It’s springtime, as well as pollen time, so some of us are painfully aware of mucus. It turns out mucus is also the source of grief for scientists who are trying to deliver drugs through the lungs on nanoparticles. The nanoparticles end up trapped in the lung mucus barrier. Now researchers have developed biodegradable, medically safe polymer coveringsÂ for the nanoparticles that let them get past the mucus barrier and into the body to do their job.
Justin Hanes and colleagues at Johns Hopkins University were working with synthetic nanoparticles made from poly(lactic-co-glycolic acid), a material approved for drug delivery applications. The nanoparticles by themselves can’t burrow through the mucus layers in the lung so they get ejected from the body.
But Hanes’ team had previously shown that coating the nanoparticles with the uncharged hydrophilic polymer, poly(ethylene glycol) (PEG), greatly boosted the nanoparticles’ ability to get through the mucus. But the problem was that attaching PEG to the nanoparticles demands a covalent bond. The creation of the covalent bond would mean that regulatory authorities, like the U.S. Food and Drug Administration (FDA), will classify the material as a new chemical entity. It would have to go through expensive and time-consuming experiments to get FDA approval.
So the researchers took a different tack, which they described in their recent scientific paper.Â They covered the nanoparticles with a copolymer that had two strips of PEG on either side of a stretch of poly(propylene oxide) (PPO). The PEG-PPO-PEG materials are called Pluronics. The FDA considers them to be adequately safe for medical applications.
The hydrophobic PPO adsorbed to the surface of the nanoparticle. The PEG parts formed a layer around the nanoparticle. Because the polymer and nanoparticle interacted with each other non-covalently, the system was not a new chemical entity for FDA purposes.
Satyanarayana Somavarapu of the University of London’s School of Pharmacy describes the study as ‘excellent’ and says that the improved rate of diffusion provided by simply treating the nanoparticle with Pluronics ‘shows tremendous potential in overcoming one of the key barriers to nanoparticle delivery systems where there is mucus’.
Source:Â ”Polymer coat helps nanoparticles penetrate mucus,” Chemistry World, 02/23/11
Source: “Biodegradable Nanoparticles Composed Entirely of Safe Materials that Rapidly Penetrate Human Mucus,” Angewandte Chemie International Edition, 02/18/11
Image by medical illustrator Patrick J. Lynch, used under its Creative Commons license.
Rajendrani "Raj" Mukhopadhyay is a science writer and editor who contributes news stories and feature articles on scientific advances to a variety of magazines. Raj holds Ph.D. in biophysics from Johns Hopkins University.