Fluorodeoxyglucose-based positron emission tomography imaging to monitor drug responses in solid tumors

Positron emission tomography (PET) is used to monitor the uptake of the labeled glucose analogue fluorodeoxyglucose (¹⁸F-FDG) by solid tumor cells, a process generally believed to reflect viable tumor cell mass. The use of ¹⁸F-FDG exploits the high demand for glucose in tumor cells, and serves to document over time the response of a solid tumor to an inducer of apoptosis. The apoptosis inducer crizotinib is a small-molecule inhibitor of c-Met, a receptor tyrosine kinase that is often dysregulated in human tumors. In this protocol, we describe how to monitor the response of a solid tumor to crizotinib. Human gastric tumor cells (GTL-16 cells) are injected into recipient mice and, on tumor formation, the mice are treated with crizotinib. The tracer ¹⁸F-FDG is then injected into the mice at several time points, and its uptake is monitored using PET. Because ¹⁸F-FDG uptake varies widely among different tumor models, preliminary experiments should be performed with each new model to determine its basal level of ¹⁸F-FDG uptake. Verifying that the basal level of uptake is sufficiently above background levels will assure accurate quantitation. Because ¹⁸F-FDG uptake is not a direct measure of apoptosis, it is advisable to carry out an additional direct method to show the presence of apoptotic cells.