Besides being anti-diabetic drug, metformin also has anti-proliferation and growth in several tumors; however, details of possible mechanism have not been elucidated. Here, we investigated the effects of metformin in neuroblastoma which has been termed as extra-cranial solid tumor that is due to a differentiation block with more stemness. The results showed that 5 mM metformin inhibited cell cycle progression at G0/G1 phase. Metformin also induced morphological differentiation of neuroblastoma into neuron-like phenotypes by which upregulation of MAP2, β-tubulin III and tyrosine hydroxylase expressions with no significant difference to retinoic acid (RA)-treated cells. We also tested proliferative, growth and self-renewal ability after neuroblastoma being differentiated by metformin for 24 h. The proliferative rate, sizes and numbers of colonies and spheroids were significantly reduced in differentiated neuroblastoma compared to undifferentiated neuroblastoma. A significant increase of ROS and ADP/ATP ratio with decreased mitochondrial membrane potential (MMP) were observed in metformin-treated cells, indicating mitochondrial biogenesis and metabolic change during metformin-mediated differentiation. The further studies exhibited that p-Erk1/2 and Cdk5 levels were reduced in metformin treatment whereas using PD98095 and roscovitine, selectively inhibited Erk1/2 and Cdk5, respectively, significantly increased neurite length and MAP2 expression. In addition, cell proliferation was decreased by cell cycle arrested at G0/G1 phase. Taken together, this study suggests the inhibitory effects of metformin against proliferation and growth of neuroblastoma due to induced morphological differentiation may be through Erk1/2 and Cdk5 pathways. Therefore, metformin might be eventually considered as a differentiation agent for neuroblastoma treatment in term of differentiation therapy.
Keywords: Cdk5; Differentiation; Erk1/2; Metformin; Neuroblastoma; Proliferation.
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