Photodynamic therapy (
PDT) is a promising new modality in the treatment of
cancers, which employs the interaction between a
tumor-localizing
photosensitizer and light of an appropriate wavelength to bring about molecular
oxygen-induced cell death. We have investigated the efficacy of
photosensitizers from the family
perylenequinone, namely
Hypericin,
Hypocrellin A and B, in the treatment of
cancer. These
photosensitizers are known as potent second generation natural
photosensitizers that have phototherapeutic advantages over the presently used
porphyrins. We have studied the in vitro signaling mechanism involved in the photodynamic action following
PDT in various human
carcinoma cell lines. The difference of
tumor cell death between two modes of action i.e., vascular- and cellular-mediated cell death, were evaluated in order to compare treatments that can efficaciously eradicate
tumor in xenografts model. The antivascular effect of
PDT was demonstrated in the chick chorioallantoic membrane (CAM) model.
Tumor therapy based on targeting the vasculature of the
tumor is indeed promising as demonstrated in the higher relative regression percentage of treated
tumor compared to cellular targeted
PDT. The favorable
tumor response derived from short
drug-light interval mediated
PDT was primarily based on the differential uptake of the
photosensitizer into
tumor-associated vasculature as opposed to the cellular compartments of the
tumor.