Abstract

Introduction

Transthyretin amyloidosis (ATTR) is both an inherited and an age-related amyloidosis. The most common phenotypic presentations of hereditary ATTR are sensorimotor and autonomic polyneuropathy (TTR familial amyloid polyneuropathy (TTR-FAP)) and cardiomyopathy [1]. The protein implicated in ATTR, TTR, is a tetrameric transport protein for thyroxine and the retinol-binding protein–retinol (vitamin A) complex [2, 3]. TTR is synthesized primarily in the liver [4]. Mutations in the gene that encodes for TTR cause dissociation of the TTR tetramer to monomers. This leads to the formation of insoluble fibrillar proteins (or amyloid) that accumulate and produce deleterious effects on tissues and organ function [5–8].

The age at onset of ATTR varies between the second and ninth decades of life, and there is great heterogeneity in genetic penetrance, depending on phenotype, genotype, and environmental factors [1, 9]. However, the outcome of ATTR is invariably progressive and fatal: After a mean interval of 10 years from initial presentation of symptoms, patients usually die from progressive and relentless worsening of the neuropathy, secondary infections, cachexia, or cardiac complications [1, 9, 10].

More than 100 amyloidogenic TTR point mutations have been identified in patients with familial ATTR [11, 12]. The most common genetic variant associated with polyneuropathy is Val30Met (valine replaced by methionine at position 30 of the amino acid chain), which accounts for ≈85 % of TTR-FAP cases worldwide [13, 14]. Generally, non-Val30Met mutations are associated with greater cardiac involvement than Val30Met mutations [12, 14], and patients with non-Val30Met mutations and a cardiac phenotype tend to be older men and have lower survival rates [15].

Liver transplantation, which removes the main site of mutant TTR production, has been the only disease-modifying treatment option for TTR-FAP. Following transplantation, mutant transthyretin protein becomes undetectable in serum [16, 17]; neurological symptoms frequently halt or improve [18]; and the reported 5-year survival rate is 77 % [18, 19]. However, cardiac disease tends to progress even after successful liver transplantation, especially in non-Val30Met patients, most likely due to the deposition of wild-type TTR on pre-existing amyloid deposits [1, 9]. Indeed, several non-Val30Met variants, including Glu42Gly, Ala36Pro [20], Ser52Pro, and Ile84Thr [21], have been linked to rapid postoperative progression of TTR cardiac amyloidosis. This partially explains why, according to recent data from the Familial Amyloid Polyneuropathy World Transplant Registry, the rate of survival at 5 years is significantly worse in patients with non-Val30Met mutations compared to patients with the Val30Met mutation (59 % versus 82 %; p<0.0001) [14] and has led to the proposal to consider the extremely challenging procedure of combined heart and liver transplantation in certain ATTR patients with cardiac involvement [1, 22]. Taken together, this underlines the need for additional treatment options not only for patients with ATTR in general but also for patients with non-Val30Met mutants in particular.

Tafamidis meglumine (Pfizer Inc, New York, NY, USA) is an oral agent that occupies the two thyroxine binding sites on TTR. This is associated with inhibition of dissociation of TTR into monomers, the rate-limiting step in amyloid formation [11, 23]. In an 18-month, double-blind, placebo-controlled, randomized trial, tafamidis demonstrated TTR stabilization and slowed the progression of peripheral neurological impairment compared with placebo in patients who had TTR-FAP associated with Val30Met mutations [24]. Individuals with other TTR variants were excluded from that study. The primary objective of our open-label, single-arm study was to determine the pharmacodynamic stabilization effects of tafamidis on non-Val30Met TTR variants. The safety and exploratory efficacy of tafamidis were also evaluated.

Materials and Methods

Results

Patients

Of the 21 patients enrolled, 18 (85.7 %) completed the trial. One patient discontinued in part 1 due to an SAE (transient ischemic attack), and two patients discontinued in part 2 due to organ transplants. The baseline demographics for the intent-to-treat population are presented in Table 1. The mean (±standard deviation (SD)) duration of ATTR-related symptoms at baseline was 64.7±60.8 months (median, 45.5 months), with a mean age at onset of 59.3±9.2 years (median, 61.0). Table 2 displays the results of the patients’ baseline assessments. The patients demonstrated significant impairment in neurological function (NIS: mean ± SD, 48.7±44.3 and median, 45.0; Σ5 NCS: mean ± SD, 6.1±5.9 and median, 6.7) and disease-specific QOL (mean ± SD Norfolk TQOL score, 47.8±35.1; median, 38.0). Of note, the mean mBMI at the baseline visit was 1,052.5±206.7 kg/m²×g/L (median, 1,047.8), which meaningfully exceeds the screening threshold associated with improved survival following liver transplantation of 600 kg/m²×g/L [39].

Table 1

Baseline demographic characteristics (intent-to-treat population)

Characteristic	Tafamidis 20 mg (N=21)
Age, years
Mean ± SD	63.1±9.9
Median	64.3
Range	43.9–76.8
Gender, n (%)
Male	13 (61.9)
Female	8 (38.1)
TTR genotype, n (%)
Asp38Ala	1 (4.8)
Gly47Ala	3 (14.3)
Leu58His	4 (19.0)
Thr60Ala	4 (19.0)
Phe64Leu	4 (19.0)
Ser77Phe	1 (4.8)
Ser77Tyr	2 (9.5)
Ile107Val	2 (9.5)
Duration of ATTR-related symptoms, months
Mean ± SD	64.7±60.8
Median	45.5
Range	5.2–253.1
Age at ATTR symptom onset, years
Mean ± SD	59.3±9.2
Median	61.0
Range	43.0–72.0

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ATTR transthyretin amyloidosis, SD standard deviation, TTR transthyretin

Table 2

Baseline assessments (intent-to-treat population)

Characteristic	Tafamidis 20 mg (N=21)
Baseline mBMI, kg/m2×g/L
N	20a
Mean ± SD	1,052.5±206.7
Median	1,047.8
Range	725.0–1,409.6
NIS total score (range, 0–244)
Mean ± SD	48.7±44.3
Median	45.0
Range	0–131.9
NIS-LL (range, 0–88)
Mean ± SD	27.6±24.7
Median	18.0
Range	0–69.9
NIS-UL (range, 0–156)
Mean ± SD	21.1±21.4
Median	13.0
Range	0–65.6
Σ5 NCS nds composite (range, –15 to 15)
Mean ± SD	6.1±5.9
Median	6.7
Range	−3.7 to 14.8
Norfolk QOL-DN (TQOL) (range, –2 to 138)
Mean ± SD	47.8±35.1
Median	38.0
Range	5.0–104.0

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mBMI modified body mass index, NIS Neuropathy Impairment Score, NIS-LL NIS of the lower limbs, NIS-UL NIS of the upper limbs, Σ5 NCS nds summated five-nerve conduction studies normal deviate scores, QOL-DN quality of life–diabetic neuropathy, TQOL total quality of life

^aOne patient had no mBMI value because there was no screening serum albumin level

The enrolled patients had eight different non-Val30Met TTR mutations (Table 1). All patients except one reported symptoms of peripheral neuropathy, 13 of 21 (62 %) reported symptoms of cardiac involvement, and 5 of 21 (23.8 %) had peripheral and autonomic neuropathy plus cardiomyopathy. All patients demonstrated at least one echocardiographic abnormality, the most common being left ventricular posterior wall thickness and left ventricular septal thickness of >12 mm, which were each observed in 17 of 19 (89.5 %) patients. Abnormalities on electrocardiography were also common at baseline, occurring in 16 of 21 (76.2 %) of patients. Of these, conduction abnormalities were the most common, in 13 of 21 (61.9 %) patients, and left anterior hemiblock and first-degree atrioventricular block were the most frequent conduction abnormalities.

