Engineered virus shrinks tumors

Viruses have been known to shrink tumors. A reduction in tumor size can be observed after vaccinating a cancer patient, because vaccinating introduces a small amount of virus. The challenge has been to get enough virus cells to target the tumor without damaging healthy cells.

By genetically modifying the pox virus, David Kirn at Jennerex Biotherapeutics in San Francisco has engineered a special virus to seek and destroy tumors. Kirn's genetically-modified virus spreads more easily within tumors thanks to a tail composed of a protein called actin. Kirn has also modified the virus so that it is unable to produce an enzyme called thymidine kinase, without which the virus is unable to replicate and damage healthy tissue. Since cancerous cells contain an abundance of thymidine kinase, it is easy for the modified virus to multiply within tumors, and once the virus enters a cancer cell, it replicates itself until the cancer cell bursts. The third modification to the pox virus makes it produce a signalling molecule called cytokine, which attracts the body's immune cells towards tumors.

Clinical trials on the virus treatment was conducted with 13 patients with advanced liver cancer. The patients were so advanced that all previous therapies had failed, and they had a life expectancy of only three to four months. Beginning in July 2006, researchers started treating by administering the engineered virus directly into the participants' tumors every three weeks.

Seven of the participants survived for more than eight months, and three are still alive today, over 15 months later. The virus shrank the tumors of 10 of the 13 participants, including five whose tumors were reduced more than 50 percent. The only notable side effect experienced by the participants was temporary flu-like symptoms. link