The patatin-like protein PlpD forms structurally dynamic homodimers in the Pseudomonas aeruginosa outer membrane

Members of the Omp85 superfamily of outer membrane proteins (OMPs) found in Gram-negative bacteria, mitochondria and chloroplasts are characterized by a distinctive 16-stranded β-barrel transmembrane domain and at least one periplasmic POTRA domain. All previously studied Omp85 proteins promote critical OMP assembly and/or protein translocation reactions. Pseudomonas aeruginosa PlpD is the prototype of an Omp85 protein family that contains an N-terminal patatin-like (PL) domain that is thought to be translocated across the OM by a C-terminal β-barrel domain. Challenging the current dogma, we find that the PlpD PL-domain resides exclusively in the periplasm and, unlike previously studied Omp85 proteins, PlpD forms a homodimer. Remarkably, the PL-domain contains a segment that exhibits unprecedented dynamicity by undergoing transient strand-swapping with the neighboring β-barrel domain. Our results show that the Omp85 superfamily is more structurally diverse than currently believed and suggest that the Omp85 scaffold was utilized during evolution to generate novel functions.

TGF-β uncouples glycolysis and inflammation in macrophages and controls survival during sepsis

Changes in metabolism of macrophages are required to sustain macrophage activation in response to different stimuli. We showed that the cytokine TGF-β (transforming growth factor-β) regulates glycolysis in macrophages independently of inflammatory cytokine production and affects survival in mouse models of sepsis. During macrophage activation, TGF-β increased the expression and activity of the glycolytic enzyme PFKL (phosphofructokinase-1 liver type) and promoted glycolysis but suppressed the production of proinflammatory cytokines. The increase in glycolysis was mediated by an mTOR-c-MYC-dependent pathway, whereas the inhibition of cytokine production was due to activation of the transcriptional coactivator SMAD3 and suppression of the activity of the proinflammatory transcription factors AP-1, NF-κB, and STAT1. In mice with LPS-induced endotoxemia and experimentally induced sepsis, the TGF-β-induced enhancement in macrophage glycolysis led to decreased survival, which was associated with increased blood coagulation. Analysis of septic patient cohorts revealed that the expression of PFKL, TGFBRI (which encodes a TGF-β receptor), and F13A1 (which encodes a coagulation factor) in myeloid cells positively correlated with COVID-19 disease. Thus, these results suggest that TGF-β is a critical regulator of macrophage metabolism and could be a therapeutic target in patients with sepsis.

CBMS-5 STEAROYL-COA DESATURASE INHIBITOR INDUCES APOPTOSIS VIA ENHANCING LIPOLYSIS IN IDH MUTANT GLIOMA

Background

Little is known about the antineoplastic effect and the mechanism of Stearoyl-CoA desaturase (SCD) inhibitor which catalyzes the biosynthesis of monounsaturated fatty acids (MUFA). Mutant isocitrate dehydrogenase (IDH) catalyzes the NADPH-mediated reduction of α-ketoglutarate (αKG) to 2-hydroxyglutarate (2HG) and causes metabolic reprograming of lipid. In this study, to develop a feasible drug for IDH mutant glioma, we have investigated the changes of the lipid distribution and the mechanism of antineoplastic effect of SCD inhibition in IDH mutant glioma.

Materials and Methods

We prepared genetically engineered glioma cell lines (U251 wild type: U251WT and U251 IDH mutant: U251mut) and patient derived cell lines (TS603 and GSC923). Lipid metabolic analysis was conducted by using Raman imaging spectroscopy and LC-MS, and functional analysis for the role of SCD expression in IDH mutant glioma was investigated by RNA sequence and Western-blotting. Results: In LC-MS analysis of the extracted Endoplasmic Reticulum, MUFAs were distributed significantly higher in IDH mutant than wild type. SCD expression was increased in IDH mutant compared to wild type due to 2HG-mediated upregulation of SCD. Therefore, IDH mutant in which SCD expression level was high indicated high sensitivity to SCD inhibitor, and apoptosis was highly induced in IDH mutant compared to wild type. RNA sequencing was performed in U251mut treated with SCD inhibitor compared to U251mut treated with DMSO, and lipid droplet metabolism-associated RNA expression was significantly changed in U251mut treated with SCD inhibitor. We checked lipid droplet in U251mut with presence or absence of SCD inhibitor, and lipolysis was induced by SCD inhibitor treatment, suggesting that SCD inhibition is associated with the apoptosis in IDH mutant via enhanced lipolysis mechanism.

Conclusions

2HG produced in IDH mutant glioma directly induces SCD expression and enhances sensitivity to SCD inhibitor, which suggests that SCD inhibitor is an IDH mutant glioma-specific treatment strategy.

TMET-03. STEAROYL-COA DESATURASE INHIBITOR SUPPRESSES IDH MUTANT GLIOMA GROWTH VIA ENHANCING LIPOLYSIS

BACKGROUND

Mutant isocitrate dehydrogenase (IDH) produces 2-hydroxyglutarate (D2HG) and causes metabolic reprograming, but so far, little is known about the role of mutant IDH and D2HG in de novo lipogenesis and fatty acids synthesis. In this study, to develop a feasible drug for IDH mutant glioma, we targeted Stearoyl-CoA desaturase 1 (SCD1) catalyzing the biosynthesis of monosaturated fatty acids (MUFA) to suppress IDH mutant glioma progression. Materials and

METHODS

We prepared genetically engineered glioma cell lines (U251 wild type: U251WT and U251 IDHR132H mutant: U251RH), normal human astrocytes (empty vector induced-NHA: NHAEV and IDHR132H mutant: NHARH) and patient derived cell lines. Lipid metabolic analysis was conducted by using LC-MS, and functional analysis for the role of SCD1 expression was investigated by RNA sequence and Western-blotting.

RESULTS

LC-MS analysis of extracted Endoplasmic Reticulum revealed that there was significantly higher amount of MUFA in IDH mutant than wild type. SCD1 expression was increased in IDH mutant compared to wild type due to D2HG-mediated upregulation of SCD1 in IDH mutant. Therefore, IDH mutant in which SCD1 expression level was higher than wild type indicated high sensitivity to SCD inhibitor, and apoptosis was highly induced in IDH mutant compared to wild type. RNA sequencing was performed in U251RH treated with SCD inhibitor compared to U251RH treated with DMSO, and lipid droplet metabolism-associated RNA expression was significantly changed in SCD inhibitor-treated U251RH. Based on the RNA sequence data, we checked lipid droplet in U251RH with presence or absence of SCD inhibitor, and lipolysis was induced by SCD inhibitor treatment, suggesting that SCD inhibition is associated with the apoptosis in IDH mutant via enhanced lipolysis mechanism.

CONCLUSIONS

D2HG produced in IDH mutant glioma directly induces SCD1 expression and enhances sensitivity to SCD inhibitor, which suggests that SCD inhibitor would be IDH mutant glioma-specific treatment strategy.

