Tumor Targeted Therapy
Targeted Therapy: Monoclonal Antibodies,
Anti-angiogenesis, and other Cancer Therapies
Targeted therapy is the result of about 100 years of research dedicated to understanding the differences between cancer cells and normal cells. To date, cancer treatment has focused primarily on killing rapidly dividing cells because one feature of cancer cells is that they divide rapidly. Unfortunately, some normal cells divide rapidly too, which can cause multiple side effects.
Targeted therapy is intended to identify other features of cancer cells. Scientists look for specific differences between the cancer cells and normal cells. This information allow for creation of a targeted therapy which attacks the cancer cells without damaging normal cells -- leading to fewer side effects. Each type of targeted therapy works a little differently but all are designed to interfere with cancer cell to growth, division, repair and/or communication with other cells. Modern targeted therapy types include the use of monoclonal antibodies and anti-angiogenesis drugs.
The different types of targeted therapies are defined in three broad categories. Some targeted therapies focus on internal components and function of the cancer cell. The targeted therapies use small molecules that can get into the cell and disrupt the function of the cells, causing them to die. There are several types of targeted therapy that focus on the inner parts of the cells. Other targeted therapies target receptors that are on the outside of the cell. Therapies that target receptors are also known as monoclonal antibodies. Anti-angiogenesis drugs target the blood vessels that supply oxygen to the cells, ultimately causing the cells to starve.
Researchers agree that targeted therapies are not a replacement for traditional therapies. Targeted therapies involve production of components such as monoclonal antibodies or anti-angiogenesis drugs may best be used in the short term, combination with traditional therapies. More research is needed to identify which cancers may be best treated with targeted therapies such as monoclonal antibodies or anti-angiogenesis drugs and to identify additional targeting for more types of cancer.
Targeted Cancer Therapies
Monoclonal antibodies are a relatively new type of "targeted" cancer therapy. Antibodies are part of the immune system. Normally, the body creates antibodies in response to an antigen (such as a protein in a germ) entering the body. The antibodies attach to the antigen in order to mark the antigen for destruction by the body's immune system. In the laboratory, scientists analyze specific antigens on the surface of cancer cells (target) to determine a protein to match the antigen. Then, using protein from animals and humans, scientists work to create a special antibody that will attach to the target antigen. An antibody will attach to a matching antigen like a key fits a lock. This technology allows treatment to target specific cells, causing less toxicity to healthy cells. Monoclonal antibody therapy can be done only for cancers in which antigens (and the respective antibodies) have been identified. The following are monoclonal antibodies:
Anti-Angiogenesis (Angiogenesis Inhibitors)
Anti-angiogenesis is the process of stopping the formation of new blood vessels. A little background on angiogenesis would be helpful to understand how this works.
In normal tissue, new blood vessels are formed during tissue growth and repair (i.e. a healing wound). Blood vessels carry oxygen and nutrients to tissue that are necessary for growth and survival. Cancer tumors need blood vessels to grow and spread. Through a complex process, endothelial cells (which line the blood vessels) are able to divide and grow and create new blood vessels. This process is called angiogenesis and it occurs in both healthy and cancerous tissue.
There are known substances that both stimulate angiogenesis and stop, or inhibit, angiogenesis (blood vessel formation). Scientists study the production of both natural and synthetic (man-made) substances, called anti-angiogenesis agents or angiogenesis inhibitors currently, there are more than 20 compounds being tested on a variety of cancers in clinical trials. Some of these angiogenesis inhibitors are available commercially, approved by the FDA for other uses. Drugs like Interferon-alpha and Thalidomide are believed to have ability to inhibit angiogenesis and are being studied in specific cancer types of cancers. Other anti-angiogenesis drugs are not yet approved by the U.S. FDA but available outside the U.S.