Cytotoxic and genotoxic effect of the [166Dy]Dy/166Ho-EDTMP in vivo generator system in mice

Multiple myeloma and other hematological malignancies have been treated by myeloablative radiotherapy/chemotherapy and subsequent stem cell transplantation. [¹⁶⁶Dy]Dy/¹⁶⁶Ho-ethylenediaminetetramethylene phosphonate (EDTMP) forms a stable in vivo generator system with selective skeletal uptake in mice; therefore, it could work as a potential and improved agent for marrow ablation. Induced bone marrow cytotoxicity and genotoxicity are determined by the reduction of reticulocytes (RET) and elevation of micronucleated reticulocyte (MN-RET) in peripheral blood and ablation by bone marrow histological studies. The aim of this study was to determine the bone marrow cytotoxic and genotoxic effect of the [¹⁶⁶Dy]Dy/¹⁶⁶Ho-EDTMP in vivo generator system in mice and to evaluate by histopathology its myeloablative potential.

Enriched ¹⁶⁶Dy₂O₃ was irradiated and [¹⁶⁶Dy]DyCl₃ was added to EDTMP in phosphate buffer (pH 8.0) in a molar ratio of 1:1.75. QC was determined by TLC. Dy-EDTMP complex was prepared the same way with nonirradiated dysprosium oxide. A group of BALB/c mice were intraperitoneally injected with the radiopharmaceutical and two groups of control animals were injected with the cold complex and with 0.9% sodium chloride, respectively. A blood sample was taken at the beginning of the experiments and every 48 h for 12 days postinjection. The animals were sacrificed, organs of interest taken out and the radioactivity determined. The femur was used for histological studies. Flow cytometry analysis was used to quantify the frequency of RET and MN-RET in the blood samples. The MCNP4B Monte Carlo computer code was used for dosimetry calculations.

Radiochemical purity was 99% and the mean specific activity was 1.3 MBq/mg. The RET and MN-RET frequency were statistically different in the treatment at the end of the 12-day period demonstrating cytotoxicity and genotoxicity induced by the in vivo generator system. The histology studies show that there was complete, or almost complete, acellularity, which means significant suppression of the bone marrow activity. Bone marrow absorbed dose was 18–23 Gy. [¹⁶⁶Dy]Dy/¹⁶⁶Ho-EDTMP induces cytotoxicity, genotoxicity and severe myelosuppression in mice. Potentially, it is a good agent for use in humans.     

In vivo evaluation in mice and metabolism in blood of human volunteers of [123I]iodo-PK11195: a possible single-photon emission tomography tracer for visualization of inflammation

We report the in vivo evaluation (biodistribution, displacement and metabolization in blood, brain and heart) in mice and the metabolism in blood of human volunteers of iodine-123 labelled 1-(2-iodophenyl)-N-methyl-N-(1-methyl-propyl)-3-isoquinoline carboxamide ([¹²³I]iodo-PK11195), a potential radioligand for visualization of inflammation in humans by single-photon emission tomography. In three series of 18 white mice (NMRI, 20–25 g), the concentration of radioactivity was measured during 48 h. Blood samples were taken, organs and intestines were excised, excretion was collected and all tissues were weighed and counted for radioactivity. The tissue uptake of radioactivity was measured as % of the injected activity/g of tissue. The excretion was expressed as % of the injected activity. Selective tissue uptake was investigated by pretreatment of another three series of 18 mice with cold PK11195 (1 mg/kg body weight). There was an inflow of [¹²³I]iodo-PK11195 in the brain and among peripheral organs, heart (42.3%), lungs (133.5%) and kidneys (18.4%) had the highest uptake. After pretreatment with cold PK11195, there was a decrease in accumulation in the latter three organs, especially in heart (ca. 55%) and lungs (ca. 80%). Metabolite analysis was performed using high-performance liquid chromatography (HPLC). First, the extraction yield of [¹²³I]iodo-PK11195 from blood and tissue was assessed, and found to be >90%. From blank blood samples and organs spiked with [¹²³I]iodo-PK11195 it was concluded that no metabolization took place during the extraction procedure. Analysis of plasma, brain and heart of mice showed that 10 min p.i. [¹²³I]iodo-PK11195 was the only significant (ca. 95%) radioactive compound in brain and heart where-as in plasma other radioactive products (>60%) appeared. Analysis of plasma samples of the three human volunteers at 7, 20, 37 and 50 min p.i. showed that [¹²³I]iodo-PK11195 rapidly decomposes into two polar metabolites, which at these time points accounted for, respectively 31%, 62%, 75% and 77% of the total activity. Received 9 July and in revised form 17 October 1998     

