Research Progress on the Phthalocyanine Based Targeting Photosensitizers in Photodynamic Therapy

In recent years, photodynamic therapy (PDT) technology, as a noninvasive method of treating malignant tumors and age-related macular degeneration, which is different from the traditional cancer treatments, has drawn more and more attention of scientists. PDT treatment relies on the combination of photosensitizer, oxygen and light, when the photosensitizer is irradiated by special light, it can generate singlet oxygen, which is a cytotoxic agent can eradicate tumors via vasculature damage and cell damage, and sometimes the response of immune system. Due to its special advantages, i.e small traumatic, low toxicity, good compatibility, collaborative surgical treatment and repeatable treatment etc., PDT is widely used in many kinds of tumor treatments. Current practice of photodynamic therapy is limited to a few functionalized photosensitizers, for example porphyrins, however these compounds has several disadvantageous properties such as low absorption in the tissue transparency window (650 similar to 900 nm), prolonged skin photosensitivity, and slow clearance rate from body. This has inspired efforts to develop more effective PDT photosensitizers with improved photophysical characteristics and special targeting advantages. So in this review, the authors briefly outline the theories of PDT as well as the development process of photosensitizer, and summarize the characteristics of ideal photosensitizer. At present, the third generation photosensitizers mainly based on phthalocyanines have become a research highlight in PDT. However, how to improve the targeting of photosensitizer so as to achieve precise photodynamic efficiency is still an urgent problem to be solved. Therefore, this review mainly summarizes the recent research on phthalocyanine based targeting photosensitizers. In addition, the development of key research directions in the future has also been pointed out. According to the present researches, in the aspects of PDT, overcoming the limitation of cancer hypoxic microenvironment, developing Type I independently from oxygen, and penetrating more deeply targeting photosensitizers possess enormous potential, and they may become a kind of photosensitizer with excellent performance in the field of photodynamic therapy.