Synthesis and evaluation of benzoxazolinonic imidazoles and derivatives as non-steroidal aromatase inhibitors

New compounds were tested in vitro on aromatase activity in human placental and equine testicular microsomes. Equine aromatase, very well characterized biochemically, is used as a comparative model to understand the mechanism of aromatase inhibition. Among 15 molecules screened, 5 of them (11 - 15) strongly inhibit human and equine aromatases with IC50 values ranging from 13-85 nM and from 23-103 nM respectively. These results were corroborated by K-i/K-m values. Moreover, spectral studies showed a type II spectrum with both enzymes, which is characteristic of an interaction between the nitrogen atom of the molecule and the heme of the cytochrome P450. Compound 12 , which has the lowest IC50 and K-i/K-m ratio, inactivates aromatase in a dose and time-dependent manner. This might be very important for the treatment of estrogen-dependent diseases such as breast cancer. Finally, MTT assays on E293 cells revealed that the molecules were not cytotoxic.