Viruses That Fight Brain Tumors
New Approaches to Fighting Cancers of the Central Nervous System
Surgery, radiation and chemotherapy are the mainstays of treatment for malignancies of the brain and spinal cord. Oncolytic viruses may someday provide a new alternative.
Brain Tumor Incidence. Data from the Central Brain Tumor Registry of the United States predicted that more than 40,000 new cases of primary brain tumors would be diagnosed in the United States in 2005. Primary brain tumors are those that arise within the substance of the brain and spinal cord. Tumors that develop in the central nervous system as a result of metastatic growth are not considered primary brain tumors. Irrespective of their initial source, malignant brain tumors carry with them a very poor prognosis for the patient.
Current Treatments for Brain Tumors. For the vast majority of tumors in the central nervous system (CNS), therapies have relied on three typical treatments:
a) The surgical excision of as much tumor as possible, if surgery is even possible
b) Radiation therapy to try and destroy as many malignant cells as possible while limiting damage to surrounding normal brain tissue.
c) Systemic or locally administered chemotherapy to stop tumor growth
Not surprisingly, all of these approaches have their own limitations and difficulties. Treating malignancies in the brain can be an exceedingly arduous task and the returns for the patient can sometimes be minimal.
Using Viruses to Fight Brain Tumors. The idea of using viruses to fight and kill cancer cells has been around for several years. Many different types of viruses that are capable of infecting cancer cells can be grown in laboratories in large enough quantity to be useful. However, in order to be as safe as possible for use, most of these viruses have been crippled in their ability to reproduce themselves. In numerous published tests, different ‘engineered’ viruses have been shown to infect some, or even many, tumors but their utility in destroying the tumors has been rather limited. For many of these tests the viruses were injected directly into tumors that were present in laboratory mice. Needless to say these studies required a great deal more experimentation before they might be tested for use in humans.
A New Viral Approach. In the February 20, 2008 issue of The Journal of Neuroscience, a new viral approach to the treatment of brain tumors was reported by researchers at Yale University School of Medicine (1). Using a modified, laboratory grown version of a virus known as Vesicular Stomatitis Virus (VSV), they reported a very high success rate in infecting and killing brain tumors in mice. Some key features of their work included:
a) The VSV that they were using was still able to reproduce itself
b) It was delivered via intravenous injection and was still able to infect the brain tumors
c) The virus infected the tumors, replicated itself to keep infecting more tumor cells, and appeared to not infect surrounding normal tissue.
d) The strain of virus had been grown in the lab to be specific for a particular type of brain tumor cells.
Will this be Applicable to Treating Brain Tumors in the Future? The strain of VSV that was used in these studies had a high affinity not only for brain tumor cells but also for other cancer cells. It did show a high degree of specificity for infecting and killing tumor cells only, an outcome linked, the researchers believe, to the fact that normal cells typically have the capacity to fight off this virus while many cancer cells do not. One of the possible shortcomings of this study is the fact that the studies were conducted in mice with compromised immune systems, making it unclear if this technology would work in animals with normal immune function. While it will certainly be some time before these approaches are clinically useful, nonetheless, these studies are quite promising and may herald a new direction in the use of viruses for development of therapeutic approaches for brain tumors.
1: Ozduman K, Wollmann G, Piepmeier JM, van den Pol AN. Journal of Neuroscience 2008 Feb 20;28(8):1882-93. Systemic vesicular stomatitis virus selectively destroys multifocal glioma and metastatic carcinoma in brain.
