Further evidence for the existence of NK2 tachykinin receptor subtypes

Tachykinin NK2 antagonist for treatments of various disease states

Tachykinin NK₂ receptors are distributed in periphery, in the smooth muscle of the respiratory, gastrointestinal, genitourinary tract, and within the brain. Substance P (SP), neurokinin A (NKA), and neurokinin B (NKB) are endogenous ligands for NK₂ receptors and are active in the peripheral and central nervous systems. NK₂ antagonists have the potential to reduce airway motor responses and prevent hyperactivity by inhibiting NKA-induced bronchoconstriction in asthmatic patients. Due to its abundance, peripherally and centrally, tachykinin NK₂ receptor antagonists have high potential in treating various disease states ranging from asthma to irritable bowel syndrome, to detrusor hyperactivity, to anxiety. This review is an evaluation of NK₂ receptor antagonists as possible therapeutics for a myriad of pharmacological treatments.

Structure-activity relationship of neuropeptide γ derived from mammalian and fish

This study of relationship between structure and biologic activity was performed using five neuropeptide gammas [NPgamma; mammalian-NPgamma (M-NPgamma), trout-NPgamma (T-NPgamma), goldfish-NPgamma (G-NPgamma), bowfin-NPgamma (B-NPgamma), and shark-NPgamma (S-NPgamma)]. Circular dichroism (CD) spectra showed that all peptides took random structure in buffer solution. In neutral and acidic liposomes, M-NPgamma, T-NPgamma, B-NPgamma, and S-NPgamma still adopted random structure, while G-NPgamma had an alpha-helical structure. The biologic activity of NPgammas has been estimated by their effects on the intestinal motility and arterial relaxation. The intestinal motility was investigated with rat duodenum (RD), carp intestine (CI), and guinea-pig ileum (GPI). The arterial relaxing effect was tested with guinea-pig aorta (GPA) and rat mesenteric artery (RMA). In RD, the order of potency compared with the EC50 value was M-NPgamma >> S-NPgamma >> B-NPgamma >> G-NPgamma >> T-NPgamma. G-NPgamma was the most contractile agent in CI. S-NPgamma was the most contractile agent in GPI. Using an arterial relaxing test, the order of potency was G-NPgamma >> T-NPgamma >> B-NPgamma >> S-NPgamma >> M-NPgamma in GPA, and all NPgammas remarkably reduced relaxing activity in RMA. Despite their structural similarities to NPgammas, G-NPgamma has high affinity to tachykinin receptor-binding sites in GPA and CI, indicating an alpha-helical structure may have a critical role for receptor binding. However, an alpha-helical structure does not play a critical role in recognizing receptor-binding sites in RD and GPI.

Species differences in tachykinin receptor distribution: further evidence that the substance P (NK1) receptor predominates in human brain

Marked species differences in the distribution of central tachykinin receptors are reported but uncertainty remains about the ability of available ligands to detect NK2 and NK3 receptors in human brain. We compared the distribution of NK1, NK2, and NK3 receptors in sections from rodent, primate, and human brain using the 125I-labeled ligands substance P (SP) for the NK1 receptor, neurokinin A (NKA) for the NK2 receptor, and neurokinin B (NKB) and eledoisin for NK3 receptors. Duration of exposure to autoradiographic film was from 7 days for [125I]SP up to 90 days for the other ligands. High levels of specific [125I]SP binding were seen throughout the brains of all species studied. Specific [125I]NKA binding was detected in brains from neonatal rat, and to a lesser level in adult rat, gerbil, and guinea pig; it was not detected in monkey or human brain, but was present in circular muscle of human duodenum, confirming that this ligand binds to human NK2 receptors under our experimental conditions. Specific [125I]NKB and [125I]eledoisin binding was widespread in brain sections from rats, gerbils, and guinea pigs, and very low levels were also detected in marmoset, squirrel monkey, and rhesus monkey brain after prolonged (up to 90 days) exposure. We failed to identify specific eledoisin binding in human brain, even after prolonged exposures. These findings demonstrate that the NK1 receptor is the predominant tachykinin receptor expressed in primate and human brain, but that low levels of NK3 receptor are present in nonhuman, primate brain.

Design, synthesis and biological activity of carbohydrate-containing peptidomimetics as new ligands for the human tachykinin NK-2 receptor

Enantiopure cycloadducts between glycals and alkyl or aryl heterodienes were selected as small, rigid, nonpeptide molecules able to superimpose to the structure of the cyclopeptide tachykinin NK-2 antagonist 1. The presence of three aromatic groups in the pyranose ring resulted essential for NK-2 affinity, while an increase in activity was shown by the corresponding sulfoxides.

Substance P

Substance P is considered to be an important neuropeptide in nociceptive processes. Although substance P was described more than 60 years ago, there is still controversy about its exact role in nociception. This article reviews the current knowledge about the function of substance P in pain. Special emphasis is put on how to use this knowledge in the development of new ways to treat pain.

Importance of the aromatic residue at position 6 of [Nle(10)]neurokinin A(4-10) for binding to the NK-2 receptor and receptor activation

Steric and electrostatic requirements at position 6 of [Nle(10)]NKA(4-10), a full agonist of NK-2 receptors, for molecular recognition by the receptor were studied. Two series of peptide analogues, (a) p-substituted analogues, [p-X-Phe(6), Nle(10)]NKA(4-10), where X = F, Cl, Br, I, NH(2), NO(2), and (b) [D-Phe(6),Nle(10)]NKA(4-10), [Trp(6),Nle(10)]NKA(4-10), and [Chex-Ala(6),Nle(10)]NKA(4-10), were synthesized, and their biological activity was examined. Competition binding experiments with [(3)H]NKA were performed using cloned human NK-2 receptors expressed in CHO cells. Antagonistic and agonistic properties of the analogues were studied using an in vitro functional assay with hamster tracheal rings. The rank order of potency of agonists was [Nle(10)]NKA(4-10) approximately [p-F-Phe(6),Nle(10)]NKA(4-10) > [p-NH(2)-Phe(6),Nle(10)]NKA(4-10) > [p-Cl-Phe(6),Nle(10)]NKA(4-10) > [p-NO(2)-Phe(6),Nle(10)]NKA(4-10) > [Trp(6),Nle(10)]NKA(4-10). Size and planarity of the aromatic side chain were crucially important for the biological activity, whereas electron-donating and electron-withdrawing properties of the para-substituent were less important. The results favor the hypothesis that weakly polar pi-pi interactions exist between the aromatic group and the receptor.

An investigation of tachykinin NK2 receptor subtypes in the rat

The heterogeneity of tachykinin NK2 receptor subtypes was examined in five tissues from the rat, using binding and functional techniques. Initial experiments with the selective radioligand [125I][Lys5,Tyr(I2)7,MeLeu9,Nle10]neurokinin A-(4-10) showed no specific binding to rat spinal cord membranes or sections. However, this radioligand exhibited high specific binding (80-95% of total) in membranes from the rat fundus, colon, bladder and vas deferens. Dissociation constants (KD) were lower in bladder and colon (0.4 nM) than in fundus (1.9 nM) or vas deferens (1.4 nM). Neurokinin A, neuropeptide gamma, [Lys5,MeLeu9,Nle10]NK(4-10), SR 48968 [(S)-N-methyl-N[4-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophen yl)butyl]benzamine], GR 94800 [PhCO-Ala-Ala-DTrp-Phe-DPro-Pro-Nle-NH2] and MEN 10627 [cyclo(Met-Asp-Trp-Phe-Dap-Leu)cyclo(2beta-5beta)] displayed high affinity (pIC50 8.4-9.5) as competitors, with no significant difference in potency between these four tissues. [Lys5,MeLeu9,Nle10]neurokinin A-(4-10) contracted the isolated fundus (EC50 117 nM) and bladder (EC50 10 nM) and these responses were similarly inhibited by the tachykinin NK2 receptor antagonists, SR 48968 and MEN 10627 (pA2 values 7.6-8.2). In spite of differences in KD seen in some tissues, these results do not provide compelling evidence for tachykinin NK2 receptor heterogeneity in smooth muscle-containing tissues in the rat. The absence of detectable binding in rat spinal cord may be due to very low expression of tachykinin NK2 receptors, or to existence of a different receptor subtype.

