title: Reversal of etoposide resistance in non-P-glycoprotein expressing multidrug resistant tumor cell lines by novobiocin.
abstract: Previous reports from this laboratory have demonstrated that novobiocin produces supraadditive cytotoxicity and increases the formation of drug-stabilized topoisomerase II-DNA covalent complexes in WEHI-3B myelomonocytic leukemia and A549 lung carcinoma cells when combined with etoposide (VP-16). Inhibition of the efflux of VP-16 by novobiocin is responsible for the increase in VP-16 accumulation, which in turn leads to increased formation of VP-16-stabilized topoisomerase II-DNA covalent complexes and increased cytotoxicity. We now report that novobiocin synergistically enhanced the sensitivity of the multidrug resistant variants, WEHI-3B/NOVO and A549(VP)28, to VP-16, causing almost complete reversal of the resistance to the epipodophyllotoxin. These two tumor cell variants are resistant to several topoisomerase II-targeted drugs, particularly VP-16, but not to Vinca alkaloids; this finding corresponds to the fact that they do not overexpress the P-glycoprotein. The effects of novobiocin in these resistant sublines are mediated through the intracellular accumulation of VP-16, resulting in an increase in the formation of lethal VP-16-induced topoisomerase II-DNA covalent complexes. In the P-glycoprotein expressing multidrug resistant HCT116(VM)34 colon carcinoma and L1210/VMDRC0.06 leukemia cell lines, the latter being transfected with the human mdr-1 gene, novobiocin did not potentiate the cytotoxic activity of VP-16 nor increase the intracellular accumulation of VP-16 and the formation of covalent complexes, whereas their normal counterparts were sensitive to the potentiating activity of novobiocin when used in combination with VP-16. These results indicate that the action of novobiocin on the intracellular transport of VP-16 is not directed at the level of the P-glycoprotein, but that the action of novobiocin is antagonized by the presence of the P-glycoprotein. Since novobiocin is a clinically available antibiotic, has numerous structural analogues available for comparative studies, and has a relatively low toxicity profile, this drug, as well as structurally related agents, would appear to have significant clinical potential in combination with an epipodophyllotoxin for the treatment of non-P-glycoprotein expressing multidrug resistant tumors.
authors.affiliation: Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510.
authors.forename: G
authors.initials: G
authors.lastname: Rappa
authors.forename: A
authors.initials: A
authors.lastname: Lorico
authors.forename: A C
authors.initials: AC
authors.lastname: Sartorelli
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000230:Adenocarcinoma / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000032:analysis; D003110:Colonic Neoplasms / Q000737:chemistry; D004250:DNA Topoisomerases, Type II / Q000032:analysis / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000032:analysis / Q000378:metabolism*; D004351:Drug Resistance; D005047:Etoposide / Q000378:metabolism / Q000494:pharmacology*; D005434:Flow Cytometry; D006801:Humans; D007939:Leukemia L1210 / Q000188:drug therapy / Q000378:metabolism; D008175:Lung Neoplasms / Q000737:chemistry / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000032:analysis; D051379:Mice; D009675:Novobiocin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002352:Carrier Proteins; D004273:DNA, Neoplasm; D008562:Membrane Glycoproteins; D009675:Novobiocin; D005047:Etoposide; D004250:DNA Topoisomerases, Type II