Development of QSAR models to predict estrogenic, carcinogenic, and cancer protective effects of phytoestrogens.

An integrated QSAR model has been formulated to predict estrogenic, carcinogenic, and cancer protective effects of phytoestrogens (PE). Relative binding of PEs to estrogen receptors ER alpha and ER beta exhibited a parabolic relationship with dipole moment (mu). The high-affinity binding of PEs to ER alpha correlated with Dif0 (0 chi-0 chi v difference index encoding nonsigma electronic charge), while the low-affinity binding of PEs to ER alpha correlated with H bonding (positive coefficient) and % hydrophilic surface (negative coefficient). The high-affinity binding of PEs to ER beta correlated with molecular with (MWd) and Dif0, while the low-affinity binding of PEs to ER beta correlated with H bonding (positive coefficient) and hydrophilic-lipophilic balance (negative coefficient). Thus an increase in electronic or ionic charge, formation of H bonds, or a decrease in hydrophilic property of PEs may increase their binding to ER. The relative transcription activity (RTA) of ER alpha correlated with Dif0-Dif1, while RTA of ER beta correlated with H bonding and polarity. The PE-induced stimulation of DNA synthesis in estrogen-sensitive breast cancer (BC) cells correlated positively with (MD4 chi v) where MD is molecular depth and 4 chi v is the valence of a 4th order fragment. IC50 for PE-induced inhibition of DNA synthesis in estrogen-sensitive BC cells correlated with (MDLog P) and Dif3 (3 chi-3 chi v difference index encoding nonsigma electronic charge of fragments consisting of four atoms and three bonds) and Dif3(2). IC50 for PE-induced inhibition of DNA synthesis in estrogen-independent cancer cell lines correlated with (MD*Log P) and 1/water solubility. Thus molecular shape and molecular connectivity of PEs play a key role in modulating estrogen-induced transactivation activity and DNA synthesis in BC cells.