Anesth Analg 2007;104:378-383
© 2007 International Anesthesia Research Society
doi: 10.1213/01.ane.0000253501.07183.2a
CRITICAL CARE AND TRAUMA
A Phase II, Double-Blind, Placebo-Controlled, Ascending-Dose Study of Eritoran (E5564), a Lipid A Antagonist, in Patients Undergoing Cardiac Surgery with Cardiopulmonary Bypass
Elliott Bennett-Guerrero, MD*,
Hilary P. Grocott, MD*,
Jerrold H. Levy, MD
,
Kevin A. Stierer, MD
,
Charles W. Hogue, MD
,
Albert T. Cheung, MD||,
Mark F. Newman, MD*,
Alison A. Carter, PhD¶,
Daniel P. Rossignol, PhD¶, and
Charles D. Collard, MD#
From the *Department of Anesthesiology, Duke University Medical Center, Durham, NC (EBG, HPG, MFN); Department of Anesthesiology, Emory University School of Medicine, Atlanta, GA (JHL); The Heart Institute at St. Joseph Medical Center, Towson, MD (KAS); Johns Hopkins University Medical School, Baltimore, MD (CWH); ||Department of Anesthesiology and Critical Care, University of Pennsylvania, Philadelphia, PA (ATC); ¶Eisai Medical Research, Ridgefield Park, NJ (AAC, DPR); #Division of Cardiovascular Anesthesiology, Baylor College of Medicine, Texas Heart® Institute, St. Luke's Episcopal Hospital, Houston, TX (CDC).
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Abstract
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BACKGROUND: Lipid A, the toxic moiety of endotoxin, is linked to multiple complications after cardiac surgery, including fever, vasodilation, and pulmonary and renal dysfunction. The lipid A antagonist eritoran (or E5564) prevents endotoxin-induced systemic inflammation in animals and humans. In this study we assessed the safety of eritoran administration in patients undergoing cardiac surgery and obtained preliminary efficacy data for the prophylaxis of endotoxin-mediated surgical complications.
METHODS: A double-blind, randomized, ascending-dose, placebo-controlled study was conducted at nine hospitals. Patients undergoing coronary artery bypass graft and/or cardiac valvular surgery with cardiopulmonary bypass were enrolled. Patients received a 4-h infusion of placebo (n = 78) vs 2 mg (n = 24), 12 mg (n = 26), or 28 mg (n = 24) of eritoran initiated approximately 1 h before cardiopulmonary bypass.
RESULTS: No significant safety concerns were identified with continuous safety monitoring, and enrollment continued to the highest prespecified dose (28 mg). No statistically significant differences were observed in most variables related to systemic inflammation or organ dysfunction/injury.
CONCLUSIONS: This Phase II safety study suggests that the administration of the novel lipid A antagonist, eritoran, is not associated with overt toxicity in cardiac surgical patients. Blocking lipid A with eritoran does not appear to confer any clear benefit to elective cardiac surgical patients.
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Introduction
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A significant portion of the morbidity and mortality after cardiac surgery has been attributed to surgery-induced inflammatory responses that result from multiple causes, including contact activation of blood with the foreign surfaces of the cardiopulmonary bypass (CPB) circuit, organ ischemia-reperfusion processes, and heparin neutralization with protamine (1). Extensive laboratory and clinical data have implicated endotoxin as an important participant in the inflammatory response to CPB surgery (2). Endotoxin, also known as lipopolysaccharide (LPS), enters the systemic circulation by leakage from the intestinal lumen during surgery, likely as a result of mesenteric hypoperfusion (3–6). Endotoxin levels are in the range of several 100 pg/mL during CPB (7), and can be as high as 12,500 pg/mL in patients undergoing left ventricular assist device insertion (8). Further evidence implicates endotoxin as one factor that may contribute to poor surgical outcome after cardiac surgery (2).