[111In]DOTATOC as a dosimetric substitute for kidney dosimetry during [90Y]DOTATOC therapy: results and evaluation of a combined gamma camera/probe approach

Purpose During [⁹⁰Y]DOTATOC therapy, for determination of kidney doses a conventional approach using co-injected [¹¹¹In]DOTATOC was evaluated for validity, reliability and reproducibility as well as for the influence of methodological variations and bremsstrahlung. Biologically effective doses were estimated by calculating the relative effectiveness (RE) of kidney doses.Methods Fractionated [⁹⁰Y]DOTATOC therapy (n=20 patients, 3.1±0.7 GBq/therapy cycle, 45 therapy cycles) included co-injection of 157±37 MBq [¹¹¹In]DOTATOC and a nephroprotective infusion regimen. From serial gamma camera/probe measurements, individual region of interest (ROI) sets were established and kidney doses were determined according to MIRDOSE3 (corrected for individual kidney mass) by use of three methodological variants: (1) correction for interfering organs (liver/spleen) and background activity, (2) correction for interfering organs alone and (3) no corrections. A phantom study was performed with ¹¹¹ In alone and with ¹¹¹In +⁹⁰Y to estimate the influence of ⁹⁰Y bremsstrahlung.Results Mean kidney dose (method 1, n=20 patients, 20 therapy cycles) was 1.51±0.60 Gy/GBq [⁹⁰Y]DOTATOC (1.41±0.48 Gy/GBq for n=20 patients, 45 therapy cycles). With partial correction (method 2) or no correction (method 3) for interfering activity, kidney doses increased significantly, to 2.71±1.26 Gy/GBq and 3.15±1.22 Gy/GBq, respectively. The span of REs ranged from 1.02 to 1.24. Inter-observer variability was as high as ±32% (±2SD). ⁹⁰Y bremsstrahlung accounted for a 4–11% underestimation of obtained target activity.Conclusion The obtained kidney doses are highly influenced by methodological variations. Full correction for interfering activity clearly underestimates kidney doses. By comparison, ⁹⁰Y bremsstrahlung and variability in the relative effectiveness of kidney doses cause minor bias. Inter-observer variability must be considered when interpreting kidney doses.     

Characteristics of specific in vivo labeling of neuroleptic binding sites with 3-N-[11C]methylspiperone

In vivo binding of 3-N-[¹¹C]methylspiperone ([¹¹C]NMSP) was saturable in the rat forebrain, but not in the cerebellum. Nonspecific binding was almost equivalent in all brain regions except for the white matter. [¹¹C]NMSP binding was localized to receptor-rich fractions when low doses were administered (less than 20 nmol/kg body weight). The striatum-to-cerebellum ratio was a function of time after injection and administered dose. This radio remained constant in low doses of under 30 nmol/kg. The radioactivity curve of the cerebellum in a control positron-emission tomographic study almost equaled that of the striatum in the dog pretreated with spiperone (2 mg). This indicates that the amount of binding in the cerebellum might be considered a nonspecific binding and unbound pool. The data obtained by the pretreatment study was different from that of displacement, which suggested that displaceable [¹¹C]NMSP in the specific binding sites of the striatum was not completely cleared from the brain tissue by a large amount of unlabeled spiperone.     

Development and evaluation of muscarinic cholinergic receptor ligands n-[c]ethyl-4-piperidyl benzilate and n-[c]propyl-4-piperidyl benzilate: a pet study in comparison with n-[c]methyl-4-piperidyl benzilate in the conscious monkey brain

The muscarinic cholinergic receptor ligands N-[¹¹C]ethyl-4-piperidyl benzilate (4-EPB) and N-[¹¹C]propyl-4-piperidyl benzilate (4-PPB) were developed and evaluated in comparison with N-[¹¹C]methyl-4-piperidyl benzilate (4-MPB) in the conscious monkey brain using positron emission tomography (PET). Time-activity curves of [¹¹C]4-EPB, unlike [¹¹C]4-MPB, showed peaks within 91 min in regions rich in muscarinic receptors. [¹¹C]4-PPB showed no specific binding even in the regions rich in these receptors. These observation demonstrated that increases in [¹¹C]alkyl chain length could alter the kinetic properties of receptor ligands for PET.     

