title: Overcoming resistance to gamma-rays in squamous carcinoma cells by poly-drug elevation of ceramide levels.
abstract: Recent strategies to sensitize radioresistant tumours are based on combining gamma-irradiation with inducers of apoptosis. We report that the combination of three inhibitors of sphingolipid metabolism, DL-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol.HCl(DL-PDMP)+imipramine +/- D-erythro-2-(N-myristoylamino)-1-phenyl-1-propanol (D-MAPP), with 10-Gy irradiation triggers both mitotic and apoptotic killing in radioresistant SQ20B squamous carcinoma cells. In these cells, apoptosis is defective due to a lack of ceramide generation upstream, which cannot be explained by sphingomyelinase (neutral and acidic) deficiency or rapid derivation to the sphingolipid pathway. We present evidence of a functional transduction death pathway when ceramide generation is restored, which involves the mitochondrial-mediated pathway coupled to alterations in redox status and to executive caspases activation. The poly-drug treatment restored apoptosis to levels similar to those observed in radiosensitive SCC61 squamous carcinoma cells. Simultaneous exposure to gamma-irradiation and poly-drug treatment acted synergistically in SQ20B cells to produce a marked increase in both mitochondrial dysfunction and caspase cleavage, which led to a 7.8-fold increase in apoptosis within 48 h, relative to irradiated cells. Moreover, the results suggest that the ceramide released by irradiation or poly-drug treatment converges upon common cellular targets. Modulation of endogenous ceramide levels by inhibitors of sphingolipid metabolism may represent a new cellular target for the sensitization of radioresistant tumours to gamma-ray therapy.
authors.affiliation: Department of Biochemistry, INSERM U189, Lyon-Sud Medical School, BP12, 69921 Oullins Cedex, France.
authors.forename: Gersende
authors.initials: G
authors.lastname: Alphonse
authors.forename: Clara
authors.initials: C
authors.lastname: Bionda
authors.forename: Marie-Thérèse
authors.initials: MT
authors.lastname: Aloy
authors.forename: Dominique
authors.initials: D
authors.lastname: Ardail
authors.forename: Robert
authors.initials: R
authors.lastname: Rousson
authors.forename: Claire
authors.initials: C
authors.lastname: Rodriguez-Lafrasse
mesh_terms: D017209:Apoptosis; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000378:metabolism / Q000532:radiotherapy*; D053148:Caspase 3; D053181:Caspase 8; D061945:Caspase Inhibitors; D020169:Caspases / Q000096:biosynthesis / Q000378:metabolism; D045744:Cell Line, Tumor; D002518:Ceramides / Q000378:metabolism / Q000494:pharmacology*; D002851:Chromatography, High Pressure Liquid; D004307:Dose-Response Relationship, Radiation; D004789:Enzyme Activation; D005434:Flow Cytometry; D005720:Gamma Rays; D005964:Glucosyltransferases / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006258:Head and Neck Neoplasms / Q000378:metabolism / Q000532:radiotherapy; D006801:Humans; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism; D008938:Mitosis; D009226:Myristates / Q000494:pharmacology; D019158:N-Acetylneuraminic Acid / Q000378:metabolism; D010084:Oxidation-Reduction; D011412:Propanolamines / Q000494:pharmacology; D017382:Reactive Oxygen Species; D013107:Sphingolipids / Q000037:antagonists & inhibitors; D013997:Time Factors
chemical_list: D061945:Caspase Inhibitors; D002518:Ceramides; D009226:Myristates; D011412:Propanolamines; D017382:Reactive Oxygen Species; D013107:Sphingolipids; C099657:2-(N-myristoylamino)-1-phenyl-1-propanol; D005964:Glucosyltransferases; C023246:ceramide glucosyltransferase; C505407:CASP3 protein, human; C505530:CASP8 protein, human; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases; D005978:Glutathione; D019158:N-Acetylneuraminic Acid