title: Stability and in vitro metabolism of the mitogenic neuropeptide antagonists [D-Arg1,D-Phe5, D-Trp7,9, Leu11]-substance P and [Arg6, D-Trp7,9, MePhe8]-substance P (6-11) characterized by high-performance liquid chromatography.
abstract: The substance P (SP) analogues [D-Arg1, D-Phe5, D-Trp7,9, Leu11]-SP and [Arg6, D-Trp7,9, MePhe8]-SP (6-11) (antagonists D and G, respectively) are under consideration as new anticancer drugs. In this report, the stability and in vitro metabolism of both antagonists in up to seven different media (water, 1 M acetic acid, human plasma, nude mouse liver and WX 322 human SCLC xenograft homogenized in either 1 M acetic acid or phosphate buffered saline (PBS), pH 7.4) have been characterized by both isocratic and gradient elution reversed-phase HPLC. Antagonist D was stable (never > 13% degradation over 24 h, at 37 degrees C) in water, 1 M acetic acid and plasma but was metabolized by PBS liver homogenates (10%, w/v) sequentially to two stable metabolites with a half life of 0.98 h at a concentration of 500 micrograms ml-1. The major pathway of degradation of antagonist G appeared to be C-terminal methionine oxidation (particularly in plasma) as well as hydrolysis, with even aqueous solutions being significantly affected at low concentrations of peptide (0.1 micrograms ml-1, half life 20.9 h at 37 degrees C). Stable metabolites of antagonist G were also detected in incubations with PBS liver homogenates (half life 1.53 h at 500 micrograms ml-1, 37 degrees C). Overall, the data presented indicate that the modifications made to SP have been relatively successful in preserving chemical and biological stability.
authors.affiliation: Imperial Cancer Research Fund, Medical Oncology Unit, Western General Hospital, Edinburgh, UK.
authors.forename: J
authors.initials: J
authors.lastname: Cummings
authors.forename: A
authors.initials: A
authors.lastname: MacLellan
authors.forename: S P
authors.initials: SP
authors.lastname: Langdon
authors.forename: J F
authors.initials: JF
authors.lastname: Smyth
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism*; D018288:Carcinoma, Small Cell / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004355:Drug Stability; D006207:Half-Life; D006801:Humans; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism*; D013373:Substance P / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D010446:Peptide Fragments; C046958:substance P (6-11), Arg(6)-Trp(7,9)-Me-Phe(8)-; D013373:Substance P; C045800:substance P, Phe(5)-Trp(7,9)-Leu(11)-