Treatment of Pancreatic Cancer Patient–Derived Xenograft Panel with Metabolic Inhibitors Reveals Efficacy of Phenformin

Abstract

To identify effective metabolic inhibitors to suppress the aggressive growth of pancreatic ductal adenocarcinoma (PDAC), we explored the antitumor efficacy of metabolic inhibitors, as single agents, in a panel of patient-derived PDAC xenograft models (PDX) and investigated whether genomic alterations of tumors correlate with the sensitivity to metabolic inhibitors. Mice with established PDAC tumors from 6 to 13 individual PDXs were randomized and treated, once daily for 4 weeks, with either sterile PBS (vehicle) or the glutaminase inhibitor bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide (BPTES), transaminase inhibitor aminooxyacetate (AOA), pyruvate dehydrogenase kinase inhibitor dichloroacetate (DCA), autophagy inhibitor chloroquine (CQ), and mitochondrial complex I inhibitor phenformin/metformin. Among the agents tested, phenformin showed significant tumor growth inhibition (>30% compared with vehicle) in 5 of 12 individual PDXs. Metformin, at a fivefold higher dose, displayed significant tumor growth inhibition in 3 of 12 PDXs similar to BPTES (2/8 PDXs) and DCA (2/6 PDXs). AOA and CQ had the lowest response rates. Gene set enrichment analysis conducted using the baseline gene expression profile of pancreatic tumors identified a gene expression signature that inversely correlated with phenformin sensitivity, which is in agreement with the phenformin gene expression signature of NIH Library of Integrated Network-based Cellular Signatures (LINCS). The PDXs that were more sensitive to phenformin showed a baseline reduction in amino acids and elevation in oxidized glutathione. There was no correlation between phenformin response and genetic alterations in , or Phenformin treatment showed relatively higher antitumor efficacy against established PDAC tumors, compared with the efficacy of other metabolic inhibitors and metformin. Phenformin treatment significantly diminished PDAC tumor progression and prolonged tumor doubling time. Overall, our results serve as a foundation for further evaluation of phenformin as a therapeutic agent in pancreatic cancer. .

The effects of metformin on gut microbiota and the immune system as research frontiers

“…First, both older (reviewed in [4]) and more recent [46] models demonstrate tumour growth inhibition by biguanides in immune-deficient mice, suggesting that mechanisms other than immune modulation operate. Second, the relevance of all the preclinical models to patient care remains to be established, despite a plausible theoretical rationale and encouraging preclinical data [47] as the first randomised, placebo-controlled trial of metformin in cancer treatment failed to demonstrate a benefit of the drug in treatment of pancreatic cancer [48].…”

Clonal Heterogeneity Supports Mitochondrial Metabolism in Pancreatic Cancer

“…Indeed, tumor metabolism has been an attractive target in PDA given the limited impact of conventional chemotherapy and immunotherapy on patient survivial 49 . Phenformin was recently identified as the most effective metabolic inhibitor in a screen of PDA patient-derived xenografts 50 , is being explored clinically in other cancer types (NCT03026517), and our data show this can be potentiated by asparagine depletion using asparaginase, a widely used clinically for the treatment of blood cancers 51 . As there are more specific and potent mitochondrial inhibitors currently being deployed in the clinic 52 , including use in pancreatic cancer (NCT03291938), these could potentially also benefit from combination with asparaginase.…”

Asparagine signals mitochondrial respiration and can be targeted to impair tumour growth

“…5e). Moreover, the combination of phenformin, a metformin-related biguanide that has been suggested to have anti-tumour activity in pancreatic cancer 15 , and asparaginase significantly reduces tumour growth in a syngeneic orthotopic model of pancreatic cancer in immune-competent mice ( Fig. 3d).…”