Can the virus that causes the common cold also cure cancer? A company that has exploited an odd link between the mildest and the most serious of diseases hopes the answer may be yes.
Scientists at Onyx Pharmaceuticals of Richmond, Calif., report that a specially tailored strain of adenovirus, the cause of colds, can kill tumor cells while leaving normal cells unaffected. Standard treatments like radiation and chemotherapy kill all cells indiscriminately, causing severe side effects.
The Onyx researchers, led by the company’s chief scientific officer, Dr. Frank McCormick, report in today’s issue of the journal Science that they have had promising results in animal experiments, with 60 percent of tumors disappearing when injected with adenovirus.
Studies to test the safety of the procedure in patients began in April. The trials are not intended at this stage to gather statistically meaningful data about efficacy, but “we have seen some responses and they are encouraging,” said Dr. Gail Eckhardt of the Cancer Therapy and Research Center in San Antonio.
“In a couple of patients we have seen some regression after a single injection,” she said. “This is proof of principle that you can inject the tumor.”
McCormick declined to comment on the possible efficacy of the virus, saying it is “easy” to be duped “into thinking something is happening when it’s not.”
Other experts doubt that the approach can work, since almost everyone has been exposed to cold viruses and has antibodies that are likely to fight Onyx’s adenovirus as well.
“I don’t think it’s likely to work but I’m hoping it does,” said Dr. Arnold Berk, a microbiologist at UCLA.
Dr. Robert Weinberg, a cancer researcher at the Massachusetts Institute of Technology, said, “This approach is very clever, very provocative, but it’s hard to know yet if it will work in humans.”
McCormick acknowledged these objections but said the immune system may in fact prove helpful because it is likely to attack any tumor cells that the virus has infected, thus helping to kill them.
The Onyx approach is based on a scheme involving a protein that is the guarantor of a cell’s normality. The pivotal protein, known as p53, blocks the cell from dividing if it detects any foreign or damaged DNA, and then commands the cell to destroy itself.
Many human cancers consist of cells that have run amok because their p53 gene is damaged and the defective guarantor protein it makes fails to order the aberrant cells to commit suicide.
Adenoviruses come into the picture because their life cycle requires a delicate dance of death with the p53 suicide machine. When the virus infects a cell, it must first induce the cell to divide in order to replicate and then go on to infect other cells. But as the cells enter division, the p53 safety mechanism is triggered.
The adenovirus has a second genetic trick, a chemical missile that snaps onto p53 and blocks it from sending the cell into its self-destruct mode, thus giving the virus time to reproduce itself. The variant virus developed by Berk lacks the gene that makes the anti-p53 system, and hence cannot reproduce itself in normal cells.