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Color coded healing
By Sharon Souther-Bethea
In the infinite world of biomedical research, some of the most incredible discoveries are made when scientists focus on the most basic theories.
Why blood is red and why plants are green are not normally questions associated with cancer cures, but Louisiana State University researchers are using these colors of life to produce new and potent cancer drugs.
"This is a very exciting time for researchers at LSU and in the nation," says chemist Graça Vicente, Ph.D., associate professor, LSU Department of Chemistry. "As we glean more information about how drugs work at the molecular level, our research has led to colored organic compounds that may be more selective to disease sites. In our case, pigments found in blood and plants are contributing to more targeted and effective cancer drugs that can minimize side effects."
Heme, a molecule in hemoglobin, makes blood red. Chlorophyll, heme's relative, makes plants green. First investigated by scientists more than 400 years ago, the colors are used commercially in dyes and as natural conduits of energy. Their molecules are photoactive-they respond to light. Some of the compounds are also fluorescent. Such molecules are found in many common plants and foods, including carrots, celery, fennel and figs.
Scientists have suspected for years that these colored organic compounds that respond to light, called porphyrin-based sensitizers, would prove effective delivery vehicles for cancer killing drugs because cancer cells quickly absorb and retain the compounds. A recent review of the field found 20 volumes of research about the pigments. Yet only one light-activated cancer fighting drug, Photofrin, has been approved by the U.S. Food and Drug Administration. That was in 1995.
In her lab at LSU, Vicente is working to add more pigments to medical arsenals and to advance a wider range of cancer treatments and detection methods. Vicente theorizes that even boron-a semi-metallic black element used, among other things, for nuclear reactions-can be combined with the pigments to treat cancer.
Her research centers on creating new porphyrin-based compounds for use in two therapies for treatment delivery: photodynamic therapy (PDT) and neutron capture therapy (NCT). Currently, PDT is limited in the types of cancers it can treat. NCT has yet to be approved by the FDA for treatment.
In PDT, fluorescent colored compounds are injected into patients and absorbed by cells all over the body. The fluorescent agent remains in cancer cells for a longer period of time than healthy cells, highlighting the dangerous cells for treatment like a fluorescent marker.
When low-powered light beams are directed on the highlighted cells, a chemical reaction occurs that destroys the cancer cells. This precise delivery leaves surrounding tissues intact, reducing the hair loss, nausea and other side effects of conventional treatments.
PDT has its limitations, however. Because light beams penetrate less than an inch through tissue, this procedure is used only to treat cancers on or just below the skin or on the lining of internal organs such as in the esophagus, lungs and bladder. The therapy cannot activate photosensitizing agents in the brain or in tumors deep within the body.
The brain, unlike every other part of the body, has natural barriers that prevent harmful substances from penetrating its membranes, making conventional drug therapy difficult. Brain cancer is also one of the most lethal forms of cancer.
Vicente is studying how boron and neutron capture therapy may be used to treat cancers deeper within the body's tissue and brain. The chemist and her team have developed a boron-carrying compound that is showing promise in research trials involving mice.
With NCT, the theory is that organic pigments can be combined with boron and delivered intravenously. Tumors absorb the boron-containing compound, which marks the tumor for treatment. Subatomic particles created by a nuclear generator beamed at the cancer cells produce a chemical reaction that destroys the cancer cells.
Though it has yet to be approved by the FDA for cancer treatments, researchers believe NCT may be effective because radiation can penetrate as much as two inches deeper through tissue than light. Vicente estimates it will take five to 10 years for NCT to be available for widespread use, but the research at LSU could pave the way for using nature's own pigments to battle a host of chronic diseases.
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