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NEUROPHARMACOLOGY

Studies of the Biogenic Amine Transporters. 12. Identification of Novel Partial Inhibitors of Amphetamine-Induced Dopamine Release

Clinical Psychopharmacology Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland (J.J.P., J.S.P., C.M.D., R.B.R.); and Department of Organic Chemistry, Southern Research Institute, Birmingham, Alabama (S.A.)

Previous studies identified partial inhibitors and allosteric modulators of 5-hydroxytryptamine ([5-amino-3-(3,4-dichlorophenyl)-1,2-dihydropyrido[3,4-b]pyrazin-7-yl]carbamic acid ethyl ester [SoRI-6238], 4-(2-[bis(4-fluorophenyl)methoxy]ethyl)-1-(2-trifluoromethyl-benzyl)-piperidine [TB-1-099]) and dopamine transporters N-(diphenylmethyl)-2-phenyl-4-quinazolinamine, [SoRI-9804]). We report here the identification of three novel allosteric modulators of the dopamine transporter [N-(2,2-diphenylethyl)-2-phenyl-4-quinazolinamine [SoRI-20040], N-(3,3-diphenylpropyl)-2-phenyl-4-quinazolinamine [SoRI-20041], and [4-amino-6-[(diphenylmethyl)amino]-5-nitro-2-pyridinyl]carbamic acid ethyl ester [SoRI-2827]]. Membranes were prepared from human embryonic kidney cells expressing the cloned human dopamine transporter (hDAT). [¹²⁵I]3β-(4'-Iodophenyl)tropan-2β-carboxylic acid methyl ester ([¹²⁵I]RTI-55) binding and other assays followed published procedures. SoRI-20040, SoRI-20041, and SoRI-2827 partially inhibited [¹²⁵I]RTI-55 binding, with EC₅₀ values ranging from 1.4 to 3 µM and E_max values decreasing as the [¹²⁵I]RTI-55 concentrations increased. All three compounds decreased the [¹²⁵I]RTI-55 B_max value and increased the apparent K_d value in a manner well described by a sigmoid dose-response curve. In dissociation rate experiments, SoRI-20040 (10 µM) and SoRI-20041 (10 µM), but not SoRI-2827 (10 µM), slowed the dissociation of [¹²⁵I]RTI-55 from hDAT by 30%. Using rat brain synaptosomes, all three agents partially inhibited [³H]dopamine uptake, with EC₅₀ values ranging from 1.8 to 3.1 µM and decreased the V_max value in a dose-dependent manner. SoRI-9804 and SoRI-20040 partially inhibited amphetamine-induced dopamine transporter-mediated release of [³H]1-methyl-4-phenylpyridinium ion from rat caudate synaptosomes in a dose-dependent manner. Viewed collectively, we report several compounds that allosterically modulate hDAT binding and function, and we identify novel partial inhibitors of amphetamine-induced dopamine release.

Address correspondence to: Dr. Richard B. Rothman, National Institute on Drug Abuse, National Institutes of Health, Clinical Psychopharmacology Section, Suite 4500, Triad Bldg., 333 Cassell Dr., Baltimore, MD 21224. E-mail: rrothman{at}mail.nih.gov