CSIG-40. STEAROYL-COA DESATURASE 1 (SCD1) IS REQUIRED FOR WNT SIGNALING TO INDUCE AN APOPTOSIS IN IDH MUTANT GLIOMA

BACKGROUND AND HYPOTHESES

SCD1, a major enzyme of saturated fatty acids, has been implicated to be important for tumor metabolic reprograming. Our previous study show that a high level of SCD1 mRNA is associated with IDH1mut lower grade gliomas. IDH1mut glioma cells are more sensitive to SFA induced apoptosis. However, the underlying mechanism remains unclear. In this study, we investigate the functions of SCD1 in IDHmut glioma and the potential contribution of SCD1 for cancer therapy of glioma.

STUDY DESIGN AND METHODS

The genetically engineered IDH wild-type, IDHmut and patient derived glioma cell lines were used to evaluate SCD1 functions. The expression of proteins were checked by Western-blotting assay. SCD1 was silenced by CRISPR or siRNA. The transcriptome change after SCD1 knockdown was profiled by RNA-seq or single cell RNA-seq (scRNA-seq).

RESULTS AND CONCLUSIONS

SCD1 transient silencing slowed down the cell growth, suggesting that SCD1 may possess an oncogenic property. RNA-seq analysis revealed that SCD1 inhibition decreased the expression of wnt-signaling pathway genes in IDH-1mut cells. scRNA confirmed that CRISPR SCD1 significantly decreased wnt signaling in the patient cell line Ts603. Therefore, we activated wnt pathway using a small chemical compound, BML-2838. Consistent with recent studies, wnt pathway induction led to a dramatically suppression of glioma cells growth. However, SCD1 silencing reversed this inhibitory effect. Further investigation revealed that SCD1 inhibition reduced the nucleus translocation of phosphorylated beta-catenin. Overall, the results suggest that SCD1 is vital for the onset of wnt pathway in glioma cells. High level of SCD1 expression may render the IDHmut glioma cells more sensitive to wnt pathway induced apoptosis.

RELEVANCE AND IMPORTANCE

In clinical, the 5-years survival rate of glioma remains low. SCD1 have been considered as a target for glioma therapy, recently. Our data provides a new insight on the strategy to target SCD1 in clinical.

TMET-36. ACID CERAMIDASE INHIBITION EXPLOITS SPHINGOLIPID VULNERABILITIES IN IDH MUTANT GLIOMAS

The presence of the IDH mutation in gliomas is a major classifier of brain tumor subtypes and has several important implications for cancer growth. Our recent work uncovered that IDH-mutant tumors are susceptible to increased apoptosis via alterations of the sphingolipid pathway due to their excess production of pro-apoptotic ceramides over pro-proliferative sphingosine 1-phosphate (S1P). To that end, we proposed that this rheostat can be modulated to induce cell death in IDHmut tumors by targeting acid ceramidase, a critical sphingolipid enzyme in gliomas. We hypothesize that pharmacological inhibition of acid ceramidase will increase ceramide levels and therefore induce apoptosis in IDHmutgliomas. Using a preliminary drug screen, we have identified a group of haloacetate C2-ceramide derivatives known as SOBRACs that potently inhibit acid ceramidase. We selected five candidate compounds from this family and assessed the effectiveness of each drug in 3 I IDHmut (BT142, TS603, & U251mut) and 3 IDHmut (GSC923, GSC827, U251wt) patient-derived glioma cell lines, as well as non-immortalized normal human astrocytes, using the CCK8 cell viability assay. Our results indicate that the SOBRAC drugs are nearly 10 times more potent in IDH-mutant tumors compared to IDHmut cell lines. Additionally, the SOBRAC drugs are more effective than other known acid ceramidase inhibitors, making them attractive as potential novel therapeutics. To date, azide-SOBRAC is the most potent drug in the family, with EC50 value of 300 nM in BT142 cells (IDHmutmut

DDDR-09. TARGETED DYSREGULATION OF SPHINGOLIPID RHEOSTAT BALANCE IN IDH1MUT GLIOMAS TRIGGERS PRO-APOPTOTIC METABOLIC AND SIGNALING ACTIVITY

BACKGROUND

IDHwt gliomas exhibit sphingolipid rheostat balance that permits tumors to evade apoptosis by elevating the sphingosine-1-phosphate (S1P)-to-ceramide ratio. Overexpression of sphingosine kinase (SPHK) and consequent accumulation of S1P contribute to progression, chemoresistance, migration, and metastasis in malignant glioblastoma (GBM). We discovered that IDH1mut gliomas present a characteristic sphingolipid rheostat in which pro-apoptotic ceramides and sphingosines are elevated over oncopotent S1P. This characteristic involves inherent silencing of the SPHK2; obliging spheroids to rely on SPHK1 exclusively. We postulated that targeting this unique metabolic vulnerability would abrogate the growth-promoting and anti-apoptotic effects of S1P.

METHODS

IDH1mut glioma cell lines (TS603, BT142 & NCH1681) and empty vector-induced normal human astrocytes (NHAEV) were cultured and treated with a combination of SPHK1 inhibitor, N,N-dimethylsphingosine and C17-sphingosine to dysregulate sphingolipid rheostat. Biostatic response (i.e., IC50) was measured via spectrophotometric assay. Metabolic and signaling mechanisms were investigated by LC-MS lipidomic and RNA sequencing analysis. Mechanism of apoptosis was determined via western-blotting.

RESULTS

Following combination treatment, a global increase in ceramides, sphingosines, and their derivatives over S1P was detected in the sphingolipid rheostat. A decline in growth-promoting MAPK signaling enzymes and elevation of enzymes indicative of mitochondria-driven apoptosis occurred. Elevation of TNFα-related regulatory enzymes (NR1H3, MYLIP, INSIG, ABCA1) negatively impacted cholesterol homeostasis along with catalytic enzymes involved in cholesterol (and isoprenoid) biosynthesis. The effective concentration against IDH1mut spheroids was not cytotoxic to NHA spheroids.

CONCLUSION

The combination treatment potentiated a pro-apoptotic shift in sphingolipidome and revealed a novel mechanism of drug action involving concomitant global attenuation of cholesterol metabolism. While previous studies reported that decreasing cholesterol in gliomas compromises viability and induces apoptosis a link between cholesterol and sphingolipid metabolism remains unknown. Our data demonstrated that targeting sphingolipid rheostat triggers a cascade of pro-apoptotic signaling and metabolic activity that lower the threshold for apoptosis in IDHmut gliomas.

