How to Starve a Tumor

By Christine Gorman

It is the point of no return for many cancer patients. A clump of malignant cells in the body has fooled some nearby blood vessels into reaching out and embracing it. Now the tiny mass can soak up all the nutrients it needs to become a solid tumor and a major, life-threatening menace. Not much can stop it from growing until its cells spread, or metastasize, throughout the body, traveling along those same blood vessels to far-distant points in the lungs, bones and brain.

For years, doctors have searched for ways to cut those crucial supply lines and, in effect, starve their patients' tumors to death. But the biology of blood-vessel growth is so complicated that most of their efforts have failed. Last week scientists from the Scripps Research Institute in La Jolla, California, announced that they may have found an effective strategy. In a study published in the journal Cell, the Scripps researchers report that they have discovered a single biochemical switch that triggers the growth of blood vessels in almost all tumors in laboratory animals. By knocking out the switch with two proteins that they have developed, the researchers caused the blood vessels to dissolve. Deprived of their food supply, the tumors quickly shrank and, in some cases, disappeared entirely.

What is particularly exciting about the potential treatments is that unlike more traditional cancer therapies, they do not appear to damage normal tissue. Instead, the proteins interfere with a step that is important only in the creation of new blood vessels. Arteries, veins and capillaries that have been in existence for some time seem to be unaffected. Furthermore, the scientists found that the blocking agents they had created were so powerful that only a single injection was needed to produce unexpectedly dramatic results. "We're a ways from treating human beings," cautions David Cheresh, an immunologist who led the Scripps research team. "But if this theoretical approach is successful, it should have a major impact in the treatment of cancer."

Two companies are already planning to test the antitumor proteins in people. However, clinical trials probably will not begin until 1996 at the earliest. One of the most important issues that scientists will have to address is whether the blocking agents will also prevent the body from forming new blood vessels during the normal course of repairing cuts and other wounds. In addition, researchers must pay particular attention to the proteins' safety for women. The creation of new blood vessels is a regular part of the menstrual cycle and crucial to pregnancy as the fetus grows and develops. So any protein that dissolves new blood vessels may not be appropriate for younger women who have not yet entered menopause.

Even though much more research has to be done, the Scripps findings look promising. As doctors and their patients know all too well, malignant tumors have a nasty habit of outwitting whatever treatments are aimed at them. A one- two punch that deprives the tumor of its blood supply while at the same time attacking it with more traditional weapons could prove to be a powerful strategy in the fight against cancer.