The Effect of Cytochalasans on the Actin Cytoskeleton of Eukaryotic Cells and Preliminary Structure⁻Activity Relationships

Abstract

In our ongoing search for new bioactive fungal metabolites, two new cytochalasans were isolated from stromata of the hypoxylaceous ascomycete Hypoxylon fragiforme. Their structures were elucidated via high-resolution mass spectrometry (HR-MS) and nuclear magnetic resonance (NMR) spectroscopy. Together with 23 additional cytochalasans isolated from ascomata and mycelial cultures of different Ascomycota, they were tested on their ability to disrupt the actin cytoskeleton of mammal cells in a preliminary structure⁻activity relationship study. Out of all structural features, the presence of hydroxyl group at the C7 and C18 residues, as well as their stereochemistry, were determined as important factors affecting the potential to disrupt the actin cytoskeleton. Moreover, reversibility of the actin disrupting effects was tested, revealing no direct correlations between potency and reversibility in the tested compound group. Since the diverse bioactivity of cytochalasans is interesting for various applications in eukaryotes, the exact effect on eukaryotic cells will need to be determined, e.g., by follow-up studies involving medicinal chemistry and by inclusion of additional natural cytochalasans. The results are also discussed in relation to previous studies in the literature, including a recent report on the anti-Biofilm activities of essentially the same panel of compounds against the pathogenic bacterium, Staphylococcus aureus.

Keywords: Ascomycota; Xylariales; actin cytoskeleton; chromatography; secondary metabolites; structure elucidation.

Figure 1

Chemical structures of cytochalasans employed in this study.

Figure 2

Immunofluorescence staining with phalloidin of U2OS cells treated with cytochalasans. (A) Treated with 1 µM cytochalasin H (8). (B) Treated with 5 µM cytochalasin H. (C) Treated with 1 µM cytochalasin B (4). (D) Treated with 5 µM cytochalasin B. (E) treated with 1 µM chaetoglobosin D (25). (F) Treated with 5 µM chaetoglobosin D. (G) Treated with 5 µM DMSO (negative control). (H) Washout after treatment with 5 µM cytochalasin H.