Metabolic biomarkers of radiotherapy response in plasma and tissue of an IDH1 mutant astrocytoma mouse model

Astrocytomas are the most common subtype of brain tumors and no curative treatment exist. Longitudinal assessment of patients, usually via Magnetic Resonance Imaging (MRI), is crucial since tumor progression may occur earlier than clinical progression. MRI usually provides a means for monitoring the disease, but it only informs about the structural changes of the tumor, while molecular changes can occur as a treatment response without any MRI-visible change. Radiotherapy (RT) is routinely performed following surgery as part of the standard of care in astrocytomas, that can also include chemotherapy involving temozolomide. Monitoring the response to RT is a key factor for the management of patients. Herein, we provide plasma and tissue metabolic biomarkers of treatment response in a mouse model of astrocytoma that was subjected to radiotherapy. Plasma metabolic profiles acquired over time by Liquid Chromatography Mass Spectrometry (LC/MS) were subjected to multivariate empirical Bayes time-series analysis (MEBA) and Receiver Operating Characteristic (ROC) assessment including Random Forest as the classification strategy. These analyses revealed a variation of the plasma metabolome in those mice that underwent radiotherapy compared to controls; specifically, fumarate was the best discriminatory feature. Additionally, Nuclear Magnetic Resonance (NMR)-based 13C-tracing experiments were performed at end-point utilizing [U-13C]-Glutamine to investigate its fate in the tumor and contralateral tissues. Irradiated mice displayed lower levels of glycolytic metabolites (e.g. phosphoenolpyruvate) in tumor tissue, and a higher flux of glutamine towards succinate was observed in the radiation cohort. The plasma biomarkers provided herein could be validated in the clinic, thereby improving the assessment of brain tumor patients throughout radiotherapy. Moreover, the metabolic rewiring associated to radiotherapy in tumor tissue could lead to potential metabolic imaging approaches for monitoring treatment using blood draws.

Cryo-EM structures reveal multiple stages of bacterial outer membrane protein folding

Transmembrane β barrel proteins are folded into the outer membrane (OM) of Gram-negative bacteria by the β barrel assembly machinery (BAM) via a poorly understood process that occurs without known external energy sources. Here, we used single-particle cryo-EM to visualize the folding dynamics of a model β barrel protein (EspP) by BAM. We found that BAM binds the highly conserved "β signal" motif of EspP to correctly orient β strands in the OM during folding. We also found that the folding of EspP proceeds via "hybrid-barrel" intermediates in which membrane integrated β sheets are attached to the essential BAM subunit, BamA. The structures show an unprecedented deflection of the membrane surrounding the EspP intermediates and suggest that β sheets progressively fold toward BamA to form a β barrel. Along with in vivo experiments that tracked β barrel folding while the OM tension was modified, our results support a model in which BAM harnesses OM elasticity to accelerate β barrel folding.

IDH-mutated gliomas promote epileptogenesis through d-2-hydroxyglutarate-dependent mTOR hyperactivation

BACKGROUND

Uncontrolled seizures in patients with gliomas have a significant impact on quality of life and morbidity, yet the mechanisms through which these tumors cause seizures remain unknown. Here, we hypothesize that the active metabolite d-2-hydroxyglutarate (d-2-HG) produced by the IDH-mutant enzyme leads to metabolic disruptions in surrounding cortical neurons that consequently promote seizures.

METHODS

We use a complementary study of in vitro neuron-glial cultures and electrographically sorted human cortical tissue from patients with IDH-mutant gliomas to test this hypothesis. We utilize micro-electrode arrays for in vitro electrophysiological studies in combination with pharmacological manipulations and biochemical studies to better elucidate the impact of d-2-HG on cortical metabolism and neuronal spiking activity.

RESULTS

We demonstrate that d-2-HG leads to increased neuronal spiking activity and promotes a distinct metabolic profile in surrounding neurons, evidenced by distinct metabolomic shifts and increased LDHA expression, as well as upregulation of mTOR signaling. The increases in neuronal activity are induced by mTOR activation and reversed with mTOR inhibition.

CONCLUSION

Together, our data suggest that metabolic disruptions in the surrounding cortex due to d-2-HG may be a driving event for epileptogenesis in patients with IDH-mutant gliomas.

Cysteine is a limiting factor for glioma proliferation and survival

Nutritional intervention is becoming more prevalent as adjuvant therapy for many cancers in view of the tumor dependence on external sources for some nutrients. However, little is known about the mechanisms that make cancer cells require certain nutrients from the microenvironment. Herein, we report the dependence of glioma cells on exogenous cysteine/cystine, despite this amino acid being nonessential. Using several ¹³C‐tracers and analysis of cystathionine synthase and cystathioninase levels, we revealed that glioma cells were not able to support glutathione synthesis through the transsulfuration pathway, which allows methionine to be converted to cysteine in cysteine/cystine‐deprived conditions. Therefore, we explored the nutritional deprivation in a mouse model of glioma. Animals subjected to a cysteine/cystine‐free diet survived longer, although this increase did not attain statistical significance, with concomitant reductions in plasma glutathione and cysteine levels. At the end point, however, tumors displayed the ability to synthesize glutathione, even though higher levels of oxidative stress were detected. We observed a compensation from the nutritional intervention revealed as the recovery of cysteine‐related metabolite levels in plasma. Our study highlights a time window where cysteine deprivation can be exploited for additional therapeutic strategies.

DDRE-19. SPHINGOSINE KINASE 1 AS A THERAPEUTIC TARGET FOR IDH1-R132H mut GLIOMA

BACKGROUND

Our study aimed to identify vulnerabilities within sphingolipid metabolism with potential to translate to therapeutics. While the vital role of sphingolipids in maintaining rheostat balance and as secondary messengers for signaling pathways (involving proliferation, invasion, migration, and angiogenesis) has been well-documented, their role has not been widely investigated in gliomas. Therefore, metabolic analysis of sphingolipid pathway for IDH1-R132H (IDH1 mut ) glioma cell lines was conducted in order to elucidate susceptible targets.

METHODS

Global sphingolipid quantification utilized high-throughput LCMS analysis. Pathway protein expression was measured via Western blots in vitro and derived from patients using The Cancer Genome Atlas analysis.

RESULTS

We probed the impact of decreasing D-2HG on the sphingolipid metabolism after treating a panel of IDH1 mut glioma cells with IDH1-R132H mut inhibitor, AGI5198. This revealed significant downregulation of N,N-dimethylsphingosine (NDMS), C17-sphingosine, and C18-sphinganine. Coincidentally, sphingosine-1-phosphate (S1P) was significantly upregulated in these gliomas. We conducted rational drug screen which revealed that inhibition of SPHK1 with N,N-dimethylsphingosine in combination with C17-sphingosine triggered biostatic dose-response across IDH1 mut gliomas and low impact on IDH WT glioblastoma (GBM) cells. Western analysis revealed that the IDH1 mut gliomas and IDH WT GBM expressed sphingosine kinase-1 (SPHK1). Data also unveiled a discovery that SPHK2 was highly expressed in the GBM cells while remarkably absent in the glioma cells.

CONCLUSION

Herein, we provide evidence that certain IDH1 mut gliomas present epigenetic silencing of SPHK2 which creates dependency on SPHK1 for S1P; thus, increasing sensitivity to targeting sphingolipid metabolism, and creating susceptibility to proliferation arrest and subsequent cellular death. S1P production has been reported to be elevated particularly for malignant glioblastomas in prior studies; whereas our research revealed that it is relatively low in IDH mut by comparison with IDH WT tumor cells. These findings suggest targeting the sphingolipid metabolism may present a promising strategy to improve survival for patients diagnosed with IDH1 mut gliomas.

