Cancer researchers may have found new `magic bullet'

Researchers in the US may have discovered a new form of "magic bullet" against cancer, a treatment that selectively attacks cancer cells while leaving healthy cells untouched.

The original magic bullet concept was based on developing antibodies that would seek out only cancer cells, with either the antibodies themselves or toxins carried by them doing the damage. Unfortunately the technique never quite delivered and researchers had only limited success.

Dr Richard Youle and colleagues at the biochemistry section, surgical neurology branch of the National Institutes of Health in Bethesda, Maryland, describe a wholly new approach in the current issue of Nature Biotechnology.

They engineered one of the human body's own proteins, ribonuclease A (RNaseA), to be 5,000 times more toxic to cancer cells than healthy cells. RNaseA is an enzyme which chops up RNA, the essential messaging system that enables a cell to function.

There are inhibitors in the cell which limit the actions of RNaseA, but Dr Youle's version does not respond to the inhibitors. Instead it runs amok in the cancer cell, attacking RNA and eventually killing off the cell.

The group managed to strongly target the cancer cells by adding the human iron storage protein, transferrin, to its construct.

Cancer cells have extra iron demands and so have an increased number of receptors for transferrin. This in turn brings more of the damaging RNaseA to cancer cells than to healthy cells.

Although the results are preliminary, Dr Youle believes that the RNaseA approach holds considerable promise for the development of new therapies against cancer. These would be expected to have fewer harmful side-effects than current treatments.