Molecular Mechanisms of the Cardiotoxicity of the Proteasomal-Targeted Drugs Bortezomib and Carfilzomib
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Bortezomib and carfilzomib are anticancer drugs that target the proteasome. However, these agents have been shown to exhibit some specific cardiac toxicities by as yet unknown mechanisms. Bortezomib and carfilzomib are also being used clinically in combination with doxorubicin, which is also cardiotoxic. A primary neonatal rat myocyte model was used to study these cardiotoxic mechanisms. Exposure to submicromolar concentrations of bortezomib and carfilzomib resulted in significant myocyte damage and induced apoptosis. Both bortezomib and carfilzomib inhibited the chymotrypsin-like proteasomal activity of myocyte lysate in the low nanomolar concentration range and exhibited time-dependent inhibition kinetics. The high sensitivity of myocytes, which were determined to contain high specific levels of chymotrypsin-like proteasomal activity, to the damaging effects of bortezomib and carfilzomib was likely due to the inhibition of proteasomal-dependent ongoing sarcomeric protein turnover. A brief preexposure of myocytes to non-toxic nanomolar concentrations of bortezomib or carfilzomib greatly increased doxorubicin-mediated damage, which suggests that the combination of doxorubicin with either bortezomib or carfilzomib may produce more than additive cardiotoxicity. The doxorubicin cardioprotective agent dexrazoxane partially protected myocytes from doxorubicin plus bortezomib or carfilzomib treatment, in spite of the fact that bortezomib and carfilzomib inhibited the dexrazoxane-induced decreases in topoisomerase IIβ protein levels in myocytes. These latter results suggest that the doxorubicin cardioprotective effects of dexrazoxane and the doxorubicin-mediated cardiotoxicity were not exclusively due to targeting of topoisomerase IIβ.
KeywordsBortezomib Carfilzomib Doxorubicin Dexrazoxane Cardiac myocytes Topoisomerase IIβ Cardiotoxicity Proteasome Chymotrypsin-like
Dulbecco’s modified Eagle medium/Ham’s F-12 medium 1:1, where x is % (v/v) serum
Dulbecco’s phosphate-buffered saline (pH 7.4)
- λEx and λEm
Excitation and emission wavelengths, respectively
This research was supported by grants from the Canadian Institutes of Health Research (Grant MOP13748), the Canada Research Chairs Program and a Canada Research Chair in Drug Development to Brian Hasinoff. The authors declare no competing financial interests. The funding sources had no involvement in the study design, in the collection, analysis and interpretation of data, in the writing of the report and in the decision to submit the article for publication.
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