HONG KONG (Reuters) - Using ultrasound and powerful magnets, researchers in Taiwan managed to deliver anti-cancer drugs directly to brain tumours in mice, and they hope to refine the less invasive technique so it can be used on people.

The human brain is separated from the blood stream by a tightly knit layer of cells called the blood brain barrier (BBB), which protects it from harmful substances in the blood. But that also means it is very difficult to deliver drugs to the brain.

Researchers in Taiwan attempted to get around this problem using highly focused ultrasound to temporarily disrupt the BBB so tiny drug-laced magnetic particles can be pushed through.

Once inside the brain cavity, these particles are guided to tumours using strong magnetic fields from magnetic resonance imaging (MRI) machines, they wrote in a paper published on Tuesday in the Proceedings of the National Academy of Sciences.

"The main purpose of my method is to increase the concentration of the chemotherapy (anti-cancer drugs) in the brain," said lead author Kuo-Chen Wei, chief neurosurgeon at the Chang Gung Memorial Hospital in Taoyuan, Taiwan.

Wei said temozolomide — the leading treatment for the most common form of brain cancer — was administered orally but the amount getting into the brain or the site of the tumour was too low. Temozolomide is sold as Temodar by Merck & Co.

"It can go through the blood brain barrier but in very small amounts. The concentration is very low so the tumours always recur," Wei said in a telephone interview from Taiwan.

Brain cancer drugs can also be injected, but usually in huge doses to ensure that adequate concentrations reach affected areas. Patients may also opt for the more invasive method of surgery.

Demand for more effective, less invasive brain cancer treatments has gained urgency in recent years because cancer patients are being kept alive longer, which means chances of their cancer spreading to the brain are higher, Wei said.

In the study, Wei and colleagues applied ultrasound to the brains of mice after injecting the animals with drug-carrying magnetic particles. They then guided the particles to the tumour sites with the help of MRI.

Mice treated with this combined therapy lived longer than mice given single therapies of ultrasound, magnetic targetting, conventional treatment or no treatment at all.