Cytotoxic and topoisomerase I inhibitory activities from extracts of endophytic fungi isolated from mangrove plants in Zhuhai, China

Cai Xiaoling¹*, Liang Xiaoli¹, Zhou Shining², Gao Junping¹, Wu Shuiping¹, Lai Xiaoming³, She Zhigang¹ and Lin Yongcheng¹

¹School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, People’s Republic of China.

²School of Life Science, Sun Yat-Sen University, Guangzhou, People’s Republic of China.

³Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, People’s Republic of China.

*Corresponding author. E-mail: cescxl@mail.sysu.edu.cn. Tel/Fax: (86)-20-84039623.

Accepted January 8, 2010

   Abstract

To isolate endophytic fungi from mangrove plants in Zhuhai, China and examine their DNA topoisomerase I inhibitory and antitumor activity. Endophytic fungi were isolated using surface-sterilization methods and were identified by morphological or molecular evidence. DNA topoisomerase I inhibitory activities were measured by topoisomerase I-mediated DNA plasmid relaxation assay. Antitumor activity in vitro was measured by MTT (3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di- phenytetrazoliumromide) method. A total of 209 endophytic fungal strains were isolated from surface sterilized leaves and branches of eight mangrove plants collected in Qi’ao island of Zhuhai, China. Crude ethyl acetate extracts of fermentation broths from 54 fungal cultures were tested for antitumor activities. Extracts of 19 isolates inhibited the activity of DNA topoisomerase I and extracts of 16 isolates displayed strong cytotoxicity against KB and KBv200 cells (IC₅₀ < 11 µg ml^-1). Among them, nine isolates of fungi showed both cytotoxic and topoisomerase I inhibitory activities, which are potential producers of antitumor compounds targeting at topoisomerase I. Endophytic fungal strains were successfully isolated and identified and nine strains showed both cytotoxic and topoisomerase I inhibitory activities. Endophytic fungal strains displaying both topoisomerase I inhibitory and antitumor activity together may indicate their potential ability of producing antitumor compounds targeting at topoisomerase I.

Key words: Mangrove endophytic fungi, antitumor activity, molecular characteristic.