ABSTRACT
INTRODUCTION Proteins are a versatile class of biopolymers whose functional properties are dictated by their amino acid composition. The biodegradation of proteins into simple amino acids makes them attractive polymers for drug delivery applications. As a result, protein polymers are being increasingly investigated for various nanoenabled drug delivery systems (1). In fact, the first protein-based nanoparticulate system is already in the market. Albumin-bound paclitaxel nanoparticles (Abraxanetm) was approved by the U.S. Food and Drug Administration (FDA) in 2005. In general, nanosystems used in drug delivery range in size from 100 to 1000 nm and are prepared using natural or synthetic polymers or lipids. The drug is encapsulated inside the nanosystem (nanocapsule or nanospheres) or is entrapped in the matrix of the nanosystem (nanoparticles). Alternatively, drugs or other agents of interest are adsorbed, complexed, or conjugated to the surface of the nanosystems. Proteins offer a number of advantages over synthetic polymers. Unlike synthetic polymers, which usually have a single type of functional groups, proteins have numerous functional groups (–NH2, –COOH, and –SH) for covalent and noncovalent modifications of the nanosystems. A distinct advantage over synthetic polymers is the proven biocompatibility of proteins. Furthermore, they are biodegradable and are broken down into nontoxic by-products. Protein polymers are derived from animals or plants and are, therefore, devoid of monomers or initiators that are found in synthetic polymers. However, the composition and purity of protein biopolymers are difficult to control. Similarly, it is important to protect the protein from premature proteolytic degradation in the body. Although most of the proteins are generally safe, nonautologus proteins can be immunogenic (2). Recombinant DNA (rDNA) technology or combination of synthetic and protein polymers is used to address these limitations of protein polymers (3,4).
