Cancer Research Information - Targeted Therapy

A relatively new avenue of cancer research is the use of “targeted therapies.” In contrast to traditional chemotherapy which uses drugs to kill rapidly growing cells (which does not distinguish between cancer cells and say, the cells of the lining of the intestines), targeted therapy attempts to focus directly on cancer cells themselves. There are several types of drugs that are considered targeted therapies. One targeted therapy may focus on interfering with the molecules that can convert normal cells into cancer cells. Another targeted therapy may use the power of the body’s own immune system to search out and destroy cancer cells. Since these targeted therapies focus on molecular targets a term that may be used is molecular targeted therapies. Regardless of the name, targeted therapies promise to have fewer or less severe side effects than traditional chemotherapy since the cancer is specifically targeted leaving healthy cells unscathed. Targeted therapies have their own, sometimes serious side effects, however.

 

 

In order to create a targeted therapy, scientists have to discover molecular differences between cancer cells and all other normal cells. A quarter of all breast cancer tumors express a protein called HER2 in large quantities. Incidentally tumors that have a lot of this protein are usually more aggressive and recur more often than other types of breast cancer. Breast cancers researchers have capitalized on this molecular difference to devise several targeted therapies that focus on the HER2 receptor.

 

One of the earliest developed targeted therapies is trastuzumab, sold under the brand name Herceptin. Herceptin is a monoclonal antibody. Similar to the antibodies that our bodies generate to recognize, bind to, and help destroy foreign invaders, this monoclonal antibody is constructed in a laboratory to specifically recognize the HER2 receptor. Herceptin (trastuzumab) seeks out any HER2-positive cells in the body and binds to them tightly on the outside of the cell. Then the person’s own immune system searches for the bound Herceptin and works to remove them from the body. Herceptin, when bound to the HER2 protein, also blocks the HER2 receptor from doing its cancer-promoting work.

 

Lapatinib, or Tykerb, acts on cells that overexpress HER2 protein but this drug inhibits the pro-cancer properties of the HER2 receptor itself. Tykerb binds to the HER2 receptor that is on the inside of the cell and blocks the cellular machinery that keeps the cell alive and thriving. Tykerb can be used in conjunction with Herceptin in metastatic breast cancer. In order to be considered for Tykerb or Herceptin, a patient usually must have the kind of tumor that expresses HER2. When a breast cancer is removed or biopsied, it is tested in a laboratory for HER2. These treatments are currently used in conjunction with traditional chemotherapy and other cancer treatments.

 

Another targeted therapy that is used in breast cancer is bevacizumab or Avastin. Like trastuzumab, Avastin is a monoclonal antibody but binds to a different location than the HER2 protein. It has been known for some time that solid tumors are locations of high degrees of metabolic activity. Tumors, including breast cancers, need a lot of blood to support these metabolic functions and they highjack and grow a lot of blood vessels for this purpose. Avastin binds to a receptor called VEGF that is important for the blood vessels that form around and deliver blood to tumors. When Avastin is bound to the VEGF receptor it blocks its ability to grow more blood vessels for the tumor, thus starving it of blood, oxygen, and nutrients and causing it to die.