Morusin, isolated from root bark of Moms alba L., inhibits tumour promotion of teleocidin

Morusin is an isoprenylated flavone, isolated from the root bark of Mom alba L. Morusin, which is structurally unrelated to 12‐O‐tetradecanoylphorbol‐l3‐acetate (TPA), inhibited the specific binding of [3H]TPA to a particulate fraction of mouse skin as well as activation of protein kinase C by teleocidin in vitro. Pretreatment with morusin for 10 min also inhibited induction of ornithine decarboxylase by teleocidin in mouse skin. The results of these three biochemical tests indicated that morusin may have anti‐tumour promoting activity. In week 20 of a two‐stage carcinogenesis experiment on mouse skin, tumours were found in 100% of the mice treated with 7,U‐dimethylbenz(a)anthracene (DMBA) plus teleocidin, but in 60% of those treated with DMBA plus teleocidin and morusin. The average numbers of tumours per mouse in these groups were 5.3 and 1.1, respectively. Morusin per se did not show any tumour promoting activity in DMBA‐initiated mouse skin. Thus, morusin inhibited tumour promotion of teleocidin in a two‐stage carcinogenesis experiment. Morusin is a new, isoprenylated flavonoid anti‐tumour promoter.