MEN 11420 (Nepadutant), a novel glycosylated bicyclic peptide tachykinin NK2 receptor antagonist

1. The pharmacological profile was studied of MEN 11420, or cyclo[[Asn(beta-D-GlcNAc)-Asp-Trp-Phe-Dap-Leu]cyclo(2beta-5beta )], a glycosylated derivative of the potent, selective, conformationally-constrained tachykinin NK2 receptor antagonist MEN 10627 (cyclo(Met-Asp-Trp-Phe-Dap-Leu)cyclo(2beta-5beta)). 2. MEN 11420 competitively bound with high affinity to the human NK2 receptor stably transfected in CHO cells, displacing radiolabelled [125I]-neurokinin A and [3H]-SR 48968 with Ki values of 2.5+/-0.7 nM (n = 6) and 2.6+/-0.4 nM (n = 3), respectively. 3. MEN 11420 showed negligible binding affinity (pIC50 < 6) at 50 different receptors (including tachykinin NK1 and NK3 receptors) and ion channels. 4. In the rabbit isolated pulmonary artery and rat urinary bladder MEN 11420 potently and competitively antagonized tachykinin NK2 receptor-mediated contractions (pK(B) = 8.6+/-0.07, n = 10, and 9.0+/-0.04, n = 12; Schild plot slope = -1.06 (95% c.l. = -1.3; -0.8) and -1.17 (95% c.l. = -1.3; -1.0), respectively). MEN 11420 produced an insurmountable antagonism at NK2 receptors in the hamster trachea and mouse urinary bladder. However, in both preparations, the effect of MEN 11420 was reverted by washout and an apparent pK(B) of 10.2+/-0.14, n = 9, and 9.8+/-0.15, n = 9, was calculated in the hamster trachea and mouse urinary bladder, respectively. 5. MEN 11420 showed low affinity (pK(B) < 6) at guinea-pig and rat tachykinin NK1 (guinea-pig ileum and rat urinary bladder) and NK3 (guinea-pig ileum and rat portal vein) receptors. On the whole, the affinities (potency and selectivity) showed by MEN 11420 for different tachykinin receptors, measured either in binding or in functional bioassays, were similar to those shown by the parent compound, MEN 10627. 6. The in vivo antagonism of the contractions produced by [betaAla8]neurokinin A(4-10) (1 nmol kg(-1)) was observed after intravenous (dose range: 1-10 nmol kg(-1)), intranasal (3-10 nmol kg(-1)), intrarectal (30-100 nmol kg(-1)) and intraduodenal (100-300 nmol kg(-1)) administration of MEN 11420. MEN 11420 was more potent (about 10 fold) and longer lasting than its parent compound MEN 10627, possibly due to a greater metabolic stability. 7. A dose of MEN 11420 (100 nmol kg(-1), i.v.), that produced potent and long lasting inhibition of the contraction of the rat urinary bladder induced by challenge with the NK2 selective receptor agonist [betaAla8]neurokinin A(4-10) (10-300 nmol kg(-1)), was without effect on the responses produced by the NK1 receptor selective agonist [Sar9]substance P sulphone (1-10 nmol kg(-1)). 8. These findings indicate that MEN 11420 is a potent and selective tachykinin NK2 receptor antagonist. The introduction of a sugar moiety did not produce major changes in the affinity profile of this antagonist as compared to MEN 10627, but markedly improved its in vivo potency and duration of action. With these characteristics, MEN 11420 is a suitable candidate for studying the pathophysiological significance of tachykinin NK2 receptors in humans.

Transglutaminase-synthesized gamma-(glutamyl5) spermidine derivative of substance P is a selective tool for neurokinin-2 receptors characterization

The ability of transglutaminase-synthesized 1,3-diaminopropane, spermidine (Spd), spermine (Spm), and monodansylcadaverine gamma-(glutamyl5)derivatives of substance P (SP) to produce bronchoconstriction was investigated. In urethane-anaesthetized guinea pigs, intravenous injections of SP derivatives contracted differently bronchial smooth muscle and caused hypotension. The most effective bronchoconstrictor among SP analogs was the gamma-(glutamyl5)Spd derivative of SP (Spd-SP; EC50 = 5.3 nmol/kg), which was more potent than the native peptide (EC50 = 26.5 nmol/kg). In contrast, the gamma-(glutamyl5)Spm derivative of SP (Spm-SP) was found completely unable to cause bronchoconstriction and was significantly less effective than SP in determining hypotension. The contractile effect of Spd-SP and Spm-SP was investigated in vitro on rat isolated colon, a well-characterized preparation rich in NK2 receptors. In addition, Spd-SP was tested on the endothelium-denuded rabbit pulmonary artery (RPA) and the hamster isolated trachea (HT), both tissue preparations containing only a single functional receptor subtype (NK2A and NK2B, respectively). The results obtained showed that Spd-SP recognizes NK2 receptors occurring on rat isolated colon more effectively (EC50 = 11 nM) than the native peptide (EC50 = 45 nM). Conversely, Spm-SP evokes a contractile response less effective than that elicited by SP (EC50 = 312 nM). Furthermore, Spd-SP (0.1-10 microg kg(-1)) produced a concentration-dependent contraction of both HT and RPA, exhibiting a potency respectively 12 and 30 times higher than SP in contracting HT and RPA. Our results indicate that the introduction of a Spd moiety at the level of glutamine-5 of SP gives rise to an analog that possesses a different capability to recognize NK2 receptors than the parent peptide. Moreover, since Spd-SP seems to contract more effectively RPA than HT, we conclude that it preferentially recognizes the NK2A receptor subtype.

Characterization of tachykinin receptors in the uterus of the oestrogen-primed rat

