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BACKGROUND - There is an increased incidence of heart failure in patients treated concurrently with anthracyclines and the chemotherapeutic anti-erbB2 agent trastuzumab (Herceptin). On the basis of our previous studies with recombinant neuregulin-1beta (NRG-1beta), a ligand for the erbB2 receptor tyrosine kinase, we hypothesized that activation of erbB2 by anti-erbB2 versus NRG-1 would cause differential effects on myocyte intracellular signaling as well as anthracycline-induced myofibrillar injury and might potentially account for the clinical toxicity of trastuzumab in the setting of concurrent anthracycline therapy.
METHODS AND RESULTS - We tested this hypothesis using adult rat ventricular myocytes (ARVMs) in culture, assessing myofibrillar structure by immunostaining for myomesin and filamentous actin. Activation of erbB2, extracellular signal-regulated kinase 1/2 (Erk1/2), and Akt was assessed by use of antibodies to phosphorylated activated receptor or kinase detected by immunoblot. ARVMs treated with doxorubicin (0.1 to 0.5 micromol/L) showed a concentration-dependent increase in myofilament disarray. NRG-1beta (10 ng/mL) activated erbB2, Erk1/2, and Akt in ARVMs and significantly reduced anthracycline-induced disarray. In contrast to NRG-1beta, anti-erbB2 (1 microg/mL) caused rapid phosphorylation of erbB2 but not Erk1/2 or Akt, with downregulation of erbB2 by 24 hours. Concomitant treatment of myocytes with anti-erbB2 and doxorubicin caused a significant increase in myofibrillar disarray versus doxorubicin alone.
CONCLUSIONS - NRG-1beta/erbB signaling regulates anthracycline-induced myofilament injury. The increased susceptibility of myofilaments to doxorubicin in the presence of antibody to erbB2 may explain the contractile dysfunction seen in patients receiving concurrent trastuzumab and anthracyclines.