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A pilot clinical trial of recombinant human angiotensin-converting enzyme 2 in acute respiratory distress… Khan, Akram; Benthin, Cody; Zeno, Brian; Albertson, Timothy E; Boyd, John; Christie, Jason D; Hall, Richard; Poirier, Germain; Ronco, Juan J; Tidswell, Mark; Hardes, Kelly; Powley, William M; Wright, Tracey J; Siederer, Sarah K; Fairman, David A; Lipson, David A; Bayliffe, Andrew I; Lazaar, Aili L Sep 7, 2017

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RESEARCH Open AccessA pilot clinical trial of recombinant humanangiotensin-converting enzyme 2 in acuterespiratory distress syndromeAkram Khan1, Cody Benthin1, Brian Zeno2, Timothy E. Albertson3, John Boyd4, Jason D. Christie5, Richard Hall6,Germain Poirier7, Juan J. Ronco8, Mark Tidswell9, Kelly Hardes10, William M. Powley11, Tracey J. Wright11,Sarah K. Siederer11, David A. Fairman11, David A. Lipson5,12, Andrew I. Bayliffe11† and Aili L. Lazaar5,12*†AbstractBackground: Renin-angiotensin system (RAS) signaling and angiotensin-converting enzyme 2 (ACE2) have beenimplicated in the pathogenesis of acute respiratory distress syndrome (ARDS). We postulated that repleting ACE2using GSK2586881, a recombinant form of human angiotensin-converting enzyme 2 (rhACE2), could attenuateacute lung injury.Methods: We conducted a two-part phase II trial comprising an open-label intrapatient dose escalation and arandomized, double-blind, placebo-controlled phase in ten intensive care units in North America. Patients werebetween the ages of 18 and 80 years, had an American-European Consensus Criteria consensus diagnosis ofARDS, and had been mechanically ventilated for less than 72 h. In part A, open-label GSK2586881 was administered atdoses from 0.1 mg/kg to 0.8 mg/kg to assess safety, pharmacokinetics, and pharmacodynamics. Following review ofdata from part A, a randomized, double-blind, placebo-controlled investigation of twice-daily doses of GSK2586881(0.4 mg/kg) for 3 days was conducted (part B). Biomarkers, physiological assessments, and clinical endpoints werecollected over the dosing period and during follow-up.Results: Dose escalation in part A was well-tolerated without clinically significant hemodynamic changes. Part B wasterminated after 39 of the planned 60 patients following a planned futility analysis. Angiotensin II levels decreasedrapidly following infusion of GSK2586881, whereas angiotensin-(1–7) and angiotensin-(1–5) levels increased andremained elevated for 48 h. Surfactant protein D concentrations were increased, whereas there was a trend for adecrease in interleukin-6 concentrations in rhACE2-treated subjects compared with placebo. No significant differenceswere noted in ratio of partial pressure of arterial oxygen to fraction of inspired oxygen, oxygenation index, or SequentialOrgan Failure Assessment score.Conclusions: GSK2586881 was well-tolerated in patients with ARDS, and the rapid modulation of RAS peptides suggeststarget engagement, although the study was not powered to detect changes in acute physiology or clinical outcomes.Trial registration:, NCT01597635. Registered on 26 January 2012.Keywords: Angiotensin-converting enzyme 2, Acute lung injury, Respiratory distress syndrome, Adult, Acute respiratoryfailure, Renin-angiotensin system, Humans, Interleukin-6* Correspondence:†Equal contributors5Division of Pulmonary, Allergy, and Critical Care Medicine, University ofPennsylvania School of Medicine, Philadelphia, PA, USA12GlaxoSmithKline R&D, King of Prussia, PA, USAFull list of author information is available at the end of the article© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (, which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver( applies to the data made available in this article, unless otherwise stated.Khan et al. Critical Care  (2017) 21:234 DOI 10.1186/s13054-017-1823-xBackgroundThe renin-angiotensin system (RAS) regulates vasculartone and fluid-electrolyte homeostasis in a wide range oftissues [1–4]. Angiotensin II (Ang II), formed by the activ-ity of angiotensin-converting enzyme (ACE) on angioten-sin I (Ang I), is the key effector peptide of the RAS and,via the angiotensin type I receptor (AT1R), mediatesphysiological effects, including vasoconstriction, inflam-mation, apoptosis, capillary leak, and fibroproliferation[5–8]. ACE2 is a membrane-bound carboxypeptidase thathydrolyzes Ang II to the heptapeptide Angiotensin-(1–7)(Ang 1–7). ACE2 regulates RAS signaling, both directlyby reducing Ang