The LPS molecule is composed of a variable polysaccharide domain containing two major structural regions: the outer O-polysaccharide, or O-specific side chain, which is heterogeneous and species-specific, and the core oligosaccharide region, which is conserved between species (9). The variable polysaccharide domain is covalently bound to a diglucosamine-based acylated phospholipid known as lipid A. This lipid A portion of the molecule, which is highly conserved among bacterial species, is the portion primarily responsible for binding of LPS to receptors on various target cells, and is thus the toxic moiety of the molecule (9). The structure of LPS and its role in elaborating inflammatory cytokines have been extensively studied (10,11).
Genetic and biochemical data suggest that an interleukin (IL)-1-like receptor called toll-like receptor (TLR)-4 is the transmembrane protein receptor for LPS that mediates cellular activation (12). Eritoran is a structural analog of the lipid A portion of the LPS molecule, and was, by design, intended to be an LPS antagonist (Fig. 1). Eritoran has been shown to inhibit TLR-4-mediated cell stimulation and to be an effective inhibitor of the toxic effects of LPS in animal models of endotoxemia (13,14).
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Figure 1. Eritoran,  -d-Glucopyranose, 3-O-decyl-2-deoxy6-O-[2-deoxy3-O-](3R)-3-methoxydecyl)-6-O-methyl-2-[[(11Z)-1-oxo-11- octadecenyl) amino]-4-O-phosphono-ß-d-glucopyranosyl]-2-[(1,3-dioxotetradecyl) amino]-, 1-(dihydrogen phosphate), tetrasodium salt, molecular formula: (C66H122N2Na4O19P2) is shown next to the Lipid A portion of the LPS molecule. Structural differences between Lipid A and E5564: 1) E5564 contains four lipid chains, 2) the side chain on the 2-N- position has a ß-keto-acyl functionality, 3) the side chain at position 2'-N- is acylated with cis-vaccenic acid, 4) positions 3-O- and 3'-O- have ether-linked side chains, 5) positions 3-O- and 3'-O- have side chains 10 carbons in length, 6) carbon 3 on the 3-O- side chain does not contain a hydroxyl group, 7) carbon 3 on the 3'-O- side chain contains a methyl ether, 8) the 6'- position contains a methyl ether.
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Eritoran has been evaluated in healthy volunteers in six Phase I studies. For example, in a human endotoxemia study, healthy volunteers were randomized to receive placebo or one of three doses of eritoran (50, 100, or 250 µg) prior to challenge with a standard IV dose (4 ng/kg) of reference endotoxin (15). In contrast to placebo-treated subjects, who experienced typical manifestations of endotoxemia (e.g., fever, tachycardia, cytokinemia), those who received eritoran exhibited few or no signs and symptoms of endotoxemia in a dose-dependent manner (15).
Due to the potential for eritoran to ameliorate inflammatory responses to endotoxemia, we sought to evaluate its role in patients undergoing cardiac surgery with CPB. The primary objective of this study was to evaluate the safety of eritoran in patients undergoing cardiac surgery. A secondary objective was to obtain preliminary data on the efficacy of eritoran for the prophylaxis of endotoxin-mediated surgical complications.
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METHODS
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This was a Phase II, double-blind, prospectively randomized, placebo-controlled ascending-dose study of eritoran in patients undergoing cardiac surgery with CPB. This multicenter study was sponsored by Eisai Medical Research (Ridgefield Park, NJ), and was coordinated by the Global Perioperative Research Organization/Duke Clinical Research Institute, Durham, NC. It was conducted at nine sites in the United States between July 2003 and April 2004.
