A possible mechanism for the long-lasting antitumor effect of the macromolecular conjugate DE-310: mediation by cellular uptake and drug release of its active camptothecin analog DX-8951.
DE-310, a new macromolecular prodrug, was designed to enhance the pharmacological profiles of a novel camptothecin analog (DX-8951f), and a single treatment with DE-310 exhibits a similar or greater therapeutic effect than do optimally scheduled multiple administrations of DX-8951f in several types of tumors. In this study, the drug-release mechanism by which DE-310 excites antitumor activity was investigated in Meth A cells, a malignant ascites model of murine fibrosarcoma. A single i.v. injection of DE-310 at the maximum tolerated dose (MTD) prolonged survival of Meth A-bearing mice by 300%. DX-8951 and glycyl-8951 (G-DX-8951), enzymatic cleavage products of DE-310, were detected in serum and ascites fluid, and also in the culture medium of Meth A ascites cells incubated in vitro with DE-310. The total amounts of DX-8951, G-DX-8951, and conjugated DX-8951 in Meth A tumor cells were three times higher than that in macrophages. Furthermore, DX-8951-related fluorescence was observed in Meth A ascites cells obtained from Meth A-bearing mice that had received DE-310 or CM-Dex-PA-DX-8951 that does not release free DX-8951. DX-8951-related fluorescence was also observed at the site of lysosomes in cells incubated in vitro with DE-310 at 37 degrees C, but not in those incubated at 4 degrees C. Drugs were released from DE-310 by cysteine proteinase prepared from Meth A tumor tissue. These results suggest that the mechanism by which DX-8951 is released from DE-310 in vivo is involved in the process of uptake of DE-310 into tumor or macrophages, digestion by intracellular lysosomal cysteine proteinase, and subsequent secretion of the drugs.
Ochi
Yusuke
Y
New Product Research Laboratories III, Daiichi Pharmaceutical Co., Ltd., Tokyo R&D Center, 16-13, Kita-Kasai 1-Chome, Edogawa-ku, Tokyo, 134-8630, Japan. ochiyh1i@daiichipharm.co.jp.
Shiose
Yoshinobu
Y
New Product Research Laboratories III, Daiichi Pharmaceutical Co., Ltd., Tokyo R&D Center, 16-13, Kita-Kasai 1-Chome, Edogawa-ku, Tokyo, 134-8630, Japan.
Kuga
Hiroshi
H
New Product Research Laboratories III, Daiichi Pharmaceutical Co., Ltd., Tokyo R&D Center, 16-13, Kita-Kasai 1-Chome, Edogawa-ku, Tokyo, 134-8630, Japan.
Kumazawa
Eiji
E
New Product Research Laboratories III, Daiichi Pharmaceutical Co., Ltd., Tokyo R&D Center, 16-13, Kita-Kasai 1-Chome, Edogawa-ku, Tokyo, 134-8630, Japan.
D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology*; D001201:Ascites / Q000378:metabolism; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology*; D002851:Chromatography, High Pressure Liquid; D004705:Endocytosis; D005354:Fibrosarcoma / Q000188:drug therapy* / Q000378:metabolism; D005453:Fluorescence; D007274:Injections, Intraperitoneal; D008247:Lysosomes / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D018613:Microscopy, Confocal; D009368:Neoplasm Transplantation; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; C452060:DE-310 cpd; C095887:exatecan; D002166:Camptothecin