MONOCLONAL-ANTIBODIES TO THIOGUANINE - INFLUENCE OF COUPLING POSITIONON FINE SPECIFICITY

Thioguanine derivatives with reactive ester groups at positions 6,7, o r 9 of the purine ring were synthesized and coupled to a protein carri er. The purified protein derivative of tuberculin was used as the carr ier for immunizing bacillus Calmette-Guerin primed mice. This led to h igh antibody titers against the homologously coupled hapten, and splee n cells from the immunized mice were used to produce monoclonal antibo dies against thioguanine. All monoclonal antibodies were selected for their ability to recognize free thioguanine and were analyzed for thei r fine specificity by inhibition experiments with a panel of thiopurin e derivates. The specificity of the monoclonal antibodies showed a str ong dependence on the coupling position of the thioguanine. Within eac h group of monoclonal antibodies, raised against one of the three diff erent conjugates, there was a high degree of heterogeneity, with antib odies differing in their binding according to the substitution on the thioguanine analogues used in the inhibition experiments. This panel o f antibodies may be used for quantitative assays of thiopurines and th eir metabolites in patients undergoing treatment with thioguanine, 6-m ercaptopurine, and azathioprine.