A series of unconjugated ferrocenyl phenols: prospects as anticancer agents.

We recently reported that a ferrocenyl diphenol butene derivative showed a very strong cytotoxic effect on both hormone-dependent and -independent breast cancer cell lines. In order to obtain more information about the structure-activity relationship in the cytotoxicity of small ferrocene compounds, we have prepared a series of simple unconjugated ferrocenyl diphenol complexes (ortho,para; meta,para; para,para). These compounds retain a reasonable to good affinity for both estrogen receptor types, with higher values for the beta form, and superior binding for the para,para diphenol complex (RBA=28%). In vitro these complexes exhibit significant cytotoxic effects on hormone-independent prostate (PC3) and breast cancer cell lines (MDA-MB231), with IC50 values between 2.5 and 4.1 microM. This effect is more marked with PC3, the ortho,para diphenol complex proving the most effective. On the hormone-dependent MCF7 breast cancer cell line, the observed effect seems to be the result of two components, one cytotoxic (antiproliferative), the other estrogenic (proliferative). Electrochemical studies show that the cytotoxic effect of the complexes correlates with the ease of oxidation of the ferrocene group. All these complexes are much less cytotoxic than the ferrocenyl diphenol butene derivative.