title: Metformin impairs Rho GTPase signaling to induce apoptosis in neuroblastoma cells and inhibits growth of tumors in the xenograft mouse model of neuroblastoma.
abstract: Metformin has been shown to inhibit tumor growth in xenograft rodent models of adult cancers, and various human clinical trials are in progress. However, the precise molecular mechanisms of metformin action are largely unknown. In the present study we examined the anti-tumor activity of metformin against neuroblastoma, and determined the underlying signaling mechanisms. Using human neuroblastoma xenograft mice, we demonstrated that oral administration of metformin (100 and 250 mg/kg body weight) significantly inhibited the growth of tumors. The interference of metformin in spheroid formation further confirmed the anti-tumor activity of metformin. In tumors, the activation of Rac1 (GTP-Rac1) and Cdc42 (GTP-Cdc42) was increased while RhoA activation (GTP-RhoA) was decreased by metformin. It also induced phosphorylation of JNK and inhibited the phosphorylation of ERK1/2 without affecting p38 MAP Kinase. Infection of cells by adenoviruses expressing dominant negative Rac1 (Rac1-N17), Cdc42 (Cdc42-N17) or constitutively active RhoA (RhoA-V14), or incubation of cells with pharmacological inhibitors of Rac1 (NSC23766) or Cdc42 (ML141) significantly protected neuroblastoma cells from metformin-induced apoptosis. Additionally, inhibition of JNK activity along with Rac1 or Cdc42 attenuated cytotoxic effects of metformin. These studies demonstrated that metformin impairs Rho GTPases signaling to induce apoptosis via JNK pathway.
authors.affiliation: Department of Pathology, Microbiology and Immunology, University of South Carolina, Columbia, SC, USA.
authors.forename: Ambrish
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Department of Pathology, Microbiology and Immunology, University of South Carolina, Columbia, SC, USA.
authors.forename: Nadia
authors.initials: N
authors.lastname: Al-Sammarraie
authors.affiliation: Department of Internal Medicine, School of Medicine, University of South Carolina, Columbia, SC, USA.
authors.forename: Donald J
authors.initials: DJ
authors.lastname: DiPette
authors.affiliation: Department of Pathology, Microbiology and Immunology, University of South Carolina, Columbia, SC, USA.
authors.forename: Ugra S
authors.initials: US
authors.lastname: Singh
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D016923:Cell Death; D045744:Cell Line, Tumor; D002470:Cell Survival; D053938:DNA Fragmentation; D006801:Humans; D020935:MAP Kinase Signaling System; D008687:Metformin / Q000737:chemistry*; D051379:Mice; D008819:Mice, Nude; D009447:Neuroblastoma / Q000473:pathology*; D010766:Phosphorylation; D023041:Xenograft Model Antitumor Assays; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000037:antagonists & inhibitors*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; C107953:RAC1 protein, human; C066737:RHOA protein, human; D008687:Metformin; D053148:Caspase 3; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein