Screening of red extracts from actinomycetes and fungi for photodynamic therapy
2008
How, S. E. | Wong, N. K. | Teo, S. H. | Ong, C. Y. | Teoh, H. H. | S. H. Mahassan | Puah, S. H. | Ho, A. S. H. | Ho, C. C. | K. Suppayah | Lee, H. B.
Photodynamic therapy (PDT) is a promising new modality for the treatment of cancer. This technique is based on the ability of photosensitisers to acumulate preferentially in tumor cells and to generate singlet oxygen (¹0₂) when activated by visible light of a specific wavelength to induce cellular toxicity. At present, an ideal photosensitiser with respect to chemical purity, tumor selectivity, chemical and physical stability as well as rapid body clearance has not been found. In our screening program for bioactive compounds from actinomycetesandfungi inSabah,purecultures ofactinomycetes(H7891 andH11825)andfungi (H9010and H93l7) with orange to red extra-cellular pigment and non reddish actinomycetes (H7372, H7530, H7667, H7763 and H11855) were successfully isolated mainly from soils collected from Maliau Basin and Danum Valley. These pure isolates were grown aerobically to produce secondary metabolites. The acetone extracts ofthese microbes were screened for photocytotoxic activity against a human leukaemic cell line HL60 using an MTf-based cell viability assay. The red actinomycetes and fungi crude freeze-dried acetone extracts were shown to have mild photocytotoxicity at 20 I!g/mL with no cytotoxicity when cells were kept in the dark. But surprisingly H1I855, a non reddish actinomycete also showed this mild photocytotoxicity. Extraction of H11825 that was cultured in a different medium (solid oatmeal agar) also yielded the same level of photocytotoxicity, even though the extracts showed slightly different coloration. H7372 extract displayed a very interesting trend, where the dark cytotoxicity was lost upon photo-irradiation. The photocytotoxic activity of these extracts warrants their further investigation as PDT photosensitisers and experiments are currently underway to evaluate the activity on semi-pure fractions and pure compounds.
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