C60 does not inhibit cell proliferation. MCF 10A and (Panel A) MDA MB 231 (Panel B) cell lines were cultured either in the absence or presence of methanol C60 (0.2 mg/ml) and cell proliferation was assayed by crystal violet staining. ◆ Control, no C60, ■ 10 μg C60, ▲ 50 μg C60, X 250 μg C60. (Panel C). MDA MB 231 cells were simultaneously stained with calcein and ethidium using a live-dead assay kit. Lack of red-colored cells and the presence of cells stained in green indicate the lack of toxicity (Panel D). MDA MB 231 cells were either untreated (open box □) cultured with varying amounts 10 (gray ), 50 (patterned ) and 100 μg (filled ■) of C60 for 48 h and analyzed for cell cycle progression by flow cytometry.