Using viruses to treat cancer has long been of interest to medical researchers. One type of virus in particular — oncolytic viruses — can kill tumor cells.
But so far, the Food and Drug Administration (FDA) has only approved one of these: a genetically modified form of herpes to treat melanoma.
The reason that viruses can target tumors is pretty simple. Cancerous tumors are invisible to the immune system, allowing them to grow and spread.
But when a virus enters a cancerous cell and replicates itself, this allows the cancer to be seen, prompting the immune system to treat the disease as it would a common cold.
Melanoma is not the only type of cancer that viruses can affect. Researchers have recently tested a similar treatment on brain tumors.
A new study has found promising results in a form of bladder cancer.
Researchers, many of whom are from the University of Surrey, in the United Kingdom, have investigated the impact of a strain of the common cold virus on non-muscle invasive bladder cancer (NMIBC). Their findings appear in the journal Clinical Cancer Research.
Current bladder cancer treatments
Bladder cancer is the seventh most common cancer among males and the seventeenth most common among females. Between 70% and 80% of bladder cancer diagnoses fall into the NMIBC category at the time of diagnosis.
“[NMIBC] is a highly prevalent illness that requires an intrusive and often lengthy treatment plan,” says Hardev Pandha, Ph.D., lead study investigator and a professor of medical oncology at the University of Surrey.
“Current treatment is ineffective and toxic in a proportion of patients, and there is an urgent need for new therapies,” he explains.
One treatment that removes any visible tumors has a high tumor recurrence rate (between 50% and 70%) and a high progression rate (between 10% and 20%) over the course of 2–5 years.
Immunotherapy is another option, but this has no effect on one-third of patients and can cause serious side effects in another third.
Replicate and attack
For the present study, the U.K.-based team decided to look to a strain of the common cold called coxsackievirus, or CVA21, for short.
The researchers gave 15 patients who had been diagnosed with NMIBC a dose of CVA21 one week before surgery to remove their tumors.
Nine received the CVA21 alone, via a catheter into the bladder, while the final six received CVA21 combined with a low dose of a chemotherapy drug called mitomycin C.
Each patient gave urine samples on alternate days and the researchers obtained tissue samples after the surgery.
The urine samples showed that the virus was able to copy itself and attack and kill cancer cells in the majority of patients. The tissue samples indicated that the virus was only successful in attacking cancerous cells, rather than healthy ones.
“Reduction of tumor burden and increased cancer cell death was observed in all patients,” Prof. Pandha notes. The researchers believe that the virus was able to inflame the bladder tumor, kickstarting the work of the immune system.
What was most surprising was that, during surgery, one patient exhibited no sign of NMIBC. An additional positive result was that “No significant side effects were observed in any patient.”
The study may have only used a small number of participants, but its results could pave the way for future research into the CVA21 virus and cancer.
According to Prof. Pandha, the common cold strain “could help revolutionize treatment for this type of cancer.”
Nicole Annels, Ph.D., who is the first author of the paper and a research fellow at the University of Surrey, adds that “Oncolytic viruses such as the coxsackievirus could transform the way we treat cancer” overall.
She notes that the therapy could even “signal a move away from more established treatments such as chemotherapy.”