Pharmacokinetics and pharmacodynamics of mibavademab (a leptin receptor agonist): Results from a first-in-human phase I study.

Mibavademab (previously known as REGN4461), a fully human monoclonal antibody, is being investigated for the treatment of conditions associated with leptin deficiency. Here, we report pharmacokinetics (PKs), pharmacodynamics, and immunogenicity from a phase I study in healthy participants (NCT03530514). In part A, lean or overweight healthy participants were randomized to single-ascending-dose cohorts of 0.3, 1.0, 3.0, 10, and 30 mg/kg intravenous (i.v.), or 300 and 600 mg subcutaneous doses of mibavademab or placebo. In part B, overweight or obese participants were randomized to receive multiple doses of mibavademab (15 mg/kg i.v. loading dose and 10 mg/kg i.v. at weeks 3, 6, and 9) or placebo, stratified by body mass index and baseline leptin levels: low leptin (<5 ng/mL) or relatively low leptin (5-8 ng/mL in men and 5-24 ng/mL in women). Fifty-six and 55 participants completed the single-ascending-dose and multiple-dose parts, respectively. In the single-ascending-dose cohorts, mibavademab PKs were nonlinear with target-mediated elimination, greater than dose-proportional increases in exposure, and there were no dose-dependent differences in total soluble leptin receptor (sLEPR) levels in serum over time. Following multiple-dose administration of mibavademab in participants with leptin <8 ng/mL, lower mean mibavademab concentrations, higher mean total sLEPR concentrations, and larger mean decreases in body weight than in the relatively low leptin cohorts were observed. Baseline leptin was correlated with mibavademab PKs and pharmacodynamics. No treatment-emergent anti-mibavademab antibodies were observed in any mibavademab-treated participant. Results from this study collectively inform further development of mibavademab to treat conditions associated with leptin deficiency.

Preclinical, randomized phase 1, and compassionate use evaluation of REGN4461, a leptin receptor agonist antibody for leptin deficiency.

Deficiency in the adipose-derived hormone leptin or leptin receptor signaling causes class 3 obesity in individuals with genetic loss-of-function mutations in leptin or its receptor LEPR and metabolic and liver disease in individuals with hypoleptinemia secondary to lipoatrophy such as in individuals with generalized lipodystrophy. Therapies that restore leptin-LEPR signaling may resolve these metabolic sequelae. We developed a fully human monoclonal antibody (mAb), REGN4461 (mibavademab), that activates the human LEPR in the absence or presence of leptin. In obese leptin knockout mice, REGN4461 normalized body weight, food intake, blood glucose, and insulin sensitivity. In a mouse model of generalized lipodystrophy, REGN4461 alleviated hyperphagia, hyperglycemia, insulin resistance, dyslipidemia, and hepatic steatosis. In a phase 1, randomized, double-blind, placebo-controlled two-part study, REGN4461 was well tolerated with an acceptable safety profile. Treatment of individuals with overweight or obesity with REGN4461 decreased body weight over 12 weeks in those with low circulating leptin concentrations (<8 ng/ml) but had no effect on body weight in individuals with higher baseline leptin. Furthermore, compassionate-use treatment of a single patient with atypical partial lipodystrophy and a history of undetectable leptin concentrations associated with neutralizing antibodies to metreleptin was associated with noteable improvements in circulating triglycerides and hepatic steatosis. Collectively, these translational data unveil an agonist LEPR mAb that may provide clinical benefit in disorders associated with relatively low leptin concentrations.

MYC overrides HIF-1α to regulate proliferating primary cell metabolism in hypoxia.

Hypoxia requires metabolic adaptations to sustain energetically demanding cellular activities. While the metabolic consequences of hypoxia have been studied extensively in cancer cell models, comparatively little is known about how primary cell metabolism responds to hypoxia. Thus, we developed metabolic flux models for human lung fibroblast and pulmonary artery smooth muscle cells proliferating in hypoxia. Unexpectedly, we found that hypoxia decreased glycolysis despite activation of hypoxia-inducible factor 1α (HIF-1α) and increased glycolytic enzyme expression. While HIF-1α activation in normoxia by prolyl hydroxylase (PHD) inhibition did increase glycolysis, hypoxia blocked this effect. Multi-omic profiling revealed distinct molecular responses to hypoxia and PHD inhibition, and suggested a critical role for MYC in modulating HIF-1α responses to hypoxia. Consistent with this hypothesis, MYC knockdown in hypoxia increased glycolysis and MYC over-expression in normoxia decreased glycolysis stimulated by PHD inhibition. These data suggest that MYC signaling in hypoxia uncouples an increase in HIF-dependent glycolytic gene transcription from glycolytic flux.

