The photodynamic process induces cell damage and death by the combined effect of a
photosensitizer (PS), visible light, and molecular
oxygen, which generate
singlet oxygen ((1)O(2)) and other
reactive oxygen species that are responsible for cytotoxicity. The most important application of this process with increasing biomedical interest is the
photodynamic therapy (
PDT) of
cancer. In addition to
hematoporphyrin-based drugs, 2nd generation PSs with better photochemical properties are now studied using cell cultures, experimental
tumors and clinical trials.
Porphycene is a structural isomer of
porphyrin and constitutes an interesting new class of PS.
Porphycene derivatives show higher absorption than
porphyrins in the red spectral region (lambda > 600 nm, epsilon > 50000 M-(1)cm(-1)) owing to the lower molecular symmetry. Photophysical and photobiological properties of porphycenes make them excellent candidates as PSs, showing fast uptake and diverse subcellular localizations (mainly membranous organelles). Several tetraalkylporphycenes and the tetraphenyl derivative (
TPPo) induce photodamage and cell death in vitro. Photodynamic treatments of cultured tumor cells with
TPPo and its
palladium(II) complex induce cytoskeletal changes, mitotic blockage, and dose-dependent apoptotic or necrotic cell death. Some pharmacokinetic and phototherapeutic studies on experimental
tumors after intravenous or topical application of lipophilic alkyl-substituted
porphycene derivatives are known. Taking into account all these features,
porphycene PSs should be very useful for
PDT of
cancer and other biomedical applications.