Charging ahead

Recently, drug formulators have been experimenting with dendrimers: spherical polymers about 2–10 nm in size. A dendrimer's charge can be determined by the composition of different amine groups on its surface. The charge can in turn dictate the dendrimer's use.

For example, says Nan, positively charged dendrimers can be used in gene therapy by attracting and binding with negatively charged DNA. This interaction "not only makes the entire polymer–DNA complex compact, it also, because of its overall positive charge, has the likelihood of interacting with the cell membranes, which are slightly negative." The positive charge of the polymer–DNA complex facilitates endocytosis, the process by which the cell absorbs the complex. Scientists choose the dendrimer with the appropriate charge to ensure that it is absorbed by the particular target cell.

Nanoparticulate delivery systems have several applications for cancer treatment, notes Oliver. Some binding ligands are tumor-specific and selectively target specific tissue or tumor types. Using site-specific ligands is a way to enhance a drug's bioavailability, she adds.

Nanoparticles can also be used to package other types of anticancer agents such as siRNA, Oliver says. Besides delivering therapies, nanoparticles can be designed as imaging agents.

In addition to cancer, scientists can treat diseases of the central nervous system by designing nanoparticles that deliver drugs across the blood-brain barrier. Diseases of the spleen or liver can likewise be treated with nanoparticles that target phagocytic cells of the reticuloendothelial system.

Conclusion

Nanoparticulate drug-delivery systems are increasingly viewed as an advantageous solution for biological drugs. This technique can mitigate some of these drugs' unique problems by safeguarding stability and preserving protein structure. In addition, nanoparticles provide efficient treatment by enabling targeted delivery and controlled release. This method of drug delivery, like most others, requires attention to certain manufacturing and biological considerations to be successful. Judging by the current interest and previous successes, however, nanoparticulate drug-delivery systems seem to be a viable and promising strategy for the biopharmaceutical industry.

For more on this topic, see "A Broad Palette for Biological Drug Delivery"