The deadliest type of brain tumour may be treated with poliovirus

Contracting poliovirus can have life-changing consequences like paralysis, long-term muscle weakness and in some cases death so using it in cancer treatment may not seem like the brightest idea. However, a paper published in the New England Journal of Medicine late last month suggested that an inactivated modification of the virus could be part of an effective immunotherapy for the deadliest type of brain tumour, glioblastoma.

The study looked at 61 patients with “recurrent grade IV malignant glioma”, also known as glioblastoma, for whom other treatments had been ineffective. The patients were administered various dosages of a poliovirus which had had some of its genes swapped with those of rhinovirus, causative agent of the common cold. The results found that 21% of those who received the treatment were still alive after three years, compared with 4% from standard therapy. Given glioblastoma’s resilience, there is plenty to be excited about but further and larger clinical trials will be necessary to see if the therapy can live up to the promising results so far.

The patients were administered various dosages of a poliovirus which had had some of its genes swapped with those of rhinovirus, causer of the common cold

The treatment comes under the banner of immunotherapy, a term which covers a wide variety of processes that are all methods of tackling diseases by engaging the body’s immune system. Immunotherapy is not new but its usage against cancer is in its relative infancy but has already found success with those that are resistant to conventional radiation and chemotherapy.

Our immune system looks to target and eradicate foreign objects in the body like bacteria and viruses and can also remove mutated cells that may develop into cancer, doctors believe it is very likely this happens on a regular basis. However, an aggressive tumour or those with particular DNA can cause a tipping point in the cancer’s favour and the immune system can no longer hold it back.

Immunotherapy is not new but its usage against cancer is in its relative infancy but has already found success with those that are resistant to conventional radiation and chemotherapy

This is where immunotherapy comes in. With the recent trial, the modified poliovirus was injected directly into the brain. The advantage of polio is it has evolved to adeptly infect cells with a specific molecular receptor, CD155, found in motor nerves in the spinal canal but also on many solid tumours like glioblastoma. Once infected, the bug itself started to kill some of the cancer cells but more importantly, it called in the immune system to further attack the cancer. In cases, the attack was too aggressive and the dosage had to be reduced to prevent inflammation but regardless of how big the initial reaction, the effectiveness can quickly fade as the virus dies off.

Despite some shortfalls, the team behind the study are hopeful that their results in combination with other developing immunotherapy advances like checkpoint inhibitors could increase the method’s long-term effectiveness. The group is already conducting a trial comparing using the treatment alone versus following up with a single dose of chemotherapy after the dramatic positive effect chemo had on their patients whose cancer grew back. With these and other avenues to explore, glioblastoma’s days as the deadliest cancer might be numbered.