PharmacologyandFunctionofTachykininReceptors Alessandro Lecci Clinical Research Department, Menarini Ricerche, via Sette Santi 1, Firenze 50131, Italy. Following his degree in biology in 1986, Alessandro Lecci has worked closely with the pioneer of tachykinin receptor pharmacology, Dr Carlo Alberto Maggi, at Menarini Ricerche in Florence. The majority of Dr Lecci’s work has focused on the pharmacology of tachykinin receptors at the visceral level. Historical perspective Tachykinins are a family of structurally-related peptides of which substance P (SP) is the most famous component. All mammalian tachykinins known up to now share a common C-terminal amino acid sequence (Table 1), i.e. Phe-Xaa-Gly-Leu- MetNH 2, that is the minimal structural motif for the activation of tachykinin receptors. The existence of SP was described in the 1930s by Von Euler and Gaddum1 in mammals, and tachykinin peptides were identified and sequenced by Erspamer in non-vertebrated (eledoisin) and then in nonmammalian species (physalaemin). 2,3 In the 1960s Lembeck continued Von Euler and Gaddum’s studies, describing the effects of SP and other tachykinins in the central nervous system (CNS) and peripheral preparations of mammals. 4 The CNS physiology of SP was further developed by Konishi and Otsuka in the 1970s, 5 whereas Hokfelt gave a major contribution6 in defining the neuroanatomical localisation of this peptide. Meanwhile, Chang and Leeman had defined the amino acid sequence of SP, 7 which was then followed in the 1980s by the discovery of two other mammalian tachykinins, namely neurokinin A (NKA), also known as substance K, and neurokinin B (NKB), also known as neuromedin K, by Matsuo, 8 Munekata9 and co-workers (Table 1). In the 1980s, following an intense pharmacological investigation by means of mammalian and nonmammalian tachykinins, selective agonists and prototype antagonists, the existence of 3 tachykinin receptors termed NK 1, NK 2, and NK3 was proposed by Regoli. 10 In the same period, 2 genes for tachykinins, namely preprotachykinin-A, encoding both SP and NKA, 11 and preprotachykinin-B, which encodes NKB, 12 were identified by Nakanishi and coworkers (Table 2). Two elongated forms of NKA originating from alternative splicings of preprotachykinin-A mRNA, defined as neuropeptidegamma and kappa (Table 1) were then discovered in mammals. 13,14 In between the late 1980s and the begin of the 1990s, the hypothesis of the existence of 3 tachykinin receptors, belonging to the family of G- protein coupled receptors (GPCRs), was demonstrated by the cloning of NK 1, NK 2, and NK3 receptors in various mammal species by Nakanishi’s and other independent groups. 15,16,17 In the course of the 1990s, the synthesis of potent and selective peptide and non-peptide tachykinin receptor antagonists has allowed a substantial improvement in the knowledge about the role that tachykinin receptors play in physiological and pathological conditions (Table 3). This information was implemented at the end of 1990s through the construction of mutant mice lacking the preprotachykinin-A gene18 or tachykinin NK1 receptor. 19 Two major recent achievements in the field include the discovery of a new tachykinin, hemokinin- 1 (HK-1) (Table 1, Figure 1), coded by a new tachykinin gene termed preprotachykinin-C in the mouse20 or TAC4 in humans (Table 2), and the registration of aprepitant, a selective NK1 receptor antagonist, for the treatment of emesis and nausea associated with the use of chemotherapy. Notwithstanding the fact that tachykinins are among the most investigated peptides, basic and applied research in this field is still an exciting challenge because tachykinins regulate a very large number of functions, both at the CNS and peripheral level. Tachykinin NK1 receptor agonists Until the mid-1990s, the order of potency of mammalian tachykinins in the stimulation of human NK receptors was believed to be SP>NKA=NKB. 21 1 Table 1. Amino acid sequences of mammalian tachykinins Substance P (SP) Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-MetNH2 Mouse Hemokinin-1 (mHK-1) Arg-Ser-Arg-Thr-Arg-Gln-Phe-Tyr-Gly-Leu-MetNH2 Human Hemokinin-1 (hHK-1) Thr-Gly-Lys-Ala-Ser-Gln-Phe-Phe-Gly-Leu-MetNH2 Neurokinin A (NKA) His-Lys-Thr-Asp-Ser-Val-Phe-Gly-Leu-MetNH2 Neurokinin B (NKB) Asp-Met-His-Asp-Phe-Phe-Val-Gly-Leu-MetNH2 Neuropeptide gamma (NP-gamma) Asp-Ala-Gly-His-Gly-Gln-Ile-Ser-His-Lys-Arg-Lys-Asp-Ser-Val-Phe-Gly-Leu-MetNH2 Neuropeptide kappa (NP-kappa) Asp-Ala-Asp-Ser-Ser-Ile-Glu-Lys-Gln-Val-Ala-Leu-Leu-Lys-Ala-Leu-Tyr-Gly-His-Gly-Gln- Ile-Ser-His-Lys-Arg-His-Gly-Gln-Ile-Ser-His-Lys-Arg-Lys-Asp-Ser-Val-Phe-Gly-Leu-MetNH (Bold text denotes compounds available from Tocris) 2 Tocris Cookson Ltd., UK Tel: + 44 (0)117 916 3333 Fax: + 44 (0)117 916 3344 customerservice@tocris.co.uk technicalsupport@tocris.co.uk www.tocris.com Tocris Cookson Inc., USA Tel: (800) 421-3701 Fax: (800) 483-1993 customerservice@tocrisusa.com technicalsupport@tocrisusa.com
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