title: High concentrations of retinoids induce differentiation and late apoptosis in pancreatic cancer cells in vitro.
abstract: BACKGROUND
  Our previous investigations showed that retinoids, at specific concentrations, can inhibit cell proliferation. In this investigation, we hypothesize that high concentrations of retinoids can induce phenotypic changes (differentiation) and late apoptosis in pancreatic cancer cells in vitro.
  
  
  METHODS
  To test our hypothesis, retinoid-induced differentiation was assessed: (1) phenotypically by light and electron microscopy and (2) biochemically by measuring carbonic anhydrase, aerobic metabolic and mucin producing activities. Modulation of transforming growth factor-beta (TGF-beta) and epidermal growth factor (EGF) autocrine pathways were utilized as mechanistic and differentiation markers.
  
  
  RESULTS
  The extensive differentiation-indicative phenotypic changes correlated with several folds increase in the aerobic metabolism (MTT reduction and Mitochondrial mass), carbonic anhydrase activity and mucin production. There was a marked increase in TGF-beta (Bioassay and ELISA) and TGF-beta (RIA) secretion. EGF receptor density (Receptor binding assay) was reduced by 50% within six hours and was reflected on abolishment of EGFR ligand-induced proliferation. Cotreatment with the RAR-alpha antagonist, Ro41-5253 or pan-TGF-beta neutralizing antibody abolished the phenotypic and antiproliferative effects of all-trans retinoic acid. Apoptosis (TUNEL assay) was undetectable after three days of treatment with the maximum concentration used. However, apoptosis was extensively induced after six days of treatment.
  
  
  CONCLUSIONS
  High concentrations of retinoids were able to induce phenotypic changes (differentiation) and late apoptosis in pancreatic cancer cells in vitro. The clinical ramifications of these observations await further investigations.
authors.affiliation: Department of Biomedical Sciences, Creighton University School of Medicine, Eppley Cancer Institute, University of Nebraska Medical Center, Omaha, NE, USA. thelmetwally@hotmail.com
authors.forename: Tarek H
authors.initials: TH
authors.lastname: El-Metwally
authors.forename: Mahmoud R
authors.initials: MR
authors.lastname: Hussein
authors.forename: Parviz M
authors.initials: PM
authors.lastname: Pour
authors.forename: Charles A
authors.initials: CA
authors.lastname: Kuszynski
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Adrian
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D002256:Carbonic Anhydrases / Q000096:biosynthesis; D002454:Cell Differentiation / Q000187:drug effects*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction / Q000187:drug effects; D066246:ErbB Receptors / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D008854:Microscopy, Electron; D010190:Pancreatic Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology*; D018168:Receptors, Retinoic Acid / Q000037:antagonists & inhibitors; D000072482:Retinoic Acid Receptor alpha; D012176:Retinoids / Q000494:pharmacology*; D013997:Time Factors; D016212:Transforming Growth Factor beta / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology
chemical_list: C000607071:RARA protein, human; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D012176:Retinoids; D016212:Transforming Growth Factor beta; D014212:Tretinoin; D066246:ErbB Receptors; D002256:Carbonic Anhydrases