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Purpose The adenosine A3 receptor (A3R) is involved in cardiovascular, neurological and tumour-related pathologies and serves as an exceptional pharmaceutical target in the clinical setting. A3R antagonists are considered antiinflammatory, antiallergic and anticancer agents, and to have potential for the treatment of asthma, COPD, glaucoma and stroke. Hence, an appropriate A3R PET tracer would be highly beneficial for the diagnosis and therapy monitoring of these diseases. Therefore, in this preclinical in vivo study we evaluated the potential as a PET tracer of the A3R antagonist [18F]FE@SUPPY. Methods Rats were injected with [18F]FE@SUPPY for baseline scans and blocking scans (A3R with MRS1523 or FE@SUPPY, P-gp with tariquidar; three animals each). Additionally, metabolism was studied in plasma and brain. In a preliminary experiment in a mouse xenograft model (mice injected with cells expressing the human A3R; three animals), the animals received [18F]FE@SUPPY and [18F]FDG. Dynamic PET imaging was performed (60 min in rats, 90 min in xenografted mice). In vitro stability of [18F]FE@SUPPY in human and rat plasma was also evaluated. Results [18F]FE@SUPPY showed high uptake in fat-rich regions and low uptake in the brain. Pretreatment with MRS1523 led to a decrease in [18F]FE@SUPPY uptake (p = 0.03), and pretreatment with the P-gp inhibitor tariquidar led to a 1.24-fold increase in [18F]FE@SUPPY uptake (p = 0.09) in rat brain. There was no significant difference in metabolites in plasma and brain in the treatment groups. However, plasma concentrations of [18F]FE@SUPPY were reduced to levels similar to those in rat brain after blocking. In contrast to [18F]FDG uptake (p = 0.12), the xenograft model showed significantly increased uptake of [18F]FE@SUPPY in the tissue masses from CHO cells expressing the human A3R (p = 0.03). [18F]FE@SUPPY was stable in human plasma. Conclusion Selective and significant tracer uptake of [18F]FE@SUPPY was found in xenografted mice injected with cells expressing human A3R. This finding supports the strategy of evaluating [18F]FE@SUPPY in “humanized animal models”. In conclusion, preclinical evaluation points to the suitability of [18F]FE@SUPPY as an A3R PET tracer in humans.

P-glycoprotein (P-gp) acts at the blood-brain barrier (BBB) as an active cell membrane efflux pump for several endogenous and exogenous compounds. The P-gp substrate (R)-[11C]verapamil (VPM) can be used to measure P-gp-mediated transport at the BBB in vivo with positron emission tomography (PET). The distribution volume (DV) of VPM has been shown to inversely reflect P-gp function in the BBB [1].

Background Gastric cancer at advanced stage of disease is a major health problem and the prognosis with the current therapeutic treatment strategies remains poor. PI3K/mTOR pathway mutations, especially PTEN, PI3K3C and AKT mutations and pS6 overexpression, are found frequently in gastric cancer patients and are linked with poor outcome. Thus, we evaluated the dual PI3K and mTOR inhibitor BEZ235 against gastric cancer in vitro and in vivo.