Novel Drugs Targeting Transthyretin Amyloidosis

PHARMACOLOGIC THERAPY (WHW TANG, SECTION EDITOR)

Novel Drugs Targeting Transthyretin Amyloidosis

Mazen Hanna

Published online: 25 January 2014# Springer Science+Business Media New York 2014

Abstract Transthyretin amyloidosis (ATTR) is either ahereditary disease related to a mutation in the transthyretingene that leads to neuropathy and/or cardiomyopathy or anacquired disease of the elderly that leads to restrictivecardiomyopathy. The prevalence of this disease is higherthan once thought and awareness is likely to increaseamongst physicians and in particular cardiologists. Untilrecently there have been no treatment options for thisdisease except to treat the heart failure with diureticsand the neuropathy symptomatically. However, there areseveral emerging pharmacologic therapies designed to slowor stop the progression of ATTR. This article reviews noveltherapeutic drugs that work at different points in the patho-genesis of this disease attempting to change its natural historyand improve outcomes.

Keywords Transthyretin . Amyloid . Amyloidosis .

Cardiac . Cardiomyopathy . Neuropathy . Familial . Senile .

Hereditary . Pharmacologic . Therapy . Drugs

Introduction

Amyloidosis is a condition in which misfolded proteinsaggregate into amyloid fibrils and deposit extracellularlyinto tissues disrupting organ architecture and function.There are over twenty-five proteins that have the propensityto form amyloid and each precursor protein defines the amy-loid type and predicts the organs involved [1]. The two maintypes of amyloidosis that affect the heart are light chain amy-loidosis (AL) and transthyretin amyloidosis (ATTR). Thesecause a restrictive cardiomyopathy with diffuse thickening ofboth ventricles, biatrial dilatation, and occasionally conductionsystem abnormalities [2, 3, 4••].

Light chain amyloidosis (AL) is a systemic disease inwhich the precursor protein is an immunoglobulin light chainsecreted by a clonal expansion of plasma cells in the bonemarrow. In AL, the treatment is chemotherapy for the under-lying plasma cell disorder and cardiac involvement has beenassociated with a worse prognosis with an untreated mediansurvival of less than one year [5]. This type of amyloidosis isnot the subject of this review.

Transthyretin amyloidosis (ATTR) is due tomisfolding of theprecursor protein transthyretin (TTR), either related to a muta-tion in the transthyretin gene leading to a hereditary form of thedisease, or related to the wild type protein leading to an acquiredform of the disease (see Table 1). The hereditary form is typi-cally referred to as Familial Amyloid Polyneuropathy (FAP) orFamilial Amyloid Cardiomyopathy (FAC). The acquired form isnamed Senile Systemic Amyloidosis (SSA) and is also referredto aswild type TTR cardiac amyloid. ATTR, both hereditary andacquired, is arguably not as rare as once thought and is becom-ing increasingly recognized amongst cardiologists [6•, 7]. Al-though the prognosis for ATTR is better than for AL, it is aprogressive disease that ultimately leads to death within 3 to15 years from either heart failure or disabling neuropathy [8].Until recently, there were no specific treatments for this type ofamyloidosis. However, over the past decade, there have beensignificant advancements in the development of specific drugstargeting the pathogenesis of this disease aiming to slow or haltamyloid deposition. The purpose of this review is to discussATTR with respect to these novel and emerging therapies.

What is Transthyretin?

Transthyretin (TTR) is a protein synthesized and secretedalmost exclusively by the liver that circulates in the plasma.TTR was formerly named Prealbumin because on electropho-resis it traveled faster than albumin. It was renamed“Transthyretin” in 1981 due to the fact that it serves as atransport protein for about 15 % of circulating plasma thyrox-ine as well as for retinol binding protein, hence, the name

M. Hanna (*)Section of Heart Failure and Cardiac Transplantation, ClevelandClinic, 9500 Euclid Avenue, Desk J3-4, Cleveland, OH 44195, USAe-mail: [email protected]

Curr Heart Fail Rep (2014) 11:50–57DOI 10.1007/s11897-013-0182-4

“trans-thy-retin” [9]. (Note, in laboratories today it is stillmeasured and reported as Prealbumin). TTR circulates as atetramer composed of four identical 127 amino acid mono-mers. The gene encoding the protein is found on chromosome18 and has four exons and five introns [10].

What is Hereditary Transthyretin Amyloidosis?

