Raymond Yung, Yael P. Mosse, Stephen W. Erickson, Yuelong Guo, Erkan Baloglu, Yosef Landesman, Kyle A. Jensen, William Senapedis, Beverly A. Teicher, Malcolm A. Smith, Richard B. Lock, John M. Maris. Pediatric Preclinical Testing Consortium evaluation of the second-generation selective inhibitor of nuclear export (SINE) compound KPT-8602 [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr LB-B14.

Refractory urgency urinary incontinence treatment in women: impact of age on outcomes and complications

BACKGROUND

Women with refractory urgency urinary incontinence (ie, unresponsive to behavioral and pharmacological interventions) are treated with onabotulinumtoxinA or sacral neuromodulation.

OBJECTIVE

The objective of the study was to compare treatment efficacy and adverse events in women <65 and ≥65 years old treated with onabotulinumtoxinA or sacral neuromodulation.

STUDY DESIGN

This study was a planned secondary analysis of a multicenter, randomized trial that enrolled community-dwelling women with refractory urgency urinary incontinence to onabotulinumtoxinA or sacral neuromodulation treatments. The primary outcome was a change in mean daily urgency urinary incontinence episodes on a bladder diary over 6 months. Secondary outcomes included ≥75% urgency urinary incontinence episode reduction, change in symptom severity/quality of life, treatment satisfaction, and treatment-related adverse events.

RESULTS

Both age groups experienced improvement in mean urgency urinary incontinence episodes per day following each treatment. There was no evidence that mean daily urgency urinary incontinence episode reduction differed between age groups for onabotulinumtoxinA (adjusted coefficient, -0.127, 95% confidence interval, -1.233 to 0.979; P = .821) or sacral neuromodulation (adjusted coefficient, -0.698, 95% confidence interval, -1.832 to 0.437; P = .227). Among those treated with onabotulinumtoxinA, women <65 years had 3.3-fold greater odds of ≥75% resolution than women ≥65 years (95% confidence interval, 1.56 -7.02). Women <65 years had a greater reduction in Overactive Bladder Questionnaire Short Form symptom bother scores compared with women ≥65 years by 7.49 points (95% confidence interval, -3.23 to -11.74), regardless of treatment group. There was no difference between quality of life improvement by age. Women ≥65 years had more urinary tract infections following onabotulinumtoxinA and sacral neuromodulation (odds ratio, 1.9, 95% confidence interval, 1.2-3.3). There was no evidence of age differences in sacral neuromodulation revision/removal or catheterization following onabotulinumtoxinA treatment.

CONCLUSION

Younger women experienced greater absolute continence, symptom improvement, and fewer urinary tract infections; both older and younger women had beneficial urgency urinary incontinence episode reduction, similar rates of other treatment adverse events, and improved quality of life.

Abstract LB-B16: The AKR1C3-Activated Prodrug OBI-3424 Exerts Profound In Vivo Efficacy Against Preclinical Models of T-Cell Acute Lymphoblastic Leukemia (T-ALL); a Pediatric Preclinical Testing Consortium Study

