Down-regulation of bcr-abl and bcl-xL expression in a leukemia cell line and its doxorubicin-resistant variant by topoisomerase II inhibitors

K562 cells are usually resistant to apoptosis induction, probably because of the expression of bn-abl, the hybrid gene characteristic of the Philadelphia chromosome (t 9;22). However, we have previously shown that amsacrine and, to a lesser extent, doxorubicin, could induce apoptosis in the doxorubicin-resistant variant of this cell line. In order to elucidate the role of bcr-abt in triggering apoptosis, we investigated the effect of the topoisomerase II inhibitors doxorubicin, amsacrine, and etoposide on the expression of several genes that: may be related to apoptosis induction in both cell lines. This was done using a technique of reverse transcription-polymerase chain reaction coupled with HPLC of the amplified fragments to obtain semiquantitative evaluations. We showed that amsacrine, at pharmacologically relevant concentrations, was able to decrease the expression of bcr abl down to 20% of the basal value in the doxorubicin-resistant variant only, whereas doxorubicin and etoposide were unable to do so. No effect of these drugs was seen on the expression of the normal abl gene. In addition, there was an effect of amsacrine on the expression of bcl-x(L) in the resistant cell line only, but at concentrations higher than the IC50 of this drug. Our results emphasize the role of bcr-abl in protecting cells from apoptosis and the possible involvement of specific topoisomerase II inhibitors in overcoming resistance to apoptosis. BIOCHEM PHARMACOL 60;12:1823-1828, 2000. (C) 2000 Elsevier Science Inc.