THE POLYOXYETHYLENE POLYOXYPROPYLENE BLOCK COPOLYMER POLOXAMER-407 SELECTIVELY REDIRECTS INTRAVENOUSLY INJECTED MICROSPHERES TO SINUSOIDAL ENDOTHELIAL-CELLS OF RABBIT BONE-MARROW

Small colloidal particulates (150 nm and below, in diameter) can be redirected specifically to the rabbit bone marrow following intravenous administration by coating their surface with the block co-polymer poloxamer-407, a non-ionic surfactant. The coated colloids are sequestered by the sinusoidal endothelial cells of the bone marrow and are accumulated in dense bodies within these cells. The uptake of poloxamer-407-coated colloids by marrow endothelial cells suggests that the steric repulsive barrier, imposed by the polyoxyethylene segment of the polymer, to particle-cell interaction can apparently be overcome by a specific interaction mechanism(s) with the cell surface. Such a dramatic uptake cannot be achieved with other block co-polymers of similar structure to poloxamer-467. The application of the current model for the site-specific targeting of drug carriers to bone marrow and the prevention of the adherence of metastases of tumours which selectively colonize the bone marrow endothelium is discussed.