ABNORMAL DIFFERENTIATION OF THYMOCYTES INDUCED BY FREE CYCLOSPORINE IS AVOIDED WHEN CYCLOSPORINE BOUND TO N-(2-HYDROXYPROPYL)METHACRYLAMIDECOPOLYMER CARRIER IS USED

Background. The side effects of cyclosporine (CsA)-including nephrotox icity and abnormal differentiation of thymocytes developing in the thy mus-can be decreased or even avoided using targeted conjugates of CsA, where both targeting moiety and drug are bound to water-soluble polym eric carrier based on N-(2-hydroxypropyl) methacrylamide (HPMA). Metho ds. Irradiated, syngeneic bone marrow transplanted-mice (BALB/c and A/ Ph) were treated intraperitoneally for 4 weeks with 20 mg/kg of free C sA, HPMA-conjugated CsA, or antibody-targeted HPMA-bound CsA, Immunohi stology of the thymus was performed together with two-color flow cytom etry to detect the effect of different forms of CsA on individual thym ocyte subpopulations. Results. We have shown that free CsA strongly ab rogated T-cell development, The appearance of mature thymocytes expres sing CD3(high) is almost completely inhibited (1.8%) after fr ee CsA t reatment, whereas these cells are well detectable in controls (22%) an d HPMA polymer-bound CsA-treated animals (19%). Immunohistological stu dies have shown acellular rests of the medulla after free CsA treatmen t, whereas well-stained medullary thymocytes were detected in controls and after exposure to antibody-targeted HPMA-conjugated CsA. Conclusi ons. HPMA-conjugates of CsA are generally more specific in their targe ting to T lymphocytes. It was found that nonspecific binding of CsA to erythrocytes and plasma lipoproteins is significantly reduced using a nti-CD3 targeted, HPMA polymer-bound CsA. In addition, the entry of th ese macromolecules into the thymus is limited-probably due to the bloo d-thymus barrier-and HPMA conjugates of CsA, unlike free drug, do not abrogate T-cell development in bone marrow transplanted mice.