Dextran-methylprednisolone succinate as a prodrug of methylprednisolone: in vitro immunosuppressive effects on rat blood and spleen lymphocytes

The in vitro immunosuppressive activity of a conjugate of methylprednisolon e (MP) with dextran 70 kDa (DEX-MPS) was tested using the lymphocyte prolif eration assay after stimulation of lymphocytes with concanavalin 4 (Con-A). Blood and spleen lymphocytes, isolated from drug-free male Sprague-Dawley rats, were used in the assay. First, the optimum concentration of Con-A for stimulation of lymphocytes was determined. The inhibition of the lymphocyt e proliferation was then tested in the presence of 0.25, 0.5, 1.0: 2.5, 5.0 , 10, 20, and 50 nM concentrations (MP equivalent) of DEX-MPS or free MP. T he maximum stimulation of lymphocytes with Con-A was observed at mitogen co ncentrations of 2.5 and 10 mug/ml for the spleen and blood lymphocytes, res pectively. For free MP, sigmoidal relationships were observed between the e ffect (% inhibition of lymphocyte proliferation) and the logarithm of MP co ncentration. Additionally, the maximum inhibitory effect (I-max) and MP con centration producing half of I-max (IC50) were, respectively, 98% and 1.38 nM For the blood and 86% and 3.1 nM for the spleen lymphocytes. For MP conj ugated to dextran, the response-log concentration curves were substantially shifted to the right with IC50 values of 40 and 52 nhl for the blood and s pleen lymphocytes, respectively. It is concluded that compared with free MP I the steroid attached to dextran has minimal immunosuppressive activity. T herefore, to be effective in vivo, DEW-MPS should release MP in the body. ( C) 2000 Elsevier Science B.V. All rights reserved.