[(11)C]PR04.MZ, a promising DAT ligand for low concentration imaging: Synthesis, efficient (11)C-O-methylation and initial small animal PET studies.

PR04.MZ was designed as a highly selective dopamine transporter inhibitor, derived from natural cocaine. Its binding profile indicates that [{sup 11}C]PR04.MZ may be suited as a PET radioligand for the non-invasive exploration of striatal and extrastriatal DAT populations. As a key feature, its structural design facilitates both, labelling with fluorine-18 at its terminally fluorinated butynyl moiety and carbon-11 at its methyl ester function. The present report concerns the efficient [{sup 11}C]MeI mediated synthesis of [{sup 11}C]PR04.MZ from an O-desmethyl precursor trifluoroacetic acid salt with Rb{sub 2}CO{sub 3} in DMF in up to 95 {+-} 5% labelling yield. A preliminary {mu}PET-experim…

[68Ga]Ga-DO2A-(OBu-l-tyr)2: Synthesis, 68Ga-radiolabeling and in vitro studies of a novel 68Ga-DO2A-tyrosine conjugate as potential tumor tracer for PET

The synthesis, (68)Ga-labeling and in vitro study of the novel tyrosine chelate derivative [(68)Ga]Ga-1,4,7,10-tetraazacyclododecane-1,7-diacetic acid-4,10-di-(O-butyl)-l-tyrosine ([(68)Ga]Ga-DO(2)A-(OBu-l-tyr)(2)) as a potential tracer for imaging tumor metabolism by positron emission tomography (PET) is presented. This approach combines the biological amino acid transporter targeting properties of l-tyrosine with the outstanding availability of (68)Ga(III) via the (68)Ge/(68)Ga generator. In vitro studies utilizing the F98-glioblastoma cell line revealed specific uptake of [(68)Ga]Ga-DO2A-(OBu-l-tyr)(2) that was comparable to that of the reference O-(2-[(18)F]fluoroethyl)-l-tyrosine (FET)…

Radiolabelling and preliminary evaluation of 68Ga-tetrapyrrole derivatives as potential tracers for PET

article i nfo Tetrapyrroles are multisided natural products which are of relevance in clinical medicine. Owing to their specific accumulation in tumour tissue, porphyrins, metalloporphyrins and chlorins have been used as in photodynamic therapy and optical imaging. Moreover, their specific uptake into inflammatory atheromatous plaques via LDL endocytosis has been reported. The present study is concerned with the synthesis of 68 Ga labelled porphyrin derivatives and an in vitro assessment of the utility of radiotracers in positron emission tomography. A set of five porphyrin derivatives were labelled using 68 Ga from a commercially obtained radionuclide generator. Dedicated post-processing o…

[18F]PR04.MZ PET/CT Imaging for Evaluation of Nigrostriatal Neuron Integrity in Patients With Parkinson Disease.

Introduction Degeneration of dopaminergic, nigrostriatal neurons is the hallmark of Parkinson disease (PD), and PET quantification of dopamine transporters is a widely accepted method for differential diagnosis between idiopathic PD and essential tremor. [18F]PR04.MZ is a new PET tracer with excellent imaging properties allowing for precise quantification of striatal and extrastriatal dopamine transporter. Here we describe our initial experience with [18F]PR04.MZ PET/CT in a larger cohort of healthy controls and PD patients as a proof-of-concept study for this tracer. Methods Eighteen healthy subjects, 19 early PD patients (Hoehn-Yahr I–II), and 13 moderate-advanced PD patients (Hoehn-Yahr …

A convenient chemo-enzymatic synthesis and 18F-labelling of both enantiomers of trans-1-toluenesulfonyloxymethyl-2-fluoromethyl-cyclopropane

The present report is concerned with a stereoselective, reliable route to trans-1,2-disubstituted cyclopropanes and in particular to (S,S)-1-tosyloxymethyl-2-fluoromethyl-cyclopropane (1) and (R,R)-1-tosyloxymethyl-2-fluoromethyl-cyclopropane (ent-1) as conformationally restricted, terminally fluorinated C4-building blocks for medicinal chemistry. The enzymatic kinetic resolution based synthesis of 1 and ent-1 utilises inexpensive, commercially available starting materials. It is based on enantiomeric resolution of rac-cyclopropane carboxylic esters using esterase from Streptomyces diastatochromogenes. Both enantiomers of 1 were prepared selectively in high overall yield over nine steps, st…