1 The aim of our study was to characterize the tachykinin receptor population in the oestrogen-primed rat uterus. For this purpose, we investigated the receptor type(s) responsible for tachykinin-induced contraction of longitudinally-arranged smooth muscle layer. The effects of substance P (SP), neurokinin A (NKA), neurokinin B (NKB) and several of their analogues with well-defined selectivities for tachykinin NK1, NK2 and NK3 receptors were studied and their inhibition by the selective nonpeptide tachykinin receptor antagonists (S)1-(2-[3-(3,4-dichlorophenyl)-1-(3-isopropoxyphenylacetyl)pip eridin-3-yl]ethyl)-4-phenyl- -azoniabicyclo[2.2.2]octane chloride (SR 140333, NK1-selective), (S)-N-methyl-N[4-(4acetylamino-4-phenylpiperidino)-2-(3,4-dichloro phenyl)butyl]benzamide (SR 48968, NK2-selective) and (R)-(N)-(1-(3-(1-benzoyl-3-(3,4-dichlorophenyl)piperidin-3-yl)prop yl)-4-phenylpiperidin-4-yl)-N- methyla-cetamide (SR 142801, NK3-selective) was evaluated. Additionally, expression of tachykinin receptor mRNA was examined by using the reverse transcription-polymerase chain reaction (RT-PCR). 2 SP, NKA, [Nle10]-NKA(4-10), the analogue with selectivity at the tachykinin NK2 receptor type, and NKB elicited concentration-dependent contractions of the rat uterus. The pD2 values were 5.95+/-0.19; 6.73+/-0.21; 7.53+/-0.12 and 5.76+/-0.21, respectively. The selective agonist for the tachykinin NK1 receptor [Sar9Met(O2)11]-SP produced a small phasic response in the nanomolar concentration range. The selective tachykinin NK3 receptor agonist [MePhe7]-NKB failed to induce any significant contraction. 3 In the presence of the neutral endopeptidase inhibitor phosphoramidon (1 microM), the log concentration-response curves to exogenous tachykinins and their analogues were shifted significantly leftwards. The pD2 values were 6.12+/-0.10, 8.04+/-0.07, 7.89+/-0.03 and 6.59+/-0.07 for SP, NKA, [Nle10]-NKA(4-10) and NKB, respectively. In the presence of phosphoramidon (1 microM), [Sar9Met(O2)11]-SP (1 nM - 0.3 microM) induced concentration-dependent contractions of increasing amplitude when only one concentration of drug was applied to each uterine strip and the pD2 value was 7.61+/-0.89. [MePhe7]-NKB induced small, inconsistent contractions and, therefore, a pD2 value could not be calculated. 4 In experiments performed in the presence of phosphoramidon (1 microM), SR 48968 (3 nM - 0.1 microM) caused parallel and rightward shifts in the log concentration-response curves of NKA. The calculated pKB value was 9.16+/-0.08 and the slope of the Schild regression was 1.28+/-0.24. SR 48968 (0.1 microM) also antagonized responses to SP with an apparent pKB value of 7.63+/-0.13. SR 48968 (0.1 microM) inhibited contractions elicited by NKB (1 nM - 3 microM) and [Nle10]-NKA(4-10) (0.1 nM - 3 microM) but had no effect on the response evoked by [Sar9Met(O2)11]-SP (0.1 microM). 5 SR 140333 (0.1 microM) inhibited responses to SP with an apparent pKB value of 7.19+/-0.22. This compound did not significantly affect responses to NKA, [Nle10]-NKA(4-10) and NKB, but suppressed [Sar9Met(O2)11]-SP (0.1 microM)-induced contraction. SR 142801 (0.1 microM) had no effect on responses to natural tachykinins or their analogues. 6 Total RNA was extracted from some of the uteri used in functional studies. RT-PCR assays revealed single bands corresponding to the expected product sizes encoding cDNA for tachykinin NK1 (587 base pairs) and NK2 receptors (491 base pairs) (n=6 different animals). A very low abundance transcript corresponding to the 325 base pairs product expected for the tachykinin NK3 receptor was detected. 7 The present data show that functionally active tachykinin NK1 and NK2 receptors are expressed in the oestrogen-primed rat uterus. The NK2 receptor type seems to be the most important one involved in the contractile responses elicited by tachykinins. NK3 receptors are present in trace amounts and seem not to be involved in tachykinin-induced contractions.

Tachykinin receptors mediating non-cholinergic contraction of the guinea-pig isolated main bronchus in response to field stimulation

1. The primary aim of the present study was to classify the receptors activated by tachykinins released by field stimulation of intramural nerve terminals of the guinea-pig isolated main bronchus by using the novel non-peptide NK1 and NK2 receptor-selective antagonists SR 140333 and SR 48968, respectively. 2. Log concentration-response curves to substance P (SP), the NK1 receptor-selective agonist [Sar9, Met(O2)11]-SP and the NK2 receptor-selective agonist [Nle10]-neurokinin (NK) A(4-10) were constructed in the presence of indomethacin (2 mumol/L) and phosphoramidon (5 mumol/L). Substance P was the least potent of these agonists. 3. In left and right main bronchi, SR 140333 (100 nmol/L) antagonized concentration-related contractions evoked by SP yielding pKB values of 8.02 and 7.68, respectively. SR 140333 (10 nmol/L) antagonized the effects of [Sar9, Met(O2)11]-SP on the left bronchus with a pKB value of 8.04. 4. SR 48968 (100 nmol/L) antagonized the effects of SP yielding pKB estimates of 7.88 (left bronchus) and 7.31 (right bronchus). 5. [Nle10]-NKA(4-10) was more potent in the left than in the right main bronchus. SR 48968 (0.1-10 nmol/L) antagonized the effects of [Nle10]-NKA(4-10) on the left bronchus with pKB estimates of 8.26-10.25. 6. In the presence of indomethacin (2 mumol/L), phosphoramidon (5 mumol/L) and atropine (1 mumol/L), electrical field stimulation (EFS; 30 V, 1 ms, 15 s at 1, 3, 10 and 30 Hz) produced prolonged contractions. SR 48968 (0.1 mumol/L) markedly reduced responses to stimulation, whereas SR 140333 (0.3 mumol/L) caused a small but significant rightward displacement of the log frequency-response curve. In combination, these concentrations of SR 48968 and SR 140333 produced complete inhibition to field stimulation at 10 Hz. 7. These results indicate that: (i) both NK1 and NK2 receptor subtypes are present in the guinea-pig main bronchi with the left bronchus being more sensitive to an NK2 receptor agonist; and (ii) EFS of the main bronchus leads to frequency dependent contractions due to the release of tachykinin(s) that predominantly activate an NK2 receptor.

Pro-inflammatory effects induced by bradykinin in a murine model of pleurisy

Bradykinin caused a dose-related increase in cell influx 4 h after its administration into the mouse pleural cavity (ED50 = 3.2 nmol/cav., 95% confidence limits = 0.6-15.5). Cell influx peaked at 4 h and remained elevated for up to 72 h, whereas exudation was detected between 2 and 6 h after bradykinin administration. Both HOE 140 (D-Arg-[Hyp3,Thi5,D-Tic7, Oic8]bradykinin) and NPC 17731 (D-Arg0-[Hyp3 D-HypE(transpropyl7)Oic8]bradykinin) inhibited bradykinin-induced cell influx (ID50 0.028 (0.05-0.16) and 0.4 (0.3-0.7) pmol/cav., respectively). Des-Arg9-[Leu8]bradykinin (0.1 and 3.0 nmol/cav., 30 min before) did not inhibit the effects of bradykinin. Pre-treatment of animals with either indomethacin, terfenadine, dexamethasone, N(omega)-nitro-L-arginine benzyl ester, cromolyn, theophylline, salbutamol, FK 888 (N2-[(4R)-4-hydroxy-1-(1-methyl-1H-indol-3-yl)carbonyl-L-propyl]N-met hyl-N-phenyl-methyl-3-(2-naphthyl)-L-alaninamide) or SR 142801 ((N)-(1-[3-[1-benzoyl-3-(3,4-dichloro-phenyl)-piperidin-3-yl]pr opy l]-4-phenyl-piperidin-4-yl)-N-methyl-acetamide) significantly inhibited cell migration (P < 0.01). These results indicate that bradykinin had a significant pro-inflammatory effect on the pleural cavity of the mice. This effect seems to be primarily mediated via activation bradykinin B2 receptors which trigger the release of other mediators.

Effect of several bicyclic peptide and cyclic pseudopeptide tachykinin NK2 receptor antagonists in the human isolated ileum and colon

The affinities of the monocyclic pseudopeptides MEN10,508, MEN10,573, MEN10,581, MEN10,612, MEN10,619 and MEN10,677, and the bicyclic peptides MEN10,627, MEN10,692, MEN10,771, MEN10,882 and MEN10,993 were evaluated at the tachykinin NK2 receptors of the human isolated ileum and colon circular muscle preparations, by using [betaAla8]neurokinin A(4-10) as an agonist. All of the antagonists tested produced a concentration-dependent and competitive antagonism of [betaAla8]neurokinin A(4-10)-mediated contractions in both preparations. MEN10,612 (pKB = 8.1) and MEN10,627 (pKB = 8.4-8.8) were among the most potent analogs within their chemical classes. In general, the bicyclic peptide antagonists were more potent than the monocyclic peptide compounds, showing a nanomolar affinity for the human NK2 receptor. By comparing the affinities shown by the antagonists under study at NK2 receptors of the human gut with the affinities measured at NK2 receptors of the rabbit isolated pulmonary artery and hamster isolated trachea, a high degree of pharmacological homology was found between human and rabbit NK2 receptors. The present results point out the class of NK2 receptor antagonists bearing a bicyclic peptide structure, like MEN10,627, as candidates for testing in pathological conditions characterized by exaggerated gut motility, in which tachykinins might play a role as non-cholinergic excitatory neurotransmitters.

