In Vitro Anti-Tubulin Activity on MCF10A Cell Line and In Silico Rigid/Semiflexible-Residues Docking, of Two Lignans from Bursera Fagaroides var. Fagaroides.

Podophyllotoxins are natural lignans with known cytotoxic activity on several cell lines. The structural basis for their actions is mainly by the aryltetralin-lignan skeleton. Authors have proposed a cytotoxic mechanism of podophyllotoxins through the topoisomerase-II inhibition activity; however, several studies have also suggested that podophyllotoxins can inhibit the microtubules polymerization. In this work, the two possible mechanisms of action of two previously isolated compounds from the stem bark of Bursera fagaroides var. fagaroides: acetylpodophyllotoxin (1) and 5'-desmethoxydeoxypodophyllotoxin (2), was analyzed. An in vitro anti-tubulin epifluorescence on the MCF10A cell line and enzymatic topoisomerase II assays were performed. The binding affinities of compounds 1 and 2 in the colchicine binding site of tubulin by using rigid- and semiflexible-residues were calculated and compared using in silico docking methods. The two lignans were active by the in vitro anti-tubulin assay but could not inhibit TOP2 activity. In the in silico analysis, the binding modes of compounds into both rigid- and semiflexible-residues of tubulin were predicted, and only for the semiflexible docking method, a linear correlation between the dissociation constant and IC50 previously reported was found. Our results suggest that a simple semiflexible-residues modification in docking methods could provide an in vitro correlation when analyzing very structurally similar compounds.

Cytotoxicity, Post-Treatment Recovery, and Selectivity Analysis of Naturally Occurring Podophyllotoxins from Bursera fagaroides var. fagaroides on Breast Cancer Cell Lines.

Despite prevention and treatment options, breast cancer (BC) has become one of the most important issues in the present day. Therefore, the need for more specific and efficient compounds remains paramount. We evaluated four previously isolated aryltetralin lignans: 5'-demethoxy-ß-peltatin-A-methylether (1), acetylpodophyllotoxin (2), 5'-demethoxydeoxypodophyllotoxin (3), and 7',8'-dehydroacetylpodophyllotoxin (4) for cytotoxicity, clonogenicity, and selectivity against three BC cell lines: MCF-7, MDA-MB-231, and BT-549, as well as the non-tumorigenic mammary epithelial cell line MCF-10A. Cytotoxicity was evaluated after 72 h of treatment, and clonogenicity was determined at 72 h post-treatment; experiments were performed using the sulforhodamine B staining assay. Selective-index (SI) was calculated by comparing pure compound IC50 values in MCF-10A cell line against the IC50 of the same compound in cancer cell lines. Structural similarities among lignans and controls (podophyllotoxin and etoposide) were analyzed using the Tanimoto coefficient (Tc). Lignans were cytotoxic against all tested cell lines (0.011-7.22 µM) and clonogenicity testing showed a dose-dependent cytocidality for all lignans (≥0.08 µg/mL); compounds 2 and 3 were more potent (14.1 and 7.6 respectively) than etoposide in BT-549 cell line, while compound 2 displayed selectivity (SI = 28.17) in BT-549 cell line. Tc values of lignans suggested a greater similarity with podophyllotoxin structure.