049P University of Oxford
BPS 75th Anniversary Meeting December 2006

 

Comparative binding kinetics of [3H]DASB at human, baboon and rat 5-HT transporters

F. Andreetta1, L. Kay2, M. Negri1, R. Benedetti1, M. Antolini1, S. Faedo1, M. Corsi1 & P.B. Wren1 . 1GlaxoSmithKline, Psychiatry Centre of Excellence for Drug Discovery, Verona, Italy. 2MRC Centre for Developmental Neurobiology, King's College London, UK.

 

PET imaging studies of the serotonin (5-HT) transporter (SERT) in primates and man using [11C]DASB ( [11C]-3-amino-4-(2-dimethylaminomethylphenylsulfanyl)-benzonitrile) have revealed that an occupancy >80% is needed for therapeutic efficacy in psychiatric diseases ( Meyer et al., 2004 ). In this study, the binding kinetics of [3H] DASB on rat, human and baboon SERT was characterized with the aim to understand if potential differences across preclinical and clinical species may exist.

 

 

Classical methods

Adapted method

 

K+1 (M-1min-1)

K-1 (min-1)

K+1 (M-1min-1)

K-1 (min-1)

pKi

Rat*

2.74

±0.34x108

0.05547

±0.0049

2.60

±0.24x108

0.04796

±0.0051

9.83

±0.06

Human

4.80

±0.21x108

0.0683

±0.001

4.51

±0.10x108

0.0743

±0.004

9.45

±0.05

Baboon

4.82

±0.21x108

0.0745

±0.001

5.08

±0.43x108

0.0795

±0.004

9.52

±0.04

 

Data shown are means (± standard error of the means) of at least three independent experiments. pKi ( –LogKi) obtained bydisplacement experiments. *p<0.05 in one way ANOVA versus human and baboon data using Bonferroni’s Multiple Comparison Test.

The pharmacology of DASB binding in rat was statistically different to that at both human and baboon SERT in terms of all the parameters measured; affinity and binding kinetics. These parameters were identical for human and baboon SERT. DASB displayed a higher affinity from competition binding studies at rat SERT than at primate SERTs. DASB also displayed a slower dissociation and association kinetic profile at rat SERT, in agreement with published value for [11C]DASB ( Lundquist et al., 2005 ), compared with primate SERTs using either classical or previously described methods (Motulsky & Mahan, 1984). The Motulsky & Mahan method employed may therefore be an appropriate tool to measure the kinetics of unlabeled compounds at SERT.

In conclusion, this report revealed differences of kinetic binding profile of DASB at rat native SERT with respect to recombinant human and baboon SERT. These results agree well with the finding of difference in [3H]citalopram binding kinetics between rat and human native SERT (Erreboe et al., 1995), supporting the existence of structural variation of the transporter across species. However an understanding of the binding kinetics of DASB in native human and baboon tissues is required.

 

Meyer et al., (2004). Am. J. Psychiatry. 161: 826-833
Motulsky & Mahan (1984). Mol. Pharm. 25: 1-9
Lundquist et al., (2005). Nucl. Med. Biol. 32, 129-136.
Erreboe et al., (1995). Pharmacol. Toxicol.76: 376-379