Effect of several bicyclic peptide and cyclic pseudopeptide tachykinin NK2 receptor antagonists in the human isolated urinary bladder

1. We have studied several tachykinin NK2 receptor antagonists, bearing a monocyclic pseudopeptide (MEN 10,508, MEN 10,573, MEN 10,581, MEN 10,612, MEN 10,619 and MEN 10,677), or bicyclic peptide (MEN 10,627, MEN 10,692, MEN 10,771, MEN 10,882 and MEN 10,993) structure, on the human isolated urinary bladder detrusor muscle against neurokinin A as an agonist, and compared their affinities in this preparation with those for NK2 receptors expressed in the rabbit isolated pulmonary artery and hamster isolated trachea. 2. In the human bladder, all the antagonists tested produced a concentration-dependent and competitive antagonism of neurokinin A-mediated contractions: among the cyclic pseudopeptides MEN 10,677 (pKB = 8.0) was the most potent antagonist, while among the bicyclic analogues it was MEN 10,993 (pKB = 8.8). 3. In general, the bicyclic peptide antagonists tested were more potent than the monocyclic pseudopeptide compounds, either in the human urinary bladder or in the rabbit pulmonary artery or hamster trachea, showing a nanomolar affinity for the human NK2 receptor. 4. A highly significant correlation was found between the estimated pKB values of all the antagonists tested in the human urinary bladder and rabbit pulmonary artery (r2 = 0.94, n = 12, P < 0.01), whereas no linear correlation was found between pKB values measured in the human urinary bladder and hamster trachea (r2 = 0.52, n = 12, P > 0.05): these observations provide further pharmacological evidence for receptor homology between the human and rabbit NK2 receptor. 5. The present results point out the class of NK2 receptor antagonists bearing a bicyclic peptide structure, like MEN 10,627, as candidates for testing in pathological conditions, such as bladder hyperactivity, for which preclinical evidence indicates that a therapeutic effect could result from the block of the tachykinin NK2 receptor.

A review of the design, synthesis and biological activity of the bicyclic hexapeptide tachykinin NK2 antagonist MEN 10627

We review the reported data on the design, the conformational features and the pharmacological properties of the bicyclic peptide tachykinin NK2 receptor antagonist MEN 10,627 or cyclo(Met-Asp-Trp-Phe-Dap-Leu)cyclo(2 beta-5 beta). MEN 10,627 possesses a highly constrained structure characterized by two consecutive beta-turns, as confirmed by the almost coincident results of NMR and X-ray analyses. The compound has been efficiently synthesized by solid-phase methodology using either Boc or Fmoc strategies. It is quite stable to metabolic degradation and is endowed with high affinity and selectivity for NK2 receptor expressed in various species. At the hamster NK2 receptor MEN 10,627 is about 30-fold more potent than the nonpeptide NK2 receptor antagonist, SR 48,968, while the converse is true for the rabbit NK2 receptor. MEN 10,627 and SR 48,968 show comparable affinities for the human NK2 receptor. MEN 10,627 produces a long lasting inhibition of the response to the selective NK2 receptor agonist [beta Ala8]NKA(4-10) in the rat urinary bladder in vivo after intravenous, intranasal and intraduodenal administration. Therefore different administration routes are possible for this compound that overcomes the usual drawbacks for the application of peptides as drugs.

Tachykinins: receptor to effector

Tachykinins belong to an evolutionarily conserved family of peptide neurotransmitters. The mammalian tachykinins include substance P, neurokinin A and neurokinin B, which exert their effects by binding to specific receptors. These tachykinin receptors are divided into three types, designated NK1, NK2 and NK3, respectively. Tachykinin receptors have been cloned and contain seven segments spanning the cell membrane, indicating their inclusion in the G-protein-linked receptor family. The continued development of selective agonists and antagonists for each receptor has helped elucidate roles for these mediators, ranging from effects in the central nervous system to the perpetuation of the inflammatory response in the periphery. Various selective ligands have shown both inter- and intraspecies differences in binding potencies, indicating distinct binding sites in the tachykinin receptor. The interaction of tachykinin with its receptor activates Gq, which in turn activates phospholipase C to break down phosphatidyl inositol bisphosphate into inositol trisphosphate (IP3) and diacylglycerol (DAG). IP3 acts on specific receptors in the sarcoplasmic reticulum to release intracellular stores of Ca2+, while DAG acts via protein kinase C to open L-type calcium channels in the plasma membrane. The rise in intracellular [Ca2+] induces the tissue response. With an array of actions as diverse as that seen with tachykinins, there is scope for numerous therapeutic possibilities. With the development of potent, selective non-peptide antagonists, there could be potential benefits in the treatment of a variety of clinical conditions, including chronic pain, Parkinson's disease, Alzheimer's disease, depression, rheumatoid arthritis, irritable bowel syndrome and asthma.

The mammalian tachykinin receptors

The tachykinins (TKs) are a family of small peptides which share the common C-terminal sequence Phe-X-Gly-Leu-MetNH2. Three peptides of this family, substance P, neurokinin A and neurokinin B, have an established role as neurotransmitters in mammals. 2. Three receptors for TKs have been cloned: they are G-protein coupled receptors with seven putative transmembrane spanning segments and have been termed NK1 (substance P-preferring), NK2 (neurokinin A-preferring) and NK3 (neurokinin B-preferring). 3. Synthetic agonists are available to selectively stimulate only one receptor, while natural TKs can act as full agonist at each one of the three receptors, albeit at different concentrations. 4. A number of potent and selective antagonists, both peptide and nonpeptide in nature, have recently been developed. 5. The introduction of these ligands has revealed an unforeseen pharmacological heterogeneity of NK1, NK2 and NK3 receptors which appears largely, if not exclusively, linked to the existence of species homologues of the three receptors.

Tachykinin receptors in gastrointestinal motility

For a long time research on the action of TKs on gastrointestinal tissue has been demonstrating the importance of the TKs as non-cholinergic stimulators of motility in most parts of the mammalian gastrointestinal tract. The past years witnessed the development of TK agonists and antagonists selective for the various receptor types, which prompted a wealth of new insight into the pharmacology and molecular biology of the TK receptors. This knowledge now allows a more specific elucidation of the role of TKs and their receptors in the various aspects of gastrointestinal motility, not only in normal tissue but also under pathological conditions.

Pharmacological evidence for neurokinin receptors in murine neuroblastoma C1300 cells

We found that neurokinin A (NKA) and neurokinin B (NKB) induce an increase in the concentration of intracellular free Ca2+ ([Ca2+]i) in murine neuroblastoma C1300 cells (EC50: NKA 87 +/- 13 nM, NKB 97 +/- 15 nM). Substance P (SP) also caused a transient Ca2+ increase, although the potency of SP was much less than that of NKA and NKB. The increase in [Ca2+]i induced by NKA and NKB was inhibited by SR 48,968, a selective antagonist for NK2, and [beta Ala8]NKA(4-10), a selective agonist for NK2, did not stimulate the increase in [Ca2+]i. NKA- and NKB-induced Ca2+ mobilization was not inhibited by CP-96,345 and [Trp7, beta Ala8]NKA(4-10), selective antagonists for NK1 and NK3, respectively. These results suggested that C1300 cells express endogenous NK2 neurokinin receptors that have different features from known NK2 receptors.

