Development of an antibody to actinomycin D and its application for the detection of serum levels by radioimmunoassay.

An antibody specific for actinomycin D (Act D) has been developed and used in a rapid, sensitive radioimmunoassay for detection of this anticancer drug in serum. The 2-amino group of the heterocyclic chromophore of Act D was covalently coupled to available free carboxyl groups of bovine serum albumin with carbodiimide. The resulting complex was then used for the production of a specific antibody to Act D in two male New Zealand rabbits. Antibody production was of sufficient titer in both rabbits to allow the development of a radioimmunoassay for the free drug which is rapid and sensitive enough to accurately measure 0.1 pmol of Act D. The antibody produced was characterized to be immunoglobulin G by virtue of its ability to bind to Protein A:Sepharose columns. With the use of Act-D analog, actinomine, the antibody was characterized to be specific for the pentapeptide portion of the molecule. Pharmacokinetic analysis of serial serum samples obtained from a patient who received the drug i.v. revealed a biphasic response with an alpha-serum half-life of 1.78 and a beta serum half-life of 34 min. An i.v. injection of Act D into a dog and assay of serum concentration revealed a similar biphasic response with an alpha serum half-life of 0.78 min and a beta-serum half-life of 208 min.