Altered Cold Viruses Invade, Kill Cancer Cells

Two treatments that use cold viruses to invade and destroy cancer cells are showing promise in experiments on gravely ill patients.

Both approaches involve one of the hottest ideas in cancer research - finding ways to exploit the genetic flaws that allow cancer cells to divide and spread endlessly.

Cells become cancerous when they develop a series of genetic errors that let them escape the body’s standard repair and surveillance machinery. The most common of these flaws - present in about half of all cancers - are in a gene called p53. This gene is a kind of genetic watch dog that ordinarily stops cells from reproducing if any of their other genes are damaged.

The two experimental approaches were described Tuesday at a meeting of the American Society for Clinical Oncology. Both use cold viruses to carry in genes that exploit cancer’s reliance on a damaged p53 gene.

The treatments are in very early stages of development, but both have shown at least some effect against tumors when given to patients who have failed all standard treatments.

The new approaches were developed by researchers at M.D. Anderson Cancer Center in Houston and Onyx Pharmaceuticals of Richmond, Calif. Both involve genetically manipulating the adenovirus, a usually modest microbe that causes colds and intestinal upsets.

At M.D. Anderson, scientists weakened the adenovirus and gave it a normal copy of the p53 gene. Then they injected it into the tumors of 20 patients with advanced lung cancer. The intention was to supply a good p53 gene that would take over for the bad one.

“We hope this will induce the cells to kill themselves,” said Dr. Stephen Swisher, one of the researchers.

Even in such gravely ill patients, there are signs this is happening. After 5-1/2 months of treatment with both the cold virus and chemotherapy, the cancer is stable in eight patients and has shrunk in one. Among those getting the virus alone, five have gotten worse, five are stable, and one has improved.

The Onyx researchers have created a form of the adenovirus that won’t hurt healthy cells.

But if it invades a cancer cell that lacks p53, it will kill the cell and release more virus that in turn attacks neighboring cancer cells.

Dr. Daniel Von Hoff and others from the Cancer Therapy and Research Center in San Antonio have tested this on 27 patients with head and neck cancers.

Nineteen have received at least two injections, and in three of them, the tumors have shrunk substantially.