title: Relationship between cellular accumulation of rhodamine 123 (R123) and cytotoxicity in B16 melanoma cells.
abstract: Rhodamine 123 (R123) is a mitochondria-specific prototype anticancer agent because its target is the energy-producing mechanism of the cell. The goal of this study was to investigate the relationship between intracellular R123 accumulation and cytotoxicity in a R123-sensitive cell line (RS) and a R123-resistant subline (RR) that we developed. Cytotoxicity after exposure to R123 (0-60 micrograms/ml) was assessed using the clonogenic assay. Intracellular R123 was extracted with acid-alcohol and measured by fluorimetry. The rate of R123 accumulation over 1 hr was significantly higher (P less than 0.0001) for RS cells (4.65 +/- 0.39 micrograms/min/10(6) cells) than for RR cells (1.29 +/- 0.24 micrograms/min/10(6) cells). R123 accumulation in RS cells was strongly correlated (r = 0.80; P less than 0.0001) with cytotoxicity. Treatment of RR cells with verapamil (100 microM) reversed R123 resistance. The resulting dose-survival curve was identical to the dose-response curve of RS cells treated with R123 alone. Cellular content of R123 in RR cells treated with verapamil increased to a level similar to that of RS cells and correlated with cytotoxicity. These data suggest that cytotoxicity of R123 in B16 cells results from increased cellular accumulation of R123.
authors.affiliation: Department of Surgery, University of California, Davis, School of Medicine, Sacramento 95817.
authors.forename: D N
authors.initials: DN
authors.lastname: Krag
authors.forename: A P
authors.initials: AP
authors.lastname: Theon
authors.forename: L
authors.initials: L
authors.lastname: Gan
authors.forename: J
authors.initials: J
authors.lastname: Wardell
authors.forename: S Z
authors.initials: SZ
authors.lastname: Tao
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D004351:Drug Resistance; D008546:Melanoma, Experimental / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D020112:Rhodamine 123; D012235:Rhodamines / Q000378:metabolism* / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000494:pharmacology; D014966:Xanthenes / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D012235:Rhodamines; D014966:Xanthenes; D020112:Rhodamine 123; D014700:Verapamil