II/AT1R signaling and indirectly byactivating the counterregulatory Ang 1–7/Mas receptorpathway [9–12].RAS signaling and ACE2 have been implicated in thepathogenesis of acute respiratory distress syndrome(ARDS). Mice deficient in ACE2 developed severe acutelung injury (ALI) following challenge with a variety ofinsults [13, 14], which improved on repletion with re-combinant ACE2 [15]. The importance of ACE/Ang IIsignaling in human disease is suggested by increasedlevels of ACE and Ang II in patients with ARDS and pa-tients with sepsis [16–19], and it is further underlined bygenetic studies of an insertion/deletion (I/D) polymorph-ism within the ACE gene, with the D allele conferringhigher ACE and Ang II levels in tissue and serum [20].A number of studies and meta-analyses [20–23] suggestan association between the ACE D allele and mortalityin ARDS cohorts.A recombinant version of the catalytic ectodomain ofhuman ACE2 (rhACE2, GSK2586881) attenuated arterialhypoxemia in a piglet model of lipopolysaccharide-induced ALI [24] and was well-tolerated when adminis-tered to healthy human volunteers [25]. We postulatedthat the addition of exogenous ACE2 in patients withARDS could attenuate lung injury without compromis-ing systemic hemodynamics. We report the results of aprospective, placebo-controlled trial of GSK2586881 inmechanically ventilated patients with ARDS. The aim ofthe trial was to establish preliminary safety, pharmaco-kinetics (PK), and pharmacodynamics (PD) in criticallyill patients and to explore the effects of GSK2586881 onrelevant physiological measures of ARDS.MethodsStudy design and data collectionBetween September 2012 and October 2014, we con-ducted a phase II study in ten intensive care units in theUnited States and Canada (GSK protocol ACE114622, identifier NCT01597635). After insti-tutional review board approval was obtained at each in-stitution, written informed consent was obtained fromeach patient or the patient’s legally authorized surrogateprior to conduct of study-specific procedures. The studywas conducted in accordance with International Confer-ence on Harmonisation of Technical Requirements forRegistration of Pharmaceuticals for Human Use GoodClinical Practice and all applicable subject privacy re-quirements, as well as the ethical principles outlined inthe 2013 Declaration of Helsinki [26].The study was designed in two parts. Part A was anopen-label, within-subject dose escalation of GSK2586881in hemodynamically stable patients with ARDS. The pri-mary objective of part A was to ascertain whether ACE2would adversely impact systemic hemodynamics in critic-ally ill patients. Four consecutive intravenous (IV) doses ofGSK2586881 (0.1 mg/kg, 0.2 mg/kg, 0.4 mg/kg, and0.8 mg/kg) were administered to each subject at baselineand intervals of 2, 4, and 18 h, respectively. Hemodynamicassessments were carried out after each infusion and priorto escalating to the next higher dose. The 0.1 mg/kg waschosen as the starting dose because it was anticipated thatthis dose would produce a minimal pharmacological ef-fect, based on the limited preclinical data derived from thepiglet model and from the first-in-human study. On thebasis of modelling predictions and using a conservativetotal dose of 0.7 mg/kg on the first day, this dose escal-ation strategy was not expected to result in drug accumu-lation. The highest dose (0.8 mg/kg) to be administeredon day 2 of part A was selected to provide generous safetymargins that were based on preclinical findings, because itwas believed that doses < 0.8 mg/kg would prove effica-cious in lowering Ang II levels.Part B was a double-blind (sponsor unblinded) inves-tigation comparing 3 days of twice-daily infusions of0.4 mg/kg GSK2586881 with matched placebo. Thesponsor was unblinded to allow for in-stream analysisof safety data only. The exploratory statistical decision-making framework related to PD, physiological, andclinical endpoints, as well as all outputs and reportingand analysis plans, were all defined, prepared, andapproved prior to unblinding of any part B data. Sub-jects were randomized using a 1:1 allocation. Dose se-lection was based on modeling of PK and PD profiles(e.g., Ang II levels) of healthy subjects dosed with IVGSK2586881 in previous trials [25] and dose-response/duration relationships established in large animal ARDSmodels [24]. The primary objective of part B was to as-sess the safety and tolerability of GSK2256881, includ-ing adverse event (AE) reporting, clinical laboratorytests