Doxorubicin (DOX) is a potent anticancer drug limited by its dose-dependent cardiotoxicity, making combination treatments that reduce DOX cardiotoxicity while maintaining anticancer activity essential for improving clinical outcomes. This study investigated combination treatment of DOX with a formaldehyde-releasing prodrug called AN-7.
Rat cardiomyocyte cells (H9c2), rat breast carcinoma (MTLn3) and human breast carcinoma (MDA-MB-231) cells were treated with single agent or combination treatments of DOX and AN-7 to investigate the response in terms of DOX Top2 activity and cell death.
The combination of DOX and AN-7 showed increased DOX-DNA adducts in cardiomyocytes and breast cancer cell lines compared to DOX alone. Significantly greater adduct formation was seen in cardiomyocytes compared to either breast cancer cell lines. The combination of DOX and AN-7 reduced the amount of DNA strand breaks occurring in all cell lines compared to DOX single agent treatments, in both the comet and γH2AX assays. Cardiomyocytes showed significantly greater reduction in DNA double strand breaks compared to breast cancer cells, agreeing with the significant increase in DOX adduct formation shown in cardiomyocytes. DOX combination treatments had increased cell death in breast cancer cells compared to DOX and AN-7 as single agents. However the combination of DOX and AN-7 reduced cardiomyocyte cell death compared to DOX alone.
The combination of DOX and AN- treatments caused a shift in DOX activity from a Top2 poison to forming DX-DNA covalent adducts, significantly more in cardiomyocytes compared to breast cancer cells. This shift in activity was associated with a cardioprotective effect, while enhancing cell death in breast cancer cell lines. The cardiomyocyte protection observed as a result of combination treatments of DOX and AN-7 raises the possibility of making DOX a safer and more effective chemotherapeutic agent by employing similar combinations in the clinic.