TTR Stabilization

TTR stabilization at Week 6 was achieved in 18 (94.7 %) of the 19 intent-to-treat patients for whom both baseline and Week 6 data were available (Table 3). Two intent-to-treat patients were not included in the analysis at Week 6: One discontinued prior to Week 6 due to a SAE, and one had a missing baseline assay value (thus, postbaseline TTR stabilization could not be determined for this patient at any timepoint). Only one patient (TTR mutation Gly47Ala) did not demonstrate TTR stabilization at Week 6. In the absence of apparent issues with compliance or AEs, this patient was reassessed at Month 3 and allowed to continue in the study because he did achieve stabilization at Months 3 and 6 but discontinued before Month 12 to undergo an organ transplant. At Months 6 and 12 (the secondary endpoints), 100 % of the patients available for assessment achieved TTR stabilization (Table 3).

Table 3

TTR stabilization

Parameter	Tafamidis 20 mg (N=21)
Week 6a	n=19
Number (%) stabilized	18 (94.7)
95 % CI	74.0 %–99.9 %
Month 6b	n=18
Number (%) stabilizedc	18 (100.0)
95 % CI	81.5 %–100.0 %
Month 12c	n=17
Number (%) stabilized	17 (100.0)
95 % CI	80.5 %–100.0 %

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^aTwo patients were excluded from the 6-week analysis: One patient discontinued prior to Week 6 due to a serious adverse event. The other patient did not have a baseline pharmacodynamic assay assessed; therefore, TTR stabilization at Week 6 and Months 6 and 12 could not be determined

^bOne additional patient was excluded from the 6-month analysis. The patient was discontinued prior to Month 6 for organ transplant. The patient achieved TTR stabilization at Week 6

^cOne additional patient was excluded from the 12-month analysis. The patient was not stabilized at Week 6 but was stabilized at Months 3 and 6 and was discontinued prior to Month 12 for organ transplant

Changes in Neurological Function

At Month 12, the mean increases from baseline in NIS, NIS-LL, and NIS-UL were 5.3 (95 % CI, –1.0, 11.5; median change, 1.6), 2.7 (95 % CI, –0.4, 5.8; median change, 1.0), and 2.5 (95 % CI, –1.2, 6.2; median change, 0.5), respectively (Fig. 1). Patients with a higher baseline NIS (>70) experienced a greater increase in NIS (i.e., a worsening of impairment) after 12 months compared with patients whose baseline scores were lower. Twelve of the 18 patients with data at Month 12 experienced a change in NIS of ≤4 points at 12 months. These 12 patients represented all enrolled mutations, suggesting a similar treatment effect across mutations.

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Fig. 1

Change from baseline in NIS, NIS-LL, and NIS-UL scores in the intent-to-treat population. While the baseline scores in the NIS (mean ± SEM, 48.7±9.7; median, 45.0), NIS-LL (mean ± SEM, 27.6±5.4; median, 18.0), and NIS-UL (mean ± SEM, 21.1±4.7; median, 13.0) indicated the presence of significant neurological impairment affecting both lower and upper limbs, mean and median changes from baseline to Months 6 and 12 in NIS, NIS-LL, and NIS-UL presented in this figure increased marginally, with the maximal mean change from baseline being an increase of 5.3 (SEM=3.0) in the NIS total score at Month 12. This suggests that neuropathy progressed minimally during tafamidis treatment. This is an observed cases analysis including the values of those patients for whom both baseline and Month 6 or baseline and Month 12 data were available. Bars indicate the range of scores; boxes span from the 25th to the 75th percentiles; the horizontal line within the box indicates the median change; plus sign indicates the mean change. SEM standard error of the mean, NIS Neuropathy Impairment Score, NIS-LL NIS of the lower limbs, NIS-UL NIS of the upper limbs

There was a small mean increase of 0.2 (95 % CI −1.5, 1.8) in Σ5 NCS nds score from baseline to Month 12, with a median change of −0.1. When the analysis was performed excluding patients with maximal abnormality in large nerve-fiber function at baseline (and, thus, no possibility of further worsening), the results at Month 12 were similar, with a mean change of 0.3 (95 % CI −2.1, 2.6).

QOL and mBMI

The mean changes from baseline in the TQOL were −4.3 (95 % CI, –10.7, 2.1; median change, 0.0) at Month 6 and 0.1 (95 % CI, –8.9, 9.0; median change, 1.0) at Month 12 (Fig. 2). The mean mBMI (kilograms per square meter×grams per liter) decreased by −22.4 (95 % CI, –62.0, 17.2; median change, –26.7) at Month 6 and increased by 16.6 (95 % CI, –31.0, 64.2; median change, 8.3) at Month 12 (Fig. 3).