and immunogenicity, vital signs, electrocardio-grams, and physical examinations. Secondary endpointsincluded an assessment of PK, PD, and biomarkers (de-tails described in Additional file 1). Physiological andclinical endpoints were considered exploratory. On thebasis of the anticipated pharmacology of the com-pound, 3 days of dosing was felt to be adequate toKhan et al. Critical Care  (2017) 21:234 Page 2 of 9define the initial safety of the drug in critically illpatients, its PK, and to show a PD effect.Inclusion and exclusion criteriaEligible patients included male or female subjects 18–80years of age who were diagnosed with ARDS within 48 hof randomization that was associated with infection, sep-sis, pneumonia, aspiration, or similar disease, based on theAmerican-European Consensus Criteria [27]. Subjectswere enrolled if hemodynamically stable in the 4–6 h pre-ceding the initiation of study treatment, with stablepressor requirements, on mechanical ventilation for < 72 hbefore dosing began, and were managed with low tidalvolume mechanical ventilation. Full eligibility criteria aredescribed in Additional file 1.Statistical methodsPart B of the study was designed to randomize 60 subjects,with planned interim analyses after approximately half thesubjects had completed 7 days of follow-up. In the originalprotocol, the interim analysis in part B was planned toallow for a sample size reestimation based on Ang II andAng 1–5 responses. Following a planned review of datafrom five subjects in part A in which the effects ofGSK2586881 on RAS peptides were clearer than expected,the protocol was amended to switch the objective of thepart B interim analysis from confirmation of pharmacol-ogy (e.g., plasma Ang II and Ang 1–5) to a futility analysisassessing the impact on ratio of partial pressure of arterialoxygen to fraction of inspired oxygen (PaO2/FiO2) as asurrogate for potential beneficial physiological activity.This change was implemented prior to reviewing/unblind-ing of any data from part B.A Bayesian statistical framework was employed, whichallows quantitative statements of statistical significanceto be constructed from posterior distributions [28]. Thisapproach was considered most appropriate for a studywhere the potential treatment effects of the investiga-tional medicine were less well defined. Additional detailsare provided in Additional file 1.ResultsForty-six subjects were enrolled, of whom 44 (5 in part Aand 39 in part B) received at least one dose of study medi-cation (Fig. 1). In part B, 16 of 20 patients on placebo and16 of 19 patients receiving GSK2586881 received all 6planned doses. Baseline characteristics and demographicsare shown in Table 1 and Additional file 1: Table S1. Atbaseline, subjects who received GSK2586881 in part B hadhigher Sequential Organ Failure Assessment (SOFA)scores and lower PaO2/FiO2 ratios than patients receivingplacebo (Table 1); other characteristics were similarbetween groups. The study was terminated after random-izing 39 of the planned 60 patients in part B, following theplanned futility analysis.Safety and tolerabilityIn part A, no clinically significant changes in hemodynamicparameters were observed. The most commonly reportedAE was atrial fibrillation (Additional file 1: Table S2); noAEs were considered drug-related. Three subjects who diedhad ten serious adverse events (SAEs). None of the SAEswas considered drug-related, with the exception of onePlacebo BID20 subjectsrhACE2 BID 19 subjectsrhACE25 subjects44 subjects dosedPart A: escalating dose5 subjectsPart B:39 subjectsCompleted: 2 subjectsWithdrew: 3 subjectsPrimary reason for withdrawal:Adverse event = 3Completed: 15 subjectsWithdrew: 4 subjectsPrimary reason for withdrawal:Adverse event = 1Protocol deviation = 0Reached protocol-definedstopping criteria = 3Withdrew consent = 0Primary reason for withdrawal:Adverse event = 0Protocol deviation = 1Reached protocol-definedstopping criteria = 4Withdrew consent = 1Completed: 14 subjectsWithdrew: 6 subjects46 subjects randomized50 subjects screened2 subjects found ineligibleafter randomizationbut prior to dosing4 subjects excluded (did not meet inclusion criteria)Fig. 1 (Consolidated Standards of Reporting Trials (CONSORT) diagram of subject dispositionKhan et al. Critical Care  (2017) 21:234 Page 3 of 9subject who developed acute renal failure 4 days after thelast dose of study drug (Additional file 1: Table S5).In part B, 29 (75%) subjects experienced an AE (Add-itional file 1: Table S3). Hypernatremia, rash, dysphagia,and