Tropane-derived11C-labelled and18F-labelled DAT ligands

Radiolabelling of cocaine-derived 3-phenyltropanes for dopamine transporter positron emission tomography with 18F and 11C is reviewed. Copyright © 2013 John Wiley & Sons, Ltd.

Efficient microwave-assisted direct radiosynthesis of [(18)F]PR04.MZ and [(18)F]LBT999: selective dopamine transporter ligands for quantitative molecular imaging by means of PET.

Abstract PR04.MZ 8-(4-fluoro-but-2-ynyl)-3- p -tolyl-8-aza-bicyclo[3.2.1]octane-2-carboxylic acid methyl ester ( 1 ) and LBT999 8-(( E )-4-fluoro-but-2-enyl)-3b- p -tolyl-8-aza-bicyclo[3.2.1]octane-2β-carboxylic acid methyl ester ( 2 ) are selective dopamine reuptake inhibitors, derived from cocaine. Compounds 1 and 2 were labelled with fluorine-18 at their terminally fluorinated N-substituents employing microwave enhanced direct nucleophilic fluorination. K[ 18 F]F − Kryptofix ® 222 cryptate, tetrabutyl ammonium [ 18 F]fluoride and caesium [ 18 F]fluoride were compared as fluoride sources under conventional and microwave enhanced conditions. Fluorination yields were remarkably increased un…

Two-step radiosynthesis of [18F]FE-β-CIT and [18F]PR04.MZ

The cocaine-derived dopamine reuptake inhibitors FE-β-CIT (8-(2-fluoroethyl)-3-(4-iodophenyl)-8-azabicyclo[3.2.1]octane-2-carboxylic acid methyl ester) (1) and PR04.MZ(8-(4-fluorobut-2-ynyl)-3-p-tolyl-8-azabicyclo[3.2.1]octane-2-carboxylic acid methyl ester) (2) were labelled with (18)F-fluorine using a two-step route. 2-[(18)F]Fluoroethyltosylate and 4-[(18)F]fluorobut-2-yne-1-yl tosylate were used as labelling reagents, respectively. Radiochemically pure (>98%) [(18)F]FE-β-CIT and [(18)F]PRD04.MZ (32-86 GBq/µmol) were obtained after a synthesis time of 100 min in about 25% non-decay-corrected overall yield.

No carrier-added nucleophilic aromatic radiofluorination using solid phase supported arenediazonium sulfonates and 1-(aryldiazenyl)piperazines

Abstract This Letter concerns the investigation of a solid phase based method for no carrier-added nucleophilic [ 18 F]fluorination of aromatic compounds via de-diazofluorination. Initial screening of reaction conditions was conducted using soluble analogues, that is, substituted benzenediazonium tosylates and 1-(phenyldiazenyl)piperazines in solution. This was followed by translation of the principle conditions to solid phase bound analogues. A variety of substituted aryldiazonium cations were immobilised using a sulfonate functionalised ion exchange resin and labelled with [ 18 F]fluoride ion by Balz–Schiemann like thermal decomposition in the presence of no carrier-added [ 18 F]fluoride …

Characterisation of [11C]PR04.MZ in Papio anubis baboon: A selective high-affinity radioligand for quantitative imaging of the dopamine transporter

N-(4-fluorobut-2-yn-1-yl)-2β-carbomethoxy-3β-(4′-tolyl)nortropane (PR04.MZ, 1) is a PET radioligand for the non-invasive exploration of the function of the cerebral dopamine transporter (DAT). A reliable automated process for routine production of the carbon-11 labelled analogue [11C]PR04.MZ ([11C]-1) has been developed using GMP compliant equipment. An adult female Papio anubis baboon was studied using a test–retest protocol with [11C]-1 in order to assess test–retest reliability, metabolism and CNS distribution profile of the tracer in non-human primates. Blood sampling was performed throughout the studies for determination of the free fraction in plasma (fP), plasma input functions and m…

