Current Concepts in Gastrointestinal Photodynamic Therapy

Abstract

ObjectiveTo review current concepts of photodynamic therapy (PDT) applied to the treatment of tumors of the gastrointestinal tract. Summary Background DataPDT initially involves the uptake or production of a photosensitive compound by tumor cells. Subsequent activation of the photoreactive compound by a specific wavelength of light results in cell death, either directly or as a result of vascular compromise and/or apoptosis. MethodsThe authors selectively review current concepts relating to photosensitization, photoactivation, time of PDT application, tissue selectivity, sites of photodynamic action, PDT effects on normal tissue, limitations of PDT, toxicity of photosensitizers, application of principles of PDT to tumor detection, and current applications of PDT to tumors of the gastrointestinal tract. ResultsPDT is clearly effective for small cancers, but it is not yet clear in which cases such treatment is more effective than other currently acceptable approaches. The major side effect of PDT is cutaneous photosensitization. The major limitation of PDT is depth of tumor kill. As data from current and future clinical trials become available, a clearer perspective of where PDT fits in the treatment of cancers will be gained. Many issues regarding pharmacokinetic data of photosensitizers, newer technology involved in light sources, optimal treatment regimens that take advantage of the pharmacophysiology of photoablation, and light dosimetry still require solution. One can foresee application of differing sensitizers and light sources depending on the specific clinical situation. As technologic advances occur, interstitial PDT may have significant application.

5-Aminolevulinic-acid-mediated Photodynamic Diagnosis Enhances the Detection of Peritoneal Metastases in Biliary Tract Cancer in Mice

“…Blue light excitation is used for 5-ALA PDD. However, blue light penetration depth is shallower than that of red light (mean, 0.6 cm) (14,15), and blue light penetration depth is significantly affected by adipose tissue. Therefore, it would be difficult to observe tumors originating outside the bile duct, but 5-ALA PDD might be useful for detection of exposed tumor cells such as those on the resected stump of the bile duct.…”

Intraoperative photodynamic diagnosis of lymph node metastasis in esophageal cancer patients using 5-aminolevulinic acid

“…Usually, lymph nodes are surrounded by a number of connective tissues. The penetration depth of red light ranges from 0.2 to 2 cm, with a mean depth of ~0.6 cm, and that of blue light is even shallower (12,13). The penetration depth of excitation blue light is too short to reach metastatic lesions buried in tissues.…”

Nonsurgical approaches to esophageal malignancy

“…Some patients may also require placement of a feeding gastrostomy tube for nutritional support [38]. Tissue ablation can be performed by argon plasma coagulation (APC) [39], photodynamic therapy (PDT) [40][41][42][43], laser therapy [44,45], or other techniques of thermal or chemical ablation [3••]. Newer treatment modalities may include gene therapy [46].…”