NCMP-07. IDH MUTANT GLIOMAS PROMOTE EPILEPTOGENESIS VIA D-2-HYDROXYGLUTARATE DEPENDENT MTOR HYPER-ACTIVATION

Uncontrolled seizures in patients with low grade gliomas have a significant impact on quality of life and morbidity, yet the mechanisms through which these tumors cause seizures remain unknown. Albeit there are multiple features that contribute to tumor related epileptogenesis, IDH mutations are determined to be an independent factor, although the pathogenesis remains poorly understood. Here, we hypothesize that the active metabolite D-2-hydroxyglutarate (D-2-HG) produced by the IDH-mutant enzyme leads to metabolic disruptions in surrounding cortical neurons that consequently promote seizures. We use a complementary study of in vitro cortical cultures and electrographically sorted human cortical tissue from patients (n=5) with IDH-mutant gliomas to test this hypothesis. We demonstrate that D-2-HG leads to increased neuronal spiking activity (p< 0.0001) and promotes a distinct metabolic profile in surrounding neurons and upregulation of mTOR signaling (p< 0.0001), which is consistent in human epileptic cortex compared to peritumoral nonepileptic cortex. Furthermore, increases in neuronal activity are induced by mTOR activation and reversed with mTOR inhibition. Together, our data suggest that metabolic disruptions and mTOR signaling upregulation in the surrounding cortex due to D-2-HG may be a driving event for epileptogenesis in patients with IDH-mutant low grade gliomas.

TAMI-37. STEAROYL-COA DESATURASE 1 IS ESSENTIAL FOR THE GROWTH OF IDH MUTANT GLIOMA

BACKGROUND

Increased de novo lipogenesis is a hallmark of cancer metabolism. In this study, we interrogated the role of de novo lipogenesis in IDH1 mutated glioma’s growth and identified the key enzyme, Stearoyl-CoA desaturase 1 (SCD1) that provides this growth advantage.

MATERIALS ANDMETHODS

We prepared genetically engineered glioma cell lines (U251 wild-type: U251WT and U251 IDHR132H mutant: U251RH) and normal human astrocytes (empty vector induced-NHA: NHAEV and IDHR132H mutant: NHARH). Lipid metabolic analysis was conducted by using LC-MS and Raman imaging microscopy. SCD1 expression was investigated by The Cancer Genome Atlas (TCGA) data analysis and Western-blotting method. Knock-out of SCD1 was conducted by using CRISPR/Cas9 and shRNA.

RESULTS

Previously, we showed that IDH1 mut glioma cells have increased monounsaturated fatty acids (MUFAs). TCGA data revealed IDH mut glioma shows significantly higher SCD1 mRNA expression than wild-type glioma. Our model systems of IDH1 mut (U251RH, NHARH) showed increased expression of this enzyme compared with their wild-type counterpart. Moreover, addition of D-2HG to U251WT increased SCD1 expression. Herein, we showed that inhibition of SCD1 with CAY10566 decreased relative cell number and sphere forming capacity in a dose-dependent manner. Furthermore, addition of MUFAs were able to rescue the SCD1 inhibitor induced-cell death and sphere forming capacity. Knock out of SCD1 revealed decreased cell proliferation and sphere forming ability. Decreasing lipid content from the media did not alter the growth of these cells, suggesting that glioma cells rely on de novo lipid synthesis rather than scavenging them from the microenvironment.

CONCLUSION

Overexpression of IDH mutant gene altered lipid composition in U251 cells to enrich MUFA levels and we confirmed that D-2HG caused SCD1 upregulation in U251WT. We demonstrated the glioma cell growth requires SCD1 expression and the results of the present study may provide novel insights into the role of SCD1 in IDH mut gliomas growth.

TAMI-53. CYSTEINE IS A LIMITING FACTOR FOR GLIOMA PROLIFERATION AND SURVIVAL

BACKGROUND

Little is known about the mechanisms that render cancer cells dependent on certain nutrients from the microenvironment. Cysteine is a non-essential amino acid, since it can be synthetized from methionine through the transsulfuration pathway; moreover, cysteine is also uptake from the diet as cystine. We have investigated the metabolism of cysteine in glioma cell lines, and how cysteine/cystine-deprivation alters their antioxidant response in addition to the effect of this nutrient restriction to viability and proliferation in vitro and in vivo.

METHODS

Cysteine metabolism was investigated through LCMS-based 13C-tracing experiments and the expression levels of key enzymes in the transsulfuration pathway were also explored. Finally, a mouse model of IDH1 mutant glioma was subjected to a cysteine/cystine-free diet and tumor metabolism was analyzed by LCMS.

RESULTS

Herein, we report the dependence of glioma cells on exogenous cysteine/cystine, despite this amino acid being nonessential. Using several 13C-tracers and analysis of cystathionine synthase and cystathioninase levels, we revealed that glioma cells were not able to upregulate the transulfuration pathway cysteine, which allows methionine to be converted to cysteine in cysteine/cystine deprived conditions. We demonstrated that exogenous cysteine/cystine are crucial for glutathione synthesis, and impact growth and viability. Therefore, we explored the nutritional deprivation in a mouse model of glioma. Animals subjected to a cysteine/cystine-free diet survived longer, with concomitant reductions in glutathione and cysteine plasma levels. At the endpoint higher levels of oxidative stress were detected despite the systemic recovery of cysteine-related metabolites in the plasma.

CONCLUSION

The results presented herein reveal an alternative therapeutic approach combining cysteine/cysteine-deprivation diets and treatments involving ROS production by limiting the ability of glioma cells to quench oxidative stress through dietary interventions. Our study highlights a time window where cysteine deprivation can be exploited for additional therapeutic strategies.

Reversing Epigenetic Gene Silencing to Overcome Immune Evasion in CNS Malignancies

Glioblastoma (GBM) is an aggressive brain malignancy with a dismal prognosis. With emerging evidence to disprove brain-immune privilege, there has been much interest in examining immunotherapy strategies to treat central nervous system (CNS) cancers. Unfortunately, the limited success of clinical studies investigating immunotherapy regimens, has led to questions about the suitability of immunotherapy for these cancers. Inadequate inherent populations of tumor infiltrating lymphocytes (TILs) and limited trafficking of systemic, circulating T cells into the CNS likely contribute to the poor response to immunotherapy. This paucity of TILs is in concert with the finding of epigenetic silencing of genes that promote immune cell movement (chemotaxis) to the tumor. In this study we evaluated the ability of GSK126, a blood-brain barrier (BBB) permeable small molecule inhibitor of EZH2, to reverse GBM immune evasion by epigenetic suppression of T cell chemotaxis. We also evaluated the in vivo efficacy of this drug in combination with anti-PD-1 treatment on tumor growth, survival and T cell infiltration in syngeneic mouse models. GSK126 reversed H3K27me³ in murine and human GBM cell lines. When combined with anti-PD-1 treatment, a significant increase in activated T cell infiltration into the tumor was observed. This resulted in decreased tumor growth and enhanced survival both in sub-cutaneous and intracranial tumors of immunocompetent, syngeneic murine models of GBM. Additionally, a significant increase in CXCR3⁺ T cells was also seen in the draining lymph nodes, suggesting their readiness to migrate to the tumor. Closer examination of the mechanism of action of GSK126 revealed its ability to promote the expression of IFN-γ driven chemokines CXCL9 and CXCL10 from the tumor cells, that work to traffic T cells without directly affecting T maturation and/or proliferation. The loss of survival benefit either with single agent or combination in immunocompromised SCID mice, suggest that the therapeutic efficacy of GSK126 in GBM is primarily driven by lymphocytes. Taken together, our data suggests that in glioblastoma, epigenetic modulation using GSK126 could improve current immunotherapy strategies by reversing the epigenetic changes that enable immune cell evasion leading to enhanced immune cell trafficking to the tumor.

