- Patrick Wen (Boston, US)
18IN - Glioma and IDH targeting
- Daniel Cahill (Boston, US)
- Daniel Cahill (Boston, US)
Abstract
Background
Approximately 80% of WHO grade II and III gliomas, and secondary glioblastomas (representing 25% of adult diffuse gliomas overall) harbor mutations in the metabolic isocitrate dehydrogenase enzymes encoded by the IDH1/2 genes. These mutations, now recognized as the genetic hallmark of these cancers, result in neomorphic enzymatic activity driving overproduction of the oncometabolite 2-hydroxyglutarate (2-HG), which leads to profound reprogramming of tumor cellular metabolism. As a result, IDH1-mutant gliomas are dependent upon the canonical coenzyme NAD+ for survival. It is known that poly(ADP-ribose) polymerase (PARP) activation consumes NAD+ during base excision repair of chemotherapy-induced DNA damage. We therefore hypothesized that a strategy combining NAD+ biosynthesis inhibitors with the alkylating chemotherapeutic agent temozolomide could potentiate NAD+ depletion-mediated cytotoxicity in mutant IDH1 cancer cells.
Methods
We used several IDH mutant cancer models to study NAD+ metabolism. To investigate the impact of temozolomide (TMZ) on NAD+ metabolism, patient-derived xenografts and engineered mutant IDH1-expressing cell lines were exposed to TMZ, in vitro and in vivo, both alone and in combination with nicotinamide phosphoribosyltransferase (NAMPT) inhibitors, which block NAD+ biosynthesis.
Results
We found that TMZ is an NAD+ stressor, specifically in IDH1 mutant cancers. Mechanistically, TMZ stimulates NAD+ consumption by PARP via activation of DNA damage repair in exposed cells. The acute time period (<3 hours) after TMZ treatment displayed a burst of NAD+ consumption driven by PARP activation, but the dynamic capacity of the base excision repair system typically is able to withstand the metabolic stress induced by these DNA repair processing demands. However, in IDH1-mutant-expressing cells, this consumption of NAD+ critically reduced the abnormally lowered basal steady-state levels of NAD+, introducing a window of hypervulnerability to NAD+ biosynthesis inhibitors. This effect was selective for IDH1-mutant cells and independent of methylguanine methyltransferase or mismatch repair status, which are known rate-limiting mediators of adjuvant temozolomide genotoxic sensitivity. Combined temozolomide and NAMPT inhibition in an in vivo IDH1-mutant cancer model exhibited enhanced efficacy compared with each agent alone.
Conclusions
In conclusion, we find that IDH1-mutant cancers have distinct metabolic stress responses to chemotherapy-induced DNA damage and that combination regimens targeting nonredundant NAD+ pathways yield potent anticancer efficacy in vivo. More generally, our results suggest that effective targeting of convergent metabolic pathways in genetically selected cancers could minimize treatment toxicity and improve durability of response to therapy. Highlighting the central importance of NAD+ levels in IDH mutant gliomas, our observations suggests that metabolic strategies targeting NAD+ homeostasis may be combined with standard-of-care therapies to improve efficacy against these tumors.
Legal entity responsible for the study
Harvard-Massachusetts General Hospital
Disclosure
D. Cahill: Consulting: Merck, Lilly.
Funding
NIH, Burroughs Wellcome Foundation
19IN - Tumor metabolism and drug targeting with a focus on in sarcoma and the tissue microenvironment (glutamate and arginine)
- Brian Van Tine (St. Louis, US)
- Brian Van Tine (St. Louis, US)
Abstract
Background
Argininosuccinate Synthetase 1 (ASS1) is silenced in ∼90% of sarcomas. Loss of this urea cycle enzyme causes cells to become dependent upon extracellular arginine for continued cell growth and proliferation. Upon arginine starvation, ASS1(-) sarcoma cells undergo autophagy, increase their glutamine dependence and undergo growth arrest. In order to identify potentially exploitable synthetic lethal targets arising from the induction of autophagy following arginine deprivation, we investigated the metabolic alterations caused by arginine deprivation resulting from treatment with PEGylated arginine deiminase (ADI-PEG20). Mass spectroscopy was performed and revealed a significant increase in the level of serine biosynthesis from glucose which resulted from the up regulation of PHGDH. When paired with ADI-PEG20 treatment, inhibition of serine metabolism results in significant cell death. With recent studies showing the importance of serine biology in cancer, as well as recent generation of a small molecule PHGDH inhibitor to the rate limiting enzyme in serine biosynthesis, this newly identified synthetic lethality proves to be an exploitable therapeutic option for ASS1 deficient sarcomas.
