Glioblastoma tumors are the most common form of malignant brain tumor and affect approximately two to three adults per 100,000 each year. Due to the aggressive nature of glioblastoma, existing treatments are relatively ineffective and the prognosis for affected patients is quite poor. According to the National Brain Tumor Society, the five-year survival rate for those afflicted with glioblastoma is a mere 5.6%. In fact, the majority of glioblastoma patients only survive 12 to 15 months post-diagnosis. With the recent passing of U.S. Senator John McCain, as well as former Vice President Joe Biden’s son, Beau, who both succumbed to this dreaded brain cancer, the search for an effective treatment has been brought back into the limelight. Recently, researchers at the Duke Cancer Institute have seen promising experimental results using a genetically modified poliovirus (called PVS-RIPO) in patients diagnosed with a glioblastoma brain tumor. The poliovirus is administered directly into the cancerous mass by inserting a catheter through the skull and into the tumor.
The virus subsequently infects only the cancerous cells, which ultimately induces the patient’s immune response, engendering the use of the body’s natural defenses against its own mutated cells. The genetically modified virus affects only tumor cells while leaving normal cells unharmed. With this novel treatment, 21% of the 61 patients enrolled in the initial trial were still alive three years post-treatment. This represents a 7% increase in the survival rate after 18 months and a 17% increase in the survival rate after three years when compared to patients who did not receive the poliovirus therapy but were treated with standard chemotherapy instead (the control). Based on these results, the poliovirus therapy has now been designated as a “breakthrough therapy” by the FDA. This means that the development of the treatment and its review process will be expedited by the FDA and a response will be provided within 60 days of receipt of the new drug submission.
Unfortunately, this treatment does not come without potential complications; at higher doses of PVS-RIPO, the treatment has been shown to cause brain inflammation, leading to seizures. Additionally, some patients have been observed to exhibit no response to the poliovirus therapy, though the reasons why are unknown. At this time, there is no way to identify whether or not a patient will respond to the treatment. While the results of this Phase I Clinical Trial are promising, many other cancer trials have also shown similar long-term survival statistics. Therefore, it is difficult to determine whether these long-term survivors are truly benefiting from the therapy. Phase II of this study is currently underway, which will compare the effectivity of a poliovirus/chemotherapy combination therapy with poliovirus therapy alone. Scientists are currently working with other viruses in addition to polio; such as herpes, vaccinia, and respiratory viruses to battle cancer. With continued efforts towards an efficacious cure, glioblastoma patients may have hope of an improved treatment in the future.