Patient Selection
After IRB approval was obtained for each site and written informed consent for each individual, patients scheduled to undergo nonemergent coronary artery bypass graft surgery and/or cardiac valve repair or replacement using CPB were enrolled. Inclusion criteria included: 1) age 45–90 yr, 2) male or nonpregnant female, and 3) patients agreeing to be available for evaluation from baseline until final evaluation 28 days after surgery. Exclusion criteria were: 1) unavailability for all follow-up visits, 2) emergent surgery, 3) refusal to accept medically indicated blood products, 4) evidence of significant hepatic disease, defined as total bilirubin >2.0 mg/dL, alanine aminotransferase or aspartate aminotransferase more than three times the upper normal limit, or international normalized ratio more than two times the upper normal limit, 5) receipt of an investigational drug or device in the previous month, 6) participation in an interventional study using procedures other than normal standard of care, 7) peripheral access for drug administration could not be established or maintained, 8) preoperative ventilatory support, 9) chronic renal failure requiring dialysis, 10) suspicion or likelihood of systemic infection or active endocarditis, 11) planned use of leukocyte-depletion filtration during surgery, 12) females of child-bearing age unwilling to continue to use effective means of birth control for at least 1 mo after infusion of study drug, and 13) any condition that would make the patient, in the opinion of the investigator or sponsor, unsuitable for the study.
Study Drug, Blinding, Randomization, and Justification of Dosing Regimens
The study drug (eritoran) was supplied by Eisai Medical Research, and stored in the investigational/research pharmacy at each study site. Placebo and each dose of eritoran were prepared in identical 100 mL IV bags. Patients, clinicians, investigators, and study personnel were blinded to study group assignment.
Before the start of surgery, subjects were randomized using a computer-generated list to receive either eritoran or placebo (1:1), according to a computerized randomization schedule (Table 1). Enrollment of the second and third eritoran dose groups (1:1 randomization with placebo) occurred only after approval by the study's Safety Committee after the review of safety data from the prior dosing regimen.
All doses were administered by infusion pump through a dedicated peripheral IV catheter. This 4-h infusion was initiated approximately 1 h before CPB initiation. Pharmacokinetic and pharmacodynamic analysis of the ex vivo data from a previous Phase I study of eritoran indicated that small doses of eritoran (0.35–3.5 mg) have a long pharmacokinetic half-life, but a short pharmacodynamic half-life (16). However, studies using larger doses of eritoran (
12 mg) indicated that longer-lasting activity is measurable, and plasma levels and pharmacodynamic activity are correlated (17,18). The lowest dose of eritoran tested in this Phase II trial (0.5 mg/h for 4 h) was approximately 2.5 times the minimum effective dose needed to completely block signs and symptoms of endotoxin exposure when endotoxin (4 ng/kg) was administered during drug infusion (15). The middle dose (3 mg/h x 4 h) has been found to block the activity of small-dose endotoxin (4 ng/kg) 8 h or more after ending drug infusion (17). The largest dose (7 mg/h x 4 h) was thought likely to provide a wide therapeutic margin of endotoxin antagonism for more than 8 h after administration and was significantly below levels found to be toxic in animal models.
Subject Assessment
Subjects underwent the following assessments: 1) physical examination, vital signs, and collection of relevant medical history and concomitant medications and treatments through postoperative day 28, 2) withdrawal of blood for liver function tests, troponin-I, creatinine, complete blood count, plasma eritoran level determination (16), and specialized inflammation-related assays (e.g., IL-6, IL-8, c-reactive protein [CRP]), 3) recording of all serious and nonserious adverse events from randomization through postoperative day 28, 4) recording of variables related to blood product transfusion, 5) recording of commonly measured postoperative variables (e.g., duration of mechanical ventilation), and 6) recording of intensive care unit and hospital length of stay and 28-day all-cause mortality. All patients were assigned a System 97 score, a validated measure of surgical risk (19).
Statistical Methods
All patients who received any amount of test medication were evaluated for safety, even if they were withdrawn from the study before completing all requirements specified in the protocol. The primary analysis was done in the intent-to-treat population, defined as all patients who received any volume of study drug.
