Suppression of angiopoietin-like 4 reprograms endothelial cell metabolism and inhibits angiogenesis

Angiopoietin-like 4 (ANGPTL4) is known to regulate various cellular and systemic functions. However, its cell-specific role in endothelial cells (ECs) function and metabolic homeostasis remains to be elucidated. Here, using endothelial-specific Angptl4 knock-out mice (Angptl4iΔEC), and transcriptomics and metabolic flux analysis, we demonstrate that ANGPTL4 is required for maintaining EC metabolic function vital for vascular permeability and angiogenesis. Knockdown of ANGPTL4 in ECs promotes lipase-mediated lipoprotein lipolysis, which results in increased fatty acid (FA) uptake and oxidation. This is also paralleled by a decrease in proper glucose utilization for angiogenic activation of ECs. Mice with endothelial-specific deletion of Angptl4 showed decreased pathological neovascularization with stable vessel structures characterized by increased pericyte coverage and reduced permeability. Together, our study denotes the role of endothelial-ANGPTL4 in regulating cellular metabolism and angiogenic functions of EC.

UCP2-dependent redox sensing in POMC neurons regulates feeding

Paradoxically, glucose, the primary driver of satiety, activates a small population of anorexigenic pro-opiomelanocortin (POMC) neurons. Here, we show that lactate levels in the circulation and in the cerebrospinal fluid are elevated in the fed state and the addition of lactate to glucose activates the majority of POMC neurons while increasing cytosolic NADH generation, mitochondrial respiration, and extracellular pyruvate levels. Inhibition of lactate dehydrogenases diminishes mitochondrial respiration, NADH production, and POMC neuronal activity. However, inhibition of the mitochondrial pyruvate carrier has no effect. POMC-specific downregulation of Ucp2 (Ucp2PomcKO), a molecule regulated by fatty acid metabolism and shown to play a role as transporter in the malate-aspartate shuttle, abolishes lactate- and glucose-sensing of POMC neurons. Ucp2PomcKO mice have impaired glucose metabolism and are prone to obesity on a high-fat diet. Altogether, our data show that lactate through redox signaling and blocking mitochondrial glucose utilization activates POMC neurons to regulate feeding and glucose metabolism.

Comprehensive Analysis of Metabolic Isozyme Targets in Cancer

Metabolic reprogramming is a hallmark of malignant transformation, and loss of isozyme diversity (LID) contributes to this process. Isozymes are distinct proteins that catalyze the same enzymatic reaction but can have different kinetic characteristics, subcellular localization, and tissue specificity. Cancer-dominant isozymes that catalyze rate-limiting reactions in critical metabolic processes represent potential therapeutic targets. Here, we examined the isozyme expression patterns of 1,319 enzymatic reactions in 14 cancer types and their matching normal tissues using The Cancer Genome Atlas mRNA expression data to identify isozymes that become cancer-dominant. Of the reactions analyzed, 357 demonstrated LID in at least one cancer type. Assessment of the expression patterns in over 600 cell lines in the Cancer Cell Line Encyclopedia showed that these reactions reflect cellular changes instead of differences in tissue composition; 50% of the LID-affected isozymes showed cancer-dominant expression in the corresponding cell lines. The functional importance of the cancer-dominant isozymes was assessed in genome-wide CRISPR and RNAi loss-of-function screens: 17% were critical for cell proliferation, indicating their potential as therapeutic targets. Lists of prioritized novel metabolic targets were developed for 14 cancer types; the most broadly shared and functionally validated target was acetyl-CoA carboxylase 1 (ACC1). Small molecule inhibition of ACC reduced breast cancer viability in vitro and suppressed tumor growth in cell line- and patient-derived xenografts in vivo. Evaluation of the effects of drug treatment revealed significant metabolic and transcriptional perturbations. Overall, this systematic analysis of isozyme expression patterns elucidates an important aspect of cancer metabolic plasticity and reveals putative metabolic vulnerabilities.

SIGNIFICANCE

This study exploits the loss of metabolic isozyme diversity common in cancer and reveals a rich pool of potential therapeutic targets that will allow the repurposing of existing inhibitors for anticancer therapy. See related commentary by Kehinde and Parker, p. 1695.

