Plants-occurring Anthraquinones as Photosensitive Compounds for Photodynamic Method: A Critical Overview

The review focuses on the recent knowledge on natural anthraquinones (AQs) of plant origin and their potential for application in an exclusive medicinal curative and palliative method named photodynamic therapy (PDT). Green approach to PDT is associated with photosensitizers (PS) from plants or other natural sources and excitation light in visible spectrum. The investigations of plants are of high research interests due to their unique health supportive properties as herbs and the high percentage availability to obtain compounds with medical value. Up-to-date many naturally occurring compounds with therapeutic properties are known and are still under investigations. Some natural quinones have already been evaluated and clinically approved as anti-tumor agents. Recent scientific interests are beyond their common medical applications but also in directions to their photo-properties as natural PSs. The study presents a systematic searches on the latest knowledge on AQ derivatives that are isolated from the higher plants as photosensitizers for PDT applications. The natural quinones have been recognized with functions of natural dyes since the ancient times. Lately, AQs have been explored due to their biological activity including the photosensitive properties useful for PDT especially towards medical problems with no other alternatives. The existing literature' overview suggests that natural AQs possess characteristics of valuable PSs for PDT. This method is based on an application of a photoactive compound and light arrangement in oxygen media, such that the harmful general cytotoxicity could be avoided. Moreover, the common anticancer and antimicrobial drug resistance has been evaluated with very low occurrence after PDT. Natural AQs have been focused the scientific efforts to further developments because of the high range of natural sources, desirable biocompatibility, low toxicity, minimal side effects and low accident of drug resistance, together with their good photosensitivity and therapeutic capacity. Among the known AQs, only hypericin has been studied in anticancer clinical PDT. Currently, the natural PSs are under intensive research for the future PDT applications for diseases without alternative effective treatments.