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THE PRESENT AND FUTURE

STATE-OF-THE-ART REVIEW

The Path to an Angiotensin ReceptorAntagonist-Neprilysin Inhibitorin the Treatment of Heart Failure

Eugene Braunwald, MD*

ABSTRACT

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Me

Lis

Yo

Ma

The PARADIGM-HF (Prospective comparison of ARNi with ACEi to Determine Impact on Global Mortality and Morbidity in

Heart Failure) trial demonstrated that a new angiotensin receptor antagonist-neprilysin inhibitor was superior to an

angiotensin-converting enzyme inhibitor in reducing mortality in patients with heart failure and reduced ejection fraction.

This paper traces the research path that culminated in the development of this drug. The first phase, elucidation of the

renin-angiotensin-aldosterone system, began with Tigerstedt’s discovery of renin, followed by isolation of angiotensin,

isolation of angiotensin-converting enzyme, and synthesis of its inhibitors and of angiotensin receptor blockers. Phase 2

began with de Bold’s discovery of atrial natriuretic peptide, followed by isolation of the enzyme that degrades it

(neprilysin) and its inhibitors. Phase 3 consists of blocking both the renin-angiotensin-aldosterone and atrial natriuretic

peptide–degrading systems simultaneously. A molecular complex, LCZ696, developed by scientists at Novartis, combines

an angiotensin receptor blocker with a neprilysin inhibitor, is well tolerated, and represents an important step in the

management of heart failure and reduced ejection fraction. (J Am Coll Cardiol 2015;65:1029–41) © 2015 by the American

College of Cardiology Foundation.

“If I have seen further, it is by standingon the shoulders of giants.”

—Isaac Newton, 1676 (1)

On March 31, 2014, the cardiology world, and manyother medical professionals were excited by the pressstatement released by Novartis regarding a clinicaltrial on the treatment of heart failure (HF) with a newdrug: “.the Data Monitoring Committee unanimouslyrecommended early closure of the PARADIGM-HF[Prospective comparison of ARNi with ACEi toDetermine Impact on Global Mortality and morbidityin HF trial], indicating patients with chronic heartfailure with reduced ejection fraction [HFrEF] whoreceived LCZ696 lived longer without being hospital-ized for heart failure than those who received standardcare with [angiotensin-converting enzyme] inhibitor

m the *TIMI Study Group, Cardiovascular Division, Brigham and Women’

dical School, Boston, Massachusetts. Dr. Braunwald serves as a noncomp

ten to this manuscript’s audio summary by JACC Editor-in-Chief Dr. Vale

u can also listen to this issue’s audio summary by JACC Editor-in-Chief D

nuscript received December 29, 2014; revised manuscript received Janua

[ACEi] enalapril. Based on the compelling efficacy andprimary endpoint having been met, the trial will nowclose early” (2).

In the paper describing the design of the trial,McMurray et al. (3) outlined a comparison betweenLCZ696, a first-in-class angiotensin receptor-neprilysin inhibitor (ARNi), and enalapril. In anothercommunication, the same authors stated that bothcomponents of the primary endpoint of the trial, car-diovascular death or hospitalization for HF, would “beanalyzed separately and these additional analyses willbe considered as part of the primary endpoint” (4).Therefore, there must have been compelling evidencethat, when compared with enalapril in patients withHFrEF (5), LCZ696 further reduced not only the com-posite endpoint of cardiovascular death and hospital-ization for HF, but also cardiovascular death alone.

s Hospital, and the Department of Medicine, Harvard

ensated consultant to Novartis.

ntin Fuster.

r. Valentin Fuster.

ry 15, 2015, accepted January 19, 2015.

ABBR EV I A T I ON S

AND ACRONYMS

ACEi = angiotensin-converting

enzyme inhibitor

ADM = adrenomedullin

ANP = atrial natriuretic peptide

ARB = angiotensin

receptor blocker

ARNi = angiotensin receptor

antagonist-neprilysin inhibitor

BNP = B-type natriuretic

peptide

HFrEF = heart failure with

reduced ejection fraction

NEP = neprilysin

NEPi = neprilysin inhibitor

RAAS = renin-angiotensin-

aldosterone system

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The results of the PARADIGM-HF trialwere presented at the European Society ofCardiology on August 30, 2014, and publishedsimultaneously in the New England Journalof Medicine (6). It was praised in an accom-panying editorial by Jessup, who wrote:“PARADIGM-HF may well represent a newthreshold of hope for patients with heartfailure.The beneficial results seen inPARADIGM-HF may apply to a wide spectrumof patients, even those who are currently re-ceiving the best possible therapy” (7). A per-spective in the same issue of the New EnglandJournal of Medicine stated, “We may beentering a new era of treatment for heart fail-ure with reduced ejection fraction” (8), strongwords indeed by 2 editors of this journal.

LCZ696 is the first of a new class of drugs

that simultaneously block the angiotensin II type Ireceptors (angiotensin receptor blocker [ARB]) andinhibit neprilysin (neprilysin inhibitor [NEPi]), hence,the acronym ARNi. This dual action places this drug atthe center of 2 critically important systems that haveprofound effects on the circulation, as well as onother tissues: the renin-angiotensin-aldosterone sys-tem (RAAS), and the natriuretic peptide system (NPS)(Central Illustration). Although PARADIGM-HF ap-pears to represent a very important advance in thetreatment of HFrEF, LCZ696 did not burst on thescene like a comet from outer space, but insteadrepresents the most recent in a series of brilliant in-vestigations carried out over more than 11 decades.The objective of this paper is to summarize the keysteps leading to this new therapy (Figure 1).

