Simulation of Drug Release from PLGA Particles In Vivo

Specific targeting of tissues and/or cells is essential for any type of drug delivery system because this determines the efficacy and side effects of the drug. Poly lactic-co-glycolic acids (PLGA) have long been used as biomaterials for drug delivery due to their excellent biocompatibility and biodegradability. Direct visualization of PLGA particles is feasible even within tissues, and cell specificity of the drug delivery system is normally assessed by using labeled particles. However, particle labeling alone does not address factors such as the release and distribution of the drug. Thus, it is desirable to set up a simulation system of drug release and distribution in vivo. In the present study, we aimed to establish a method to simulate drug distribution in PLGA drug delivery by using Hoechst 33342 as an imitating drug. Our approach enabled us to identify, isolate, and characterize cells exposed to Hoechst 33342 and to deduce the concentration of this fluorescent dye around both targeted and nontargeted cells. We believe that the method described herein will provide essential information regarding the specificity of cell targeting in any type of PLGA drug delivery system. 1. Introduction Drug delivery systems (DDS) are designed to increase the therapeutic properties of a drug and reduce its side effects. Poly lactic-co-glycolic acids (PLGA), which have been approved by the US FDA, are frequently used as biomaterials for drug delivery due to their excellent biocompatibility and biodegradability [1]. PLGA particles are prepared by single- or double emulsion-solvent evaporation. In particular, a water-in-oil-in-water (w/o/w) method is widely used to encapsulate water soluble drugs [2]. The mechanism of degradation of PLGA particles generally involves a hydrolytic process. The maximum effect of a drug can only be achieved by strictly controlling target cell specificity. Moreover, reduced exposure of nontargeted cells to the drug may prevent undesirable side effects. In the context of in vivo distribution of PLGA “particles,” visualization of the particles themselves is feasible when markers such as fluorescent dyes are used [3–5]. However, other details of the DDS, such as the type and number of cells exposed to the drug, in situ drug concentration, and functional consequence for each cell population after drug exposure, are often more difficult to determine. These problems frequently arise with PLGA DDS. For example, although drug behavior depends on the chemical properties of the drug in question, the distribution of the drug is also affected by other