Cytotoxic activity of a methanol extract of Phallusia nigra (Tunicata, Ascidiacea)

RESUMO

Tunicates have been reported to be a rich source of biologically active compounds. In this study, we demonstrate the presence of cytotoxic substances in Phallusia nigra, a common tunicate from Brazilian coastal waters. An extract of tunicate tissue was obtained by homogenizing the visceral organs from 50 specimens in methanol, followed by filtration and concentration in a rotary vacuum evaporator. Finally, the concentrate was partitioned with chloroform to remove lipids. The resulting extract possessed antimitotic and hemolytic activity. The former was demonstrated as a delay in the development of sea urchin eggs by partially inhibiting the process of cleavage (first cleavage, EC50 ñ SEM = 3.44 ñ 0.84 mg/ml). The <500 molecular fraction of the extract obtained by ultrafiltration also inhibited cell proliferation (the number of viable cells was decreased by 68 per cent with 500 mug/ml) and DNA synthesis of T47D cells derived from human breast carcinoma as measured by [3H]-thymidine incorporation (66 per cent of the control value after 24-h incubation with 100 mug/ml). Dose-dependent hemolysis obtained with P. nigra extract on mouse erythrocytes had an EC50 ñ SEM = 1.12 ñ 0.02 mglml for a 0.5 per cent erythrocyte suspension. Hemolysis could be reduced by pre-incubating the cells with choline-containing phospholipid. Sphingomyelin (40 mug/ml) increased the EC50 by twofold to 2.86 ñ 0.04 mg/ml, but phosphatidylcholine (80 mug/ml) did not modify hemolysis.