RENIN-ANGIOTENSIN-ALDOSTERONE

SYSTEM

In 1898, Finnish physiologist Robert Tigerstedt, whocan be considered to be the first giant on whoseshoulders later investigators stood, and his Swedishmedical student Per Bergman, working at the Kar-olinska Institute in Stockholm, discovered that whensaline extracts of rabbit renal cortex were injectedinto rabbits, a pressor response was elicited (9,10)(Figure 2). They named the active component of theextract renin, which is now known to be an aspartylprotease. The next major step in the elucidation ofthe RAAS was taken in 1934, when Goldblatt et al. (11)demonstrated that constriction of the renal arteries ofdogs caused persistent hypertension. Six years later,2 groups, working in Argentina (12) and in the UnitedStates (13), demonstrated that renin catalyzed theformation of a peptide pressor substance, later

named angiotensin. There were 2 forms of the latter, alargely inactive decapeptide (angiotensin I) that wascleaved by a second enzyme—a dipeptide hydrolase-angiotensin converting enzyme (ACE)—to form theactive pressor substance, the octapeptide angiotensinII (Central Illustration). Subsequently, additional an-giotensins, the products of further enzymatic hydro-lysis, were discovered, but they are not central to thisstory (14).

In addition to its action on vascular smooth mus-cle, angiotensin II also causes retention of sodium byenhancing reabsorption of this ion in the proximaltubule and by stimulating the release of aldosteronefrom the zona glomerulosa of the adrenal cortex,thereby playing a critical role in the control of extra-cellular fluid volume and electrolyte balance. Angio-tensin II also stimulates cell proliferation, oxidativestress, and fibrosis. The RAAS acts within the blood-stream, in a classical endocrine mode, and within thekidneys and other tissues in paracrine (local) andautocrine (intracellular) modes. ACE also inactivatesthe vasodilator peptide, bradykinin, which contrib-utes to its pressor action, giving the enzyme itsalternate name—kininase II.

RAAS INHIBITORS. As these important actions ofACE/kininase II became clarified, the search for in-hibitors of this enzyme was begun. Ferreira made 2important contributions. First, in 1965, he observedthat the venom of Bothrops Jararaca, the Brazilian pitviper, contained an inhibitor of the kininase that de-grades the vasodilator, bradykinin (15). Subsequently,he reported that this kininase inhibitor also inhibitedACE (16). He thus showed that the bradykinin poten-tiating substance and the ACEi were identical. Theearliest ACEi/kininase were synthetic analogues of theactive peptides in the venom and required parenteraladministration. One of these, the nonapeptide,teprotide, was shown to reduce renal vasoconstric-tion, lower arterial pressure in hypertensive patients(17), and improve the disordered hemodynamics inpatients with HF, demonstrating the important role ofactivation of the RAAS in the latter (18). Teprotide andother ACEis, in addition to raising bradykinin levels,increase the concentration of plasma and urinaryprostaglandins, which are also vasodilators (19).

These favorable effects in patients with hyperten-sion and with HF stimulated the development oforally active ACEis, the first of which was captopril,synthesized in 1977 by Ondetti et al. (20), a notablefeat. Captopril soon became a useful antihypertensive(21). In animal studies, it prevented ventricularremodeling in rats with myocardial infarction (22) andreduced all-cause mortality when administered

CENTRAL ILLUSTRATION Angiotensin-Neprilysin Inhibition in Heart Failure: Central Role of LCZ696 inCardiovascular Regulation

HFrEF

Cardiac injury/overload

Renin

Angiotensinogen

Na retention NatriuresisVasodilation

Fibrosis

Aldosterone PKG

MRCA

ARB

VasoconstrictionProliferation

ROSFibrosis

Ang I

β1 blocker

ACEi

ACEBradykinindegradation

NPS/Wall stressSNS

LCZ 696

NEPi

NEP

ANP/BNP

AT1R cGMP

GC-A

NPRA

Ang II

RAAS

Braunwald, E. J Am Coll Cardiol. 2015; 65(10):1029–41.

The central role of LCZ696 in the dual inhibition of the RAAS and of NEP. Green lines and arrows denote stimulation or activation. Red lines denote

blockade. HFrEF activates both the SNS and the RAAS, which act in concert to increase the release of renin. RAAS acts on angiotensinogen to produce ANG I.

ACE catalyzes the formation of ANG II, which acts on the ATIR, whose biological actions include the release of aldosterone from the adrenal cortex.

b1 receptor blockers, ACEis, ARBs, and MRCBs block the SNS and RAAS at several levels; ACEi also blocks the degradation of bradykinin. The increasing wall

stress in HFrEF activates the NPS with release of ANP and BNP, which in turn activate the NPRA, GC-A, cGMP, and PKG, and result in vasodilation,

natriuresis, diuresis, and fibrosis inhibition. ANP also blocks the release of renin. NEP breaks down ANP, whereas NEPi preserves ANP by blocking NEP.

