Abstract 1755: Chromatin trapping is a key factor for anticancer cytotoxicity of DNA-binding small molecule drugs

DNA-targeting small molecules have been widely used for cancer treatment due to their ability to induce DNA damage. The DNA-damaging effect of small molecules depends on chromatin organization, however, the exact mechanism by which small molecules affect the chromatin, as well as the role of chromatin alterations in their biological activity is poorly understood. We previously identified the curaxin CBL0137 which showed a broad anti-cancer activity. CBL0137 is a small molecule which binds DNA but does not cause DNA damage. Rather, the curaxin alters DNA/histone interactions and causes nucleosome disassembly in vitro and in cells, leading to the phenomenon we named "chromatin damage." We have previously shown, that disassembled nucleosomes are bound by the histone chaperone FACT (FAcilitates Chromatin Transcription. We named this massive binding of FACT to different components of disassembled chromatin in curaxin-treated cells “c-trapping”. This finding led us to believe that other small DNA-binding molecules may also have the ability to induce c-trapping and chromatin damage. We selected a set of DNA-targeting agents, representing different modes of DNA binding and inhibition of topoisomerases: inhibitors of topoisomerase cleavage activity, inhibitors of topoisomerases re-ligation, compounds that do not bind DNA directly while form a cleavable complex with DNA and topoisomerases I or II, as well as topoisomerases II catalytic inhibitors that do not bind DNA. We investigated this set of compounds examining their cytotoxicity, and their ability to induce c-trapping, which we detected with western blotting, fluorescent imaging and immunofluorescent staining. We examined their effect on nucleosome stability and chromatin destabilization via micrococcal nuclease assays and recombinant mononucleosomes. DNA - damaging activity of tested compounds was also evaluated. We found that only compounds that directly bind DNA are able to induce c-trapping, which in turn correlates with nucleosome destabilization of tested compounds and their cytotoxicity. We showed that this effect was not dependent on DNA damage. Additionally, we showed that FACT can bind DNA at different stages of nucleosome disassembly, including the linker histone removal followed by core histone9s eviction, and negative supercoiling accumulation. This work suggests that cytotoxicity of DNA binding molecules is based not on their direct DNA-damage but on the ability of these compounds to induce the chromatin disruption. Citation Format: Elimelech Nesher, Alfiya Safina, Ieman Aljahdali, Scott Portwood, Eunice Wang, Jianmin Wang, Igor Koman, Katerina Gurova. Chromatin trapping is a key factor for anticancer cytotoxicity of DNA-binding small molecule drugs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1755.