| pA2 online © Copyright 2004 The British Pharmacological Society |
086P
University of Newcastle Winter Meeting December 2004 |
The structure-affinity relationship of BU98008 and its derivatives for imidazoline2 binding sites
Abu Ghazaleh, H, Lalies, MD, Tyacke, RJ, *Husbands, SM, *Rees, C, *Hudson, N, *Kwan, J, *Purchase, L, Nutt DJ & Hudson, AL. Psychopharmacology Unit, University of Bristol, Bristol, BS1 3NY. *Department of Pharmacy and Pharmacology, University of Bath, Bath, BA2 7AY. |
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Print abstractImidazoline binding sites (IBS) are divided into three main classes based on function and selective ligands: I1BS, modulation of blood pressure; I2BS regulation of monoamine turnover; I3BS regulation of insulin secretion (see Eglen et al., 1998). We have previously reported to the Society (Abu Ghazaleh et al., 2004) that a series of newly synthesised compounds related to the recently characterised I1BS ligand, BU98008 (1-[4,5-dihydro-1H-imidazol-2-yl]isoquinoline) (Robinson et al., 2003), exhibited high affinity at I1BS. To verify their selectivity for I1BS the aim of the present study was to assess the affinities of these novel isoquinoline compounds: BU04003 (1-[1-benzyl-4,5-dihydro-1H-imidazol-2-yl]isoquinoline), BU04004 (1-[1H-imidazol-2-yl]isoquinoline), BU04005 (1-isoquinolin-1-ylmethanamine) and BU04006 (1-[5-methyl-4,5-dihydro-1H-imidazol-2-yl]isoquinoline) for I2BS.
Brains were obtained from male Wistar rats (250-275g) and membranes prepared according to the methods of Lione et al. (1998). In competition binding studies the displacing ligands were assessed over a concentration range: 1nM – 100µM. Brain membrane homogenates were incubated with [3H]2-BFI (1nM) at room temperature for 30 minutes. Non-specific binding was defined using 10µM BU224. Incubations were terminated by rapid filtration and radioactivity was determined by liquid scintillation counting. Data were analysed by iterative non-linear regression using GraphPad Prism version 3.03 for Windows.
Compound |
Ki1 (µM) ± s.e.mean (n) |
Ki2 (µM)± s.e.mean (n) |
BU04003 |
0.397 ± 0.243 (3) |
104.4 ± 84.5 (3) |
BU04004 |
0.097 ± 0.044 (3) |
54.6 ± 27.1 (3) |
BU04005 |
0.016 ± 0.003 (3) |
5.48 ± 2.38 (3) |
BU04006 |
0.070 ± 0.013 (3) |
191.6 ± 101.8 (3) |
BU98008 |
0.00728 ± 0.00134 (6) |
5.20 ± 1.52 (6) |
Table 1. The binding affinities of BU98008 and its derivatives at I2BS.
The biphasic pattern of binding displayed by these compounds illustrates the presence of high and low affinity binding components. Unexpectedly, the reported I1BS ligand and parent compound BU98008 demonstrated very high nM affinity for I2BS (Table 1) and this contradicts a previous report (Robinson et al., 2003). BU04005 also exhibited high binding affinity for I2BS in comparison to the other tested compounds. Overall these compounds demonstrated a higher binding affinity for I2BS than for I1BS (Abu Ghazaleh et al., 2004). In conclusion, these unpredicted results should help us to synthesise a further series of compounds with the goal of obtaining I1BS ligands.
Abu Ghazaleh, H. et al., (2004) http://www.pa2online.org/Vol2Issue2abst063P.html
Eglen, R. et al., (1998) Trends. Pharmacol. Sci., 19, 381-390.
Lione, L. et al. (1998) Eur.J.Pharmacol. 353, 123-135.
Robinson, E.S.J. et al. (2003) Ann.N.Y.Acad. Sci., 1009, 283-287.