ИСТИНА

Olivomycin A is a promising anticancer agent that belongs to a family of aureolic acid antibiotics. However, the mechanism of its action is not completely understood. The drug binds to the DNA minor groove in GC-rich regions as Mg2+-containing complexes. Given that minor groove ligands are known to disrupt a key epigenetic process of DNA methylation, we aimed to investigate the impact of olivomycin A and its synthetic derivative LCTA-1599 on the functioning of de novo murine DNA methyltransferase Dnmt3a. This enzyme establishes the DNA methylation pattern in eukaryotic cells. Using specially designed fluorescently labelled oligonucleotide substrates, we determined the optimal conditions for drug-DNA binding, including the concentration of Mg2+ ions that allowed for both olivomycin binding and Dnmt3a functioning. The impact of olivomycin on the Dnmt3a-DNA complex formation under these conditions turned out to be minimal. The binding of olivomycin A and LCTA-1599 to Dnmt3a was not observed. We then examined the inhibitory effect of olivomycin A and LCTA-1599 on DNA methylation by Dnmt3a. Employing the efficient method for in vitro quantification of DNA methylation that was recently developed in our laboratory, we have shown that both drugs can substantially inhibit the methylation reaction with IC50 values of 6±1 μM and 7.1±0.7 μM, respectively. Other minor groove ligands such as dimeric bisbenzimidazoles were found to have similar IC50 values. The inhibitory effect of olivomycin A and LCTA-1599 may be attributed to the disruption of movement of Dnmt3a catalytic loop toward DNA, which is necessary for the enzymatic activity of Dnmt3a and occurs via the DNA minor groove. Our results point at an epigenetic contribution to the mechanism of anticancer effect of aureolic acid family antibiotics. This work was supported by the RFBR grant 16-04-01087A.