A recent trial indicates that a viral therapy delivered intravenously can consistently infect and spread within tumors without harming normal tissue in humans.

“Intravenous delivery is crucial for cancer treatment because it allows us to target tumors throughout the body as opposed to just those that we can directly inject,” explained study senior coauthor John C. Bell, PhD, a senior scientist at Ottawa Hospital Research Institute in Ontario, Canada, in a statement describing his group’s work.

According to Bell, the study—described in a letter published in the journal Nature (2011;477:99-102)—is also important because it shows that the approach can be used to selectively express foreign genes in tumors, “opening the door to a whole new suite of targeted cancer therapies.”

The 23 trial participants all had advanced cancers that had spread to multiple organs and failed to respond to standard treatments. Each patient received a single intravenous infusion of the JX-594 virus, at one of five dose levels. JX-594 was developed in partnership with a biotherapeutics company cofounded by Bell; the virus is derived from a strain of vaccinia virus that has been used extensively as a live vaccine against smallpox. The virus has a natural ability to replicate preferentially in cancer cells, but has also been genetically engineered to enhance its anticancer properties.

Biopsies obtained 8 to 10 days after virus administration exhibited evidence of viral replication in the tumor, but not in normal tissues, for 7 of 8 patients (87%) in the highest-dose groups. All of these patients also showed tumor-selective expression of a foreign gene that was engineered into the virus to help with detection.

In addition, tumors in 6 of 8 patients (75%) receiving the two highest virus doses stabilized or shrank. Those in the lower-dose groups were less likely to experience this effect.

The virus was well-tolerated at all dose levels. The most common side effect was mild to moderate flulike symptoms that lasted less than 24 hours.