In spite of their clinical promise and market potential, biological drugs present unique challenges for drug formulators and manufacturers. For example, their size and structure make these drugs difficult to deliver to the patient without stimulating an immune reaction. And the lability of these drugs makes it difficult to store them for any period of time.
To overcome these challenges, drug companies and researchers are devising many programs for delivering biologically based drugs. Among the most interesting are nanoparticle-based drug-delivery systems.In February 2008, Upperton (Nottingham, UK), a biotechnology company specializing in spray-drying and particle technologies, and Novozymes (Bagsvaerd, Denmark) announced that they would commercialize their jointly-owned "rP-nano" technology. The technology uses the natural binding properties of recombinant protein nano-particles to provide targeted drug delivery and enhance bioavailability. The rP-nano technology produces nanoparticles from peptides and proteins, including monoclonal antibodies and enzymes, without denaturing them.
Andrew Yates, senior group leader of drug-product research and development with UCB (Brussels), says that polymeric nanoparticles "have the potential to change our way of thinking" about drug-product delivery. Ping Yeh, director of protein-pharmaceutical development at Biogen Idec (Cambridge, MA), explains that polymeric nanoparticles used for protein-drug delivery are often made of polysaccharides or poly(lactide-co-glycolide) copolymers. These small, colloidal particles can be about 50–1000 nm in size. When a manufacturer mixes a protein with a polymer, the polymer forms as a nanoparticle or sphere around the protein.
One benefit of polymeric nanoparticles is that they can maintain the stability of biological drugs, according to Anjan Nan, research assistant professor at the University of Maryland School of Pharmacy. Manufacturers can encapsulate or conjugate a protein drug in a nanoparticle to provide direct protection against unfavorable biological environments.
Coating nanoparticles' surface with biocompatible, water-soluble polymers such as polyethylene glycol makes them nonimmunogenic. This tactic also reduces the chance that the reticuloendothelial system of the body (i.e., the liver, spleen, and macrophages) will absorb the nanoparticles. The coating minimizes nonspecific adsorption effects such as protein binding. All of these effects enhance the stability of the biotech product, Nan explains. Safeguarding a drug's stability enhances its bioavailability and increases its effective half-life.