Cytotoxicity of Amrubicin, a Novel 9‐Aminoanthracycline, and Its Active Metabolite Amrubicinol on Human Tumor Cells

Abstract

Amrubicin, a completely synthetic 9-aminoanthracycline derivative, was previously shown to have potent antitumor activities against various human tumor xenografts. In this study, the in vitro activities of amrubicin and its major metabolite, amrubicinol, were examined using 17 human tumor cell lines. Amrubicinol was 5 to 54 times more potent than amrubicin, and as potent as doxorubicin, in inhibiting the growth of the cells following 3-day continuous drug exposure. Amrubicinol closely resembled doxorubicin in its profile of activities on the 17 human tumor cell lines. Cells were incubated with the drugs for 1 h, and the intracellular drug concentration and cell growth inhibition after 3 days were determined. Amrubicinol attained similar intracellular concentrations at lower medium concentrations compared to amrubicin, and the intracellular concentration of amrubicinol necessary to produce 50% cell growth inhibition was 3 to 8 times lower than that of amrubicin in 4 cell lines tested. Amrubicinol has a higher activity level inside the cells than does amrubicin. When cells were incubated with amrubicin for 5 h, a substantial amount of amrubicinol, more than 9% of that of amrubicin, was found in cells in 4 of the 8 cell lines tested. Amrubicinol may contribute to the in vitro growth-inhibitory effect of amrubicin on these cells. The results suggest that amrubicinol plays an important role in the in vivo antitumor effect of amrubicin as an active metabolite.Key words: Anthracycline -Amrubicin -SM-5887 -Metabolism Amrubicin hydrochloride, (+)-(7S,9S)-acetyl-9-amino-7-[(2-deoxy-β-D-erythro-pentopyranosyl)oxy]-7,8,9,10-tetrahydro-6,11-dihydroxy-5,12-naphthacenedione hydrochloride (SM-5887), is a completely synthetic 9-aminoanthracycline derivative.1) It has potent antitumor activities against various human tumor xenografts, being more potent than doxorubicin.2) In contrast to its potent in vivo antitumor activities, the in vitro growth-inhibitory activities of amrubicin were more than 5 times lower than those of doxorubicin in several human tumor cell lines.3)The dissociation between the in vitro and in vivo activities suggests that amrubicin is converted in vivo to metabolites which are more effective cell growth inhibitors than the parent compound. To test this possibility, the growthinhibitory activities of the metabolites of amrubicin were examined using various human tumor cell lines.A major pathway of anthracycline metabolism is known to be the reduction of the C-13 carbonyl group to a hydroxyl group by cytoplasmic carbonyl reductase, and another involves the reductive cleavage of the glycosidic bond between the amino sugar and the chromophore by microsomal glycosidases.4) The C-13 hydroxy derivatives and aglycones of doxorubicin, epirubicin, daunorubicin and idarubicin were found in the plasma of cancer patients, [5][6][7][8] as well as in the plasma and tissues of experimental animals treated with these drugs.9-11) These metabolites were also formed in vitro in human hepatocytes and human tumor cells. [12][13][...

Enhancement of radiosensitivity by topoisomerase II inhibitor, amrubicin and amrubicinol, in human lung adenocarcinoma A549 cells and kinetics of apoptosis and necrosis induction

“…The anthracycline derivative AMR and its active metabolite AMROH are synthesized antitumor agents and have been shown to be DNA topoisomerase II inhibitors (5,6). It has been reported that DNA topoisomerase II is vital for essential biological reactions, such as replication, transcription, and genetic recombination (45,46), and Nelson et al reported that mAMSA [4'-(9-acridinylamino) methane sulfonm-anisidide], an antitumor agent, inhibited topoisomerase II in mammals (47).…”

Uptake and Intracellular Distribution of Amrubicin, a Novel 9‐Amino‐anthracycline, and Its Active Metabolite Amrubicinol in P388 Murine Leukemia Cells

“…5) In nude mouse-human tumor models, amrubicinol was detected in plasma, normal tissues and tumor tissues of mice treated with amrubicin. Amrubicinol was distributed more in tumor tissues than in normal tissues compared to doxorubicin, and the level of amrubicinol in the tumor correlated to the in vivo efficacy of amrubicin.…”

“…It was also found that the intracellular concentration of amrubicinol was higher than that of amrubicin in human tumor cells. 5) In the present study, the growth-inhibitory activities, cellular uptake and release, and intracellular distribution of amrubicin and amrubicinol were further examined using P388 murine leukemia cells and doxorubicin-resis- …”

Tumor‐selective Distribution of an Active Metabolite of the 9‐Aminoanthracycline Amrubicin

“…7) It is thus likely that doxorubicin itself contributes mainly to the cytotoxicity. We found that amrubicinol, in contrast, was more than ten times more active than the parent compound and was almost as active as doxorubicin in vitro, 6) and the levels of amrubicinol in all tissues except bone marrow and plasma were more than 10% of the total of amrubicin and its metabolites in this study. Considering these data, we think that it is appropriate to compare the tissue level of amrubicinol with that of doxorubicin in order to evaluate the cytotoxic effects of amrubicin and doxorubicin.…”

“…5) We found that the 13-hydroxy alcohol, amrubicinol, showed about 10 to 100 times higher activity in an in vitro cell growth inhibition assay using 17 human tumor cell lines. 6) This characteristic of amrubicin distinguishes it from doxorubicin, daunorubicin, epirubicin and also idarubicin. Kuffel et al showed that doxorubicinol, daunorubicinol and epirubicinol were 7-52 times less active than the respective parent drugs, and that idarubicinol was essentially equipotent to idarubicin against three human tumor cell lines in growth inhibition assays.…”