title: Rapamycin response in tumorigenic and non-tumorigenic hepatic cell lines.
abstract: BACKGROUND
  The mTOR inhibitor rapamycin has anti-tumor activity across a variety of human cancers, including hepatocellular carcinoma. However, resistance to its growth inhibitory effects is common. We hypothesized that hepatic cell lines with varying rapamycin responsiveness would show common characteristics accounting for resistance to the drug.
  
  
  RESULTS
  We profiled a total of 13 cell lines for rapamycin-induced growth inhibition. The non-tumorigenic rat liver epithelial cell line WB-F344 was highly sensitive while the tumorigenic WB311 cell line, originally derived from the WB-F344 line, was highly resistant. The other 11 cell lines showed a wide range of sensitivities. Rapamycin induced inhibition of cyclin E-dependent kinase activity in some cell lines, but the ability to do so did not correlate with sensitivity. Inhibition of cyclin E-dependent kinase activity was related to incorporation of p27(Kip1) into cyclin E-containing complexes in some but not all cell lines. Similarly, sensitivity of global protein synthesis to rapamycin did not correlate with its anti-proliferative effect. However, rapamycin potently inhibited phosphorylation of two key substrates, ribosomal protein S6 and 4E-BP1, in all cases, indicating that the locus of rapamycin resistance was downstream from inhibition of mTOR Complex 1. Microarray analysis did not disclose a unifying mechanism for rapamycin resistance, although the glycolytic pathway was downregulated in all four cell lines studied.
  
  
  CONCLUSIONS
  We conclude that the mechanisms of rapamycin resistance in hepatic cells involve alterations of signaling downstream from mTOR and that the mechanisms are highly heterogeneous, thus predicting that maintaining or promoting sensitivity will be highly challenging.
authors.affiliation: Department of Pediatrics, Rhode Island Hospital and Brown University, Providence, Rhode Island, USA.
authors.forename: Rosa H
authors.initials: RH
authors.lastname: Jimenez
authors.forename: Joan M
authors.initials: JM
authors.lastname: Boylan
authors.forename: Ju-Seog
authors.initials: JS
authors.lastname: Lee
authors.forename: Mirko
authors.initials: M
authors.lastname: Francesconi
authors.forename: Gastone
authors.initials: G
authors.lastname: Castellani
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Sanders
authors.forename: Philip A
authors.initials: PA
authors.lastname: Gruppuso
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D002460:Cell Line; D045744:Cell Line, Tumor; D019927:Cyclin E / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D020869:Gene Expression Profiling; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008099:Liver / Q000187:drug effects* / Q000378:metabolism*; D008113:Liver Neoplasms / Q000188:drug therapy* / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D051381:Rats; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases
chemical_list: D000903:Antibiotics, Antineoplastic; D019927:Cyclin E; D047908:Intracellular Signaling Peptides and Proteins; D012313:RNA; C546842:MTOR protein, human; C546845:mTOR protein, rat; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus