Anthracyclines are important and effective anticancer drugs used in the treatment of many
adult and children malignancies. Doxorubicin (DOX) is the anthracycline most commonly
used in cancer patients but its cardiotoxicity limits its clinical use. The precise molecular
basis of anthracyclines cardiotoxicity remains elusive, but a number of theories have been
proposed, one of which is the formation of reactive oxygen species (ROS).
Iron aggravates the cardiotoxicity of DOX; indeed, dexrazoxane (DRZ) is the only agent
able to protect the myocardium from anthracycline-induced toxicity both in experimental
and clinical settings. Iron has been proposed to catalyse ROS formation in reactions
primed by DOX. However, the oxidative nature of the role of iron in cardiotoxicity is
challenged by results showing that antioxidants do not always protect against
cardiotoxicity. Therefore, the mechanisms of DOX-mediated cardiotoxicity, and the
protective role of DRZ, remain to be established.
The hypoxia inducible factors (HIF, HIF-1a and HIF-2a) are transcription factors which
regulate the expression of several genes mediating adaptive responses to lack of oxygen.
Iron is required for HIF degradation and therefore decreased iron availability activates HIF
in normoxic cells. In consideration of the antiapoptotic and protective role of some HIFinduced
genes, we tested the hypothesis that DRZ-dependent HIF activation may mediate
the cardioprotective effect of DRZ.
Treatment with DRZ induced HIF protein levels and transactivation capacity in the H9c2
cardiomyocytes cell line. DRZ also prevented the induction of cell death and apoptosis
caused by the exposure of H9c2 cells to clinically-relevant concentrations of DOX.
Experiments involving suppression of HIF-1a activity or HIF-1a overexpression showed
that the protective effect of DRZ was dependent on HIF-1 activity.
By examining the expression of HIF target genes with a possible role in cell survival in
DRZ-treated H9c2 cells we found that a strong increase in protein levels of antiapoptotic
genes and haem oxygenase (HO-1) plays a role in the HIF-mediated cardioprotection
offered by DRZ.
We also explored two possible alternative pharmacological strategies to prevent DOXinduced
toxicity.
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The first one was based on a small molecular mimic of hypoxia that could be exploited in
an attempt to limit anthracycline cardiotoxicity. We examined HIF-1a levels and activity,
as well as protection from DOX damage, in H9c2 cardiomyocytes pre-exposed to DMOG,
an antagonist of \u3b1-ketoglutarate which activates HIF under normoxic conditions.
However, we did not find any kind of protection from damage induced by DOX in H9c2
cells pre-treated with DMOG.
The second one was based on the activation of the sodium-dependent glucose transporter-
1 (SGLT-1), which has been shown to protect different types of cells from various
injuries. We found that pre-treatment with D-glucose protected H9c2 cells from DOXinduced
toxicity, but the non-metabolizable glucose analog 3-O-methylglucose, and the
SLGT-1 agonist BLF50 were ineffective, thus indicating that the protection was not
mediated by the activation of SGLT-1