1. Pharmacological assessment of spantide II analogues
G R Strichartz, Y L Wang, K Wong, Z Y Wang, R Håkanson, D M Feng, K Folkers, S R Tung Eur J Pharmacol . 1994 Aug 1;260(2-3):121-8. doi: 10.1016/0014-2999(94)90327-1.
We have studied the structure-activity relationship of a series of tachykinin receptor antagonists based on spantide II. Fifteen novel peptides were tested for their ability to antagonize the electrically evoked tachykinin receptor-mediated response in the isolated rabbit iris sphincter muscle. Substitution or deletion of one to three amino acids in the spantide II sequence caused significant changes in biological activity. Eight of the novel analogues were found to be as potent as or more potent than spantide II and some were found to have better water solubility. We tested the selectivity for different tachykinin receptors of spantide II and two of the eight most potent analogues. They all interacted with tachykinin NK1 (rabbit jugular vein) and tachykinin NK2 (rabbit pulmonary artery) receptors with pA2 values of about 6.5-7.5 at the NK1 receptor and of 5.9-7.2 at the NK2 receptor, while being inactive at the tachykinin NK3 receptor (rat portal vein). Spantide II and the novel analogues were without effect on electrically evoked cholinergic responses of the isolated rabbit iris sphincter and on electrically evoked sympathetic responses of the guinea-pig vas deferens; moreover, they were without local anaesthetic-like effects on action potentials of the frog sciatic nerve, which suggests that they do not produce a general neurosuppressive effect. They were as effective as or slightly less effective than spantide II in causing histamine release from rat peritoneal mast cells.
2. Stability and degradation profiles of Spantide II in aqueous solutions
Narayanasamy Kanikkannan, Loice Kikwai, Mandip Singh, R Jayachandra Babu Eur J Pharm Sci . 2006 Feb;27(2-3):158-66. doi: 10.1016/j.ejps.2005.09.005.
Spantide II is an 11 amino acid peptide that has been shown to be a potential anti-inflammatory agent. The stability and degradation profiles of Spantide II in aqueous solutions were evaluated with the long-term objective of developing topical formulations of this compound for various skin disorders. The stability profile of Spantide II at various temperature and pH conditions was monitored by high performance liquid chromatography (HPLC) and the resulting degradation products were identified by liquid chromatography-mass spectroscopy (LC-MS). Forced degradation of Spantide II was performed at extreme acidic (pH 10.0) conditions and by addition of hydrogen peroxide (oxidizing agent). The degradation pattern of Spantide II followed pseudo first-order kinetics. The shelf life (T90%) of Spantide II in aqueous ethanol (50%) was determined to be 230 days at 25 degrees C. Spantide II was susceptible to degradation at pH 5 and showed maximum stability at pH 3-5. The stability under various pH conditions indicates that Spantide II was most stable at pH 3.0 with a half-life of 95 days at 60 degrees C. Spantide II degradation was attributed to hydrolysis of peptide bonds [Pro2-(pyridyl)Ala3, (nicotinoyl)Lys1-Pro2, Pro4-PheCl2(5), Trp7-Phe8, Phe8-Trp9, Nle11-NH2), racemization of the peptide fragments that resulted from hydrolysis, cleavage and formation of (nicotinoyl)Lys1-Pro2 diketopiperazine. In the presence of an oxidizing agent, Pro(2,4) residues degraded by ring opening to form glutamyl-semialdehyde and by bond cleavage at Pro4 to form 2-pyrrolidone, while Phe(5,8) degraded to form 2-hydroxyphenylalanine. Spantide II was found to be stable in aqueous medium with T90% of 230 days. The major degradation pathways of Spantide II were identified as hydrolysis, racemization, cleavage and formation of diketopiperazine.
3. Spantide II, an effective tachykinin antagonist having high potency and negligible neurotoxicity
N Asano, S Leander, R Håkanson, D M Feng, K Folkers, Z Weisenfeld-Hallin Proc Natl Acad Sci U S A . 1990 Jun;87(12):4833-5. doi: 10.1073/pnas.87.12.4833.
Spantide (D-Arg1-Pro2-Lys3-Pro4-Gln5-Gln6-D-Trp7-Phe8-D-Trp9-++ +Leu10-Leu11-NH2) was introduced as a tachykinin antagonist in 1984 and has served as a starting point in the design of new antagonists that have proven to be more effective and have exhibited no neurological side effects. The most remarkable and unpredictable structural change that significantly increased potency was deletion of a methylene group by changing Gln6 to Asn6. On the basis that D-Arg1 and Lys3 of spantide contribute to neurological side effects, many new designs led to D-Lys(Nic)1-Pro2-Pal(3)3-Pro4-D-Phe(Cl2)5-Asn6-D-Trp7-Phe8-D-Trp9- Leu10-Nle11- NH2 [spantide II, where D-Lys(Nic) is N epsilon-nicotinoyllysine, Pal(3) is 3-(3-pyridyl)alanine, D-Phe(Cl2) is 3,4-dichloro-D-phenylalanine, and Nle is norleucine], which is a potent antagonist without neurotoxicity. Spantide II, an undecapeptide, has a total of seven substitutions in the sequence of substance P, consisting of two natural L amino acids, and one unnatural L amino acid, and four unnatural D amino acids. The pi- and sigma-bond amino acid substituents of substance P and spantide II are compared toward a future understanding of the essential substituents for mechanism and inhibition binding. Spantide II has five pi-bond and six sigma-bond amino acid moieties, and substance P has two pi-bond and nine sigma-bond moieties.