Methodological aspects for in vitro characterization of receptor binding using C-labeled receptor ligands: A detailed study with the benzodiazepine receptor antagonist [C]Ro 15-1788

As a complement to in vivo studies with positron emission tomography (PET), it is desirable to perform in vitro characterization of newly developed ¹¹C tracers. In this report we describe the technique for determination of receptor-ligand kinetics utilizing ligands labeled with the short-lived radionuclide ¹¹C. The limitations and advantages are discussed. The benzodiazepine antagonist [¹¹C]Ro 15-1788 was used as a model substance, and the use of storage phosphor plates for quantification of radioactivity was validated. Storage phosphor plates showed an excellent linear range (˜10³) and acceptable resolution (˜ 0.5 mm). Receptor-ligand kinetics, including depletion, association and dissociation, saturation and displacement were evaluated with good results through the use of short-lived radiotracers and storage phosphor plates.     

Synthesis and in vivo evaluation of [11C]methyl-Ro 64-6198 as an ORL1 receptor imaging agent.

(1S,3aS)-8-(2,3,3a,4,5,6-Hexahydro-1H-phenalen-1-yl)-3-N-[¹¹C]methyl-1-phenyl-1,3,8-triaza-spiro[4.5]decan-4-one ([¹¹C]methyl-Ro 64-6198), a N-methylated analog of Ro 64-6198, was synthesized and evaluated as a potential radiopharmaceutical for investigating brain nociceptin/orphanin FQ receptors (ORL1 receptors) by positron emission tomography. A racemate of methyl-Ro 64-6198, Ro 66-7931, showed a high affinity and selectivity for the ORL1 receptor in vitro. An in vivo distribution study in mice demonstrated moderate brain uptake, however, only slight difference was observed among brain regions. Furthermore, pretreating with nociceptin or Ro 66-7931 did not affect the accumulation. Therefore, despite its high affinity, [¹¹C]methyl-Ro 64-6198 does not appear to be a suitable tracer for in vivo ORL1 receptor imaging studies.     

2-[F]-fluoroisonicotinic acid hydrazide: biological evaluation in an acute infection model

We have synthesized 2-[¹⁸F]-fluoroisonicotinic acid hydrazide by nucleophilic displacement reaction on ethyl-2- (trimethylammonium)-isonicotinate precursor in acetonitrile. Kryptofix^® 222 was used as the phase transfer catalyst. The intermediate fluorinated ethyl ester reacted with hydrazine hydrate to produce the hydrazide. Excellent radiochemical yield was attained with total synthesis time of approximately 60 min. Biological evaluation was performed in bacterial cells and biodistribution in normal as well as E. coli infected CBA/J mice. It was found that the S. pneumoniae cells retained the radiotracer in an in vitro assay. The tracer showed positive localization at the infection/inflammation site in E. coli infected mice.     

Pharmacological effects of dopaminergic drugs on in vivo binding of [99mTc]TRODAT-1 to the central dopamine transporters in rats

