Anandamide was the first brain metabolite shown to act as a ligand of ‘‘central’’ CB1 cannabinoid receptors. Here we report that the endogenous cannabinoid potently and selectively inhibits the proliferation of human breast cancer cells in vitro. Anandamide dose-dependently inhibited the proliferation of MCF-7 and EFM-19 cells with IC50 values between 0.5 and 1.5 mM and 83–92% maximal inhibition at 5–10 mM. The proliferation of several other nonmammary tumoral cell lines was not affected by 10 mM anandamide. The anti-proliferative effect of anandamide was not due to toxicity or to apoptosis of cells but was accompanied by a reduction of cells in the S...
