Robust preclinical models of pediatric acute lymphoblastic leukemia (ALL) are essential in prioritizing promising therapies for clinical assessment in high-risk patients. Patient-derived xenograft ...(PDX) models of ALL provide a clinically relevant platform for assessing novel drugs, with efficacy generally assessed by enumerating circulating human lymphoblasts in mouse peripheral blood (PB) as an indicator of disease burden. While allowing indirect measurement of disease burden in real time, this technique cannot assess treatment effects on internal reservoirs of disease. We explore benefits of bioluminescence imaging (BLI) to evaluate drug responses in ALL PDXs, compared with PB monitoring. BLI-based thresholds of drug response are also explored.
ALL PDXs were lentivirally transduced to stably express luciferase and green fluorescent protein.
PDX responses to an induction-type regimen of vincristine, dexamethasone, and
-asparaginase were assessed by BLI and PB. Residual disease at day 28 after treatment initiation was assessed by flow cytometric analysis of major organs. BLI and PB were subsequently used to evaluate efficacy of the Bcl-2 inhibitor venetoclax.
BLI considerably accelerated and enhanced detection of leukemia burden compared with PB and identified sites of residual disease during treatment in a quantitative manner, highlighting limitations in current PB-based scoring criteria. Using BLI alongside enumeration of human lymphoblasts in PB and bone marrow, we were able to redefine response criteria analogous to the clinical setting.
BLI substantially improves the stringency of preclinical drug testing in pediatric ALL PDXs, which will likely be important in prioritizing effective agents for clinical assessment.
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Current therapy is ineffective for relapsed and metastatic Ewing sarcoma (EwS) owing to development of drug resistance. Macromolecular prodrugs potentially lead to lower drug exposure in normal ...tissues and reduced toxicity. We evaluated the efficacy of PEGylated talazoparib (PEG∼TLZ), a PARP1 inhibitor, alone or in combination with the DNA-alkylating agent temozolomide (TMZ) in EwS and other pediatric tumors using conventional testing or single-mouse trial (SMT). A single dose of PEG∼TLZ (10 μmol/kg on day 0) combined with 5 daily doses of TMZ (40 mg/kg starting on day 3/4) produced minimal toxicity, and the combination achieved maintained complete response in EwS and glioblastoma models. The SMT trial with the 3-day interval between PEG∼TLZ and TMZ resulted in objective responses in EwS and other xenografts. Thus, PEG∼TLZ + TMZ demonstrated a broad range of activity in pediatric solid tumor models. Furthermore, the therapeutic window of PEG∼TLZ + TMZ was enhanced compared with the free-TLZ combination.
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•Nanoparticle-formulated drugs minimize drug-induced toxicity•PEG∼TLZ enhances in vivo activity of TMZ in pediatric tumor xenografts•A 3-day interval between each drug's administration widens the therapeutic window•A single IV dose of PEG∼TLZ is advantageous for treating infants/young children
Oncology; Pharmacology; Molecular medicine;
VS‐4718, a novel inhibitor of focal adhesion kinase (FAK), was tested against the Pediatric Preclinical Testing Program's (PPTP's) in vitro cell line panel and showed a median relative IC50 of 1.22 ...μM. VS‐4718 was tested in vivo against the PPTP xenograft models using a dose of 50 mg/kg administered by the oral route twice daily for 21 days. VS‐4718 induced significant differences in an event‐free survival distribution compared with control in 18 of 36 of the evaluable solid tumor xenografts and in 0 of 8 acute lymphoblastic leukemia (ALL) xenografts, but no xenograft lines showed tumor regression. Future plans include further evaluation of the role of FAK inhibition in combination with ABL kinase inhibitors for Ph+ ALL.
Patient-derived xenografts (PDX) remain valuable models for understanding the biology and for developing novel therapeutics. To expand current PDX models of childhood leukemia, we have developed new ...PDX models from Hispanic patients, a subgroup with a poorer overall outcome. Of 117 primary leukemia samples obtained, successful engraftment and serial passage in mice were achieved in 82 samples (70%). Hispanic patient samples engrafted at a rate (51/73, 70%) that was similar to non-Hispanic patient samples (31/45, 70%). With a new algorithm to remove mouse contamination in multi-omics datasets including methylation data, we found PDX models faithfully reflected somatic mutations, copy-number alterations, RNA expression, gene fusions, whole-genome methylation patterns, and immunophenotypes found in primary tumor (PT) samples in the first 50 reported here. This cohort of characterized PDX childhood leukemias represents a valuable resource in that germline DNA sequencing has allowed the unambiguous determination of somatic mutations in both PT and PDX.
