Stabilization and activation of Pluronic micelles for tumor-targeted drug delivery

In order to be used as drug carriers, Pluronic micelles require stabilization to prevent degradation caused by significant dilution accompanying IV injection. This article studies three routes of Pluronic micelle stabilization. The first route was direct radical crosslinking of micelles cores which resulted in micelle stabilization. However, this compromised the drug loading capacity of Pluronic micelles. In the second route, a small concentration of vegetable oil was introduced into diluted Pluronic solutions. This decreased micelle degradation upon dilution while not compromising the drug loading capacity of oil-stabilized micelles. The: third route was a novel technique based on polymerization of the temperature-responsive LCST hydrogel in the core of Pluronic micelles. The hydrogel phase was in a swollen state at room temperature, which provided a high drug loading capacity of the system. The hydrogel collapsed at physiological temperatures which locked the core of micelles thus preventing them from fast degradation upon dilution. This new drug delivery system was called Plurogel(R). Phase transitions in Plurogel(R) caused by variations in temperature or concentration were studied by the EPR. The effect of Pluronic concentration in the incubation medium on the intracellular uptake of two anti-cancer drugs was studied. At low Pluronic concentrations, when the drugs were located in the hydrophilic environment, drug uptake was increased, presumably due to the effect of a polymeric surfactant on the permeability of cell membranes. In contrast. when the drugs were encapsulated in the hydrophobic cores of Pluronic micelles, drug uptake by the cells was substantially decreased. This may be advantageous in the prevention of undesired drug interactions with normal cells. Ultrasonication enhanced intracellular drug uptake from dense Pluronic micelles. These findings permitted the formulation of a new concept of a localized drug delivery. (C) 1999 Elsevier Science B.V. All rights reserved.