Novel Transporter Targeted Lipid Ester Prodrugs of Cidofovir and Sustained Release Formulations for Cytomegalovirus Infection

Abstract

Cidofovir (CDF) has shown potential in vitro and in vivo antiviral activity against cytomegalovirus (CMV) retinitis. However, low CDF permeability due to its hydrophilic nature limits its effectiveness. Furthermore, physicochemical properties such as high water solubility (170 mg/mL) and log p (-3.9) of CDF are unfavorable for passive transcellular absorption. Therefore, we have tested novel transporter targeted lipid prodrugs of CDF and their nanoparticle formulations to achieve sustain drug delivery for the treatment of CMV retinitis. These prodrugs contains lipid linker of different carbon chain length (e.g. C2, C6, and C12) carrying minimum two functional groups to link one end with CDF and another end with ligand (biotin) targeting sodium dependent multivitamin transporter (SMVT). We have successfully synthesized three biotinylated (B) derivatives (B-C2-cCDF, B-C6-cCDF, and B-C12-cCDF) and two lipid ester derivatives (C6-cCDF and C12-cCDF) of cCDF. Structure and purity of all the produgs were confirmed using ³¹P NMR and LC-MS/MS analysis. All synthesized prodrugs were characterized in terms of its physicochemical properties, in vitro cellular accumulation, cytotoxicity, transporter affinity, ocular tissue stability and in vitro antiviral potency against various virus strains. Furthermore, prodrug loaded PLGA nanoparticle formulations were prepared and characterized. Overall, improvement in physicochemical properties, lipophilicity, interaction with SMVT transporter, higher tissue-buffer partition coefficient and rapid conversion into parent molecule (in retina–choroid) were observed with higher lipid chain length (B-C12-cCDF > B-C6-cCDF > B-C2-cCDF). In vitro antiviral activity shows B-C12-cCDF as the potential prodrug candidate for future in vivo evaluation. Sustained release (~3 weeks) formulation of B-C12-cCDF loaded PLGA nanoparticles may serve as a viable intravitreal delivery approach for the treatment of CMV retinitis. Based on the above finding we hypothesized that lipid raft facilitates enhanced prodrug interaction with cell membrane and thereby assist docking of targeted ligand into the binding domain of transporter. Therefore, current novel approach combines both lipids mediated facilitate diffusion and transporter targeted delivery to generate synergistic drug effect. Overall, these findings indicate that transporter-targeted lipid analogue of CDF could be a viable strategy for the treatment of CMV retinitis.