R -(exo-exo)]-, [^99mTc]TRODAT-1, to DAT. This paper describes the further characterization of [^99mTc]TRODAT-1 binding sites in rats under conditions which may exist in patients receiving various drug treatments. All experiments were carried out using an i.v. injection of [^99mTc]TRODAT-1 into male Sprague-Dawley rats. Measurements of % dose/gram ratio of (striatum–cerebellum)/cerebellum at 1 h post injection were used as an indicator for specific DAT binding. The biodistribution studies were performed in the presence of drugs which compete for the binding site, such as CFT (WIN 35,428) and methylphenidate, drugs which influence dopamine levels, such as l-DOPA, γ-hydroxybutyrolactone, and α-methyl-p-tyrosine, and d-amphetamine, which both acts as a competitor for DAT binding and increases dopamine levels. Additionally, the influence of dopamine receptor agonists, such as apomorphine and (+)bromocriptine, on biodistribution was tested. Binding of [^99mTc]TRODAT-1 to DAT was found to be inhibited by CFT, methylphenidate, and d-amphetamine in a dose-dependent manner. The specific binding of [^99mTc]TRODAT-1 was not altered by dopamine receptor agonists or by drugs which cause minor changes in dopamine levels. When administered in high doses (634 μmol/kg), l-DOPA also decreased the binding of [^99mTc]TRODAT-1. It is likely that a low dose of l-DOPA (normally needed in the treatment of Parkinson’s disease) will not affect the results on [^99mTc]TRODAT-1 single-photon emission tomographic (SPET) imaging studies. In conclusion, the results clearly demonstrate the specificity of [^99mTc]TRODAT-1 binding to DAT in vivo. Competition for [^99mTc]TRODAT-1 binding was observed only with drug treatment that significantly increases dopamine levels or actively competes for binding at DAT. The results suggest that prior knowledge of whether patients are receiving various drug treatments may assist in the interpretation of DAT status as assessed by SPET imaging studies using [^99mTc]TRODAT-1. Received 7 July and in revised form 27 September 1997     

Role of [18F]FDG-PET/CT after radiofrequency ablation of liver metastases: preliminary results

PURPOSE: Focal metastasis may be treated with radiofrequency ablation (RFA), a low invasive method yet limited by the lack of direct evidence of radicality of treatment. We, hereby, aimed at assessing the role of positron emission tomography-computed tomography (PET/CT) with fluoride radiolabeled deoxy-glucose ([(18)F]FDG) in RFA treatment success evaluation and early diagnosis of local relapse of liver metastasis after RFA procedure. METHODS: RFA was performed in nine patients on 12 liver metastasis, serially imaged through [(18)F]FDG-PET/CT and multidetector CT (MDCT) at 1, 3, 6, and 9 months after treatment. Eight lesions were also scanned with [(18)F]FDG-PET/CT at 1 week after treatment. Imaging analyses were performed on 47 [(18)F]FDG-PET/CT and 51 MDCT. Imaging reading outcomes were compared to each other and to biopsy tissue results when available. RESULTS: In one case, [(18)F]FDG-PET/CT revealed radiotracer uptake at RFA site a week after procedure. Negative concordant outcome was obtained on eight lesions at 1 month after RFA, on eight cases at 3 months, on four at 6 months, and on two cases at 9 months. Extra-liver (peritoneal) disease was detected in one case by both [(18)F]FDG-PET/CT and MDCT. In seven cases, [(18)F]FDG-PET/CT revealed the presence of local recurrence earlier than MDCT. In no cases did MDCT detect local relapse earlier than [(18)F]FDG-PET/CT. CONCLUSION: [(18)F]FDG-PET/CT may detect RFA treatment failure as well as local relapse after RFA earlier than MDCT.     

Radiolabeling and in vitro and in vivo evaluation of [18F]-FE-DABP688 as a PET radioligand for the metabotropic glutamate receptor subtype 5

INTRODUCTION: Fluoroethyl-desmethyl-ABP688 (FE-DABP688) is a novel derivative of the previously described positron emission tomography (PET) ligand 3-(6-methyl-pyridin-2-ylethynyl)-cyclohex-2-enone-O-[11C]-methyl-oxime. FE-DABP688 was radiolabeled with fluorine-18 and characterized as a PET imaging agent for the metabotropic glutamate receptor subtype 5 (mGluR5). METHODS: FE-DABP688 was radiolabeled by reacting 2-[18F]-fluoroethyl tosylate with the sodium salt of 3-(pyridin-2-ylethynyl)-cyclohex-2-enone-oxime in dry DMF. The in vitro affinity of [18F]-FE-DABP688 for mGluR5 was determined by Scatchard analysis of saturation binding data using rat whole-brain membranes (without cerebellum). Further in vitro characterization of the tracer involved plasma stability and lipophilicity testing. In vivo evaluation of [18F]-FE-DABP688 was performed by postmortem biodistribution experiments and PET studies in rats using the dedicated small-animal PET tomograph quad-HIDAC. RESULTS: The radiotracer was obtained in good radiochemical yields in an overall synthesis time of 150 min. The radiochemical yield after semipreparative HPLC was 25+/-8% (n>7, decay corrected), and specific activity was 30+/-5 GBq/micromol (n>7). [18F]-FE-DABP688 exhibited optimal lipophilicity with a logD value of 2.1+/-0.1 and high plasma stability. Saturation assays of [(18)F]-FE-DABP688 revealed a single high-affinity binding site with a dissociation constant (Kd) of 1.6+/-0.4 nM and a Bmax value of 119+/-24 fmol/mg protein. PET scanning indicated radioactivity uptake in mGluR5-rich regions such as the hippocampus, striatum and cortex, while radioactivity accumulation in the cerebellum, a region with negligible mGluR5 density, was significantly lower. Biodistribution studies showed a similar distribution pattern of [18F]-FE-DABP688 binding in the brain. The hippocampus-to-cerebellum and striatum-to-cerebellum ratios were 1.81+/-0.16 and 1.93+/-0.36, respectively. Blocking studies using coinjection of [18F]-FE-DABP688 and unlabeled 2-methyl-6-((3-methoxyphenyl)ethynyl)-pyridine (1 mg/kg) revealed more than 45% specific binding in the hippocampus and striatum, thus demonstrating the in vivo specificity of tracer binding. CONCLUSIONS: [18F]-FE-DABP688 may be a useful PET tracer for imaging mGluR5 in rodents.     

