Photodynamic therapy of cancer: second and third generations of photosensitizers

Photodynamic therapy of cancer (PDT) at early stages of various types of cancer is based on the use of the phototoxicity of photosensitizers (PS) which appear; upon their excitation by light in tumor tissues. The review concentrates mainly on the data for the second and third generations of photosensitizers: the structure of PS, their photophysical and photochemical properties, and some results of their in vitro and in vivo application. A carefully designed PS should exhibit the following properties: long-wave absorption, good singlet oxygen quantum yield, an intramolecular polarity axis, and low in vivo (photooxidation) stability. Uncharged PS that are lipophilic, positively charged, and capable of binding with monoclonal antibodies are discussed as an example.