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Fig. 2

Change from baseline in Norfolk QOL-DN (TQOL) scores in the intent-to-treat population. While the baseline TQOL score (mean ± SEM, 47.8±7.7; median, 38.0) indicated impaired quality of life, this figure shows that mean and median changes from baseline in TQOL at Months 6 and 12 were negligible, indicating that overall quality of life was maintained during 12 months of tafamidis treatment. This is an observed cases analysis. Bars indicate the range of scores; boxes span from the 25th to the 75th percentiles; the horizontal line within the box indicates the median change; plus sign indicates the mean change. SEM standard error of the mean, QOL-DN quality of life–diabetic neuropathy, TQOL total quality of life, CI confidence interval

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Fig. 3

Change from baseline in mBMI scores (expressed as kilograms per square meter×grams per liter) in the intent-to-treat population. Starting with a relatively normal mBMI at baseline (mean ± SEM, 1,052.5±46.2; median, 1,047.8), the mBMI decreased slightly from baseline to Month 6 (mean change ± SEM, –22.4±18.7; median change, –26.7) and subsequently increased, producing a small positive overall change from baseline to Month 12 (mean change ± SEM, 16.6±22.3; median change, 8.3), indicating that the overall nutritional status was maintained after 12 months of tafamidis treatment. The mBMI has been adapted as a measure of nutritional status in TTR amyloidosis patients, as multiplying the BMI (kilograms per square meter) by serum albumin level (grams per liter) corrects for weight gains due to swelling and edema formation frequently associated with TTR amyloidosis. Bars indicate the range of scores; boxes span from the 25th to the 75th percentiles; the horizontal line within the box indicates the median change; plus sign indicates the mean change. SEM standard error of the mean, mBMI modified body mass index

Cardiac Function and Progression of Amyloid Heart Disease

Table 4 summarizes echocardiographic parameters in the study group at baseline and 12-month follow-up (pre-specified analysis). Values remained relatively stable from baseline to Month 12, with no clinically relevant changes.

Table 4

Change from baseline in echocardiographic parameters

	Tafamidis 20 mg
Parameter	Baseline	Change from baseline at Month 12
Posterior LVW thickness, mm	n=19	n=14
Mean ± SD	14.6±2.6	0.7±1.7
Median	14.0	1.0
Range	9, 20	−2, 4
Interventricular septal thickness, mm	n=19	n=14
Mean ± SD	15.2±2.8	1.0±2.0
Median	15.0	1.0
Range	8.5, 20.0	−1.0, 6.0
Left atrial diameter (anterior–posterior), mm	n=21	n=16
Mean ± SD	36.3±6.2	1.6±3.5
Median	37.0	2.0
Range	22, 48	−6, 10
LV Mass, g	n=19	n=14
Mean ± SD	230.8±62.5	20.9±35.1
Median	224.0	19.3
Range	142.0, 369.0	−27.0, 113.0
LV ejection fraction, %	n=21	n=18
Mean ± SD	60.3±10.0	−2.2±5.4
Median	61.0	−2.5

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LVW left ventricular wall, SD standard deviation, LV left ventricular

Results of the post hoc analysis in patients with amyloid heart involvement at baseline (based on the standard diagnostic criterion IVS >12 mm [1, 38]) and a valid assessment at Month 12 (n=12) were consistent with the findings for the entire group; no clinically meaningful changes in morphological or functional parameters were observed over the 12-month treatment period. Four of the 12 patients did demonstrate disease progression as indexed by International Society of Amyloidosis criteria (increase in IVS thickness ≥2 mm [38]).

Mean baseline troponin I concentrations were normal compared with established laboratory test ranges and remained stable throughout the study. Baseline mean and median NT-pro-BNP levels were elevated in all patients, with no clinically relevant changes over time. Mean increases in NT-pro-BNP concentrations were 228.4 (95 % CI −186.8, 643.6) pg/mL at Month 6 and 306.6 (95 % CI −464.8, 1078.0) pg/mL at Month 12. Median values for change from baseline in NT-pro-BNP were 66.5 pg/mL at Month 6 and 75.5 pg/mL at Month 12.