Tachykinin receptors in the spinal cord

In summary, all three tachykinin receptors appear to be important modulators of physiological systems in the spinal cord. However, although there is a good deal of data concerning binding characteristics in peripheral tissues, work done in the spinal cord is scanty, leading to a number of unanswered questions. Firstly, Lui et al. (1993) have suggested a discrepancy between the location of SP binding sites and SP containing terminals. This might explain the conflicting evidence on the role of NK1 receptors in the dorsal horn. Furthermore, evidence that NK2 receptors are involved in nociception is increasing, however binding sites for these receptors in the spinal cord have not been demonstrated. This appears to be due to the difficulty in locating an ideal receptor specific ligand. The role of NK2 receptors in autonomic function is also unclear, perhaps for the same reason. Finally, there is evidence indicating that NK3 binding sites are increased following transection of the LIV-VI dorsal roots, however, studies on the effects of inflammation have not been done, as they have with the NK1 and NK2 receptors. All of these and many more unanswered questions require further investigation.

Tachykinin receptors involved in the contractile effect of the natural tachykinins in the rat gastric fundus

1. The receptors involved in mammalian tachykinin-induced contractions of longitudinal smooth muscle strips of the rat gastric fundus were characterized pharmacologically. 2. Substance P (SP), neurokinin A, neurokinin B and senktide contracted the strips in a concentration-dependent manner with a potency order of neurokinin A > or = senktide > neurokinin B > substance P. The contractions were not influenced by tetrodotoxin and atropine. 3. L 659877, a NK2B-receptor-preferring antagonist reduced neurokinin A- and neurokinin B-induced contractions (estimated pKB 6.9 and 6.3, respectively) but had less pronounced effects on SP-induced contractions and none on contractions induced by senktide. MEN 10376, an NK2A-receptor-preferring antagonist, reduced the neurokinin A-induced contractions (estimated pKB 5.2), while dactinomycin, reduced the neurokinin A-induced contractions only to a minor extent at 10(-4) M. 4. CP 96345, an NK 1-receptor antagonist, reduced substance P- and neurokinin A-induced responses, but also reduced the contractions induced by KCl and methacholine. RP 67580, another non-peptide NK1-receptor antagonist had no effect on the substance P-, neurokinin A- and neurokinin B-induced contractions up to a concentration of 3 x 10(-6) M. 5. These results suggest that the mammalian tachykinins induce contractions of the longitudinal smooth muscle strip of the rat gastric fundus by direct action at muscular NK2B- and NK3-receptors.

A selective NK-2 antagonist blocks the increase of canine colonic tone and ileal contractions induced by the NK-2 selective receptor agonist, [beta Ala8] neurokinin A-(4-10)

BACKGROUND

The regulatory roles of tachykinins in intestinal motor function may be clarified by use of novel, stable and selective antagonists of neurokinin receptors. We studied the effects of the non-peptide NK-2 receptor antagonist SR48968 on canine colonic tone under resting conditions and after stimulation by the selective NK-2 receptor agonist [beta Ala8] neurokinin A-(4-10).

METHODS

Experiments were performed in three conscious female dogs. Proximal colonic tone was recorded by a barostat and intraluminal pressures were recorded in the terminal ileum. 10, 15 and 20 cm orad to the ileocaecal junction. In separate experiments, and in a random sequence, dogs received an i.v. injection of the NK-2 antagonist SR48968, 10, 100, 1000 micrograms/kg, followed after 30 min by 2 micrograms/kg of the agonist [beta Ala8] neurokinin A-(4-10). Experiments were replicated twice in each dog.

RESULTS

The NK-2 agonist increased colonic tone, and SR48968 antagonized these effects in a dose-dependent fashion (Spearman's rank, r = 0.86; P < 0.01); antagonism was complete at the highest dose. SR48968 alone had no effect on colonic tone and ileal motility. When given during phase I or II of the interdigestive motor complex, [beta Ala8] neurokinin A-(4-10) increased ileal contractions: pre-treatment with SR48968 blocked this increase in ileal motility. When given during phase III, [beta Ala8] neurokinin A-(4-10) interrupted the motility front; this effect was not antagonized by SR48968.

CONCLUSIONS

SR48968 antagonizes the increase in canine colonic tone and ileal motility induced by activation of NK-2 receptors. However, SR48968 by itself had no effect on the control of colonic tone and ileal motility under unstimulated conditions. SR48968 may be useful for investigating the physiological role of tachykinins on the gastrointestinal tract.

Intestinal motility responses to neuropeptide gamma in vitro and in vivo in the rat: comparison with neurokinin 1 and neurokinin 2 receptor agonists

We have studied the effect of a novel tachykinin, neuropeptide gamma (NP gamma) on small intestinal motility in the rat. Experiments were done in vitro on longitudinal muscle strips of duodenum, and in vivo on the migrating myoelectric complex (MMC) of the small intestine. In vitro, contractile effects of NP gamma were compared with those of a selective neurokinin 1 (NK1) receptor agonist, substance P methyl ester (SPME), and a selective neurokinin 2 (NK2) receptor agonist, Nle10-NKA(4-10)(NleNKA). NP gamma, SPME and NleNKA caused concentration-dependent contractions (P < 0.001). NP gamma was eight-fold more potent than NleNKA, and 118-fold more potent than SPME. Contractile responses to NP gamma were reduced by hexamethonium (P < 0.01) and atropine (P < 0.05). The non-selective NK receptor antagonist spantide I only slightly reduced the contractile response to NP gamma, as did the selective NK1 antagonist GR 82,334, and the selective NK2 antagonist L-659,877 and MEN 10,376. In vivo, effects of NP gamma on the MMC were compared with those of the natural tachykinins substance P (SP) and neurokinin A (NKA). NP gamma disrupted the MMC and induced irregular spiking in a dose-dependent manner from 25 to 100 pmol kg-1 min-1 i.v. (P < 0.05). The effect of NP gamma was more prominent than that of NKA at equal doses, while SP had no effect. Our findings show that NP gamma exerts potent stimulatory effects on small intestinal motility, most likely mediated directly via distinct NK receptors on smooth muscle cells, but also indirectly via a cholinergic link.

Physiological and pharmacological characterization of the spinal tachykinin NK2 receptor

The goal of these investigations was to study the role of tachykinin NK2 receptors in neonatal spinal cords using the selective NK2 receptor agonist [beta-Ala8]neurokinin A-(4-10) and the new NK2 receptor antagonist GR 94800. Experiments were performed with superfused hemisected rat and gerbil spinal cords. Dorsal roots were electrically stimulated and the synaptically elicited responses and the DC-potentials were recorded extracellularly from the corresponding ventral roots. [beta-Ala8]neurokinin A-(4-10) depolarized ventral roots (0.01-10 microM) and increased their spontaneous activity in a concentration-dependent manner. These effects of [beta-Ala8]neurokinin A-(4-10) were reduced by GR 94800. The action of GR 94800 was selective because the depolarizing effects of similar magnitude evoked by the NK1 receptor agonist [Sar9,Met(O2)11]substance P were not affected by GR 94800. The pA2 values of GR 94800 amounted to 6.0 +/- 0.4 in the rat and 5.4 +/- 0.3 in the gerbil. The NK2 receptor agonist was more potent in the rat than in the gerbil. The estimated EC50 (mean +/- S.E.M.) was found to be 3.9 + 6.0/-1.3 microM in the rat and 2.4 + 2.9/-1.3 microM in the gerbil spinal cord. The NK2 receptor agonist [beta-Ala8]neurokinin A-(4-10) potentiated the monosynaptic reflex evoked by dorsal root stimulation. The potentiation manifested itself as an increase in the amplitude of the early component of the response. The receptor type mediating this effect could not be elucidated. The potentiation ranged between 30 +/- 27 and 110 +/- 36% (0.3 and 10 microM), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the tachykinin NK2 receptor in the human bronchus: influence of amastatin-sensitive metabolic pathways