Introduction: Aldo-keto reductase family 1 member C3 (AKR1C3) belongs to a superfamily of oxidoreductases that are broadly expressed in human tissues. AKR1C3 catalyzes the reduction of a diverse group of substrates, and is expressed at high levels in several human cancers including T-ALL. We previously showed that AKR1C3 is a biomarker of T-ALL sensitivity to the hypoxia-activated pre-prodrug PR-104, which is also activated under aerobic conditions by AKR1C3 (Manesh et al, Blood, 2015;126:1193-202). Therefore, it was of interest to test the in vivo efficacy of OBI-3424 against preclinical models of T-ALL, since OBI-3424 is a highly selective prodrug that is converted by AKR1C3 to a DNA alkylating agent. Methods: ALL patient-derived xenografts (PDXs) grew in an orthotopic manner following intravenous inoculation into NSG mice. Engraftment and response to treatment were assessed by enumeration of the % human leukemic blasts in the murine peripheral blood (%huCD45+). Treatment commenced when the %huCD45+ exceeded a median of 1%, and mice received OBI-3424 (2.5 mg/kg by the intraperitoneal route once weekly x 3) or vehicle. An event was defined as the %huCD45+ exceeding 25% or leukemia-related morbidity. The Kaplan-Meier method was used to compare event-free survival (EFS) between treated (T) and control (C) groups. Stringent objective response measures were assigned to each mouse and reported as group medians (Houghton et al, PBC, 2007;49:928-40). Leukemia infiltration into the femoral bone marrow was also assessed at Day 28 following treatment initiation. OBI-3424 was provided by Threshold Pharmaceutical and is being developed by OBI Pharma, Inc. (ex-Asia) and Ascenta Pharma (Asia). Results: OBI-3424 was well tolerated, with only a 2.8% toxicity rate in the drug-treated groups. OBI-3424 induced significant differences in EFS distribution compared to control in 9 of 9 (100%) of the evaluable PDXs. T-C values ranged from 17.1 to 65.2 days (T/C 2.3-14.0), and objective responses were observed in 8 of 9 PDXs (2 complete responses, CRs; 6 maintained CRs, MCRs). A significant reduction (P&lt;0.0001) in bone marrow infiltration at Day 28 was observed in 4 of 6 evaluable T-ALL PDXs. The importance of AKR1C3 in the in vivo responses of ALL PDXs to OBI-3424 was verified using a B-cell precursor ALL PDX (ALL-11) that had been lentivirally transduced to stably overexpress AKR1C3 (ALL-11/1C3) compared with empty vector control (ALL-11/EV). Mice engrafted with ALL-11/1C3 exhibited an MCR (T-C &gt;37.3 days, T/C &gt;3) compared with a CR for ALL-11/EV (T-C 21.1 days, T/C 2.5). Infiltration of ALL-11/1C3 cells into the murine bone marrow was significantly reduced at Day 28 in OBI-3424-treated compared with vehicle-treated mice (P&lt;0.0001) but not in mice engrafted with ALL-11/EV. Conclusions: At a dose of 2.5 mg/kg, which is estimated to achieve exposure levels in mice that will be readily attainable in humans, OBI-3424 exerted profound in vivo efficacy against a broad range of T-ALL PDXs and significantly reduced leukemia infiltration in the bone marrow. Since these PDXs were derived predominantly from aggressive and fatal disease, OBI-3424 may represent a novel treatment for aggressive and chemoresistant T-ALL in an AKR1C3 biomarker-driven clinical trial. (Supported by NCI Grants CA199222 & CA199000)

Citation Format: Richard B. Lock, Kathryn Evans, Raymond Yung, Tara Pritchard, Beverly A. Teicher, JianXin Duan, Yuelong Guo, Stephen W. Erickson, Malcolm A. Smith. The AKR1C3-Activated Prodrug OBI-3424 Exerts Profound In Vivo Efficacy Against Preclinical Models of T-Cell Acute Lymphoblastic Leukemia (T-ALL); a Pediatric Preclinical Testing Consortium Study [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr LB-B16.

Trichloroethylene-induced alterations in DNA methylation were enriched in polycomb protein binding sites in effector/memory CD4+ T cells

Exposure to industrial solvent and water pollutant trichloroethylene (TCE) can promote autoimmunity, and expand effector/memory (CD62L) CD4+ T cells. In order to better understand etiology reduced representation bisulfite sequencing was used to study how a 40-week exposure to TCE in drinking water altered methylation of ∼337 770 CpG sites across the entire genome of effector/memory CD4+ T cells from MRL+/+ mice. Regardless of TCE exposure, 62% of CpG sites in autosomal chromosomes were hypomethylated (0-15% methylation), and 25% were hypermethylated (85-100% methylation). In contrast, only 6% of the CpGs on the X chromosome were hypomethylated, and 51% had mid-range methylation levels. In terms of TCE impact, TCE altered (≥ 10%) the methylation of 233 CpG sites in effector/memory CD4+ T cells. Approximately 31.7% of these differentially methylated sites occurred in regions known to bind one or more Polycomb group (PcG) proteins, namely Ezh2, Suz12, Mtf2 or Jarid2. In comparison, only 23.3% of CpG sites not differentially methylated by TCE were found in PcG protein binding regions. Transcriptomics revealed that TCE altered the expression of ∼560 genes in the same effector/memory CD4+ T cells. At least 80% of the immune genes altered by TCE had binding sites for PcG proteins flanking their transcription start site, or were regulated by other transcription factors that were in turn ordered by PcG proteins at their own transcription start site. Thus, PcG proteins, and the differential methylation of their binding sites, may represent a new mechanism by which TCE could alter the function of effector/memory CD4+ T cells.

