Blood clearance and organ distribution of intravenously administered polymethacrylic nanoparticles in mice

Polymethacrylic nanospheres (mean diameter 0.25-0.30 microns), prepared by aqueous emulsion copolymerization, were developed as a new site-specific drug delivery system. The nanoparticles were labeled either with indium-111 or iodine-125, and after a single iv injection of labeled particles into mice, their blood clearance and organ distribution were analyzed. A rapid clearance of 111In-labeled nanoparticles from the blood circulation to the mononuclear phagocyte system (MPS) was visualized using external scintigraphic imaging. From 10 to 60 min, radioactivity measurements in blood and organs (liver, spleen, kidneys, lungs, heart) showed that the 125I-labeled nanospheres were rapidly removed from the bloodstream (distribution half-life approximately 3-5 min) and mainly deposited in the liver (60% of the administered dose, 10 min after administration). Up to 1 h, radioactivity in heart and lungs remained insignificant, while in the kidneys, radioactivity levels increased from 8 to 11%.