Dr. Wachiraporn Arunothong
What Are Targeted Cancer Therapies?
Targeted cancer therapies are drugs or other substances that block the growth and spread of cancer by interfering with specific molecules (“molecular targets”) that are involved in the growth, progression, and spread of cancer. Targeted cancer therapies are a personalized form of medicine. Targeted therapies differ from standard chemotherapy in several ways:
- Targeted therapies act on specific molecular targets that are associated with cancer, whereas most standard chemotherapies act on all rapidly dividing normal and cancerous cells.
- Targeted therapies are deliberately chosen or designed to interact with their target, whereas many standard chemotherapies were identified because they kill cells.
- Targeted therapies block tumor cell proliferation. Whereas standard chemotherapy agents kill tumor cells.
- Targeted therapies are currently the focus of anticancer drug development. They are a cornerstone of precision medicine, a form of medicine that uses information about a person’s genes and proteins to prevent, diagnose, and treat disease.
- Diagnosis and treatment of reproductive health problems
What are the goals of targeted therapies?
- Cure cancer
- Kill cancer cells
- Slow tumor growth
- Relieve symptoms from cancers
What types of targeted therapies are available?
The therapies include hormone therapies, signal transduction inhibitors, gene expression modulators, apoptosis inducers, angiogenesis inhibitors, immunotherapies, and toxin delivery molecules.
Hormone therapies slow or stop the growth of hormone-sensitive tumors, which require certain hormones to grow. Hormone therapies act by preventing the body from producing the hormones or by interfering with the action of the hormones. Hormone therapies have been approved for both breast cancer and prostate cancer.
Signal transduction inhibitors block the activities of molecules that participate in signal transduction, the process by which a cell responds to signals from its environment. During this process, once a cell has received a specific signal, the signal is relayed within the cell through a series of biochemical reactions that ultimately produce the appropriate response(s). In some cancers, the malignant cells are stimulated to divide continuously without being prompted to do so by external growth factors. Signal transduction inhibitors interfere with this inappropriate signaling.
Gene expression modulators modify the function of proteins that play a role in controlling gene expression.
Apoptosis inducers cause cancer cells to undergo a process of controlled cell death called apoptosis. Apoptosis is one method the body uses to get rid of unneeded or abnormal cells, but cancer cells have strategies to avoid apoptosis. Apoptosis inducers can get around these strategies to cause the death of cancer cells.
Angiogenesis inhibitors block the growth of new blood vessels to tumors, a process called tumor angiogenesis. Blood supply is necessary for tumors to grow beyond a certain size because blood provides the oxygen and nutrients that tumors need for continued growth. Treatments that interfere with angiogenesis may block tumor growth. Some targeted therapies that inhibit angiogenesis interfere with the action of vascular endothelial growth factor (VEGF), a substance that stimulates new blood vessel formation. Other angiogenesis inhibitors target other molecules that stimulate new blood vessel growth.
Immunotherapies trigger the immune system to destroy cancer cells. Some immunotherapies are monoclonal antibodies that recognize specific molecules on the surface of cancer cells. Binding of the monoclonal antibody to the target molecule results in the immune destruction of cells that express that target molecule. Other monoclonal antibodies bind to certain immune cells to help these cells better kill cancer cells. Monoclonal antibodies that deliver toxic molecules can cause the death of cancer cells specifically. Once the antibody has bound to its target cell, the toxic molecule that is linked to the antibody, such as a radioactive substance or a poisonous chemical, is taken up by the cell, ultimately killing that cell. The toxin will not affect cells that lack the target for the antibody.
Cancer vaccines and gene therapy are targeted therapies because they interfere with the growth of specific cancer cells.
What are the forms of targeted cancer therapies?
There are two forms of targeted cancer therapies, monoclonal antibody drugs, and small-molecule drugs. Monoclonal antibody drugs are synthetic versions of large immune system proteins (called antibodies) designed to attack a very specific cancel cell target or other cells. These types of drugs are referred to as “biologics” because they are made in living cells. Small-molecule drugs are chemicals like most other types of drugs. They are not antibodies. Since antibodies are large molecules, they are referred to as “small-molecule” targeted drugs.
How are targeted cancer therapy drugs given?
The most common ways to give targeted therapy drugs are by mouth, either as a pill or capsule or into a vein via intravenous administration. Some targeted drugs might be injected through the skin into the muscle layer.
If you take a targeted drug by mouth, it is very important to take the exact dose, at the right time, for the entire duration of the prescription. For some cancers, targeted drugs are taken by mouth for many years. IV drugs are usually given as an infusion that can last 30 minutes to a few hours. A mixed drug solution flows from a plastic bag through an IV line into one of your veins. The infusion might be done in your doctor’s office, in a clinic, in a hospital’s outpatient department, or even at home. Talk to your doctor or nurse ahead of time so that you know what to expect during treatment.
What are the limitations of targeted therapies? Targeted therapies have been discovered in recent years, the impact is limited to some specific types of cancer. Although targeted therapies are typically tolerated better with less toxicity compared with conventional cytotoxic drugs, they can lead to serious adverse effects.
Drug resistance also limits the efficacy of these targeted therapies, as is the current clinical situation regarding conventional chemotherapy. As the malignant phenotype is often regulated by multiple parallel pathways, the cancer cell will use alternative signaling components in order to survive. Importantly, understanding resistance mechanisms could provide the basis for the design of second-generation therapies.
What are the side effects of targeted therapies?
- The common side effects of targeted therapies include
- Skin change – Skin side effects vary from color change to desquamation of skin.
- High blood pressure – Targeted therapy targeting blood vessel formation can raise blood pressure.
- Wound healing problem
Autoimmune reactions – Sometimes, targeted therapy will activate the immune system and causes autoimmune reactions in multiple organs including lungs, liver, skin, eyes, or nervous system. This side effect is not common but can be life-threatening.
What causes side effects?
Although targeted therapy drugs don’t affect the body the same way that standard chemo drugs do, they can still cause side effects. There are many different types of targeted drugs, and the side effects of these drugs depend largely on what each drug targets. Some drugs target substances that are more common in cancer cells, but are also found on healthy cells. These drugs can affect healthy cells, too, causing side effects.
Some types of targeted drugs seem to cause more side effects than others. For example, when drugs attack more than one target, side effects are more likely. Drugs that act as angiogenesis inhibitors affect new blood vessel growth all over the body, not just near cancer, which can lead to side effects. Some drugs that boost the immune system can sometimes cause it to attack other parts of the body, which can also lead to side effects.
What should I know about side effects?
Not every person gets every side effect, and some people get few if any. The severity of side effects can vary greatly from drug to drug and from person to person. Be sure to talk to your doctor and nurse about which side effects are most likely with your treatment, how long they might last, how bad they might be. Your doctor may give you medicines to prevent some side effects before they happen or to treat certain side effects once they occur.
Rare and unusual side effects can happen with some of these drugs, and some can be serious. All changes and side effects should be reported to your doctor.
Although side effects can be unpleasant, the less serious ones must be measured against the need to fight cancer.