Phenformin Inhibits Hedgehog-Dependent Tumor Growth through a Complex I-Independent Redox/Corepressor Module

Laura Di Magno,Giuseppe Giannini,Enrico De Smaele,Paola Infante,Manolo Sambucci,Marella Maroder,Fiorella Di Pastena,Luca Battistini,Gianluca Canettieri,Lucia Di Marcotullio,Egidio Iorio,Marta Moretti,Carmine Nicoletti,Sonia Coni,Marialaura Petroni,Bianca Maria Goffredo,Carlo Capalbo,Alberto Macone,Enzo Agostinelli,Sara Cairoli,Simona Manni

doi:10.1016/j.celrep.2020.01.024

Abstract

The antidiabetic drug phenformin displays potent anticancer activity in different tumors, but its mechanism of action remains elusive. Using Shh medulloblastoma as model, we show here that at clinically relevant concentrations, phenformin elicits a significant therapeutic effect through a redox-dependent but complex I-independent mechanism. Phenformin inhibits mitochondrial glycerophosphate dehydrogenase (mGPD), a component of the glycerophosphate shuttle, and causes elevations of intracellular NADH content. Inhibition of mGPD mimics phenformin action and promotes an association between corepressor CtBP2 and Gli1, thereby inhibiting Hh transcriptional output and tumor growth. Because ablation of CtBP2 abrogates the therapeutic effect of phenformin in mice, these data illustrate a biguanide-mediated redox/corepressor interplay, which may represent a relevant target for tumor therapy.

Highlights

The biguanides metformin and phenformin are antidiabetic drugs associated with well-established anticancer properties in preclinical and clinical settings (Pollak, 2013)
Clinical Doses of Phenformin Elicit a Therapeutic Effect on Hh-Dependent Tumors We tested the effect of metformin and phenformin on the growth of Med1-MB cells, a tumor cell line in which developmental Hh signaling is aberrantly activated (Hayden Gephart et al, 2013; Tang et al, 2014; Goodrich et al, 1997). Both biguanides were tested within the micromolar range (1–100 mM) in media containing 5.5 and 0.75 mM glucose, corresponding to the average physiological plasma fasting and estimated cancer tissue glucose concentrations, respectively (Birsoy et al, 2014)
To determine the physiological relevance of this observation, we studied phosphorylation of T172-AMPK (pAMPK), phosphorylation of ACC (pACC), and phosphorylation of Raptor (pRaptor) in tumor tissues from mice treated at various time points (1, 2, and 4 h) with the maximum tolerated dose (12.5 mg/kg) of phenformin (Figure S2C)

Summary

Introduction

The biguanides metformin and phenformin are antidiabetic drugs associated with well-established anticancer properties in preclinical and clinical settings (Pollak, 2013). Metformin is the only biguanide currently approved for the treatment of type 2 diabetes, and it is the most prescribed oral antidiabetic drug worldwide. Phenformin was prescribed for the treatment of diabetes until 1977, and its use was discontinued because of the relatively more frequent occurrence of lactic acidosis compared with metformin (Berger, 1985). Studies in the last few years have documented a wider and more pronounced antitumor efficacy of phenformin compared with metformin, renewing interest in this drug (Janzer et al, 2014; Rosilio et al, 2013; Shackelford et al, 2013). The most widely accepted model links the effect of these drugs to their ability to inhibit mitochondrial respiratory complex I, thereby inducing an imbalance of the intracellular redox and energetic states and an increase in the NADH/ NAD+ and AMP/ATP ratios, respectively (Foretz et al, 2014)

Results

Discussion

Conclusion