The success exhibited by Photofrin and the potential
shown by a number of the second-generation photosensitizers
has caused an explosion in photodynamic therapy,
resulting in the unveiling of new photosensitizers along
with an investigation into well-known naturally occurring
Hypericin, for example, is welldocumented
as having photodynamic activity as it causes
hypericism or photopoisoning in grazing animals that consume
large quantities of plants containing this compound,
often leading to skin irritation, fever and even death.
This multicyclic quinione, which absorbs light at around
590 nm, is being investigated as a photosensitizer
for PDT and is presently in Phase I clinical trials for the
treatment of psoriasis, warts and skin cancer.
The naturally occurring perylenequinones such as
hypocrellins, which are produced by fungi and insects,
are also under evaluation as PDTs.
Several pharmaceutical companies are actively developing
new synthetic photosensitizers.
For example, Scotia
Pharmaceuticals is interested in bacteriochlorins for
while Hamamatsu Phototonics is investigating ATXS10, a
In reality, any chromophore that can
effectively produce photocytotoxicity upon illumination
has the potential to be used in photodynamic therapy,
leading to endless possibilities.