pneumonia occurred more frequently in subjects re-ceiving GSK2586881. Three subjects in each treatmentgroup had AEs that were considered by the investigatorto be possibly related to study drug (Additional file 1:Table S4). Four (20%) subjects on placebo experiencedsix SAEs, and three (16%) subjects treated withGSK2586881 experienced four SAEs (Additional file 1:Table S5). Three subjects experienced fatal AEs, two inthe placebo group (multiorgan failure and septic shock)and one in the GSK2586881 group (anastomotic dehis-cence following lobectomy). None of the fatal events wasconsidered related to study treatment. One patient onplacebo was withdrawn because of increased hepatictransaminases. There were ten deaths in part B, includ-ing six (30%) subjects on placebo and four (21%) sub-jects who received GSK2586881. A full listing of AEs isincluded in Additional file 1: Tables S2–S5.Pharmacodynamics and biomarkersRAS biomarkersBaseline concentrations of plasma Ang II varied consid-erably between subjects (Additional file 1: Figure S1). Inpatients who received GSK2586881, Ang II levels de-creased dramatically after infusion and were sustainedfor up to 5 days (Fig. 2a). The nadir of Ang II was ob-served within the first 12 h and as early as 30 minutesTable 1 Demographic and baseline characteristicsPart A Part BrhACE2 0.1 -> 0.2 -> 0.4 -> 0.8 mg/kg Placebo BID rhACE2 0.4 mg/kg BIDNumber of subjects planned 5 30 30All subjects population 5 20 19Age, years, mean (SD) 50.8 (17.04) 50.5(15.44) 50.6(16.36)Sex, n (%)Female 2 (40) 7 (35) 6 (32)Male 3 (60) 13 (65) 13 (68)BMI, kg/m2, mean (SD) 31.4 (5.43) 29.59 (6.896) 29.21 (4.997)Time since ARDS, h 17.8 (10.8) 26.899 (13.82) 26.916 (13.99)Glasgow Coma Scale 6.6 (2.51) 8.2 (4.47) 7.1 (3.20)SOFA score 10.8 (2.49) 7.8 (2.79) 8.9 (2.36)PaO2/FiO2, geometric mean (SD on logarithmic scale) 140.3 (0.468) 160.5 (0.523) 143.6 (0.522)PEEP, cmH2O 14.0 (0.196) 10.4 (0.438) 10.4 (0.340)Ang II, pg/ml 26.5 (0.513) 11.4 (1.834) 19.6 (1.858)Abbreviations: Ang Angiotensin, ARDS Acute respiratory distress syndrome, BMI Body mass index, PaO2/FiO2 Ratio of partial pressure of arterial oxygen to fractionof inspired oxygen, PEEP Positive end-expiratory pressure, rhACE2 Recombinant human angiotensin-converting enzyme 2, SOFA Sequential Organ Failure AssessmentAdjusted median plasma Ang1-7 (pg/mL)100.5 2 6Planned time since start of 1st dose (hours)121619161616151416510CAdjusted median plasma Ang1-5 (pg/mL)100.5 2 6Planned time since start of 1st dose (hours)121518151615161316510BTreatmentPlacebo rhACE2Adjusted median plasma AngII (pg/mL)100.5 2 6Planned time since start of 1st dose (hours)121618161616151415510AFig. 2 Change from baseline in plasma concentrations of angiotensin II (Ang II) (a), Ang 1–7 (b), and Ang 1–5 (c) following treatment with placebo orGSK2586881 (recombinant human angiotensin-converting enzyme 2 [rhACE2]). Data are expressed as adjusted median ± 95% credible interval (CrI). n*is number of subjects available for each measurementKhan et al. Critical Care  (2017) 21:234 Page 4 of 9following dosing with GSK2586881. In contrast, Ang IIlevels in subjects receiving placebo remained elevatedover the first 5 days and decreased thereafter. PlasmaAng 1–7 (Fig. 2b) and Ang 1–5 (Fig. 2c) levels increasedrapidly and were sustained over the first 12 h followingdosing with GSK2586881 and remained substantially ele-vated. Similarly, Ang 1–5 levels (a product of Ang 1–7catabolism) also increased rapidly over the first 6 h andremained elevated over a time frame similar to that ofAng 1–7 (Fig. 2c). Plasma levels of Ang 1–7 and Ang 1–5 were unchanged over the same period in patients whoreceived placebo.Baseline plasma Ang II concentrations were higher innonsurvivors than in survivors (Additional file 1: FigureS2a), consistent with literature reports suggesting a linkbetween Ang II concentrations and outcome in ARDS[16, 17]. Although baseline concentrations were higherin patients with ARDS than previously reported forhealthy subjects [25], overall Ang II levels were low(Table 1). Among patients in part B, 44% presented withconcentrations < 10 pg/ml (within the normal range),and the majority of subjects recruited (~70%) had Ang IIconcentrations < 50 pg/ml (Additional file 1: Figure S2b).Plasma renin levels were decreased in both groups at72 h compared with baseline. Aldosterone levels weredecreased in subjects receiving GSK2586881 at 72 hcompared with placebo; however, the difference was notsignificant (data not