Search

Introduction [ 11 C]Erlotinib PET has shown promise to distinguish non-small cell lung cancer (NSCLC) tumors harboring the activating epidermal growth factor receptor (EGFR) mutation delE746-A750 from tumors with wild-type EGFR. To assess the suitability of [ 11 C]erlotinib PET to detect the emergence of acquired erlotinib resistance in initially erlotinib-responsive tumors, we performed in vitro binding and PET experiments in mice bearing tumor xenografts using a range of different cancer cells, which were erlotinib-sensitive or exhibited clinically relevant resistance mechanisms to erlotinib. Methods The following cell lines were used for in vitro binding and PET experiments: the epidermoid carcinoma cell line A-431 (erlotinib-sensitive, wild-type EGFR) and the three NSCLC cell lines HCC827 (erlotinib-sensitive, delE746-A750), HCC827 EPR (erlotinib-resistant, delE746-A750 and T790M) and HCC827 ERLO (erlotinib-resistant, delE746-A750 and MET amplification). BALB/c nude mice with subcutaneous tumor xenografts underwent two consecutive [ 11 C]erlotinib PET scans, a baseline scan and a second scan in which unlabeled erlotinib (10mg/kg) was co-injected. Logan graphical analysis was used to estimate total distribution volume (V T ) of [ 11 C]erlotinib in tumors. Results In vitro experiments revealed significantly higher uptake of [ 11 C]erlotinib (5.2-fold) in the three NSCLC cell lines as compared to A-431 cells. In all four cell lines co-incubation with unlabeled erlotinib (1μM) led to significant reductions in [ 11 C]erlotinib uptake (−19% to −66%). In both PET scans and for all four studied cell lines there were no significant differences in tumoral [ 11 C]erlotinib V T values. For all three NSCLC cell lines, but not for the A-431 cell line, tumoral V T was significantly reduced following co-injection of unlabeled erlotinib (−20% to −35%). Conclusions We found no significant differences in the in vitro and in vivo binding of [ 11 C]erlotinib between erlotinib-sensitive and erlotinib-resistant NSCLC cells. Our findings suggest that [ 11 C]erlotinib PET will not be suitable to distinguish erlotinib-sensitive NSCLC tumors from tumors with acquired resistance to erlotinib.

Radiochemists/radiopharmacists, involved in the preparation of radiopharmaceuticals are regularly confronted with the requirement of continuous high quality productions in their day-to-day business. One of these requirements is high specific or molar activity of the radiotracer in order to avoid e.g. receptor saturation and pharmacological or even toxic effects of the applied tracer for positron emission tomography. In the case ofIn this study, diverseThe manifold contributions to low molar activity can be attributed to three main categories, namely technical parameters (e.g. quality of target gases, reagents or tubings), inter/intralaboratory parameters (e.g. maintenance interval, burden of the module, etc.) and interoperator parameters (e.g. handling of the module).Our study provides a better understanding of different factors contributing to the overall carbon load of a synthesis module, which facilitates maintenance of high molar activity of carbon-11-labeled radiopharmaceuticals.

In recent years extra-corporal application of boron neutron capture therapy (BNCT) was evaluated for liver primary tumors or liver metastases. A prerequisite for such a high-risk procedure is proof of preferential delivery and high uptake of aTumor bearing mice (hepatocellular carcinoma cell line, HuH-7) were either subject of a [We found a significant correlation between [[Despite differences in chemical structure and administered dose [

With the aim to develop a PET tracer to visualize P-glycoprotein (Pgp) expression levels in different organs, the Pgp inhibitor MC113 was labeled with (11)C and evaluated using small-animal PET.[(11)C]MC113 was synthesized by reaction of O-desmethyl MC113 with [(11)C]methyl triflate. Small-animal PET was performed with [(11)C]MC113 in FVB wild-type and Mdr1a/b((-/-)) mice (n=3 per group) and in a mouse model of high (EMT6Ar1.0) and low (EMT6) Pgp expressing tumor grafts (n=5). In the tumor model, PET scans were performed before and after administration of the reference Pgp inhibitor tariquidar (15mg/kg).Brain uptake of [(11)C]MC113, expressed as area under the time-activity curve from time 0 to 60min (AUC(0-60)), was moderately but not significantly increased in Mdr1a/b((-/-)) compared with wild-type mice (mean±SD AUC(0-60), Mdr1a/b((-/-)): 88±7min, wild-type: 62±6min, P=0.100, Mann Whitney test). In the tumor model, AUC(0-60) values were not significantly different between EMT6Ar1.0 and EMT6 tumors. Neither in brain nor in tumors was activity concentration significantly changed in response to tariquidar administration. Half-maximum effect concentrations (IC(50)) for inhibition of Pgp-mediated rhodamine 123 efflux from CCRFvcr1000 cells were 375±60nM for MC113 versus 8.5±2.5nM for tariquidar.[(11)C]MC113 showed higher brain uptake in mice than previously described Pgp PET tracers, suggesting that [(11)C]MC113 was only to a low extent effluxed by Pgp. However, [(11)C]MC113 was found unsuitable to visualize Pgp expression levels presumably due to insufficiently high Pgp binding affinity of MC113 in relation to Pgp densities in brain and tumors.