Descriptive analyses were applied to every potential efficacy outcome. Parametric or nonparametric analyses were used to compare placebo with treatment. Two-sample t-tests were used for continuous safety end points. Binary and categorical safety end points were tested by Fisher's exact test (for fewer than five occurrences in one or more categories) or the 
2 test for more frequent observations. ANOVA for continuous outcomes and the Cochran–Mantel–Haenszel test for binary outcomes were applied to compare placebo with treatment, adjusting for dosing phase. All statistical tests were two-sided and declared significant at 
0.05. To analyze dose response, the Cochran–Armitage trend test was used for categorical outcome variables, and regression analysis for continuous variables. Plasma levels were analyzed using an appropriate population model using nonlinear mixed effect models.
Consistent with many Phase II trials, a sample size calculation was not performed, given the exploratory nature of this study.
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RESULTS
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A total of 152 patients were enrolled into the following groups: placebo (n = 78), eritoran 2 mg (n = 24), eritoran 12 mg (n = 26), and eritoran 28 mg (n = 24). Patient preoperative demographic data and medical information are listed in Table 2 (also in supplemental Table 2 available at www.anesthesia-analgesia.org). The groups were similar with regard to age, presence of comorbid medical conditions, and preoperative renal function. System 97 Scores were similar in all four groups, and did not reveal a very high risk population, which is consistent with the fact that there was only one death within the 28-day study period (eritoran 28 mg group). Operative variables are listed in Table 3. The operative procedures performed, the percent of patients receiving aprotinin, duration of CPB, and duration of aortic cross-clamping were all similar among the randomized groups. Nadir temperature during CPB was significantly lower in the 2 mg eritoran group.
Postoperative peak temperature and serum markers of systemic inflammation are listed in Table 4. Eritoran plasma levels were significantly different among dosing groups at all three time points tested. Plasma levels of CRP, IL-6, and IL-8 increased in the postoperative period, but with a few exceptions no statistically significant differences were observed between placebo- and eritoran-treated subjects. Changes in IL-6 levels at the 4-hour time point as well as clinically significant fever (requiring treatment) appeared to be lower in eritoran-treated subjects.
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Table 4. Postoperative Temperature, Leukocyte Count, Systemic Inflammatory Markers, and Eritoran Plasma Levels for Placebo and Eritoran Study Groups
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There were no significant differences among groups in the volumes of IV fluids and blood products administered during the first 24 h, the duration of mechanical ventilation, the incidence of infections or arrhythmias, or the duration of intensive care unit or hospital length of stay (Table 5 and supplemental Table 5). Similarly, no significant differences were observed among study groups in the incidence or mean number of serious adverse events, magnitude of myonecrosis as manifested by c-Troponin-I level, serum creatinine change, or liver function tests (supplemental Table 6).
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DISCUSSION
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Inflammation induced by CPB is widely believed to be an important mediator of adverse postoperative outcomes and organ dysfunction (2). Effective inhibition of this inflammatory response has the potential to significantly reduce perioperative morbidity. We report that administration of a novel lipid A antagonist (eritoran) to patients undergoing cardiac surgery is not associated with overt toxicity. Eritoran administration was not found, however, to significantly reduce the incidence of any measured adverse postoperative outcome or marker of systemic inflammation/organ dysfunction.
As reviewed previously (2), it is known that: 1) endotoxemia causes systemic inflammation in humans and organ injury and dysfunction in animal models (2), 2) endotoxemia occurs during cardiac surgery (2), and 3) eritoran robustly protects humans from endotoxin-induced systemic inflammation (15). Therefore, it is surprising that eritoran, even at the highest dose tested, was not associated with a significant reduction in any marker of systemic inflammation, including fever, the white blood cell count, or serum levels of IL-6 or CRP. There are several possible explanations for this observation.
First, the drug may not have been administered long enough or the total dose may have been insufficient. Predicted levels for the doses chosen were comparable to doses previously shown to be effective at preventing endotoxin-mediated systemic inflammation in volunteers (15). However, the magnitude of endotoxin exposure in cardiac surgical patients might be significantly greater than that used in the human endotoxin model. For example, we have observed plasma levels of LPS in excess of 10 ng/mL during complex cardiac surgery (8). This issue is difficult to resolve for two reasons: 1) methods used to assess the magnitude of endotoxin exposure in cardiac surgical patients (e.g., predominantly plasma LPS levels by the limulus amoebocyte lysate assay) may underestimate or fail to measure endotoxin that moves from the intestine to the liver via the portal circulation, and 2) eritoran plasma levels do not necessarily correlate with pharmacodynamic activity (17). Thus, given the hemodilution and administration of blood products, and other potential confounding influences, it is possible that the concentration of active drug (which we cannot measure) was much lower than observed plasma levels.
