Comprehensive Cell Biological Investigation of Cytochalasin B Derivatives with Distinct Activities on the Actin Network

In search of a more comprehensive structure-activity relationship (SAR) regarding the inhibitory effect of cytochalasin B (<b>2</b>) on actin polymerization, a virtual docking of <b>2</b> onto monomeric actin was conducted. This led to the identification of potentially important functional groups of <b>2</b> (i.e., the NH group of the isoindolone core (N-2) and the hydroxy groups at C-7 and C-20) involved in interactions with the residual amino acids of the binding pocket of actin. Chemical modifications of <b>2</b> at positions C-7, N-2, and C-20 led to derivatives <b>3</b>-<b>6</b>, which were analyzed for their bioactivities. Compounds <b>3</b>-<b>5</b> exhibited reduced or no cytotoxicity in murine L929 fibroblasts compared to that of <b>2</b>. Moreover, short- and long-term treatments of human osteosarcoma cells (U-2OS) with <b>3</b>-<b>6</b> affected the actin network to a variable extent, partially accompanied by the induction of multinucleation. Derivatives displaying acetylation at C-20 and N-2 were subjected to slow intracellular conversion to highly cytotoxic <b>2</b>. Together, this study highlights the importance of the hydroxy group at C-7 and the NH function at N-2 for the potency of <b>2</b> on the inhibition of actin polymerization.