[18F]DPA-C5yne, a novel fluorine-18-labelled analogue of DPA-714: radiosynthesis and preliminary evaluation as a radiotracer for imaging neuroinflammation with PET.

DPA-C5yne, the lead compound of a novel series of DPA-714 derivatives in which the fluoroethoxy chain linked to the phenylpyrazolopyrimidine scaffold has been replaced by a fluoroalkyn-1-yl moiety, is a high affinity (Ki : 0.35 nM) and selective ligand targeting the translocator protein 18 kDa. In the present work, DPA-C5yne was labelled with no-carrier-added [(18)F]fluoride based on a one-step tosyloxy-for-fluorine nucleophilic substitution reaction, purified by cartridge and HPLC, and formulated as an i.v. injectable solution using a TRACERLab FX N Pro synthesizer. Typically, 4.3-5.2 GBq of [(18)F]DPA-C5yne, ready-to-use, chemically and radiochemically pure (> 95%), was obtained with specific radioactivities ranging from 55 to 110 GBq/µmol within 50-60 min, starting from a 30 GBq [(18)F]fluoride batch (14-17%). LogP and LogD of [(18)F]DPA-C5yne were measured using the shake-flask method and values of 2.39 and 2.51 were found, respectively. Autoradiography studies performed on slices of ((R,S)-α-amino-3-hydroxy-5-methyl-4-isoxazolopropionique (AMPA)-lesioned rat brains showed a high target-to-background ratio (1.9 ± 0.3). Selectivity and specificity of the binding for the translocator protein was demonstrated using DPA-C5yne (unlabelled), PK11195 and Flumazenil (central benzodiazepine receptor ligand) as competitors. Furthermore, DPA-C5yne proved to be stable in plasma at 37°C for at least 90 min.

Médran-Navarrete V ，Bernards N ，Kuhnast B ，Damont A ，Pottier G ，Peyronneau MA ，Kassiou M ，Marguet F ，Puech F ，Boisgard R ，Dollé F ... -  《-》

Preparation and evaluation of novel pyrazolo[1,5-a]pyrimidine acetamides, closely related to DPA-714, as potent ligands for imaging the TSPO 18kDa with PET.

A series of four novel analogues of DPA-714, bearing a fluoroalkynyl side chain (with a length ranging from three to six carbon atoms) in replacement of the fluoroethoxy motif, have been synthetized in six steps from commercially available methyl 4-iodobenzoate. The synthetic strategy for the preparation of these N,N-diethyl-2-(2-(4-(ω-fluoroalk-1-ynyl)phenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl)acetamides (7a-d) consisted in derivatizing a key iodinated building block featuring the pyrazolopyrimidine acetamide backbone of DPA-714, by Sonogashira couplings with various alkynyl reagents. The resulting alkynols were subsequently fluorinated, yielding the expected target derivatives. All four analogues exhibited slightly higher affinity and selectivity towards the TSPO 18kDa (Ki vs [(3)H]PK11195: 0.35-0.79nM; Ki vs [(3)H]flunitrazepam: >1000nM) when compared to DPA-714 (Ki vs [(3)H]PK11195: 0.91nM; Ki vs [(3)H]flunitrazepam: >1000nM). Lipophilicities (HPLC, logD7.4) increased with the chain length (from 3.6 to 4.3) and were significantly higher than the one determined for DPA-714 (2.9). Preliminary in vitro metabolism evaluation using rat microsomal incubations and LC-MS analyses showed, for all four novel analogues, the absence of defluorinated metabolites. Among them, the fluoropentynyl compound, DPA-C5yne (7c), was selected, labelled in one single step with fluorine-18 from the corresponding tosylate and in vivo evaluated with PET on our in-house-developed rat model of acute local neuroinflammation.

Médran-Navarrete V ，Damont A ，Peyronneau MA ，Kuhnast B ，Bernards N ，Pottier G ，Marguet F ，Puech F ，Boisgard R ，Dollé F ... -  《-》

Comparative evaluation of the translocator protein radioligands 11C-DPA-713, 18F-DPA-714, and 11C-PK11195 in a rat model of acute neuroinflammation.

Chauveau F ，Van Camp N ，Dollé F ，Kuhnast B ，Hinnen F ，Damont A ，Boutin H ，James M ，Kassiou M ，Tavitian B ... -  《JOURNAL OF NUCLEAR MEDICINE》

Synthesis and in vitro characterization of novel fluorinated derivatives of the translocator protein 18 kDa ligand CfO-DPA-714.

The translocator protein 18 kDa (TSPO) is today a validated target for a number of therapeutic applications, but also a well-recognized diagnostic/imaging biomarker for the evaluation of inflammatory related-disease state and progression, prompting the development of specific and dedicated TSPO ligands worldwide. For this purpose, pyrazolo[1,5-a]pyrimidine acetamides constitute a unique class of high affinity and selectivity TSPO ligands; it includes DPA-714, a fluorine-containing derivative that has also been labelled with the positron-emitter fluorine-18, and is nowadays widely used as a Positron Emission Tomography imaging probe. Recently, to prevent defluorination issues encountered in vivo with this tracer, a first series of analogues was reported where the oxygen atom bridging the phenyl ring of the core structure and the fluorinated moiety was replaced with a more robust linkage. Among this new series, CfO-DPA-714 was discovered as a highly promising TSPO ligand. Herein, a novel series of fluorinated analogues of the latter molecule were synthesized and in vitro characterized, where the pharmacomodulation at the amide position of the molecule was explored. Thirteen compounds were thus prepared from a common key-ester intermediate (synthesized in 7 steps from 4-iodobenzoate - 11% overall yield) and a set of commercially available amines and obtained with moderate to good yields (23-81%) and high purities (>95%). With one exception, all derivatives displayed nanomolar to subnanomolar affinity for the TSPO and also high selectivity versus the CBR (Ki (CBR)/Ki (TSPO) > 103). Within this series, three compounds showed better Ki values (0.25, 0.26 and 0.30 nM) than that of DPA-714 (0.91 nM) and CfO-DPA-714 (0.37 nM), and favorable lipophilicity for brain penetration (3.6 < logD7.4 < 4.4). Among these three compounds, the N-methyl-N-propyl amide analogue (9) exhibited similar metabolic stability when compared to CfO-DPA-714 in mouse, rat and human microsomes. Therefore, the latter compound stands out as a promising candidate for drug development or for use as a PET probe, once fluorine-18-labelled, for in vivo neuroinflammation imaging.

Cacheux F ，Médran-Navarrete V ，Dollé F ，Marguet F ，Puech F ，Damont A ... -  《-》

DPA-714, a new translocator protein-specific ligand: synthesis, radiofluorination, and pharmacologic characterization.

James ML ，Fulton RR ，Vercoullie J ，Henderson DJ ，Garreau L ，Chalon S ，Dolle F ，Costa B ，Guilloteau D ，Kassiou M ... -  《-》