Abstract P5-17-01: Targeting Acetyl-CoA carboxylase in pre-clinical breast cancer models

Background: Cancer cells and normal cells of the same lineage differ in their metabolism. We previously described large scale shifts in isoenzyme distribution between matching cancer and normal tissues and identified Acetyl-coA carboxylase (ACC1/ACACA) as a cancer dominant enzyme that is overexpressed in multiple cancer types. ACC1 catalyzes the initial rate-limiting step in de novo fatty acid synthesis, the conversion of acetyl-CoA to malonyl-CoA. Gene knock-out experiments demonstrated that this enzyme is essential for cancer growth. In this study, we evaluated the in vitro and in vivo efficacy of a small molecule ACC inhibitor, PF05175157 as a potential anticancer drug. This drug has been tested in clinical trials for diabetes, but development was discontinued due to grade 2 thrombocytopenia.Methods: We performed in vitro cytotoxicity assays in 15 breast cancer cell lines and in normal mammary epithelial HMEC cells, examined effect on apoptosis and cell cycle progression, and tested for synergy with alpelisib, docetaxel, doxorubicin, everolimus, iniparib, neratinib and TEPP46 (PKM2 and PKLR activator). We next assessed in vivo single agent activity in a triple negative patient derived (PDX) model (J000102184) in NSGTM mice and in MDAMB468 xenografts implanted into Rag2/IL2RG double knockout mice. We performed RNA sequencing and metabolomic profiling of cells treated with PF05175157 to study metabolic and transcriptomic effects of the drug. Results: PF05175157 induced time and dose dependent growth inhibition in all but 1 of the 15 cancer cell lines. The estimated EC50 after 72h exposure ranged from 0.95 to 76 μg/mL in T47D and BT549 cells, respectively (Cmax of 20 μg/mL can be achieved in human serum). There was no significant inhibitory effect on HMEC cells. In cancer cell lines, the % of apoptotic cells increased from 4% to 8% in BT474 and from 7.7% to 17.8% in MDMBA468 cells upon treatment with the compound, and there was a trend towards G2/M cell cycle arrest in both cell lines after 72 hours of exposure (10μg/mL). In drug combination experiments, PF05175157 added to iniparib, or to the PKM2 activator, TEPP46, decreased cell viability compared to single agent therapies in several cell lines. PF05175157 significantly delayed tumor growth compared to vehicle, when administered orally (20mg/kg gavage BID) in a TNBC PDX model (median tumor volume after 33 days: 334.1 mm3 in PF05175157-treated vs. 490.5 mm3 in methylcellulose-treated mice; p=3.39e-7) and intraperitoneally (20 mg/kg in DMSO) in an MDAMB468 xenograft model (median tumor volume after 40 days: 244.5 mm3 in PF05175157-treated vs. 303.3 mm3 in DMSO-treated mice; p<0.05). Transcriptomic and metabolic profiling of MDAMB468 and BT474 cells treated with 10 ug/ml PF05175157 for 6 and 24 hours revealed activation of immune signaling, epigenetic regulation and DNA damage repair pathways along with down-regulation of a broad range of metabolic pathways. Conclusions: The small molecule ACC inhibitor, PF05175157, has significant single agent in vitro and in vivo growth inhibitory effect on a range of breast cancer cell lines at concentrations that can be achieved in human serum. It showed synergy with iniparib and another metabolic inhibitor (TEPP46). Targeting de novo fatty acid synthesis by inhibiting ACC is a promising therapeutic strategy.

Citation Format: Julia Foldi, Michal Marczyk, Vignesh Gunasekharan, Tao Qing, Raghav Sehgal, Naing Lin Shan, Viswanathan Muthusamy, Sheila Umlau, Yulia V. Surovtseva, Richard Kibbey, Lajos Pusztai. Targeting Acetyl-CoA carboxylase in pre-clinical breast cancer models [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-17-01.

A Single Virtual Consult Reduces Severe Hyperglycemia in Patients Admitted with COVID19 Infection

Diabetes and hyperglycemia are risk factors for morbidity and mortality in hospitalized patients with COVID19. Subspecialty consultative resources to help front-line clinicians treat these conditions is often limited. We implemented a “Virtual Hyperglycemia Surveillance Service (VHSS)” to guide glucose management in COVID19 patients admitted to our 1541-bed academic medical center.