Mutations in the transthyretin gene can alter the 127-aminoacid sequence of the protein leading to mutant or “varianttransthyretin” that is prone to misfolding and forming amyloidfibrils. There have been over 100 mutations described andalmost all are single amino acid substitutions that lead to anautosomal dominant inherited disease that predominantly af-fects the nerves and the heart. The age of onset, diseasepenetrance, clinical phenotype, and prognosis all vary depend-ing on the specific mutation [11]. Patients usually present witheither a progressive sensorimotor and autonomicpolyneuropathy termed Familial Amyloid Polyneuropathy(FAP), or with a restrictive cardiomyopathy termed FamilialAmyloid Cardiomyopathy (FAC). Other organ systems canbe involved and several mutations can lead to a combinedneuropathy / cardiomyopathy phenotype [12••].

The most common mutation causing FAP is V30M (me-thionine replacing valine at amino acid 30), and althoughfound worldwide, is mainly clustered in Portugal, Japan, andSweden [13, 14]. Most patients present in their 30’s to 50’sand develop a progressive disabling neuropathy with an aver-age survival of 10 years. The most common mutation causingFAC is V122I (Isoleucine replacing Valine at amino acid 122)and is seen almost exclusively in African Americans. It isestimated that up to 4 % of African Americans are carriers ofthis mutation, which can lead to a late onset restrictive cardio-myopathy with minimal neuropathy phenotypically similar tosenile systemic amyloidosis (SSA) [15–17]. Many African-

Americans with this disease are likely to be misdiagnosed ashaving hypertensive heart disease or heart failure with pre-served ejection fraction (HFpEF). The average survival fromtime of diagnosis is about 2-3 years [18].

What is Senile Systemic Amyloidosis (SSA)?

Senile Systemic amyloidosis (SSA) is an acquired form of thedisease that occurs in older patients and, besides commonlycausing carpal tunnel syndrome, is clinically limited to the heart[12••]. It used to be named “Senile Cardiac Amyloidosis”;however, because there are subclinical deposits in several otherorgans including the GI tract and lungs, it was renamed SSA[19]. In this disorder, there is no mutation in the transthyretingene and the transthyretin protein is normal or “wild type”.Patients develop restrictive cardiomyopathy with significantthickening of the ventricles, often preceded by the appearanceof carpal tunnel syndrome about a decade earlier. The averageage of onset is 70 years of age and it is rare in those under theage of 60 [20]. There is a marked preponderance of males overfemales and most patients are Caucasian [21]. SSA is a moreindolent disease with an average survival of about 5-7 years.Based on autopsy studies, it is estimated that 5 % to 10 % ofpatients over the age of 80 years may have clinically significantSSA, andwith the expected increase in aging population, it maybecome the most common form of cardiac amyloid [22, 23].

What is the Pathogenesis of TransthyretinAmyloidosis?

Transthyretin is produced and secreted by hepatocytes as atetramer made up of four identical monomers and is boundtogether as a pair of dimers. Within the transthyretin tetramer,there is central channel at the dimer-dimer interface that

Table 1 Basics characteristics of hereditary and acquired transthyretin amyloidosis

Transthyretin Amyloidosis

Hereditary Acquired

Mutation in Transthyretin gene No mutation in Transthyretin gene

Mutant Protein Wild type protein

Greater than 100 mutations described “Senile Systemic Amyloidosis” (SSA)

Phenotype varies by mutation Average age of onset 70, prevalence ↑ w/ age

“Familial Amyloid Polyneuropathy” (FAP) Late onset Restrictive Cardiomyopathy +

“Familial Amyloid Cardiomyopathy” (FAC) Carpal tunnel syndrome

Survival varies by mutation Average Survival 5 – 7 years

Curr Heart Fail Rep (2014) 11:50–57 51

extends through the molecule and contains two indistinguish-able binding sites for thyroxine (see Fig. 1). The rate-limitingstep of amyloid fibril formation is dissociation of the TTRtetramer into two dimers. The dimers further dissociate intotheir constituent monomers which misfold and form oligo-mers that ultimately aggregate into mature amyloid fibrils [24,25]. The extracellular amyloid deposits not only contain themisfolded TTR fragments but, like in all forms of amyloid,also contain nonfibrillar components such as calcium, serumamyloid P component (SAP), and sulfonated glycosaminogly-cans. Amyloid fibrils are resistant to degradation, and it is rarefor fibrils to be cleared unless sustained reduction in the levelof the precursor protein is achieved [26].

