HYDROXYRUBICIN, A DEAMINATED DERIVATIVE OF DOXORUBICIN, INHIBITS MAMMALIAN DNA TOPOISOMERASE-II AND PARTIALLY CIRCUMVENTS MULTIDRUG-RESISTANCE

In vivo effectiveness of doxorubicin remains restricted due to toxicit y and drug resistance. Hydroxyrubicin is a synthetic analog of doxorub icin in which the basic amino group at the C-3' has been replaced by a hydroxyl group in order to overcome recognition by the multidrug resi stant (MDR) P-glycoprotein and limit cardiotoxicity. The present study shows that hydroxy-rubicin is a less potent intercalator than doxorub icin. Induction of topoisomerase II-mediated DNA cleavage in the human c-myc origin by the two drugs was similar, reaching a maximum at 0.5 mu M. Results from the NCI Cell Screening program indicate a relativel y good correlation between the cytotoxicity of the 2 drugs on 55 cell lines of various origins (r = 0.723). Using a clonogenic assay, we obs erved that hydroxyrubicin was 20-fold more cytotoxic against the MDR K B-VI cell line than doxorubicin and was slightly more cytotoxic than d oxorubicin in the sensitive KB3.1 cell line. Uptake studies showed tha t doxorubicin was retained up to 1 hr in KB3.1 cells and rapidly elimi nated from resistant KB-V1 cells. In contrast, hydroxyrubicin was rapi dly eliminated from both sensitive KB3.1 and MDR-positive KB-V1 cells. Both drugs induced protein-linked DNA single-strand breaks (SSBs) in both KB3.1 and KB-V1 cells, which is consistent with topoisomerase inh ibition. However, the kinetics of DNA SSBs induced by both drugs was v ery different. DNA breaks disappeared quickly in both KB3.1 and KB-VI cell lines after hydroxyrubicin removal while DNA breaks induced by do xorubicin disappeared very slowly in KB3.1 cells and rapidly in KB-V1 cells. We conclude that removal of the basic amino group at the C-3' o f doxorubicin modifies drug transport and partially circumvents MDR wi thout changing topoisomerase II inhibition when compared with doxorubi cin. (C) 1994 Wiley-Liss, Inc.