1Universitätsklinikum Heidelberg Innere Medizin VIII, Institut für Experimentelle Kardiologie Heidelberg, Deutschland; 2Universitätsklinikum Heidelberg Klinik für Innere Med. III, Kardiologie, Angiologie u. Pneumologie Heidelberg, Deutschland
Cancer therapy-associated cardiotoxicity often results in heart failure. The topoisomerase 2 (top2b) inhibitor Doxorubicin (DOX) is effective in treating cancer but associated with cardiotoxicity which can even manifest years after exposure. Top2b is the predominant isoform in cardiomyocytes and cardiomyocyte-specific deletion of top2b protects from DOX-induced cardiomyopathy. However, the exact pathological mechanism how DOX leads to cardiotoxicity is unknown.
In preliminary work it was found, that most promoters of poised top2b-bound genes overlapped with binding sites for the transcription factor MEF2 (myocyte enhancer factor 2). Since MEF2-dependent genes are crucial for pathological cardiac remodelling, we hypothesized that MEF2 inhibition might be cardioprotective. The FDA-approved pan HDAC-inhibitor SAHA lead to an accumulation of class II HDACs, accompanied by a possibly HDAC4-mediated inhibition of MEF2-transcriptional activity.
To prove the accumulation of HDAC4 in the nucleus after SAHA treatment, the localization of HDAC4 was investigated by overexpression with an HDAC4-AV and detection by Immunostaining in DOX/SAHA treated neonatal rat cardiomyocytes.
In a long-term in-vivo model in mice DOX-treated mice showed a reduction in left ventricular ejection fraction compared to SAHA co-treatment (Control 50.3 ± 3.1%, n=12 vs. DOX 43.0 ± 3.4%, n=12; p<0.05; vs. DOX+SAHA 50.6 ± 7.4%, n=11, p>0.05). DOX-dependent dysregulation of pathological genes such as myh7 was blunted in SAHA treated animals.
To prove the importance of HDAC4 in MEF2 inhibition, the in-vivo model in mice was repeated and SAHA was replaced by the selective HDAC class II inhibitor TMP195. The results reveal no improvement of DOX-dependent cardiac dysfunction in the co-treatment with TMP195 (Control 49.1 ± 7.8%, n=12 vs. DOX 40.8 ± 4.8%, n=10, p<0.05; vs. DOX+TMP195 37.1 ± 6.2%, n=6, p<0.05). MEF2 target genes such as myh7 were not reversed in the DOX+TMP195 group. Furthermore, a significant reduction in the survival rate was evident in the co-treatment with TMP195.
These results indicate a potential HDAC4-mediated MEF2 inhibition by SAHA that might be cardioprotective in DOX-induced cardiotoxicity.