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 (CB) on actin polymerization, a virtual docking of CB onto monomeric actin was conducted. This led to the identification of potentially important functional groups of CB (i.e. the NH group of the isoindolone core (N-2), and the hydroxyl groups at C-7 and C-20) involved in interactions with the residual amino acids of the binding pocket of actin. Chemical modifications of CB at positions C-7, N-2, and C-20 led to derivatives CB1-CB4, which were analyzed for their bioactivities. CB1-CB4 exhibited reduced or no cytotoxicity in murine L929 fibroblasts compared to CB. Moreover, short- and long-term treatments of human osteosarcoma cells (U-2OS) affected the actin network to variable extent, partially accompanied by the induction of multinucleation. Derivatives displaying acetylation at C-20 and N-2 were subject to slow intracellular conversion to highly cytotoxic CB. Together, this study highlights the importance of the hydroxy group at C-7 and the NH function at N-2 for CB potency on the inhibition of actin polymerization.