Synthesis, labeling, and biological evaluation of halogenated 2-quinolinecarboxamides as potential radioligands for the visualization of peripheral benzodiazepine receptors.
The previous exploration of the structure-affinity relationships concerning 4-phenyl-2-quinolinecarboxamide peripheral benzodiazepine receptor (PBR) ligands 6 showed as an interesting result the importance of the presence of a chlorine atom in the methylene carbon at position 3 of the quinoline nucleus. The subnanomolar PBR affinity shown by N-benzyl-3-chloromethyl-N-methyl-4-phenyl-2-quinolinecarboxamide (6b) suggested its chlorine atom to be replaced with other halogens in order to optimize the interaction of the quinolinecarboxamide derivatives with PBR and to develop suitable candidates for positron emission tomography (PET) or single photon emission computed tomography (SPECT) studies. The binding studies led to the discovery of fluoromethyl derivative 6a, which showed an IC50 value of 0.11 nM and is, therefore, one of the most potent PBR ligands so far described. Fluoromethyl derivative 6a has been labeled with 11C (t1/2=20.4 min, beta+=99.8%) starting from the corresponding des-methyl precursor (14) using [11C]CH3I in the presence of tetrabutylammonium hydroxide in DMF with a 35-40% radiochemical yield (corrected for decay) and 1.5 Ci/micromol of specific radioactivity. Ex vivo rat biodistribution and inhibition (following intravenous pre-administration of PK11195) studies showed that [11C]6a rapidly and specifically accumulated in PBR-rich tissues such as heart, lung, kidney, spleen, and adrenal, and at a lower level in other peripheral organs and in the brain. The images obtained in mouse with small animal YAP-(S)PET essentially confirmed the result of the ex vivo biodistribution experiments. The biological data suggest that [11C]6a is a promising radioligand for peripheral benzodiazepine receptor PET imaging in vivo.
Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università degli Studi di Siena, Via A. Moro, 53100 Siena, Italy. cappelli@unisi.it
Andrea
A
Cappelli
Mario
M
Matarrese
Rosa Maria
RM
Moresco
Salvatore
S
Valenti
Maurizio
M
Anzini
Salvatore
S
Vomero
Elia Anna
EA
Turolla
Sara
S
Belloli
Pasquale
P
Simonelli
Maria Azzurra
MA
Filannino
Michela
M
Lecchi
Ferruccio
F
Fazio
D000577:Amides / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites; D002250:Carbon Radioisotopes; D066298:In Vitro Techniques; D007553:Isotope Labeling / Q000379:methods; D007700:Kinetics; D008024:Ligands; D008297:Male; D015394:Molecular Structure; D049268:Positron-Emission Tomography / Q000379:methods; D011804:Quinolines / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000378:metabolism; D012680:Sensitivity and Specificity; D013329:Structure-Activity Relationship; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods
D000577:Amides; D002250:Carbon Radioisotopes; D008024:Ligands; D011804:Quinolines; D011963:Receptors, GABA-A