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Last Updated: Monday, 25 July 2005, 15:21 GMT 16:21 UK
Jab cuts hepatitis virus levels
Image of test tube and blood
Hepatitis B can lead to cancer
Scientists have harnessed genetic technology to develop a potentially potent treatment for the B strain of the viral liver disease hepatitis.

They have found a way to inject tiny molecules into the blood that switch off genes that play a vital role in the reproduction of the virus.

The jabs have cut viral levels in infected animals by around 90%.

The Nature Biotechnology study, by Sirna Therapeutics, raises hopes of new drugs to tackle the disease.

It is interesting, but we are long, long way from clinical application
Dr Mark Thursz

Hepatitis B is the most common serious liver infection in the world. It is thought to be the leading cause of liver cancer.

The World Health Organization estimates that hepatitis B infections lead to more than one million deaths every year.

There are vaccines to protect against infection, but drug treatments are expensive and relatively ineffective.

Protective fat

The researchers incorporated the key molecules - called small interfering RNAs (siRNAs) into fat-like particles that protect them from attack by digestive enzymes in the blood.

These enzymes normally degrade RNA molecules in cells or the circulation.

Not only did this increase the stability when injected into mice, it also reduced the dose needed for therapeutic effect.

Previous studies suggested that the amounts of siRNA needed to achieve a therapeutic effect in people far exceed safe levels of exposure.

The researchers say their work paves the way for the development of human jab that is both safe and effective.

In their experiments, mice carrying replicating hepatitis B virus were given daily doses of encapsulated siRNAs.

The new formulation was much more effective than previous attempts to use unprotected siRNAs - and worked at much lower doses.

It also showed signs of blocking the virus when administered just once a week.

The researchers plan to begin the first human trials next year.

Lead researcher Dr David Morrissey said: "Our research shows low doses of siRNA introduced into an animal's circulatory system can reach its intended target, in this case hepatitis B virus in the liver, and result in a very significant reduction of virus levels.

"Based on this, we are confident we will be able apply these approaches to developing efficacious therapies for people."

Dr Mark Thursz, secretary of the British Association for Study of the Liver, told the BBC News website it was a major achievement to translate siRNA technology from a cell culture into a living animal.

However, he warned that there was still a long way to go before it could be applied to humans.

"The problem is that you might get lots of problems with toxicity when you scale up to a human-sized animal from a mouse-sized animal," he said.

Dr Thursz said other technologies - such as therapeutic vaccination - had failed to work in humans despite producing promising effects in mice.

Professor Roger Williams, consultant hepatologist at University College London, agreed that a human application was a long way off.

But he said potentially the therapy might benefit patients who did not respond to current anti-viral drugs, or those who carried the virus without showing any symptoms.

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