OTME-4. IDH mutated gliomas promote epileptogenesis via D-2-hydroxyglutarate dependent mTOR hyperactivation

Epilepsy in the context of brain tumors provides a great burden in these patients, yet mechanisms underlying this process are poorly understood. It has been demonstrated that isocitrate dehydrogenase (IDH) mutations are an independent factor in epileptogenesis in patients with low grade gliomas. Here, using electrographically sorted human cortical tissue from patients with IDH mutated tumor related epilepsy and in vitro cortical cultures, we explore a metabolic paradigm and its impact on increased neuronal excitability. We hypothesize the IDH mutation promotes epileptogenesis through its neomorphic activity of D-2-hydroxyglutarate (D-2-HG) production in turn interrupts surrounding normal neuronal circuitry potentially through metabolic perturbations. We demonstrate D-2-HG increases neuronal spiking activity, promotes distinct metabolic profiles independent of neuronal spiking activity, as well as increases neuronal mTOR signaling, which is reflected in human peritumoral epileptic cortex. Increased mTOR signaling is sufficient to upregulate neuronal spiking activity and, reciprocally, inhibition of mTOR corrects neuronal activity as well as partially corrects metabolic reprogramming. Our results suggest D-2-HG can lead to mTOR activation within the peritumoral neurons, thereby suggesting an additional possible mechanism of epileptogenesis in patients with IDH mutated low grade gliomas. Ultimately, our results raise the possibility of mTOR inhibition may be a promising treatment of seizures in patients with these tumors.

Metabolic reprogramming associated with aggressiveness occurs in the G-CIMP-high molecular subtypes of IDH1mut lower grade gliomas

BACKGROUND

Early detection of increased aggressiveness of brain tumors is a major challenge in the field of neuro-oncology because of the inability of traditional imaging to uncover it. Isocitrate dehydrogenase (IDH)-mutant gliomas represent an ideal model system to study the molecular mechanisms associated with tumorigenicity because they appear indolent and non-glycolytic initially, but eventually a subset progresses toward secondary glioblastoma with a Warburg-like phenotype. The mechanisms and molecular features associated with this transformation are poorly understood.

METHODS

We employed model systems for IDH1 mutant (IDH1mut) gliomas with different growth and proliferation rates in vivo and in vitro. We described the metabolome, transcriptome, and epigenome of these models in order to understand the link between their metabolism and the tumor biology. To verify whether this metabolic reprogramming occurs in the clinic, we analyzed data from The Cancer Genome Atlas.

RESULTS

We reveal that the aggressive glioma models have lost DNA methylation in the promoters of glycolytic enzymes, especially lactate dehydrogenase A (LDHA), and have increased mRNA and metabolite levels compared with the indolent model. We find that the acquisition of the high glycolytic phenotype occurs at the glioma cytosine-phosphate-guanine island methylator phenotype (G-CIMP)-high molecular subtype in patients and is associated with the worst outcome.

CONCLUSION

We propose very early monitoring of lactate levels as a biomarker of metabolic reprogramming and tumor aggressiveness.

DDRE-27. IDH MUTATED GLIOMAS PROMOTE EPILEPTOGENESIS VIA D-2-HYDROXYGLUTARATE DEPENDENT MTOR HYPERACTIVATION

INTRODUCTION

Epileptic seizures in patients with low-grade, isocitrate dehydrogenase (IDH) mutated gliomas reach 90%, a major source of morbidity for these patients. Albeit there are multiple features that contribute to tumor related epileptogenesis, IDH mutations are determined to be an independent factor, although the pathogenesis remains poorly understood. We demonstrate IDH-mutated tumors promote epileptogenesis through D-2-hydroxyglutarate (D-2-HG) dependent mTOR hyperactivation and metabolic reprogramming.

METHODS

Human epileptic and nonepileptic cortex were identified via subdural electrodes in patients with IDH-mutated gliomas (n=5). An in vitro rat cortical neuronal model on microelectrode arrays were utilized to investigate the role of D-2-HG on neuronal excitability. mTOR and lysine demethylase (KDM) modulators were applied to elucidate the epileptogenic mechanism. Tetrodotoxin was utilized to evaluate the contribution of neuronal activity to mTOR signaling and metabolism. mTOR signaling was evaluated through western blot analysis and multiplex immunofluorescence. Metabolic function were analyzed via Seahorse assays and metabolomic analysis.

RESULTS

D-2-HG increased normalized bursting rate in the neuronal cultures (p<0.0001). Inhibition of mTOR with rapamycin corrected bursting levels to control levels. Furthermore, D-2-HG induced mTOR hyperactivation, independent of bursting activity, which correlated with upregulation of mTOR signaling in human epileptic tissue. KDM inhibition resulted in mTOR hyperactivation and neuronal hyperexcitability, which we demonstrated with D-2-HG, succinate, and PFI-90, a small molecule KDM inhibitor. Epileptic cortex and D-2-HG-treated neurons, have distinct metabolisms independent of neuronal activity compared to peritumoral nonepileptic cortex and control, respectively.

CONCLUSION

We demonstrate IDH-mutated gliomas promote epileptogenesis through a D-2-HG dependent mTOR hyperactivation via KDM inhibition, a putative mechanism and potential therapeutic targets. Furthermore, we argue mTOR hyperactivation results in metabolic reprogramming, independent of neuronal firing, which may contribute to epileptogenesis, a heretofore unrecognized aspect of pathologic mTOR signaling in neurological diseases.

DDRE-16. CYSTEINE IS AN ESSENTIAL AMINO ACID IN GLIOMAS

BACKGROUND

Cysteine is a non-essential amino acid, since it can be synthetized from methionine through the transsulfuration pathway; moreover, cysteine is also uptake from the diet as cystine. We have investigated the metabolism of cysteine in glioma cell lines, and how cysteine/cystine-deprivation alters their antioxidant response in addition to the effect of this nutrient restriction to viability and proliferation in vitro and in vivo.

