CYTOTOXICITY AND MODE OF ACTION OF AEROPLYSININ-1 AND A RELATED DIENONE FROM THE SPONGE APLYSINA-AEROPHOBA

Aeroplysinin-1 (1) and the structurally related dienone 2 were cytotox ic to Ehrlich ascites tumor (EAT) cells and HeLa tumor cells in the mi croculture tetrazolium (MTT) and clonogenic assays. Both compounds are bromotyrosine derivatives, isolated from the marine spong Aplysina ae rophoba. As the effective concentrations in the MTT assay were lower t han in the clonogenic assay, 1 and 2 are able to cause growth inhibiti on as well as actual cell death in these cell lines. With an IC50 valu e of 8.2 mu M (MTT assay, 2-h incubation, EAT cells), 1 was the more t oxic compound. When the cells were depleted of glutathione by pretreat ment with buthionine sulfoximine, they were significantly more sensiti ve toward 1 and 2 in the MTT assay. A dose-enhancement factor as high as 11.8 was found in EAT cells after 2-h incubation with 2. Using elec tron paramagnetic resonance we were able to measure free radical forma tion of 1 and 2, yielding the semiquinone structures 3 and 4, respecti vely, in a culture medium with tumor cells. It is concluded that free radicals are, at least in part, responsible for the cytotoxicity of 1 and 2. This conclusion is in line with expectations derived from the c hemical structures of both compounds.