Viral Cure

Scientists have identified an 

anti-cancer agent in a virus, reports Biplab Das

For therapeutic purposes, viruses are often genetically engineered. But this method may soon make way for a new cancer therapy that promises to revolutionise treatment of the terminal disease. It will also prevent researchers from tampering with the genetic make-up of viruses. A simple injection loaded with reovirus will work wonders. 

This interesting clue has emerged from the laboratory of Patrick Lec, virologist at the University of Calgary in Alberta. A few years ago, Lec and colleagues were experimenting with human reoviruses (a double-stranded RNA virus) to find out how they worked in general. While doing so, the research team discovered reo's potential as anti-cancer agent. 

The finding inspired the team to take up the present work. According to them, reoviruses exploit the signalling pathway of inappropriately activated proto-oncogene (precursor to cancer gene) 'ras' and kill tumour cells selectively. This faulty gene makes ras protein in excess, facilitating reo's replication within cancer cells. 

To test reoviruses' edge over cancer cells, researchers selected severe combined immune deficient (SCID) mice for in vitro replication of reovirus. After injection into the hind flank of mice, palpable tumours developed in two weeks. The mice which developed tumours were given intratumoural injections of reovirus. But the controls were given the injection of ultra-violet-inactivated virus. By the 12th day, the size of the tumour decreased in six out of the eight reo-recipients. In controls, the tumour size increased abnormally. 

In the next phase of research, Lec's colleagues looked at the human tumour cells. For this, they selected human glioblastoma (malignant tumours in brain and spinal chord) U87 cells which are flooded with activated ras. Then they implanted human U87 cells as xenograft into the SCID mice. When tumours occupied a mean area of about 0.5 sq cm, an intratumoural injection of reovirus was given. After four weeks, the tumours got reduced in size. Tests revealed no tumour cell progression into the underlying skeletal muscle. 

Researchers then located reovirus beyond the boundary of cancer cells. It helped them detect antibodies specific to viral proteins. But no trespassers were detected beyond the cancer territory. So far, reoviruses were exposed to feeble immune response. 

To check how they responded to a strong immune response, researchers turned to immunologically competent mice. Lec's teammates applied the same treatment as had been done to the SCID mice. But the result showed that their immune system did not interfere with tumour regression. Further, the system forgets its previous encounter with reovirus. So, it cannot reject the multiple exposures to reovirus. Lec and his colleagues believe it is the best bet to combat cancer.