title: Glucose modulation induces reactive oxygen species and increases P-glycoprotein-mediated multidrug resistance to chemotherapeutics.
abstract: OBJECTIVE
  Cancer cells develop resistance to stress induced by chemotherapy. In tumours, a considerable glucose gradient exists, resulting in stress. Notably, hypoxia-inducible factor-1 (HIF-1) is a redox-sensitive transcription factor that regulates P-glycoprotein (Pgp), a crucial drug-efflux transporter involved in multidrug resistance (MDR). Here, we investigated how glucose levels regulate Pgp-mediated drug transport and resistance.
  
  
  METHODS
  Human tumour cells (KB31, KBV1, A549 and DMS-53) were incubated under glucose starvation to hyperglycaemic conditions. Flow cytometry assessed reactive oxygen species (ROS) generation and Pgp activity. HIF-1α, NF-κB and Pgp expression were assessed by reverse transcriptase-PCR and Western blotting. Fluorescence microscopy examined p65 distribution and a luciferase-reporter assay assessed HIF-1 promoter-binding activity. The effect of glucose-induced stress on Pgp-mediated drug resistance was examined after incubating cells with the chemotherapeutic and Pgp substrate, doxorubicin (DOX), and performing MTT assays validated by viable cell counts.
  
  
  RESULTS
  Changes in glucose levels markedly enhanced cellular ROS and conferred Pgp-mediated drug resistance. Low and high glucose levels increased (i) ROS generation via NADPH oxidase 4 and mitochondrial membrane destabilization; (ii) HIF-1 activity; (iii) nuclear translocation of the NF-κB p65 subunit; and (iv) HIF-1α mRNA and protein levels. Increased HIF-1α could also be due to decreased prolyl hydroxylase protein under these conditions. The HIF-1α target, Pgp, was up-regulated at low and high glucose levels, which led to lower cellular accumulation of Pgp substrate, rhodamine123, and greater resistance to DOX.
  
  
  CONCLUSIONS
  As tumour cells become glucose-deprived or exposed to high glucose levels, this increases stress, leading to a more aggressive MDR phenotype via up-regulation of Pgp.
authors.affiliation: Molecular Pharmacology and Pathology Program, Department of Pathology and Bosch Institute, Blackburn Building (D06), University of Sydney, Sydney, NSW, Australia.
authors.forename: N A
authors.initials: NA
authors.lastname: Seebacher
authors.forename: D R
authors.initials: DR
authors.lastname: Richardson
authors.forename: P J
authors.initials: PJ
authors.lastname: Jansson
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D002452:Cell Count; D045744:Cell Line, Tumor; D004317:Doxorubicin / Q000494:pharmacology; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008928:Mitochondria / Q000378:metabolism; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors; D016328:NF-kappa B / Q000096:biosynthesis; D034741:RNA, Small Interfering / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D016328:NF-kappa B; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; D004317:Doxorubicin; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases; C498910:NOX4 protein, human; D005947:Glucose