Sulfate-conjugated methylprednisolone: Evaluation as a colon-specific methylprednisolone prodrug and comparison with sulfate-conjugated prednisolone and dexamethasone

Methylprednisolone 21-sulfate sodium (MPS) was prepared and evaluated as a colon-specific methylprednisolone prodrug and its colon-specific property was compared with prednisolone 21-sulfate sodium (PDS) and dexamethasone 21-sulfate sodium (DS), reported previously as colon-specific prodrugs of the glucocorticoids. The synthetic process and yield of MPS was simple and high. The apparent partition coefficient of methylprednisolone (MP) was greatly reduced by sulfate conjugation. The sulfate conjugates MPS, PDS, and DS were (bio)chemically stable in the homogenates of the upper intestine. In marked contrast, the sulfate conjugates were deconjugated to liberate the corresponding glucocorticoids in the cecal contents. Although the rates of deconjugation were not significantly different, the corresponding glucocorticoids were accumulated with distinct profiles depending on the metabolic susceptibility of the unconjugated glucocorticoids to microbial reductase(s). Upon oral administration of the sulfate conjugates to rats, the plasma concentrations of the conjugates were extremely low and the urinary recoveries were less than 5% of the doses. These results suggest that, like PDS and DS, MPS administered orally is delivered efficiently to the large intestine followed by deconjugation to liberate MP and the metabolic susceptibility of the unconjugated glucocorticoids may affect therapeutic availability of the sulfate conjugates.