Anti-Angiogenesis Therapy--Our Best Hope against Cancer?
Anti-angiogenic agents or angiogenesis inhibitors (as they are sometimes called) are a relatively new arsenal of weapons against cancer. Although they have already been approved for use against some types of cancer, their ultimate efficacy is still being evaluated. To put it more bluntly, this is a technology which, in spite of showing great promise, is only in the earliest stages of development and utilization.
Just What Is Angiogenesis?
Before delving into how these agents work, one must first understand the physiology in place. Simply put, angiogenesis is a living organisms' ability to create blood vessels in order to bring nutrients and oxygen to cells, organs, bone and tissues. At the embryonic stage (when a fetus is forming into a human being), the process is categorized as vasculogenesis; later on, angiogenesis takes over and is responsible for blood vessel formation during growth/development and in the midst of trauma and disease.
What everyone must understand is that angiogenesis is a natural process which is necessary both for growth/development, as well as for repairs during trauma and disease. If we were to use inhibitors to completely stop angiogenesis in the human body (whether perfectly healthy or suffering from such a devastating disease as cancer), harm (possibly culminating in death) would result.
Consequently, angiogenesis inhibition can only be used within very restrictive parameters.
Actually, similar restrictions are in place for most chemotherapy agents. Their ability to destroy cancerous cells can be a wonderful tool to use against cancer (in theory); the drawback, however, is the fact that they usually also destroy healthy cells. If we could find a way to limit said damage--to, in essence, "target" or focus the damage to only those cells in need of repair/destruction--chemotherapy would be a more effective treatment than it is right now.
Almost the same caveats may be applied to angiogenesis inhibitors. Ideally, you want these agents to only block the formation of new blood vessels meant to feed tumors; in reality, however, inhibition may also take place for healthy tissue, as well as for the tumors under attack. Under such circumstances--to cite an example of a complication--wounds may not heal properly.
How Do Angiogenesis Inhibitors Work?
First of all, angiogenesis seeks to create new blood vessels from pre-existing lines (one of several distinctions from vasculogenesis, which creates vessels basically from "scratch"). Several processes have to take place in order for these vessels to form. One such process is the release/utilization of angiogenic growth factors; these factors motivate receptors on endothelial cells to produce the enzymes necessary for the creation of new blood vessels.
Angiogenesis inhibitors seek to derail, decrease the rate of or stop these processes. The challenge is (as has been stated) how to make this happen primarily, if not exclusively, for just the tumor(s) in question. Because this is, at best, merely an imperfect weapon (perhaps comparable to a rifle with a malfunctioning scope), a number of complications and side-effects may accompany their use. These include:
- Bleeding and the inability for some wounds to hear properly
- Blood clots (potentially leading to strokes, heart attacks, etc.
- High blood pressure
- Protein in urine samples
- Fistulas & intestinal/stomach perforation (in rare cases)
Some examples of angiogenesis inhibitors include:
- Avastin (Bevacizumab)
- Afinitor (Everolimus)
- Thalomid (Thalidomide)
- Nexavar (Sorafenib)
- Votrient (Pazopanib)
As a general rule, these agents are given to patients in conjunction with other treatments--most notably, chemotherapy. These substances are not meant to kill tumors on their own but, rather, to limit their growth and, in some cases, ability to spread (metastasize) throughout the body.
Conclusion
Angiogenesis inhibitors are only one of several promising areas of research for a cure. While other areas may ultimately prove to be more useful or practical, this weapon has the potential to eventually be a very effective tool against most types of cancer. The stark reality is that malignant tumors cannot grow without massive ongoing supplies of glucose, oxygen and nutrients; angiogenesis is the main tool these diseased cells use to obtain these supplies.
While much more research is still needed, angiogenesis inhibitors are already being used with some success. With our present knowledge of angiogenesis physiology, the technology in its present state may be compared to attempting to bring down an elephant with a .22 caliber rifle. As our understanding of these mechanisms improve, however, we may be able to "shoot" (for lack of a better word) basically the same technology at cancer only, eventually, using perhaps a 10 gauge shotgun.
No elephant (if we may further dwell on this metaphor), regardless of its size, can continue to stand once its oxygen/nutrients supplies are essentially cut off--or so anti-angiogenesis therapy proponents posit.
Copyright, 2015. Fred Fletcher. All rights reserved.
Resources & References
1. http://www.cancer.gov/cancertopics/factsheet/Therapy/angiogenesis-inhibitors
2. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/Angiogenesis.html
