Light – so common that we usually take it for granted, but so basic that we couldn’t live without it.
Ancient civilizations practiced different forms of phototherapy (treatment with light). Ancient Egyptians used sunbathes to cue bone and dermatological illnesses, while in the 20th century Switzerland, Bernhard and Rollier called it heliotherapy and used it in the treatment of tuberculosis.
It is absolutely required by the body in the production of Vitamin D and we know that a lack of sunlight, particularly in winter, leads to depression in a syndrome called SAD (Seasonal Affect Disorder).
Today, we use many types and forms of light in treating illness and disease, including ultraviolet, infrared and the highly concentrated light of a laser.
Given the long history of treating with light, it should come as no surprise that an effective method of battling cancer with light has been discovered. Cancer, the second largest disease killer of mankind, can affect almost every part of the human body.
For this reason, many different kinds of treatment have been developed, including surgery, radiation, chemotherapy and hormone therapy.
PhotoDynamic therapy, or PDT, offers a unique solution to those suffering from cancer mainly because it does not require hospitalization, surgery, chemotherapy, radiation or immunotherapy.
It can be used routinely and repeatedly as it selectively destroys only affected cancerous cells, thus proving it to be one of the most effective, and safest, forms of treatment.
But, what is PDT? Well, in 1900, a medical student named Oscar Raab worked in a pharmaceutical laboratory observing the effect of minute concentrations of acridine, a hydrocarbon dye, on single-celled animals called paramecia.
He noticed that somehow daylight was affecting the results, and upon more careful study, discovered that the acridine killed the paramecia only in the presence of light, while acridine alone and light in the absence of the acridine, didn’t.
Light served to activate the dye, which became known as a photosensitizing agent. In fact, in 1903, a Nobel Prize was awarded to Niels Finsen for his pioneering research in light treatment.
Over the years, other photosensitizing agents were discovered and systematic clinical studies were undertaken, especially in the 1970s, led by Dr. T. J. Dougherty of the Park Institute in Buffalo, NY, in the United States.
He used porphyrin compounds as the photosensitizing agents. This research ultimately led to the U.S. Federal Drug Administration (FDA) to approve it as a cancer treatment.
The technique itself is rather straightforward. The photosensitizing agent is either injected into the patient’s bloodstream or applied topically. It concentrates in cancer cells of all types. Then, the mass, with its accumulated photosensitizing agent, is subjected to a dose of light of a specific wavelength.
The light activates the photosensitive agent causing the release of a highly reactive free-radical oxygen molecule that leads to the destruction of the cancer cell (necrosis) and especially the blood vessels feeding it.
Often, the necrotized tissue just sloughs away and there is normal healing of the wound. However, function and structure of delicate non-cancerous underlying tissue is preserved.
PDT can be used to treat not only superficial tumors, but, by repeated use, large tumors in a process called debulking, where the tumor is progressively reduced in size.
PDT isn’t contra-indicated if other therapies are concurrently utilized, i.e. chemotherapy, while potentially disfiguring results, as can occur with surgery, are minimized if not entirely eliminated.
Traditionally, the limitations have been the photosensitizing agents, as they can have a “spillover” effect, thus affecting normal tissue to some degree.
Also, there were inherent limitations of the light sources, usually lasers, in terms of the depth of penetration through the skin.
That necessitated surgery, particularly endoscopic surgery, in order to be able to introduce the light source to the location of the tumor. New laser light delivery systems are currently being developed to address this limitation.
What about PDT Side Effects?
So what are the side effects of PDT? The major side effect is photosensitivity, or sensitivity to light. While inconvenient, it is hardly an “unacceptable” risk.
While previous types of photosensitizing agents remained in the body sometimes for several months, requiring the patient to stay indoors during the day (to avoid getting a severe sunburn), new agents, like hemoporfin, Foscan, or 5-ALA (a naturally occurring amino acid) are usually eliminated from the body after 24 hours.
Pain is the other potential side effect of PDT. A secondary complication, it results from the breaking down of the tumor tissue, which can cause inflammation and subsequent pain.
But, it can be thought of as a “good pain”, as it indicates that the process is working! Fortunately, it is usually mild to moderate and easily controlled with short-acting painkillers.
Other short-term side effects may include nausea/ vomiting, fever (also associated with inflammation) and occasionally, a metallic taste. Rarely do any of these side effects last more than a day or so.
The Leeds Centre for Photobiology and Photodynamic Therapy in England continues to do substantial research in this field, and isn’t limited to just PDT and oncology. An outpatient clinic specializing in photodynamic therapy has also opened in Ireland, where it is known as Cytoluminescent Therapy (CLT).
The clinic employs the newest photosensitizing agents, derived from green plants, which tend to be more tumor-sensitive and therefore more effective. Under the leadership of William Porter, MD, they report astounding treatment results and cannot keep up with patient demand.
Then He Saw Light
PDT is also being studied in non-oncology related illness, including the treatment of atherosclerosis and both rheumatoid and inflammatory arthritis, among other diseases.
But one of the most promising uses is in the treatment of Age-Related Macular Degeneration (AMD or ARMD). Results are nothing short of exceptional!
ARMD affects 40% of individuals 75 years or older and is the leading cause of blindness in developed countries.
One form of ARMD, the “wet” form, is the result of new blood vessels formation.
Termed “choroidal neovascularisation” (CNV), these vessels grow under the center of the retina, in an area known as the macula.
There, these vessels can leak fluid and bleed, causing scar tissue to form. That scarring can destroy vision in as little as three months!
In ARMD, the photosensitizing agent is also injected into the patient’s bloodstream. The light sensitive dye sticks to the inner lining of the new vessels.
Then, the macula of the patient’s eye is subjected to the dose of light, which activates the photosensitive agent resulting in damage to the blood vessels, causing them to close, preventing the leaking vessels from doing further damage.
The procedure is done on an outpatient basis and takes about 30 minutes.
A study for the treatment of Age-Related Macular Degeneration with Photodynamic Therapy was performed in 22 centers in Europe and the United States in 2003. Vision was stable or improved in 61% of patients treated with photodynamic therapy with virtually no side effects!
As research continues, the application of light as a treatment modality will expand and provide a safe and effective means of treating a large variety of diseases.
Amazing, this thing we call light!