Sulfide catabolism ameliorates hypoxic brain injury.

The mammalian brain is highly vulnerable to oxygen deprivation, yet the mechanism underlying the brain's sensitivity to hypoxia is incompletely understood. Hypoxia induces accumulation of hydrogen sulfide, a gas that inhibits mitochondrial respiration. Here, we show that, in mice, rats, and naturally hypoxia-tolerant ground squirrels, the sensitivity of the brain to hypoxia is inversely related to the levels of sulfide:quinone oxidoreductase (SQOR) and the capacity to catabolize sulfide. Silencing SQOR increased the sensitivity of the brain to hypoxia, whereas neuron-specific SQOR expression prevented hypoxia-induced sulfide accumulation, bioenergetic failure, and ischemic brain injury. Excluding SQOR from mitochondria increased sensitivity to hypoxia not only in the brain but also in heart and liver. Pharmacological scavenging of sulfide maintained mitochondrial respiration in hypoxic neurons and made mice resistant to hypoxia. These results illuminate the critical role of sulfide catabolism in energy homeostasis during hypoxia and identify a therapeutic target for ischemic brain injury.

Myocarditis in the Setting of Cancer Therapeutics: Proposed Case Definitions for Emerging Clinical Syndromes in Cardio-Oncology

Recent developments in cancer therapeutics have improved outcomes but have also been associated with cardiovascular complications. Therapies harnessing the immune system have been associated with an immune-mediated myocardial injury described as myocarditis. Immune checkpoint inhibitors are one such therapy with an increasing number of case and cohort reports describing a clinical syndrome of immune checkpoint inhibitor­associated myocarditis. Although the full spectrum of immune checkpoint inhibitor­associated cardiovascular disease still needs to be fully defined, described cases of myocarditis range from syndromes with mild signs and symptoms to fatal events. These observations in the clinical setting stand in contrast to outcomes from randomized clinical trials in which myocarditis is a rare event that is investigator reported and lacking in a specific case definition. The complexities associated with diagnosis, as well as the heterogeneous clinical presentation of immune checkpoint inhibitor­associated myocarditis, have made ascertainment and identification of myocarditis with high specificity challenging in clinical trials and other data sets, limiting the ability to better understand the incidence, outcomes, and predictors of these rare events. Therefore, establishing a uniform definition of myocarditis for application in clinical trials of cancer immunotherapies will enable greater understanding of these events. We propose an operational definition of cancer therapy-associated myocarditis that may facilitate case ascertainment and report and therefore may enhance the understanding of the incidence, outcomes, and risk factors of this novel clinical syndrome.

Histone demethylase KDM6A directly senses oxygen to control chromatin and cell fate.

Oxygen sensing is central to metazoan biology and has implications for human disease. Mammalian cells express multiple oxygen-dependent enzymes called 2-oxoglutarate (OG)-dependent dioxygenases (2-OGDDs), but they vary in their oxygen affinities and hence their ability to sense oxygen. The 2-OGDD histone demethylases control histone methylation. Hypoxia increases histone methylation, but whether this reflects direct effects on histone demethylases or indirect effects caused by the hypoxic induction of the HIF (hypoxia-inducible factor) transcription factor or the 2-OG antagonist 2-hydroxyglutarate (2-HG) is unclear. Here, we report that hypoxia promotes histone methylation in a HIF- and 2-HG-independent manner. We found that the H3K27 histone demethylase KDM6A/UTX, but not its paralog KDM6B, is oxygen sensitive. KDM6A loss, like hypoxia, prevented H3K27 demethylation and blocked cellular differentiation. Restoring H3K27 methylation homeostasis in hypoxic cells reversed these effects. Thus, oxygen directly affects chromatin regulators to control cell fate.

Transaminase Inhibition by 2-Hydroxyglutarate Impairs Glutamate Biosynthesis and Redox Homeostasis in Glioma.

IDH1 mutations are common in low-grade gliomas and secondary glioblastomas and cause overproduction of (R)-2HG. (R)-2HG modulates the activity of many enzymes, including some that are linked to transformation and some that are probably bystanders. Although prior work on (R)-2HG targets focused on 2OG-dependent dioxygenases, we found that (R)-2HG potently inhibits the 2OG-dependent transaminases BCAT1 and BCAT2, likely as a bystander effect, thereby decreasing glutamate levels and increasing dependence on glutaminase for the biosynthesis of glutamate and one of its products, glutathione. Inhibiting glutaminase specifically sensitized IDH mutant glioma cells to oxidative stress in vitro and to radiation in vitro and in vivo. These findings highlight the complementary roles for BCATs and glutaminase in glutamate biosynthesis, explain the sensitivity of IDH mutant cells to glutaminase inhibitors, and suggest a strategy for maximizing the effectiveness of such inhibitors against IDH mutant gliomas.