Another explanation for the lack of a demonstrable effect on variables related to systemic inflammation stems from the possibility that endotoxin may be a cause of systemic inflammation, but not the primary cause in this setting (2). Eritoran's activity appears to be focused on TLRs such as TLR-4, and may block the proinflammatory response to LPS or heat shock proteins (20). Thus, other important mediators of systemic inflammation during cardiac surgery, such as cytokines, are not blocked by eritoran.
This trial was not sufficiently powered to determine differences in clinical outcomes. This limitation is common in small Phase II "safety" studies which use multiple dosing groups. Although the use of multiple dosing groups is important to assess the effects of different doses of an investigational drug, it decreases the sample size of each group, making statistical comparisons regarding the safety and efficacy (or lack thereof) difficult.
There are many similarities in systemic inflammation between cardiac surgical patients and critically ill patients with sepsis. Therefore, it is possible that the pathophysiology of organ dysfunction in these two patient populations may be similar. It is interesting to note the recent results of a study of eritoran in patients with sepsis (n = 293) (Press Release, Eisai Medical Research, August 29, 2005). Patients were randomized to three groups: eritoran high dose (105 mg/6 days), eritoran low dose (45 mg/6 days), and placebo. The mortality in the large-dose group was reduced by 6.4% (P = 0.34) compared to placebo. Mortality was 33.3% in placebo, 32.0% in the small-dose group, and 26.9% in the large-dose group. The mortality rate in patients who were compliant with the protocol was reduced by 12.2% (P = 0.09) in the large-dose group compared to placebo. In these compliant patients, mortality was 34.6% in the placebo group, 32.5% in the small-dose group, and 22.4% in the large-dose group. It is possible that, compared with the patients in the sepsis trial, our cohort of cardiac surgical patients was too low risk (overall mortality of <1%) for us to see the benefits of this drug, and that higher risk patients should be enrolled in future clinical trials.
In summary, this Phase II safety study suggests that the administration of the novel lipid A antagonist, eritoran, is not associated with overt toxicity in cardiac surgical patients. The impact of this investigational drug on systemic inflammation and organ dysfunction is not different from placebo in the dose and duration of therapy tested here. Nonetheless, the relatively small sample size used in the present study prevents us from drawing any firm conclusions regarding rare adverse events or the potential clinical benefits of this investigational drug. A larger clinical trial will be needed to access the clinical efficacy of eritoran.
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ACKNOWLEDGMENTS
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We thank Pamela Monds, Mary Creed, Nancy Newark, and Yvonne Noble for their assistance in the coordination and execution of this clinical trial. The author also acknowledge the help provided by Mark E. Sand, MD, of Orlando Heart Center, Orlando, FL; Ervant Nishanian, MD, of Department of Anesthesiology, Columbia University College of Physicians & Surgeons, New York, NY; and Jane C. Fitch, MD, of University of Oklahomsa Health Sciences Center, Oklahoma City, OK, for studies conducted at their sites.
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Footnotes
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Accepted for publication November 2, 2006.
Supported by Eisai Medical Research Inc., Ridgefield Park, NJ.
Dr. Charles Hogue, Associate Editor-in-Chief for Cardiovascular Anesthesia, was recused from all editorial decisions related to this manuscript.
Address for correspondence and reprint requests to Elliott Bennett-Guerrero, MD, Duke Clinical Research Institute, Duke University (DUMC Box 3094), Durham, NC 27710. Address e-mail to elliott.bennettguerrero{at}duke.edu.
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Abstract
Introduction
