Monoclonal antibodies (or MAb in medical shorthand) are antibodies that are identical, each derived from one type of immune cell and each a clone of a single parent cell. For science, that means that the extraordinarily specific nature of antibodies becomes a tool with wide and potentially revolutionary applications. In essence, they can be deployed to find a single targeted substance, such as an antigen found only on a cancer cell, and make it possible to pinpoint the cell and destroy it. In addition to cancer therapies, MAbs are also used in diagnostic tests for everything from pregnancy, to AIDS, to drug screening. Further, the antibodies can be used to lessen the problem of organ rejection in transplant patients and to treat viral diseases that are traditionally considered "untreatable." Scientists are looking at MAbs for a variety of illnesses including chronic inflammatory and infectious diseases.
The antibodies bind to the surface of an intruding agent for the purpose of creation of conditions suitable for elimination of the intruder. The blood proteins called antibodies, or immunoglobins, have the ability to distinguish extraneous molecules from ones native to the body. Organisms produce immunoglobins in response to an invasion by an infectious agent such as a bacterium or a virus. The antibody molecule has a recognition site that binds tightly to specific sites -- proteins or carbohydrates -- located on the surface of the infectious agent. Organisms produce antibodies in response to the intrusion of a foreign polymer that is larger than a certain size; such antibodies will bind tightly to the invading substance but will not bind to unrelated molecules. The binding of an antibody to a bacterium or virus allows certain white blood cells to recognize the invading body as hostile, and they respond by degrading it. In short, the antibody acts as a signal for the elimination of infectious agents.
Most drugs are small molecules – on the order of 10 to 100 atoms. Monoclonal antibodies are enormous in comparison, on the order of 2000 to 20,000 atoms.
Fighting Cancer With Monoclonal Antibodies
Trial treatment of cancer with MAbs started in the 1990s, but in recent years the interest in monoclonal antibodies for oncology has increased considerably. Rituximab (aka Rituxan or MabThera) was approcved by the FDA for non-Hodgkins lymphoma in 1997. Rituximab binds to the CD20 antigen on B-cell lymph cells. Alemtuzumab (aka Campath) recognizes the CD52 antigen on B-cell and T-cell lymph system components and has been used in treatment of chronic lymphocytic leulemia, the most common form of leukemia.
Panitumumab binds to the epidermal growth factor receptor (EGFR). It was approved by the FDA in 2006 for advanced colorectal cancer. Bevacizumab and Cetuximab were both approved by the FDA for colorectal cancer in 2004. Link Panitumumab, Cetuximab binds to EGFR and disrupts cancer cell proliferation. MAbs have been used both as single treatments and in combination with traditional chemotherpy drugs. EGFR inhibitos in particular help reverse the cancer's resistance to chemoptherapy agents.
Bevacizumab (trade name Avastin) was the first anti-angiogenesis drug approved by the FDA. It prevents (or at least slows) the growth of blood vessels. The idea is that the cancerous tumors can't get big if they can't grow capillaries to supply their cells with food and oxygen. One side effect is hypertension. At a molecular level, bevacizumab binds to vascular endothelial growth factor (it's called a VEGF inhibitor) and stops endothelial cell growth.