Doxorubicin-induced cardiotoxicity — A key role of altered protein kinase signaling in the response to energetic, oxidative and genotoxic stress

Doxorubicin is one of the most powerful drugs used in chemotherapy of a large number of cancers. However, its anti-tumor effects are associated with serious cardiotoxicity, which can lead to heart failure. So far, mechanisms responsible for cardiotoxicity are not fully understood. Here we provide evidence that persistent alterations in protein kinase cell signaling may play a key role in the etiology of cardiotoxicity. In this study, we apply targeted analysis of key protein kinase pathways as well as non-biased analysis of the entire cardiac phosphoproteome in two different model systems: isolated perfused rat heart, and heart from doxorubicin-treated rats. Although doxorubicin induces energetic, oxidative and genotoxic stress in the heart, activity of the energy stress sensor AMP-activated protein kinase is paradoxically down-regulated. Pro-survival MAPK and Akt pathways are activated, the latter via DNA damage sensed by DNA-PK. This is at least partially responsible for low AMPK activity, since Akt inhibition can restore AMPK activation. Combined inhibition of AMPK and activation of Akt and MAPKs also leads to activation of growth-stimulating mTOR signaling. Such signalling increases cellular energy deficits and, via active mTOR signaling, also contributes to the pathological cardiac phenotype. Cardiac phosphoproteomics based on 2D-gels and mass spectrometry revealed further alterations of phosphorylation and dephosphorylation events that are associated with the early response to doxorubicin. Some candidate phosphoproteins with putative functions in cardiotoxicity are currently under investigation. This study emphasizes the importance of cell signaling for our understanding of doxorubicin cardiotoxicity.