Combination of photodynamic therapy with anti-cancer agents

Degenerative diseases such as cancer usually involve more than one pathological process. Therefore, attempts to combat such diseases with monotherapeutic approaches may not always do so efficiently. For this reason, the use of combination therapy with modalities that target different disease pathways represents an alternative strategy. Photodynamic therapy (PDT) has already been established as an alternative therapy for the treatment of various types of malignant disorders, including oesophageal, lung and bladder cancer as well as other degenerative diseases. This technique involves the administration of a tumor localizing photosensitizer followed by its activation with light of a specific wavelength. In the presence of tissue oxygen, the photoactive sensitizer triggers a series of photochemical and photobiological processes that may lead to direct cancer cell damage, tumor microvascular occlusion and host immune response. Due to these multiple actions, PDT has increasingly gained recognition as a potential adjuvant for conventional cancer treatments. Several preclinical studies and some clinical trials suggest that the use of PDT in combination with established treatments or with newly-developed modalities may be of benefit as compared to the individual modalities. In this review, we briefly introduce the reader to the main photobiological aspects of PDT, and then discuss the use of PDT in combination with other pharmacological approaches for the treatment of cancer.