Four natural analogues of podophyllotoxin obtained from the Mexican medicinal plant Bursera fagaroides, namely, acetyl podophyllotoxin (2), 5'-desmethoxy-β-peltatin A methyl ether (3), 7',8'-dehydro acetyl podophyllotoxin (4), and burseranin (5), have been characterized, and their interactions with tubulin have been investigated. Cytotoxic activity measurements, followed by immunofluorescence microscopy and flow cytometry studies, demonstrated that these compounds disrupt microtubule networks in cells and cause cell cycle arrest in the G2/M phase in the A549 cell line. A tubulin binding assay showed that compounds 1-4 were potent assembly inhibitors, displaying binding to the colchicine site with Kb values ranging from 11.75 to 185.0 × 10(5) M(-1). In contrast, burseranin (5) was not able to inhibit tubulin assembly. From the structural perspective, the ligand-binding epitopes of compounds 1-3 have been mapped using STD-NMR, showing that B and E rings are the major points for interaction with the protein. The obtained results indicate that the inhibition of tubulin assembly of this family of compounds is more effective when there are at least two methoxyl groups at the E ring, along with a trans configuration of the lactone ring in the aryltetralin lignan core.

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By using a zebrafish embryo model to guide the chromatographic fractionation of antimitotic secondary metabolites, seven podophyllotoxin-type lignans were isolated from a hydroalcoholic extract obtained from the steam bark of Bursera fagaroides. The compounds were identified as podophyllotoxin (1), β-peltatin-A-methylether (2), 5′-desmethoxy-β-peltatin-A-methylether (3), desmethoxy-yatein (4), desoxypodophyllotoxin (5), burseranin (6), and acetyl podophyllotoxin (7). The biological effects on mitosis, cell migration, and microtubule cytoskeleton remodeling of lignans 1–7 were further evaluated in zebrafish embryos by whole-mount immunolocalization of the mitotic marker phospho-histone H3 and by a tubulin antibody. We found that lignans 1, 2, 4, and 7 induced mitotic arrest, delayed cell migration, and disrupted the microtubule cytoskeleton in zebrafish embryos. Furthermore, microtubule cytoskeleton destabilization was observed also in PC3 cells, except for 7. Therefore, these results demonstrate that the cytotoxic activity of 1, 2, and 4 is mediated by their microtubule-destabilizing activity. In general, the in vivo and in vitro models here used displayed equivalent mitotic effects, which allows us to conclude that the zebrafish model can be a fast and cheap in vivo model that can be used to identify antimitotic natural products through bioassay-guided fractionation.

Isothiocyanates (ITCs) have a significant impact on food and natural product chemistry. Several dietary components and food chemicals contain the isothiocyanate moiety. In addition, many ITCs interact with macromolecules of biological relevance, making these compounds relevant for potential therapeutic applications and disease prevention. However, there is a lack of systematic analysis of ITCs in chemical and biological databases. Herein, we conducted a comprehensive analysis of ITCs present in public domain databases, including natural products, food chemicals, macromolecular targets of drugs, and the Protein Data Bank. A total of 154 ITCs were found, which can be classified into seven categories: acyclic, cyclic, polycyclic, aromatic, polyaromatic, indolic, and glycosylated. 24 ITCs were reported in 18 vegetable sources, mainly in cruciferous vegetables (Brassica oleracea L.). Calculated properties of pharmaceutical relevance indicated that 11 % of the 154 ITCs would be suitable to be orally absorbed and 48 % permeate the blood-brain-barrier. It was also found that seven molecular targets have been co-crystallized with ITCs and the most frequent is the macrophage migration inhibitory factor. It is expected that this work will contribute to the sub-disciplines of natural products and food informatics.

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