METHODS

Cysteine metabolism was investigated through LCMS-based ¹³C-tracing experiments involving different probes such as ¹³C-methyl-Methionine, ¹³C-C3-Cysteine, ¹³C-C3,3’-Cystine, ¹³C-C3-Serine and ¹³C-U-Glutamine and the expression levels of key enzymes in the transsulfuration pathway were also explored. Finally, a mouse model of IDH1 mutant glioma was subjected to a cysteine/cystine-free diet and tumor metabolism was analyzed by LCMS.

RESULTS

We demonstrated that exogenous cysteine/cystine are crucial for glutathione synthesis, and impact growth and viability. We also found that methionine cycle is disconnected from the transsulfuration pathway based on ¹³C-tracing data and protein expression levels of cystathionine synthase and cystathioninase. Accordingly, cysteine-related metabolites such as GSH, involved in REDOX hemostasis, are downregulated, revealing a hypersensitive phenotype to ROS. Animal models upon a cysteine/cystine-free diet experienced an increase in survival and elevated levels of oxidative stress in tumor tissue.

CONCLUSION

This results presented herein reveal an alternative therapeutic approach combining cysteine/cysteine-deprivation diets and treatments involving ROS production by limiting the ability of glioma cells to quench oxidative stress through dietary interventions.

DDRE-20. TARGETING SPHINGOLIPID PATHWAY REVEALS VULNERABILITY IN IDH1MUT GLIOMA

BACKGROUND

While central carbon metabolism has been studied extensively in cancer, lipidomic research is sparse. Sphingolipids participate in cellular functions including secondary messengers, lymphocyte trafficking, inflammation, angiogenesis, migration, proliferation, necrosis and apoptosis, thus highlighting the importance of understanding their role to tumor phenotype. Our investigation into metabolic alterations involving sphingolipid pathway in patient-derived IDH1^mut glioma cultures aimed to identify points of metabolic vulnerability.

METHODS

Dysregulation of sphingolipid metabolism was interrogated for brain tumor cultures via LCMS. Expression of enzymes within the pathway was assessed for IDH^mut 1/2 and IDH^WT glioblastoma patient cohorts via The Cancer Genome Atlas (TCGA) analysis and Western blot for tumor cultures. Biostatic drug response was examined via viability and cytotoxicity assays.

RESULTS

We probed the effect that decreasing D-2HG levels with IDH1^mut inhibitor (AGI5198) treatments had on sphingolipid metabolism in tumor cultures. The probe revealed N,N-dimethylsphingosine (NDMS), and sphingosine were significantly elevated, while sphingosine-1-phosphate (S1P) was downregulated in IDH1^mut cultures following treatment. Drug panel screening revealed that SPHK inhibitor (SPHKi), N,N-dimethylsphingosine in combination with sphingosine triggered lethal dose-dependent response in IDH1^mut cultures; contrary to IDH^WT. Westerns presented differential expression of SPHK1 and SPHK2 in IDH^WT glioblastoma cells, while IDH^mut exclusively expressed SPHK1.

CONCLUSION

This novel discovery showed how targeting sphingolipid metabolism in IDH1^mut gliomas presents therapeutic implications. Elevated S1P was reported particularly for malignant glioblastomas in prior studies; whereas our research revealed relatively low S1P in the IDH^mut compared with IDH^WT cultures. In addition to reduced or silenced expression of SPHK2, we postulate that S1P levels in IDH^mut gliomas might be closer to a critical threshold allowing treatment with SPHK1i to effectively suspend proliferation and anti-apoptotic defense mechanisms. Our findings revealed that the manipulation of pivotal, endogenous sphingolipids can ultimately trigger apoptosis in IDH^mut gliomas. Future studies will probe these targets in preclinical models.

BIMG-10. IDH1 MUTATIONS INDUCE ORGANELLE DEFECTS VIA DYSREGULATED PHOSPHOLIPIDS

BACKGROUND

Metabolic alterations of lipids have been identified as a hallmark of neoplasms, with the most prevalent being the balance between saturated fatty acid (SFA) and monosaturated fatty acid (MUFA). Stearoyl-CoA desaturase1 (SCD1), converting SFA to MUFA, is increased in many cancers, leading to worse prognosis. In glioma, the role of SCD1 remains unknown. Isocitrate dehydrogenase (IDH) mutations have been most commonly observed in glioma, but the involvement of mutant IDH in SCD1 expression also remains unknown.

METHODS

We conducted metabolic analysis to examine the alteration of SCD1 expression in genetically engineered glioma cell lines and normal human astrocyte (NHA). Lipid metabolic analysis was conducted by using LC-MS, Raman Imaging Microscopy and SCD1 expression was examined by Western-blotting and RT-PCR method. Electron microscopy was employed for organelle structure and genetic knock-down of SCD1 gene was performed.

RESULT

Herein, we uncovered increased MUFA and their phospholipids in Endoplasmic Reticulum (ER), generated by IDH1 mutation, that were responsible for Golgi and ER dilation. RNA seq data from The Cancer Genome Atlas, showed that SCD1 expression was significantly higher in IDH mutant gliomas compared with wild-type, and high SCD1 expression was associated with longer survival. Inhibition of IDH1 mutation or SCD1 silencing restored ER and Golgi morphology, while D-2HG and oleic acid induced morphological defects in these organelles. Moreover, addition of oleic acid, which tilts the balance towards elevated levels of MUFA, produced IDH1 mutant-specific cellular apoptosis.

CONCLUSION

Collectively, our results suggest that IDH1 mutant-induced SCD overexpression can rearrange the distribution of lipids in the organelles of glioma cells, providing a new insight on the link between lipids metabolism and organelle morphology in these cells, with potential and unique therapeutic implications. The results of the present study may also provide novel insights into the discovery of metabolic biomarkers for IDH mutant gliomas.

IDH1 mutations induce organelle defects via dysregulated phospholipids

Infiltrating gliomas are devastating and incurable tumors. Amongst all gliomas, those harboring a mutation in isocitrate dehydrogenase 1 mutation (IDH1^mut) acquire a different tumor biology and clinical manifestation from those that are IDH1^WT. Understanding the unique metabolic profile reprogrammed by IDH1 mutation has the potential to identify new molecular targets for glioma therapy. Herein, we uncover increased monounsaturated fatty acids (MUFA) and their phospholipids in endoplasmic reticulum (ER), generated by IDH1 mutation, that are responsible for Golgi and ER dilation. We demonstrate a direct link between the IDH1 mutation and this organelle morphology via D-2HG-induced stearyl-CoA desaturase (SCD) overexpression, the rate-limiting enzyme in MUFA biosynthesis. Inhibition of IDH1 mutation or SCD silencing restores ER and Golgi morphology, while D-2HG and oleic acid induces morphological defects in these organelles. Moreover, addition of oleic acid, which tilts the balance towards elevated levels of MUFA, produces IDH1^mut-specific cellular apoptosis. Collectively, these results suggest that IDH1^mut-induced SCD overexpression can rearrange the distribution of lipids in the organelles of glioma cells, providing new insight into the link between lipid metabolism and organelle morphology in these cells, with potential and unique therapeutic implications.

