nb-506 and edotecarin

The antitumor drugs NB-506 and J-107088 are potent topoisomerase I inhibitors with an indolocarbazole structure. To clarify the factors involved in resistance to these drugs, we established two NB-506-resistant mouse fibroblast cell lines (LY/NR1 and LY/NR2), a human colon carcinoma cell line (HCT116/NR1), and a lung cancer cell line (PC13/NR1). These cell lines were highly resistant to NB-506 and J-107088, and LY/NR2 cells showed markedly reduced accumulation and strong efflux of NB-506, suggesting activation of a drug efflux pump in the resistant cells. To identify the molecules responsible for efflux of NB-506, we compared the gene expressions of the mouse resistant LY/NR1 cells, LY/NR2 cells, and their parental cells by oligonucleotide microarray. Of 34,020 genes analyzed, we found that an ATP-binding cassette transporter BCRP/MXR/ABCP (BCRP) gene showed the highest increase in the expression, 31-fold higher in the LY/NR2-resistant cells than in their parental cells. The selective overexpression of this gene was also detected in the two human resistant cell lines, suggesting the involvement of breast cancer resistant protein (BCRP) in the resistance and efflux of these drugs. Finally, a PC-13 cell line transfected with BCRP expression vector displayed 22- and 17-fold resistance to NB-506 and J-107088 and enhanced efflux activity of J-107088. However, the transfectants were not resistant to mitoxantrone or topotecan, the drugs previously thought to be the substrates of BCRP. Thus, our study presents a novel mechanism of drug resistance mediated by BCRP.

Topics: Animals; Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters; Biological Transport; Carbazoles; Colonic Neoplasms; DNA, Complementary; DNA, Neoplasm; Drug Resistance, Multiple; Enzyme Inhibitors; Fibroblasts; Gene Expression Profiling; Glucosides; Humans; Indoles; Lung Neoplasms; Mice; Neoplasm Proteins; Oligonucleotide Array Sequence Analysis; RNA, Messenger; Topoisomerase I Inhibitors; Transfection; Tumor Cells, Cultured

A new indolocarbazole compound, NB-506 (1), modified at the glucose group yielded a beta-D-glucopyranoside, J-107,088 (2), which showed potent anticancer activity. A beta-D-ribofuranoside, J-109,534 (3), was found to be 6 times more potent than J-107,088 at inhibiting topoisomerase I.

Topics: Antineoplastic Agents; Carbazoles; Enzyme Inhibitors; Glucose; Glucosides; Humans; Indoles; Magnetic Resonance Spectroscopy; Mass Spectrometry; Stereoisomerism; Topoisomerase I Inhibitors; Tumor Cells, Cultured

J-107088 [6-N-(1-hydroxymethyl-2-hydroxy)ethylamino-12,13-dihydro-2,10-dihydroxy- 13-(beta-D-glucopyranosyl)-5H-indolo[2,3-a]-pyrrolo[3,4-c]-carb azo le-5,7(6H)-dione] is a new derivative of NB-506, an indolocarbazole antitumor agent. J-107088 induced single-strand DNA cleavage only in the presence of topoisomerase I (top1) more effectively than NB-506 or camptothecin. The preferable sequences of the DNA cleaved by J-107088 were C/T / G as in the case of NB-506. This base-preference of J-107088 in top1-mediated cleavage was different from that of camptothecin, which was T / G/A. top1 poisons stabilize the complex between DNA and top1 (cleavable complex). This cleavable complex is released on addition of a high concentration of monovalent cation or removal of top1 poisons. The complex induced by J-107088 was quite stable; it was scarcely released on the addition of NaCl or dilution of J-107088, contrary to the case with camptothecin and NB-506. J-107088-inducing complexes were also stable in cultured cells, when the compound was added to the culture medium. These unique in vitro activities of J-107088 on top1 that differed from those of camptothecin and NB-506 may be relevant to its more potent in vivo antitumor efficacy in a human tumor xenographted nude mouse model.

Topics: Animals; Antineoplastic Agents; Carbazoles; Cell Line; DNA; Enzyme Inhibitors; Glucosides; Humans; Indoles; Mice; Sodium Chloride; Topoisomerase I Inhibitors