Biomedical Engineering – From Theory to Applications

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Biomedical Engineering – From Theory to Applications
Fig. 6. General frame of the porphyrin type structures involved in biomedical studies
Porphyrinoid photosensitizers are classified as belonging to the first, second or third
generation of photosensitizers as shown in Figure 6, or depending on the platform to which
they belong (porphyrin, chlorophyll, dyes) (Allison R.R. et al., 2004). They could also be
classified according to their primary mechanism of action and/or according to their use
(type of cancer, photodiagnosis or therapy).
The first generation of photosensitizers consists only of hematoporphyrin derivatives and
was developed during the 70’s. Photosensitizers belonging to the second generation are
porphyrin derivatives or synthetics made from the late ‘80s on. Second generation 10
photosensitizers are improved compared to the first generation: they have a definite
structure (which means they are no more a combination of monomers, dimers and
oligomers), absorb light at longer wavelengths and cause less skin photosensitization.
Third generation photosensitizers use available drugs and then modify them with different
carriers in order to obtain tailored characteristics.
Examples of clinically available porphyrin sensitizers are presented in Table 2.