The multidrug efflux transporter breast cancer resistance protein (BCRP) is highly expressed in the blood-brain barrier (BBB), where it limits brain entry of a broad range of endogenous and exogenous substrates. Methyl is a recently discovered BCRP-selective inhibitor, which is structurally derived from the potent P-glycoprotein (P-gp) inhibitor tariquidar. The aim of this study was to develop a new PET tracer based on 1 to map BCRP expression levels in vivo.Compound 1 was labelled with (11)C in its methyl ester function by reaction of the corresponding carboxylic acid 2 with [(11)C]methyl triflate. Positron emission tomography (PET) imaging of [(11)C]-1 was performed in wild-type, Mdr1a/b((-/-)), Bcrp1((-/-)) and Mdr1a/b((-/-))Bcrp1((-/-)) mice (n=3 per mouse type) and radiotracer metabolism was assessed in plasma and brain.Brain-to-plasma ratios of unchanged [(11)C]-1 were 4.8- and 10.3-fold higher in Mdr1a/b((-/-)) and in Mdr1a/b((-/-))Bcrp1((-/-)) mice, respectively, as compared to wild-type animals, but only modestly increased in Bcrp1((-/-)) mice. [(11)C]-1 was rapidly metabolized in vivo giving rise to a polar radiometabolite which was taken up into brain tissue.Our data suggest that [(11)C]-1 preferably interacts with P-gp rather than BCRP at the murine BBB which questions its reported in vitro BCRP selectivity. Consequently, [(11)C]-1 appears to be unsuitable as a PET tracer to map cerebral BCRP expression.

[(11)C]Flumazenil, a highly selective benzodiazepine antagonist is the most extensively used GABA(A) ligand for PET so far. To overcome half life disadvantages of (11)C a [(18)F]-labeled flumazenil derivative, 2'-[(18)F]fluoroflumazenil (FFMZ) was developed and biologically evaluated with respect to the GABA(A) receptor. Organ with the highest uptake was the pituitary gland. Brain uptake was high and followed the order cortex>thalamus>cerebellum>rest brain. Fluoroflumazenil displaced [(3)H]flumazenil binding from membrane GABA(A) receptors with an IC(50)value (3.5 nM) comparable to that of Flumazenil (2.8 nM). The presented data confirm the potential of [(18)F]FFMZ for PET imaging of the GABA-ergic system.

(1R,2S)-4-[18F]fluorometaraminol (4-[18F]FMR), a tracer for cardiac sympathetic innervation, was synthesized by electrophilic aromatic substitution. A trimethylstannyl precursor, protected with tert-butoxycarbonyl protecting groups, was radiofluorinated with high specific radioactivity [18F]F2. Specific radioactivity of 4-[18F]FMR, in average 11.8 +/-3.3 GBq/micromol, was improved 40-800-fold in comparison to the previous electrophilic fluorinations. The biodistribution of 4-[18F]FMR in rat was in accordance with the known distribution of sympathetic innervation. 4-[18F]FMR showed no metabolic degradation in left ventricle of rat heart, where the uptake was high, rapid and specific.

Ciprofloxacin (1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-quinoline-3-carboxylic acid), a widely-prescribed antibiotic, was labeled with fluorine-18 with the aim to perform positron emission tomography studies in humans for pharmacokinetic measurements. Due to a lack of chemical activation of ciprofloxacin for a direct nucleophilic exchange reaction a novel two-step synthetic approach, which employed an activated 6-fluoro-7-chloro substituted precursor molecule, was developed. The radiosynthesis yielded, starting from 52.5 ± 11.3 GBq of [ 18 F]fluoride, 1.3 ± 0.6 GBq (n = 13) [ 18 F]ciprofloxacin ready for intravenous administration in about 130 min synthesis time. A series of analytical tests was performed in order to prove the identity of the radiolabeled compound and its suitability for human applications.

