3'-Azido-3'-deoxythymidine (AZT, Zidovudine), clinically approved by FDA to treat human HIV infection, is a typical member of the nucleoside analogues. Recently, the well known clinical limitations related with AZT therapy (especially dose-related toxicity, short half-life in plasma, inability to reach the brain) have prompted the synthesis of different types of 5'-O-conjugates of zidovudine. Accordingly, we designed and synthesized an AZT prodrug, by its conjugation with the ursodehoxycholic acid (UDCA-AZT). The aim of this study was to characterized the in vitro permeability across human epithelia and the stability in human plasma, whole blood and homogenates of brain and liver of AZT and AZT-prodrug. Transport studies were conducted across the spontaneously arising human retinal pigment epithelium (HRPE) cell line, which forms polarized epithelial monolayers when cultured on porous filters placed in a two-chamber Millicell device, with an apical and a basolateral side at different composition of medium. The result is a useful epithelium playing in vitro characteristics similar to those of the blood-retinal barrier and the choroid plexus [1]. Interestingly, hydrolysis rate of UDCA-AZT increased progressively from plasma to whole blood, brain and liver. Moreover, prodrug significantly counteracted the efflux system in the transport of AZT, potentially extending its permanence in the apical side, comparable to an in vivo neural compartment. Every further detail concerning stability and permeability will be discussed.

[1] Strauss O. The retinal pigment epithelium in visual function. Physiol Rev, 2005, 85(3):845–881.