Abstract
BackgroundPreclinical imaging requires anaesthesia to reduce motion-related artefacts. For direct translational relevance, anaesthesia must not significantly alter experimental outcome. This study reports on the effects of both anaesthetic and carrier gas upon the uptake of [64Cu]-CuATSM, [99mTc]-HL91 and [18F]-FMISO in a preclinical model of tumor hypoxia.Methodology/Principal FindingsThe effect of carrier gas and anaesthetic was studied in 6 groups of CaNT-bearing CBA mice using [64Cu]-CuATSM, [99mTc]-HL91 or [18F]-FMISO. Mice were anaesthetised with isoflurane in air, isoflurane in pure oxygen, with ketamine/xylazine or hypnorm/hypnovel whilst breathing air, or in the awake state whilst breathing air or pure oxygen. PET or SPECT imaging was performed after which the mice were killed for organ/tumor tracer quantitation. Tumor hypoxia was confirmed. Arterial blood gas analysis was performed for the different anaesthetic regimes. The results demonstrate marked influences on tumor uptake of both carrier gas and anaesthetic, and show differences between [99mTc]-HL91, [18F]-FMISO and [64Cu]-CuATSM. [99mTc]-HL91 tumor uptake was only altered significantly by administration of 100% oxygen. The latter was not the case for [18F]-FMISO and [64Cu]-CuATSM. Tumor-to-muscle ratio (TMR) for both compounds was reduced significantly when either oxygen or anaesthetics (isoflurane in air, ketamine/xylazine or hypnorm/hypnovel) were introduced. For [18F]-FMISO no further decrease was measured when both isoflurane and oxygen were administered, [64Cu]-CuATSM did show an additional significant decrease in TMR. When using the same anaesthetic regimes, the extent of TMR reduction was less pronounced for [64Cu]-CuATSM than for [18F]-FMISO (40–60% versus 70% reduction as compared to awake animals breathing air).Conclusions/SignificanceThe use of anaesthesia can have profound effects on the experimental outcome. More importantly, all tested anaesthetics reduced tumor-hypoxia uptake. Anaesthesia cannot be avoided in preclinical studies but great care has to be taken in preclinical models of hypoxia as anaesthesia effects cannot be generalised across applications, nor disease states.
Highlights
Research into the hypoxic tumor microenvironment is accelerating as the importance of tumor hypoxia becomes more and more apparent
While anaesthesia is preferred in preclinical imaging studies to reduce motion artefacts, anaesthetic agents, and their carrier gases, in the case of volatile anaesthetics, have the potential to alter the study outcome dramatically
The results presented in this study established the marked influences on tumor uptake of both carrier gas and anaesthetic, and demonstrated pronounced differences between [99mTc]-HL91, [18F]-FMISO and [64Cu]-CuATSM despite the fact they are all designed to target hypoxia
Summary
Research into the hypoxic tumor microenvironment is accelerating as the importance of tumor hypoxia becomes more and more apparent. Most solid tumors develop regions of hypoxia as they grow and evidence from experimental and clinical studies points to a significant role for tumor hypoxia in tumor propagation, resistance to radio- and chemotherapy and malignant progression [1]. As the presence of tumor hypoxia represents a barrier for effective cancer treatment, identifying patients whose tumors contain hypoxic areas will have an important role in tumor prognosis, treatment and outcome. Preclinical imaging requires anaesthesia to reduce motion-related artefacts. Anaesthesia must not significantly alter experimental outcome. This study reports on the effects of both anaesthetic and carrier gas upon the uptake of [64Cu]-CuATSM, [99mTc]-HL91 and [18F]-FMISO in a preclinical model of tumor hypoxia
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