Tumours targeted by stealth particles
they believe may some day target tumour cells and deliver
medication to specific locations. The polymer shell protection
ensures the drug can circulate longer without being removed by the
immune system.
The idea of using nanoparticles as a therapeutic 'Trojan horse', attacking the cancer cell by stealth from within, is entirely new, and demonstrates the possibilities nanotechnology has, especially in drug delivery.
The researchers, from Penn State University, first produce nano-sized powders of the drug they wanted to deliver and encapsulated them in a polymer nanoshell.
The drug used for this project was paclitaxel - an anti breast cancer drug - and dexamethasone - a steroid frequently used to treat eye inflammation. This shell allows the drug to travel in stealth mode through the bloodstream.
The researchers tested their nanoshell in cell culture and found that it had less phagocytosis - removal of the drug - during a 24-hour period than the unencapsulated drug.
Working at nanometre dimensions makes them preferentially taken into the tumour. They are small enough to pass through tumour vessels, but too large for the pores of normal vessels.
"A layer-by-layer self-assembly technique was used to encapsulate core charged drug nanoparticles in a polymeric nanoshell," the researchers commented, as they presented their results at the 230th American Chemical Society Meeting, Washington, D.C.
Normally, drugs, especially the toxic drugs used for chemotherapy, trigger the human immune system into action, but, with the polymer shell for protection, these drugs can circulate longer without being removed.
"If the drugs do not trigger an immune response, then lower levels of drug can be used than currently are necessary in chemotherapy," said Pishko.
Combined with longer retention in the body, the researchers engineered the nanoparticle shells to target specific cells by attaching a functionalised polymer to the shell.
They designed this tentacle-like projection to target a receptor on a tumour cell, or a specific location in the eye, for example. Once the drug arrives via the blood to the tumour or eye, it attaches and slowly releases its contents.
This type of drug delivery system works especially well in such highly vascularised areas such as tumours and the eye, because the drug can travel right up to the target area.
Delivery to areas in the brain would not be feasible because of the blood brain barrier that prevents foreign substances from moving from the blood into the cells of the brain.
"For targeting, we could exploit the fact that cancer tumours have a lot more folic acid receptors and target those," said Pishko. "We could also use specific monoclonal antibodies to target specific tumours."
The researchers also considered delivery of drugs to specific type cells, like those in the eye. This type of stealth targeting drug delivery system could also deliver genes or gene fragments in gene therapy.
Nanotechnology has empowered scientists to manipulate materials at the atomic level. This remarkable ability enables manufacturers to offer materials with customisable properties such as unsurpassed electrical as well as optical conductivity and mechanical strength.
There are several European research programmes relating to nanomaterials that are carried out in collaboration with industry majors such as BASF Corporation and The Dow Chemical Company. These programmes are conducted with specific commercialisation plans.
In addition, governments in Europe are also making funding available to support nanotechnology. Most recently, Germany made a €50m fund available to help start-up companies in the 'bionanotechnology' sector, while the European Union has committed €15.6m to applications in life sciences and in 2003 the UK government earmarked £90 million for micro- and nanotechnology research across all sectors.