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•Patient-derived xenografts (PDXs) are important preclinical models•50 pediatric leukemia PDXs are largely derived from Hispanic ethnicity•Paired patient tumor, PDX, and germline for sequencing analysis•This cohort uncovers genomic, transcriptomic, and epigenomic features
Cancer; Omics; Transcriptomics
Over the past 35 years, cure rates for pediatric cancers have increased dramatically. However, it is clear that further dose intensification using cytotoxic agents or radiation therapy is not ...possible without enhancing morbidity and long-term effects. Consequently, novel, less genotoxic, agents are being sought to complement existing treatments. Here, we discuss preclinical human tumor xenograft models of pediatric cancers that may be used practically to identify novel agents for soft tissue and bone sarcomas, and "omics" approaches to identifying biomarkers that may identify sensitive and resistant tumors to these agents.
Background
MK‐8242 is an inhibitor of MDM2 that stabilizes the tumor suppressor TP53 and induces growth arrest or apoptosis downstream of TP53 induction.
Procedures
MK‐8242 was tested against the ...Pediatric Preclinical Testing Program (PPTP) in vitro cell line panel at concentrations from 1.0 nM to 10.0 μM and against the PPTP in vivo xenograft panels using oral gavage on Days 1–5 and Day 15–19 at a dose of 125 mg/kg (solid tumors) or 75 mg/kg (acute lymphoblastic leukemia ALL models).
Results
The median IC50 for MK‐8242 was 0.07 μM for TP53 wild‐type cell lines versus >10 μM for TP53 mutant cell lines. MK‐8242 induced a twofold or greater delay in time to event in 10 of 17 (59%) of TP53 wild‐type solid tumor xenografts, excluding osteosarcoma xenografts that have very low TP53 expression. Objective responses were observed in seven solid tumor xenografts representing multiple histotypes. For the systemic‐disease ALL panel, among eight xenografts there were two complete responses (CRs) and six partial responses (PRs). Two additional MLL‐rearranged xenografts (MV4;11 and RS4;11) grown subcutaneously showed maintained CR and PR, respectively. The expected pharmacodynamic responses to TP53 activation were observed in TP53 wild‐type models treated with MK‐8242. Pharmacokinetic analysis showed that MK‐8242 drug exposure in SCID mice appears to exceed that was observed in adult phase 1 trials.
Conclusions
MK‐8242‐induced tumor regressions across multiple solid tumor histotypes and induced CRs or PRs for most ALL xenografts. This activity was observed at MK‐8242 drug exposures that appear to exceed those observed in human phase 1 trials.
Despite aggressive multiagent protocols, patients with metastatic rhabdomyosarcoma (RMS) have poor prognosis. In a recent high-risk trial (ARST0431), 25% of patients failed within the first year, ...while on therapy and 80% had tumor progression within 24 months. However, the mechanisms for tumor resistance are essentially unknown. Here we explore the use of preclinical models to develop resistance to complex chemotherapy regimens used in ARST0431.
A Single Mouse Testing (SMT) protocol was used to evaluate the sensitivity of 34 RMS xenograft models to one cycle of vincristine, actinomycin D, cyclophosphamide (VAC) treatment. Tumor response was determined by caliper measurement, and tumor regression and event-free survival (EFS) were used as endpoints for evaluation. Treated tumors at regrowth were transplanted into recipient mice, and the treatment was repeated until tumors progressed during the treatment period (i.e., became resistant). At transplant, tumor tissue was stored for biochemical and omics analysis.
The sensitivity to VAC of 34 RMS models was determined. EFS varied from 3 weeks to > 20 weeks. Tumor models were classified as having intrinsic resistance, intermediate sensitivity, or high sensitivity to VAC therapy. Resistance to VAC was developed in multiple models after 2-5 cycles of therapy; however, there were examples where sensitivity remained unchanged after 3 cycles of treatment.
The SMT approach allows for
assessment of drug sensitivity and development of drug resistance in a large number of RMS models. As such, it provides a platform for assessing
drug resistance mechanisms at a "population" level, simulating conditions
that lead to clinical resistance. These VAC-resistant models represent "high-risk" tumors that mimic a preclinical phase 2 population and will be valuable for identifying novel agents active against VAC-resistant disease.
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