The Renaissance of the 68Ge/68Ga Radionuclide Generator Initiates New Developments in 68Ga Radiopharmaceutical Chemistry

⁶⁸Ge/⁶⁸Ga radionuclide generators have been investigated for almost fifty years now, since the cyclotron-independent availability of positron emitting ⁶⁸Ga via the ⁶⁸Ge/⁶⁸Ga system had always attracted researches working in basic nuclear chemistry as well as radiopharmaceutical chemistry. However, it took decades and generations of research (and researchers) to finally approach a reliable level of ⁶⁸Ge/⁶⁸Ga generator designs, adequate to the modern requirements of radiometal labeling chemistry. ⁶⁸Ga radiopharmacy now is awaking from a sort of hibernation. The exciting perspective for the ⁶⁸Ge/⁶⁸Ga generator, now - more than ever, asks for systematic chemical, radiochemical, technological an…

Spectroscopic, radiochemical, and theoretical studies of the Ga3+-N-2-hydroxyethyl piperazine-N'-2-ethanesulfonic acid (HEPES buffer) system: evidence for the formation of Ga3+ - HEPES complexes in (68) Ga labeling reactions.

Recent reports have claimed a superior performance of HEPES buffer in comparison to alternative buffer systems for 67/68 Ga labeling in aqueous media. In this paper we report spectroscopic (1H and 71 Ga NMR), radiochemical, mass spectrometry and theoretical modeling studies on the Ga3+/HEPES system (HEPES = N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid) performed with the aim of elucidating a potential contribution of HEPES in the 68/67 Ga radiolabeling process. Our results demonstrate that HEPES acts as a weakly but competitive chelator of Ga3+ and that this interaction depends on the relative Ga3+: HEPES concentration. A by-product formed in the labeling mixture has been identified …

A methodical 68Ga-labelling study of DO2A-(butyl- l-tyrosine)2 with cation-exchanger post-processed 68Ga: practical aspects of radiolabelling

Positron emission tomography (PET) with 68Ga is a fast-growing field in molecular imaging, both in research and in clinical routine. The availability of 68Ga via the 68Ge/68Ga radionuclide generator facilitates the development and production of radiopharmaceuticals independent of a cyclotron. The presented work shows a complete 68Ga labelling study exemplified on [68Ga]DO2A-(butyl- l-tyrosine)2, a potential tumour tracer for PET. A methodical sequence is followed to optimize the 68Ga-labelling reaction. Practical aspects are described and the different parameters contributing to the labelling yield are demonstrated. The influence of temperature, time, amount of labelling precursor and pH va…

The DAT ligand [(18)F]PR17.MZ mirrors the in vivo pharmacokinetic profile of [(11)C]cocaine with significantly improved monoamine transporter selectivity.

Ex vivo and in vivo evaluation of [18F]PR04.MZ in rodents: a selective dopamine transporter imaging agent.

N-4-Fluorobut-2-yn-1-yl-2beta-carbomethoxy-3beta-phenyltropane (PR04.MZ) has been developed as dopamine transporter (DAT) ligand for molecular imaging. It contains a terminally fluorinated, conformationally constrained nitrogen substituent that is well suited for the introduction of fluorine-18. The present report describes the pharmacological characterisation of [18F]PR04.MZ. The ligand shows an IC50 value of 2 nM against human DAT, whereas the IC50 value against human serotonin transporter and human noradrenalin transporter are lower (110 nM and 22 nM, respectively). Furthermore, its ex vivo organ distribution, its binding profile in the rat brain and reversibility of binding were examine…

Synthesis and radiosynthesis of N5-[18F]fluoroethyl-Pirenzepine and its metabolite N5-[18F]fluoroethyl-LS 75