The circulating metabolome of human starvation.

The human adaptive starvation response allows for survival during long-term caloric deprivation. Whether the physiology of starvation is adaptive or maladaptive is context dependent: activation of pathways by caloric restriction may promote longevity, yet in the context of caloric excess, the same pathways may contribute to obesity. Here, we performed plasma metabolite profiling of longitudinally collected samples during a 10-day, 0-calorie fast in humans. We identify classical milestones in adaptive starvation, including the early consumption of gluconeogenic amino acids and the subsequent surge in plasma nonesterified fatty acids that marks the shift from carbohydrate to lipid metabolism, and demonstrate findings, including (a) the preferential release of unsaturated fatty acids and an associated shift in plasma lipid species with high degrees of unsaturation and (b) evidence that acute, starvation-mediated hypoleptinemia may be a driver of the transition from glucose to lipid metabolism in humans.

Autochthonous tumors driven by Rb1 loss have an ongoing requirement for the RBP2 histone demethylase.

Inactivation of the retinoblastoma gene (RB1) product, pRB, is common in many human cancers. Targeting downstream effectors of pRB that are central to tumorigenesis is a promising strategy to block the growth of tumors harboring loss-of-function RB1 mutations. One such effector is retinoblastoma-binding protein 2 (RBP2, also called JARID1A or KDM5A), which encodes an H3K4 demethylase. Binding of pRB to RBP2 has been linked to the ability of pRB to promote senescence and differentiation. Importantly, genetic ablation of RBP2 is sufficient to phenocopy pRB's ability to induce these cellular changes in cell culture experiments. Moreover, germline Rbp2 deletion significantly impedes tumorigenesis in Rb1+/- mice. The value of RBP2 as a therapeutic target in cancer, however, hinges on whether loss of RBP2 could block the growth of established tumors as opposed to simply delaying their onset. Here we show that conditional, systemic ablation of RBP2 in tumor-bearing Rb1+/- mice is sufficient to slow tumor growth and significantly extend survival without causing obvious toxicity to the host. These findings show that established Rb1-null tumors require RBP2 for growth and further credential RBP2 as a therapeutic target in human cancers driven by RB1 inactivation.

Prolyl Hydroxylase Domain-2 Inhibition Improves Skeletal Muscle Regeneration in a Male Murine Model of Obesity.

Obesity leads to a loss of muscle mass and impaired muscle regeneration. In obese individuals, pathologically elevated levels of prolyl hydroxylase domain enzyme 2 (PHD2) limit skeletal muscle hypoxia-inducible factor-1 alpha and vascular endothelial growth factor (VEGF) expression. Loss of local VEGF may further impair skeletal muscle regeneration. We hypothesized that PHD2 inhibition would restore vigorous muscle regeneration in a murine model of obesity. Adult (22-week-old) male mice were fed either a high-fat diet (HFD), with 60% of calories derived from fat, or a regular diet (RD), with 10% of calories derived from fat, for 16 weeks. On day 5 following cryoinjury to the tibialis anterior muscle, newly regenerated muscle fiber cross-sectional areas were significantly smaller in mice fed an HFD as compared to RD, indicating an impaired regenerative response. Cryoinjured gastrocnemius muscles of HFD mice also showed elevated PHD2 levels (twofold higher) and reduced VEGF levels (twofold lower) as compared to RD. Dimethyloxalylglycine, a cell permeable competitive inhibitor of PHD2, restored VEGF levels and significantly improved regenerating myofiber size in cryoinjured mice fed an HFD. We conclude that pathologically increased PHD2 in the obese state drives impairments in muscle regeneration, in part by blunting VEGF production. Inhibition of PHD2 over activity in the obese state normalizes VEGF levels and restores muscle regenerative potential.

Biochemical Underpinnings of Immune Cell Metabolic Phenotypes.

The metabolism of immune cells affects their function and influences host immunity. This review explores how immune cell metabolic phenotypes reflect biochemical dependencies and highlights evidence that both the metabolic state of immune cells and nutrient availability can alter immune responses. The central importance of oxygen, energetics, and redox homeostasis in immune cell metabolism, and how these factors are reflected in different metabolic phenotypes, is also discussed. Linking immune cell metabolic phenotype to effector functions is important to understand how altering metabolism can impact the way in which immune cells meet their metabolic demands and affect the immune response in various disease contexts.

