Subcellular localization of anthracyclines in cultured rat cardiomyoblasts as possible predictors of cardiotoxicity

In this study, we compared the cellular uptake, intracellular localization and cytotoxicity of two groups of anthracycline derivatives in cultured H9c2(2-1) rat cardiomyoblasts. The first group consisted of doxorubicin (DOX) and two of its derivatives containing a formamidino group (–N = CH–N<) at the C-3′ position with a morpholine (DOXM) or a hexamethyleneimine (DOXH) ring. The second group consisted of daunorubicin (DRB) and its derivatives containing a morpholine (DRBM) or a hexamethyleneimine (DRBH) ring. DOXH and DRBH were taken up by cardiomyoblasts more efficiently than estimated for other tested anthracyclines. The cellular uptakes of DOXM and DRBM were reduced compared to those of the parent compounds. Applied structural modifications of DOX and DRB influenced the subcellular localization of the tested derivatives. DOX and DOXH were localized primarily in nuclei, whereas the other anthracyclines were found in the nuclei and cytoplasm. The percentages of the compounds that accumulated in the nuclei were 80.2 and 54.2 % for DOX and DOXH, respectively. The lowest nuclear accumulation values were observed for DRBM (19.9 %), DRBH (21.9 %) and DOXM (23.7 %). The ability of anthracyclines to accumulate in the nuclei correlated with their DNA binding constants (r = 0.858, P = 0.029). A correlation was found between the accumulation of the tested anthracyclines in the nuclei of cardiomyoblasts and their cardiotoxicity in vivo, which was observed in our previous study. We suggest that cytotoxicity and the anthracycline accumulation level in the nuclei of cultured cardiomyoblasts could be used for early prediction of their cardiotoxicity.