1. The aim of this study was to characterize the tachykinin NK2 receptor subtype mediating the spasmogenic response in the human isolated bronchus. The motor response to neurokinin A (NKA) and the selective NK2 agonist [beta Ala8]NKA(4-10), as well as the antagonistic effects of cyclic (L659,877) and linear (MEN 10376) peptide NK2 antagonists were assessed in the presence or absence of amastatin (an inhibitor of aminopeptidases A and M). 2. NKA was more potent than [beta Ala8]NKA(4-10) in eliciting bronchoconstriction (pD2 being 7,43 and 6,87 respectively). In the presence of amastatin (1 microM), the estimated affinity of [beta Ala8]NKA(4-10), but not that of NKA, was significantly increased to yield a pD2 of 7,44. 3. L659,877 and MEN 10376 inhibited [beta Ala8]NKA(4-10)-induced contraction with similar affinities; pA2 values were 5.7 +/- 0.22 and 6.3 +/- 0.32, respectively. Amastatin (1 microM) increased the potency of MEN 10376 to 7.28 +/- 0.46, whereas that of L659,877 was unaffected. 4. In the presence of amastatin the pseudopeptide MDL 28,564 behaved as a partial agonist. 5. We conclude that the NK2 receptor subtype present in the human bronchus has properties similar to those described for the circular muscle of the human colon and thus may be classified as a 'NK2A' subtype. We show that the apparent potency of peptides, bearing N-terminal acidic residues, is influenced by an amastatin-sensitive peptidase, possibly aminopeptidase A.

Evidence for tachykinin NK-2 receptors in guinea-pig airways from binding and functional studies, using [125I]-[Lys5,Tyr(I2)7,MeLeu9,Nle10]-NKA(4-10)

The potent contractile responses of guinea-pig airways to neurokinin A (NKA) and neuropeptide gamma (NP gamma) are thought to be mediated by NK-2 receptors. However, NK-2 binding sites are not detectable using the radioligand [125I]-iodohistidyl-NKA. Here, a novel, highly selective iodinated radioligand, [125I]-[Lys5,Tyr(I2)7,MeLeu9,Nle10]-NKA(4-10), and a number of related peptides have been used to characterize NK-2 receptors on guinea-pig airways, using binding and functional studies. Specific binding of [125I]-[Lys5,Tyr(I2)7,MeLeu9,Nle10]-NKA(4-10), was saturable and to a single high affinity site, with KD 1.29 +/- 0.36 nM (n = 4). The rank order of potency for tachykinins and analogues as competitors for the binding was: [Lys5,Tyr(I2)7,MeLeu9,Nle10]-NKA(4-10) > or = NP gamma > or = [Lys5,MeLeu9,Nle10]-NKA(4-10) > NKA > or = SR 48968 >> MDL 29913 > or = substance P (SP) = [127I]-Bolton-Hunter NKA (BHNKA) > or = MEN 10207 > neurokinin B (NKB). Septide, [DPro9,Pro10,Trp11]-SP, the NK-1 selective ligands [Sar9,Met(O2)11]-SP, [Pro9]-SP and CP 96345, the NK-3 selective senktide, and calcitonin gene-related peptide (CGRP) were weak or ineffective. On guinea-pig isolated bronchi, the potency order of contractile agonists was: [Lys5,MeLeu9,Nle10]-NKA(4-10) > NKA > or = NP gamma > or = [Lys5,Tyr7,MeLeu9, Nle10]-NKA(4-10) > or = septide = BHNKA > or = [Lys5,Tyr(I2)7,MeLeu9,Nle10]-NKA(4-10) > or = [Sar9,Met(O2)11]-SP > or = NKB = [Pro9]-SP > or = SP >> senktide.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of scyliorhinin I and synthetic scyliorhinin I derivatives at mammalian tachykinin NK1, NK2 and NK3 receptors

The dogfish tachykinin peptide scyliorhinin I and a number of its analogues substituted in position 7 were tested in bioassays for tachykinin NK1, NK2 and NK3 receptors. Scyliorhinin I behaved as a full agonist at tachykinin NK1 receptors of the guinea-pig ileum longitudinal muscle and at NK2 receptors of the rabbit pulmonary artery and hamster trachea. In these three preparations scyliorhinin I was as potent agonist as substance P methylester and neurokinin A, respectively. Evidence for activation of tachykinin NK1 and NK2 receptors by scyliorhinin I was obtained by using the selective tachykinin antagonists FK 888, MEN 10,376 and L 659,877. Scyliorhinin I was poorly active as an agonist at NK3 receptors of the rat portal vein. Among scyliorhinin I analogues, [beta-(2-naphthyl)-Ala7]scyliorhinin I, [Val7]scyliorhinin I and [Ile7]scyliorhinin I were 3-25 times weaker than scyliorhinin I itself at NK1 and NK2 receptors. [Phe7]scyliorhinin I, [Phe(F)7]scyliorhinin I and [Phe(Cl)7]scyliorhinin I were as potent as scyliorhinin I at NK1 receptors in the guinea-pig ileum, while they showed 10-30 times lower affinity than scyliorhinin I for NK2 receptors. The present results are discussed in relation to the importance of position 7 in determining the potency and selectivity of scyliorhinin I analogues at tachykinin receptors.

MEN 10,573 and MEN 10,612, novel cyclic pseudopeptides which are potent tachykinin NK-2 receptor antagonists

The activity and selectivity of MEN 10,573 and MEN 10,612, novel cyclic pseudopeptides which are selective tachykinin NK-2 receptor antagonists is described, as compared to that of previously characterized linear and cyclic compounds. For the NK-2 receptor, the activity of test compounds was investigated in the hamster isolated trachea (HT) and the endothelium-deprived rabbit isolated pulmonary artery (RPA), two preparations which are endowed with pharmacologically distinct forms of the NK-2 receptor. The novel cyclic pseudopeptides, MEN 10,573 and MEN 10,612 displayed very high affinity for the NK-2 receptor in the HT (pA2 8.66 and 9.06, respectively) which is higher than that observed in the RPA (pA2 7.31 and 7.41 for MEN 10,573 and MEN 10,612, respectively). The antagonism exerted by MEN 10,573 and MEN 10,612 was of competitive nature in both preparations. MEN 10,573 and MEN 10,612 also displayed competitive antagonism for NK-2 receptor-mediated responses in the rabbit bronchus (RB), rat vas deferens (RVD), circular muscle of the human colon (HUC) and ileum (HUI). In the RB, HUC and HUI, the potency of the novel cyclic pseudopeptides was comparable to that of MDL 29,913 and about 10-fold greater than that of L659,877. In the RVD however, the potency of MEN 10,573 MEN 10,612 or MDL 29,913 was similar to that of L659,877. In anaesthetized rats, i.v. injection of MEN 10,612 produced a selective and long-lasting blockade of the urinary bladder contraction produced by the i.v. injection of the NK-2 receptor selective agonist [beta Ala8]neurokinin A(4-10), without affecting the response to the NK-1 receptor selective agonist [Sar9]substance P sulfone.(ABSTRACT TRUNCATED AT 250 WORDS)