Exploring effects of remote ischemic preconditioning in a pig model of hypothermic circulatory arrest.

OBJECTIVES: During aortic and cardiac surgery, risks for mortality and morbidity are inevitable. Surgical setups involving deep hypothermic circulatory arrest (DHCA) are effective to achieve organ protection against ischemic injury. The aim of this study was to identify humoural factors mediating additive protective effects of remote ischemic preconditioning (RIPC) in a porcine model of DHCA. DESIGN: Twenty-two pigs were randomized into the RIPC group (n = 11) and the control group (n = 11). The RIPC group underwent four 5-minute hind limb ischemia-reperfusion cycles prior to cardiopulmonary bypass and DHCA. All animals underwent identical surgical procedures including 60 min DHCA at 18 °C. Blood samples were collected from vena cava and sagittal sinus at several time points. After the 8-hour follow-up period, the brain, heart, and kidney tissue samples were collected for tissue analyses. RESULTS: Serum levels of brain damage marker S100B recovered faster in the RIPC group, after 4 hours of the arrest, (p < .05). Systemic lactate levels were lower and cardiac index was higher in the RIPC group postoperatively. Immunohistochemical cerebellum regional scores of antioxidant response regulator Nrf2 were better in the RIPC group (mean: 1.1, IQR: 0.0-2.5) compared with the control group (mean: 0.0, IQR: 0.0-0.0), reaching borderline statistical significance (p = .064). RIPC induced detectable modulations of plasma proteome and metabolites. CONCLUSIONS: The faster recovery of S100B, lower systemic lactate levels and favourable regional antioxidant response suggest possible neuronal cellular and mitochondrial protection by RIPC, whereas better cardiac index underlines functional effects of RIPC. The exact humoural factor remains unclear.

Fulminant Myocarditis with Combination Immune Checkpoint Blockade.

Immune checkpoint inhibitors have improved clinical outcomes associated with numerous cancers, but high-grade, immune-related adverse events can occur, particularly with combination immunotherapy. We report the cases of two patients with melanoma in whom fatal myocarditis developed after treatment with ipilimumab and nivolumab. In both patients, there was development of myositis with rhabdomyolysis, early progressive and refractory cardiac electrical instability, and myocarditis with a robust presence of T-cell and macrophage infiltrates. Selective clonal T-cell populations infiltrating the myocardium were identical to those present in tumors and skeletal muscle. Pharmacovigilance studies show that myocarditis occurred in 0.27% of patients treated with a combination of ipilimumab and nivolumab, which suggests that our patients were having a rare, potentially fatal, T-cell-driven drug reaction. (Funded by Vanderbilt-Ingram Cancer Center Ambassadors and others.).

Paracrine Induction of HIF by Glutamate in Breast Cancer: EglN1 Senses Cysteine.

The HIF transcription factor promotes adaptation to hypoxia and stimulates the growth of certain cancers, including triple-negative breast cancer (TNBC). The HIFα subunit is usually prolyl-hydroxylated by EglN family members under normoxic conditions, causing its rapid degradation. We confirmed that TNBC cells secrete glutamate, which we found is both necessary and sufficient for the paracrine induction of HIF1α in such cells under normoxic conditions. Glutamate inhibits the xCT glutamate-cystine antiporter, leading to intracellular cysteine depletion. EglN1, the main HIFα prolyl-hydroxylase, undergoes oxidative self-inactivation in the absence of cysteine both in biochemical assays and in cells, resulting in HIF1α accumulation. Therefore, EglN1 senses both oxygen and cysteine.

Environment Impacts the Metabolic Dependencies of Ras-Driven Non-Small Cell Lung Cancer.

Cultured cells convert glucose to lactate, and glutamine is the major source of tricarboxylic acid (TCA)-cycle carbon, but whether the same metabolic phenotype is found in tumors is less studied. We infused mice with lung cancers with isotope-labeled glucose or glutamine and compared the fate of these nutrients in tumor and normal tissue. As expected, lung tumors exhibit increased lactate production from glucose. However, glutamine utilization by both lung tumors and normal lung was minimal, with lung tumors showing increased glucose contribution to the TCA cycle relative to normal lung tissue. Deletion of enzymes involved in glucose oxidation demonstrates that glucose carbon contribution to the TCA cycle is required for tumor formation. These data suggest that understanding nutrient utilization by tumors can predict metabolic dependencies of cancers in vivo. Furthermore, these data argue that the in vivo environment is an important determinant of the metabolic phenotype of cancer cells.

