Water-soluble prodrugs of cyclosporine A with tailored conversion rates
A novel type of water-soluble prodrugs of cyclosporine A (CsA) is described, featuring a modular system of an enzyme-cleavable group, a solubilizing moiety and a chemodegradable spacer attached to the hydroxyl function of (4R)-4-[(E)-2-butenyl]-4-,N-dimethyl-L-threonine (MeBmt)-1 of CsA. The chemical synthesis of these double prodrugs proceeds in high yield and purity and allows for a systematic study of the influence of the structural parameters upon physicochemical and pharmacological properties. The evaluation of the chemical and enzymatic stability results in differential values of the conversion rates (minutes to several hours) in support of an enzyme-triggered release of the parent drug as the rate-limiting step. In vitro studies show that the designed prodrug systems can be regarded as soft prodrugs in being devoid of cyclophiline A (CypA) binding and that complete conversion to the parent drug occurs in whole rat blood, setting the stage for therapeutic use.