The increasing incidence of cancer has been the driving force behind numerous research projects dealing with new cancer treatments. Based on the rapid replication of cancer cells, enzymes from the family of topoisomerases have established themselves as logical and promising targets for cancer treatment due to their ability to modulate DNA topology needed for DNA replication and transcription. Based on the extensive research work performed at the Department of pharmaceutical chemistry on the Faculty of Pharmacy, University of Ljubljana, we designed and synthesised a new series of human DNA topoisomerase IIα inhibitors with N-(2-isopropoxyphenyl)-pyrrolamide basic structure. We proposed that a replacement of the acidic structural part on the right-hand side of the molecule with a more basic moiety would improve cytotoxic properties of our compounds, while the pyrrolamide fragment bound to the 2-isopropoxy substituted benzene backbone will preserve the inhibitory effect on the enzyme.
All the synthesised compounds were evaluated using spectroscopic and chromatographic methods and their physicochemical properties were determined. The inhibitory properties of five final and three pre-final compounds were evaluated using an in vitro DNA topoisomerase IIα relaxation assay to confirm their inhibitory activities on the enzyme. Lastly, all five final compunds that showed adequate inhibitory activity in the enzyme relaxation test, were subjected to cytotoxic testing using MCF-7 and HepG2 cancer cell lines. All five final compounds exerted very good inhibitory properties on the enzyme test with an IC50 value ranging between 1,4 µM and 37 µM. The most potent was compound 22, which showed an IC50 of 1,4 µM. Cytotoxic testing also revealed promising results, with 4 out of the 5 final compounds having excellent inhibitory properties on both cell lines with an IC50 ranging from 1,5 – 9,3 µM. The most potent compound was once again compound 22, which showed an IC50 of 4,2 µM and 1,5 µM on the MCF-7 and HepG2 cell lines respectively. Through the good results from the relaxation assay testing, we confirmed the importance of the pyrrolamide fragment bound to the 2-isopropoxy substituted benzene backbone as the smallest structural motif that allows good ATP competitive inhibition of human DNA topoisomerase IIα. Furthermore, the excellent inhibitory properties of four final compounds (19, 20, 21 and 22) on both cancer cell lines confirmed the importance of introducing a basic centre in the form of an amidopiperidine structural element to achieve good cytotoxic activity.
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