Utilizing coordination chemistry through formation of a CuII-quinalizarin complex to manipulate cell biology: An in vitro, in silico approach

Quinalizarin, an analogue of anthracycline anticancer agents, is an anticancer agent itself. A Cu-II complex was prepared and characterized by elemental analysis, UV-Vis & IR spectroscopy, mass spectrometry, EPR and DFT. The intention behind the preparation of the complex was to increase cellular uptake, compare its binding with DNA against that of quinalizarin, modulation of semiquinone formation, realization of human DNA topoisom-erase I & human DNA topoisomerase II inhibition and observation of anticancer activity. While the first two attributes of complex formation lead to increased efficacy, decrease in semiquinone generation could results in a compromise with efficacy. Inhibition of human DNA topoisomerase makes up this envisaged compromise in free radical activity since the complex shows remarkable ability to disrupt activities of human DNA topoisomerase I and II. The complex unlike quinalizarin, does not catalyze flow of electrons from NADH to O-2 to the extent known for quinalizarin. Hence, decrease in semiquinone or superoxide radical anion could make modified quinalizarin [as Cu-II complex] less efficient in free radical pathway. However, it would be less cardiotoxic and that would be advantageous to qualify it as a better anticancer agent. Although binding to calf thymus DNA was comparable to quinalizarin, it was weaker than anthracyclines. Low cost of quinalizarin could justify consider-ation as a substitute for anthracyclines but the study revealed IC50 of quinalizarin/Cu-II-quinalizarin was much higher than anthracyclines or their complexes. Even then, there is a possibility that Cu-II-quinalizarin could be an improved and less costly form of quinalizarin as anticancer agent.