Pediatric brain tumors, while rare, are the most common form of solid tumors in children, and compose 20% of all pediatric cancers. The prognosis is bad for many patients with pediatric brain tumors as it is difficult to recognize signs of brain tumors in children. Therefore, to diagnose and treat them .
While substantial progress has been made in the treatment of certain forms of pediatric brain tumors, there are still a number of brain tumors that are either incurable or have dismal survival rates. In particular, there has been very little progress made in treating patients with malignant gliomas as most children die within three years of diagnosis. The prognosis is even worse for patients that have recurrent tumors. In many cases, surgery, radiotherapy, and chemotherapy for treatment of pediatric brain tumors are not enough to save the children, which is why it is important to look for more innovative strategies in treating these children .
In short, viruses can be engineered to carry genetic information to cells within the body which provide instructions to the cells to create certain products that can be used to fight the tumor. Many types of cancers have mutations in genes called tumor suppressors, which are involved in stopping tumor growth. If gene therapy could be utilized then tumor suppressor genes can be expressed in tumor cells, where they will then be able to carry out their function of stopping tumor growth .
Issues associated with gene therapy in pediatric brain tumors
Firstly, one of the major issues is that when a virus is introduced into a host, it goes into every cell, but ideally it should only go into the tumor cells. Next, the virus should be able to gain entry into enough tumor cells that all of the tumors would be targeted and lastly, scientists need to discover what gene should be introduced into each particular tumor that would appropriately halt tumor growth and cause remission .
Scientists have been interested in using gene therapy to treat tumors for a long time, particularly localized tumors such as high-grade gliomas. When a tumor is localized and not widespread, it is a lot easier to deliver gene therapy to target most of the tumor cells, which can be performed using neurosurgical techniques. Often, certain types of gene therapies can be programmed to only enter into cells that are rapidly dividing, which makes targeting the central nervous system ideal as most cells in the CNS are not dividing .
A study conducted by the National Institutes of Health (NIH) utilized gene therapy for the treatment of malignant glioma in adults using a type of virus called called Retrovirus .
In the central nervous system, most cells, which are called neurons, stop proliferating by birth and therefore, the Retrovirus would not be integrated into the genome of normal neurons, only tumor cells. In this particular study, the Retrovirus was designed to carry a gene that would cause a cessation of replication in the cell. Therefore, cells that harbor the Retrovirus would not divide. For the purpose of this study, high quantities of this virus were delivered to the cells over a long period of time. The virus was engineered to carry another gene which made cells more sensitive to anti-viral treatment. Hence, once the Retrovirus was delivered to the tumor cells, the gene that makes cells more sensitive to anti-viral treatment was expressed and then anti-viral treatment was administered to these patients .
This treatment would allow only the tumor cells to be destroyed. As the only cells in the brain of a child with a brain tumor that are actively dividing are tumor cells, the Retrovirus would be integrated into the tumor cell genome and then anti-viral therapy would work against those specific cells. In this case, an anti-viral drug called ganciclovir was used to kill the cells. In this particular clinical study, gene therapy showed both safety and efficacy. On the basis of this study, a study was developed in the late 1990s that targeted children with recurrent malignant gliomas. The treatment in children showed good results in terms of safety and one child that was treated with multiple other therapies and had failed to respond to any did very well on gene therapy and is now disease-free. Unfortunately, this therapy was not effective in all patients .
Despite the fact that this method of treatment is just beginning to gain traction and attention of researchers, scientists believe that this technique can be used to treat children with malignant gliomas. Since there are few treatment options at this time for the treatment of pediatric brain tumors, labs around the world are conducting extensive research into using gene therapy as a treatment .