How Targeted Treatments Work
Standard chemotherapy drugs are powerful medications that can kill cancer cells. They offer an effective way to treat tumors, but they can also harm healthy tissues. One day, targeted treatments may replace chemotherapy. But for now, doctors will continue to use chemotherapy, sometimes in combination with targeted drugs. (In some cases, doctors combine two targeted treatments without chemotherapy.)
There are many targeted treatments already available, and many more drugs are being studied in laboratories and clinical trials. A number of these medications are oral drugs, which are easier and more convenient for patients to take. To kill a cancer cell, targeted treatments disrupt many different types of cell mechanisms.
Drugs made of small molecules are able to get past the tumor cell’s outer layer and interfere with cell growth from the inside. These small molecules block signals from proteins that tell cancer cells to grow and divide. (Proteins are controlled by genes.) This type of targeted treatment can help stop tumor growth and may cause cancer cells to die.
Examples of small-molecule targeted treatments include dasatinib (Sprycel), which is approved by the U. S. Food and Drug Administration (FDA) to treat people with chronic myelogenous leukemia (CML) or acute lymphoblastic leukemia, and nilotinib (Tasigna), which is approved to treat some people with CML.
Other types of small-molecule drugs disrupt tumor cells by changing some of their cell functions or by directly causing their death in a process known as apoptosis. Two examples are romidepsin (Istodax), approved by the FDA for the treatment of cutaneous T-cell lymphoma, and bortezomib (Velcade), approved for the treatment of multiple myeloma.
Some small-molecule drugs block the growth of blood vessels to tumors. To grow beyond a certain size, tumors must have a blood supply to get oxygen and nutrients. Treatments that interfere with the formation of these blood vessels may block tumor growth. An example of this type of drug is pazopanib (Votrient), approved by the FDA for the treatment of advanced kidney cancer.
Monoclonal antibodies track down tumor cells and bind to their surface to disrupt the cells’ function from the outside. Made in the laboratory, monoclonal antibodies are a type of protein. Although they cannot get past a tumor cell’s outer layer, monoclonal antibodies can attach themselves to the cell surface and block its receptors, or doorways. When receptors are blocked, growth signals cannot get in and the cell dies. There are many types of monoclonal antibodies. Each type is designed to find a specific kind of tumor cell.
Sometimes, monoclonal antibodies are used to carry an anti-cancer medicine directly to the tumor cell to kill it. The advantage of using this technique is that the treatment bypasses healthy tissue and goes directly to the tumor. Brentuximab vedotin (Adcetris) is an example of an antibody combined with a targeted treatment. Hitching a ride on the monoclonal antibody, the drug enters the cell and kills it. Brentuximab vedotin is approved by the FDA for the treatment of Hodgkin’s lymphoma and systemic anaplastic large cell lymphoma.
Some monoclonal antibodies are designed to trigger the immune system to fight the cancer. In the case of ipilimumab (Yervoy), the antibody seeks out a substance on tumor cells called CTLA-4, which blocks the immune system. By blocking CTLA-4, ipilimumab stimulates the immune system to attack melanoma cells. This medication has been approved by the FDA for treating melanoma that has spread.