Rapid identification of cyclic tetrapyrrolic photosensitisers for photodynamic therapy using on-line hyphenated LC-PDA-MS coupled with photo-cytotoxicity assay.

ABSTRACT

INTRODUCTION: Photodynamic therapy is a treatment modality that involves site-directed generation of cytotoxic reactive oxygen species by light-activated photosensitisers. OBJECTIVE: In order to rapidly identify new photosensitisers from natural extracts, we developed a liquid chromatography-photodiode array-mass spectrometry (LC-PDA-MS) method to rapidly identify plant extracts that contain photosensitisers, particularly those possessing a cyclic tetrapyrrole structure. METHOD: Six previously isolated compounds (1-6) were identified in bioactive fractions derived from 15 plant extracts on the basis of their chromatographic retention times, UV-visible profiles, accurate mass and fragmentation patterns. RESULTS: Samples containing uncommon photosensitisers were rapidly identified using this method, and subsequent scale-up isolation efforts led to two new compounds (7 and 8) which were confirmed to be active photosensitisers in a photo-cytotoxicity assay. CONCLUSION: This method serves as a useful tool in prioritising samples that may contain new photosensitisers out of a larger group of photo-cytotoxic natural products extracts.