TL response study of the CaSO4 : Dy pellets with graphite for dosimetry in beta radiation and low-energy photons fields

The CaSO₄ : Dy is a good thermoluminescent dosimeter because of its high sensitivity and low cost. With graphite in the pellets it is possible to reduce the energy dependence. The sensitivity and energy dependence of the different thicknesses of CaSO₄ : Dy pellets was studied with different amounts of graphite. The results have shown the optimal quantity of the graphite and the appropriate thickness of the pellets that can be used in dosimetry of beta field, photons or both simultaneously.     

A micro-PET/CT approach using O-(2-[F]fluoroethyl)-l-tyrosine in an experimental animal model of F98 glioma for BNCT

The present study focuses on a micro-PET/CT application to be used for experimental Boron Neutron Capture Therapy (BNCT), which integrates, in the same frame, micro-CT derived anatomy and PET radiotracer distribution. Preliminary results have demonstrated that ¹⁸F-fluoroethyl-tyrosine (FET)/PET allows the identification of the extent of cerebral lesions in F98 tumor bearing rat. Neutron autoradiography and α-spectrometry on axial tissues slices confirmed the tumor localization and extraction, after the administration of fructose–boronophenylalanine (BPA). Therefore, FET–PET approach can be used to assess the transport, the net influx, and the accumulation of FET, as an aromatic amino acid analog of BPA, in experimental animal model. Coregistered micro-CT images allowed the accurate morphological localization of the radiotracer distribution and its potential use for experimental BNCT.     

Human biodistribution and dosimetry of [123I]FP-CIT: a potent radioligand for imaging of dopamine transporters

This study reports on the biodistribution and radiation dosimetry of iodine-123-labelled N-ω-(flu- oropropyl)-2β-carbomethoxy-3β-(4-iodophenyl)tropane ([¹²³I]FP-CIT), a promising radioligand for the imaging of dopamine transporters. In 12 healthy volunteers, conjugate whole-body scans were performed up to 48 h following intravenous injection of approximately 100 MBq [¹²³I]FP-CIT. Attenuation correction was performed using a transmission whole-body scan obtained prior to injection of the radioligand, employing a ¹²³I flood source. Blood samples were taken and urine was freely collected up to 48 h after injection of the radiotracer. For each subject, the percentage of injected activity measured in regions of interest over brain, striatum, lungs and liver were fitted to a multicompartmental model to give time-activity curves. The cumulative urine activity curve was used to model the urinary excretion rate and, indirectly, to predict faecal excretion. Using the MIRD method, nine source organs were considered in estimating absorbed radiation doses for organs of the body. The images showed rapid lung uptake and hepatobiliary excretion. Diffuse uptake and retention of activity was seen in the brain, especially in the striatum. At 48 h following the injection of [¹²³I]FP-CIT, mean measured urine excretion was 60%±9% (SD), and mean predicted excretion in faeces was 14%±1%. In general, the striatum received the highest absorbed dose (average 0.23 mGy/MBq), followed by the urinary bladder wall (average 0.054 mGy/MBq) and lungs (average 0.043 mGy/MBq). The average effective dose equivalent of [¹²³I]FP-CIT was estimated to be 0.024 mSv/MBq. The amount of [¹²³I]FP-CIT required for adequate dopamine transporter imaging results in an acceptable effective dose equivalent to the patient. Received 14 July and in revised form 26 September 1997     