LCZ696 has 2 components—an ARB and a NEPi, which block RAAS activation while enhancing the adaptive actions of ANP. ACE ¼ angiotensin-converting

enzyme; ACEi ¼ angiotensin-converting enzyme inhibitor; ANG ¼ angiotensin; ANP ¼ atrial natriuretic peptide; ARB ¼ angiotensin receptor blocker; AT1R ¼angiotensin II type 1 receptor; BNP ¼ brain natriuretic peptide; cGMP ¼ cyclic guanosine monophosphate; GC-A ¼ guanylyl cyclase A; HFrEF ¼ heart failure

with reduced ejection fraction; MRCB ¼ mineralocorticoid receptor blocker; NEP ¼ neprilysin; NEPi ¼ neprilysin inhibitor; NPRA ¼ natriuretic peptide

receptor A; NPS ¼ natriuretic peptide system; PKG ¼ protein kinase G; RAAS ¼ renin angiotensin aldosterone system; SNS ¼ sympathetic nervous system.

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long-term to patients with left ventricular dysfunc-tion following acute myocardial infarction (23). Otheroral ACEis soon followed. Enalapril, the ACEi used asthe comparator in the PARADIGM HF-trial (6), is aprodrug that is rapidly converted into enalaprilat, itsactive form. The latter was shown to prolong survivalin severe HF (24), whereas the prodrug improvedsurvival in chronic HFrEF (5). ACEis rapidly became,and remain, first-line drugs worldwide for the treat-ment of both hypertension and HF.

Although ACEis are well tolerated by the majorityof patients, an annoying dry cough occurs in 10%to 15%. A related, but more serious adverse event,angioedema, can lead to life-threatening obstruc-tion of the upper airway, and is caused by in-creased concentrations of bradykinin and vasoactiveprostaglandins consequent to kininase inhibition.It occurs in 0.1% or 0.2% of Caucasians, but in alarger percentage of African Americans receivingACEis.

FIGURE 1 Timeline of the Path to the PARADIGM HF Trial

angiotensin isolated (12,13) renin discovered (9)

1960

1970

1980

HF mortality ↓ ACEi (24)

20001990 2010

1940

NEP isolated (63)

ACE isolated (16)

ANP discovered (34)

First oral ARB (26) Patent for ARNi (97)

Omapatrilat synthesized (88)First oral ACEi (20)

NEPi characterized (69)

PARADIGM-HF (6)

1920 1900

Numbers in parentheses refer to text references. ACE ¼ angiotensin-converting enzyme; ACEi ¼ angiotensin-converting enzyme inhibitor;

ANP ¼ atrial natriuretic peptide; ARB ¼ angiotensin receptor blocker; ARNi ¼ angiotensin receptor antagonist-neprilysin inhibitor; HF ¼ heart

failure; NEP ¼ neprilysin; NEPi ¼ neprilysin inhibitor; PARADIGM-HF ¼ Prospective comparison of ARNi with ACEi to Determine Impact on

Global Mortality and morbidity in the Heart Failure.

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After it was discovered that the actions of angio-tensin II are mediated primarily by its type 1 receptor,a G-protein coupled receptor, the search for compet-itive blockers of this receptor (ARBs) began (CentralIllustration). Marshall et al. (25) described the first ofthese, a peptide, in 1970. The angiotensin II analogue,saralasin, reduced arterial pressure in patients withmalignant or resistant hypertension. Like the firstACEi, it was active only parenterally (26). Timmer-mans et al. (27) described orally active nonpeptideARBs with high affinity. Losartan was the first ARB tobe used clinically; a closely related agent, valsartan,has been shown to improve outcomes in patientshospitalized for HF by Cohn et al. (28) and is acomponent of the ARNi, LCZ696 (6).

Like ACEis, ARBs are potent antihypertensiveagents and are indicated as first-line drugs in bothhypertension and HFrEF. However, a major differ-ence between ACEis and ARBs is the greater speci-ficity of the latter. Because ARBs do not block thedegradation of kinins, angioedema and persistentcough are quite uncommon with their use. Whenblockade of the RAAS is desired, it is common clinicalpractice to begin with an ACEi and switch to an ARBin patients who are intolerant. Blockers of aldoste-rone and other mineralocorticoid receptors were

described in 1959 (29). By reducing renal sodiumreabsorption, they have a diuretic action and havealso been shown to reduce mortality in patients withHFrEF (30). These agents are also purported to exertantifibrotic actions.

NATRIURETIC PEPTIDE SYSTEM

In 1 of the first electron microscopic examinations ofmammalian cardiac tissue, Kisch (31), in 1956,described granules in the atria. In 1978, Adolfo deBold (32), another giant, and his collaborators, inKingston, Ontario, suggested that these atrial gran-ules were sites of storage of a protein or polypeptide.They then observed an inverse relation betweenwater-electrolyte balance and atrial granularity, withhypergranularity developing in rats deprived of waterand sodium, and the converse in sodium-loaded rats(33). In their now classic paper, published in 1981,they described an experiment that is reminiscent ofthe one reported by Tigerstedt and Bergman (9) 83years earlier (Figures 1 and 2). Their infusion of crudeextracts of rat atrium caused hypotension and a morethan 30-fold increase of sodium excretion, whereasurine volume rose 10-fold (34). de Bold et al. (32)named the substance responsible for these effects

FIGURE 2 The Tigerstedt and Bergman Experiments

Robert Adolf ArmandTigerstedt (ca. 1910)

"A [rabbit] kidney was pulverized with 21 ml of water. Injection into jugular vein.Within 80 s, there is a rise in mean arterial pressure from 62-67 mmHg to100 mmHg, i.e. an increase by ca. 50%."

