by Acad. Georgi GEORGIEV and Alexandr SOBOLEV, Dr. Sc. (Biol.), Institute of Gene Biology, Russian Academy of Sciences
The main problem of drug treatment of cancer using chemo-, radio, photodynamic therapy or other methods is in grave side effects from which the patients suffer. All types of cancer cell exposure unfortunately involve normal, intensely dividing cells with the same characteristics. The task of scientists is to increase the selectivity of drug action. This can be attained by drug delivery to transformed cells by means of multimodular carriers.
THERAPEUTIC EFFECT OF LIGHT
Therapeutic and diagnostic methods based on recent progress in photochemistry, photobiology, nuclear physics and chemistry have been ever more often used in oncology in these two last decades. One promising approach is offered by photodynamic therapy (PDT), when a photosensitizer drug accumulated in the tumor destroys it by absorbing the irradiating light. The photosensitizer proper is nontoxic for the malignant tumor, but the so-called active oxygen forms (AOF), appearing during its illumination in the presence of O2, are destructive: these are singlet oxygen (1O2), hydroxyl radical (•OH), and others; many molecules in the cell (proteins, lipids, nucleic acids) and supramolecular structures formed by them serve as targets for AOF. An intricate succession of photochemical and photobiological processes leads to irreversible damage to cancer tumor cells and/or vessels.
As it often happens, the idea of using light-activated chemical compounds for the treatment of various diseases is not new. Vitiligo (skin disease) was treated in ancient Egypt using plants containing psoralenes* and sunlight. Recently (in 1903) a Danish scientist Niels R.
* Psoralenes are natural photosensitizers contained in extracts from seeds of umbellate plants (Ammi majus L.) and legumes (Psoralea corylifolia L.) and their synthetic analogs. - Auth.
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