Radioimmunoassay for ubenimex in human serum

Anti-ubenimex antibody was produced by immunization of rabbits with ubenimex-bovine serum albumin (BSA) conjugate which was synthesized by coupling ubenimex directly to BSA using 1-ethyl-3-(3-dimethyl-aminopropyl)carbodiimide. The resulting antibody exhibited little cross-reactivity with p-hydroxyubenimex or (2S,3R)AHPA, (2S,3R)-3-amino-2-hydroxy-4-phenylbutanoic acid present in human serum as metabolites. Ubenimex in human serum could be measured selectively without prior drug extraction and purification. The standard curve prepared using the present assay method gave good linearity in the range 0.25-25 ng per assay tube. The detection limit was 125 pg per assay tube. The concentrations of ubenimex in human serum determined by the present method were in good agreement with those obtained by GC-SIM. The present method with its high sensitivity and specificity may be a valuable tool for the study of the pharmacokinetics of ubenimex.