The understanding of altered lipid metabolism by isocitrate dehydrogenase 1 (IDH1) mutations in gliomas at a compartment-specific level is limited. Here, the authors use Raman spectroscopy to monitor organelle-specific metabolic changes and report that IDH1 mutations induce phospholipid imbalances which lead to ER and Golgi dilation.

Metabolic plasticity of IDH1-mutant glioma cell lines is responsible for low sensitivity to glutaminase inhibition

Background

Targeting glutamine metabolism in cancer has become an increasingly vibrant area of research. Mutant IDH1 (IDH1^mut) gliomas are considered good candidates for targeting this pathway because of the contribution of glutamine to their newly acquired function: synthesis of 2-hydroxyglutarate (2HG).

Methods

We have employed a combination of ¹³C tracers including glutamine and glucose for investigating the metabolism of patient-derived IDH1^mut glioma cell lines through NMR and LC/MS. Additionally, genetic loss-of-function (in vitro and in vivo) approaches were performed to unravel the adaptability of these cell lines to the inhibition of glutaminase activity.

Results

We report the adaptability of IDH1^mut cells’ metabolism to the inhibition of glutamine/glutamate pathway. The glutaminase inhibitor CB839 generated a decrease in the production of the downstream metabolites of glutamate, including those involved in the TCA cycle and 2HG. However, this effect on metabolism was not extended to viability; rather, our patient-derived IDH1^mut cell lines display a metabolic plasticity that allows them to overcome glutaminase inhibition.

Conclusions

Major metabolic adaptations involved pathways that can generate glutamate by using alternative substrates from glutamine, such as alanine or aspartate. Indeed, asparagine synthetase was upregulated both in vivo and in vitro revealing a new potential therapeutic target for a combinatory approach with CB839 against IDH1^mut gliomas.

Sphingolipid Pathway as a Source of Vulnerability in IDH1mut Glioma

In addition to providing integrity to cellular structure, the various classes of lipids participate in a multitude of functions including secondary messengers, receptor stimulation, lymphocyte trafficking, inflammation, angiogenesis, cell migration, proliferation, necrosis and apoptosis, thus highlighting the importance of understanding their role in the tumor phenotype. In the context of IDH1mut glioma, investigations focused on metabolic alterations involving lipidomics' present potential to uncover novel vulnerabilities. Herein, a detailed lipidomic analysis of the sphingolipid metabolism was conducted in patient-derived IDH1mut glioma cell lines, as well as model systems, with the of identifying points of metabolic vulnerability. We probed the effect of decreasing D-2HG levels on the sphingolipid pathway, by treating these cell lines with an IDH1mut inhibitor, AGI5198. The results revealed that N,N-dimethylsphingosine (NDMS), sphingosine C17 and sphinganine C18 were significantly downregulated, while sphingosine-1-phosphate (S1P) was significantly upregulated in glioma cultures following suppression of IDH1mut activity. We exploited the pathway using a small-scale, rational drug screen and identified a combination that was lethal to IDHmut cells. Our work revealed that further addition of N,N-dimethylsphingosine in combination with sphingosine C17 triggered a dose-dependent biostatic and apoptotic response in a panel of IDH1mut glioma cell lines specifically, while it had little effect on the IDHWT cells probed here. To our knowledge, this is the first study that shows how altering the sphingolipid pathway in IDH1mut gliomas elucidates susceptibility that can arrest proliferation and initiate subsequent cellular death.

Metabolic Landscape of a Genetically Engineered Mouse Model of IDH1 Mutant Glioma

Understanding the metabolic reprogramming of aggressive brain tumors has potential applications for therapeutics as well as imaging biomarkers. However, little is known about the nutrient requirements of isocitrate dehydrogenase 1 (IDH1) mutant gliomas. The IDH1 mutation involves the acquisition of a neomorphic enzymatic activity which generates D-2-hydroxyglutarate from α-ketoglutarate. In order to gain insight into the metabolism of these malignant brain tumors, we conducted metabolic profiling of the orthotopic tumor and the contralateral regions for the mouse model of IDH1 mutant glioma; as well as to examine the utilization of glucose and glutamine in supplying major metabolic pathways such as glycolysis and tricarboxylic acid (TCA). We also revealed that the main substrate of 2-hydroxyglutarate is glutamine in this model, and how this re-routing impairs its utilization in the TCA. Our 13C tracing analysis, along with hyperpolarized magnetic resonance experiments, revealed an active glycolytic pathway similar in both regions (tumor and contralateral) of the brain. Therefore, we describe the reprogramming of the central carbon metabolism associated with the IDH1 mutation in a genetically engineered mouse model which reflects the tumor biology encountered in glioma patients.

Glutaminase-1 (GLS1) inhibition limits metastatic progression in osteosarcoma

BACKGROUND

Osteosarcoma (OS) is a malignant bone tumor that often develops during the period of rapid growth associated with adolescence. Despite successful primary tumor control accompanied by adjuvant chemotherapy, death from pulmonary metastases occurs in approximately 30% of patients within 5 years. As overall survival in patients remains unchanged over the last 30 years, urgent needs for novel therapeutic strategies exist. Cancer metastasis is characterized by complex molecular events which result from alterations in gene and protein expression/function. Recent studies suggest that metabolic adaptations, or "metabolic reprogramming," may similarly contribute to cancer metastasis. The goal of this study was to specifically interrogate the metabolic vulnerabilities of highly metastatic OS cell lines in a series of in vitro and in vivo experiments, in order to identify a tractable metabolically targeted therapeutic strategy for patients.

METHODS

Nutrient deprivation and drug treatment experiments were performed in MG63.3, 143B, and K7M2 OS cell lines to identify the impact of glutaminase-1 (GLS1) inhibition and metformin treatment on cell proliferation. We functionally validated the impact of drug treatment with extracellular flux analysis, nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry. 13C-glucose and 13C-glutamine tracing was employed to identify specific contributions of these nutrients to the global metabolic profiles generated with GLS1 inhibition and metformin treatment in vivo.

RESULTS

Highly metastatic OS cell lines require glutamine for proliferation, and exposure to CB-839, in combination with metformin, induces both primary tumor growth inhibition and a distinct reduction in metastatic outgrowth in vivo. Further, combination-treated OS cells showed a reduction in cellular mitochondrial respiration, while NMR confirmed the pharmacodynamic effects of glutaminase inhibition in tumor tissues. We observed global decreases in glycolysis and tricarboxylic acid (TCA) cycle functionality, alongside an increase in fatty acid oxidation and pyrimidine catabolism.

CONCLUSIONS

This data suggests combination-treated cells cannot compensate for metformin-induced electron transport chain inhibition by upregulating glutaminolysis to generate TCA cycle intermediates required for cell proliferation, translating into significant reductions in tumor growth and metastatic progression. This therapeutic approach could be considered for future clinical development for OS patients presenting with or at high risk of developing metastasis.

