Immuno-oncological research is exploring several different approaches to immunotherapy, including vaccines, checkpoint inhibitors, and monoclonal antibodies. At present, several different types of monoclonal antibody drugs exist, but researchers are still exploring how to employ them most effectively in a treatment plan. The term monoclonal antibody refers to a molecule produced in a laboratory that has special programming allowing it to attach to specific biomarkers on cancer cells. These molecules look like the antibodies that our bodies naturally produce in response to infections and vaccines.
When used to treat patients, monoclonal antibodies are introduced to the body intravenously. Often, these therapies are used in combination with other approaches, such as chemotherapy, although they may also be administered alone. The number of sessions that people must undergo depends on the specific drug and the type of cancer. Researchers found that monoclonal antibody drugs effectively treated some advanced cancers that had not responded to chemotherapy or that had recurred. Because of this success, oncologists often choose to introduce them earlier in the course of disease treatment. With some diseases, such as non-Hodgkin’s lymphoma, monoclonal antibody drugs are now used as an initial treatment. However, many of these drugs are still in experimental phases.
Five Strategies for Treating Cancer with Monoclonal Antibody Drugs
Monoclonal antibodies can help treat cancer in a number of ways:
- Researchers use them largely to make cancer cells more recognizable by the patient’s immune system. The immune system naturally attacks foreign invaders, but because cancer cells derive from healthy cells, the immune system may not recognize them as something that is non-self. When a monoclonal antibody attaches to a part of the cancer cell, it marks it so that the immune system begins to recognize it as non-self. For example, one monoclonal antibody drug called rituximab attaches to the CD20 protein found on B cells in the immune system and triggers an attack. Rituximab can also cause drops in the number of healthy B cells, but the body will naturally regenerate them.
- Some monoclonal antibody drugs are designed to block certain chemicals, known as growth factors, from attaching to cancer cells. These chemicals promote growth, and cancer cells can sometimes express additional copies of growth factor receptors to grow more quickly than normal cells. When monoclonal antibodies block the connection with receptors, the cell can no longer grow. This mechanism is used by cetuximab, which is approved to treat colon cancer and head and neck cancers. Cetuximab attaches to receptors for epidermal growth factor so that this signal can no longer get to the cell. As a result, the cancer slows or even stops growing.
- Another strategy that researchers have employed is using monoclonal antibodies to deliver radiation to cancer cells. To achieve this, biological engineers attach a radioactive particle to the monoclonal antibody, allowing for targeted irradiation that does not damage nearby healthy cells. Through radiation-linked monoclonal antibodies, oncologists can deliver low levels of radiation over long periods of time, which some researchers believe to be more effective than the conventional high-dose external beam radiation. Ibritumomab treats non-Hodgkin’s lymphoma using this strategy by attaching to receptors found only on cancerous blood cells.
- Monoclonal antibodies can also deliver targeted chemotherapy to cancer cells by attaching them to effective chemotherapy drugs. Ado-trastuzumab emtansine has earned approval for use in treating HER2-positive breast cancer. The drug has an antibody that attaches to HER2 receptors. When the cancer cells consume the antibody, it release chemotherapy. This approach prevents chemical damage to healthy cells.
- A final cancer treatment strategy made possible by monoclonal antibodies involves the inhibition of blood vessel formation. Because cancer cells require blood vessels for oxygen and other nutrients, they will produce growth signals that trigger the formation of new blood vessel networks. Monoclonal antibodies have been designed to block growth signals so that tumors cannot develop the blood vessel network they need to grow. This strategy can keep tumors small, or it can trigger the death of blood vessels around a tumor so that it shrinks. Bevacizumab blocks vascular endothelial growth factor signals so that they no longer connect to cancer cells.
The Side Effects Tied to Monoclonal Antibodies
Treatment with monoclonal antibodies typically involves fewer side effects than more traditional approaches to treatment, such as chemotherapy. Some of the common side effects include nausea and flu-like symptoms, as well as allergic reactions such as hives. Some patients may experience diarrhea or skin rash. More serious side effects remain fairly rare, but they can prove life-threatening. Severe reactions to infusion can lead to death, so doctors typically monitor patients closely and may give them medicine to block allergic reactions prior to treatment. Some monoclonal antibodies have been associated with heart problems, such as heart attack or even heart failure. Severe skin reactions can lead to very serious infections. Doctors also monitor red blood cell, white blood cell, and platelet counts to ensure that they remain at healthy levels over the course of treatment.