The new method, developed by scientists at the University of Buffalo (UB) and recently published in Molecular Pharmaceutics, may lead to treatments that exploit the advantages of photodynamic therapy (PDT) and that have the potential to reduce drug accumulation in normal tissues.
Not only does the new system allow the guided and precise delivery of drugs to chosen areas of the body, a tumour for example, avoiding serious side effects, but it also enhances the cellular uptake of the PDT drugs it transfers.
For their drug delivery vehicle, researchers used polymer micelles, which are nanosized, water-dispersible clusters of polymeric molecules, and so are excellent nanocarriers for PDT drugs, which are mostly water-insoluble.
Along with the photodynamic drug, they encapsulated inside the nanocarriers iron oxide nanoparticles, which allowed them to respond to externally applied magnetic fields.
"This is a novel way to enhance drug delivery to cells," said Paras Prasad, executive director of UB's Institute for Lasers, Photonics and Biophotonics.
"The externally applied magnetic field acted as a kind of remote control, directing the nanocarriers to the targeted area in the cell culture."
In the experiments, nanocarriers were shown to be efficiently taken up in vitro by cultured tumour cells in the area exposed to the magnetic field, as demonstrated by confocal microscopy.
Once the magnetic field was applied, the concentration of drug inside the tumor cells in the target area increased.
"The magnetically guided drug delivery would allow for the use of lower concentrations of the drug to deliver a therapeutic dose, thus significantly reducing the amount of PDT drug that accumulates in normal tissue," said Prasad.
"Because the nanocarriers proved to be significantly stable and because they retained the PDT drugs, we are optimistic that they will be able to deliver a wide range of therapies to tumors or other disease sites in the body without any significant loss in the circulatory system or in normal tissues."
Although PDT is one of the most promising treatments for cancer as well as cardiovascular, dermatological and ophthalmic diseases, it has numerous side effects, including the patient's strong sensitivity to light for four to six weeks after treatment.
This is because PDT exploits the propensity of tumours to retain higher concentrations of photosensitive drugs than normal tissues, so when exposed to laser light, these drugs generate toxic molecules that destroy the cancer cells and the resulting sensitivity stems from the drugs that accumulate in the skin.
While the team demonstrated their method with PDT drugs, Prasad said the technique would be useful in delivering gene therapy, chemotherapy or practically any kind of pharmaceutical treatment into cells.
Preliminary studies in live animals have indicated that an applied magnetic field can effect a localized accumulation in the tumor site and the team is beginning in vivo studies on the new drug delivery method.