Results of a long-term clinical trial have shown that combining chemotherapy with a treatment known as "suicide gene therapy," can safely and successfully kill prostate tumor cells.
Suicide gene therapy is a technique that involves genetically modifying prostate cancer cells so they trigger the body's immune system to attack them.
In the study published in the Journal of Radiation Oncology on Dec. 12, researchers from the Houston Methodist Hospital manipulated prostate cancer cells using a combination of viruses and adenovirus, the virus known to cause the common cold, to deliver a herpes virus gene into the patients' cells.
Once the herpes virus gene was delivered and began producing thymidine kinase, patients were given valacyclovir, an anti-herpes drug.
"The combination attacked the herpes DNA, and the TK-producing tumor cells self-destructed, which is why the procedure is called 'suicide gene therapy,'" explained Brian Butler, from Houston Methodist.
The researchers divided 66 patients with prostate cancer into two groups. Participants of the study, which was conducted between 1999 and 2003, were grouped depending on the severity of their illness.
Those with less severe cases of cancer were treated with radiotherapy while those with more severe cases were given both radiotherapy and hormonal therapy. Patients in both groups underwent suicide gene therapy. Patients with less severe cases were administered the therapy two times over the period of the study and those with more severe cases were treated thrice.
Patients with less severe cases of cancer had a 97 percent five-year survival rate while patients suffering from more severe cancer cases had 94 percent survival rate, which showed that survival rate of these patients were between five to 20 percent better compared to what is obtained by current procedures.
The patients who completed the clinical trial were also found to have high five-year freedom from failure rates, which means there were no indication of cancer recurrence in biochemical testing.
The researchers said the results were very pleasing given that some of the patients involved in the study were already deemed by their doctors incurable.
"The combination of immunomodulatory in situ gene therapy and IMRT with or without hormonal therapy is feasible, safe, and effective in the treatment of prostate cancer. The effectiveness of this combined approach was likely through enhanced cytotoxicity, antitumor immune response, and abscopal effects," the researchers wrote in their study.
