Figure 5: General virus functions.
Alternative Gene Therapy
There are many other methods of gene therapy. A brief outline of these includes the direct insertion of a gene by soaking a tissue in a solution containing high quantities of the desired DNA. However, due the economic purposes it is not feasible. It is expensive and the tissue has to be taken and then re-inserted into the patient, or the individual will be a walking genetic reaction if the tissue is drowned within his body (figure 6). As well, only certain (few) tissues accept this method for the acquisition of genes. (1)
Figure 6: The genetic modification of cells; the re-introduction of these cells into a patient.
Alternatively, there is also the use of bacteria, which is very similar to the use of viral vectors. They both have their genetic structure modified, and they both inject the gene into their target cell. Bacteria are more difficult to make target-specific, however, and thus are less favoured. (4)
Cancer
Cancer is one type tissue which has differentiated away from its original purpose. What is special about cancer is that it undergoes mitosis without self-termination. As such, this tissue becomes invasive on other surrounding tissues, often destroying it to make room for itself. Figure 7 an example of the invasive nature of cancer. (12)
Figure 7: Various stages of cancer.
A cancerous cell is determined by its inability to self-terminate. As this cell divides, it creates another cancerous cell, until there is a tissue of cancerous cells. This tissue develops its own vessels in order to take blood from its surroundings and feed itself for its further growth. The root of the problem, however, is that the "suicide gene" is deactivated. The suicide gene cannot be targeted itself, but the cancer itself can be targeted. There are many targetable proteins on cancer, in which the proper modifications to a virus could become attractive. (3)
Cancers can be targeted by the specificity of the cancer. Cancers have different methods of becoming cancerous, and below is a list of the number of known cancer genes to date distinguished by their method of mutation. For instance, the amplification section lists the 7 known cancer genes which are amplified. An example of such would be ovarian cancer. When an individual has ovarian cancer, a cancer gene is amplified and can thus be identified. (2)
Cancer Gene Census
Sorted By
- Amplification
- Chromosome
- Frameshift Mutation
- Germline Mutation
- Large Deletion
- Missense Mutation
- Nonsense Mutation
- Other Mutation
- Somatic Mutation
- Splicing Mutation
- Symbol
- Translocation
Number
- 7
- 367
- 67
- 68
- 28
- 87
- 63
- 10
- 330
- 42
- 367
- 275
Cancer is developed through a stepwise mutation of one cell. It is only when this cell divides that the cancer starts to become a cancerous tissue. Many times our body gets rid of the malignant cell before it develops into a cancerous tissue, but when the cell divides without getting destroyed, cancer results. (11) See figure 8 for an outline of cancerous mutation.
Figure 8: Progressive cancer mutation.
Figure 9: Cancerous neuron.
Figure 9: a brain cancer cell. Figure 10: a cancer cell being attacked by the immune system.
Figure 10: Breast cancer cell attacked by immune system.
Current Research
Today there is already some research into fighting cancer with gene therapy. This included methods which embed DNA which enable surrounding tissue to attack cancer cells, as well as targeting the cancer itself and attempting to weaken it enough for your body to better fight it off. (8)
One of the most interesting approaches to curing cancer with viral gene therapy is the introduction of a "suicide gene" into the cancer, thus causing it to self terminate; this allows for the body to heal over the damaged spot while the cancer continues to remove itself. (8)
Viral gene therapy is not limited to curing cancer, however. This method is being used to cure other genetic diseases. In fact, the very first clinical trial for viral gene therapy was on the disease ADA, a serious and rare genetically imposed immunodeficiency disorder. (8)
Due to the potential dangers of viral gene therapy (such as the accidental introduction of a gene into a different cell or tissue), laborious steps have to be taken before a clinical trial is considered, and extensive trials are made following approval. So far, there have been no uses of viral gene therapy outside of clinical trials. (8)
Conclusion
Due to the genetic mutation which causes cancer, viral gene therapy appeals to be an appealing method to attempt to cure it despite the risks during the clinical trials. Gene therapy also seems a promising route to cure or help cure any genetic disorder. However, the risks are high, as the insertion of an unstable gene could result in a mutation which could worsen the conditions instead of treat them. As such, gene therapy is a very promising and real opportunity; with great promise comes great risk, however. Hopefully the use of viral gene therapy can help make cancer a pandemic for the history books.
