Is Targeted Therapy the new face of Cancer Treatment?

The idea behind Targeted Therapy involves administering a specific type of drug to a patient which interferes with, or blocks, the growth and division of cancerous cells. Currently, many forms of chemotherapy and radiotherapy exist which also kill cancerous cells however they are not considered to be "specific"; that is, they don’t target cancerous cells exclusively and so non-cancerous cells are also destroyed, although in relatively small numbers.

Targeted Therapy will interfere with the mechanisms by which cancerous cells grow and divide meaning that this future form of treatment really is targeted towards cancerous cells. Currently there are 11 drugs that have been approved by the FDA and are being used in clinical trials while many more are in the animal model stage. Even so, the research is still in its infancy and there is a long way to go before these drugs are available to cancer patients in general.

How does Targeted Therapy work?

Cancerous cells develop when healthy cells start to grow and divide uncontrollably. This often happens when the regulatory mechanisms that control the rate at which a cell divides become damaged e.g. by toxic chemicals such as carcinogens, and so the signals that tell a healthy cell to stop growing and dividing no longer reach the cell’s nucleus where the all important DNA is stored.

Several types of Targeted Therapy block the signals that tell a cell to grow and divide so that it no longer acts in an uncontrollable manner. This may be able to stop excessive cell division altogether which would effectively stop the growth and spread of a cancer.

There are a number of potential Targeted Therapies that are currently being developed, each of which works in a slightly different way. For example:

• "Small molecule" drugs block essential enzymes which are required by cancerous cells to continue dividing. These drugs are one of the main areas of research and so far the FDA has approved a number of ‘small molecule’ drugs which have been designed to treat cancers such as non-small cell lung cancer and some forms of Chronic Myeloid Leukaemia.
• "Apoptosis inducing" drugs interfere with the manufacturing process of a number of essential enzymes and proteins that a cancerous cell needs to carry on living. Hence, the cell can no longer function and it undergoes spontaneous death i.e. apoptosis. Again the FDA has already approved a variety of drugs for use in clinical trials, most of which are for use against leukaemia, non-Hodgkin’s lymphoma and a few solid tumour cancers.
• Immunotoxins are possibly the most promising of the Targeted Therapies so far developed. These drugs are composed of a toxin molecule attached to a specific antibody fragment. The antibody fragment is designed to attach itself to a particular receptor which is only present on the surface of cancerous cells so that the drug is highly specific and normal healthy cells stay safe from harm. Once the drug molecule has attached itself to a cancerous cell then the toxin part enters the cancerous cell and kills it from the inside out. So far, this type of drug has already gone through three generations because of problems however the Immunotoxins that are being tested today only contain the elements they need to seek out, recognise and kill cancerous cells. Unfortunately, researchers are finding that the human body quickly forms an immune response to the toxin portion of these drug molecules and so only a few cycles can be administered before the immune system destroys the drug. This is another problem that needs to be overcome.

Immunotoxins and the other forms of Targeted Therapy will hopefully be developed further so that they can treat specific types of cancer. In this way, the treatment of cancer may become highly individual and every patient will be given a unique drug regime specific to their condition.

Much research is still needed though and as yet scientists have had little success treating solid tumours with Targeted Therapies. This is because it is difficult to get the drugs into the mass of a solid tumour and so only the cancerous cells at the edges are killed successfully. Haematological cancers i.e. those that affect the cells of the blood, bone marrow and spleen, are showing signs of improvement in clinical trials however and so it may be that the use of Targeted Therapies will be restricted to certain types of cancer.

While these new drug therapies are showing promising results they are sadly still a long way from being available in general hospitals. Many are still in the preclinical stage i.e. being tested on animal models, although a small number have reached the clinical trial stage. Here they are proving to be highly selective with regards to the types of cells they kill; that is they target cancer cells and leave healthy cells to function as normal. This will mean that Targeted Therapies should produce fewer side effects and patients will be able to enjoy a better quality of life.

Whether these Targeted Therapies will be used alone or in conjunction with current forms of malignant mesothelioma cancer treatment such as radiotherapy and chemotherapy remains to be seen however from the evidence available so far, they do seem to be one of the leading contenders for the face of cancer treatment in the future.