F 11356, a novel 5-hydroxytryptamine (5-HT) derivative with potent, selective, and unique high intrinsic activity at 5-HT(1B/1D) receptors in models relevant to migraine

F 11356 (4-[4-[2-(2-aminoethyl)-1H-indol-5-yloxyl]acetyl]piperazinyl-1- yl]benzonitrile) was designed to take advantage of the superior potency and efficacy characteristics of 5-hydroxytryptamine (5-HT) compared with tryptamine at 5-HT(1B/1D) receptors. F 11356 has subnanomolar affinity for cloned human and nonhuman 5-HT(1B) and 5-HT(1D) receptors, and its affinity for 5-HT(1A) and other 5-HT receptors, including the 5-ht(1F) subtype, is 50- fold lower and micromolar, respectively. In C6 cells expressing human 5- HT(1B) or human 5-HT(1D) receptors, F 11356 was the most potent compound in inhibiting forskolin-induced cyclic AMP formation (pD₂ = 8.9 and 9.6), and in contrast to tryptamine and derivatives, it produced maximal enhancement of [³⁵S]guanosine-5'-O-(3-thio)triphosphate-specific binding equivalent to 5- HT. F 11356 was equipotent to 5-HT (pD₂ = 7.1 versus 7.2) and more potent than tryptamine derivatives in contracting rabbit isolated saphenous vein. In isolated guinea pig trigeminal ganglion neurons, F 11356 was more potent (pD₂ = 7.3 versus 6.7) and induced greater increases in outward hyperpolarizing Ca²⁺-dependent K⁺ current than sumatriptan. In anesthetized pigs, F 11356 elicited highly cranioselective, more potent (from 0.16 μg/kg i.v.) and greater carotid vasoconstriction than tryptamine derivatives. Decreases in carotid blood flow were observed in conscious dogs from 0.63 mg/kg oral F 11356 in the absence of changes in heart rate or behavior. Oral activity was confirmed when hypothermic responses were elicited in guinea pigs (ED₅₀ = 1.6 mg/kg), suggesting that F 11356 also accesses the brain. F 11356 thus is a selective, high-potency agonist at 5- HT(1B/1D) receptors, which distinguishes itself from tryptamine and derivatives in exerting high intrinsic activity at these receptors in vascular and neuronal models relevant to migraine.