Experiment 1B, November 8, 1896Tigerstedt and Bergman, Niere und KreislaufSkand. Arch. Physiol. 8: 223–271, 1898

160

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100

90

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0 10 20 30 40 50 60 70 80 90 100Time (seconds)

110 120

Bloo

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mHg

)

XUV

XXXVIII

IB

IB

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XLIVXI

XXXVIII

Excerpts from Tigerstedt and Berman’s paper (9), which led to the discovery of renin. Four separate experiments are illustrated. Figure supplied

by M. P. Lefkowitz.

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atrial natriuretic factor, which has subsequently beenreferred to as atrial natriuretic peptide (ANP). Theyisolated and purified ANP, determined its amino acidsequence, and developed a radioimmunoassay (35),establishing the heart to be an endocrine organ (36).An endocrine function of the heart had, in fact, beensuggested in 1964 (37).

In 1988, Sudoh et al. (38), in the first of severalimportant contributions to this field, identified apeptide in porcine brain and named it brain natri-uretic peptide (also known as B-type natriureticpeptide [BNP]). Although not identical to ANP, BNPhas similar structural, hypotensive, natriuretic, anddiuretic properties. BNP is also present in the heartand is released primarily from the ventricles (39). Athird peptide in this family, C-type natriuretic pep-tide (CNP), was also extracted first from porcinebrain, and then from endothelial cells (40).

These 3 peptides, which form the natriuretic pep-tide system (NPS), are the products of separate genesthat encode 3 prohormones. The latter undergo pro-teolytic cleavage to form the 3 active hormoneshaving several structural homologies. ANP has 28,BNP has 32, and CNP has 22 amino acids. ANP andBNP bind to and activate membrane-bound natri-uretic peptide receptors-A (Central Illustration). Theseare coupled to and activate guanylyl cyclase A, which

increases the intracellular concentrations of the sec-ond messenger, cyclic guanosine monophosphate(41). The latter, in turn, activates protein kinase G,leading to vasorelaxation, natriuresis, and diuresis(42). ANP and BNP also inhibit renin secretion (43)and aldosterone production (44) and attenuate car-diac and vascular remodeling, apoptosis, ventricularhypertrophy, and fibrosis (44–47); they also enhancemyocardial relaxation. CNP is released primarily fromendothelial cells, and only trace quantities are foundin the blood. In contrast to ANP and BNP, CNP appearsnot to exert a marked effect on sodium or waterexcretion, but instead to act as a vasodilator inparacrine and autocrine modes and to stimulate thegrowth of long bones (41,45,48). Although it mayseem inappropriate to label CNP as a “natriuretic”peptide (NP), all 3 polypeptide hormones are stillwidely referred to as NPs, and constitute the NPS.

Distension of the atria and ventricles, as occurs incardiac injury and/or overload, ventricular dysfunc-tion, and HF results in significant increases in theexpression of ANP and BNP. In 1986, Burnett (49),another important investigator in this field, andhis collaborators demonstrated elevations of circu-lating ANP in patients with HF. The concentrationsof circulating BNP and of its inactive precursor,N-terminal fragment of pro–B-type natriuretic

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peptide (NT-proBNP) have become extremely valu-able in the recognition of hemodynamic overload,ventricular dysfunction, and HF (50,51). Measure-ments of these peptides are also useful in assessingprognosis and monitoring therapy, and appear to beuseful as therapeutic targets as well (52). Althoughthe infusion of synthetic human ANP, named car-peritide (53), and human recombinant BNP (nesiri-tide) have exhibited the desired physiologic effects(i.e., vasorelaxation, natriuresis, and diuresis) andhave been approved for the treatment of HF in somecountries, they require parenteral administration andhave yet to demonstrate an unambiguous improve-ment in clinical outcomes (54).

ADRENOMEDULLIN. In 1993, Kitamura et al. (55)isolated another novel, potent, hypotensive peptidecomposed of 52 amino acids from human pheochro-mocytoma, as well as from normal adrenal medulla,which they termed adrenomedullin (ADM). Althoughit shares the vasorelaxant and natriuretic propertiesof ANP and BNP, ADM is structurally unrelated. ADMhas also been shown to reduce myocyte hypertrophy,fibroblast proliferation, collagen synthesis, and aldo-sterone secretion. Kitamura developed a sensitiveradioimmunoassay for ADM, reported its presence innormal human plasma (55), and characterized thecomplementary deoxyribonucleic acid encoding theprecursor of the peptide. The vascular endothelium isnow also known to produce ADM, and it is found inmany organs, including the kidney, where it reducesrenal vascular resistance and increases glomerularfiltration rate (56).

Infusion of ADM into normal subjects showed it tobe a potent vasodilator. In patients with HF, itreduces systemic and pulmonary arterial and wedgepressures and plasma aldosterone, while raising car-diac output, urinary volume, and sodium excretion(57). ADM acts on a specific receptor, 1 of the so-calledcalcitonin gene-related peptide receptors, elevatesintracellular cyclic adenosine monophosphate, andincreases intracellular [Ca2þ], which, in turn, acti-vates NO synthase and intracellular NO; the latter isbelieved to be responsible for the vasodilator actionof ADM (56).

