Synthesis and cancer cell growth inhibitory activity of icaritin derivatives

A series of icaritin derivatives bearing carboxylic acid or carboxylic ester groups are synthesized, and their in vitro cytotoxic activity against three cancer cell lines, MCF-7, MDA-MB-435s, and A549, are evaluated by MTT assay . Several derivatives including 2h , 2j , 5b and 5d show higher cytotoxic activity than the parent compound icaritin against these cancer cell lines. Compounds 5b and 5d are even more cytotoxic to MCF-7 cells than the clinic drug tamoxifen . Moreover, compound 5b is found to be non-toxic to normal cells (Vero) and both 5b and 5d exhibit good selectivity towards estrogen receptor positive MCF-7 breast cancer cells over estrogen receptor negative MDA-MB-435s breast cancer cells. The structure activity relationship analysis has revealed that mono-substitution at either C-3 or C-7 hydroxyl group of icaritin could improve the cytotoxicity of icaritin, and the C-3 hydroxyl group may be a preferable site for chemical modification. In addition, the length, the flexibility and the additional branching substituent group of the substitution chain(s) at both C-3 and C-7 hydroxyl groups can all affect the anti-cancer activity of these derivatives.