In vitro activity: BRL-15572 displays high affinity and selectivity for h5-HT1D receptors. BRL-15572 has 60-fold higher affinity for h5-HT1D than 5-HT1B receptors. BRL-15572 binds to h5-HT1B and h5-HT1D receptors with pKB of less than 6 and 7.1, respectively. BRL-15572 stimulates [35S]GTP γ S binding in both cell lines, with potencies that correlated with their receptor binding affinities in both h5-HT1B and h5-HT1D receptor expressing cell lines. BRL-15572 reveals receptor binding affinities for 5-HT1A, 5-HT1B, 5-HT1E, 5-HT1F, 5-HT2A, 5-HT2B, 5-HT2C, 5-HT6 and 5-HT7 with pKi of 7.7, 6.1, 5.2, 6.0, 6.6, 7.4, 6.2, 5.9 and 6.3, respectively. In the h5-HT1D cell line, both BRL-15572 (1 µM) shifts the 5-HT concentration response curve with pKB of 7.1, respectively. BRL-15572 does have moderately high affinity at human 5-HT1A and 5-HT2B receptors. In human atrial appendages, the electrically evoked tritium overflow is inhibited by 5-HT in a manner susceptible to antagonism by BRL-15572 (300 nM; 23 times Ki at h5-HT1D receptors). The inhibitory effect of 5-HT on the K+-evoked overflow of glutamate is antagonized by the h5-HT1D receptor ligand BRL-15572. BRL-15572 (1 μM) is unable to modify the effect of 5-HT at the autoreceptor regulating [3H]5-HT release. The selective 5-HT1D/1B receptor antagonist BRL 15572 inhibits the effect of the agonist L-694 247.

Cell Assay: [35S]GTPγS binding studies. [35S]GTPγS binding studies in CHO cells expressing the h5-HT1B or h5-HT1D receptors are performed. In brief, membranes from 1 × 106 cells are preincubated at 30°C for 30 minutes, in HEPES buffer (HEPES [20 mM], MgCl2 [3 mM], NaCl [100 mM], ascorbate [0.2 mM]), containing GDP (10 µ M), with or without BRL-15572. The reaction is started by the addition of 10 µL of [35S]GTPγS (100 pM, assay concentration) followed by a further 30 minutes incubation at 30°C. Non-specific binding is determined by addition of unlabelled GTPγS (10 µM), prior to the addition of cells. The reaction is stopped by rapid filtration using Whatman GF/B grade filters followed by five washes with ice-cold HEPES buffer. Radioactivity is determined by liquid scintillation spectrometry.