Role of transcriptional and translational gene regulation in the mechanism of doxorubicin cardiotoxicity

Doxorubicin, one of the most widely used and effective anticancer drugs, is limited in its therapeutic use by cardiotoxicity. Multiple hypotheses have been advanced to explain the cardiotoxicity. In this project I utilised novel global genomic analysis of mRNA and miRNA transcription and mRNA translation to investigate the mechanism of doxorubicin cardiotoxicity in vivo. A comparator naphthoquinone was employed in parallel to specifically investigate the potential role of redox activity in the mechanism of cardiotoxicity. For both compounds mouse models were used where cardiac damage was characterised at several dose levels (acute and chronic repeat dosing for 7 weeks). A major transcriptionally and translationally affected pathway was the electron transport chain, this was further confirmed biochemically. These changes were reflected by a rapid loss of ATP and an associated increase in the AMP:ATP ratio and associated activation of AMPK indicating a change in cellular energy dynamics. In tandem mtDNA copy number and caspase 3 were rapidly increased. Comparison of all the data led to the hypothesis that the mechanism of doxorubicin toxicity was via interference with the electron transport chain, possibly through electron shuttling, leading to mitochondrial damage and activation of the intrinsic pathway of apoptosis. In further analysis miRNA alterations associated with the cardiotoxicity of both compounds were investigated. Several miRNAs appeared to be intrinsically involved and one of these, miR-181a was followed up in vitro in HL-1 cells and showed an association with susceptibility to doxorubicin cardiotoxicity. The findings provide a novel insight into doxorubicin cardiotoxicity, through the utilization of genomics and suggest the major mechanism of doxorubicin toxicity is via interference with the electron transport chain, and unrelated to the pharmacological action. These data offer the possibility of molecule alteration to retain the pharmacological profile without the associated cardiotoxicity.