shown).Other biomarkersBaseline serum interleukin (IL)-6 concentrations weresubstantially higher at baseline in the rhACE2 arm(763.6 pg/ml, 95% credible interval (CrI) 427.4–1364.4;vs 223.5 pg/ml, 95% CrI 80.1–623.6) (Fig. 3a). Followingadjustment for baseline differences, there was an ap-parent treatment-related decrease in IL-6 concentra-tions in GSK2586881-treated patients compared withplacebo after 24 h that did not reach statistical signifi-cance (posterior probability distribution of 0.5130–0.9254). The trend for lower IL-6 concentrations is sup-ported by posterior probabilities of 0.92 and 0.88 thatDAdjusted median SP-D ratio to placebo0 2412 60Planned time since start of 1st dose (hours) 48 72 84 96 108120Adjusted median plasma SP-D (ng/mL)0 2412 60Planned time since start of 1st dose (hours)1518n*=14181317111512161011100500C100036 48 72 84 96 108120TreatmentPlacebo rhACE2 Ratio rhACE2/PlaceboAdjusted median IL-6 ratio to placebo0 2412 60Planned time since start of 1st dose (hours)1.02.0B2. 48 72 84 96 108120Adjusted median plasma IL-6 (pg/mL)0 2412 60Planned time since start of 1st dose (hours)1518n*=14161417111512161010100500A100036 48 72 84 96 108120Fig. 3 Change from baseline in plasma concentrations over time and in ratio to placebo for interleukin (IL)-6 (a, b) and surfactant protein D(SP-D) (c, d). Data are expressed as adjusted median ± 95% credible interval. n* is the number of subjects available for each measurement.rhACE2 Recombinant human angiotensin-converting enzyme 2Khan et al. Critical Care  (2017) 21:234 Page 5 of 9GSK2586881 reduced IL-6 levels at 48 h and 120 h,respectively (Fig. 3b).Concentrations of surfactant protein D (SP-D) increasedcompared with baseline (257.7 ng/ml, 95% CrI 162.2–409.5) in subjects receiving GSK2586881, reaching a max-imum at 48 h (494.7 ng/ml, 95% CrI 391.6–628.3) and thengradually decreasing (Fig. 3c). SP-D levels were significantlyelevated (posterior probability > 0.95) in GSK2586881-treated subjects following dosing compared with placebo-treated subjects at 12, 24, 48, and 72 h (Fig. 3d), indicatingstrong evidence for a treatment-related effect.In both groups, myeloperoxidase levels remained rela-tively constant for 48 h before decreasing, and there wasa trend toward lower levels in placebo-treated subjects(posterior probabilities 0.93 at 24 h and 0.92 at 72 h).No significant difference was observed among treatmentgroups for other biomarkers, including C-X-C motif che-mokine ligand 8, soluble tumor necrosis factor receptor1, C-reactive protein, receptor for advanced glycationendproducts, Club cell protein-16, angiopoietin-2, vonWillebrand factor, or plasminogen activator inhibitor 1.Tumor necrosis factor-α concentrations were below thelevel of assay quantification (23.5 pg/ml) for all samplesin the GSK2586881-treated group.Clinical efficacyPhysiological and ventilatory endpointsThere were no significant differences in PaO2/FiO2 overthe dosing period in part B, and PaO2/FiO2 was not in-creased at the final time point (168 h postdose) in therhACE2 group compared with placebo (rhACE2/placeboratio 0.85, 95% CrI 0.62–1.1) (Fig. 4a). Similarly, therewere no differences between treatment groups in oxygen-ation index or positive end-expiratory pressure [29]. Thelack of effect on oxygenation was observed regardless ofbaseline Ang II levels (data not shown). There were nosignificant differences in either peak or plateau pressuresbetween placebo and GSK2586881 over the 72 h of treat-ment; however, increases in both peak and plateau pres-sures in those subjects who had received GSK2586881was evident following the end of treatment. The increasein peak pressures at 72 h was statistically significant (ratio1.28, 95% CrI 1.059–1.514, posterior probability [ratio > 1]0.9946) (Fig. 4b). Static compliance was lower in theGSK2586881-treated group than in the placebo groupthroughout the study, but it decreased more notably after60 h (Fig. 4c). The ratio for static compliance at 72 h was0.58 (95% CrI 0.303–1.308) with a posterior probability(ratio ≥ 1) of 0.0750, suggesting a statistically significantdifference favoring placebo. It should be noted, however,that the analysis at 72 h for these parameters was basedon 10 subjects (4 in placebo, 6 on GSK2586881) comparedwith 23 at baseline (13 and 10, respectively).Organ failureSOFA scores were higher in the GSK2586881-treatedgroup at baseline, and when they could be computed, theywere also higher at all postdose time points (Additionalfile 1: Table S6). Notably, there