Abstract 1942: The nicotinamide phosphoribosyltransferase (NAMPT) inhibitor, OT-82, exhibits in vitro and in vivo efficacy against patient-derived xenograft models of high-risk acute lymphoblastic leukemia

Cancer cells are highly dependent on nicotinamide phosphoribosyltransferase (NAMPT) for the biosynthesis of nicotinamide adenine dinucleotide (NAD). Besides its role in energy metabolism, NAMPT influences the activity of NAD-dependent enzymes, including poly (ADP-ribose) polymerase-1 (PARP-1) and sirtuins, and thereby regulates cellular survival and stress response. Disruption of NAD synthesis through NAMPT inhibition represents a potential therapeutic strategy for treating cancer. The aim of this study was to evaluate the efficacy of the novel NAMPT inhibitor OT-82, initially isolated for its selective toxicity against a panel of adult leukemia cell lines, in a diverse panel of leukemia cell lines in vitro and pediatric acute lymphoblastic leukemia (ALL) patient-derived xenografts (PDXs) in vivo, and to identify potential biomarkers predictive of OT-82 response. OT-82 demonstrated low nanomolar IC50 values (0.9 – 3.4 nM) in 3 ALL and 3 acute myeloid leukemia cell lines as determined by resazurin reduction assays. In vivo efficacy of OT-82 (40 mg/kg x 3 days x 3 weeks, p.o.) was evaluated as a single agent against pediatric ALL PDXs, including B-cell precursor ALL (n = 3), Philadelphia chromosome (Ph) positive ALL (n = 2), Ph-like ALL (n = 2), T-cell ALL (n = 3), and early T-cell precursor ALL (n = 3) in immune deficient (NSG) mice. Response to treatment was assessed by time to event or stringent objective response criteria modeled after the clinical setting. OT-82 was well tolerated, significantly increased event-free survival (EFS) relative to control mice in 11/13 ALL PDXs, and elicited objective responses in 11/13 (85%) PDXs [3 Partial Responses, 4 Complete Responses (CRs) and 4 Maintained CRs (MCRs)]. Analysis of basal protein expression revealed elevated levels of poly (ADP-ribosyl)ated (PARylated) PARP-1 in 4/5 responders versus 0/2 non-responders. In vitro studies examining various chemotherapeutic agents used for childhood leukemia showed synergy between cytarabine (AraC) and OT-82 in an ALL cell line. In an OT-82 sensitive Mixed Lineage Leukemia (MLL) PDX, treatment with AraC (25 mg/kg x 5 days x 2 weeks, i.p.) and OT-82 (40 mg/kg x 3 days x 2 weeks, p.o.) significantly increased EFS compared to OT-82 (P&lt;0.0001) or AraC (P&lt;0.0001) alone. Moreover, the OT-82/AraC combination elicited an MCR compared to OT-82 (CR) and AraC (Progressive Disease) alone. The results herein demonstrate significant activity of OT-82 against leukemia cell lines and a range of pediatric ALL subtypes in vivo, and the potential for PARylated PARP-1 expression as a biomarker for predicting OT-82 response. Moreover, the enhanced activity of OT-82 in combination with AraC over single agent therapy further suggests NAMPT inhibition as an attractive strategy for treating high-risk pediatric ALL. Supported by U01CA199000 from the NCI.

Citation Format: Kathryn Evans, Tara Pritchard, Michelle J. Henderson, Klaartje Somers, Mawar Karsa, Leanna Cheung, Raymond Yung, Stephen W. Erickson, Lioubov Korotchkina, Olga Chernova, Andrei Gudkov, Malcolm A. Smith, Richard B. Lock. The nicotinamide phosphoribosyltransferase (NAMPT) inhibitor, OT-82, exhibits in vitro and in vivo efficacy against patient-derived xenograft models of high-risk acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1942. doi:10.1158/1538-7445.AM2017-1942

Characteristics Associated with Treatment Response and Satisfaction in Women Undergoing OnabotulinumtoxinA and Sacral Neuromodulation for Refractory Urgency Urinary Incontinence

PURPOSE

We sought to identify clinical and demographic characteristics associated with treatment response and satisfaction in women undergoing onabotulinumtoxinA and sacral neuromodulation therapies.

