Interfacial behavior of PEGylated lipids and their effect on the stability of squalenoyl-drug nanoassemblies.

Squalenoyl-gemcitabine (Sq-Gem) and squalenoyl-dideoxycytidine (Sq-ddC) are amphiphilic prodrugs that self-assemble in water to form nanoassemblies (NAs) with well-defined structures and size. However, like other drug nanocarriers, these nanoassemblies are rapidly cleared from the blood stream by the reticulo-endothelial system. By adding squalenoyl-PEG (Sq-PEG) or cholesterol-PEG (Chol-PEG) to the squalenoyl prodrugs, composite nanoassemblies (CNAs) were formed, with different sizes and structures. The effect of the PEG-lipids on the formation and stability of these nanoassemblies was assessed by transmission electron microscopy, quasi-elastic light scattering and surface tension measurements in various conditions. The results revealed different stabilities with time for Sq-ddC and Sq-Gem nanoassemblies in aqueous medium, the latter being much less stable than the former. They also demonstrated that the presence of Sq-PEG or Chol-PEG in composite Sq-ddC nanoassemblies contributed to their rapid destabilization. The analysis of the adsorption kinetics of Sq-PEG into a prodrug monolayer below and above its critical aggregation concentration allowed getting a better insight into prodrug-lipopolymer molecular interactions, and their consequences on the formation of composite prodrug nanoassemblies.

Anti-HIV efficacy and biodistribution of nucleoside reverse transcriptase inhibitors delivered as squalenoylated prodrug nanoassemblies.

Due to their hydrophilic nature, most nucleoside reverse transcriptase inhibitors (NRTIs) display a variable bioavailability after oral administration and a poor control over their biodistribution, thus hampering their access to HIV sanctuaries. The limited cellular uptake and activation in the triphosphate form of NRTIs further restrict their efficacy and favour the emergence of viral resistance. We have shown that the conjugation of squalene (sq) to the nucleoside analogues dideoxycytidine (ddC) and didanosine (ddI) leads to amphiphilic prodrugs (ddC-sq and ddI-sq) that spontaneously self-organize in water as stable nanoassemblies of 100-300 nm. These nanoassemblies can also be formulated with polyethylene glycol coupled to either cholesterol (Chol-PEG) or squalene (sq-PEG). When incubated with peripheral blood mononuclear cells (PBMCs) in vitro infected with HIV, the NRTI-sq prodrugs enhanced the antiviral efficacy of the parent NRTIs, with a 2- to 3-fold decrease of the 50% effective doses and a nearly 2-fold increase of the selectivity index. This was also the case with HIV-1 strains resistant to ddC and/or ddI. The enhanced antiviral activity of ddI-sq was correlated with an up to 5-fold increase in the intracellular concentration of the corresponding pharmacologically active metabolite ddA-TP. The ddI-sq prodrug was further investigated in vivo by the oral route, the preferred route of administration of NRTIs. Pharmacokinetics studies performed on rats showed that the prodrug maintained low amounts of free ddI in the plasma. Administration of (3)H-ddI-sq led to radioactivity levels higher in the plasma and relevant organs in HIV infection as compared to administration of free (3)H-ddI. Taken together, these results show the potential of the squalenoylated prodrugs of NRTIs to enhance their absorption and improve their biodistribution, but also to enhance their intracellular delivery and antiviral efficacy towards HIV-infected cells.