Viruses to treat metastatic cancers

There exists a "type" of cancer that is common yet rarely discussed—metastatic cancer, or cancer that has spread from the part of the body where it originated (the primary tumor) to another (such as lungs, bones or liver). Although much research is being done to combat primary tumors, there still exists a crucial need to find a treatment that can be effective against metastatic cancer, or "mets." Could a virus be the answer that finally beats the mets?

Researchers are looking into harnessing viruses to infect, multiply within and subsequently destroy cancer cells; the virus targets tumors without affecting normal tissue. Several types of these viruses have been developed to date, with names like adenovirus, poxvirus and picornavirus. Even the herpes simplex virus is under consideration for this type of use. Another class of viruses, known as reoviruses, is being studied by the National Institutes of Health. These viruses appear to be especially effective in treating metastatic cancers.

Reoviruses are found everywhere in nature and have been isolated from untreated sewage, river and stagnant waters. These viruses choose to colonize cancer cells that exhibit a group of common mutations, that result in an "activated Ras pathway," while sparing normal cells. Normal cells are unaffected by the reovirus becausethey lack these mutations. Approximately two-thirds of human cancers have the mutation that makes them a prime target for reoviruses.

One of the new drugs based on reovirus is known as REOLYSIN, and three factors seem to contribute to the possibility that metastatic disease would be susceptible to treatment with it. First, reovirus appears to spread particularly easily to organs where metastasis is common, so a concentration of the drug can be built up in those regions of the body. Second, the cells that colonize a tumor to form the metastasis are believed to harbor genetic defects that provide a more accommodating environment for reovirus to colonize. Finally, a growing body of literature suggests Ras activation is required for metastasis to occur in the first place. REOLYSIN is being developed by Calgary-based Oncolytics Biotech Inc. The company believes its treatment is most effective in conjunction with chemotherapy, and it is studying the effect of REOLYSIN in combination with the chemotherapy drugs carboplatin and paclitaxel.

REOLYSIN is now being tested in a randomized setting in head and neck cancer (Phase III), non-small cell lung cancer, colorectal cancer, castration-resistant prostate cancer, drug-resistant ovarian cancer and pancreatic cancer. All of these indications are associated with metastatic disease.

Future research studies will give us an even clearer perspective on whether REOLYSIN, or some other virus-based treatment like it, offers the most effective route toward "beating the mets."