Variant or mutant TTR, although different by only a singleamino acid, is more prone to tetramer disassembly andmisfolding at a lower thermodynamic threshold. Given thatthe phenotypic expression of the same mutation can varybetween patients, there are likely metabolic and environmen-tal factors that influence variant TTR misfolding. Since mostpatients are heterozygous for the mutation, amyloid depositsmay contain a mixture of variant and wild type TTR [27•].

In the case of SSA, it is not clear why the normal, wild typeprotein misfolds to form amyloid. It is also not clear why thishappens at older ages, and why some patients are more sus-ceptible than others. There is some evidence to suggest thatoxidative modifications of TTR that occur with aging changeits kinetic stability [28]. Based on autopsy studies, it appearsthat the susceptibility to develop wild type TTR amyloiddeposits steadily increases with age [22, 23].

Therapy for Transthyretin Amyloidosis

Therapy for ATTR consists of treatment of the affected organsystem and specific treatment of the disease process itself.Treating the restrictive cardiomyopathy of ATTR involves di-uretics and sodium restriction, trying to maintain normal sinusrhythm, and in general avoidance of negative chronotropic orinotropic agents like beta-blockers, unless needed for rate con-trol of atrial fibrillation. Treating the peripheral and autonomicneuropathy involves pain medications, Midodrine and anti-diarrheal agents. These treatments do not deal with the progres-sive nature of the amyloid deposition in the heart and nervesand are only temporizing and symptomatic.

Specific treatment for the disease process of ATTR initiallyemerged to treat FAP. The first therapy developed was livertransplantation as a strategy to remove the source of mutant“amyloidogenic” TTR and replace it with wild type non-mutantTTR. First performed in Sweden in 1990, there have been over2,000 liver transplants for hereditary ATTR,mainly for the mostcommon mutation V30M [29–31]. When performed early inthe course of disease, liver transplantation has been shown toslow progression of neuropathy and improve survival [32–34].

There are several limitations to liver transplantation as astrategy for ATTR. First, it does not eliminate progressionof amyloid deposition because wild type TTR can still formamyloid deposits on the preexisting template of mutantTTR deposits. Hence, there have been many reports ofprogression and even acceleration of amyloid depositiondespite liver transplantation, particularly in patients withnon-V30M mutations [35]. Second, there are the caveatsof organ availability, surgical morbidity and mortality, andthe need for lifelong immunosuppression. Third, it is not asolution for SSA in which wild type protein is deposited.Therefore, liver transplantation is not an ideal or practicalsolution for the problem of ATTR underscoring the needfor better and more generally applicable therapies. Al-though heart transplantation (with or without liver trans-plantation) can be done in highly selected cases with sig-nificant heart involvement, there are similar limitationswith this approach in addition to the fact that manypatients are not candidates due to advanced age [36, 37].

Fortunately over the past decade, with considerableprogress in understanding the pathophysiology of ATTR,great strides have been made in identifying pharmaco-logic agents that target various points in the diseaseprocess. The following is a discussion of novel drugstargeting ATTR and review of therapeutic strategies ac-cording to their mechanisms of action. There are threebasic pharmacologic strategies to treat ATTR (seeFig. 1).

1) Block hepatocyte synthesis of TTR2) Stabilize the TTR tetramer3) Promote clearance of TTR amyloid fibrils

Block Hepatocyte Synthesis of TTR

There has been substantial research in the area of preventinghepatocyte production of TTR at the translational level. Thebenefit of this approach is that it will, unlike liver transplan-tation, prevent production of both mutant and wild type TTRand thus be a potential treatment for both hereditary andacquired TTR amyloid. The theory is that reducing plasmaTTR to a very low level in a sustained fashion will ultimatelylead to less amyloid deposition and slow if not halt the diseaseprocess. The DNA sequence that encodes TTR is transcribedto a messenger RNA (mRNA). By interfering or binding tothat mRNA and not allowing it to be translated in the ribo-somal complex to make the TTR protein, a marked reductionin plasma TTR level can be achieved. There are two ap-proaches currently being studied in TTR amyloidosis, oneusing small interfering RNA’s and the other using anti-senseoligonucleotides; both achieving the same goal of blocking

52 Curr Heart Fail Rep (2014) 11:50–57

the transfer of genetic information from DNA to protein (seeFig. 1).

