The clinical application of
anthracyclines, like
daunorubicin and
doxorubicin, is limited by two factors: dose-related
cardiotoxicity and drug resistance. Both have been linked to reductive metabolism of the parent drug to their metabolites
daunorubicinol and
doxorubicinol, respectively. These metabolites show significantly less anti-neoplastic properties as their parent drugs and accumulate in cardiac tissue leading to chronic
cardiotoxicity. Therefore, we aimed to identify novel and potent natural inhibitors for
anthracycline reductases, which enhance the anticancer effect of
anthracyclines by preventing the development of
anthracycline resistance. Human
enzymes responsible for the reductive metabolism of
daunorubicin were tested for their sensitivity towards anthrachinones, in particular
emodin and
anthraflavic acid. Intense inhibition kinetic data for the most effective
daunorubicin reductases, including IC50- and Ki-values, the mode of inhibition, as well as molecular docking, were compiled. Subsequently, a cytotoxicity profile and the ability of
emodin to reverse
daunorubicin resistance were determined using multiresistant A549
lung cancer and HepG2
liver cancer cells.
Emodin potently inhibited the four main human
daunorubicin reductases in vitro. Further, we could demonstrate that
emodin is able to synergistically sensitize human
cancer cells towards
daunorubicin at clinically relevant concentrations. Therefore,
emodin may yield the potential to enhance the therapeutic effectiveness of
anthracyclines by preventing
anthracycline resistance via inhibition of the
anthracycline reductases. In symphony with its known pharmacological properties,
emodin might be a compound of particular interest in the management of
anthracycline chemotherapy efficacy and their adverse effects.