Introduction Transport of 2-[ 18 F]fluoro-2-deoxy-d-glucose ([ 18 F]FDG) by the multidrug efflux transporters P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) at the blood–brain barrier (BBB) may confound the interpretation of [ 18 F]FDG brain PET data. Aim of this study was to assess the influence of ABCB1 and ABCG2 at the BBB on brain distribution of [ 18 F]FDG in vivo by performing [ 18 F]FDG PET scans in wild-type and transporter knockout mice and by evaluating changes in [ 18 F]FDG brain distribution after transporter inhibition. Methods Dynamic small-animal PET experiments (60min) were performed with [ 18 F]FDG in groups of wild-type and transporter knockout mice ( Abcb1a/b (−/−) , Abcg2 (−/−) and Abcb1a/b (−/−) Abcg2 (−/−) ) and in wild-type rats without and with i.v. pretreatment with the known ABCB1 inhibitor tariquidar (15mg/kg, given at 2h before PET). Blood was sampled from animals from the orbital sinus vein at the end of the PET scans and measured in a gamma counter. Brain uptake of [ 18 F]FDG was expressed as the brain-to-blood radioactivity concentration ratio in the last PET time frame (K b,brain ). Results K b,brain values of [ 18 F]FDG were not significantly different between different mouse types both without and with tariquidar pretreatment. The blood-to-brain transfer rate constant of [ 18 F]FDG was significantly lower in tariquidar-treated as compared with vehicle-treated rats (0.350±0.025mL/min/g versus 0.416±0.024mL/min/g, p =0.026, paired t-test) but K b,brain values were not significantly different between both rat groups. Conclusion Our results show that [ 18 F]FDG is not transported by Abcb1 at the mouse and rat BBB in vivo . In addition we found no evidence for Abcg2 transport of [ 18 F]FDG at the mouse BBB. Advances in knowledge and implications for patient care Our findings imply that functional activity of ABCB1 and ABCG2 at the BBB does not need to be taken into account when interpreting brain [ 18 F]FDG PET data.

The dopamine D 4 receptor (D 4 R) is expressed in low density in various extrastriatal brain regions. This receptor subtype is discussed in relation to the pathophysiology and treatment of schizophrenia but no selective positron emission tomography (PET) ligand is available to date to study the distribution in vivo. The arylpiperazine derivative N -[2-[4-(4-chlorophenyl)piperazin-1-yl]ethyl]-3-methoxybenzamide (PB-12) is a novel, high-affinity ( K i =0.040 nM ) and selective D 4 R ligand. We radiolabeled PB-12 with carbon-11 (t 1/2 20.4 min) by O -methylation of the corresponding desmethyl analogue N -[2-[4-(4-chlorophenyl)piperazin-1-yl]ethyl]-3-hydroxybenzamide (LM-190) with [ 11 C]methyl triflate. Derivative LM-190 was prepared by condensing 3-hydroxybenzoic acid with the appropriate amine. For the radiolabeling, the incorporation yield was >90% and the total synthesis time including high performance liquid chromatography (HPLC) purification was about 35 min. The specific radioactivity of [ 11 C]PB-12 at time of injection was 67–118 GBq · μmol −1 . PET studies in a cynomolgus monkey showed a high uptake and widespread distribution of radioactivity in the brain, including the neocortex and thalamus. About 40% of total radioactivity in plasma represented unchanged radioligand at 60 min after injection as determined by HPLC. Pretreatment with the D 4 R ligand 3-{[4-(4-chlorophenyl)piperazin-1-yl]methyl}-1H-pyrollo[2,3-b]pyridine (L-745,870) prior to radioligand injection failed to demonstrate receptor-specific binding in the monkey brain. Furthermore, the brain radioactivity distribution was left unaffected by pretreating with unlabeled PB-12. This failure to detect a D 4 R-specific signal may be related to a very low density of the D 4 R in primate brain, insufficient binding affinity of the radioligand, and a high background of nonspecific binding. It can be concluded from these findings that [ 11 C]PB-12 is not suitable to visualize the D 4 R in the primate brain with PET.

