Mobilization of Copper ions by Flavonoids in Human Peripheral Lymphocytes Leads to Oxidative DNA Breakage: A Structure Activity Study.

Mohd Farhan,Nida Rehmani,Aamir Ahmad,Hussain Arif,Sheikh Hadi

doi:10.3390/ijms161125992

Abstract

Epidemiological studies have linked dietary consumption of plant polyphenols with lower incidence of various cancers. In particular, flavonoids (present in onion, tomato and other plant sources) induce apoptosis and cytotoxicity in cancer cells. These can therefore be used as lead compounds for the synthesis of novel anticancer drugs with greater bioavailability. In the present study, we examined the chemical basis of cytotoxicity of flavonoids by studying the structure–activity relationship of myricetin (MN), fisetin (FN), quercetin (QN), kaempferol (KL) and galangin (GN). Using single cell alkaline gel electrophoresis (comet assay), we established the relative efficiency of cellular DNA breakage as MN > FN > QN > KL > GN. Also, we determined that the cellular DNA breakage was the result of mobilization of chromatin-bound copper ions and the generation of reactive oxygen species. The relative DNA binding affinity order was further confirmed using molecular docking and thermodynamic studies through the interaction of flavonoids with calf thymus DNA. Our results suggest that novel anti-cancer molecules should have ortho-dihydroxy groups in B-ring and hydroxyl groups at positions 3 and 5 in the A-ring system. Additional hydroxyl groups at other positions further enhance the cellular cytotoxicity of the flavonoids.

Highlights

Development of cancer is a complex process that involves factors that are important in the significant steps of initiation, promotion and progression, resulting in the uncontrolled proliferation and growth of cancer cells
Flavonoids are a subclass of plant polyphenols that include flavonols like myricetin, fisetin, quercetin, kaempferol and galangin
A number of reports have suggested that a number of these flavonoids including myricetin, fisetin, apigenin quercetin and kaempferol induce apoptotic cell death in cancer cell lines [9,10,11,12]

Summary

Introduction

Development of cancer is a complex process that involves factors that are important in the significant steps of initiation, promotion and progression, resulting in the uncontrolled proliferation and growth of cancer cells. .QTuheisrcleestisner(hFyigdurorege8n)bopnodssiensgseressufilvteedhinydlorwoxeyrl groups, less than myricetin and greater than fisetin, but it shows the formation of only three hydrogen bonds with nitrogenous bases of B-D26N7A61(G-2, G-4 and G-10) The reason for this may be that a larger portion of the quercetin molecule lies away from the minor groove, as preventing the negative binding energy ( ́5.56 kcal/mol). It is to be noted that the degree of fluorescence enhancement (Figure 2) of various flavonoids upon binding to DNA follows the same pattern as the capacity of flavonoids to reduce Cu(II) (Figure 3); (iii) The results indicate the importance of ortho-dihydroxy groups in the B-ring (such as 3’–4’ or 4’–5’) in myricetin, fisetin and quercetin-mediated effects on cellular DNA degradation as well as in the generation of H2O2 (Figure 4). In support of such an argument, it has been shown that apoptosis could be induced in adenocarcinoma prostate cancer cells (CA-HPV10 cells) by 10 μM concentration of apigenin whereas the normal cells were refractory to even 20 μM concentration of apigenin [49]

Experimental Section

Isolation of Lymphocytes

Viability Assessment of Lymphocytes

Fluorescence Studies

Detection of H2O2 in the Incubation Medium by FOX Assay

Molecular Docking Studies

Statistics

Findings

Conclusions