Small Interfering RNAs

RNA interference (RNAi) is an endogenous cellular mecha-nism for controlling gene expression in which small interfer-ing RNAs (siRNAs) that are bound to the RNA-inducedsilencing complex (RISC) mediate cleavage of target messen-ger RNA [38•]. Alnylam Pharmaceuticals (Cambridge, MA)has developed a lipid nanoparticle formulation of a syntheticsiRNA (patisiran, formerly known as ALN-TTR02) that tar-gets both mutant and wild-type TTR mRNA. By packagingthe siRNA inside a lipid nanoparticle, they are able to effi-ciently deliver the drug to hepatocytes in the liver where it istaken up by LDL receptors and released into the cytoplasm.The medication is given as an intravenous infusion andrequires premedication. Thus far, patisiran has been evaluatedin small dose-ranging studies in nonhuman primates, healthyvolunteers, and FAP patients. With mutlidosing, sustained sup-pression of serum TTR levels by >80 % was observed and wasgenerally safe and well-tolerated [39•]. A multinational PhaseIII randomized placebo-controlled study (APOLLO trial)testing patisiran in FAP patients with defined neuropathyendpoints was initiated in November 2013.

Alnylam has also developed a GalNAc conjugate formula-tion of an siRNA targeting mutant and wild-type TTR pro-duction by the liver that allows it to be given subcutaneouslywithout premedication (ALN-TTRsc). This has been tested in

a Phase I study in healthy volunteers showing similar dramaticreductions in serum TTR levels to >90 % of baseline withmultidosing. A Phase II open-label pilot trial will study thepharmacodynamics and clinical activity of ALN-TTRsc inpatients with TTR cardiac amyloidosis (both SSA and FACpatients) and started enrollment in December of 2013. ThePhase I and Phase II studies mentioned above will pave theway for a pivotal Phase III trial in TTR cardiac amyloidosisplanned to start in late 2014. Given that TTR is a carrierprotein for retinol binding protein and a minor carrier forthyroxine, all studies will follow vitamin A levels and thyroidfunction.

Antisense Oligonucleotides

Antisense oligonucleotides (ASOs) are synthetic single-stranded oligomers of typically 20 nucleotides in length thatare designed to be complementary to a specific region in atarget mRNA and bind to the mRNA via Watson-Crick basepairing. Binding of the ASO to the target mRNA engages anendogenous enzyme called RNase H1 that degrades the boundmRNA, thus preventing production of the disease-associatedprotein [40]. Isis Pharmaceuticals (Carlsbad, CA) has devel-oped an ASO targeted to the TTRmRNA named ISIS-TTRRx.Binding of ISIS-TTRRx to the TTR mRNA prevents produc-tion of both mutant and wild-type TTR protein, therefore,potentially treating all forms of TTR amyloidosis. ISIS-TTRRx is water-soluble and is administered in saline withoutspecial formulation via a weekly subcutaneous injection. This

Fig. 1 Schematic diagram of the pathophysiology of transthyretin amy-loidosis (ATTR). The first step is hepatocyte production of transthyretin(TTR) by translation of TTRmessenger RNA (TTRmRNA) followed bysecretion of the tetramer into the plasma. The rate-limiting step of amy-loid formation is dissociation of the tetramer into dimers, which

ultimately results in the aggregation of multiple monomeric fragmentsinto mature fibrils. Drugs for ATTR work by blocking TTR synthesis,stabilizing the tetramer by binding the thyroxine (T4) binding pocket, orpromoting removal of already deposited fibrils. EGCG: Epigallocatechin-3-gallate; TUDCA: Tauroursodeoxycholic acid; SAP: Serum amyloid P


drug has been evaluated in a Phase 1 single-dose and multiple-dose study in healthy volunteers and showed up to a 90 %reduction in TTR levels after four weeks of dosing [41].Results from the Phase 1 study allowed dose selection anddirect initiation of a pivotal Phase 3 double-blind, placebocontrolled study to assess the efficacy and safety of ISIS-TTRRx in FAP patients. This multicenter international studywas initiated in December 2012 and is currently ongoing.

