Highly Sensitive Bioluminescence in Vivo Imaging Enables Individualized Preclinical Treatment Trials On Patients ALL Tumor Cells Growing in Mice.

Abstract 2602

Novel therapeutic approaches require preclinical in vivo testing before first use in men. An important preclinical model to study acute lymphoblastic leukemia (ALL) was first described more than 2 decades ago (Dick et al., Science 1989). In this model, primary human tumor cells from patients with ALL are transplanted into severely immuno-compromised mice.

The model is hampered by the lack of a sensitive readout for disease progression and treatment effects. As ALL is a systemic disease per se, tumor mass is difficult to measure; bone marrow aspirations remain exhausting for mice; secretion of tumor cells into the blood stream remains a late and only partially reliable surrogate parameter.

Here, we optimized the preclinical individualized mouse model of ALL by introducing a highly sensitive and reliable readout parameter for disease progression and treatment efficacy. We introduced the lentiviral transduction of patient-derived ALL cells to express transgenes such as luciferase and fluochromes. Transduction efficiency ranged between 0,5 and 70 %, depending on the sample used. Expression of fluochromes was used for enrichment of transgenic cells by FACs sorting. Expression of luciferase was used to perform bioluminescence in vivo imaging in mice.

Bioluminescence in vivo imaging was easy to perform and well tolerated by the mice, even as often as 3 times per week. Imaging enabled highly reliable measurement of disease progression over time in single mice and revealed a strictly logarithmic growth of leukemia in mice. Imaging results correlated perfectly well with post mortem determination of leukemic burden using immunohistochemistry and FACs analysis. In contrast to the later, imaging was highly sensitive and detected leukemia at disease stages representing minimal residual disease. Depending on the expression level of the transgenes, imaging was able to detect as few as 1 human ALL cells in >> 10.000 normal mouse bone marrow cells. By following up groups of mice over time, imaging revealed especially helpful for readout of limiting dilution transplantation assays to determine frequencies of leukemia initiating cells, e.g., with and without prior in vitro treatment.

In preclinical treatment trials on ALL cells from individual patients, imaging quantified therapy effects precisely and with low variances discriminating treatment failure from partial and complete response as early as 4 days after treatment. Due to follow up of mice over time, imaging visualized disease regrowth after successful therapy and allowed determining classical clinical readout parameter such as time to tumor regrowth.

Taken together, the most demanding challenges in anti-cancer treatment are modeled precisely and individually in mice using bioluminescence in vivo imaging. In vivo imaging upgrades the individualized xenograft mouse model of ALL by highly sensitive and reliable disease monitoring. Imaging enables performing preclinical trials at defined disease stages and using classical clinical readout parameters. Imaging-based individualized preclinical trials of ALL will facilitate translation of novel therapeutic approaches from bench to bedside.