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
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,
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.
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"