MATERIALS AND METHODS

We analyzed data from the ROSETTA (Refractory Overactive Bladder: Sacral NEuromodulation versus BoTulinum Toxin Assessment) trial. Baseline participant characteristics and clinical variables were associated with 2 definitions of treatment response, including 1) a reduction in mean daily urgency incontinence episodes during 6 months and 2) a 50% or greater decrease in urgency incontinence episodes across 6 months. The OAB-S (Overactive Bladder-Satisfaction) questionnaire was used to assess satisfaction.

RESULTS

A greater reduction in mean daily urgency incontinence episodes was associated with higher HUI-3 (Health Utility Index-3) scores in the onabotulinumtoxinA group and higher baseline incontinence episodes (each p <0.001) in the 2 groups. Increased age was associated with a lesser decrease in incontinence episodes in the 2 groups (p <0.001). Increasing body mass index (adjusted OR 0.82/5 points, 95% CI 0.70-0.96) was associated with reduced achievement of a 50% or greater decrease in incontinence episodes after each treatment. Greater age (adjusted OR 0.44/10 years, 95% CI 0.30-0.65) and a higher functional comorbidity index (adjusted OR 0.84/1 point, 95% CI 0.71-0.99) were associated with reduced achievement of a 50% or greater decrease in urgency incontinence episodes in the onabotulinumtoxinA group only (p <0.001 and 0.041, respectively). In the onabotulinumtoxinA group increased satisfaction was noted with higher HUI-3 score (p = 0.002) but there was less satisfaction with higher age (p = 0.001).

CONCLUSIONS

Older women with multiple comorbidities, and decreased functional and health related quality of life had decreased treatment response and satisfaction with onabotulinumtoxinA compared to sacral neuromodulation for refractory urgency incontinence.

Germline Genetic Variants in TEK, ANGPT1, ANGPT2, MMP9, FGF2 and VEGFA Are Associated with Pathologic Complete Response to Bevacizumab in Breast Cancer Patients

BACKGROUND

We previously reported improved pathologic complete response (pCR) in a prospective phase II study using neoadjuvant bevacizumab in combination with chemotherapy compared to chemotherapy alone in breast cancer patients (41% vs. 25%, p = 0.0291). In this study, we queried germline single-nucleotide polymorphisms (SNPs) in angiogenesis-related genes for their impact on pCR and overall survival (OS).

METHODS

DNA for genotyping was available from 34 subjects who received bevacizumab in addition to chemotherapy and 29 subjects who did not. Using Illumina® technology, we queried 504 SNPs with a minor allele frequency (MAF) of at least 5%, located in 10 angiogenesis-related genes, for their effect on pCR via logistic regression with an additive-inheritance model while adjusting for race and bevacizumab treatment. SNPs that showed significant associations with pCR were selected for additional characterization.

RESULTS

After adjusting for race and tumor type, patients who had bevacizumab added to their neoadjuvant therapy were found to experience a significantly improved rate of pCR compared to patients who did not (adjusted OR 8.40, 95% CI 1.90-37.1). When patients were analyzed for SNP effects via logistic regression with race and bevacizumab treatment included as covariates, two SNPs in angiopoietin 1 (ANGPT1), six in ANGPT2, three in fibroblast growth factor 2 (FGF2), four in matrix metalloproteinase 9 (MMP9), three in tyrosine kinase, endothelial (TEK) and two in vascular endothelial growth factor A (VEGFA) were associated with pCR (P<0.05). However, when overall survival was considered, there was no difference between treatment groups or between genotypes.

CONCLUSION

Genetic variability in TEK, ANGPT1, ANGPT2, FGF2, MMP9 and VEGFA is associated with pCR in bevacizumab-treated patients. Consistent with other studies, adding bevacizumab to standard chemotherapy did not impact OS, likely due to other factors and thus, while SNPs in TEK, ANGPT1, ANGPT2, FGF2, MMP9 and VEGFA were associated with pCR, they were not predictive of OS in this patient population.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00203502.

