Gene therapy is a type of biological therapy for cancer 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 may 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 may make a cell become cancerous are caused by environmental or lifestyle factors, such as smoking.
Some people have inherited faulty genes that increase their risk of particular types of cancer. Inherited damaged genes cause between 2 and 3 in every 100 (2% to 3%) of cancers.
What gene therapy is
Gene therapy is a type of treatment which uses genes to treat illnesses. Researchers hope that some types of gene therapy will be able 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 very early days for this type of treatment and progress has been slow in this very complicated area.
Some clinical trials are looking at using gene therapy for cancer.
A number of new types of gene therapy treatments are also being developed.
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 of which are explained below.
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 to make 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 such as chemotherapy or radiotherapy.
This type of gene therapy aims to make the other cancer treatments 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.
After giving the carrier containing the gene, the doctor gives the patient the pro drug. The pro drug may be a tablet or capsule that is swallowed, or it could be delivered into the bloodstream.
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. Doctors hope 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.
One example of this type of research uses the cold sore virus (herpes simplex virus). The changed virus is called Oncovex. It has been tested in early clinical trials for advanced melanoma, pancreatic cancer and head and neck cancers.