Chemotherapy is currently the most common cancer treatment. This involves the administration of various anti-cancerous chemicals which are highly toxic. Although single drugs can be utilized, a cocktail of numerous chemicals is often more effective. However, this increases the toxicity, and many adverse effects occur on the patient. Chemotherapy involves the use of chemicals which are known cancer-fighters, or chemicals which enable the cells and tissues around a certain cancer to better fight the cancer. In other words, it makes the cancerous area a more favourable battle ground for the patient. An example of a chemotherapy agent is Vinblastine, a chemical which targets leukemia, lymphoma, breast, and lung cancers. (14) The side effects of various chemotherapy agents, such as Vinblastine, include nausea, anaemia, lowered resistance to infection, fatigue and a general feeling of being week. (14) Some chemotherapy agents also inhibit the division of cells in the body, thus demonstrating the characteristic hair loss and low immune system. Chemotherapy is a commonly used cancer treatment; gene therapy could be the cancer treatment of the future.
Gene therapy is the process of inserting genetic material into an organism in order to alter genetic code. (1) The modification of the genome (a change in its structure) will change how it codes everything in the organism (function). An example of this expression of the structure-function relationship is the correction of genetic defects that result in the malformation of proteins. The most common method is to insert a gene into the nonspecific portion of the genome: in other words, the non-functional portion of our genes becomes helpful. (1) This can be done by splitting a genetic helix (figure 1) and exchanging genetic portions or inserting a gene within the helix. The portions (detailed in Figure 2) exchanged are the interior of the helix, which then recombines. The atomic genetic helix (Figure 3) outlines how the chemical composition can be easily altered (theoretically) in order to accommodate changes in the genetic coding.
Gene therapy is frequently conducted with viruses, but has been known to be performed using bacterial vectors as well. (7) Different viruses affecting humans target different parts of the body, such as respiratory or intestinal, due to molecular flags that the viral receptors look for. If the location of a cancer is known, then the specific types of viruses could be utilized to target that area in order to correct the genetic error. The genetic material within a virus can be exchanged for different genetic material: thus accomplishing a different purpose.
For example, an intestinal cancer could use the viral shell of a virus that specifically targets intestine cells; instead of injecting an illness, however, the modified DNA within the virus would be injected into it and correct the genetic disorder causing cancer.
The specific locations for certain cancers can be located by methylating the sample DNA.
(5) Due to the lengthy explanation of the methylation of DNA,
I will not go into further detail, other than it is simply chemical methylation:
the introduction of CH3.
For example, if the gene EPHA3 (a combination of different molecules specifically structuring genetic material using nucleic acids) at the map 3p11.2 were to be methylated (using chemical methylation), leukemia would be a result.
Using this knowledge, gene therapy could be implemented in order to counter-act the leukemia at map 3p11.2. (4, 5) The genetic map is simply the location of a gene within the genome relative to the other genes.
There are many different types of viral vectors used in viral gene therapy:
Retroviruses - A class of viruses that can create double-stranded DNA copies of their RNA genomes. These copies of its genome can be integrated into the chromosomes of host cells. Human immunodeficiency virus (HIV) is a retrovirus.
Adenoviruses - A class of viruses with double-stranded DNA genomes that cause respiratory, intestinal, and eye infections in humans. The virus that causes the common cold is an adenovirus.
Adeno-associated viruses - A class of small, single stranded DNA viruses that can insert their genetic material at a specific site on chromosome 19.
Herpes simplex viruses - A class of double-stranded DNA viruses that infect a particular cell type, neurons. Herpes simplex virus type 1 is a common human pathogen that causes cold sores. (1)
These viral vectors find their host cell through the use of the receptors on the target cells in the designated cellular surface. The virus then slips through the semi-permeable membrane of the cell and injects the DNA into the nucleus of the cell.
(10) Figure 4: Gene therapy using an adenovirus vector.
Figure 4 outlines the use of an adenovirus vector in viral gene therapy. This emphasizes the huge change in the virus' original function when contrasted with figure 5. The genetically modified virus no longer tries to take over the cell and replicate; it simply injects the DNA required without the destruction of the cell. This is because the gene in the original virus is what mechanised the creation of more viruses and, ultimately, the destruction of the host cell. Since this DNA was exchanged, it now functions as it was engineered to.
