Nanoparticles in drug delivery.

Alkylcyanoacrylates can be polymerized in acidified aqueous media by a process of anionic polymerization. The small particles produced tend to be monodisperse and have sizes in the range of 20 to 3000 nm depending upon the polymerization conditions and the presence of additives in the form of surfactants and other stabilizers. The polyalkylcyanoacrylate nanoparticles so produced have been studied in recent years as a possible means of targeting drugs to specific sites in the body, with particular emphasis in cancer chemotherapy. The small colloidal carriers are biodegradable and drug substances can be incorporated normally by a process of surface adsorption. The review by Davis and others considers the formulation of nanoparticles, the important physicochemical variables such as pH, monomer concentration, added stabilizers, ionic strengths, etc., as well as the characteristics of the particle so created in terms of surface charge, particle size, and molecular weight. Monodisperse particles in the range of 20 to 3000 nm can be obtained. In addition, by the use of stabilizers such as dextran and its derivatives, which can be incorporated into the nanoparticle surface by a process of polymer grafting, it is possible to make nanoparticles with interesting surface characteristics and different surface charges (sign). The stability of nanoparticles in vitro and their biodegradation in vivo are examined, and the possible formation of toxic products such as formaldehyde is highlighted. Alternative biodegradable acrylates are mentioned. Drugs can be incorporated into nanoparticles by either direct incorporation during the polymerization process or adsorption to preformed nanoparticles. The efficiency of the incorporation and the release characteristics of model compounds as well as anticancer drugs are discussed. Methods for examining these processes, including the determination of adsorption and desorption, kinetics, and isotherms, are mentioned. Selectivity in drug targeting can, in theory, be achieved by the attachment of some form of homing device, normally a monoclonal antibody or a lectin. Work in vitro and in vivo, where nanoparticles have been coated with monoclonal antibodies, is described. Finally, methods for the labeling of nanoparticles with gamma-emitting radionuclides are presented, and results obtained in animal species are given.