EGLN1 Inhibition and Rerouting of α-Ketoglutarate Suffice for Remote Ischemic Protection.

Ischemic preconditioning is the phenomenon whereby brief periods of sublethal ischemia protect against a subsequent, more prolonged, ischemic insult. In remote ischemic preconditioning (RIPC), ischemia to one organ protects others organs at a distance. We created mouse models to ask if inhibition of the alpha-ketoglutarate (αKG)-dependent dioxygenase Egln1, which senses oxygen and regulates the hypoxia-inducible factor (HIF) transcription factor, could suffice to mediate local and remote ischemic preconditioning. Using somatic gene deletion and a pharmacological inhibitor, we found that inhibiting Egln1 systemically or in skeletal muscles protects mice against myocardial ischemia-reperfusion (I/R) injury. Parabiosis experiments confirmed that RIPC in this latter model was mediated by a secreted factor. Egln1 loss causes accumulation of circulating αKG, which drives hepatic production and secretion of kynurenic acid (KYNA) that is necessary and sufficient to mediate cardiac ischemic protection in this setting.

Outcomes in patients undergoing percutaneous ventricular assist device implantation for cardiogenic shock.

BACKGROUND: Percutaneous ventricular assist devices (PVADs) offer an important but resource-intensive option for management of severe cardiogenic shock (CS). Optimal selection of patients for PVAD support remains undefined. We investigated outcomes, including characteristics associated with in-hospital survival, during PVAD support for CS. METHODS: We established a prospective quality improvement program among patients undergoing TandemHeart PVAD implantation for CS at Brigham and Women's Hospital (Boston, MA). We evaluated 65 consecutive patients between 2006 and 2014, analyzing demographic, clinical, laboratory, hemodynamic, and survival data. RESULTS: Thirty-two patients (49.2%) survived to hospital discharge, of which 12 received destination surgical therapy. Baseline characteristics associated with survival included younger age (47 ± 15 years vs 61 ± 11 years; p<0.001), non-ischemic cardiomyopathy (NICMP) vs ischemic CMP (survival 70.4% vs 34.2%, p=0.004), and, paradoxically, lower presenting left ventricular ejection fraction (LVEF) (survival 66.7% for LVEF ⩽15%, 41.2% for LVEF 16-25%, 25.0% for LVEF >25%; p=0.010). Younger age (p=0.026) and NICMP (p=0.034) remained independent predictors of survival. Twenty-four hours after PVAD placement, a more modest increase in cardiac index (⩽0.75 L/min/m(2)) was associated with higher in-hospital mortality (OR 6.3, 95% CI 1.8-22.1), as was lack of improvement in serum anion gap (⩽2 mEq/L; OR 5.1, 95% CI 1.6-16.6). CONCLUSIONS: Despite intensive care and provision of circulatory support, survival is poor in severe CS. Patients in CS with younger age and NICMP were more likely to survive to hospital discharge. Less robust hemodynamic improvement and persistent acidosis after 24 hours of PVAD support also identified patients less likely to survive.

Providing initial transthoracic echocardiography training for anesthesiologists: simulator training is not inferior to live training.

OBJECTIVE: Transthoracic echocardiography (TTE) is finding increased use in anesthesia and critical care. Efficient options for training anesthesiologists should be explored. Simulator mannequins allow for training of manual acquisition and image recognition skills and may be suitable due to ease of scheduling. The authors tested the hypothesis that training with a simulator would not be inferior to training using a live volunteer. DESIGN: Prospective, randomized trial. SETTING: University hospital. PARTICIPANTS: Forty-six anesthesia residents, fellows, and faculty. INTERVENTIONS: After preparation with a written and video tutorial, study subjects received 80 minutes of TTE training using either a simulator or live volunteer. Practical and written tests were completed before and after training to assess improvement in manual image acquisition skills and theoretic knowledge. The written test was repeated 4 weeks later. MEASUREMENTS AND MAIN RESULTS: Performance in the practical image-acquisition test improved significantly after training using both the live volunteer and the simulator, improving by 4.0 and 4.3 points out of 15, respectively. Simulator training was found not to be inferior to live training, with a mean difference of -0.30 points and 95% confidence intervals that did not cross the predefined non-inferiority margin. Performance in the written retention test also improved significantly immediately after training for both groups but declined similarly upon repeat testing 4 weeks later. CONCLUSIONS: When providing initial TTE training to anesthesiologists, training using a simulator was not inferior to using live volunteers.