Stabilize the TTR Tetramer

Stabilizing the TTR tetramer and preventing its dissociationblocks the rate-limiting step of TTR amyloid formation. Be-cause TTR is the secondary carrier of thyroxine (T4) in plasma(the main ones being thyroid binding globulin and albumin),greater than 95 % of TTR’s T4 binding capacity remains freeand the two T4 binding sites at the dimer-dimer interface arelargely unoccupied (See Fig. 1). The strategy of administeringsmall molecules that bind in the TTR T4 pocket to kineticallystabilize the native tetramer and prevent its dissociation waspioneered by Jeff Kelly’s lab at the Scripps Research Institutein La Jolla, CA [24]. Numerous small molecules have beenstudied and thus far two drugs have come to the forefront to betested in randomized clinical trials, namely Diflunisal andTafamadis.

Diflunisal

Diflunisal (Dolobid) is a nonsteroidal anti-inflammatory drugthat has been used for decades for the treatment of arthritis. Ithas been shown that Diflunisal, unrelated to its nonsteroidal anti-inflammatory activity, binds to the thyroxine binding sites onthe TTR tetramer thus kinetically stabilizing and preventingacid mediated fibril formation in vitro [42–45]. Diflunisalwas recently studied in a 130-patient, international, multicenter,randomized, placebo-controlled trial in patients with FAP. Sub-jects were followed for 2 years with the primary endpoint beingthe difference in polyneuropathy progression as measured by astudy neurologist’s clinical assessment and specific nerve con-duction studies. The primary endpoint was met, with Diflunisaltreated patients showing substantially less polyneuropathy pro-gression compared to placebo (p value of <.001) [46••]. Drugrelated adverse events did not differ between the twogroups and Diflunisal was relatively well tolerated in thispopulation.

The concerns for using Diflunisal in TTR cardiac amyloidosisare the side effects of GI bleeding and fluid retention, particularlyin more elderly patients with significant heart failure. Castanoand colleagues conducted a single arm study of 13 patients withTTR cardiac amyloidosis who were given Diflunisal 250 mg bid(alongwith a proton pump inhibitor) in an open label fashion andfollowed for about one year [45]. Over the study period there

were no hospitalizations for heart failure, although in one patienttherapy was discontinued due to>10 lb. weight gain and inanother patient the dose was halved due to fluid retention. Therewere no GI bleeding events, but there was a mild reduction inGFR. The conclusion of this small study was that Diflunisal wasreasonably well tolerated in TTR cardiac amyloid patients, al-though careful monitoring is essential for safe administration. Todate there is no planned randomized study of Diflunisal in TTRcardiac amyloid, but given the encouraging findings in FAP,some patients are taking this medication off-label under thedirection and close scrutiny of their cardiologists.

Tafamadis

Tafamidis (Vyndaqel), like Diflunisal, is another small mole-cule that selectively binds to the thyroxine binding site andstabilizes the TTR tetramer [25]. The advantage overDiflunisal is that it does not possess NSAID activity, havingpotentially less side effects. Tafamadis was studied in a multi-center randomized, placebo-controlled trial of 126 patientswith FAP, specifically with the V30M mutation and earlystage I neuropathy [47••]. The primary endpoint was relatedto The Neuropathy Impairment Score-Lower Limbs (NIS-LL)which quantifies the motor, sensory, and reflex function in thelower limbs. Although the primary endpoint was not met inthe prespecified intent-to-treat population, there was a statis-tically significant benefit in the treatment group with respectto a prespecified efficacy evaluable analysis of those patientswho completed the 18 month treatment protocol. Based onthis data, Tafamadis received approval in Europe for FAPpatients with stage I polyneuropathy to delay progression.This data was presented to the FDA, but it has yet to beapproved in the United States.

Tafamadis will be studied in TTR cardiac amyloid (SSAand FAC) in a large international multicenter placebo-controlled trial. This trial, which began recruitment in Decem-ber 2013, plans to enroll up to 400 patients with a primaryendpoint of all-cause mortality and heart failure hospitaliza-tions over a 30 month follow up period.

Promote Clearance of TTR Amyloid Fibrils

All amyloid fibrils, regardless of the type, are composed offragments of the misfolded precursor protein as well as othercomponents such as calcium, serum amyloid P component(SAP), and glycosaminoglycans. Once amyloid fibrils havedeposited extracellularly, they are resistant to degradation.Although there is some evidence that sustained reduction inthe precursor protein can lead to amyloid reversal, this is notcommon. Recently, there have been several agents underinvestigation attempting to promote clearance of amyloidfibrils regardless of the amyloid type.


