Generality
Photochemotherapy (or photodynamic therapy ) is a non-invasive therapeutic strategy with low toxicity, which involves the use of photosensitive drugs (light-sensitive); these drugs are selectively exposed to light radiation, which is able to transform them into toxic substances for cancer cells or other specific types of cells.
Photochemotherapy has proven effective in killing bacteria, fungi and viruses, and is also used in the treatment of acne. It can also be used in the treatment of diseases such as age-related macular degeneration, psoriasis, vitiligo and various types of malignant tumors.
Photochemotherapy for the treatment of tumors
As mentioned above, this type of therapy is also used in the treatment of tumors. The photosensitive compound must be selective for malignant cells, so that - once activated - it only kills the diseased cells, sparing healthy cells.
Photochemotherapy can be used, for example, for the treatment of skin tumors or internal tumors.
For the treatment of skin tumors, the photosensitive compound is usually administered locally and only the skin affected by the pathology is irradiated.
An example of skin cancer treated with photochemotherapy is cutaneous T-cell lymphoma . In this case, the photosensitive compound used is a derivative of psoralen (P) and the light source is a long wavelength ultraviolet radiation (UVA rays); this strategy is called PUVA therapy . Psoralen is the progenitor of a family of natural molecules called furanocumarine. When psoralen or its derivatives are irradiated by UVA rays, these form bonds with the DNA of the cells in which they are found, causing death.
As regards the treatment of internal tumors, the photosensitive compound can be administered intravenously, while irradiation with light takes place via endoscopes or optical fiber catheters. Among the various photosensitive compounds that can be used we find porphyrin derivatives, which are activated by light radiation with a wavelength between 600 and 1, 000 nm. Porphyrins are natural molecules, cellulose and the heme group are part of this class; the former is essential for plant organisms to perform chlorophyll photosynthesis, while the heme group - present in the hemoglobin of red blood cells - is essential for the transport of oxygen in the body.
Side effects
The side effects may be due both to the intake of the photosensitive compound and to exposure to the light source; in this case the possible side effects depend on the area that has been irradiated.
The following are some of the adverse effects that can occur:
- Headache;
- Nausea and vomit;
- Irritation and rash;
- Chromatic changes in the skin near the treated area;
- Itch;
- Dry mouth;
- Sleep disorders.
Photochemotherapy could also induce the development of a secondary tumor. This, however, rarely happens and in order to verify it needs more factors that concur one with the other in order to favor the onset of the pathology.