was a large proportion ofmissing data at day 7 because of clinical improvement,which limits the conclusions that can be drawn. Fluid bal-ance was also assessed in patients at baseline and through-out the treatment period, with no significant differencesnoted between treatment groups across time points (datanot shown).DiscussionThe primary objective of this study was to assess thesafety of GSK2586881 in patients with ARDS, and thestudy also included measurements of inflammatoryAdjusted median Cstat (mL/cm H2O)20n*=0 12 24 7260Planned time since start of 1st dose (hours)168131079466689244060801004836CAdjusted median Pplat (cm H2O)10203040n*=0 12 24 7260Planned time since start of 1st dose (hours)168141210104797111023504836BAdjusted median PaO2:FiO2 (mmHg)Planned time since start of 1st dose (hours)TreatmentPlacebo rhACE2n*=0 12 24 7260 168201917191118141818178103002004836100AFig. 4 Change from baseline in ratio of partial pressure of arterial oxygen to fraction of inspired oxygen (PaO2/FiO2, a), plateau pressure (Pplat, b),and static compliance (Cstat, c). Data are expressed as adjusted median ± 95% credible interval. n* is the number of subjects available foreach measurementKhan et al. Critical Care  (2017) 21:234 Page 6 of 9biomarkers and exploratory endpoints relating to lungphysiology and clinical efficacy. The study met its pri-mary endpoint because there were no episodes ofhypotension associated with infusion of GSK2586881.Most AEs were equally distributed between the treat-ment and placebo groups and were consistent with acritically ill population; however, some were reportedmore frequently in subjects receiving GSK2586881, in-cluding hypernatremia; pneumonia; dysphagia; and, inparticular, rash. The occurrence of rash in patients tak-ing ACE inhibitors has been reported [30]. Rash some-times accompanies infusions of therapeutic proteins as aresult of formation of protein-protein or antibody-protein complexes that precipitate type II or III hyper-sensitivity reactions [30]. Although no antibody re-sponses to GSK2586881 were detected, given the smallnumber of subjects in this trial, the possibility ofimmune-mediated rash cannot be ruled out. Althoughall pneumonia events occurred in the treatment arm,these occurred well after the last dose of study drug(ranging from 5 to 36 days), so a clear role forGSK2586881 in the increased reports of pneumonia isdifficult to establish.Despite the increased illness severity and dysregulatedRAS signaling in the GSK2586881-treated group at base-line, infusion of GSK2586881 modulated RAS peptidesas expected, resulting in a significant decrease in con-centrations of Ang II, accompanied by similarly rapid in-creases in Ang 1–7 and Ang 1–5 concentrations. This isconsistent with the PK data that suggested a good cor-relation between plasma concentrations of GSK2256881and measured ACE2 activity (Additional file 1: FigureS4). Whereas infusion of GSK2586881 resulted in amean decrease in Ang II, levels in some subjectsremained higher than those reported in healthy volun-teers [25]. Increases in Ang 1–7 and Ang 1–5 peptideproducts were limited to the initial 30–60 minutes afterinfusion, perhaps reflecting high turnover of the initialAng II substrate pool in the presence of high concentra-tions of rhACE2. This raises the possibility that continu-ous infusions of GSK2586881 that achieve lower plasmaconcentrations over a longer duration may be more ef-fective as a result of more sustained production of Ang1–7. Further dose regimen finding studies are requiredto explore these PK/PD relationships.It is notable that 71% of patients had baseline concen-trations of Ang II < 50 pg/ml, a level suggested to be ofprognostic significance in some patient populations [17,31, 32]. This observation highlights the variability in RASactivation within heterogeneous cohorts of patients withARDS and raises the possibility that RAS activation maybe driving disease in only a subgroup of patients. Re-searchers in future studies could consider evaluatingGSK2586881 only in patients with elevated Ang II and, inlight of findings in animals, could further explore the im-pact of RAS modulation on pulmonary hemodynamicsand markers of pulmonary vascular injury.Treatment with GSK2586881 resulted in a reductionin IL-6 concentrations, although this did not reach stat-istical significance, owing to intersubject variability andbaseline imbalances. The elevations in SP-D were unex-pected and raise a number of questions aboutGSK2586881’s mechanism of