The well established M1 selective muscarinergic antagonist Pirenzepine 11-[2-(4-methyl-piperazin-1-yl)-acetyl]-5,11-dihydro-benzo[e]pyrido[3,2-b][1,4]diazepin-6-one (1) exhibits an unusual behaviour in vivo, which cannot be explained with M1 antagonism exclusively. One of the aspects discussed is a specific interaction with poly ADP-ribose polymerase (PARP-1). 1 undergoes metabolism to form LS 75 5,11-dihydro-benzo[e]pyrido[3,2-b][1,4]diazepin-6-one (2). In order to study deviations in Pirenzepine efficacy from pure M1 binding in vivo using PET, appropriate positron emitter labelled analogues of 1 and 2 were synthesised. Non-radioactive reference compounds 3 and 4 were tested for PARP-1 inh…

Comparison of different phosphorus-containing ligands complexing 68Ga for PET-imaging of bone metabolism

Abstract 99mTc-phosphonate structures are well established tracers for bone tumour imaging. Our objective was to investigate different 68Ga-labelled phosphonate ligands concerning labelling kinetics, binding to hydroxyapatite and bone imaging using μ-PET. Seven macrocyclic phosphorus-containing ligands and EDTMP were labelled in nanomolar scale with n.c.a. 68Ga in Na-HEPES buffer at pH∼4. Except for DOTP, all ligands were labelled with >92% yield. Binding of the 68Ga-ligand complexes on hydroxyapatite was analysed to evaluate the effect of the number of the phosphorus acid groups on adsorption parameters. Adsorption of 68Ga-EDTMP and 68Ga-DOTP was >83%. For the 68Ga-NOTA-phosphonates …

SYNTHESIS AND IN VITRO AFFINITIES OF VARIOUS MDL 100907 DERIVATIVES AS POTENTIAL 18F-RADIOLIGANDS FOR 5-HT2A RECEPTOR IMAGING WITH PET

Radiolabelled piperidine derivatives such as [(11)C]MDL 100907 and [(18)F]altanserin have played an important role in diagnosing malfunction in the serotonergic neurotransmission. A variety of novel piperidine MDL 100907 derivatives, possible to label with (18)F-fluorine, were synthesized to improve molecular imaging properties of [(11)C]MDL 100907. Their in vitro affinities to a broad spectrum of neuroreceptors and their lipophilicities were determined and compared to the clinically used reference compounds MDL 100907 and altanserin. The novel compounds MA-1 (53) and (R)-MH.MZ (56) show K(i)-values in the nanomolar range towards the 5-HT(2A) receptor and insignificant binding to other 5-HT…

Automated GMP production of [11C]PR04.MZ via the captive solvent method and PET studies in non-human primates: A promising tracer for extrastriatal DAT imaging

Synthesis and monoamine uptake inhibition of conformationally constrained 2β-carbomethoxy-3β-phenyl tropanes

A series of 2beta-carbomethoxy-3beta-phenyl tropanes with conformationally constrained nitrogen substituents were synthesized as potential selective dopamine transporter ligands. These novel compounds were examined for their monoamine uptake inhibition potency at the human dopamine transporter (hDAT), the human serotonin transporter (hSERT) and the human noradrenalin transporter (hNET), stably expressed in human embryonic kidney cells (HEK). A SAR-study was conducted to determine the contribution of extended, 4-fluorinated, conformationally constrained C4 chains at the tropane nitrogen to human monoamine transporter affinity and selectivity.

NODAPA-OH and NODAPA-(NCS)n: Synthesis, 68Ga-radiolabelling and in vitro characterisation of novel versatile bifunctional chelators for molecular imaging

This report concerns synthesis, (68)Ga-radiolabelling and stability data of 1,4,7-triazacyclononane-1,4-diacetic acid-7-p-isothio-cyanatophenyl-acetic acid (NODAPA-NCS), 1,4,7-triazacyclononane-1-acetic acid-4,7-di-p-isothiocyanatophenyl-acetic acid (NODAPA-(NCS)(2)) and 1,4,7-triazacyclononane-1,4-diacetic acid-7-p-hydroxyphenyl-acetic acid (NODAPA-OH), versatile bifunctional chelators with potential for molecular imaging. Protein binding and exemplified conjugation are also reported.