From April 22 to June 9, 2020, hospitalized adult patients with COVID19 and 2 or more blood glucose (BG) values greater than 250 mg/dl over 24-h were identified using a daily BG report. The VHSS reviewed BGs and treatment plans, then made recommendations for future glycemic management via a one-time note, visible to all providers. Some patients with re-admission or persistently elevated BG after 1 week received a second VHSS note. We compared BGs from 24-h pre- and 72-h post-intervention starting at 6AM on the day following VHSS review. We also evaluated for hypoglycemia, insulin infusion use and use of formal diabetes consults. A subgroup analysis was performed on patients in the intensive care unit (ICU). At the end of the intervention, we identified a retrospective control cohort admitted to the same hospital from March 21 to April 21, 2020 who met the inclusion criteria for a VHSS assessment.

The VHSS group consisted of 100 patients with 126 individual VHSS encounters, and the control group comprised 50 patients. Baseline characteristics in the VHSS and control groups, respectively, were: mean age 62.5 vs 62.1 years, % male 58 vs 56, mean weight 91.4 vs 93.4 kg, BMI 31.8 vs 33.0 kg/m², and HbA1c 9.1 vs 8.8 %. There were fewer patients in the ICU in the VHSS than control group (44% vs 66%). In the VHSS group, mean BG pre- vs. post-intervention was 260.3 ±21.7 and 227.4 ±25.3 mg/dl (p<0.001). In the control group, mean BG pre-and post- the day they met assessment criteria was 264.8 ± 6.5 mg/dl and 250.6 ± 8.6 mg/dl (p=0.18). There was no difference in the use of insulin infusions or diabetes consults between the two groups. More hypoglycemia (BG<70 mg/dl) occurred in the VHSS than control group (8.3% vs 0%, p=0.04). Within the VHSS group, the average change in BG was significantly greater in ICU than non-ICU patients (-51.8 ±8.7 vs -19.6 ±5.0 mg/dl, p<0.01) and the reduction in the % of BG over 250 mg/dl was also significantly greater in the ICU (-32.2% vs -16.8%, p=0.02).

Implementation of a single virtual consult for severely hyperglycemic hospitalized COVID19 patients was associated with rapidly reduced BG concentrations, especially in the ICU. The mean reduction in BG with VHSS intervention was more than 2-fold greater than that observed in our control group. Glucose control remained suboptimal, however, suggesting the need for subsequent input from this specialty service.

Glutamate is a positive autocrine signal for glucagon release

An important feature of glucose homeostasis is the effective release of glucagon from the pancreatic alpha cell. The molecular mechanisms regulating glucagon secretion are still poorly understood. We now demonstrate that human alpha cells express ionotropic glutamate receptors (iGluRs) that are essential for glucagon release. A lowering in glucose concentration results in the release of glutamate from the alpha cell. Glutamate then acts on iGluRs of the AMPA/kainate type, resulting in membrane depolarization, opening of voltage-gated Ca(2+) channels, increase in cytoplasmic free Ca(2+) concentration, and enhanced glucagon release. In vivo blockade of iGluRs reduces glucagon secretion and exacerbates insulin-induced hypoglycemia in mice. Hence, the glutamate autocrine feedback loop endows the alpha cell with the ability to effectively potentiate its own secretory activity. This is a prerequisite to guarantee adequate glucagon release despite relatively modest changes in blood glucose concentration under physiological conditions.

Mitochondrial dysfunction due to long-chain Acyl-CoA dehydrogenase deficiency causes hepatic steatosis and hepatic insulin resistance

Alterations in mitochondrial function have been implicated in the pathogenesis of insulin resistance and type 2 diabetes. However, it is unclear whether the reduced mitochondrial function is a primary or acquired defect in this process. To determine whether primary defects in mitochondrial beta-oxidation can cause insulin resistance, we studied mice with a deficiency of long-chain acyl-CoA dehydrogenase (LCAD), a key enzyme in mitochondrial fatty acid oxidation. Here, we show that LCAD knockout mice develop hepatic steatosis, which is associated with hepatic insulin resistance, as reflected by reduced insulin suppression of hepatic glucose production during a hyperinsulinemic-euglycemic clamp. The defects in insulin action were associated with an approximately 40% reduction in insulin-stimulated insulin receptor substrate-2-associated phosphatidylinositol 3-kinase activity and an approximately 50% decrease in Akt2 activation. These changes were associated with increased PKCepsilon activity and an aberrant 4-fold increase in diacylglycerol content after insulin stimulation. The increase in diacylglycerol concentration was found to be caused by de novo synthesis of diacylglycerol from medium-chain acyl-CoA after insulin stimulation. These data demonstrate that primary defects in mitochondrial fatty acid oxidation capacity can lead to diacylglycerol accumulation, PKCepsilon activation, and hepatic insulin resistance.