Tachykinin receptors: a radioligand binding perspective

The last decade has witnessed major breakthroughs in the study of tachykinin receptors. The currently described NK-1, NK-2, and NK-3 receptors have been sequenced and cloned from various mammalian sources. A far greater variety of tachykinin analogues are now available for use as selective agonists and antagonists. Importantly, potent nonpeptide antagonists highly selective for the NK-1 and NK-2 receptors have been developed recently. These improved tools for tachykinin receptor characterization have enabled us to describe at least three distinct receptor types. Furthermore, novel antagonists have yielded radioligand binding and functional data strongly favoring the existence of putative subtypes of NK-1 and especially NK-2 receptors. Whether these subtypes are species variants or true within-species subtypes awaits further evidence. As yet undiscovered mammalian tachykinins, or bioactive fragments, may have superior potency at a specific receptor class. The common C terminus of tachykinins permits varying degrees of interaction at essentially all tachykinin receptors. Although the exact physiological significance of this inherent capacity for receptor "cross talk" remains unknown, one implication is for multiple endogenous ligands at a single receptor. For example, NP gamma and NPK appear to be the preferred agonists and binding competitors at some NK-2 receptors, previously thought of as exclusively "NKA-preferring." Current evidence suggests that tachykinin coexistence and expression of multiple receptors may also occur with postulated NK-2 and NK-1 receptor subtypes. Other "tachykinin" receptors may recognize preprotachykinins and the N terminus of SP. In light of these recent developments, the convenient working hypothesis of three endogenous ligands (SP, NKA, and NKB) for three basic receptor types (NK-1, NK-2, and NK-3) may be too simplistic and in need of amendment as future developments occur (Burcher et al., 1991b). In retrospect, the 1980s contributed greatly to our understanding of the structure, function, and regulation of tachykinins and their various receptors. The development of improved, receptor subtype-selective antagonists and radioligands, in addition to recent advances in molecular biological techniques, may lead to a more conclusive pharmacological and biochemical characterization of tachykinin receptors. The 1990s may prove to be the decade of application, where a better understanding of the roles played by endogenous tachykinins (at various receptor subtypes) under pathophysiological conditions will no doubt hasten the realization of clinically useful therapeutic agents.

Amastatin interferes with the antagonist properties of MEN 10,208 in the rabbit pulmonary artery but not in the hamster trachea

The tachykinin peptide agonists neurokinin A and [beta Ala8]neurokinin A-(4-10), and the NK2 tachykinin receptor-selective antagonists MEN 10,208, MEN 10,207, MEN 10,282, MEN 10,376 and R396 were assayed in the isolated rabbit pulmonary artery and isolated hamster trachea in the absence and in the presence of the aminopeptidase inhibitor amastatin (10 microM for 30 min). The affinity of MEN 10,208 in the rabbit pulmonary artery was markedly reduced in the presence of amastatin (pKB values from 7.47 to 5.94), while it was unchanged in the hamster trachea. Neither neurokinin A, [beta Ala8]neurokinin A-(4-10), nor the other antagonists were affected by pretreatment with amastatin in either bioassay. The results obtained in the rabbit pulmonary artery show that MEN 10,208 is degraded by local amastatin-sensitive enzymes (possibly aminopeptidase M), which may convert the linear octapeptide MEN 10,208 to the heptapeptide MEN 10,207 by removing the N-terminal Thr from the amino acid sequence of MEN 10,208. The present results are discussed in relation to a previously reported heterogeneity between NK2 receptors of the rabbit and bovine species, and show amastatin to be a new tool for the classification of tachykinin receptors with peptide ligands.

In vivo and in vitro pharmacology of SR 48,968, a non-peptide tachykinin NK2 receptor antagonist

The activity of SR 48,968, a novel non-peptide antagonist of tachykinin NK2 receptors was evaluated in vitro in several bioassays for the NK2 receptor (rabbit pulmonary artery, rabbit bronchus, hamster trachea, rat vas deferens) and compared to that of the peptide antagonists, MEN 10,376, L 659,877 and MDL 29,913. SR 48,968 behaved as a potent and competitive antagonist in the four isolated preparations (pA2 values between 8.3 and 9.6 in different preparations), being more potent (about 10 times) in the rabbit pulmonary artery and rabbit bronchus than in the hamster trachea or rat vas deferens. The antagonistic profile of SR 48,968 resembled that of MEN 10,376, and contrasted with those of L 659,877 and MDL 29,913 which were distinctly more potent on the hamster trachea and rat vas deferens. In vivo, SR 48,968 (0.1 mumol/kg i.v.) blocked the contraction of rat urinary bladder stimulated by [beta Ala8]neurokinin A-(4-10) (NK2 receptor agonist) without affecting that produced by [Sar9]substance P sulfone (NK1 receptor agonist). The hypotension and salivary secretion produced by the latter agonist were not modified by SR 48,968. In contrast, (+/-)-CP 96,345 (10 mumol/kg i.v.) blocked bladder contraction, salivary secretion and hypotensive responses elicited by the NK1 receptor agonist while leaving unaffected the bladder contraction produced by the NK2 receptor agonist. SR 48,968 is a potent and competitive antagonist of the tachykinin NK2 receptor with a limited but distinct ability to discriminate between putative subtypes/species variants of the NK2 receptor. The high potency and selectivity of SR 48,968 make this novel compound an important tool for studying the distribution and function of tachykinin NK2 receptors.

NK2 receptors mediate plasma extravasation in guinea-pig lower airways

1. Neurokinin (NK) receptor-mediated extravasation has been examined in guinea-pig airways by use of a recently described marker for microvascular protein leakage, 125I-labelled human fibrinogen. 2. Neurokinin A (NKA) caused a dose-dependent increase in plasma [125I]-fibrinogen extravasation in trachea, main bronchi, secondary bronchi and intraparenchymal airways. In contrast, the NK2 selective agonist [beta-Ala8]NKA(4-10) only caused extravasation in the secondary and intraparenchymal airways. 3. The NK2 selective antagonist, SR 48968, caused a dose-dependent inhibition of NKA and [beta-Ala8]NKA(4-10)-induced extravasation of fibrinogen in guinea-pig secondary bronchi and intraparenchymal airways. SR 48968 was without effect on the NKA-induced extravasation in trachea and main bronchi. 4. NKA- or [beta-Ala8]NKA(4-10)-induced plasma extravasation was not modified by pretreatment with histamine H1- or H2-receptor antagonists. 5. It is concluded that NK2 receptors mediate plasma [125I]-fibrinogen extravasation in guinea-pig secondary bronchi and intraparenchymal airways. This effect is direct and does not depend upon histamine released from mast cells.

Influence of (+/-)-CP-96,345 and SR 48968 on electrical field stimulation of the isolated guinea-pig main bronchus

The aim of this study was to investigate the effects of (+/-)-CP-96,345 and SR 48968, two new nonpeptide antagonists of neurokinin NK1 and NK2 receptors, respectively, on the response of isolated guinea pig main bronchi to electrical field stimulation (EFS). Bronchi were stimulated transmurally with biphasic pulses (16 Hz, 1 ms, 320 mA for 10 s) in the presence of indomethacin (10(-6) M) and propranolol (10(-6) M). Two successive contractile responses were observed. Both responses were abolished by tetrodotoxin (10(-6) M) whereas only the first rapid phase was abolished by atropine (10(-6) M). The late and prolonged second phase was strongly reduced by the neurokinin A (NK2) receptor antagonist SR 48968 (10(-11) to 10(-8) M) with an EC50 of 0.056 nM and a maximal inhibition of 83.3 +/- 10.8% (10(-8) M, n = 4). This second response was partially inhibited by the substance P (NK1) receptors antagonist (+/-)-CP-96,345 (10(-8) to 10(-6) M). An incubation of 2 h was necessary for SR 48968 to inhibit the EFS-evoked noncholinergic contraction. These results confirm that EFS of guinea-pig bronchi involves stimulation of cholinergic and noncholinergic excitatory nerves and demonstrate that the new developed tachykinin receptors nonpeptide antagonists (+/-)-CP-96,345 and especially SR 48968 are potent inhibitors of the noncholinergic contraction induced by EFS of the isolated guinea-pig main bronchus.

