Molecular Imaging in Oncology by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783030426187
Publisher: Springer International Publishing

13.3.2 Factors Affecting BLI

In the past decades, BLI has increasingly become a method of choice for noninvasive monitoring of biologic phenomena in living cells or in animals. However, several aspects have to be considered before planning, analyzing, and quantifying a BLI experiment.

As bioluminescence depends on the presence of the enzyme expressed by living cells, but also on other components such as oxygen and the exogenously administered luciferin, the measured light emission will not be a true representation of luciferase activity if any of these components is limited. Furthermore, the reaction kinetics in animals will also depend on the substrate delivery and therefore also on the route of substrate administration (intravenous, intraperitoneal). This means that the measured bioluminescence intensity varies depending on the time after substrate injection, with a signal increase during substrate distribution in the animal body, a specific maximum (e.g., for firefly luciferase the reaction peaks ~10–12 min after injection of luciferin; Fig. 13.13a,c) and a slow decrease as the substrate is consumed. In addition, large bioluminescent tissues (e.g., tumors) will obviously need more substrate and will utilize it faster than smaller tissues (Fig. 13.13b,d). Therefore, to achieve comparable results, the optimal time for BLI (the time between injection of the substrate and the start of measurement) as well as the optimal dose of administered substrate should be standardized for each study.

Fig. 13.13The kinetics of the bioluminescence reaction differs depending on the size of the tumor. a–b Mice with (a) large and (b) small orthotopic pancreatic tumors were injected with the same amounts of luciferase, and imaged with BLI over time, showing bioluminescence intensities correlating with tumor sizes. While the mouse with large tumor shows a relatively fast increase in the measured bioluminescence intensity which peaks at 12–13 min after substrate injection, most probably due to a limitation in luciferin, (c) the bioluminescence of the mouse with small tumor also increases but reaches a long-lasting plateau (d) (Napp, unpublished data)

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