action. SP-D is a large col-lectin family protein, with expression usually restrictedto the lung [33, 34]. Its presence in serum has beensuggested to be an indicator of worsening alveolar ca-pillary permeability. However, SP-D is also an anti-inflammatory [33, 34] and antimicrobial protein [35];thus, the observed increases could be reflective of in-creased SP-D biosynthesis in the lung as a result ofGSK2586881 treatment. These data highlight a need forfurther research on the potential mechanistic linkbetween ACE2 and SP-D biology.Although difficult to assess because of study limitations,it is possible that treatment with GSK2586881 worsened re-spiratory mechanics, with the change in compliance andventilatory pressures possibly suggesting an increase in lungstiffness [29, 36, 37]. Although most of the biomarkersmeasured suggested no change or reduced disease activityin GSK2586881-treated subjects, the increase in myeloper-oxidase is difficult to explain on the basis of known ACE2biology and previous effects in animals and humans, and itcould reflect lung neutrophil accumulation and the poten-tial for altered respiratory mechanics. Some of the analyseswere impacted by missing data (e.g., subject withdrawal,extubation, technical issues, early mortality); therefore, thenumber of subjects supporting these comparisons wassmall, significantly increasing the possibility of systematicbias at later time points. There were baseline imbalances inseverity of illness (based on SOFA score and serum IL-6and Ang II levels) and case mix between treatment groups.The lack of improvement in oxygenation in patientsreceiving GSK2586881 contrasts with effects reported inlarge animal models of ARDS, where IV rhACE2 rapidlyimproved arterial hypoxemia and pulmonary hemodynamics[15, 38]. Although PaO2/FiO2 and other ventilatory parame-ters are important in the diagnosis of ARDS and in de-termining the severity of hypoxemia, they cannot bestandardized clinically to the same extent as in animalstudies, and they are influenced by numerous factors thatwere not adequately controlled for in this trial. These issueslimit interpretation of the effects of GSK2586881 on oxy-genation and ventilatory parameters.ConclusionsInfusion of GSK2586881 resulted in the expected changesin RAS biomarkers and were well-tolerated in subjectswith ARDS. However, GSK2586881 infusions did notKhan et al. Critical Care  (2017) 21:234 Page 7 of 9result in improvement in physiological or clinical mea-sures of ARDS in this small study. Because the primaryobjective (preliminary safety, PK, and PD) was met at theinterim analysis, and because statistical trial simulations ofthe interim data predicted with reasonable confidence thatthe outcome at trial completion (n = 60) would be similarto the interim outcome, continued recruitment was notjustified, and the trial was terminated early. Further ex-ploration of the effects of GSK2586881 in ARDS will needto be built on a better understanding of the role of RAS inARDS pathophysiology in humans, as well as of the effectsof rhACE2 on pulmonary physiology.Additional filesAdditional file 1: Online Supplement to Pilot trial of ACE2 in ARDS.(DOCX 408 kb)Additional file 2: Ethics Committees and Institutional Review Boards.(DOCX 13 kb)AbbreviationsACE2: Angiotensin-converting enzyme 2; AE: Adverse event; ALI: Acute lunginjury; Ang: Angiotensin; ARDS: Acute respiratory distress syndrome;AT1R: Angiotensin type I receptor; BMI: Body mass index;CONSORT: Consolidated Standards of Reporting Trials; CrI: Credible interval; I/D: Insertion/deletion; IL: Interleukin; IV: Intravenous; LLQ: Lower limit ofquantitation; PaO2/FiO2: Ratio of partial pressure of arterial oxygen to fractionof inspired oxygen; PD: Pharmacodynamics; PEEP: Positive end-expiratorypressure; PK: Pharmacokinetics; RAS: Renin-angiotensin system;rhACE2: Recombinant human angiotensin-converting enzyme 2; SAE: Seriousadverse event; SP-D: Surfactant protein D; SOFA: Sequential Organ FailureAssessmentAcknowledgementsThe authors thank the patients and their families, as well as the followingprincipal investigators and study coordinators and their institutions for theircontributions to the study:United States: Kelli Brooks (Duke University Medical Center, Durham, NC),Peter Morris (Wake Forest University School of Medicine, Winston-Salem, NC),Richard Wunderink (Northwestern Memorial Hospital, Chicago, IL), EvertEriksson (Medical University of South Carolina, Charleston, SC), JuanDuchesne (Tulane University School of