Epidepride [(S)-(-)-N-([1-ethyl-2-pyrrolidinyl]methyl)-5-iodo-2,3-dimethoxybenza mide] binds with a picomolar affinity (Ki = 24 pM) to the dopamine D2 receptor. Iodine-123-labeled epidepride has been used previously to study striatal and extrastriatal dopamine D2 receptors with single photon emission computed tomography (SPECT). Our aim was to label epidepride with carbon-11 for comparative quantitative studies between positron emission tomography (PET) and SPECT. Epidepride was synthesized from its bromo-analogue FLB 457 via the corresponding trimethyl-tin derivative. In an alternative synthetic pathway, the corresponding substituted benzoic acid was reacted with the optically pure aminomethylpyrrolidine-derivative. Demethylation of epidepride gave the desmethyl-derivative, which was reacted with [11C]methyl triflate. Total radiochemical yield was 40-50% within a total synthesis time of 30 min. The specific radioactivity at the end of synthesis was 37-111 GBq/micromol (1,000-3,000 Ci/mmol). Human postmortem whole-hemisphere autoradiography demonstrated dense binding in the caudate putamen, and also in extrastriatal areas such as the thalamus and the neocortex. The binding was inhibited by unlabeled raclopride. PET studies in a cynomolgus monkey demonstrated high uptake in the striatum and in several extrastriatal regions. At 90 min after injection, uptake in the striatum, thalamus and neocortex was about 11, 4, and 2 times higher than in the cerebellum, respectively. Pretreatment experiment with unlabeled raclopride (1 mg/kg) inhibited 50-70% of [11C]epidepride binding. The fraction of unchanged [11C]epidepride in monkey plasma determined by a gradient high performance liquid chromatography (HPLC) method was about 30% of the total radioactivity at 30 min after injection of [11C]epidepride. The availability of [11C]epidepride allows the PET-verification of the data obtained from quantitation studies with SPECT.

Introduction The adenosine triphosphate-binding cassette (ABC) transporter P-glycoprotein (Pgp) protects the brain from accumulation of lipophilic compounds by active efflux transport across the blood–brain barrier. Changes in Pgp function/expression may occur in neurological disorders, such as epilepsy, Alzheimer's or Parkinson's disease. In this work we investigated the suitability of the radiolabeled Pgp inhibitors [ 11 C]elacridar and [ 11 C]tariquidar to visualize Pgp density in rat brain with PET. Methods Rats underwent a first PET scan with [ 11 C]elacridar ( n =5) or [ 11 C]tariquidar ( n =6) followed by a second scan with the Pgp substrate ( R )-[ 11 C]verapamil after administration of unlabeled tariquidar at a dose which half-maximally inhibits cerebral Pgp (3mg/kg). Compartmental modeling using an arterial input function and Logan graphical analysis were used to estimate rate constants and volumes of distribution ( V T ) of radiotracers in different brain regions. Results Brain PET signals of [ 11 C]elacridar and [ 11 C]tariquidar were very low (~0.5 standardized uptake value, SUV). There was a significant negative correlation between V T and K 1 (i.e. influx rate constant from plasma into brain) values of [ 11 C]elacridar or [ 11 C]tariquidar and V T and K 1 values of ( R )-[ 11 C]verapamil in different brain regions which was consistent with binding of [ 11 C]inhibitors to Pgp and efflux of ( R )-[ 11 C]verapamil by Pgp. Conclusion The small Pgp binding signals obtained with [ 11 C]elacridar and [ 11 C]tariquidar limit the applicability of these tracers to measure cerebral Pgp density. PET tracers with higher (i.e. subnanomolar) binding affinities will be needed to visualize the low density of Pgp in brain.

The radiolabeled catecholamine analogue (1R, 2S)-6-[(18)F]fluorometaraminol (6-[(18)F]FMR) is a substrate for the neuronal norepinephrine transporter. It has been used as a positron emission tomography (PET) ligand to map sympathetic nerves in dog heart. 6-[(18)F]FMR could be only synthesized with low specific radioactivity, which precluded its use in human subjects. We have recently prepared (1R,2S)-4-[(18)F]fluorometaraminol (4-[(18)F]FMR), a new fluoro-analogue of metaraminol, with high specific radioactivity (56-106 GBq/micromol). In the present study, we demonstrate in rats that 4-[(18)F]FMR possesses similar affinity toward myocardial norepinephrine transport mechanisms as 6-[(18)F]FMR. When compared with control animals, an 80% and 76% reduction in myocardial uptake was observed in animals pretreated with desipramine (an inhibitor of the neuronal norepinephrine transporter) and with reserpine (a blocker of the vesicular storage of monoamines), respectively. The entire radioactivity in rat myocardium represented unmetabolized parent tracer as determined by high performance liquid chromatography analysis of tissue extracts. In dogs, myocardial kinetics of 4-[(18)F]FMR were assessed using PET. A rapid and high uptake was observed, followed by prolonged cardiac retention. A heart-to-lung ratio of 15 was reached 10 min after injection of the radiotracer. Pretreatment with desipramine reduced the heart half-life of 4-[(18)F]FMR by 90% compared with control. Moreover, an infusion of tyramine caused a rapid decline of radioactivity in the heart. This demonstrates that 4-[(18)F]FMR specifically visualizes sympathetic neurons in dog heart. High specific radioactivity 4-[(18)F]FMR is a promising alternative to 6-[(18)F]FMR for myocardial neuronal mapping with PET in humans.