In 1995, Jougasaki et al. (58) reported elevationsof circulating ADM in patients with HF, and plasmaADM was found to be an independent predictor ofprognosis in such patients. However, the clinicalapplicability of ADM measurements has been limitedby the instability of the molecule. An assay for themidregion of pro-adrenomedullin, the stable pre-cursor of ADM, was then developed (59). The BACH(Biomarkers in Acute Heart Failure) study showed

midregion of pro-adrenomedullin to be superior toNT-proBNP for the prediction of mortality in pa-tients with acute HF (60). Given the salutary prop-erties of ADM, it would seem that enhancementof circulating ADM could be beneficial in patientswith HF.

NEPRILYSIN AND ITS INHIBITION

Circulating NPs are cleared through 2 principalmechanisms: NP receptor-mediated clearance andenzyme degradation (61,62). An important paperpublished in 1974 by Kerr and Kenny (63) described aneutral glycosylated zinc endopeptidase in the prox-imal tubule cells of the rabbit kidney. An equallyimportant study by Stephenson and Kenny showedit to be a potent hydrolyzer of ANP (64). The pro-duction and release of this enzyme from endothelialcells contributes to its presence in the circulation(65). The abundance of this peptidase in the renalcortex contributes to the very brief half-life of ANP(approximately 2 min in normal human subjects) (66).Although attention was initially directed to its abilityto hydrolyze ANP (63), this membrane-bound enzymewith a large extracellular component also degradesa large number of other vasodilator peptides, in-cluding ADM (67), and bradykinin, vasoconstrictorsincluding angiotensins I and II and endothelin-1, aswell as oxytocin, opioid peptides, substance P,gastrin, vasoactive intestinal peptide, and amyloidbeta protein (68). However, BNP is relatively resistantto its digestion. Given this enzyme’s broad actionprofile, it has had a variety of names, includingatriopeptidase, neutral endopeptidase, EC 3.4.24.11,enkephalinase, common acute lymphoblastic leuke-mia antigen, CD10, as well as neprilysin (NEP) (61);the latter will be the designation used in this paper(Figure 1).

NEP INHIBITION. In 1980, Roques et al. (69) synthe-sized thiorphan, a NEPi. Sybertz et al. (70) thenshowed that by inhibiting NEP, endogenous ANPlevels rose, and the latter’s natriuretic and diureticproperties became evident. Similar observations weremade in normal humans (71). In 1995, Ksander et al.(72) at Ciba-Geigy (which became an important unitof Novartis) described sacubitril, a NEPi that had su-perior pharmacologic properties, and which laterbecame a component of LCZ696. NEPi caused diuresisin pacing-induced HF in sheep (73) and dogs (74), andsuppressed the activation of aldosterone (75),demonstrating the important interaction between theNPS and RAAS. In patients with HF, NEPi loweredboth right atrial and wedge pressures and causednatriuresis (76).

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It was hoped that NEPis would become useful inthe management of hypertension and HF, but thesebeneficial effects in patients were modest and werenot seen in all studies (77). In addition to increasingthe concentration of circulating ANP (78), NEPis werefound to increase the concentration of 2 other circu-lating vasodilators, ADM and bradykinin (78,79).However, they also increased the concentration of 2circulating pressors, angiotensin II and endothelin I(80,81). These 2 opposing actions, that is, inhibitionof degradation of both vasoconstrictor and vasodi-lator peptides, neutralized each other and, as aconsequence, NEPis alone had little effect on bloodpressure (82) or HF (77).

With the discovery and elucidation of the actionsof NEP and its inhibitors, both the similarities anddifferences between the RAAS and the NPS becameclearer (Central Illustration). In normal subjects, theRAAS is activated, in part, by reduced stretch of theefferent renal arterioles as well as by stimulation ofbeta-1-adrenergic receptors through activation of thesympathetic nervous system. Activation of the sym-pathetic nervous system and RAAS provides anadaptive response to hypovolemia, hypotension, andsodium deprivation. This response includes therelease of renin, mostly from granular juxtaglo-merular cells in the walls of the afferent arterioles ofthe kidney, leading to the production of the pressorangiotensin II. This, in turn, causes vasoconstrictionof renal efferent arterioles, as well as release ofaldosterone, increasing sodium reabsorption in thecollecting duct. However, because these actions aremaladaptive when they occur in patients with HF orhypertension, reducing the generation of angiotensinII by ACEi or blocking its action with an ARB arebeneficial in these conditions. In contrast, atrial and/or ventricular distension, as occurs in HF and hyper-tension, causes the release of NPs from the heart,which results in vasodilation and natriuresis.Although these actions are beneficial (adaptive) inpatients with HF or hypertension, rapid enzymaticdegradation of ANP by endogenous NEP greatly di-minishes their vasorelaxant, natriuretic, and diureticactions. NEPis, while raising the concentration ofcirculating vasodilator peptides, especially ANP, havecomplex actions (as outlined earlier) and appear bythemselves not to be useful in the treatment of eitherHF or hypertension.

