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Friday, May 16, 2008

Gene therapy

This information is about the use of gene therapy for people with cancer. Gene therapy is a very new type of treatment which is still being developed. This information is about how gene therapy can be used to treat cancer and gives an overview of the information available so far.

Development of gene therapy

Some types of gene therapy have been tested on cells in a test tube. These are now being given to small groups of patients in clinical trials. Clinical trials are caried out to find new and better ways of treating cancer. If a drug has been tested in a laboratory and seems to be helpful it is then tested in patients. This is the first stage of a trial and the aim is to find a safe dose and see what side effects it may cause.

Gene therapy is very new. For this reason, doctors and other medical staff carry out frequent and careful checks on every patient who is taking one of these treatments.

If you are having treatment with gene therapy your doctor will explain about the treatment, the procedures being used, and how you will be looked after while you are taking it. At any time, if you have concerns you can ask your doctor or nurse for information and advice.

What are genes?

Our bodies are made up of millions of tiny structures called cells. Inside each cell is an area called the nucleus, which contains 23 pairs of chromosomes. Chromosomes are made up of thousands of genes. Genes are tiny chemical structures. They carry the instructions that tell cells how to work and they control our growth and development. They determine what we look like and how our bodies work. They also organise the repair of damaged cells and tissues.


Chromosomes, genes and DNA
Chromosomes, genes and DNA

We have at least 30,000 different genes. They are made up of a complex chemical called DNA (deoxyribose nucleic acid). DNA controls all the processes which take place in our bodies by producing proteins which carry out the genes’ instructions. When genes are damaged they may cause the production of abnormal proteins that lead to disease. It is known that cancer can occur due to changes in particular genes.

Each one of us has two copies of every gene. One set of copies is inherited from our mother, the other from our father.

How genes cause cancer

The cells in our bodies are constantly dividing to make new cells to replace those that are damaged or worn out. This process is controlled by particular genes. They make sure that exactly the right number and type of new cells are made to meet our needs.

If a gene is damaged, cells may start to divide in an uncontrolled way. This may eventually lead to a cancer. The damage to the genes is called a mutation.

As we learn more about genes and cancer, it seems likely that almost all cancers might be caused by faulty or damaged genes.

It is likely that several changes or mutations have to happen in the genes before a cell starts to divide abnormally and multiply out of control. This series of changes may be brought about by various factors including cigarette-smoking, environmental factors, or other causes that we are not yet aware of. The faulty genes may lead to cancer in the following ways:

  • The damaged gene can trigger cancerous changes in the cells. Some genes that can do this have been identified and are called oncogenes
  • Some normal genes reduce the risk of a cancer developing, by repairing damage to other genes. These are called tumour-suppressing genes. If tumour-suppressor genes are damaged, or mutated, so that they do not work, they may then allow a cancer to develop.

What is gene therapy?

Gene therapy means putting genetic material (DNA) into cells so that the cells can produce proteins which they do not usually produce. These proteins will help to fight disease. Research so far has shown the following:

  • Single genes can be taken from human cells and grown (cloned) in the laboratory, outside the body.
  • These cloned genes can be altered to make them work differently.
  • The altered genes can be put back into cells living in the body. This is usually done by inserting the gene into particular chemicals (liposomes) or cells (such as viruses which have been treated so that they are no longer harmful). The protein or cell used to deliver the altered gene into the body is known as a vector.

Sometimes, the genes themselves are introduced directly into the tissues. These are called naked genes.

How gene therapy can be used

Gene therapy may be used to treat cancer in the following ways:

  • Specially made genes can be put into the cancer cells to make them more sensitive than normal cells to treatments such as chemotherapy.
  • Genes may be given into cancer cells and then activated to produce a poisonous substance (toxin) that kills the cell.
  • Genes could be introduced into cancer cells which make those cells more obvious to the body’s own defences (the immune system), so that they are destroyed 'naturally' by the cells of our immune system.
  • Damaged genes may be replaced by the correctly working version.
  • New genes may be put into normal cells to make them more resistant to the side effects of treatment such as radiotherapy and chemotherapy. This protects the normal cells from the treatments so that higher doses can be given. At present the risk of damage to normal cells often limits the doses that can be used.

Research is now going on into all the above types of gene therapy.

How gene therapy is given

As this is still an experimental treatment, the way in which gene therapy is given may vary or change as new techniques develop.

Initially, cells are taken from a blood sample. The genes are isolated and changed (engineered) in the laboratory. They are then attached to a chemical or inserted into a cell, known as the vector.

At present, the changed genes within the vector are usually given by a drip into a vein (intravenously) through a small tube (cannula) inserted into the vein. They may be given directly into the tumour by injection.

The results so far

Gene therapy is a new technique that is being developed for the treatment of a number of different cancers. At the moment it is experimental and it will take many years to find out if it does have an important role in the treatment of cancer. At present many clinical trials are taking place, using a wide variety of different types of gene therapy for many different types of cancer. Nearly all of these studies are at a very early stage. Again, it will be many months or even years before the results are known.

Some studies have finished. Most of these looked at the safety of gene therapy. These have shown that introducing new genes into both tumour cells and normal cells in patients is possible. There have been very few side effects with the gene-based treatments used so far, which is encouraging for the future.

References

This section has been compiled using information from a number of reliable sources including:

  • Oxford Textbook of Oncology (2nd edition). Souhami et al. Oxford University Press, 2002.
  • Cancer and its Management (5th edition). Souhami and Tobias, 2005.

For further references, please see the general bibliography.

Via: http://www.cancerbackup.org.uk

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