Chronic exposure to trichloroethylene increases DNA methylation of the Ifng promoter in CD4+ T cells

CD4+ T cells in female MRL+/+ mice exposed to solvent and water pollutant trichloroethylene (TCE) skew toward effector/memory CD4+ T cells, and demonstrate seemingly non-monotonic alterations in IFN-γ production. In the current study we examined the mechanism for this immunotoxicity using effector/memory and naïve CD4+ T cells isolated every 6 weeks during a 40 week exposure to TCE (0.5mg/ml in drinking water). A time-dependent effect of TCE exposure on both Ifng gene expression and IFN-γ protein production was observed in effector/memory CD4+ T cells, with an increase after 22 weeks of exposure and a decrease after 40 weeks of exposure. No such effect of TCE was observed in naïve CD4+ T cells. A cumulative increase in DNA methylation in the CpG sites of the promoter of the Ifng gene was observed in effector/memory, but not naïve, CD4+ T cells over time. Also unique to the Ifng promoter was an increase in methylation variance in effector/memory compared to naïve CD4+ T cells. Taken together, the CpG sites of the Ifng promoter in effector/memory CD4+ T cells were especially sensitive to the effects of TCE exposure, which may help explain the regulatory effect of the chemical on this gene.

The Redundancy of Peptidoglycan Carboxypeptidases Ensures Robust Cell Shape Maintenance in Escherichia coli

Peptidoglycan (PG) is an essential structural component of the bacterial cell wall and maintains the integrity and shape of the cell by forming a continuous layer around the cytoplasmic membrane. The thin PG layer of Escherichia coli resides in the periplasm, a unique compartment whose composition and pH can vary depending on the local environment of the cell. Hence, the growth of the PG layer must be sufficiently robust to allow cell growth and division under different conditions. We have analyzed the PG composition of 28 mutants lacking multiple PG enzymes (penicillin-binding proteins [PBPs]) after growth in acidic or near-neutral-pH media. Statistical analysis of the muropeptide profiles identified dd-carboxypeptidases (DD-CPases) that were more active in cells grown at acidic pH. In particular, the absence of the DD-CPase PBP6b caused a significant increase in the pentapeptide content of PG as well as morphological defects when the cells were grown at acidic pH. Other DD-CPases (PBP4, PBP4b, PBP5, PBP6a, PBP7, and AmpH) and the PG synthase PBP1B made a smaller or null contribution to the pentapeptide-trimming activity at acidic pH. We solved the crystal structure of PBP6b and also demonstrated that the enzyme is more stable and has a lower Km at acidic pH, explaining why PBP6b is more active at low pH. Hence, PBP6b is a specialized DD-CPase that contributes to cell shape maintenance at low pH, and E. coli appears to utilize redundant DD-CPases for normal growth under different conditions.

IMPORTANCE

Escherichia coli requires peptidoglycan dd-carboxypeptidases to maintain cell shape by controlling the amount of pentapeptide substrates available to the peptidoglycan synthetic transpeptidases. Why E. coli has eight, seemingly redundant dd-carboxypeptidases has remained unknown. We now show that one of these dd-carboxypeptidases, PBP6b, is important for cell shape maintenance in acidic growth medium, consistent with the higher activity and stability of the enzyme at low pH. Hence, the presence of multiple dd-carboxypeptidases with different enzymatic properties may allow E. coli to maintain a normal cell shape under various growth conditions.

Systemic Absorption of Cyclopentolate and Adverse Events After Retinopathy of Prematurity Exams

PURPOSE

Preterm infants undergoing Retinopathy of Prematurity Eye Exams (ROPEE) may experience adverse events, possibly from systemic absorption of cyclopentolate. The purpose of this study was to analyze the association between adverse events and drug levels found in neonates undergoing ROPEE.

MATERIALS AND METHODS

25 infants were randomized into two groups during routine ROP screening: 5 infants for blood collection before mydriatic drops and 20 for blood collection 1 h after eye drops. Blood was collected onto dried blood spot cards, extracted, and analyzed for cyclopentolate and phenylephrine using liquid chromatography and mass spectrometry. Relationships between drug levels and adverse events were assessed.

RESULTS

Cyclopentolate (range 6-53 ng/ml) was observed in 15 of 18 infants, while phenylephrine was not detected. Levels of cyclopentolate were significantly higher in infants who were on oxygen (p = 0.01). There was a significant association between cyclopentolate levels and gastric residuals in tube-fed infants not receiving oxygen (p = 0.01).

CONCLUSIONS

Cyclopentolate levels varied among preterm infants after ROPEE. Cyclopentolate was positively associated with increased gastric residuals. Underlying medical conditions requiring oxygen administration may affect absorption and metabolism of cyclopentolate. There is a need to predict infants at risk for high blood levels of cyclopentolate in order to prevent or treat adverse events after ROPEE.