A new multi-talented player has just emerged on the field of potential anticancer agents.

Poor prognosis for a cancer patient is often associated with their having high levels of certain proteins called 'matrix metalloproteinases', or MMPs. Erkki Koivunen of the University of Helsinki, Finland, and colleagues have made a special peptide molecule – a short protein that is made up of a characteristic sequence of amino acids- that targets these MMPs. They report in Nature Biotechnology [August 1999] that this new molecule blocks the action of two of the metalloproteinases called MMP-2 and MMP-9, which are both implicated in cancer growth, without affecting the normal function of other, biologically useful MMPs.

Moreover, this new peptide packs an extra punch. The peptide has a special affinity for the sites in the body where new blood vessels are growing, a process called 'angiogenesis'. Developing their own network of new blood vessels is essential for the survival of tumours to survive because they need constant nourishment. As angiogenesis is always going on around a tumour, it acts like a homing beacon for the peptide, luring the molecule directly to the area of cancerous growth.

When tested in mice, the new peptide was specific for angiogenic blood vessels. And, building on its ability to inhibit MMPs, the peptide was able to prevent the invasive growth of human tumour cells that had been transplanted into mice, thus increasing the survival of the mice.

MMPs as a group can help to rearrange the tissue surrounding cells. They are important for normal functions in the body, such as wound repair. However, only two – MMPs 2 and 9 – seem to be harnessed by tumours for their own use. Other inhibitors of MMPs are already in clinical trial, but they are all general inhibitors and not selective for the two crucial players.

Many other cancer drugs are not directed specifically to the part of the body where the tumour is growing, hence the large number of side effects associated with chemotherapy. Because the new peptide is so small – just ten amino acids – and so specific for the areas where there is tumour growth, researchers might be able to combine it with other drugs. This way it could not only act upon a tumour, but also deliver other useful but non-specific therapies to it at the same time.

Judah Folkman, in an accompanying editorial, comments on the number of possibilities for using such a peptide. He speculates on the potential for "targeting brain tumours with drugs or proteins that do not cross the blood-brain barrier," and for targeting substances which hamper angiogenesis to particularly 'angiogenic' sites such as the eye.

However, it is worth noting that this peptide has still only been tested briefly in mouse models.