A long-term clinical trial conducted by the Houston Methodist Hospital revealed that a combination of radiation and gene therapies can give a more effective treatment against prostate cancer. Suicide gene therapy is a process of genetically altering malignant prostate cells so they can signal the immune system to attack them.
The long-term study (from 1999 to 2003) is currently in its second phase. It has enrolled 66 patients, of which 33 individuals belong to two separate groups. The first group, Arm A, has a confined prostate, and the therapy is limited to radiation only. On the other hand, Arm B has a more aggressive cancer type and utilizes a combination of radiation and hormonal regimens. Gene therapy was given two times during the study in Arm A participants, while Arm B received thrice.
“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 tumor cells,” lead author E. Brian Butler explained. “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 tumor cells self-destructed, which is why the procedure is called ‘suicide gene therapy.”
Once valacyclovir is activated and begins attacking cancerous cells, the body’s immune system will start recognizing the presence of these malignant cells, thus launching a more enormous attack. The researchers created a vaccine using the patient’s own cancer cells with a treatment that complements and enhances the achievement of the result made by traditional radiation and hormonal therapies.
After a 5 year clinical trial, promising results reveal a survival rate in Arms A and B at 94 percent and 91 percent, respectively. Biopsies at 24 months after completing the treatment reveal 83 percent and 79 percent freedom from failure rates in Arms A and B, respectively. This is higher compared with the results when radiation therapy is solely given.
In addition, based on the recent trial, little to no side effects or therapy-related complications were noted. The study will undergo its next phase to finalize its safety and efficacy. It is published in the “Journal of Radiation Oncology.”