title: Metformin inhibits skin tumor promotion in overweight and obese mice.
abstract: In the present study, the ability of metformin to inhibit skin tumor promotion by 12-O-tetradecanoylphorbol-13-acetate (TPA) was analyzed in mice maintained on either an overweight control diet or an obesity-inducing diet. Rapamycin was included for comparison, and a combination of metformin and rapamycin was also evaluated. Metformin (given in the drinking water) and rapamycin (given topically) inhibited development of both papillomas and squamous cell carcinomas in overweight and obese mice in a dose-dependent manner. A low-dose combination of these two compounds displayed an additive inhibitory effect on tumor development. Metformin treatment also reduced the size of papillomas. Interestingly, all treatments seemed to be at least as effective for inhibiting tumor formation in obese mice, and both metformin and rapamycin were more effective at reducing tumor size in obese mice compared with overweight control mice. The effect of metformin on skin tumor development was associated with a significant reduction in TPA-induced epidermal hyperproliferation. Furthermore, treatment with metformin led to activation of epidermal AMP-activated protein kinase (AMPK) and attenuated signaling through mTOR complex (mTORC)-1 and p70S6K. Combinations of metformin and rapamycin were more effective at blocking epidermal mTORC1 signaling induced by TPA consistent with the greater inhibitory effect on skin tumor promotion. Collectively, the current data demonstrate that metformin given in the drinking water effectively inhibited skin tumor promotion in both overweight and obese mice and that the mechanism involves activation of epidermal AMPK and attenuated signaling downstream of mTORC1.
authors.affiliation: Dell Pediatric Research Institute, The University of Texas at Austin, 1400 Barbara Jordan Blvd., Austin, TX 78723. john.digiovanni@austin.utexas.edu.
authors.forename: L Allyson
authors.initials: LA
authors.lastname: Checkley
authors.forename: Okkyung
authors.initials: O
authors.lastname: Rho
authors.forename: Joe M
authors.initials: JM
authors.lastname: Angel
authors.forename: Jiyoon
authors.initials: J
authors.lastname: Cho
authors.forename: Jorge
authors.initials: J
authors.lastname: Blando
authors.forename: Linda
authors.initials: L
authors.lastname: Beltran
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Hursting
authors.forename: John
authors.initials: J
authors.lastname: DiGiovanni
mesh_terms: D000263:Adenylate Kinase / Q000378:metabolism; D052242:Adiponectin / Q000378:metabolism; D000818:Animals; D001835:Body Weight; D063646:Carcinogenesis; D002294:Carcinoma, Squamous Cell / Q000517:prevention & control; D004032:Diet; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D005260:Female; D007328:Insulin / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D020738:Leptin / Q000378:metabolism; D000076222:Mechanistic Target of Rapamycin Complex 1; D008687:Metformin / Q000494:pharmacology*; D051379:Mice; D008820:Mice, Obese; D046912:Multiprotein Complexes / Q000378:metabolism; D009374:Neoplasms, Experimental / Q000139:chemically induced / Q000517:prevention & control; D009765:Obesity / Q000150:complications; D050177:Overweight / Q000150:complications; D010212:Papilloma / Q000517:prevention & control; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D012878:Skin Neoplasms / Q000139:chemically induced / Q000517:prevention & control*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate
chemical_list: D052242:Adiponectin; D007328:Insulin; D020738:Leptin; D046912:Multiprotein Complexes; D007334:Insulin-Like Growth Factor I; D008687:Metformin; D000076222:Mechanistic Target of Rapamycin Complex 1; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D000263:Adenylate Kinase; D013755:Tetradecanoylphorbol Acetate; D020123:Sirolimus