Influence of ionic strength on the interaction of THA and its Cu(ii) complex with DNA helps to explain studies on various breast cancer cells

Abstract

THA, a structural analogue of the family of anthracycline anticancer drugs, was used to understand how environmental changes affect its biophysical interactions with DNA. A variation of the ionic strength of the medium was attempted at a constant pH. Under such varying conditions, the binding constant and the site size of interaction were evaluated. Owing to the close structural similarity with anthracyclines and the fact that the quinone moiety in these drugs control the chemical reactions, the effect of the ionic strength on the physicochemical and biophysical attributes of hydroxy-9,10-anthraquinones is important. With an increase in ionic strength, the dissociation of the first proton of THA is affected to a greater extent compared to the second proton. Since the pK_a1 is connected to the generation of the mono-anion of THA, an increase in its value implies that there would be less anion in the medium leading to improved DNA binding. Increased NaCl concentration neutralizes the negative charges on the DNA backbone manifesting in an overall increase in the binding constant for THA. This fact might be exploited for the use of such molecules in cancer patients. However, in the case of a Cu^II complex of THA and the formation of anions being almost negligible, there is a marked improvement in DNA binding. The cytotoxic action of THA (LH₃) and its Cu^II complex [Cu^II(LH₂)₂] was also studied on three breast carcinoma cell lines and a primary human dermal fibroblast cell line. The complex was seen to perform better than THA. The results could be explained with the help of the comet assay, the γH2AX foci assay, and DAPI staining followed by western blotting with an apoptotic protein marker. The findings of THA and its Cu^II complex were compared to anthracycline doxorubicin.