VASOPEPTIDASE INHIBITION

Because the previously mentioned elevation ofcirculating angiotensin II by NEPi (80,81) neutralizesits salutary vasorelaxant and natriuretic actions,

it appeared logical to ascertain whether the suppres-sion of angiotensin II production would correct thisproblem. In an important study published in 1991,Seymour et al. (83) compared the separate adminis-trations of a selective NEPi and of the ACEi captopril,as well as their simultaneous administration, intohypertensive rats. As predicted, the combinationresulted in a greater reduction of arterial pressurethan each inhibitor given separately (83). These ob-servations on the greater efficacy of dual therapywere confirmed in cardiomyopathic hamsters (84), aswell as in dogs and sheep with pacing-induced HF(85,86). The next important step was to developorally active molecules that inhibited both ACE andNEP, that is, dual inhibitors. This was accomplishedby Fournie-Zaluski et al. in 1994 (87).

Because of the potential promise of oral dual in-hibitors, referred to as vasopeptidase inhibitors,several pharmaceutical companies entered the field.Omapatrilat was the drug in this class that under-went the most extensive clinical testing (88). Itproduced greater reductions in arterial pressurethan did the ACEi, lisinopril, in patients with hy-pertension and increased the excretion of ANP,confirming that the dose used also exerted signifi-cant inhibition of NEP (89). IMPRESS (Inhibition ofMetalloprotease by Omapatrilat in a RandomizedExercise and Symptoms Study in Heart Failure), arandomized clinical trial, compared omapatrilat withlisinopril in 573 patients with HFrEF (90); a strongtrend toward greater benefit with omapatrilat wasreported. These early clinical studies generatedconsiderable excitement; indeed, in 2001, it wasanticipated that omapatrilat would be launched in2002 or early 2003, and that annual sales wouldquickly approach $2 billion (91).

A phase 3 trial in HF, the OVERTURE (OmapatrilatVersus Enalapril Randomized Trial of Utility inReducing Events) trial led by Packer, comparedomapatrilat with enalapril in 5,770 patients with HF.There was a nonsignificant trend for superiorityof omapatrilat in the primary endpoint (all-causemortality or hospitalization for HF) and a significantreduction of the secondary endpoint of cardiovascu-lar death or hospitalization (92). However, angioe-dema, which can obstruct the upper airways,occurred more frequently with omapatrilat (0.8%)than with enalapril (0.5%). In 4,284 hypertensivesubjects in phase 3 trials of omapatrilat, 0.9%developed angioedema and an additional 1%developed “head and neck edema” (93). In order toobtain a clearer understanding of the frequency ofthis complication, and, in particular, to compareomapatrilat with an ACEi, lisinopril, the OCTAVE

FIGURE 3 Effects

0

–4

Placebo effect = –7.72 mn = 154 to 172 /group

p=0.0–8

–12mm

Hg

–16

Mean Sitting Systolic

BP reduction in patie

drug for the NEPi LB

of the latter 2 drugs

Modified with permi

vals ¼ valsartan; oth

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(Omapatrilat Cardiovascular Treatment vs. Enalapril)trial was conducted in 25,302 hypertensive subjects.As expected, omapatrilat was superior to lisinopril inreducing blood pressure. However, the incidence ofangioedema was again significantly higher and moresevere in the subjects treated with omapatrilat(2.17%) than in those receiving lisinopril (0.68%).Among African American patients, the incidence wasgreater for both agents (5.53% vs. 1.62%) (93). Theincreased incidence of this serious, potentially life-threatening complication was presumed to berelated to the synergism between the ACE- and NEP-inhibiting actions of omapatrilat on the degradationof bradykinin (94). Omapatrilat inhibits a thirdenzyme, aminopeptidase P, which is also involved inthe breakdown of bradykinin (95). Bradykinin is notonly a vasodilator, but it also enhances prostaglandinconcentrations (19) and increases vascular perme-ability and fluid extravasation. Hence, the questionwas raised as to whether omapatrilat, which initiallyappeared to be an attractive drug, could be a “double-edged sword” (96). Primarily on the basis of obser-vations of increased angioedema in the OCTAVE trial,efforts to gain approval of omapatrilat approval and,indeed, further clinical research on the entire class ofvasopeptidase inhibitors were halted.

of LCZ696 on BP

Complementary Blood Pressure Loweringwith NEP inhibition and ARB

AHU200

–4.2 –4.7

–6.0

–5.3

–11.0

–6.4

–6.0

–12.5

–5.7

–1.3p=0.404

mHg

06 vs pbo

p=0.0006*

p=<0.0001*

Vals80

LCZ100

LCZ200

LCZ400

Vals160

Vals320

Valsartan LCZ 696 AHU 377

BP Reduction: Placebo-subtracted

nts with moderate hypertension with AHU 377 (sacubitril), the pro-

Q657, and also with various doses of valsartan and LCZ696. Doses

provided comparable degrees of angiotensin receptor blockade.

ssion from Ruilope et al. (99). BP ¼ blood pressure; pbo ¼ placebo;

er abbreviations as in Figure 1.

