Synthesis, molecular modelling and biological evaluation of salpichrolides analogues as novel antiestrogenic agents

SONEGO, JUAN M.; ALVAREZ, LAUTARO D.; RIVERO, EZEQUIEL M.; GARGIULO, LUCíA; BURTON, GERARDO; LüTHY, ISABEL; VELEIRO, ADRIANA S.

Moscú

Simposio; 5th International Symposium on Advances in Synthetic and Medicinal Chemistry; 2013

European Federation of Medicinal Chemistry

Salpichrolides are a group of naturally occurring C-28 steroids isolated from Salpichroa origanifolia (Lam.) Thell (e.g. salpichrolides A (1), G (2) and B (3)).[1] In vitro antiproliferative activity studies against a panel of human breast cancer cell lines, performed on a series of 22 withanolides, showed that the inhibitory activity was evident only in estrogen receptor-positive cells for the salpichrolides with an aromatic D ring.[2] This specificity could suggest an estrogen-signaling-mediated mechanism in which salpichrolide A (1) would act as inhibitor of the ER-dependent pathway. On this basis we have now evaluated the antiestrogenic activity of five salpichrolides analogues (4-8) with a simplified side chain, compared to the natural salpichrolides 1-3. Compounds 4-6 and 9 were prepared as previously described by us.[3] Analogues 7 and 8 were obtained from 9, the key step for this transformation being the reductive cleavage of an a,b-epoxy ketone to the corresponding allylic alcohol using NH2NH2-H2O (Scheme 1).[4] Cell proliferation was evaluated in ER-positive (ERá and ERâ) human breast cancer cells MCF-7. The antiestrogenic ability was evaluated by treating the cells in the presence of 0.1 nM 17â-estradiol and increasing concentrations of the compounds to be tested (compounds 1-8). The natural salpichrolides (1-3) reverted estrogen stimulation with an IC50 of 1.00 x 10-7M, 1.40 x 10-7M and 1.78 x 10-8M respectively. The activity of compounds 7 and 8 was similar to that of natural salpichrolides, while compounds 5 and 6 were inactive. It is noteworthy that compound 4 (IC50: 1.44 x 10-7M) showed an activity similar to salpichrolide A (1), behaving as a promising antiestrogen. Finally, in order to investigate the ligand binding mode in the ERa/compound 8 complex, we used a combination of docking and molecular dynamics methods. By comparison with results observed in the ERa/17â-estradiol complex, we concluded that the more favorable orientation of compound 8 within the ligand binding pocket is one in which the D-ring occupies the position occupied by A-ring in the 17â-estradiol system. Moreover, we observed that the C-20 carbonyl of compound 8 establish similar polar interaction with the residues that contacts the 3-OH group of 17â-estradiol. Thus, from these molecular modeling results we predict that salpichrolides analogues have an inverse ER ligand binding mode respect to classical steroids.