Doxycycline

In a transgenic mouse model, both for AL and ATTR, itwas shown that the antibiotic Doxycyline was capable ofdisrupting amyloid fibrils with a putative mechanism offibril destructuration and promotion of amyloid depositreabsorption [48, 49]. Tauroursodeoxycholic acid(TUDCA), a biliary acid with antioxidant and antiapoptoticactivities, decreases toxic TTR prefibrillar aggregates intransgenic TTR mice without a significant effect on maturefibrils [50]. Based on this animal data with these twopotentially complementary agents, a Phase II open labelstudy testing Doxycyline (100 mg bid) in combination withtauroursodeoxycholic acid (TUDCA) in 40 FAP patientswas conducted over a 12-month period. The interim anal-ysis on the first 20 patients enrolled showed no clinicalprogression in cardiac endpoints (Echo, NT-pro BNP, andNYHA class) or in neuropathy endpoints (Neuropathyimpairment score-lower limbs) [51]. Currently, Brighamand Women’s hospital is conducting an open label trialusing the same combination of Doxycyline + TUDCA inpatients with transthyretin cardiac amyloid (SSA and FAC)evaluating the rate of progression as measured by longitu-dinal strain echocardiography over an 18 month period. Todate, there is no planned randomized placebo-controlledtrial evaluating Doxycycline in transthyretin amyloid.

Epigallocatechin-3-Gallate

Epigallocatechin-3-gallate (EGCG) is the most predominantpolyphenol in green tea. In vitro experiments have shown thatEGCG efficiently inhibits fibril formation due to variousamyloid precursor proteins, including TTR, and also disruptsamyloid fibrils by converting existing fibrils into non-fibrilconformers [52–54]. EGCG also stabilizes circulating TTRtetramers by binding a dimer-dimer site distinct from the T4binding site [55]. In a cohort of patients with AL amyloidcardiomyopathy, EGCG was associated with a decrease ininterventricular septal wall (IVS) thickness, increase in leftventricular ejection fraction, and an improvement in NYHAclassification [56]. Kristen and colleagues in Germany studied14 patients with TTR cardiomyopathy who consumed greentea or green tea extracts over a one year period and found thatthere was decrease in IVS thickness and in LV mass in mostpatients [57]. Although the studies with EGCG are small, theyare encouraging and a larger placebo-controlled trial would benecessary to establish its efficacy.

Anti-SAPAntibodies

Serum Amyloid P component (SAP) is a plasma glycoproteinfrom the Pentaxrin family that is a universal component ofamyloid fibrils. It contributes to amyloidogenesis by stabilizing

amyloid fibrils and retarding their breakdown and clear-ance [58, 59]. Research into designing antibodiesagainst SAP was pioneered by Mark Pepys in Londonwith the hope that antibody mediated removal of thiscomponent would facilitate endogenous clearance mech-anisms of amyloid fibrils. This has been studied inanimal models as well as in a heterogeneous group ofamyloid patients with encouraging data that amyloidfibril burden can be reduced [26, 60, 61]. A study oftwo anti-SAP antibodies in patients with systemic amy-loidosis evaluating pharmacokinetic data and efficacywill begin recruiting in July of 2014 (ClinicalTrials.govNCT01777243).

Conclusion

Transthyretin amyloidosis (ATTR) affects patient of all agesand is found worldwide both in a hereditary form (FAP andFAC) and in an acquired form (SSA). Due to increasingawareness and better noninvasive diagnostic tools, it is likelythat this disease will be diagnosed with higher frequency andno longer be considered rare. The previously held nihilisticattitude towards pursuing a diagnosis of cardiac amyloidshould change given the substantial progress made in identi-fying novel drugs that may alter the natural history of thedisease. There are ongoing studies testing agents that blockhepatocyte production of TTR, stabilize the tetramer in plas-ma, or promote clearance of already deposited fibrils. To date,two randomized studies in FAP patients have already beencompleted, which has led to drug approval of Tafamadis inEurope [47••], and will likely lead to the repurposing ofDiflunisal for this indication [46••] Randomized clinical trialsfor TTR cardiac amyloid will hopefully be completed withinthe next 3–5 years and provide us further data in thispopulation.

Twenty years ago, HIV was a universally fatal viral infec-tion with an inexorable decline to death. Patients are nowtreated with highly active antiretroviral therapy with a combi-nation of drugs that target different mechanisms of viral rep-lication, and currently many patients with HIV can live yearswith an undetectable viral load. The future vision for ATTRwould be much like that of HIV today, to become a diseasetreated with several drugs that work in concert by differentmechanisms to halt its progression, and hopefully even oneday reverse it.