CBMT-07. BIOMARKERS OF AGGRESSIVENESS IN IDH MUTANT GLIOMA

BACKGROUND

Gliomas with isocitrate dehydrogenase (IDH) mutations in adults evolve from lower-grade gliomas to secondary glioblastomas (GBM), a fatal disease with fast progression. IDH mutation occurs early in tumorigenesis, and persistently contribute to the reprograming of glucose, lipid and amino acid metabolism. This offer a plethora of potential biomarkers of progression. However, because it is extremely difficult to detect the distribution and transfer of metabolites changing in every moment in a single cell, the involvement of metabolites produced by mutant IDH in malignant progression remains understudied.

MATERIALS AND METHODS

Raman imaging spectroscopy, which can image chemical bonds and concentration of molecules at submicron spatial resolution, enables detection of spatiotemporal changes of metabolomes in live cells. We developed the software called Biomolecular Component Analysis (BCAbox) to deconvolute the recorded raw Raman spectra, leading to detection of unique spectral features of different classes of biomolecules.

RESULTS AND CONCLUSIONS

We applied Raman imaging spectroscopy to GBM cell lines that were transfected with IDH1 mutant gene. Our results indicated that lipid metabolism has a unique profile in IDH1 mutant gliomas. Subsequent mass spectrometry analysis of extracted organelle revealed the exact classes of lipids altered in the IDH mutant glioma and suggested biomarkers unique to IDH1 mutant. We will report our validation studies of the biomarkers in patient-derived IDH mutant glioma cell lines and patients derived-orthotopic xenograft mouse models with different degrees of aggressiveness and in matched primary versus recurrent gliomas. The results of the present study may provide novel insights into the discovery of metabolic biomarkers for the malignant progression in IDH mutant gliomas.

Targeting Glycolysis through Inhibition of Lactate Dehydrogenase Impairs Tumor Growth in Preclinical Models of Ewing Sarcoma

Altered cellular metabolism, including an increased dependence on aerobic glycolysis, is a hallmark of cancer. Despite the fact that this observation was first made nearly a century ago, effective therapeutic targeting of glycolysis in cancer has remained elusive. One potentially promising approach involves targeting the glycolytic enzyme lactate dehydrogenase (LDH), which is overexpressed and plays a critical role in several cancers. Here, we used a novel class of LDH inhibitors to demonstrate, for the first time, that Ewing sarcoma cells are exquisitely sensitive to inhibition of LDH. EWS-FLI1, the oncogenic driver of Ewing sarcoma, regulated LDH A (LDHA) expression. Genetic depletion of LDHA inhibited proliferation of Ewing sarcoma cells and induced apoptosis, phenocopying pharmacologic inhibition of LDH. LDH inhibitors affected Ewing sarcoma cell viability both in vitro and in vivo by reducing glycolysis. Intravenous administration of LDH inhibitors resulted in the greatest intratumoral drug accumulation, inducing tumor cell death and reducing tumor growth. The major dose-limiting toxicity observed was hemolysis, indicating that a narrow therapeutic window exists for these compounds. Taken together, these data suggest that targeting glycolysis through inhibition of LDH should be further investigated as a potential therapeutic approach for cancers such as Ewing sarcoma that exhibit oncogene-dependent expression of LDH and increased glycolysis. SIGNIFICANCE: LDHA is a pharmacologically tractable EWS-FLI1 transcriptional target that regulates the glycolytic dependence of Ewing sarcoma.

A high-throughput screening campaign to identify inhibitors of DXP reductoisomerase (IspC) and MEP cytidylyltransferase (IspD)

The rise of antibacterial resistance among human pathogens represents a problem that could change the landscape of healthcare unless new antibiotics are developed. The methyl erythritol phosphate (MEP) pathway represents an attractive series of targets for novel antibiotic design, considering each enzyme of the pathway is both essential and has no human homologs. Here we describe a pilot scale high-throughput screening (HTS) campaign against the first and second committed steps in the pathway, catalyzed by DXP reductoisomerase (IspC) and MEP cytidylyltransferase (IspD), using compounds present in the commercially available LOPAC1280 library as well as in an in-house natural product extract library. Hit compounds were characterized to deduce their mechanism of inhibition; most function through aggregation. The HTS workflow outlined here is useful for quickly screening a chemical library, while effectively identifying false positive compounds associated with assay constraints and aggregation.

Chemopreventive Metabolites Are Correlated with a Change in Intestinal Microbiota Measured in A-T Mice and Decreased Carcinogenesis

Intestinal microbiota play a significant role in nutrient metabolism, modulation of the immune system, obesity, and possibly in carcinogenesis, although the underlying mechanisms resulting in disease or impacts on longevity caused by different intestinal microbiota are mostly unknown. Herein we use isogenic Atm-deficient and wild type mice as models to interrogate changes in the metabolic profiles of urine and feces of these mice, which are differing in their intestinal microbiota. Using high resolution mass spectrometry approach we show that the composition of intestinal microbiota modulates specific metabolic perturbations resulting in a possible alleviation of a glycolytic phenotype. Metabolites including 3-methylbutyrolactone, kyneurenic acid and 3-methyladenine known to be onco-protective are elevated in Atm-deficient and wild type mice with restricted intestinal microbiota. Thus our approach has broad applicability to study the direct influence of gut microbiome on host metabolism and resultant phenotype. These results for the first time suggest a possible correlation of metabolic alterations and carcinogenesis, modulated by intestinal microbiota in A-T mice.

Kinetic characterization and allosteric inhibition of the Yersinia pestis 1-deoxy-D-xylulose 5-phosphate reductoisomerase (MEP synthase)

The methylerythritol phosphate (MEP) pathway found in many bacteria governs the synthesis of isoprenoids, which are crucial lipid precursors for vital cell components such as ubiquinone. Because mammals synthesize isoprenoids via an alternate pathway, the bacterial MEP pathway is an attractive target for novel antibiotic development, necessitated by emerging antibiotic resistance as well as biodefense concerns. The first committed step in the MEP pathway is the reduction and isomerization of 1-deoxy-D-xylulose-5-phosphate (DXP) to methylerythritol phosphate (MEP), catalyzed by MEP synthase. To facilitate drug development, we cloned, expressed, purified, and characterized MEP synthase from Yersinia pestis. Enzyme assays indicate apparent kinetic constants of KMDXP = 252 µM and KMNADPH = 13 µM, IC50 values for fosmidomycin and FR900098 of 710 nM and 231 nM respectively, and Ki values for fosmidomycin and FR900098 of 251 nM and 101 nM respectively. To ascertain if the Y. pestis MEP synthase was amenable to a high-throughput screening campaign, the Z-factor was determined (0.9) then the purified enzyme was screened against a pilot scale library containing rationally designed fosmidomycin analogs and natural product extracts. Several hit molecules were obtained, most notably a natural product allosteric affector of MEP synthase and a rationally designed bisubstrate derivative of FR900098 (able to associate with both the NADPH and DXP binding sites in MEP synthase). It is particularly noteworthy that allosteric regulation of MEP synthase has not been described previously. Thus, our discovery implicates an alternative site (and new chemical space) for rational drug development.