Key result
Transgenic mice expressing dominant-interfering p53 or constitutively active mTOR maintained normal fractional shortening (60%) after doxorubicin treatment compared to nontransgenic mice (45%).
Why the study?
Does cardiomyocyte-restricted dominant-interfering p53 or constitutively active mTOR prevent acute doxorubicin-induced cardiotoxicity in mice?
Does cardiomyocyte-restricted dominant-interfering p53 or constitutively active mTOR prevent acute doxorubicin-induced cardiotoxicity in mice?
Absolute Event Rate: 60% vs 45%
Acute doxorubicin cardiotoxicity and loss of cardiac mass are mediated by p53-dependent inhibition of mTOR signaling, rather than cardiomyocyte apoptosis.
No immediate clinical implications; leaves open p53/mTOR modulation for doxorubicin cardiotoxicity in humans.
BACKGROUND: Doxorubicin is used to treat childhood and adult cancer. Doxorubicin treatment is associated with both acute and chronic cardiotoxicity. The cardiotoxic effects of doxorubicin are cumulative, which limits its chemotherapeutic dose. Free radical generation and p53-dependent apoptosis are thought to contribute to doxorubicin-induced cardiotoxicity. METHODS AND RESULTS: Adult transgenic (MHC-CB7) mice expressing cardiomyocyte-restricted dominant-interfering p53 and their nontransgenic littermates were treated with doxorubicin (20 mg/kg cumulative dose). Nontransgenic mice exhibited reduced left ventricular systolic function (predoxorubicin fractional shortening [FS] 61+/-2%, postdoxorubicin FS 45+/-2%, mean+/-SEM, P<0.008), reduced cardiac mass, and high levels of cardiomyocyte apoptosis 7 days after the initiation of doxorubicin treatment. In contrast, doxorubicin-treated MHC-CB7 mice exhibited normal left ventricular systolic function (predoxorubicin FS 63+/-2%, postdoxorubicin FS 60+/-2%, P>0.008), normal cardiac mass, and low levels of cardiomyocyte apoptosis. Western blot analyses indicated that mTOR (mammalian target of rapamycin) signaling was inhibited in doxorubicin-treated nontransgenic mice but not in doxorubicin-treated MHC-CB7 mice. Accordingly, transgenic mice with cardiomyocyte-restricted, constitutively active mTOR expression (MHC-mTORca) were studied. Left ventricular systolic function (predoxorubicin FS 64+/-2%, postdoxorubicin FS 60+/-3%, P>0.008) and cardiac mass were normal in doxorubicin-treated MHC-mTORca mice, despite levels of cardiomyocyte apoptosis similar to those seen in doxorubicin-treated nontransgenic mice. CONCLUSIONS: These data suggest that doxorubicin treatment induces acute cardiac dysfunction and reduces cardiac mass via p53-dependent inhibition of mTOR signaling and that loss of myocardial mass, and not cardiomyocyte apoptosis, is the major contributor to acute doxorubicin cardiotoxicity.
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Zhu et al. (2008) studied Doxorubicin-induced cardiotoxicity. Cardiomyocyte-restricted dominant-interfering p53 or constitutively active mTOR expression vs. Nontransgenic littermates was evaluated on Left ventricular systolic function (fractional shortening). Transgenic mice expressing dominant-interfering p53 or constitutively active mTOR maintained normal fractional shortening (60%) after doxorubicin treatment compared to nontransgenic mice (45%).
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