Potential antitumor activity of novel DODAC/PHO-S liposomes

In recent studies, we showed that synthetic phosphoethanolamine (PHO-S) has a great potential for inducing cell death in several tumor cell lines without damage to normal cells. However, its cytotoxic effect and selectivity against tumor cells could increase with encapsulation in cationic liposomes, such as dioctadecyldimethylammonium chloride (DODAC), due to electrostatic interactions between these liposomes and tumor cell membranes. Our aim was to use cationic liposomes to deliver PHO-S and to furthermore maximize the therapeutic effect of this compound. DODAC liposomes containing PHO-S (DODAC/PHO-S), at concentrations of 0.3-2.0 mM, prepared by ultrasonication, were analyzed by scanning electron microscopy (SEM) and dynamic light scattering. The cytotoxic effect of DODAC/PHO-S on B16F10 cells, Hepa1c1c7 cells, and human umbilical vein endothelial cells (HUVECs) was assessed by MTT assay. Cell cycle phases of B16F10 cells were analyzed by flow cytometry and the morphological changes by SEM, after treatment. The liposomes were spherical and polydisperse in solution. The liposomes were stable, presenting an average of similar to 50% of PHO-S encapsulation, with a small reduction after 40 days. DODAC demonstrated efficient PHO-S delivery, with the lowest values of IC50% (concentration that inhibits 50% of the growth of cells) for tumor cells, compared with PHO-S alone, with an IC50% value of 0.8 mM for B16F10 cells and 0.2 mM for Hepa1c1c7 cells, and without significant effects on endothelial cells. The Hepa1c1c7 cells showed greater sensitivity to the DODAC/PHO-S formulation when compared to B16F10 cells and HUVECs. The use of DODAC/PHO-S on B16F10 cells induced G2/M-phase cell cycle arrest, with the proportion significantly greater than that treated with PHO-S alone. The morphological analysis of B16F10 cells by SEM showed changes such as bleb formation, cell detachment, cytoplasmic retraction, and apoptotic bodies after DODAC/PHO-S treatment. Cationic liposomal formulation for PHO-S delivery promoted cytotoxicity more selectively and effectively against B16F10 and Hepa1c1c7 cells. Thus, the DODAC/PHO-S liposomal formulation presents great potential for preclinical studies

Determination of Halide Concentrations at the Interface of Zwitterionic Micelles by Chemical Trapping: Influence of the Orientation of the Dipole and the Nature of the Cation.

The interfacial concentrations of Cl(-) and Br(-) in aqueous zwitterionic micelles were determined by chemical trapping by analyzing product yields from spontaneous dediazoniation of micelle-bound 2,6-dimethyl-4-hexadecylbenzenediazonium ion. Interfacial concentrations of Cl(-) and Br(-) in 3-(N-hexadecyl-N, N-dimethylammonio) propane sulfonate, HPS, micelles were higher than in bulk solutions prepared with Li(+), Na(+), Rb(+), Cs(+), tetramethylammonium (TMA(+)), Mg(+2), and Ca(+2) salts. In contrast, the interfacial concentrations of Cl(-) and Br(-) were generally lower than in bulk solution in hexadecylphosphoryl choline, HDPC, micelles for all salts except Mg(+2) and Ca(+2). In both HPS and HDPC micelles the interfacial concentration of Br(-) was higher than that of Cl(-), showing that binding is anion selective. The cation had a large effect on the interfacial concentration of halide ions with HDPC micelles decreasing in the order Ca(2+) > Mg(2+) >> Li(+) > Na(+) > K(+) > Cs(+) > Rb(+) >> TMA(+). These results are the first direct and extensive determination of local halide ion concentration at the surface of zwitterionic micelles, and they demonstrate that chemical trapping methodology will work in membranes at physiologically relevant salt concentrations. Copyright 1999 Academic Press.