Factors affecting quality control of [F]FDG injection: bacterial endotoxins test, aluminum ions test and HPLC analysis for FDG and CIDG

High concentrations of citrates and phosphates which are often used in the manufacturing of [¹⁸F] fluro-d-glucose (FDG) preparations and wide deviation in the pH value from the neutral level often disturb the detection of endotoxins and aluminum ions using the turbidimetric and aluminum ion paper test method. The column temperature was found to be a major factor influencing the sensitivity of ClDG detection with the HPAEC/PAD method.     

[1-C]Octanoate as a potential PET tracer for studying glial functions: PET evaluation in rats and cats

To evaluate the ability of [1-¹¹C]octanoate as a PET tracer for imaging the brain, we examined its distribution in the brain and surrounding tissues in rats and cats with PET. In rats, owing to the accumulated radioactivity in the harderian glands, clear brain images were not obtained at rostral levels. In cats, the brain was imaged clearly at every level of the coronal brain slices, suggesting the potential of [1-¹¹C]octanoate for imaging the brain.     

O-[18F]fluoromethyl-L-tyrosine is a potential tracer for monitoring tumour response to chemotherapy using PET: an initial comparative in vivo study with deoxyglucose and thymidine

Purpose To compare the utility of a new artificial amino acid, O-[¹⁸F]fluoromethyl-L-tyrosine ([¹⁸F]FMT), for monitoring cancer chemotherapy with deoxyglucose and thymidine.Methods [¹⁸F]FMT, [¹⁴C]deoxyglucose ([¹⁴C]DG) and [6-³H]thymidine ([³H]Thd) were applied in this study. A 2.5 mg/kg dose of mitomycin (MMC) was administered to AH272 rat hepatoma-bearing Donryu rats. Tumour uptake of each tracer was measured just before (baseline) and on days 1, 3, 5 and 7 after the MMC administration, 1 h after a mixture of [¹⁸F]FMT, [¹⁴C]DG and [³H]Thd had been injected, and was shown as DURs (% injected dose/gram tissue normalised for the rat body weight). Dual-tracer macroautoradiographs with [¹⁸F]FMT and [¹⁴C]DG were also prepared.Results The tumour uptake for each tracer decreased earlier than did the tumour size. DURs (mean±SD) at baseline and on days 1, 3, 5 and 7 were as follows: [¹⁸F]FMT: 4.68±0.72, 3.34±0.66, 3.13±0.72, 3.42±0.45, 3.01±0.32; [¹⁴C]DG: 3.26±0.40, 3.09±0.55, 3.01±0.97, 2.28±0.35, 1.70±0.72; and [³H]Thd: 2.23±0.46, 1.54±0.45, 1.28±0.37, 1.35±0.20, 0.94±0.12. Decrease in [¹⁸F]FMT uptake compared with baseline was significant from day 1 (p<0.01), and the decrease in [³H]Thd uptake was also significant on day 1 (p<0.05) and days 3–7 (p<0.01). However, decrease in [¹⁴C]DG uptake was only significant from day 5 (p<0.01). Macroautoradiography suggested that the influence of inflammatory cells on the accumulation of [¹⁸F]FMT in tumours is smaller than that on the accumulation of [¹⁴C]DG.Conclusion [¹⁸F]FMT uptake shows a rapid and sensitive response to chemotherapy, comparable to that of [³H]Thd, suggesting that it may be applied as a powerful tracer for monitoring of proliferative activity after cancer chemotherapy using PET.     