Medicine, New Orleans, LA), HayleyGershengorn (Albert Einstein College of Medicine, Bronx, NY), Robert Hyzy(University of Michigan Medical Center, Ann Arbor, MI), Patrick Wright (MosesH. Cone Memorial Hospital, Greensboro, NC), Bharat Awsare (ThomasJefferson University, Philadelphia, PA), Nathan Kessler (Oregon Health &Science University, Portland, OR), Katherine Markelz and Ana Campbell(University of Pennsylvania, Philadelphia, PA), Brian Morrissey (University ofCalifornia, Davis School of Medicine, Sacramento, CA), Lori-Ann Kozikowskiand Lesley De Souza (Baystate Medical Center, Springfield, MA).Canada: Francois Lellouche (Institut Universitaire de Cardiologie et dePneumologie de Québec, Sainte-Foy, PQ), John Muscedere (Kingston GeneralHospital, Kingston, ON), Yoanna Skrobik (McGill University Health Centre,Montreal, QC), Mélissa Joseph (Charles LeMoyne Hospital, Greenfield Park,QC)The authors also acknowledge the contributions of the following GSKemployees in the United States, United Kingdom, and Canada: SandiVanBuren, Alina Goetz, Amanda Baines, Hina Abbas, Ann Barella, Kiran Ubhi,Adam Hughes, Thomas Mencken, and Thomas Lee. The authors acknowledgethe assistance of Gillian Groeger of Fishawack Communications for assistance inproducing the figures (funded by GSK).FundingFunding for this study (NCT01597635) was provided by GlaxoSmithKline.Availability of data and materialsThe datasets used and/or analyzed during the present study are availablefrom the corresponding author on reasonable request.Authors’ contributionsAll listed authors meet the criteria for authorship set forth by theInternational Committee of Medical Journal Editors. ALL, DAL, AIB, KH, WMP,TJW, SKS, and DAF were responsible for study design as well as datacollection and analysis. AK, CB, BZ, TEA, JB, JDC, RH, GP, JJR, and MTcontributed to data acquisition. All authors contributed to datainterpretation. AK and AL wrote the initial draft of the manuscript. All authorsparticipated in review and revision of the manuscript. All authors agree to beaccountable for all aspects of the work in ensuring that questions related tothe accuracy or integrity of any part of the work are appropriatelyinvestigated and resolved. All authors read and approved the finalmanuscript.Authors’ informationNot applicable.Ethics approval and consent to participateAfter institutional review board approval was provided at each institution(available as part of Additional file 2), written informed consent was obtainedfrom each patient or the patient’s legally authorized surrogate prior toconduct of study-specific procedures.Consent for publicationNot applicable.Competing interestsAK has received funding from GlaxoSmithKline, AstraZeneca, United Therapeutics,and Actelion Pharmaceuticals to conduct industry-sponsored research studies.TEA has received funding from GlaxoSmithKline to conduct industry-sponsoredresearch studies. JDC has received institutional funding from GlaxoSmithKline andBristol-Myers Squibb to conduct investigator-initiated observational studies. RHhas received funding from GlaxoSmithKline, Asahi Kasei Pharma, La JollaPharmaceutical, Eli Lilly, AstraZeneca, and Pfizer to conduct industry-sponsored research studies. KH, WMP, TJW, SKS, DAF, DAL, AIB, and ALLare employees of GSK and own shares in the company. The other authorsdeclare that they have no competing interests.Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims in publishedmaps and institutional affiliations.Author details1Div. of Pulmonary & Critical Care Medicine, Department of Medicine,Oregon Health & Science University, Portland, OR, USA. 2Riverside MethodistHospital, Columbus, OH, USA. 3School of Medicine, University of California,Davis, Sacramento, CA, USA. 4St. Paul’s Hospital, Vancouver, BC, Canada.5Division of Pulmonary, Allergy, and Critical Care Medicine, University ofPennsylvania School of Medicine, Philadelphia, PA, USA. 6Nova Scotia HealthAuthority and Dalhousie University, Halifax, NS, Canada. 7Charles LeMoyneHospital, Sherbrooke University, Greenfield Park, QC, Canada. 8Critical CareMedicine, Vancouver General Hospital, University of British Columbia,Vancouver, BC, Canada. 9Division of Pulmonary and Critical Care, Departmentof Medicine, Baystate Medical Center, Springfield, MA, USA.10GlaxoSmithKline R&D, Stockley Park, UK. 11GlaxoSmithKline R&D, Stevenage,UK. 12GlaxoSmithKline R&D, King of Prussia, PA, USA.Received: 13 March 2017 Accepted: 22 August 2017References1. 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