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Immunochemistry of conjugates prepared from serum albumins and acridine nitrogen mustards (ICR mutagens).

Antibodies elicited in rabbits by immunization with conjugates prepared from serum albumins and nitrogen mustard derivatives of quinacrine (atebrin) were found to have strong binding sites complementary to the quinacrine hapten. The characteristic absorption spectrum of quinacrine made possible accurate determinations of the antigen-antibody composition of the serological precipitates. Conclusive evidence that such antibodies, in addition to reacting with the quinacrine component of heterologous protein test conjugates, bind quinacrine itself, as well as closely related acridine haptens, was provided by quantitative inhibition studies. Atebrin and the hydroxy precursors of several heterocyclic nitrogen mustards caused more than a 50% inhibition of the antigen-antibody reactions. The antibodies elicited by the quinacrine-protein conjugates in ascites tumor-bearing mice substantially neutralized the antitumor effectiveness of the low dosages (0.5 to 2.0 mumol/kg) of the acridine nitrogen mustards that were required for a demonstration of chemotherapeutic activity. In contrast, nitrogen mustard, which has no quinacrine moiety, was not affected. Immunization with unaltered serum albumin had no influence on the activity of the acridine nitrogen mustards. Quantitative in vitro inhibition studies allowed satisfactory predictions in vivo immunological reactivity.