RNAi scores victory against Crohn's disease in mice

Thousands of people suffering from the debilitating gut condition Crohn’s disease could experience relief from their symptoms through a technique that blocks production of a key protein in the inflammation process.

Motomu Shimaoka’s team at Harvard Medical School, Boston, US, have used RNA interference to prevent expression of cyclin D1 in mice with a standard experimental model of inflammatory bowel disease, dextran sulphate-induced colitis.

RNA interference involves introducing into cells a double strand of RNA corresponding to the nucleic acid sequence of the target gene. This causes the destruction of the equivalent messenger RNA so ’silencing’ the gene and preventing expression of the relevant protein. 

Its discovery in 1998 by Andrew Fire and Craig Mello earned them the 2006 Nobel prize for medicine. But although their discovery has become a vital technique for molecular biology research it has not yet fulfilled its potential as a therapeutic method.

Shimaoka’s patented technique avoids two of the main pitfalls currently preventing the method being used more widely - by improving the delivery method and stability of the RNA particles. They encapsulated roughly 400 RNA molecules each within nanometer scale (about 80 nm diameter) liposomes stabilised by attaching the protein hyaluronan to the surface. They also attached monocolonal antibodies to the liposomes so that they would bind to integrin, a protein found on the surface of the target leukocyte cells in the bloodstream.

Dramatic results

When RNA was injected into mouse with colitis there was a dramatic reduction in intestinal tissue damage and suppression of leukocytes cells invading the gut wall. The mice were also able to absorb food through their gut wall again and started to regain weight. The team found that their results were due to a drop in the level of two cell signalling molecules (cytokines), TNF-alpha and IL-12, that normally drive inflammation and are produced as a result of cyclin D1 synthesis. They also found that the mice were making more of a protective cytokine called IL-10.

By picking out the specific immune cells responsible for regulating the inflammation process, the Harvard researchers hope to reduce the RNA dose needed to treat the disease - reducing the risk of side-effects.

’As no leukocyte-targeted delivery technologies have been tested in vivo for their capacity in gene silencing, it hard to say how much this would reduce the dose. But in general, roughly 10 to 100 times more siRNAs (small interfering RNA molecules) would probably be required for sufficiently robust gene silencing in vivo,’ Shimaoka told Chemistry World.

Powerful technology

As well as potentially helping the one in 400 people in the West affected by inflammatory bowel diseases, the same method could be used to treat a wide range of other diseases.

Angela Tyner of the University of Illinois College of Medicine researches the biology of cells lining the gut. ’This powerful new technology, that combines RNA interference with targeted delivery, has exciting potential both for identifying factors involved in the aetiology and pathogenesis of Crohn’s disease, as well as development of new therapies for this disease and many other conditions,’ she said.

Bernard Mahon, from the National University of Ireland, Maynooth, warns that the method needs further testing to prove that it can overcome the potential hazards of administering RNAi to patients. ’Nevertheless, the Harvard team have shown at least in principle that therapeutic use of siRNA is not a forlorn hope,’ he told Chemistry World.

John Bonner