Anthocyanin-rich extracts suppress the DNA-damaging effects of topoisomerase poisons in human colon cancer cells

Scope: The effect of two anthocyanin‐rich berry extracts (A, bilberry; B, red grape) on topoisomerases was investigated in a cell‐free system and in human HT29 colon carcinoma cells. In parallel, their impact on DNA integrity was determined. Methods and results: The berry extracts suppressed the activity of topoisomerase I at concentrations ≥50 μg/mL. The activity of the topoisomerase II isoform was preferentially diminished (≥1 μg/mL). Within HT29 cells, the extracts were found to act as catalytic inhibitors without stabilizing the cleavable complex. Although topoisomerase activity was inhibited, none of the extracts induced DNA strand breaks up to 50 μg/mL. Moreover, pre‐ and coincubation of HT29 cells with A (≥1 μg/mL) significantly suppressed (p‐value ≤0.001) the strand‐breaking effects of camptothecin, whereas B was found to be less effective (1 μg/mL; p‐value ≤0.05). Both extracts were found to significantly diminish doxorubicin‐mediated DNA strand breaks at concentrations ≥1 μg/mL (p‐value ≤0.001). Consistent with these results, the extracts suppressed doxorubicin‐mediated enhancement of levels of topoisomerase II covalently linked to DNA in HT29 cells. Conclusion: These results raise the possibility that high intake of berry extracts may protect DNA and thus counteract the therapeutic effectiveness of orally applied topoisomerase poisons during chemotherapy.