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

Abstract

Amrubicin, a 9-aminoanthracycline anti-cancer drug, and its C-13 hydroxyl metabolite amrubicinol, were examined for growth-inhibitory activity as well as cellular uptake and distribution in P388 murine leukemia cells and doxorubicin-resistant P388 cells. Also discussed are the differences in the mechanisms of action among amrubicin, amrubicinol and doxorubicin in terms of their cellular pharmacokinetic character. In P388 cells, amrubicinol was about 80 times as potent as amrubicin, and about 2 times more potent than doxorubicin in a 1-h drug exposure growth-inhibition test. A clear cross-resistance was observed to both amrubicin and amrubicinol in doxorubicin-resistant P388 cells, though the resistance index was lower for amrubicin. The intracellular concentration of amrubicinol was about 6 times and 2 times higher than those of amrubicin and doxorubicin, respectively. Compared to doxorubicin, amrubicin and amrubicinol were released rapidly after removal of the drugs from the medium. A clear correlation was found between the growth-inhibiting activity and the cellular level of amrubicin and amrubicinol in P388 cells. About 10 to 20% of amrubicin or amrubicinol taken up by the cells was detected in the cell nuclear fraction, whereas 70 to 80% of doxorubicin was localized in this fraction. These results suggest that amrubicin and amrubicinol exert cytotoxic activity via a different mechanism from that of doxorubicin.Key words: Anthracycline -Amrubicin -SM-5887 -Metabolite Amrubicin hydrochloride (SM-5887) is a completely synthetic 9-aminoanthracycline anti-cancer drug.1) It has potent antitumor activities, being more potent than doxorubicin against various mouse experimental tumors and human tumor xenografts.2) Phase II clinical trials of amrubicin for the treatment of malignant lymphoma, superficial bladder cancer, small cell lung cancer and non-small cell lung cancer are in progress.3, 4) The response rates were 25% and 79% against non-small cell lung cancer and small cell lung cancer, respectively.In our previous studies, amrubicinol, the C-13 hydroxy metabolite of amrubicin, was much more potent than the parent compound, amrubicin, and as potent as doxorubicin in inhibiting the growth of human tumor 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.6, 7) We thus suppose that amrubicinol plays an important role in the in vivo antitumor effect of amrubicin as an active metabolite.A major metabolic pathway of anthracyclines is known to be the reduction of the C-13 carbonyl group to a hydroxyl group by cytoplasmic carbonyl reductase. [8][9][10] Generally, the C-13 hydroxy metabolite of an anthracycline shows lower growth-inhibitory activity than the respective parent compound. Doxorubicinol, epirubicinol and daunorubicinol are less poten...

Increased cellular accumulation and distribution of amrubicin contribute to its activity in anthracycline-resistant cancer cells

“…Interestingly, previous reports have suggested that other anthracyclines may also act through regulating both internal and external membrane structures in the cell, such as binding to the phospholipid cardiolipin on the mitochondrial membrane and peroxidation of membrane-unsaturated lipids in the cytoplasmic compartment [31]. Our data are similar to those reported by Yamaoka et al [32] who observed that amrubicin remained active and cytotoxic in doxorubicin-resistant P388 murine leukemia cells. Although amrubicin could be a weak P-glycoprotein substrate, our experiments demonstrate that P-glycoprotein inhibitors do not affect the accumulation of amrubicin in doxorubicin-resistant cells.…”

Retrospective analysis of efficacy and safety of amrubicin in refractory and relapsed small-cell lung cancer

“…5 Amrubicin is a totally synthetic 9-aminoanthracycline anticancer drug and a potent inhibitor of topoisomerase II. [6][7][8][9][10][11][12][13] It is similar in chemical structure to a representative anthracycline, doxorubicin, but it is more potent than doxorubicin against various mouse experimental tumors and human tumor xenografts. Amrubicin is converted to an active metabolite, amrubicinol, through the reduction of its C-13 ketone group to a hydroxy group.…”

Efficacy and safety of amurubicin for the elderly patients with refractory relapsed small cell lung cancer as third-line chemotherapy

“…Although classified as anthracycline agents, amrubicin and amrubicinol exert cytotoxic effects as DNA topoisomerase II inhibitors, but not mainly as DNA intercalators. [10][11][12][13][14][15][16][17] A Japanese phase II study with intravenous administration of single-agent AMR at 40 mg/m 2 for three consecutive days in previously treated SCLC patients was reported. The overall RRs were 52, 50% in sensitive and refractory relapse cases respectively.…”