Determination of two neuropeptide growth factor antagonists, [D-Arg1,D-Phe5,D-Trp7,9,Leu11]-substance P and [Arg6,D-Trp7,9,N-MePhe8]- substance P(6-11), by high-performance liquid chromatography with electrochemical detection.

The neuropeptide growth factor antagonists [D-Arg1,D-Phe5,D-Trp7,9,Leu11]-substance P (D) and [Arg6,D-Trp7,9, [corrected] N-MePhe8]-substance P(6-11) (G) are currently undergoing preclinical evaluation as potential anticancer agents and clinical trials are planned for G in the near future. A reversed-phase high-performance liquid chromatographic separation has been developed which is both sensitive (limit of detection 250 pg/263 fmol for G; 500 pg/330 fmol for D) and selective, based on electrochemical detection of the two tryptophan residues present in each peptide. Two ion-pairing agents were included in the isocratic mobile phase to eliminate adsorption of the peptides onto the analytical column. Extensive sample clean-up procedures have been developed for plasma, tissue and tumour based on solid-phase extraction. Precision and accuracy of each assay was 91.3 +/- 16.9% (between-day) for G and 99.3 +/- 16.9% (between-day) for D. The assays were able to detect the intact peptides and a number of their metabolites in plasma, liver and the WX 322 SCLC human xenograft in nude mice for at least 6 hr after administration of therapeutic and pharmacological doses.