Structure-guided optimization of 4,6-substituted-1,3,5-triazin-2(1H)-ones as catalytic inhibitors of human DNA topoisomerase IIα.

Human DNA topoisomerases represent one of the key targets of modern chemotherapy. An emerging group of catalytic inhibitors of human DNA topoisomerase IIα comprises a new paradigm directed to circumvent the known limitations of topoisomerase II poisons such as cardiotoxicity and induction of secondary tumors. In our previous studies, 4,6-substituted-1,3,5-triazin-2(1H)-ones were discovered as catalytic inhibitors of topo IIα. Here, we report the results of our efforts to optimize several properties of the initial chemical series that did not exhibit cytotoxicity on cancer cell lines. Using an optimized synthetic route, a focused chemical library was designed aimed at further functionalizing substituents at the position 4 of the 1,3,5-triazin-2(1H)-one scaffold to enable additional interactions with the topo IIα ATP binding site. After virtual screening, selected 36 analogues were synthesized and experimentally evaluated for human topo IIα inhibition. The optimized series displayed improved inhibition of topo IIα over the initial series and the catalytic mode of inhibition was confirmed for the selected active compounds. The optimized series also showed cytotoxicity against HepG2 and MCF-7 cell lines and did not induce double-strand breaks, thus displaying a mechanism of action that differs from the topo II poisons on the cellular level. The new series represents a new step in the development of the 4,6-substituted-1,3,5-triazin-2(1H)-one class towards novel efficient anticancer therapies utilizing the catalytic topo IIα inhibition paradigm.

Bioassays and In Silico Methods in the Identification of Human DNA Topoisomerase IIα Inhibitors.

BACKGROUND: The family of DNA topoisomerases comprises a group of enzymes that catalyse the induction of topological changes to DNA. These enzymes play a role in the cell replication machinery and are, therefore, important targets for anticancer drugs - with human DNA topoisomerase IIα being one of the most prominent. Active compounds targeting this enzyme are classified into two groups with diverse mechanisms of action: DNA poisons act by stabilizing a covalent cleavage complex between DNA and the topoisomerase enzyme, transforming it into a cellular toxin, while the second diverse group of catalytic inhibitors, provides novel inhibition avenues for tackling this enzyme due to frequent occurrence of side effects observed during the DNA poison therapy. METHODS: Based on a comprehensive literature search we present an overview of available bioassays and in silico methods in the identification of human DNA topoisomerase IIα inhibitors. RESULTS AND CONCLUSION: A comprehensive outline of the available methods and approaches that explore in detail the in vitro mechanistic and functional aspects of the topoisomerase IIα inhibition of both topo IIα inhibitor groups is presented. The utilized in vitro cell-based assays and in vivo studies to further explore the validated topo IIα inhibitors in subsequent preclinical stages of the drug discovery are discussed. The potential of in silico methods in topoisomerase IIα inhibitor discovery is outlined. A list of practical guidelines was compiled to aid new as well experienced researchers in how to optimally approach the design of targeted inhibitors and validation in the preclinical drug development stages.