Compliance with Ethics Guidelines

Conflict of Interest Mazen Hanna received a one-time consultant feefrom Pfizer in April 2012 regarding input for the drug Tafamadis. He isalso the local principal investigator of the Tafamadis CardiomyopathyTrial and is a member of the Scientific Board for THAOS (TransthyretinOutcomes Survey), both sponsored by Pfizer.


Human and Animal Rights and Informed Consent This article doesnot contain any studies with human or animal subjects performed by anyof the authors.

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35. Okamoto S et al. Prognostic value of pre-transplant cardio-myopathy in Swedish liver transplanted patients for familialamyloidotic polyneuropathy. Amyloid. 2011;18 Suppl 1:171–3.

36. Nelson LM et al. Long-term outcome in patients treated withcombined heart and liver transplantation for familial amyloidoticcardiomyopathy. Clin Transplant. 2013;27(2):203–9.

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38.• Lachmann HJ. A new era in the treatment of amyloidosis? N Engl JMed. 2013;369(9):866–8. A very insightful editorial in response tothe New England Journal publication about small interfering RNAtreatment in TTR amyloid. This summarizes the current issues andstrategies very well.

39.•• Coelho T et al. Safety and efficacy of RNAi therapy for transthyretinamyloidosis. N Engl J Med. 2013;369(9):819–29. Along with anti-sense oligonucleotides, this is a major breakthrough and publication


in the field. Getting published in the New England Journal ofMedicine has brought transthyretin amyloidosis into greater aware-ness amongst physicians.

40. Malik R, Roy I. Making sense of therapeutics using antisensetechnology. Expert Opin Drug Discov. 2011;6(5):507–26.

41. Ackermann EJ et al. Clinical development of an antisense therapyfor the treatment of transthyretin-associated polyneuropathy.Amyloid. 2012;19 Suppl 1:43–4.

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43. Gales L et al. Human transthyretin in complex with iododiflunisal:structural features associated with a potent amyloid inhibitor.Biochem J. 2005;388(Pt 2):615–21.

44. Sekijima Y, Dendle MA, Kelly JW. Orally administered diflunisalstabilizes transthyretin against dissociation required foramyloidogenesis. Amyloid. 2006;13(4):236–49.

45. Castano A et al. Diflunisal for ATTR cardiac amyloidosis. CongestHeart Fail. 2012;18(6):315–9.

46.•• Berk JL et al. Repurposing diflunisal for familial amyloidpolyneuropathy: a randomized clinical trial. JAMA. 2013;310(24):2658–67. This is the only randomized placebo-controlled trial intransthyretin amyloidosis that has met its primary endpoint. Thislandmark clincial trial will likely lead to the approval of Diflunisalfor the indication of FAP.

47.•• Coelho T et al. Tafamidis for transthyretin familial amyloidpolyneuropathy: a randomized, controlled trial. Neurology.2012;79(8):785–92. This was the first randomized placebo-controlledtrial in transthyretin amyloidosis. Although the primary endpoint wasnot met, the results led to the approval of Tafamdis in Europe.

48. Cardoso I, SaraivaMJ. Doxycycline disrupts transthyretin amyloid:evidence from studies in a FAP transgenic mice model. FASEB J.2006;20(2):234–9.

49. Ward JE et al. Doxycycline reduces fibril formation in a transgenicmouse model of AL amyloidosis. Blood. 2011;118(25):6610–7.

50. Cardoso I et al. Synergy of combined doxycycline/TUDCAtreatment in lowering Transthyretin deposition and associatedbiomarkers: studies in FAP mouse models. J Transl Med.2010;8:74.

51. Obici L et al. Doxycycline plus tauroursodeoxycholic acid fortransthyretin amyloidosis: a phase II study. Amyloid. 2012;19Suppl 1:34–6.

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54. Palhano FL et al. Toward the molecular mechanism(s) by whichEGCG treatment remodels mature amyloid fibrils. J AmChem Soc.2013;135(20):7503–10.

55. MiyataM et al. The crystal structure of the green tea polyphenol (-)-epigallocatechin gallate-transthyretin complex reveals a novel bind-ing site distinct from the thyroxine binding site. Biochemistry.2010;49(29):6104–14.

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