Cellular determinants of resistance to indolocarbazole analogue 6-N-formylamino-12,13-dihydro-1,11-dihydroxy-13(beta-D-glucopyranosyl)- 5H-indolo[2,3-alpha]pyrrolo[3,4-c]carbazole-5,7(6H)-dione (NB-506), a novel potent topoisomerase I inhibitor, in multidrug-resistant human tumor cells.

Abstract

Membrane protein-associated alterations in cellular drug accumulation have been recently implicated in resistance to topoisomerase I (TOP-I)-interactive drugs. The present study investigated the cellular determinants of resistance to the indolocarbazole compound NB-506 [6-N-formylamino-12,13-dihydro-1,11-dihydroxy-13(beta-D-glucopyranosyl)- 5H-indolo[2,3-alpha]pyrrolo[3,4-c]carbazole-5,7(6H)-dione], a structurally novel TOP-I-interactive drug, in parental and multidrug-resistant tumor cells expressing either the P-170 glycoprotein (Pgp170) or multidrug resistance protein (MRP). MRP-expressing 250-fold doxorubicin-resistant human fibrosarcoma HT1080/DR4 tumor cells were drug sensitive to NB-506 and camptothecin (CPT) (resistance factor: 0.7 and 0.8, respectively) with no alterations of TOP-I parameters including DNA relaxation, expression of TOP-I protein and mRNA. In contrast, doxorubicin-resistant human ovarian A2780/Dx5 tumor cells [pgp170 phenotype] were 6.2-fold resistant to NB-506, whereas resistance to CPT was 2.6-fold. HPLC analysis of cellular NB-506 accumulation showed no significant differences between A2780 and A2780/Dx5 cells (peak intracellular concentrations after 120-min exposure to 10 microM NB-506: 400+/-85.0 and 352+/-95.1 nmol NB-506/mg protein, respectively). However, resistant A2780/Dx5 cells expressed a lower amount of TOP-I mRNA and 29% protein levels of TOP-I compared to parental A2780 cells, resulting in decreased TOP-I catalytic activity (3.17+/-0.02 vs. 1.16+/-0.15 rel.U/microg nuclear protein) and reduced induction of NB-506-mediated cleavable complex formation in A2780/Dx5 cells. Furthermore, the lower induction of NB-506-induced protein-linked DNA breaks (PLDB) in A2780/Dx5 cells correlated with significantly decreased DNA 12.2-440 kb size fragmentation in these cells. The present study demonstrates that expression of MRP and Pgp170 does not confer resistance to NB-506. Resistance to indolocarbazole substance NB-506 in A2780/Dx5 cells was only related to downregulation of TOP-I associated with lower induction of cleavable complex formation and DNA fragmentation. The data reported herein may indicate that the new indolocarbazole compound NB-506 has potent antitumor efficacy in membrane-associated multidrug resistance.

• Authors: U Vanhoefer, W Voigt, R A Hilger, M B Yin, A Harstrick, S Seeber, Y M Rustum
• Journal: Oncology research (Oncol Res) Vol. 9 Issue 9 Pg. 485-94 ( 1997) ISSN: 0965-0407 [Print] United States
• PMID: 9495454 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• ATP Binding Cassette Transporter, Subfamily B, Member 1
• ATP-Binding Cassette Transporters
• Carbazoles
• Enzyme Inhibitors
• Glucosides
• Multidrug Resistance-Associated Proteins
• NB 506
• RNA, Messenger
• Topoisomerase I Inhibitors
• Doxorubicin
• DNA Topoisomerases, Type I
• Camptothecin

Topics

• ATP Binding Cassette Transporter, Subfamily B, Member 1 (genetics, metabolism)
• ATP-Binding Cassette Transporters (genetics, metabolism)
• Blotting, Northern
• Camptothecin (pharmacology)
• Carbazoles (pharmacology)
• Cell Count (drug effects)
• Chromatography, High Pressure Liquid
• DNA Topoisomerases, Type I (genetics, metabolism)
• Doxorubicin (pharmacology)
• Drug Resistance, Multiple
• Drug Resistance, Neoplasm
• Enzyme Inhibitors (pharmacology)
• Female
• Fibrosarcoma (drug therapy, metabolism)
• Glucosides (pharmacology)
• Humans
• Multidrug Resistance-Associated Proteins
• Ovarian Neoplasms (drug therapy, metabolism)
• RNA, Messenger (metabolism)
• Topoisomerase I Inhibitors
• Tumor Cells, Cultured