Monoclonal Antibodies for Cancer

Although only a dozen monoclonal antibody therapies are marketed in the US, they are one of the hottest areas of drug development. There are dozens of monoclonal antibodies (also called mAbs) in clinical trials.

Monoclonal antibodies are polypeptides normally made by the immune system to fight disease or infection. They consist of two long peptide chains (heavy chains) and two shorter peptide chains (light chains). They are held together by disulfide bonds between some amino acids.

Monoclonal antibodies sold as therapies are manufactured industrially and usually intended to be given intravenously or by injection.

What makes monoclonal antibodies useful is their specificity-their ability to bind to one, and only one targeted molecule, called a receptor. Much of the antibody, called the constant region, remains the same. A small section of the antibody, called the variable region, determines binding.

By engineering the variable region of the antibody, drug makers can design it to bind to one target, and only one target. The fact that the antibody binds to only one molecule means that, in principle, it can have a therapeutic response with minimal side effects.

In practices, this is often not the case. If, for example, a receptor is found in more than one type of cell, or in multiple places throughout the body, the antibody can cause drug side effects.

When an antibody binds to the targeted molecule, also called a receptor, this may inhibit or increase the receptor's activity. Changing the receptor activity can reduce the symptoms or spread of a disease.

In cancer (oncology), many antibodies target molecules that are overabundant in cancer cells. Often this overabundance causes cells to grow and divide more rapidly than is normal. Thus, the antibody is expected to prevent further tumor growth and cell division. It does not usually kill all the cancer cells or cure the cancer. For the antibody to continue working, the patient must continue taking it.

In another strategy, aimed at curing the cancer, the firm designs an antibody that binds, as much as possible, only to the cancer cells. The company attaches a radioactive or toxic molecule, called a "payload." When the antibody binds to the tumor cells, the payload kills them.

Antibodies bound to radioactive materials could also be used to detect or image tumors.