Cancer is a term describing a broad group of different diseases having the capability of indefinite potential for cell proliferation. Human DNA topoisomerase II? already represents an established and validated drug target for cancer chemotherapy as it plays a vital role in the process of cell division. DNA topoiosmerases catalyse the induction of topological changes in the double-stranded DNA molecule. With specific inhibition of alpha isoform, we can stop the cell proliferation of cancer cells and consequently induce their apoptosis since alpha isoform is preferentially expressed in rapidly proliferating cells. Although there is already a variety of established topo II? anticancer drugs in clinical use, unfortunately they are associated with some severe adverse effects, especially cardiotoxicity and induction of secondary malignancies that occur during therapy. Thus, further research activities are focussed on the development of novel groups of catalytic inhibitors of DNA topoisomerase II?, which will tackle the enzyme via various alternative inhibition mechanisms. Currently, one of the more investigated approaches is a competitive inhibition of the ATP binding with its binding site located at its N-terminal domain. This approach is also studied in this work.
Here, based on the previously performed structure-based design we synthesized optimized derivatives of the 3,5-disubstituted 1,2,4-oxadiazoles for which we hypothesized that they can target the ATP binding site on the human topoisomerase II?. We prepared 10 final optimized compounds starting from the 3-aminobenzonitrile. Compounds were experimentally evaluated using spectroscopic methods and then also their physical and chemical properties were determined. Additionally, we acquired 8 commercially available substituted regioisomers of 3,5-disubstituted 1,2,4-oxadiazoles which are structurally similar to the synthesized compounds. We evaluated all synthesized and commercially available compounds using the in vitro topo II? DNA relaxation assay to determine whether compounds possess inhibitory activity. Seven derivatives out of all the tested compounds showed inhibitory activity. For the three newly synthesized derivatives 4, 7 and 13 we observed that the introduction of fluoro-containing substituents led to the inhibitory activity, with the most favourable position being the para substitution. However, none of the new compounds showed improved inhibition activity over the known active 1,2,4-oxadiazole 10. On the other hand, among the assayed commercially available regio-analogues compounds 19 and 20, displayed inhibition with the IC50 values of 165,9 µM and 162,7 µM which were fully comparable with the activity of the most active compound 10. This suggested that introduction of the amide and sulfonamide functional groups can also enable topo II? inhibitory activity. In these cases, meta substitution was established as preferable.
Previously known compound 10 that was resynthesized in this work was further analysed using the DNA cleavage assay which showed for the first time that 3,5-disubstituted 1,2,4-oxadiazoles act as catalytic inhibitors. The results of our work provided a lot of new and relevant information regarding structure-activity relationship, which will enable further development and optimization of the 1,2,4-oxadiazoles chemical class of catalytic topo II? inhibitors as potential anticancer agents.
|
