Screening of new photosensitizers from Argentinean plants to be used in Photodynamic Therapy of cancer

MAMONE L, DI VENOSA G, RODRIGUEZ L, GÁNDARA L, BATLLE A, CASAS A

Sao Pedro, Sao Paulo

Encuentro; VII meeting of the SFRBM South American Group; 2011

SFRBM South American Group

Photodynamic therapy (PDT) is an anticancer treatment that involves administration of a tumour-localising photosensitizer and its subsequent activation by visible light to result primarily in singlet oxygen–induced photodamage to the tumour. In addition to cancer, mainstream uses for PDT include inflammatory disorders and infections. New photosensitisers are desired to absorb at long wavelengths (600-1000 nm), while the ones useful against bacteria, viruses, etc, i.e. external eradication, often absorb at wavelengths below 600 nm. The aim of this work was to investigate a collection of regional plant extracts from Argentina as a source of new photosensitizers for use in cancer and infections. In case of flowers and fruits the selection was done based on their visible colours that would be potential producers of free radicals. Aqueous and methanol plant extracts were classified into potential use for cancer or microbiological treatment based on their fluorescence excitation wavelengths. In addition, a method based on tryptophan photodegradation was employed to screen the production of singlet oxygen from plant extracts.  So far, extracts from 40 plant species have been studied. It was found that exposure of the murine tumour cell line LM2 to the methanolic extracts of 10 µg/ml of Combretum fruticosum and 50 µg/ml of Scutia buxifolia leaves and irradiation with a light dose of 0.19 J/cm2 and 0.073 J/cm2, respectively, induced 50% death. HPLC  profiles of both extracts reveals the presence of tetrapyrrolic compound different from chlorophyll.  In a near future, we will further improve an easy method for the screening of potential photosensitizers from plants based on redox reactions.