Photodynamic Therapy in the Treatment of Cancer

Abstract

Photodynamic therapy (PDT) is a treatment modality using a photosensitising drug and light to kill cells. The clinical use of PDT requires the presence of a photosensitising agent, oxygen and light of a specific wavelength which matches the absorption characteristics of the photosensitiser. When the photosensitiser is activated by the appropriate wavelength of light, it interacts with molecular oxygen to form a toxic, short-lived species known as singlet oxygen, which is thought to mediate cellular death. The appeal of PDT in oncology is that the photosensitiser tends to be retained in tumour tissues for a longer period of time as compared with normal tissues resulting in a large therapeutic index. This potential for minimal normal tissue toxicity has prompted an interest in studying PDT as a cancer treatment. Furthermore, the use of PDT is not precluded by prior radiotherapy, chemotherapy or surgery. The development of PDT has been hampered by the limitations of the older photosensitisers, namely limited depth of tissue penetration, and extended skin phototoxicity which limits the number of applications during a course of treatment. However, newer photosensitisers are being developed which allow greater depth of tissue penetration and have minimal skin phototoxicity allowing for multiple fractionated treatments. With such advancements, PDT has great potential to become an integral part of cancer treatment in the future.

Optimized interstitial PDT prostate treatment planning with the Cimmino feasibility algorithm

“…Our comparison shows: (1) It is important to measure the optical properties of a patient because it determines the light fluence distribution. This effect is more predominant than optimizing the source position, length, and strength.…”

“…PDT has been used with a surface illumination technique to treat many superficial tumors including skin, lung, esophagus, and bladder. 1 This technique is inadequate for large bulky tumors in solid organs because of limited light penetration into tissue. A more efficient illumination scheme for such tumors is interstitial light delivery whereby optical fibers are placed directly into the bulky tumors or organs.…”

A potent cytotoxic photoactivated platinum complex

“…This can be a problem due to the hypoxic nature of many malignant and most aggressive tumors (5); therefore, photoactivatable complexes that do not require oxygen may be more effective. Light-activated drugs are routinely used in treatment of nonmelanoma skin cancers and benign hyperproliferative diseases of the skin, as well as tumors of the brain, lung, esophagus, bladder, pancreas, and bile duct (6).…”

δ-Aminolevulinic acid transport in murine mammary adenocarcinoma cells is mediated by beta transporters

“…Photodynamic therapy (PDT) is a non-thermal technique for inducing tissue damage with light following administration of a lightactivated photosensitising drug which can be selectively retained in malignant or diseased lesions relative to normal adjacent tissue (Dougherty et al, 1978;Hsi et al, 1999). In addition, the fluorescence of photosensitising chromophores has been exploited for the visualisation and diagnosis of early stage superficial cancers (Kriegmair et al, 1996).…”