Bioluminescent evaluation of the therapeutic effects of total body irradiation in a murine hematological malignancy model

An advanced preclinical mouse model for acute myeloid leukemia using patients' cells of various genetic subgroups and in vivo bioluminescence imaging

Acute myeloid leukemia (AML) is a clinically and molecularly heterogeneous disease with poor outcome. Adequate model systems are required for preclinical studies to improve understanding of AML biology and to develop novel, rational treatment approaches. Xenografts in immunodeficient mice allow performing functional studies on patient-derived AML cells. We have established an improved model system that integrates serial retransplantation of patient-derived xenograft (PDX) cells in mice, genetic manipulation by lentiviral transduction, and essential quality controls by immunophenotyping and targeted resequencing of driver genes. 17/29 samples showed primary engraftment, 10/17 samples could be retransplanted and some of them allowed virtually indefinite serial transplantation. 5/6 samples were successfully transduced using lentiviruses. Neither serial transplantation nor genetic engineering markedly altered sample characteristics analyzed. Transgene expression was stable in PDX AML cells. Example given, recombinant luciferase enabled bioluminescence in vivo imaging and highly sensitive and reliable disease monitoring; imaging visualized minimal disease at 1 PDX cell in 10000 mouse bone marrow cells and facilitated quantifying leukemia initiating cells. We conclude that serial expansion, genetic engineering and imaging represent valuable tools to improve the individualized xenograft mouse model of AML. Prospectively, these advancements enable repetitive, clinically relevant studies on AML biology and preclinical treatment trials on genetically defined and heterogeneous subgroups.

Bioluminescence imaging of leukemia cell lines in vitro and in mouse xenografts: effects of monoclonal and polyclonal cell populations on intensity and kinetics of photon emission

Background

We investigated the utility of bioluminescence imaging (BLI) using firefly luciferase in monoclonal and polyclonal populations of leukemia cells in vitro and in vivo.

Methods

Monoclonal and polyclonal human lymphoid and myeloid leukemia cell lines transduced with firefly luciferase were used for BLI.

Results

Kinetics and dynamics of bioluminescence signal were cell line dependent. Luciferase expression decreased significantly over time in polyclonal leukemia cells in vitro. Transplantation of polyclonal luciferase-tagged cells in mice resulted in inconsistent signal intensity. After selection of monoclonal cell populations, luciferase activity was stable, equal kinetic and dynamic of bioluminescence intensity and strong correlation between cell number and light emission in vitro were observed. We obtained an equal development of leukemia burden detected by luciferase activity in NOD-scid-gamma mice after transplantation of monoclonal populations.

Conclusion

The use of monoclonal leukemia cells selected for stable and equal luciferase activity is recommended for experiments in vitro and xenograft mouse models. The findings are highly significant for bioluminescence imaging focused on pre-clinical drug development.

Serial monitoring of human systemic and xenograft models of leukemia using a novel vascular disrupting agent

Advances in the treatment of acute leukemia have resulted in significantly improved remission rates, although disease relapse poses a significant risk. By utilizing sensitive, non-invasive imaging guidance, detection of early leukemic infiltration and the extent of residual tumor burden after targeted therapy can be expedited, leading to more efficient treatment planning. We demonstrated marked survival benefit and therapeutic efficacy of a new-generation vascular disrupting agent, combretastatin-A1-diphosphate (OXi4503), using reporter gene-imaging technologies and mice systemically administered luc+ and GFP+ human leukemic cells (LCs). Before treatment, homing of double-transduced cells was serially monitored and whole-body cellular distributions were mapped using bioluminescence imaging (BLI). Imaging findings strongly correlated with quantitative GFP expression levels in solid organs/tissues, suggesting that the measured BLI signal provides a highly sensitive and reliable biomarker of tumor tissue burden in systemic leukemic models. Such optical technologies can thereby serve as robust non-invasive imaging tools for preclinical drug discovery and for rapidly screening promising therapeutic agents to establish potency, treatment efficacy and survival advantage. We further show that GFP+ HL-60 cells reside in close proximity to VE-cadherin- and CD31-expressing endothelial cells, suggesting that the perivascular niche may have a critical role in the maintenance and survival of LCs.

Noninvasive bioluminescent imaging of primary patient acute lymphoblastic leukemia: a strategy for preclinical modeling

The efficient engraftment in immune-deficient mice achieved with both acute lymphoblastic leukemia (ALL) cell lines and primary samples has facilitated identification of the antileukemia activity of a wide variety of agents. Despite widespread usage, however, little is known about the early ALL localization and engraftment kinetics in this model, limiting experimental read-outs primarily to survival and endpoint analysis at high disease burden. In this study, we report that bioluminescent imaging can be reproducibly achieved with primary human ALL samples. This approach provides a noninvasive, longitudinal measure of leukemia burden and localization that enhances the sensitivity of treatment response detection and provides greater insight into the mechanism of action of antileukemia agents. In addition, this study reveals significant cell line- and species-related differences in leukemia migration, especially early in expansion, which may confound observations between various leukemia models. Overall, this study demonstrates that the use of bioluminescent primary ALL allows the detection and quantitation of treatment effects at earlier, previously unquantifiable disease burdens and thus provides the means to standardize and expedite the evaluation of anti-ALL activity in preclinical xenograft studies.

Gaussia luciferase for bioluminescence tumor monitoring in comparison with firefly luciferase

Gaussia luciferase (Gluc) is a secreted reporter, and its expression in living animals can be assessed by in vivo bioluminescence imaging (BLI) or blood assays. We characterized Gluc as an in vivo reporter in comparison with firefly luciferase (Fluc). Mice were inoculated subcutaneously with tumor cells expressing both Fluc and Gluc and underwent Fluc BLI, Gluc BLI, blood assays of Gluc activity, and caliper measurement. In Gluc BLI, the signal from the tumor peaked immediately and then decreased rapidly. In the longitudinal monitoring, all measures indicated an increase in tumor burden early after cell inoculation. However, the increase reached plateaus in Gluc BLI and Fluc BLI despite a continuous increase in the caliper measurement and Gluc blood assay. Significant correlations were found between the measures, and the correlation between the blood signal and caliper volume was especially high. Gluc allows tumor monitoring in mice and should be applicable to dual-reporter assessment in combination with Fluc. The Gluc blood assay appears to provide a reliable indicator of viable tumor burden, and the combination of a blood assay and in vivo BLI using Gluc should be promising for quantifying and localizing the tumors.

Timing of imaging after d-luciferin injection affects the longitudinal assessment of tumor growth using in vivo bioluminescence imaging

The peak signal or the signal at a predetermined, fixed time point after D-luciferin injection may be used for the quantitative analysis of in vivo bioluminescence imaging. We repeatedly performed sequential bioluminescence imaging after subcutaneous injection of D-luciferin in mice bearing subcutaneous tumors. The peak time in each measurement became shorter early after cell inoculation, presumably due to gradual establishment of intratumoral vasculature, and reached a plateau of about 10 min on day 10. Although the correlation between the signal at a fixed time point and the peak signal was high, the signal at 5 or 10 min normalized for the peak signal was lower for earlier days, which caused overestimation of tumor growth. The time course of the signals after D-luciferin injection may vary with time after cell inoculation, and this variation should be considered when determining the imaging protocol for quantitative bioluminescence tumor monitoring.