ROLE OF HIF ACTIVATION IN THE PROTECTION OF CARDIOMYOCYTES FROM DOXORUBICIN TOXICITY
Creators: name: SPAGNUOLO, ROSALIN DOLORES
Publisher: name: Universit� degli Studi di Milano
Year: 2012

description: 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. 4 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 ?-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.