Abstract
The present study was undertaken to examine the mechanistic basis for the recent observation that the pyridine nucleotide derivative 6-aminonicotinamide (6AN, NSC 21206) enhances the accumulation and resulting cytotoxicity of cisplatin in a variety of tumor cell lines. When A549 lung cancer cells or K562 leukemia cells were treated with 62.5 μM 6AN for 21 h and then pulse-labeled with [35S]methionine for 1 h, increased labeling of five polypeptides, one of which corresponded to aM r ∼78,000 glucose-regulated protein (GRP78), was observed. Two subsequent observations, however, suggested that up-regulation of these polypeptides was unlikely to explain the interaction between 6AN and cisplatin: 1) the concentration of 6AN required to induce GRP78 was 4-fold higher than the dose required to sensitize cells to cisplatin; and 2) simultaneous treatment of cells with 6AN and cycloheximide prevented the increase in GRP78 but not the sensitizing effect of 6AN. On the contrary, treatment with the protein synthesis inhibitors cycloheximide, anisomycin, or puromycin as well as prolonged exposure to the RNA synthesis inhibitor actinomycin D mimicked the biochemical modulating effects of 6AN on cisplatin action. Conversely, 6AN inhibited protein synthesis, whereas 18 6AN analogs that failed to enhance Pt-DNA adducts and cisplatin cytotoxicity failed to inhibit protein synthesis. These observations are consistent with a model in which 6AN and other inhibitors of protein synthesis act as modulating agents by increasing cisplatin accumulation, thereby enhancing the formation of Pt-DNA adducts and subsequent cisplatin-induced cell death.
Footnotes
- Received August 13, 1999.
- Accepted December 1, 1999.
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Send reprint requests to: Scott H. Kaufmann, M.D., Ph.D., Division of Oncology Research, Mayo Clinic, 200 First St., SW, Rochester, MN 55905. E-mail: Kaufmann.Scott{at}Mayo.edu
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↵1 Present address: Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Blvd., Dallas, TX 75235.
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↵2 Present address: Department of Chemistry, University of Puerto Rico, Mayaguez, PR 00681-5000.
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This work was supported in part by funds from the National Institutes of Health (R01-CA67818, N01-CM57200) and the Jack Taylor Family Foundation.
- The American Society for Pharmacology and Experimental Therapeutics
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