BACKGROUND AND PURPOSEThe expression of P-glycoprotein (P-gp), encoded by the multidrug resistance 1 (MDR1) gene, is associated with the emergence of the MDR phenotype in cancer cells. We investigated whether metformin (1,1-dimethylbiguanide hydrochloride) down-regulates MDR1 expression in MCF-7/adriamycin (MCF-7/adr) cells. EXPERIMENTAL APPROACHMCF-7 and MCF-7/adr cells were incubated with metformin and changes in P-gp expression were determined at the mRNA, protein and functional level. Transient transfection assays were performed to assess its gene promoter activities, and immunoblot analysis to study its molecular mechanisms of action. KEY RESULTSMetformin significantly inhibited MDR1 expression by blocking MDR1 gene transcription. Metformin also significantly increased the intracellular accumulation of the fluorescent P-gp substrate rhodamine-123. Nuclear factor-kB (NF-kB) activity and the level of IkB degradation were reduced by metformin treatment. Moreover, transduction of MCF-7/adr cells with the p65 subunit of NF-kB induced MDR1 promoter activity and expression, and this effect was attenuated by metformin. The suppression of MDR1 promoter activity and protein expression was mediated through metformin-induced activation of AMP-activated protein kinase (AMPK). Small interfering RNA methods confirmed that reduction of AMPK levels attenuates the inhibition of MDR1 activation associated with metformin exposure. Furthermore, the inhibitory effects of metformin on MDR1 expression and cAMP-responsive element binding protein (CREB) phosphorylation were reversed by overexpression of a dominant-negative mutant of AMPK. CONCLUSIONS AND IMPLICATIONSThese results suggest that metformin activates AMPK and suppresses MDR1 expression in MCF-7/adr cells by inhibiting the activation of NF-kB and CREB. This study reveals a novel function of metformin as an anticancer agent. AbbreviationsACC, acetyl-CoA carboxylase; aicar, 5-aminoimidazole-4-carboxamide-1-b-D-ribofuranoside; AMPK, adenosine 5′-monophosphate-activated protein kinase; CRE, cAMP-responsive element; CREB, cAMP-responsive element binding protein; DN-AMPK, dominant negative AMPK; GSK-3b, glycogen synthase kinase-3b; MDR1, multidrug resistance 1; NF-kB, nuclear factor-kB; P-gp, P-glycoprotein; PKA, protein kinase A; Rh-123, rhodamine 123; TNF-a, tumour necrosis factor a

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In this study, we investigated the mechanisms of kahweol protection of neuronal cells from cell death induced by the ParkinsonÕs disease-related neurotoxin 6-hydroxydopamine (6-OHDA). Pretreatment of SH-SY5Y cells with kahweol significantly reduced 6-OHDA-induced generation of ROS, caspase-3 activation, and subsequent cell death. Kahweol also up-regulated heme oxygenase-1 (HO-1) expression, which conferred neuroprotection against 6-OHDA-induced oxidative injury. Moreover, kahweol induced PI3K and p38 activation, which are involved in the induction of Nrf2, HO-1 expression, and neuroprotection. These results suggest that regulation of the anti-oxidant enzyme HO-1 via the PI3K and p38/Nrf2 signaling pathways controls the intracellular levels of ROS.

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