Houston: Combining radiation treatment with’ suicide gene therapy' provides a safe and effective treatment against prostate cancer, a new study has claimed.
Suicide gene therapy is a technique in which prostate cancer cells are genetically modified so they signal a patient’s immune system to attack them.
Researchers at the Houston Methodist Hospital in US compared two arms of patients and reported high five-year overall survival rates of 97 per cent and 94 per cent respectively. As many as 66 prostate cancer patients participated in the 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 E Brian Butler from Houston Methodist.
"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'," he added.
Researchers 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," Butler said.
According to researchers, the long-term outcome for prostate cancer patients receiving gene therapy in combination with radiotherapy with or without hormonal therapy is promising.
The 62 patients in both arms who completed the clinical trial had remarkably high five-year freedom from failure rates, meaning no indication by biochemical testing of cancer recurrence, of 94 per cent and 91 per cent, respectively.
Prostate biopsies performed at 24 months after completion of treatment were negative in 83 per cent of Arm A patients and 79 per cent of Arm B patients. For all evaluative factors, the outcomes were remarkably higher than those achieved with radiotherapy alone.
The findings were published in the Journal of Radiation Oncology (JRO).
