title: Molecular features of biguanides required for targeting of mitochondrial respiratory complex I and activation of AMP-kinase.
abstract: The biguanides are a family of drugs with diverse clinical applications. Metformin, a widely used anti-hyperglycemic biguanide, suppresses mitochondrial respiration by inhibiting respiratory complex I. Phenformin, a related anti-hyperglycemic biguanide, also inhibits respiration, but proguanil, which is widely used for the prevention of malaria, does not. The molecular structures of phenformin and proguanil are closely related and both inhibit isolated complex I. Proguanil does not inhibit respiration in cells and mitochondria because it is unable to access complex I. The molecular features that determine which biguanides accumulate in mitochondria, enabling them to inhibit complex I in vivo, are not known.
  
  
  
  Here, a family of seven biguanides are used to reveal the molecular features that determine why phenformin enters mitochondria and inhibits respiration whereas proguanil does not. All seven biguanides inhibit isolated complex I, but only four of them inhibit respiration in cells and mitochondria. Direct conjugation of a phenyl group and bis-substitution of the biguanide moiety prevent uptake into mitochondria, irrespective of the compound hydrophobicity. This high selectivity suggests that biguanide uptake into mitochondria is protein mediated, and is not by passive diffusion. Only those biguanides that enter mitochondria and inhibit complex I activate AMP kinase, strengthening links between complex I and the downstream effects of biguanide treatments.
  
  
  
  Biguanides inhibit mitochondrial complex I, but specific molecular features control the uptake of substituted biguanides into mitochondria, so only some biguanides inhibit mitochondrial respiration in vivo. Biguanides with restricted intracellular access may be used to determine physiologically relevant targets of biguanide action, and for the rational design of substituted biguanides for diverse clinical applications.
authors: Medical Research Council Mitochondrial Biology Unit, Wellcome Trust / MRC Building, Hills Road, Cambridge, CB2 0XY, UK.
authors: Hannah R
authors: HR
authors: Bridges
authors: Medical Research Council Mitochondrial Biology Unit, Wellcome Trust / MRC Building, Hills Road, Cambridge, CB2 0XY, UK.
authors: Ville A
authors: VA
authors: Sirviö
authors: Medical Research Council Mitochondrial Biology Unit, Wellcome Trust / MRC Building, Hills Road, Cambridge, CB2 0XY, UK.
authors: Ahmed-Noor A
authors: AN
authors: Agip
authors: Medical Research Council Mitochondrial Biology Unit, Wellcome Trust / MRC Building, Hills Road, Cambridge, CB2 0XY, UK. jh@mrc-mbu.cam.ac.uk.
authors: Judy
authors: 0000-0001-8667-6797
authors: J
authors: Hirst
mesh_terms: D000263:Adenylate Kinase / Q000378:metabolism*; D000818:Animals; D001645:Biguanides / Q000737:chemistry* / Q000494:pharmacology*; D002417:Cattle; D045744:Cell Line, Tumor; D002463:Cell Membrane Permeability / Q000187:drug effects; D019069:Cell Respiration / Q000187:drug effects; D042967:Electron Transport Complex I / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000187:drug effects / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D010629:Phenformin / Q000494:pharmacology; D051381:Rats; D012402:Rotenone / Q000494:pharmacology; D012995:Solubility
chemical_list: D001645:Biguanides; D012402:Rotenone; D010629:Phenformin; D000263:Adenylate Kinase; D042967:Electron Transport Complex I
keywords: AMP kinase; Biguanide; Metformin; NADH:ubiquinone oxidoreductase; Respiratory complex I