Abstract

Drug binding to plasma proteins is routinely determined during drug development. Albumin polymorphisms c.1075G>T (p.Ala359Ser) and c.1422A>T (p.Glu474Asp) were previously shown to alter plasma protein binding of a drug candidate (4-[1-[3-chloro-4-[n′-(2-methylphenyI)ureido]phenylacetyI]-(45)-fluoro-(2S)-pyrroIidine-2-yl]methoxybenzoic acid, D01-4582) in a colony of Beagles. Our study investigated the hypothesis that drug-protein binding in plasma from dogs with albumin H1 (reference) allele would be greater than in plasma from albumin H2 allele dogs (c.1075G>T and c.1422A>T) (n = 6 per group). Plasma protein binding extent of four drugs (D01-4582, celecoxib, mycophenolic acid, and meloxicam) was evaluated using ultracentrifugation or equilibrium dialysis. Free and total drug concentrations were analyzed by liquid chromatography-mass spectrometry. The albumin gene coding region was sequenced in 100 dogs to detect novel gene variants, and H1/H2 allele frequency determined in a large and varied population (n = 1446 from 61 breeds and mixed-breed dogs). For meloxicam, H1 allele plasma had statistically significant higher free drug fractions (P = 0.041) than H2 allele plasma. No significant difference was identified for plasma protein binding of D01-4582, celecoxib or mycophenolic acid. c.1075G>T and c.1422A>T were the most common SNPs in canine albumin, present concurrently in most study dogs and occasionally identified independently. In conclusion, albumin polymorphism c.1075G>T and c.1422A>T seems to affect the extent of plasma protein binding of meloxicam but not D01-4582, celecoxib, mycophenolic acid.