Canadian researchers are testing a new version of a small pox virus with the hope that it will help doctors deliver medicine to hard-to-treat cancerous tumors, including those typically associated with malignant mesothelioma.

A study published in the September 2011 issue of Nature explored the genetic engineering of a poxvirus known as JX-594. The drug was designed by Jennerex, Inc. to selectively infect cancerous tissue and produce proteins that tell the body to destroy the tumor.

The trial showed that the virus had no effect on healthy cells, but 87 percent of patients who received the highest dose of the virus showed that the virus had spread throughout the patients’ tumors. Ten weeks after receiving an injection of the virus, 13 of 23 patients had experienced halted growth or reduction of their tumors.

One of the most prevalent ways to deliver drugs directly to metastatic solid tumors is targeted therapy. Targeted therapy is expected to increase the efficacy and safety of cancer therapy while making cancer cells more receptive to treatment.

The JX-594 virus is different from other viruses used in earlier types of targeted therapy because it can be administered to the bloodstream. Most other genetically altered viruses need to be placed directly into the tumor in order to be effective, but the original small pox virus is blood-borne. The JX-594 virus is found to have mild side effects, many of which are no more severe than flu-like symptoms lasting approximately one day.

The virus is scheduled to be the focus of a phase IIb trial at the Ottawa Hospital Research Institute. Although the trial will examine its effects on primary liver cancer patients, researchers hope that the findings of the study can be used to help develop treatments for all forms of cancer.

Other types of gene therapy studies are being conducted to develop novel therapies for mesothelioma patients.