Cytotoxicity against insect cells of entomopathogenic fungi of the genera Hypocrella (anamorph Aschersonia): possible agents for biological control.

Extracts from entomopathogenic fungi of the genus Hypocrella (7 species) and its anamorph Aschersonia (11 species) were screened for cytotoxicity to Sf9 and C6/36 insect cells and L929, BHK(21)C13 and HepG2 mammalian cells. Cytotoxic extracts to insect cells (ID50's < or = 10 microg ml(-1)) but not to mammalian cells (ID50's > or = 10 microg ml(-1)) conformed to the criteria of the project and were considered 'lead' extracts for further investigation. 'Leads' were found in two of the Hypocrella species: H. discoidea, and H. tamurai and in three of the Aschersonia species: A. samoensis, A. badia, and A. tamurai. Bioassay-guided fractionation of the cell extract of the fungus A. samoensis BCC 1393 led to the identification of two known anthraquinone dimers, (+)rugulosin (1) and skyrin (2) which showed selective toxicity towards insect cells. (+)Rugulosin (1) and skyrin (2) exhibited strong cytotoxic activity against the insect cell line Sf9 with respective ID50 values of 1.2 and 9.6 microg ml(-1), but showed weak activity toward mammalian cells. This first report of (+)rugulosin (1) and skyrin (2) in A. samoensis is confirmed and demonstrated in another four strains of A. samoensis isolated in Thailand. The preferential cytotoxicity against Sf9 insect cells gives evidence that these insect-pathogenic fungi of the Hypocrella/Aschersonia group might be useful as an agent for pest control.