ANGIOTENSIN RECEPTOR-NEPRILYSIN

INHIBITOR

The next step was to combine the efficacy of vaso-peptidase inhibitors, that is, suppression of the RAASand inhibition of NEP, without their principal adverseeffect, that is, the inhibition of bradykinin and theresultant angioedema. This was accomplished simplyand cleverly by replacing the ACEi in omapatrilat withan ARB, because (in contrast to ACEis), ARBs do notinhibit the breakdown of bradykinin, with a resultantreduction of the risk of angioedema. In 2003, theNovartis Pharmaceutical Corporation applied forthe patent of a drug comprising a combination ofthe angiotensin antagonist valsartan and an NEPi,naming Webb and Ksander as the inventors (97).LCZ696 is a supramolecular complex of 6 molecules ofthe ARB valsartan with 6 molecules of the NEPi pro-drug, sacubitril (AHU377), creating a novel crystallinecomplex having a molecular weight of 5,748 (98) anda first-in-class ARNi. Following ingestion, sacubitril ismetabolized rapidly into the active NEPi, LBQ657. Guet al. (95) published phase I and II studies on LCZ696in 2010; the peak concentrations of both valsartanand LBQ657 occurred at about 3 h following oraladministration. The action of the ARB was reflected inthe rapid increases in the plasma renin and angio-tensin II concentrations. Simultaneously, cyclic gua-nosine monophosphate rose, reflecting an increase inthe concentration of ANP resulting from the NEPiaction of LBQ657.

In 2010, Ruilope et al. (99) compared LCZ696 withvalsartan in 1,328 hypertensive subjects. Systolic,diastolic, and pulse pressures, both sitting andambulatory, fell to a greater extent with LCZ696 thanwith either valsartan or the NEPi prodrug (AHU377)administered separately (Figure 3) (99). LCZ696was well tolerated, without excess cough and withno instances of angioedema. Similar findings werereported in an Asian population of hypertensivesubjects (100). Solomon et al. (101) conducted thePARAMOUNT (Prospective comparison of ARNiwith ARB on Management Of heart failUre with pre-served ejectioN fracTion) trial, a double-blind ran-domized trial in 301 patients with heart failurewith preserved ejection fraction (HFpEF), whichcompared LCZ696 with valsartan. The primaryendpoint, the decline in NT-proBNP at 12 weeks aftertreatment was begun, was significantly greater in theLCZ696 group than in the valsartan group (Figure 4).After 36 weeks, both left atrial volume and dimen-sion, which reflect left ventricular filling pressure,also declined more with LCZ696 (Figure 4), and therewas greater improvement in the New York Heart

FIGURE 4 Effects of LCZ696 in HFpEF

862 (733, 1,012)

783 (670, 914)

P = 0.063LCZ696/valsartan:0.77 (0.64, 0.92)P = 0.005

Weeks After Randomization

NT–p

roBN

P (p

g/m

l)

0200

300

400

500

600

700

800

900

1,000

5 10 12

605 (512, 714)

835 (710, 981)

Valsartan

LCZ696

Primary results of the PARAMOUNT trial in patients with HFpEF. Modified

with permission from Solomon et al. (101). HFpEF ¼ heart failure with pre-

served ejection fraction; NT-proBNP ¼ N-terminal fragment of pro–B-type

natriuretic peptide; PARAMOUNT ¼ Prospective comparison of ARNI with ARB

on Management Of heart failUre with preserved ejectioN fracTion.

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Association functional class with LCZ696 than withvalsartan.

In the PARADIGM-HF trial led by McMurray,Packer, and other academic investigators collabo-rating with scientists at Novartis, LCZ696 wascompared to the ACEi enalapril in 8,442 symptomaticpatients with HFrEF. As already noted, the trial wasstopped early for clinical benefit after amedian follow-up of 27 months (2,6). The hazard ratio for the primaryendpoint (cardiovascular death or hospitalization forHF), was 0.80; this ratio was also 0.80 for cardiovas-cular death, was 0.79 for hospitalization for HF, andwas 0.84 for death from any cause. The reductions inhazard ratios in each of these important endpointswere highly significant (p<0.0001). Over the course ofthe trial, the number of patients who needed to betreated to prevent 1 primary endpoint was 21, and toprevent 1 cardiovascular death was 32. AlthoughLCZ696 was associated with symptomatic hypoten-sion more frequently than was enalapril, this did notlead to more drug discontinuation. Elevations ofserum creatinine ($2.5mg/dl), potassium (>6mmol/l),and cough occurred significantly less frequently withLCZ696 than with enalapril. However, there was anonsignificant trend for an increase in angioedema(without airway compromise) with LCZ696 (n ¼ 19)compared with enalapril (n ¼ 10; p ¼ 0.13).

In a more recent report, the PARADIGM in-vestigators (102) indicated that, in comparison withenalapril, LCZ696 exhibited additional evidence ofclinical benefit, including a reduced need for inten-sification of the treatment for HF, fewer visits to anemergency department for HF, and a lower require-ment for intensive care or need for inotropic agents,an HF device, or cardiac transplantation. Progressivesymptoms of HF and elevations of NT-proBNP andtroponin were also reduced.

Although the results of PARADIGM HF are re-markably robust and promising, after the drug hasbeen approved, post-marketing observations will beof interest. Patients in the trial had a run-in periodand were randomized only if they tolerated bothstudy drugs. Both hypotension and a numeric in-crease of angioedema with LCZ696 were observedin PARADIGM HF, but neither led to serious con-sequences. It will be important to ascertain howthe drug is tolerated when it is used in clinicalpractice.

THE FUTURE

HF WITH PRESERVED EJECTION FRACTION. ThePARAMOUNT study (101) served as a hypothesis-generating trial for HFpEF. Given PARAMOUNT’s

encouraging results (Figure 4), the PARAGON (Pro-spective Comparison of LCZ696 with ARB GlobalOutcome in HF with Preserved Ejection Fraction)trial (NCT01920711) has begun. It is intended toenroll 4,300 patients with left ventricular ejectionfraction >45%.

