Radioimmunological determination of cyproterone acetate

A sensitive and specific radioimmunoassay for cyproterone acetate in serum has been developed. Antiserum was raised in rabbits by immunization with a conjugate of cyproterone acetate-11 alpha-hemisuccinate and bovine serum albumin. Radioactive tracers with high specific activities were synthesized by coupling the hemisuccinate with [3H]-tyrosine methyl ester of [125I]-iodohistamine. Competition studies with substances structurally related to cyproterone acetate have revealed that the structures of ring A and B are mainly responsible for binding to the antibody.