COMPARISON OF THE BINDING-KINETICS OF ANTIBODY-TARGETED N-(2-HYDROXYPROPYL) METHACRYLAMIDE (HPMA)-BOUND DOXORUBICIN IN-VITRO AND IN-VIVO

Antibody-targeted conjugates have been previously shown to have antitu mour and immunosuppressive activity both in vitro and in vivo. In this study we have examined the binding kinetics of antibody-targeted doxo rubicin (DOX) based on N-(2-hydroxypropyl) methacrylamide (HPMA) copol ymers following i.v. administration to mice (DOX concentration 5mg/kg) or after in vitro incubation with the cells for different time interv als using fluorescence analysis. We have found that binding of the con jugate to the target cell subpopulation is more effective and much fas ter in vivo than in vitro. In vivo, 1 min was long enough for reproduc ible binding of the conjugate to peripheral blood leukocytes (PBL), wh ile 15 min was necessary for significant binding to splenocytes. To re ach the same situation in vitro it was necessary to incubate the cells with the conjugate for at least 1 h. By fluorescence analyses it was shown that in vitro these antibody-targeted drugs are bound to PBL, sp lenocytes and thymocytes. After i.v. administration the conjugates wer e bound to PBL and splenocytes but were not present on the surface of thymocytes. These alterations in pharmacokinetics may account for the decreased toxicity and improved efficacy reported previously.