Combining radiation treatment with 'suicide gene therapy' - a technique in which prostate cancer cells are genetically modified so they signal a patient's immune system to attack them - provides an effective two-pronged punch against the disease, new research shows.
The researchers at Houston Methodist Hospital, Texas, US, compared two groups of patients and report high five-year overall survival rates of 97 percent and 94 percent, respectively.
Sixty-six prostate cancer patients participated in the phase II clinical trial between 1999 and 2003 and were split into two groups.
One group with cancer cells confined to the prostate, designated Arm A, received only radiotherapy while the other with a more aggressive prostate cancer, Arm B, received both radiation and hormonal therapies.
Patients in Arm A received the experimental gene therapy twice during the study, while the Arm B group received the treatment three times.
"We strategically used an adenovirus, similar to the one that causes the common cold, to carry the therapy agent - a herpes virus gene that produces the enzyme thymidine kinase, or TK -directly into the tumour cells," said senior study author E. Brian Butler.
"Once the herpes virus gene was delivered and it started manufacturing TK, we gave patients a commonly used anti-herpes drug, valacyclovir. The combination attacked the herpes DNA, and the TK-producing tumour cells self-destructed, which is why the procedure is called 'suicide gene therapy'," Butler said.
Butler said that once the activated valacyclovir starts destroying tumour cells, it also alerts the patient's immune system, previously unaware of the cancer's presence, that it is time to launch a massive attack.
"We have created a vaccine with the patient's own cancer cells, a treatment that complements, and may even enhance, what we can achieve with traditional radiation and hormonal therapies," said Butler, professor of radiation oncology at Weill Cornell Medicine.
The findings appeared online in the Journal of Radiation Oncology (JRO).
