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Nature has been always a great source of possible lead compounds to develop new drugs against several diseases. Here we report the identification of a natural compound, membranoid G, derived from the Antarctic sponge Dendrilla antarctica displaying an in vitro inhibitory activity against human DNA topo-isomerase 1B. The experiments indicate that membranoid G, when pre-incubated with the enzyme, strongly and irreversibly inhibits the relaxation of supercoiled DNA. This compound completely inhibits the cleavage step of the enzyme catalytic mechanism by preventing protein binding to the DNA. Membranoid G displays also a cytotoxic effect on tumour cell lines, suggesting its use as a possible lead compound to develop new anticancer drugs. [ABSTRACT FROM AUTHOR]

Human topoisomerase 1B regulates the topological state of supercoiled DNA enabling all fundamental cell processes. This enzyme, which is the unique molecular target of the natural anticancer compound camptothecin, acts by nicking one DNA strand and forming a transient protein–DNA covalent complex. The interaction of human topoisomerase 1B and dimethylmyricacene, a compound prepared semisynthetically from myricanol extracted from Myrica cerifera root bark, was investigated using enzymatic activity assays and molecular docking procedures. Dimethylmyricacene was shown to inhibit both the cleavage and the religation steps of the enzymatic reaction, and cell viability of A-253, FaDu, MCF-7, HeLa and HCT-116 tumor cell lines. [ABSTRACT FROM AUTHOR]

Human DNA topoisomerase IB controls the topological state of supercoiled DNA through a complex catalytic cycle that consists of cleavage and religation reactions, allowing the progression of fundamental DNA metabolism. The catalytic steps of human DNA topoisomerase IB were analyzed in the presence of a drug, obtained by the open-access drug bank Medicines for Malaria Venture. The experiments indicate that the compound strongly and irreversibly inhibits the cleavage step of the enzyme reaction and reduces the cell viability of three different cancer cell lines. Molecular docking and molecular dynamics simulations suggest that the drug binds to the human DNA topoisomerase IB-DNA complex sitting inside the catalytic site of the enzyme, providing a molecular explanation for the cleavage-inhibition effect. For all these reasons, the aforementioned drug could be a possible lead compound for the development of an efficient anti-tumor molecule targeting human DNA topoisomerase IB. [ABSTRACT FROM AUTHOR]