A pharmacological study of NK1 and NK2 tachykinin receptor characteristics in the rat isolated urinary bladder

1. We have estimated potencies of tachykinin receptor agonist and antagonist analogues in order to determine the recognition characteristics of tachykinin receptors mediating phasic contractile responses of the rat isolated urinary bladder in vitro. 2. The NK1-selective synthetic agonists, substance P methyl ester and GR73632, the synthetic NK2-selective agonists [beta-Ala8]-NKA(4-10) and GR64349, and the mammalian tachykinins, neurokinin A and neurokinin B, were assayed relative to substance P and were found to be approximately equipotent. The NK3-selective agonist, senktide, was inactive (10 microM). 3. Potencies of all these agonists were not significantly different (P > 0.05) when experiments were carried out in the presence of the neutral endopeptidase inhibitor, phosphoramidon, and the kininase II inhibitor, enalaprilat (both 1 microM). 4. The NK1-selective antagonist, GR82334, inhibited responses to substance P methyl ester in a competitive manner in the rat urinary bladder and the rat ileum, and also in the guinea-pig ileum. Markedly different pKB estimates were obtained in the rat bladder (6.38) and rat ileum (6.56) compared to the guinea-pig ileum (7.42). GR82334 (3 microM) was inactive against responses of the rat bladder to [beta-Ala8]-NKA(4-10). 5. The NK1-selective antagonist (+/-)-CP-96,345 also inhibited responses of the rat bladder and guinea-pig ileum to substance P methyl ester; however, in the rat bladder at 1 microM, this antagonist reversibly inhibited responses both to the NK2-selective agonist [beta-Ala8]-NKA(4-10) and to the muscarinic agonist carbachol (P < or = 0.01), thus showing evidence of some non-selective depressant actions. 6. The NK2-selective antagonists, MEN10207 and L-659,874, competitively inhibited responses of the rat bladder to the NK2-selective agonist [P-Ala5]-NKA(4-10) giving pKB estimates of 5.75 and 6.68,respectively. Both antagonists (1O microM) were inactive against responses to the NKI-selective agonist substance P methyl ester.7. These results support the proposal of a mixed population of NKI and NK2 receptors mediating contraction of the rat isolated urinary bladder. The NK2 receptor is characterized by a relatively low affinity for the NK2-selective antagonist MEN10207 but a high affinity for L-659,874. The NKImediated responses are inhibited by (+/-)-CP-96,345: this compound however, has non-specific depressant effects in the rat bladder at high concentration (1 microM). In contrast, the NK,-receptor peptide antagonist GR82334, did not have non-specific depressant effects and competitively inhibited NK, responses in the rat bladder and rat ileum with an affinity significantly lower than at the NK,-receptors in the guinea-pigileum.

Use of selective antagonists to dissociate the central cardiovascular and behavioural effects of tachykinins on NK1 and NK2 receptors in the rat

1. The effects of intracerebroventricular (i.c.v.) pretreatment with selective NK1 ((+/-)-CP 96,345), NK2a (MEN 10,207; MEN 10,376) and NK2b (R 396) tachykinin receptor antagonists on the cardiovascular and behavioural responses to i.c.v. substance P (SP) and neurokinin A (NKA) were studied in conscious rats. 2. SP and NKA (25 pmol) induced mean arterial blood pressure and heart rate increases of the same magnitude and duration. The cardiovascular responses to both peptides were accompanied by excessive face washing, sniffing, grooming and wet dog shakes. 3. The cardiovascular responses to SP but not to NKA were attenuated by pretreatment with a NK1 receptor antagonist, (+/-)-CP 96,345. Of the behavioural responses, only face washing was significantly inhibited. 4. The cardiovascular and behavioural effects of NKA but not of SP were significantly attenuated by pretreatment with the selective NK2b receptor antagonist, R 396. 5. The selective NK2a receptor antagonists, MEN 10,207 and MEN 10,376, did not affect the cardiovascular and behavioural responses to either SP or NKA. 6. These results suggest, firstly, that the cardiovascular and behavioural effects of i.c.v. SP are mediated by NK1 receptors; secondly, that NKA injected i.c.v. does not interact with NK1 receptors but with another type of tachykinin receptor which may belong to the NK2b subclass. These findings provide pharmacological evidence for the existence of functionally active NK2 receptors in the rat brain.

Heterogeneity of tachykinin NK-2 receptors in rabbit, guinea-pig and human smooth muscles

Recent evidence indicates that the tachykinin NK-2 receptor is heterogenous (subtypes/species variants) and the existence of NK-2A (or 'non-classical') and NK-2B (or 'classical') forms of the NK-2 receptor in mammalian tissues has been proposed. In this study we have compared the affinities of 7 linear octa- and heptapeptide derivatives of neurokinin A (4-10) and that of two cyclic hexapeptides endowed with selective NK-2 receptor antagonist properties in 5 mammalian smooth muscle preparations previously characterized as expressing the NK-2A receptor subtype (rabbit pulmonary artery and bronchus, guinea-pig bronchus, human ileum and colon) and 2 preparations previously characterized as expressing the NK-2B receptor subtype (rat vas deferens and hamster trachea). The results of this comparative study reinforce the concept of two broad categories of preparations expressing pharmacologically distinguishable forms of the tachykinin NK-2 receptor and suggest the possibility of a further heterogeneity within the previously defined NK-2A receptor subtype.

Effects on the isolated human bronchus of SR 48968, a potent and selective nonpeptide antagonist of the neurokinin A (NK2) receptors

Tachykinins produce concentration-dependent contraction of the human isolated bronchus by stimulation of receptors that belong to the NK2 type. The aim of this study was to investigate the inhibitory effects of a new, potent, and selective nonpeptide antagonist of the neurokinin A (NKA) (NK2) receptors, SR 48968 [(S)-N-methyl-N-[4-acetylamino-4-phenylpiperidino-2-(3,4-dichlorophenyl) butyl]benzamide] on human isolated airways. Our experiments were performed on human isolated bronchi obtained from patients with lung cancer. Phosphoramidon, 10(-5) M, was added to the bath to inhibit neurokinin metabolism. SR 48968 induced a parallel shift to the right of the concentration-response (C/R) curves to [Nle10]-NKA(4-10), a specific NK2 receptor agonist. The antagonism was of the competitive type, with a pA2 of 9.40 +/- 0.19 (slope = 0.95 +/- 0.08, n = 13). The (R)-enantiomer of SR 48968 was 100-fold less potent and a noncompetitive antagonist (slope = 0.56 +/- 0.11, n = 8); pA2 and slope of the racemate were 8.86 +/- 0.21 and 1.09 +/- 0.21 (n = 7), respectively. Under similar conditions, racemic CP-96,345, a nonpeptide NK1 antagonist, did not modify the C/R curves to [Nle10]-NKA(4-10) until 10(-7) M. SR 48968 did not modify C/R curves to acetylcholine, histamine, KCI, or PGF2 alpha on the human isolated bronchus. Finally, SR 48968 shifted to the right C/R curves to substance P on isolated human bronchi, whereas racemic CP-96,345 was without effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure-activity relationship study of R396, an NK2 tachykinin antagonist selective for the NK2B receptor subtype

We report on a structure-activity study of R396 (Ac-Leu-Asp-Gln-Trp-Phe-Gly-NH2), a linear hexapeptide tachykinin antagonist selective for the putative NK2B receptor subtype. Asp2, Trp4 and the C-terminal glycinamide have been challenged by classical amino acid substitutions with the aim of elucidating the structural requirements responsible for NK2 subtype selectivity. The biological activities indicate that Asp2 has a crucial role for the high affinity of R396 at the NK2B subtype: none of the analogues substituted in position 2 display higher affinity as compared to R396, regardless of the nature of the residue introduced. Trp4 has been replaced by other aromatic residues, again yielding weak antagonist or inactive compounds. Finally, the C-terminal amide appears to be crucial for affinity, the free acid analogue being devoid of biological activity. On the other hand, antagonistic activity is maintained both by the desGly pentapeptide and by the analogue bearing beta Ala in place of Gly in position 6. In conclusion, since the NK2B selectivity pattern was maintained throughout the whole series of R396 replacement analogues, we speculate that the overall conformational features of this family of linear hexapeptides favour the interaction with the NK2B receptor subtype.