Drugs are only effective if delivered to their intended targets. It is also important for doctors to be able to trace the path of drugs through the body. Now, researchers in Korea have combined both these functions—drug delivery and imaging—in unique nano‑sized packages that show great promise for cancer treatment.

The team, led by Tae Gwan Park at the Korea Advanced Institute of Science and Technology and Taeghwan Hyeon at Seoul National University, created the nanopackages from a biodegradable polymer acid called PLGA.1 The PLGA was formed into particles between 100 and 200 nanometres in size which carry and release doxorubicin, a drug widely used in chemotherapy.

Several other chemicals were added to the PLGA matrix to improve drug delivery. The surface of each PLGA nanoparticle was coated with folate—a form of vitamin B9. This means that the nanoparticles have greater affinity for cancer cells, which tend to have over‑expressed folate receptors.

Fig. 1: Tunneling electron microscope images of PLGA nanoparticles-containing different amounts of magnetite nanocrystals (darker dots)-which allow the drug containing PLGA nanoparticle to be viewed under magnetic resonance imaging and guided towards cancer cells using a magnetic field.

The researchers also added tiny crystals of magnetite—a magnetic form of iron oxide—to detect the nanoparticles by magnetic resonance imaging (Fig.1). Furthermore, the researchers used a magnetic field to directly move the nanoparticles towards areas near cancer cells.

In other forms of the nanoparticles, the researchers included tiny particles of the semiconductors cadmium selenide and zinc sulphide. These particles glow green under an optical microscope with laser irradiation, so were used to prove that the nanoparticles were capable of delivering doxorubicin inside cancer cells. Once inside, the drug can quickly penetrate the cell nucleus to break up DNA and kill the tumor.

The PLGA degraded quickest in an acidic environment. It therefore releases more of the drug when it reaches cancer tumors, which tend to be more acidic than normal tissue.

Overall, PLGA nanoparticles are more toxic to cancer cells than free molecules of doxorubicin. The researchers believe this is because cancer cells can use a function called ‘multi-drug resistance’ to flush out drug molecules—but for some reason the PLGA nanoparticles stop this effect.