Fighting Cancer With a Virus
When the herpes simplex virus contains a certain gene, it becomes very good at fighting cancer. That's according to a recent study done in part by researcher Timothy Cripe, MD, PhD, at Cincinnati Children's Hospital Medical Center. The study, published in the February 15 issue of Cancer Research, tested the herpes virus's ability to kill notoriously difficult tumors--neuroblastoma and peripheral nerve sheath tumors. When the virus was given an extra gene called "TIMP3," it killed a great deal of the cancer in human tissue samples and prolonged the lives of mice.
"This is not the first time that the herpes simplex virus has been used to kill cancer cells," said Cripe. "But by adding the TIMP3 gene, we were able to completely halt the growth of some tumors and in other cases make them shrink and even disappear."
Viruses are good vehicles for getting cancer-fighting genes into cells because they naturally insert their own genes into a cell after they enter the human body. Scientists can remove the disease-causing genes from a virus and add cancer-fighting genes, like the TIMP3 gene.
The TIMP3 gene works against tumors by reducing the tumor's ability to make new blood vessels (which tumors use to steal nutrients from the body), and by helping the virus to stay in the tumor longer. TIMP 3 also inhibits enzymes called "matrix metalloproteinases," known as MMPs. "MMPs are important in tumor growth because they degrade the tissue in between cancer cells, allowing the cancer to migrate and spread farther," said Cripe. "Also, they generate other proteins that help the cancer cells to grow."
Pharmaceutical companies have recently tested drugs that inhibit MMPs, but the results were not impressive, probably because the inhibitors were not able to concentrate enough in the tumor tissue to have any real effect. However, when genes in the cell are able to manufacture the inhibitor from the inside out, like in this trial, things seem to change. The mice with the TIMP3 gene-carrying virus lived almost four times longer than untreated mice, and more than twice as long as mice that got the virus without the gene.
The results are encouraging, but it will be some time before doctors can use this breed of virus to treat people. "It takes a long time to develop this kind of research into clinical trials," said Cripe. "And during that time, we may find something even better."
