Photo-induced cytotoxicity of malonic acid [C60] fullerene derivatives and its mechanism X. L. Yang*, C. H. Fan, H. S. Zhu Research Center of Materials Science, Beijing Institute of Technology, PO Box 327, Beijing 100081, PR China Accepted 10 August 2001 The biological activities of fullerenes have attracted extensive attention in recent years. The aim of this paper is to study the relation of the photo-induced cytotoxicity of fullerene derivatives to their chemical structures as well as the possible cellular mechanism involved in the photocytotoxicity. Three C60 derivatives with two to four malonic acid groups (DMA C60, TMA C60 and QMA C60) were prepared and the cytotoxicity of these compounds against HeLa cells was determined by MTT. Cell cycle was measured by flow cytometry. The results showed that the cytotoxicity of the malonic acid C60 derivatives was irradiation-and dosedependent. The sequence of their photo-induced growth inhibition was DMA C60>TMA C60>QMA C60. Hydroxyl radical quencher mannitol (10mm) was not able to prevent cells from the damage induced by irradiated DMA C60. DMA C60,together with irradiation,was found to have an ability of inducing a decrease in the number of G1 cells from 63 to 42% and a rise in that of G2+M cells from 6 to 26%. These data indicated that the number of malonic acid molecules added to C60 played an important role in the phototoxicity and the blockage of cell cycle might be a mechanism of this activity.