Amrubicin is a novel, completely synthetic 9-aminoanthracycline derivative. Amrubicin and its C-13 alcohol metabolite, amrubicinol, inhibited purified human DNA topoisomerase II (topo II). Compared with doxorubicin (DXR), amrubicin and amrubicinol induced extensive DNA-protein complex formation and double-strand DNA breaks in CCRF-CEM cells and KU-2 cells. In this study, we found that ICRF-193, a topo II catalytic inhibitor, antagonized both DNA-protein complex formation and double-strand DNA breaks induced by amrubicin and amrubicinol. Coordinately, cell growth inhibition induced by amrubicin and amrubicinol, but not that induced by DXR, was antagonized by ICRF-193. Taken together, these findings indicate that the cell growthinhibitory effects of amrubicin and amrubicinol are due to DNA-protein complex formation followed by double-strand DNA breaks, which are mediated by topo II.Key words: Amrubicin -Anthracycline -DNA-protein complex -Double-strand DNA break -DNA topoisomerase II DNA topoisomerase II (topo II) is a nuclear enzyme that regulates DNA topology through strand breakage, strand passage and religation. Thus, topo II is extensively involved in DNA metabolism, including replication, transcription, recombination and sister chromatid segregation.1) Mammalian topo II is the primary cellular target of a number of potent antitumor agents such as doxorubicin (DXR), daunorubicin (DNR), etoposide and amsacrine (m-AMSA).2) These agents interfere with the breakagereunion reaction of topo II by trapping a covalent enzyme-DNA complex, termed "cleavable complex," in which DNA strands are broken and their 5′ termini are covalently linked to the protein. In general, the cytotoxicity of these topo II poisons is dependent on stabilization of the cleavable complex followed by topo II-mediated DNA damage, rather than inactivation of topo II cellular functions. 3)Amrubicin is a novel, completely synthetic 9-aminoanthracycline derivative, and has antitumor activities in murine experimental tumor systems and human tumornude mouse systems. 4,5) Like other anthracycline derivatives, such as DXR and DNR, amrubicin is converted to its C-13 alcohol metabolite, amrubicinol.6) In contrast to doxorubicinol and daunorubicinol, amrubicinol has much higher antitumor activity than the parent drug in vitro. 6, 7)In addition, amrubicin showed much weaker cardiotoxicity than DXR in a rabbit chronic experimental model. 8)Phase II clinical trials of amrubicin for the treatment of malignant lymphoma, superficial bladder, small cell lung carcinoma, and non-small cell lung carcinoma are in progress. 9,10) Amrubicin showed substantial activity (response rate of 25%) against non-small cell lung cancer, and a response rate of 78.8% was obtained against small cell lung cancer.The mechanisms underlying the antitumor activities of amrubicin and amrubicinol are not well understood. Our present study has shown that amrubicin and amrubicinol target human topo II by stabilizing the cleavable complex. Furthermore, amrubicin and amrubicinol induced DNApro...

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][...

The antitumor effects of SM‐5887, a totally synthetic 9‐aminoanthracycline derivative, were evaluated in six murinc experimental tumor systems (P38S, Ehrlich carcinoma, sarcoma 180, Lewis lung carcinoma, B16 melanoma and colon 38) and nine human tumor‐nude mouse systems (one breast cancer, two lung cancers and six gastric cancers). Characteristically SM‐5887 showed excellent antitumor activities, superior to adriamycin (ADR), against human tumor xenografts, although its activities against murine experimental tumors were almost equal to those of ADR. When the human tumors were implanted sc in female athymic mice (BALB/c, nu/nu) and their volume reached 100‐ 300 mm3, SM‐5887 and ADR were injected iv. All nine human tumors tested showed statistically significant responses to SM‐5887, and 7 of them were strongly suppressed in their growth by SM‐5887 so that minimum T/C values were less than 30% at the maximum tolerated dose (MTD, 25 mg/kg) with a single iv injection. Compared with ADR, SM‐5887 was statistically more effective in five tumors (one breast, one lung and three gastric), equal in two tumors (two gastric), and less potent in two tumors (one lung and one gastric). In addition, the 10‐day‐interval repeated iv treatments with SM‐5887 at the MTD (25 mg/kg) resulted in remarkably potent antitumor effects (including complete regression) against human gastric cancer, 4‐1ST, implanted in nude mice without enhancement of toxic effects, SM‐5887 was also effective against ip‐inoculated P388 by oral administration as well as iv injection.

Background Miriplatin (formerly SM-11355), a novel lipophilic platinum complex developed to treat hepatocellular carcinoma, is administered into the hepatic artery using an oily lymphographic agent (Lipiodol Ultra-Fluide ® ) as a carrier. We clariWed the usefulness of miriplatin as an agent for transarterial chemoembolization. Methods Platinum compounds released from miriplatin into serum, medium and Earle's balanced salt solution were examined. Then, miriplatin and cisplatin were administered to rats bearing hepatoma AH109A tumors in livers. Platinum concentrations in tissues and DNA were assessed. Results Miriplatin showed a more sustained release than cisplatin. Dichloro[(1R, 2R)-1, 2-cyclohexane diamine-N, NЈ]platinum, the most abundant platinum compound released from miriplatin, was as eVective as cisplatin in inhibiting the growth of cells. Miriplatin was selectively disposed of in tumors, maintained in tumors longer than cisplatin and caused apparent tumor regression inducing platinum-DNA adducts to form and massive apoptosis. Conclusion Miriplatin appears to be a suitable chemotherapeutic agent for transarterial chemoembolization.

The tissue distribution of a novel antitumor anthracycline antibiotic, amrubicin, was studied using seven human tumor xenografts implanted into nude mice, in order to identify the principal factors determining its therapeutic efficacy. We found a good correlation between the level of the metabolite amrubicinol in the tumor and the in vivo efficacy. High metabolic activity of amrubicin to amrubicinol was detected in tumor tissue homogenates, especially in cell lines highly sensitive to amrubicin in vivo. In contrast to amrubicin, the administration of amrubicinol showed less tumorselective toxicity in these human tumor xenograft models. These data indicate that the tumorselective metabolism of amrubicin to amrubicinol resulted in a tumor-selective disposition of amrubicinol, leading to good efficacy in in vivo experimental therapeutic models.