Downstream effectors of Akt and Erk converge to the mitochondria and initiate a protective response. There is additional evidence that coronary delivery of constitutively active form of Akt1 gene protects the heart against doxorubicininduced chronic heart failure by improving cardiac performance. We postulate that the increase in the pro-survival proteins observed in this study serves as an innate mechanism of the heart to protect against the damaging effects of doxorubicin. We also show increased p-Akt levels when treated with mdivi-1 alone and a BMS-354825 302962-49-8 further increase when treated with the combination of mdivi-1 and doxorubicin. A link between Akt pathway and the mitochondrial fusion and fission mechanism has been suggested previously. It is believed that increase in Akt phosphorylation promotes mitochondrial fusion, which is considered to lead to its cardioprotective effects. It has also been reported that compounds which offer cardio-protection such as insulin or anti-oxidants prevent ischaemia induced fragmentation and produces elongated mitochondria. It has also been speculated that the cytokine erythropoietin induces mitochondrial fusion by activating Akt. However, a downstream effector of Akt, protein kinase G, has been reported to phosphorylate and inhibit the pro-fission activity of Drp1. A recent study reported increase in the levels insulin stimulated Akt phosphorylation when also treated with mdivi-1. Further investigations are needed to establish whether mdivi-1 treatment causes a direct effect on Akt phosphorylation. We speculate that the huge increase observed in Akt phosphorylation when co-treated with doxorubicin and mdivi-1, is due to the dual effect of doxorubicin and a direct effect of mdivi-1 on Akt phosphorylation causing a further increase. Previously, we reported a significant increase in the levels of p-Akt following doxorubicin-treatment in conditions of ischaemia and reperfusion injury, which was partially blocked when coadministered with cyclosporin A as well as providing protection against the toxic effects of doxorubicin. Further studies are required to investigate the exact role of doxorubicin-induced toxicity and the protection there from with adjunct therapy on Akt phosphorylation. Studies have also reported a link between ROS generation, mitochondrial morphology and Erk 1/2 signalling in the regulation of insulin signalling pathway. Obesity induced ROS appeared to increase the levels of Erk 1/2 phosphorylation, which were reversed when treated with mdivi-1. A similar effect is also seen in our data showing that co-treatment with mdivi-1 reverses doxorubicin induced increase in Erk 1/2 levels. Furthermore, it has been reported that doxorubicin-induced involves Erk/p53 transduction pathway. Treatment of H9c2 and cardiac myocytes with doxorubicin caused an increase in the levels of p53 which were preceded by activation and nuclear translocation of Erk 1/2. They also showed that inhibition of Erk 1/2 with U-0126 prevented activation and nuclear translocation of both Erk 1/2 and p53 whilst inhibition of p53 with pifithrin-�� only prevented doxorubicin-induced changes in p53. In the current study we show an increase in the levels of p53 and Erk 1/2 following treatment with doxorubicin. Interestingly, co-administration of doxorubicin with mdivi-1, which prevented detrimental effects of doxorubicin in the 
Langendorff and oxidative stress model and reduced the levels of p-Drp1, also prevented the increase in the levels of both p53 and Erk 1/2. Further studies are required to identify the specific role of Erk 1/2 and Akt activation using their specific inhibitors and the CP-690550 intracellular signalling pathway associate with the protective effect mdivi-1. Furthermore, we show that co-treatment with mdivi-1 does not interfere with the anti-cancer properties of doxorubicin as assessed by MTT assay using HL60 cells. It is imperative to assess the effects of adjunct therapies, aiming to reduce the cardiotoxic effect, on the anti-tumour effects. Many cardioprotective strategies fail to demonstrate beneficial effects in clinical or in vivo settings as they interfere or reduce with the anti-cancer effects and thereby reduce the clinical utility. Collectively, our data show that co-treatment with the mitochondrial fission inhibitor mdivi-1 can ameliorate the cardiotoxic effects of doxorubicin without affecting its anticancer properties. These finding warrant further investigations in the relevant animal models of cancer. The p21-activated kinase family comprises six sterile-20 group serine/threonine kinases.