Imaging of peripheral-type benzodiazepine receptor in tumor: in vitro binding and in vivo biodistribution of N-benzyl-N-[C]methyl-2-(7-methyl-8-oxo-2-phenyl-7,8-dihydro-9H-purin-9-yl)acetamide

IntroductionThe aim of this study was to evaluate N-benzyl-N-[¹¹C]methyl-2-(7-methyl-8-oxo-2-phenyl-7,8-dihydro-9H-purin-9-yl)acetamide ([¹¹C]DAC) as a novel peripheral-type benzodiazepine receptor (PBR) ligand for tumor imaging.Methods[¹¹C]DAC was synthesized by the reaction of a desmethyl precursor with [¹¹C]CH₃I. In vitro uptake of [¹¹C]DAC was examined in PBR-expressing C6 glioma and intact murine fibrosarcoma (NFSa) cells. In vivo distribution of [¹¹C]DAC was determined using NFSa-bearing mice and small-animal positron emission tomography (PET).Results[¹¹C]DAC showed specific binding to PBR in C6 glioma cells, a standard cell line with high PBR expression. Specific binding of [¹¹C]DAC was also confirmed in NFSa cells, a target tumor cell line in this study. Results of PET experiments using NFSa-bearing mice, showed that [¹¹C]DAC was taken up specifically into the tumor, and pretreatment with PK11195 abolished the uptake.Conclusions[¹¹C]DAC was taken up into PBR-expressing NFSa. [¹¹C]DAC is a promising PET ligand that can be used for imaging PBR in tumor-bearing mice.     

[carbonyl-11C]Desmethyl-WAY-100635 (DWAY) is a potent and selective radioligand for central 5-HT1A receptors in vitro and in vivo

 [carbonyl-¹¹C]Desmethyl-WAY-100635 (DWAY) is possibly a low-level metabolite appearing in plasma after intravenous administration of [carbonyl-¹¹C]WAY-100635 to human subjects for positron emission tomographic (PET) imaging of brain 5-HT_1A receptors. In this study we set out to assess the ability of DWAY to enter brain in vivo and to elucidate its possible interaction with 5-HT_1A receptors. Desmethyl-WAY-100635 was labelled efficiently with carbon-11 (t _1/2 = 20.4 min) in high specific radioactivity by reaction of its descyclohexanecarbonyl analogue with [carbonyl-¹¹C]cyclohexanecarbonyl chloride. The product was separated in high radiochemical purity by high-performance liquid chromatography (HPLC) and formulated for intravenous injection. Rats were injected intravenously with DWAY, sacrificed at known times and dissected to establish radioactivity content in brain tissues. At 60 min after injection, the ratios of radioactivity concentration in each brain region to that in cerebellum correlated with previous in vitro and in vivo measures of 5-HT_1A receptor density. The highest ratio was about 22 in hippocampus. Radioactivity cleared rapidly from plasma; HPLC analysis revealed that DWAY represented 55% of the radioactivity in plasma at 5 min and 33% at 30 min. Only polar radioactive metabolites were detected. Subsequently, a cynomolgus monkey was injected intravenously with DWAY and examined by PET. Maximal whole brain uptake of radioactivity was 5.7% of the administered dose at 5 min after injection. The image acquired between 9 and 90 min showed high radioactivity uptake in brain regions rich in 5-HT_1A receptors (e.g. frontal cortex and neocortex), moderate uptake in raphe nuclei and low uptake in cerebellum. A transient equilibrium was achieved in cortical regions at about 60 min, when the ratio of radioactivity concentration in frontal cortex to that in cerebellum reached 6. The corresponding ratio for raphe nuclei was about 3. Radioactive metabolites appeared rapidly in plasma, but these were all more polar than DWAY, which represented 52% of the radioactivity in plasma at 4 min and 20% at 55 min. In a second PET experiment, in which a cynomolgus monkey was pretreated with the selective 5-HT_1A receptor antagonist, WAY-100635, at 25 min before DWAY injection, radioactivity in all brain regions was reduced to that in cerebellum. Autoradiography of post mortem human brain cryosections after incubation with DWAY successfully delineated 5-HT_1A receptor distribution. Receptor-specific binding was eliminated in the presence of the selective 5-HT_1A receptor agonist, 8-OH-DPAT [(±)-8-hydroxy-2-dipropylaminotetralin]. These findings show that: (a) intravenously administered DWAY is well able to penetrate brain in rat and monkey, (b) DWAY is a highly effective radioligand for brain 5-HT_1A receptors in rat and monkey in vivo and for human brain in vitro, and (c) the metabolism and kinetics of DWAY appear favourable to successful biomathematical modelling of acquired PET data. Thus, DWAY warrants further evaluation as a radioligand for PET studies of 5-HT_1A receptors in human brain. Received 1 October and in revised form 12 December 1997