title: Characterization of B16 melanoma cells resistant to the CC-1065 analogue U-71,184.
abstract: U-71,184 is a CC-1065 analogue which is highly cytotoxic in vitro and has a broad spectrum of antitumor activity in vivo. Against B16 cells, U-71,184 was 8-fold and 253-fold more potent than Actinomycin D and Adriamycin, respectively. U-71,184 killed 90% of B16 cells at 0.01 ng/ml levels of drug in the medium, which was equivalent to an intracellular concentration of about 8 pg/10(6) cell (= 2 x 10(-8) pmol/cell). A B16 cell line resistant to U-71,184 developed after 3 months of in vitro exposure to gradually increasing concentrations of the drug. The sensitive and resistant cell lines were cloned and a B16/R clone was selected which was 60 to 100 times more resistant to U-71,184 than the cloned sensitive parent (B16/S). Cells grown in the absence of U-71,184 for 2 months retained resistance to the drug. B16/R was slightly cross-resistant only to Adriamycin but not to Actinomycin D, vinblastine, or colchicine. Among alkylating agents, it was slightly cross-resistant to Melphalan but not to 1,3-bis(2-chloroethyl)-1-nitrosourea or cisplatin. B16/R did not overexpress mdr mRNA. Therefore, this cell line does not exhibit the multidrug-resistant phenotype. Most karyotypes of B16/R had a marker chromosome which carried an aberrantly staining region apparently containing repetitive replication of the same segment. Resistance can be partly accounted for by the approximately 10-fold lesser uptake of [3H]-U-71,184 in B16/R, as compared to B16/S. B16/R was cross-resistant in varying degrees to several other CC-1065 analogues. The ratio of the 50% lethal dose of U-71,184 for B16/R, as compared to B16/S, was about 60 (i.e., R/S = 60). In comparison, the following compounds had an R/S ratio of less than 20 (i.e., modest level of cross-resistance to U-71,184): U-68,819, U-73,975, U-75,500, U-75,559, and CC-1065. In contrast, the following compounds had an R/S ratio greater than 20 (i.e., highly cross-resistant to U-71,184): U-71,184 analogues U-71,185, U-73,903, and U-75,012; U-73,975 analogues U-75,613, U-75,032, and U-73,896; and CC-1065 enantiomer U-76,915. We cannot yet explain the difference in the level of cross-resistance between these compounds in vitro. B16/S and B16/R cells were tumorigenic in mice and B16/R was resistant to U-71,184 in vivo. There was no clear indication of cross-resistance of B16/R in vivo to Adriamycin, Actinomycin D, cisplatin, or Melphalan. However, U-73,975, a compound with modest cross-resistance in vitro, was significantly cross-resistant in vivo.
authors.affiliation: Department of Cancer and Developmental Biology, Upjohn Company, Kalamazoo, Michigan 49001-0199.
authors.forename: B C
authors.initials: BC
authors.lastname: Moy
authors.forename: G L
authors.initials: GL
authors.lastname: Petzold
authors.forename: G J
authors.initials: GJ
authors.lastname: Badiner
authors.forename: R C
authors.initials: RC
authors.lastname: Kelly
authors.forename: P A
authors.initials: PA
authors.lastname: Aristoff
authors.forename: E G
authors.initials: EG
authors.lastname: Adams
authors.forename: L H
authors.initials: LH
authors.lastname: Li
authors.forename: B K
authors.initials: BK
authors.lastname: Bhuyan
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001692:Biological Transport; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004351:Drug Resistance / Q000235:genetics*; D007211:Indoles / Q000378:metabolism / Q000494:pharmacology*; D007621:Karyotyping; D007700:Kinetics; D008546:Melanoma, Experimental / Q000235:genetics*; D051379:Mice; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D007211:Indoles; C054483:U 71184