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Our studies revealed decreased cytotoxicity of the nanoparticle-formulated epirubicin compared to the free drug as well as a noticeable change in the drug's intracellular localization. Epirubicin-loaded nanoparticles were internalized via endocytosis, accumulated inside endosomal vesicles and induced a two-fold stronger pro-apoptotic signal when compared to the free drug. The level of the tumor suppressor protein p53 in HeLa cells increased significantly upon treatment with free epirubicin, but remained relatively unchanged when cells were treated with equivalent dose of nanoparticle-loaded drug, suggesting a possible shift from p53-dependent DNA/RNA intercalation-based induction of cytotoxicity by free epirubicin to a caspase 3-induced cell death by the epirubicin-loaded PBCA formulation.

Human bestrophin-1 protein (hBest1) is a transmembrane channel associated with the calcium-dependent transport of chloride ions in the retinal pigment epithelium as well as with the transport of glutamate and GABA in nerve cells. Interactions between hBest1, sphingomyelins, phosphatidylcholines and cholesterol are crucial for hBest1 association with cell membrane domains and its biological functions. As cholesterol plays a key role in the formation of lipid rafts, motional ordering of lipids and modeling/remodeling of the lateral membrane structure, we examined the effect of different cholesterol concentrations on the surface tension of hBest1/POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and hBest1/SM Langmuir monolayers in the presence/absence of Ca2+ ions using surface pressure measurements and Brewster angle microscopy studies. Here, we report that cholesterol: (1) has negligible condensing effect on pure hBest1 monolayers detected mainly in the presence of Ca2+ ions, and; (2) induces a condensing effect on composite hBest1/POPC and hBest1/SM monolayers. These results offer evidence for the significance of intermolecular protein–lipid interactions for the conformational dynamics of hBest1 and its biological functions as multimeric ion channel.

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