Figure 4 indicates the median baseline values and median changes from baseline in NT-pro-BNP levels in: (a) the ten patients classified as having a high likelihood of heart failure (based on NT-pro-BNP levels >1,000 pg/mL at the Screening or baseline visit); and (b) in the nine patients with a low likelihood of heart failure (based on NT-pro-BNP levels <300 pg/mL at the Screening or Baseline visit). Patients with a high likelihood of heart failure had a median increase in NT-pro-BNP levels of 521 pg/mL at Month 12, compared with a median increase of 47 pg/mL in patients with a low likelihood of heart failure. Nine of the ten patients with a high likelihood of heart failure had a pretreatment history of cardiac events, including heart failure/dyspnea (three patients) and arrhythmias (three patients). While on treatment, six of these ten patients experienced events that were suggestive of heart failure (four occurrences of peripheral edema and two of dyspnea were reported). One of the cases of moderate peripheral edema occurred in a high likelihood heart failure patient with no reported cardiac history at baseline. In addition, one of these patients was recognized to have moderate coronary artery stenosis during treatment and one required the insertion of a pacemaker. In the patients considered to be at low likelihood of heart failure, one experienced arrhythmia while on treatment with no identified prior history of arrhythmia.

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Fig. 4

Median and median change from baseline/screening in NT-pro-BNP levels in patients with a high likelihood of heart failure (baseline NT-pro-BNP >1,000 pg/mL) and b low likelihood of heart failure (baseline NT-pro-BNP <300 pg/mL). Based on their highest NT-pro-BNP level at baseline/screening, ten patients with values >1,000 pg/mL were categorized as having a high likelihood, and nine patients with levels <300 pg/mL were classified as having a low likelihood of congestive heart failure, where the normal range is <160 pg/mL. The median NT-pro-BNP level in patients with high likelihood of heart failure increased by 521 pg/mL at Month 12. In contrast, the median NT-pro-BNP level in patients with low likelihood of heart failure increased only marginally by 47 pg/mL at Month 12. NT-pro-BNP N-terminal pro-hormone brain natriuretic peptide

Discussion

In this phase II, open-label study, we demonstrated the efficacy of tafamidis in stabilizing TTR in a series of patients with TTR-FAP associated with eight different non-Val30Met TTR mutations. Stabilization of TTR was seen in all but one patient at the 6-week primary endpoint and in all patients remaining at the 6- and 12-month secondary endpoints. This finding was accompanied by some worsening of neurological function at Month 12 (NIS-LL score) but also with maintenance of QOL (Norfolk QOL-DN total score) and mBMI.

A relationship between TTR tetramer stabilization and clinical outcomes has been established in carriers of the Val30Met mutation that simultaneously carry an Arg104His or Thr119Met trans-suppressor mutation on their second TTR allele [40–42]. Such compound heterozygotes develop mild pathology or no disease because the trans-suppressor mutation increases the kinetic barrier for tetrameric dissociation, thereby blocking the rate-limiting step of amyloid formation [40–42]. Given that tafamidis also increases the threshold for tetramer dissociation, it appears reasonable to assume a similar causal relationship between TTR stabilization and the positive clinical outcomes seen in this trial.

The finding of TTR stabilization in this study is consistent with the 18-month, double-blind, placebo-controlled trial of tafamidis in patients with Val30Met TTR-FAP, in which 98 % of patients treated with tafamidis achieved TTR stabilization at 18 months [24]. Overall, tafamidis has been shown to stabilize TTR in 36 of 37 studied genotypes. In addition to the nine variants in these two studies, these genotypes include Val122Ile and wild-type TTR (from an open-label study in TTR amyloid cardiomyopathy) [43], as well as an additional 25 of 26 mutations tested in an ex vivo study, with one TTR mutation (Pro24Ser) demonstrating equivocal results potentially related to the long storage time of the plasma sample [23, 25]. This consistent response across variants is notable, given the large number of point mutations that are associated with ATTR [12].

