DETERMINATION OF 2 NEUROPEPTIDE GROWTH-FACTOR ANTAGONISTS, [D-ARG(1),D-PHE(5),D-TRP(7,9),LEU(11)]-SUBSTANCE-P AND [ARG(6),D-TRP(7,9),N-MEPHE(8)]-SUBSTANCE-P(6-11), BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION

N-MePhe8]-substance P(6-11) (G) are currently undergoing preclinical e valuation as potential anticancer agents and clinical trials are plann ed 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 re sidues present in each peptide. Two ion-pairing agents were included i n the isocratic mobile phase to eliminate adsorption of the peptides o nto the analytical column. Extensive sample clean-up procedures have b een developed for plasma, tissue and tumour based on solid-phase extra ction. Precision and accuracy of each assay was 91.3 +/- 16.9% (betwee n-day) for G and 99.3 +/- 16.9% (between-day) for D. The assays were a ble 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 do ses.