RENAL DISEASE. There is now good evidence thatblockade of the RAAS by either ACEi or ARB slowsprogression in patients with chronic kidney disease,with and without diabetes (103,104). The NEPi, can-doxatrilat, has been shown to be associated withnatriuresis in patients with moderate impairment ofrenal function (105). Studies in partially nephrec-tomized rats (106) and in rats with diabetic ne-phropathy (107) have demonstrated that thevasopeptidase inhibitor, omapatrilat, was superior toan ACEi in slowing the progression of renal injury inthe remaining renal tissue. In both the IMPRESS (90)and OVERTURE (92) trials, omapatrilat was associ-ated with significantly fewer instances of worseningrenal function than the ACEi comparator. Similarfindings were observed with LCZ696 in the PARA-MOUNT trial (101). Also, in the PARADIGM-HF trial,which excluded patients with an estimated glomer-ular filtration rate <30 ml/min, fewer patients onLCZ696 developed a serum creatinine level$2.5 mg/dl(n ¼ 139, 3.3%) than did patients on enalapril (n ¼ 188,4.5%; p ¼ 0.007) (6).

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The totality of this information suggests thatLCZ696 may be superior to blockers of the RAAS onrenal function. This is being tested prospectively inthe UKHARP (UK Heart and Renal Protection) III trial(ISRCTN11958993), which is comparing LCZ696 withthe ARB, irbesartan, in patients with proteinuric renaldisease and an estimated glomerular filtrationrate $20 and <60 ml/min/1.73 m2 (108). Furthermore,because HF is a common, serious complication inpatients with end-stage renal disease, LCZ696 mightretard the development and/or progression of bothconditions.

AORTIC STIFFNESS. In the elderly, the stiffness ofthe aorta and large arteries raises the systolic bloodpressure, pulse pressure, and pulse wave velocity, all3 of which are independent predictors of adversecardiac events (109,110) and of the progression of renaldisease (111). It has been shown that noninvasivelydetermined central aortic blood pressure is superiorto brachial arterial pressures in estimating cardiovas-cular risk (112). In the Strong Heart study, central(aortic root) systolic pressure was a potent predictor ofleft ventricular hypertrophy, whereas pulse pressurewas a predictor of vascular hypertrophy (113). In 2002,Mitchell et al. (114) demonstrated the superiority ofomapatrilat over enalapril in reducing both centralaortic and peripheral arterial pulse pressures, reflect-ing a reduced stiffness of the aorta, perhaps broughtabout by the elevation of circulating ANP consequentto the NEPi activity of omapatrilat.

In the aforementioned study of hypertensive sub-jects, LCZ696 reduced both ambulatory systolic andpulse pressures more than did valsartan (99), afinding that is compatible with a reduction of aorticstiffness. Accordingly, the PARAMETER (Prospectivecomparison of Angiotensin Receptor neprilysin in-hibitor with Angiotensin receptor blocker Measuringarterial stiffness in the Elderly) study (NCT01692301)is comparing LCZ696 with an ARB (olmesartan) in 432elderly (age $60 years) hypertensive patients with apulse pressure >60 mm Hg (109). The endpoints arechanges in central aortic systolic and pulse pressuresdetermined noninvasively (115). LCZ696 is alsopromising for the treatment of serious and/or resis-tant hypertension.

CONCLUSIONS

The unambiguous superiority of clinical outcomes inpatients with HFrEF by the first ARNi over enalapril inthe PARADIGM HF trial (6,102,116) represents a sig-nificant achievement with important clinical impli-cations. LCZ696 may replace conventional ACEis orARBs in many patients with chronic HFrEF. The po-tential value of LCZ696 in HFpEF; in acute HF; in HFpatients with the cardiorenal syndrome; in the pre-vention of HF in asymptomatic patients with leftventricular hypertrophy, dilation, and/or dysfunc-tion; and in severe hypertension remains to bedetermined.

LCZ696 developed from the stepwise researchdescribed herein (Figure 1). Progress was slow in thefirst half of the 20th century, but it then acceleratedprogressively, especially after de Bold’s importantdiscovery in 1981 (34). Academic scientists carriedout the initial work defining the components of boththe RAAS and the NPS, some of whom conductedearly experiments on blocking these systems. Once itwas realized that blockade was potentially of greatclinical value, the pharmaceutical industry steppedin and provided enormous talent and resources tomove the field forward. Millions of patients withhypertension and HF worldwide have benefited fromACEis and ARBs, which are among the most usefuldrugs in the pharmacopeia. The most recent advance,the development and clinical assessment of a drugthat simultaneously blocks the RAAS, inhibits thebreakdown of vasodilator peptides, and appears to bewell tolerated, is an excellent example of the syn-ergies that can result from academic-industrialcollaborations.

ACKNOWLEDGMENTS The author thanks Drs. M. P.Lefkowitz and S. D. Solomon for their helpful reviewof the manuscript.

REPRINT REQUESTS AND CORRESPONDENCE: Dr.Eugene Braunwald, Department of Medicine, TIMIStudy Group, Brigham and Women’s Hospital, 350Longwood Avenue, Boston, Massachusetts 02115.E-mail: ebraunwald@partners.org.

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KEY WORDS hypertension,natriuretic peptide, renin