Mitsuharu Hanada

A new antitumor agent amrubicin induces cell growth inhibition by stabilizing topoisomerase II-DNA complex

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 growth‐inhibitory effects of amrubicin and amrubicinol are due to DNA‐protein complex formation followed by double‐strand DNA breaks, which are mediated by topo II.

Intra-hepatic arterial administration with miriplatin suspended in an oily lymphographic agent inhibits the growth of tumors implanted in rat livers by inducing platinum-DNA adducts to form and massive apoptosis

BackgroundMiriplatin (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 clarified the usefulness of miriplatin as an agent for transarterial chemoembolization.MethodsPlatinum 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.ResultsMiriplatin showed a more sustained release than cisplatin. Dichloro[(1R, 2R)-1, 2-cyclohexane diamine-N, N′]platinum, the most abundant platinum compound released from miriplatin, was as effective 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.ConclusionMiriplatin appears to be a suitable chemotherapeutic agent for transarterial chemoembolization.

Intra‐hepatic arterial administration with miriplatin suspended in an oily lymphographic agent inhibits the growth of human hepatoma cells orthotopically implanted in nude rats

Miriplatin is a lipophilic platinum complex which contains myristates as leaving groups and diaminocyclohexane as a carrier ligand. In order to examine in vivo the antitumor activities of miriplatin suspended in an oily lymphographic agent (Lipiodol Ultra‐Fluide®, LPD) against human hepatocellular carcinoma (HCC) after the intra‐hepatic arterial administration, we have developed a novel orthotopic model of HCC in which the human hepatoma cell line Li‐7 was successively implanted and maintained in the liver of nude rats. Li‐7 tumors established in nude rat livers displayed a trabecular structure similar to their original morphology, and were exclusively supplied by the hepatic artery, suggesting that they exhibited in part the conditions of human HCC. Miriplatin suspended in LPD (miriplatin/LPD) administered into the hepatic artery of this model dose‐dependently inhibited the growth of Li‐7 tumors without markedly enhancing body weight loss and caused a significant reduction in the growth rate at a dose of 400 µg/head compared to LPD alone. In addition, at the therapeutic dose, miriplatin/LPD as well as cisplatin suspended in LPD (400 µg/head) was shown to be more active than zinostatin stimalamer suspended in LPD (20 µg/head) against Li‐7 tumors after a single intra‐hepatic arterial administration. These results suggest miriplatin to be a suitable candidate for use in transarterial chemoembolization (Cancer Sci 2009; 100: 189–194)

Amrubicin, a novel 9-aminoanthracycline, enhances the antitumor activity of chemotherapeutic agents against human cancer cells in vitro and in vivo

Amrubicin, a completely synthetic 9‐aminoanthracycline derivative, is an active agent in the treatment of untreated extensive disease‐small‐cell lung cancer and advanced non‐small‐cell lung cancer. Amrubicin administered intravenously at 25 mg/kg substantially prevented the growth of five of six human lung cancer xenografts established in athymic nude mice, confirming that amrubicin as a single agent was active in human lung tumors. To survey which antitumor agent available for clinical use produces a synergistic interaction with amrubicin, we examined the effects in combinations with amrubicinol, an active metabolite of amrubicin, of several chemotherapeutic agents in vitro using five human cancer cell lines using the combination index (CI) method of Chou and Talalay. Synergistic effects were obtained on the simultaneous use of amrubicinol with cisplatin, irinotecan, gefitinib and trastuzumab, with CI values after 3 days of exposure being <1. Additive effect was observed with the combination containing vinorelbine with CI values indistinguishable from 1, while the combination of amrubicinol with gemcitabine was antagonistic. All combinations tested in vivo were well tolerated. The combinations of cisplatin, irinotecan, vinorelbine, trastuzumab, tegafur/uracil, and to a lesser extent, gemcitabine with amrubicin caused significant growth inhibition of human tumor xenografts without pronouncedly enhancing body weight loss, compared with treatment using amrubicin alone at the maximum tolerated dose. Growth inhibition of tumors by gefitinib was not antagonized by amrubicin. These results suggest that amrubicin appears to be a possible candidate for combined use with cisplatin, irinotecan, vinorelbine, gemcitabine, tegafur/uracil or trastuzumab. (Cancer Sci 2007; 98: 447–454)

Uptake and intracellular distribution of amrubicin, a novel 9-amino-anthracycline, and its active metabolite amrubicinol in P388 murine leukemia cells.

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.

Amrubicin induces apoptosis in human tumor cells mediated by the activation of caspase-3/7 preceding a loss of mitochondrial membrane potential

Amrubicin, a completely synthetic 9‐aminoanthracycline derivative, inhibits cell growth by stabilizing a topoisomerase II–DNA complex. This study was designed to examine the apoptosis induced in human leukemia U937 cells by amrubicin and its active metabolite amrubicinol. Amrubicin, amrubicinol and other antitumor agents, such as daunorubicin and etoposide, induced typical apoptosis with characteristic nuclear morphological change and DNA fragmentation. Measuring the population of sub‐G1 phase cells, it was found that under conditions where cell growth was inhibited by either amrubicin or amrubicinol, U937 cells underwent apoptotic cell death in a dose‐dependent manner accompanied by an arrest of the cell cycle at G2/M. Furthermore, amrubicin‐ and amrubicinol‐induced apoptosis was mediated by the activation of caspase‐3/7, but not caspase‐1, preceding a loss of mitochondrial membrane potential. These results indicate that both a reduction in mitochondrial membrane potential and the activation of caspase‐3/7 are key events in the apoptosis induced by amrubicin and amrubicinol as well as the other antitumor agents. In addition, studies with oligomycin suggested that the apoptosis induced by amrubicin and amrubicinol involved substantially different pathways from that triggered by daunorubicin and etoposide. Oligomycin blocked the etoposide‐induced increase in the number of sub‐G1 phase cells without preventing the activation of caspase‐3/7, and had no inhibitory effect on the expansion of the sub‐G1 population in daunorubicin‐treated cells, whereas apoptosis‐related changes caused by amrubicin and amrubicinol were suppressed in the presence of oligomycin. (Cancer Sci 2006; 97: 1396–1403)