Preclinical In Vitro

Molecular imaging probes such as PET-tracers have the potential to improve the accuracy of tumor characterization by directly visualizing the biochemical situation. Thus, molecular changes can be detected early before morphological manifestation. The A3 adenosine receptor (A3AR) is described to be highly expressed in colon cancer cell lines and human colorectal cancer (CRC), suggesting this receptor as a tumor marker. The aim of this preclinical study was the evaluation of [F]FE@SUPPY as a PET-tracer for CRC using in vitro imaging and in vivo PET imaging. First, affinity and selectivity of FE@SUPPY and its metabolites were determined, proving the favorable binding profile of FE@SUPPY. The human adenocarcinoma cell line HT-29 was characterized regarding its hA3AR expression and was subsequently chosen as tumor graft. Promising results regarding the potential of [F]FE@SUPPY as a PET-tracer for CRC imaging were obtained by autoradiography as 2.3-fold higher accumulation of [F]FE@SUPPY was found in CRC tissue compared to adjacent healthy colon tissue from the same patient. Nevertheless, first in vivo studies using HT-29 xenografts showed insufficient tumor uptake due to (1) poor conservation of target expression in xenografts and (2) unfavorable pharmacokinetics of [F]FE@SUPPY in mice. We therefore conclude that HT-29 xenografts are not adequate to visualize hA3ARs using [F]FE@SUPPY.(VLID)481541

Human in vivo assessment of ketamine binding of the serotonin transporter—follow up at a higher dose

Ketamine is a rapid-acting antidepressant approved in the indication of treatment-resistant depression. As its clinical use expands, identifying underlying molecular mechanisms is essential. The serotonin transporter (SERT) is well known as a primary mechanism of several classes of monoaminergic antidepressants. Binding of ketamine to SERT has been observed in vitro and in animal studies with macaque monkeys using positron emission tomography (PET). We previously reported that a 0.5 mg/kg body weight dose of ketamine did not significantly bind to SERT in healthy human subjects assessed with PET but observed a positive trend between binding and ketamine plasma levels. Based on this finding, we hypothesized that a higher dose (0.8 mg/kg) would result in measurable SERT occupancy. Here, 10 healthy male participants were measured twice with [11C]DASB PET to test SERT occupancy following administration of 0.8 mg/kg body weight ketamine in four selected SERT rich regions amygdala, putamen, caudate and thalamus. Further, we implemented a bolus-plus-infusion radioligand infusion protocol and optimized the timing of the ketamine infusion. Contrary to our hypothesis, ketamine SERT occupancy did not significantly differ from zero, and the area under the curve of ketamine and norketamine plasma levels was not correlated with occupancy. These results suggest that even at doses up to 0.8 mg/kg, ketamine does not appreciably bind to SERT in humans, aligning with clinical observations that ketamine is routinely combined with serotonergic agents.Clinical trial registrationhttp://clinicaltrials.gov, identifier, NCT02582398. EUDAMED number, CIV-AT-13-01-009583

Neurochemical and behavioral sensitization to d-amphetamine in healthy subjects measured with [¹¹C]-(+)-PHNO-PET

IntroductionIt has been shown that patients with schizophrenia are super-sensitive towards dopamine-releasing agents such as amphetamine. Here, we studied the effects of amphetamine sensitization on amphetamine-induced dopamine release in healthy subjects.ObjectivesTo measure d-amphetamine-induced dopamine release as measured with the D2,3 agonist radioligand [11C]-(+)-PHNO-PET via change in non-displacable binding potential (BPND) and behavioral measures of d-amphetamine effects with drug effects questionnaire (DEQ) and subjective states questionnaire (SSQ).AimsTo study d-amphetamine-induced sensitization in healthy subjects on a behavioral and neurochemical level with [11C]-(+)-PHNO-PET in order to gain more knowledge on sensitization-induced changes in the dopaminergic system.MethodsTwelve stimulant-naïve healthy male subjects underwent three 90-min [11C]-(+)-PHNO-PET-scans and four oral administrations of d-amphetamine. After a naïve baseline scan, subjects underwent a PET scan with previous ingestion of 0.4 mg/kg bodyweight of d-amphetamine 90–120 minutes before scanning. Subsequently, subjects were sensitized to d-amphetamine with the same dose on two separate days. Thereafter, they underwent another PET scan with previous d-amphetamine ingestion. DEQ and SSQ were administered before, 60 min, 90–120 min, and 210 min after amphetamine ingestion.ResultsWe found significant sensitization effects on a behavioral level and on a neurochemical level after four administrations of amphetamine. Items of the SSQ, which showed significant sensitization effects were “outgoing”, “energetic”, “lively”, “alert” and “focused”.ConclusionsWe were able to induce significant behavioral and neurochemical sensitization in healthy humans, which were measured with [11C]-(+)-PHNO-PET for the first time. This sensitization model will be useful for studying the neurobiology of schizophrenia.Disclosure of interestThe authors have not supplied their declaration of competing interest.</jats:sec