Cancer diagnoses going viral
A genetically modified virus that can make hidden tumours light up may lead to a new and more effective way of screening for cancer.
Some cancers are helpful enough to give off obvious clues to their existence. Prostate cancer, for example, can be detected as it raises the levels of a protein called PSA in the blood. Many, however, leave no such trace. Sufferers of these diseases can, therefore, remain in the dark about their condition, delaying treatment and lowering their chances of survival.
What if there were to artificially force these normally hidden cancerous growths into the light? A team of scientists from Cincinnati Children’s Hospital Medical Center have succeeded in answering this question, although using a most improbable helper – the Herpes virus.
Viruses are biological machines with a singular purpose – to create more viruses. The simplest organisms on the planet, they consist of only a protein coat surrounding a tiny scrap of DNA. This is all they need, however, for the virus’s success comes from its ability to force another cell to do its dirty work. When a virus invades a host cell, its DNA becomes indistinguishable from that of its host. The unwitting host has no choice but to use the viral DNA to create new viruses who are then free to escape and infect new cells. Many of the symptoms we associate with viral disease come about, not because they help fight the invaders, but because they help spread the virus. The rabies virus causes excessive salivation in infected animals because it is transmitted via saliva. The common cold virus is spread in mucous droplets, so it is no wonder it makes us sneeze and cough each winter. This shadowy way of life has lead to viruses becoming the most common type of organism on the planet. By some estimates there could be up to 10 thousand billion billion billion of them, each manipulating their environment for their own ends.
The group of researchers have used the viral lifestyle to their advantage, by creating a specially designed virus that can invade cancerous cells and force them to reveal themselves. The Herpes virus was genetically modified to include a copy of a gene known as GLuc, which contains the instructions needed to build a fluorescent protein. At the same time, the virus was also designed to infect only cancerous cells. So, when injected with the virus, the cancerous tumours quite literally glow in the dark. Using simple laboratory tests tumours as small as 1mm across could be found. The scientists, whose results were published in the journal PLoS ONE, tested their new virus on a variety of cancer types, including skin and bone samples and found much higher rates of GLuc production than in normal cells.
Currently, many diagnostic tests for the hard-to-detect cancers either use expensive equipment or are unreliable. Screening lung cancer, for example, involves the use of X-rays or CT scans. Diagnoses are given based on the presence or absence of abnormal growths that can be seen in the images. Since many conditions can produce similar images, however, false positives are easily given. The new virus-based method requires only a simple blood test, and can detect tumours regardless of where they are located in the body.
Dr Thomas Cripe, who co-authored the work, has high hopes for this new diagnostic method. “If this technology is developed further the cost of administering a small amount of virus and performing a simple blood test could become very cheap.”
This technology could easily find its way into the developing world where current screening methods are impractical or expensive. A report for the World Health Organisation predicts 9 million new cases of cancer in the developing world if new screening and prevention methods cannot be found.
The Herpes virus has proven itself useful, not just in the detection of cancer, but also in the fight against it. Another genetically modified version of Herpes known as OncoVEX, currently in clinical trials, has been created that only reproduces inside tumour cells. The cancers become so full of viruses that they burst open, while healthy cells remain intact. Dr Cripe believes that the two approaches may one day work in tandem. “The virus might also be used to predict patients whose cancers are most likely to respond favourably to the virus-based therapy.”
Viruses, once an enemy of human health, may soon become a useful ally in the battle against cancer.
Browne, A., Leddon, J., Currier, M., Williams, J., Frischer, J., Collins, M., Ahn, C., & Cripe, T. (2011). Cancer Screening by Systemic Administration of a Gene Delivery Vector Encoding Tumor-Selective Secretable Biomarker Expression PLoS ONE, 6 (5) DOI: 10.1371/journal.pone.0019530