Abstract
Metabolic flexibility might be particularly constrained in tumors bearing mutations in isocitrate dehydrogenase 1 (IDH1) leading to the production of the oncometabolite 2-hydroxygluratate (2HG). To test the hypothesis that IDH1 mutations could generate metabolic vulnerabilities for therapeutic intervention, we utilized an MCF10A cell line engineered with an arginine-to-histidine conversion at position 132 (R132H) in the catalytic site of IDH1, which equips the enzyme with a neomorphic α-ketoglutarate to 2HG reducing activity in an otherwise isogenic background. IDH1 R132H/+ and isogenic IDH1 +/+ parental cells were screened for their ability to generate energy-rich NADH when cultured in a standardized high-throughput Phenotype MicroArrayplatform comprising >300 nutrients. A radical remodeling of the metabotype occurred in cells carrying the R132H mutation since they presented a markedly altered ability to utilize numerous carbon catabolic fuels. A mitochondria toxicity-screening modality confirmed a severe inability of IDH1-mutated cells to use various carbon substrates that are fed into the electron transport chain at different points. The mitochondrial biguanide poisons, metformin and phenformin, further impaired the intrinsic weakness of IDH1-mutant cells to use certain carbon-energy sources. Additionally, metabolic reprogramming of IDH1-mutant cells increased their sensitivity to metformin in assays of cell proliferation, clonogenic potential, and mammosphere formation. Targeted metabolomics studies revealed that the ability of metformin to interfere with the anaplerotic entry of glutamine into the tricarboxylic acid cycle could explain the hypersensitivity of IDH1-mutant cells to biguanides. Moreover, synergistic interactions occurred when metformin treatment was combined with the selective R132H-IDH1 inhibitor AGI-5198. Together, these results suggest that therapy involving the simultaneous targeting of metabolic vulnerabilities with metformin, and 2HG overproduction with mutant-selective inhibitors (AGI-5198-related AG-120 [Agios]), might represent a worthwhile avenue of exploration in the treatment of IDH1-mutated tumors.
Highlights
We hypothesized that metabolic alterations induced by cancer-promoting isocitrate dehydrogenase 1 (IDH1) mutations might confer a distinct and therapeutically vulnerable “metabolic phenotype” that could be exploited to select drugs with the highest probability of clinical success
Because cellular context-based screens rather than the standard in vitro enzymatic assays are a powerful system to identify drugs that act in a particular genetic framework, we used this approach to determine metabolic differences and therapeutic potential using a “matched pair” of wild-type and isogenic IDH1-mutant MCF10A cells, a useful model to analyze the transforming effects of candidate oncogenes [65, 66]
By using a single-codon knock-in IDH1 mutation approach, we more faithfully modeled the genetic condition in human IDH1-mutated tumors compared with systems that do not have isogenic controls, or that use nonphysiological mutant IDH1 expression
Summary
Despite the intrinsic weakness of R132H/+ cells to employ some carbon-energy sources in mitochondria, they remained sensitive to the inhibitory effects of biguanides, suggesting an inability of IDH1-mutated cells to transition their energy metabolism to the various substrates provided when challenged further with a clinically-relevant mitochondrial poison such as metformin.
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