Methods
The cell lines were with ADI-PEG20 for three days and subjected to metabolite extraction and capillary electrophoresis mass spectrometry (CE-MS). Similarly, additional samples were cultured for 2 days, with or without ADI-PEG20, and subsequently treated with U-C13 labeled glucose for an additional 24 hours before being subjected to metabolite extraction. Cell death was measured by propidium iodide fluorescent activated cell sorting after inhibition of serine metabolism by the small molecule inhibitor of PHGDH (CBR-5884) or genetic knockdown of key enzymes, with and without ADI-PEG20.
Results
Upon treatment with ADI-PEG20 and subsequent arginine deprivation induced autophagy, the radiolabeled glucose derived component of a vast majority of metabolites decreased significantly. The pathway with the largest increase in metabolic flux was serine biosynthesis, including subsequent conversion into glycine. Significant changes in the enzyme responsible for the rate limiting step of serine biosynthesis, phosphoglycerate dehydrogenase (PHGDH), as well as serine catabolism were induced upon arginine deprivation. Cell death levels were significantly higher in samples when inhibition of PHGDH was paired with ADI-PEG20 treatment.
Conclusions
Starvation mediated by arginine deprivation causes global changes in cellular metabolism. By determining the alterations in the fate of glucose and glutamine upon treatment with ADI-PEG20, we were able to illustrate a significant increase in the level of serine biosynthesis. Inhibition of this escape pathway resulted in cell death. References 1. Bean GR, Kremer JC, Prudner BC, et al: A metabolic synthetic lethal strategy with arginine deprivation and chloroquine leads to cell death in ASS1-deficient sarcomas. Cell Death Dis 7:e2406, 2016 2. Kremer JC, Prudner BC, Lange SE, et al: Arginine Deprivation Inhibits the Warburg Effect and Upregulates Glutamine Anaplerosis and Serine Biosynthesis in ASS1-Deficient Cancers. Cell Rep 18:991-1004, 2017
Conclusions
Starvation mediated by arginine deprivation causes global changes in cellular metabolism. By determining the alterations in the fate of glucose and glutamine upon treatment with ADI-PEG20, we were able to illustrate a significant increase in the level of serine biosynthesis. Inhibition of this escape pathway resulted in cell death.
Legal entity responsible for the study
B. Van Tine
Funding
Polaris, Inc., Sarcoma Foundation of America, Sarcoma Alliance for Research and Collaboration
Disclosure
B. Van Tine: This work had funding from Polaris, Inc.
20IN - T cell metabolism and metabolic reprogramming
- Jonathan Powell (Baltimore, US)
- Jonathan Powell (Baltimore, US)
21IN - Targeting of the LXR-cholesterol axis as a metabolic co-dependency for brain cancers
- Genaro Villa (Los Angeles, US)
- Genaro Villa (Los Angeles, US)
Abstract
Background
Oncogenic mutations in growth factor receptor signaling pathways are common in cancer, including in tumors that arise from or metastasize to the brain. However, most small-molecule inhibitors targeting growth factor receptors have failed to show efficacy for brain cancers, potentially due to inability to achieve sufficient drug levels in the central nervous system (CNS). Targeting tumor co-dependencies provides an alternative approach, particularly if drugs with high brain penetration can be identified.
Methods
In vitro cytotoxicity assays, mass spectoscopy, and orthotopic GBM in vivo models were used to assess cholesterol dependency and sensitivity to Liver X Receptor (LXR) activation using established GBM cell lines and patient-derived ex vivo tumor neurosphere cultures.
Results
We demonstrate that EGFR-mutant cancers, including a highly lethal form of brain cancer glioblastoma (GBM), are remarkably dependent on cholesterol for survival, rendering them sensitive to Liver X receptor (LXR) agonist-dependent cell death. We show that LXR-623, a clinically viable, highly brain-penetrant LXRα-partial/LXRβ-full agonist selectively kills GBM cells in an LXRβ- and cholesterol-dependent fashion, causing significant tumor regression and prolonged survival in mouse models.
Conclusions
Thus, a metabolic co-dependency provides a pharmacological means to kill growth factor-activated cancers in the CNS.
Legal entity responsible for the study
Ludwig Institute for Cancer Research
Disclosure
The author has declared no conflicts of interest.
Funding
National Institute of Health, National Cancer Institute, F31CA186668