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.