Impact of Anesthetics on 3′-[18F]Fluoro-3′-Deoxythymidine ([18F]FLT) Uptake in Animal Models of Cancer and Inflammation

The aim of this study was to evaluate the impact of different anesthetics on 3'-[F-18]fluoro-3'-deoxythymidine ([F-18]FLT) uptake in carcinomas and arthritic ankles. To determine the amount of [F-18]FLT uptake in subcutaneous CT26 colon carcinomas or arthritic ankles, spontaneously room air/medical air-breathing mice were anesthetized with isoflurane, a combination of medetomidine/midazolam, or ketamine/xylazine. Mice were kept conscious or anesthetized during [F-18]FLT uptake before the 10-minute static positron emission tomographic (PET) investigations. [F-18]FLT uptake in CT26 colon carcinomas and arthritic ankles was calculated by drawing regions of interest. We detected a significantly reduced (4.4 +/- 0.9 % ID/cm(3)) [F-18]FLT uptake in the carcinomas of ketamine/xylazine-anesthetized mice compared to the [F-18]FLT-uptake in carcinomas of medetomidine/midazolam-(7.0 +/- 1.5 % ID/cm(3)) or isoflurane-anesthetized mice (6.4 +/- 1.5 % ID/cm(3)), whereas no significant differences were observed in arthritic ankles regardless of whether mice were anesthetized or conscious during tracer uptake. The time-activity curves of carcinomas and arthritic ankles yielded diverse [F-18]FLT accumulation related to the used anesthetics. [F-18]FLT uptake dynamics are different in arthritic ankles and carcinoma, and the magnitude and pharmacokinetics of [F-18]FLT uptake are sensitive to anesthetics. Thus, for preclinical in vivo [F-18]FLT PET studies in experimental tumor or inflammation models, we recommend the use of isoflurane anesthesia as it yields a stable tracer uptake and is easy to handle.