Gene therapy is a cancer treatment that is still in the early stages of research.
What genes are
Genes are coded messages that tell cells how to make proteins. Proteins are the molecules that control the way cells behave. Our genes decide what we look like and how our body works. We have many thousands of separate genes.
Genes are made of DNA and they are in the nucleus of the cell. The nucleus is the cell's control centre. Genes are grouped together to make chromosomes. We inherit half our chromosomes from our mother and half from our father.
Cancer cells are different from normal cells. They have changes (called faults or mutations) in several of their genes which make them divide too often and form a tumour. The genes that are damaged might be:
- genes that encourage the cell to multiply (known as oncogenes)
- genes that stop the cell multiplying (tumour suppressor genes)
- genes that repair other damaged genes
Gene faults and cancer
Many gene changes that make a cell become cancerous are caused by environmental or lifestyle factors. A small numberof people have inherited faulty genes that increase their risk of particular types of cancer.
What gene therapy is
Gene therapy is a type of treatment which uses genes to treat illnesses. Researchers have been developing different types of gene therapy to treat cancer.
The ideas for these new treatments have come about because we are beginning to understand how cancer cells are different from normal cells. It is still early days for this type of treatment. Some of these treatments are being looked at in clinical trials. Others can now be used for some people with types of cancer such as melanoma skin cancer.
Getting genes into cancer cells
Getting genes into cancer cells is one of the most difficult aspects of gene therapy. Researchers are working on finding new and better ways of doing this. The gene is usually taken into the cancer cell by a carrier called a vector.
The most common types of carrier used in gene therapy are viruses because they can enter cells and deliver genetic material. The viruses have been changed so that they cannot cause serious disease but they may still cause mild, flu-like symptoms.
Some viruses have been changed in the laboratory so that they target cancer cells and not healthy cells. So they only carry the gene into cancer cells.
Researchers are testing other types of carrier such as inactivated bacteria.
Types of gene therapy
Researchers are looking at different ways of using gene therapy:
Some types of gene therapy aim to boost the body's natural ability to attack cancer cells. Our immune system has cells that recognise and kill harmful things that can cause disease, such as cancer cells.
There are many different types of immune cell. Some of them produce proteins that encourage other immune cells to destroy cancer cells. Some types of therapy add genes to a patient's immune cells. This makes them better at finding or destroying particular types of cancer.
There are a few trials using this type of gene therapy in the UK.
Some gene therapies put genes into cancer cells to make the cells more sensitive to particular treatments. The aim is to make treatments, such as chemotherapy or radiotherapy, work better.
Some types of gene therapy deliver genes into the cancer cells that allow the cells to change drugs from an inactive form to an active form. The inactive form of the drug is called a pro drug.
First of all you have treatment with the carrier containing the gene, then you have the pro drug. The pro drug circulates in the body and doesn't harm normal cells. But when it reaches the cancer cells, it is activated by the gene and the drug kills the cancer cells.
Some gene therapies block processes that cancer cells use to survive. For example, most cells in the body are programmed to die if their DNA is damaged beyond repair. This is called programmed cell death or apoptosis. Cancer cells block this process so they don't die even when they are supposed to.
Some gene therapy strategies aim to reverse this blockage. Researchers are looking at whether these new types of treatment will make the cancer cells die.
Some viruses infect and kill cells. Researchers are working on ways to change these viruses so they only target and kill cancer cells, leaving healthy cells alone.
This sort of treatment uses the viruses to kill cancer cells directly rather than to deliver genes. So it is not cancer gene therapy in the true sense of the word. But doctors sometimes refer to it as gene therapy.
An example is a drug called T-VEC (talimogene laherparepvec), also known as Imlygic. It uses a strain of the cold sore virus (herpes simplex virus) that has been changed by altering the genes that tell the virus how to behave. It tells the virus to destroy the cancer cells and ignore the healthy cells.
T-VEC is now available as a treatment for melanoma skin cancer. It can be used to treat some people with melanoma whose cancer cannot be removed with surgery. It is also being looked at in trials for head and neck cancer. You have T-VEC as an injection directly into the melanoma or head and neck cancer.
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