Bioluminescence Imaging Enhances Analysis of Drug Responses in a Patient-Derived Xenograft Model of Pediatric ALL

Abstract

Purpose 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 to PB monitoring. BLI-based thresholds of drug response are also explored. Experimental Design ALL PDXs were lentivirally transduced to stably express luciferase and green fluorescent protein. In vivo PDX responses to an induction-type regimen of vincristine, dexamethasone and L-asparaginase were assessed by BLI and PB. Residual disease at Day 28 post-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. Results BLI considerably accelerated and enhanced detection of leukemia burden compared to 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. Conclusions 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.

Preclinical activity of the antibody‐drug conjugate denintuzumab mafodotin (SGN‐CD19A) against pediatric acute lymphoblastic leukemia xenografts

“…Assessment of denintuzumab mafodotin activity against ALL‐11 was also monitored by BLI, as this PDX has been lentivirally transduced to stably express firefly luciferase . Imaging data showed a profound decrease in whole animal bioluminescence during the treatment period, with burden continuing to decrease up to 2 weeks following administration of the final dose, suggesting persistence of denintuzumab mafodotin in multiple tissue niches (Figure A and B; Table S2).…”

“…Briefly, leukemia cells were inoculated intravenously into groups of eight 6‐ to 8‐week‐old NOD/SCID or NSG mice (Australian BioResources, Moss Vale, NSW, Australia) and leukemia burden monitored via enumeration of human CD45 + (%huCD45 + ) cells versus total CD45 + leukocytes (human plus mouse) in the peripheral blood (PB) and tissues, as outlined previously . Monitoring of leukemia burden using bioluminescence imaging (BLI) was performed as described elsewhere . Previous power calculations indicated that a group size of eight mice was sufficient to detect a twofold difference between control and treated groups at a power of 0.9 and significance of 0.05.…”

“…Response to treatment was evaluated by two methods: (1) differences between the median EFS of the drug‐treated (T) cohort and that of the vehicle‐treated (C) cohort (treatment‐control [T‐C] and treatment/control [T/C] values) and (2) using an objective response measure modeled after stringent clinical criteria, which was assessed at Day 42 posttreatment initiation as previously described (see Supporting Information Methods). Engraftment and response to treatment was also assessed using BLI of PDXs that had been lentivirally transduced to stably express firefly luciferase, as previously described . To evaluate interactions between drugs in vivo, therapeutic enhancement was considered if the EFS of mice treated with the combination treatment was significantly greater ( P < 0.01) than those induced by both single arms of the study …”

“…17,18 Monitoring of leukemia burden using bioluminescence imaging (BLI) was performed as described elsewhere. 22 Previous power calculations indicated that a group size of eight mice was sufficient to detect a twofold difference between control and treated groups at a power of 0.9 and significance of 0.05.…”

“…25 Engraftment and response to treatment was also assessed using BLI of PDXs that had been lentivirally transduced to stably express firefly luciferase, as previously described. 22 To evaluate interactions between drugs in vivo, therapeutic enhancement was considered if the EFS of mice treated with the combination treatment was significantly greater (P < 0.01) than those induced by both single arms of the study. 26,27…”