Piperazine analog of vesamicol: in vitro and in vivo characterization for vesicular acetylcholine transporter.
The probes to detect vesicular acetylcholine transporter (VAChT) in vivo are important to evaluate the mapping and function in cholinergic system. To develop high-specific and high-affinity radiotracer for single photon emission computed tomography, we investigated piperazine analogs which replaced the piperidine ring of (-)-vesamicol with a piperazine ring. We found that the piperazine analog of iodobenzovesamicol, trans-5-iodo-2-hydroxy-3-[4-phenylpiperazinyl] tetralin (DRC140), had high affinity for VAChT in rat brain. We carried out binding assay in subcellular fraction of the rat brain. The highest B(max) for [(125)I]-DRC140 binding was observed in the synaptic vesicle fraction (1,751 fmol/mg protein), followed by the crude vesicle (821 fmol/mg protein) and the P2 fraction (187 fmol/mg protein). These K(d) values were similar to the affinity of highly purified synaptic vesicular fraction (K(d) = 0.3 nM) with a one-site model. The possibility that [(125)I]-DRC140 recognizes sigma receptor was excluded by our finding large inhibition constants (K(i) = 849 nM for haloperidol, K(i) = 3,052 nM for 1,3-di(2-tolyl)guanidine). In vivo distribution studies with the [(123)I]-DRC140 in rats showed a rapid brain uptake. The highest brain area was in striatum, followed by frontal cortex, occipital cortex, and hippocampus. The lowest brain area was cerebellum. The radioactivity of high-accumulated areas in ex vivo autoradiography was reduced by a preinjection of (-)-vesamicol and these levels were reduced to the radioactivity in cerebellum. These results show that [(125)I]-DRC140 can provide extremely high specific tracer with excellent brain permeability as a ligand for single photon emission computed tomography.
Bando
K
K
Research Center, Daiichi Radioisotope Laboratories, Ltd., Chiba, Japan.
Naganuma
T
T
Taguchi
K
K
Ginoza
Y
Y
Tanaka
Y
Y
Koike
K
K
Takatoku
K
K
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D002352:Carrier Proteins / Q000187:drug effects* / Q000378:metabolism*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D008297:Male; D026901:Membrane Transport Proteins; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010879:Piperazines / Q000494:pharmacology*; D010880:Piperidines / Q000494:pharmacology*; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D013347:Subcellular Fractions / Q000378:metabolism; D013572:Synaptic Vesicles / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D015899:Tomography, Emission-Computed, Single-Photon; D050494:Vesicular Acetylcholine Transport Proteins; D033921:Vesicular Transport Proteins
D002352:Carrier Proteins; D007457:Iodine Radioisotopes; D026901:Membrane Transport Proteins; D009467:Neuromuscular Depolarizing Agents; D010879:Piperazines; D010880:Piperidines; C493461:Slc18a3 protein, rat; D050494:Vesicular Acetylcholine Transport Proteins; D033921:Vesicular Transport Proteins; C006189:vesamicol; D000109:Acetylcholine