One unexpected finding is that the one patient who did not achieve TTR stabilization at Week 6 (but was allowed to continue tafamidis treatment as a protocol deviation) did actually achieve stabilization at later time points. This interesting result shows that a decision to exclude this patient based on the Week 6 assessment would have been premature and will be reflected in our future study designs.

In the double-blind, placebo-controlled, randomized trial of tafamidis, patients on active treatment had 52 % less neurological deterioration on the NIS-LL after 18 months compared with placebo (a secondary endpoint), with a change from baseline of 2.81 versus 5.83 points, respectively; p=0.027 [24]. In the present study, a similar change from baseline (2.7 points) was observed on the NIS-LL after 12 months of treatment. It is possible that our trial duration was not long enough to detect a significant change in neurological course of the disease. The patients in our study were also older than those in the double-blind trial, with more severe cardiac involvement and more advanced neuropathy [24].

It should be noted that efforts to address the need for data on long-term outcomes of treatment are in progress. Longer-term data are expected from an open-label extension study that includes the patients who completed the current trial as well as those from the 18-month trial (NCT00925002). All patients will be followed in the open-label study until tafamidis is commercially available in their respective countries. Of note, since European Medicines Agency approval in 2011, tafamidis is now available in most European countries for the treatment of TTR amyloidosis in adult patients with Stage 1 symptomatic polyneuropathy. In addition, long-term data on TTR-FAP patients enrolled in the Transthyretin Amyloidosis Outcomes Survey (THAOS) registry, including data from tafamidis-treated patients, will become available. These efforts are also expected to provide data on survival and functional outcomes such as ambulation.

Because of the reported high prevalence of cardiac manifestations in non-Val30Met ATTR, we assessed cardiac involvement by multiple modalities, including cardiac biomarkers, electrocardiography, and echocardiography. Only one patient had elevated concentrations of troponin I at baseline which remained elevated at all post-baseline timepoints. Patients with NT-pro-BNP levels >1,000 pg/mL (high risk for heart failure) experienced cardiac events consistent with the presence of heart failure while receiving treatment, including peripheral edema and dyspnea. This group demonstrated a median increase in NT-pro-BNP of 520.5 pg/mL over time. Patients with baseline NT-pro-BNP concentrations of <300 pg/mL (low risk for heart failure) demonstrated a median increase in NT-pro-BNP concentrations of 47 pg/mL during treatment.

Despite a large proportion of patients with electrocardiographic and echocardiographic abnormalities at baseline, some of which were of several years duration, there was very little apparent change in cardiac morbidity during the year of treatment. Only four patients demonstrated an increase in IVS thickness of ≥2 mm.

Tafamidis appeared to be well tolerated over 12 months. The AEs reported were not unexpected for the age, neurological status, and cardiac conditions of patients in the study.

In addition to its relatively short duration, this study has several other limitations, most notably the single-arm, open-label design that makes it impossible to determine the efficacy of tafamidis to slow or halt disease progression. While a double-blind, placebo-controlled trial is ideal, the exceedingly low prevalence of TTR-FAP associated with mutations other than Val30Met made such a design impractical. An inherent limitation of the primary endpoint measure is that the immunoturbidimetric assay performed under non-physiological conditions has been developed as a qualitative measure of TTR stabilization and thus cannot quantitate the degree of stabilization in vivo. The cardiac biomarkers (troponin I and NT-proBNP) may be influenced by other factors, such as sodium and fluid ingestion, blood pressure, and paroxysmal supraventricular arrhythmia.

Overall, in patients with TTR-FAP due to the eight mutations evaluated, tafamidis at a dose of 20 mg QD was well tolerated and effectively stabilized TTR in all but one patient by Week 6 and in all patients by Month 6. Although some worsening of neurological function was observed, mBMI and QOL were maintained, and there did not appear to be clinically relevant worsening in cardiac status. Longer-term follow-up is needed to delineate the potential longer-term effects of TTR stabilization on these outcomes, as well as controlled trials specifically evaluating the effects of tafamidis on cardiac function and outcomes.

Acknowledgments

Footnotes

References