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Effect of TTP488 in patients with mild to moderate Alzheimer’s disease
© Burstein et al.; licensee BioMed Central Ltd. 2014
Received: 16 May 2013
Accepted: 6 January 2014
Published: 15 January 2014
TTP488, an antagonist at the Receptor for Advanced Glycation End products, was evaluated as a potential treatment for patients with mild-to-moderate Alzheimer’s disease (AD). A previous report describes decreased decline in ADAS-cog (delta = 3.1, p = 0.008 at 18 months, ANCOVA with multiple imputation), relative to placebo, following a 5 mg/day dose of TTP488. Acute, reversible cognitive worsening was seen with a 20 mg/day dose. The present study further evaluates the efficacy of TTP488 by subgroup analyses based on disease severity and concentration effect analysis.
399 patients were randomized to one of two oral TTP488 doses (60 mg for 6 days followed by 20 mg/day; 15 mg for 6 days followed by 5 mg/day) or placebo for 18 months. Pre-specified primary analysis, using an ITT population, was on the ADAS-cog11. Secondary analyses included as a key secondary variable the Clinical Dementia Rating-Sum of Boxes (CDR-SB), and another secondary variable of the ADCS-ADL.
On-treatment analysis demonstrated numerical differences favoring 5 mg/day over placebo, with nominal significance at Month 18 (delta = 2.7, p = 0.03). Patients with mild AD, whether defined by MMSE or ADAS-cog, demonstrated significant differences favoring 5 mg/day on ADAS-cog and trends on CDR-sb and ADCS-ADL at Month 18. TTP488 plasma concentrations of 7.6-16.8 ng/mL were associated with a decreased decline in ADAS-cog over time compared to placebo. Worsening on the ADAS-cog relative to placebo was evident at 46.8-167.0 ng/mL.
Results of these analyses support further investigation of 5 mg/day in future Phase 3 trials in patients with mild AD.
Alzheimer’s Disease (AD) is a neurodegenerative disorder with aspects of inflammatory, metabolic and vascular pathology [1, 2]. An overproduction of amyloid beta (Aβ) has been implicated as the leading mechanistic factor in AD pathology. Aβ is known to bind to The Receptor for Advanced Glycation Endproducts (RAGE) an immunoglobulin supergene family member expressed on multiple cell types in the brain and the periphery [3, 4]. RAGE is found on the cells of the neurovascular compartment: endothelial cells and microglia prominently express RAGE whose expression is upregulated in AD [5, 6]. RAGE ligands include Aβ, S100b, HMGB1 and Advanced Glycation Endproducts. RAGE-ligand interactions lead to sustained inflammatory states that play a role in chronic diseases such as diabetes, inflammation, and AD [7, 8]. In AD, RAGE has been proposed to contribute to AD pathology by: promoting vascular leakage, promoting influx of peripheral Aβ into brain; mediating Aβ-induced oxidative stress and Aβ mediated neuronal death [9–12].
The pleiotropic role of RAGE has been demonstrated in AD pathology has been described using rodent models. Mice expressing the human APP transgene in neurons develop significant biochemical and behavioral changes reminiscent of human AD. Double transgenic mouse overexpressing WT RAGE in the APP transgene background exhibit accelerated behavioral changes whereas double transgenic animals expressing a dominant negative mutant of RAGE are protected . This data suggests that RAGE plays a role in augmenting the chronic inflammatory state caused by overproduction of Aβ.
RAGE is thought to be involved in the transport of Aβ from peripheral to CNS compartments . In vivo, Aβ uptake into brain is dependent on RAGE as shown in RAGE null mice . Similarly, Aβ uptake in brain can be inhibited using either the secreted, soluble form of RAGE (called sRAGE) or an anti-RAGE antibody . In addition, plaque formation in a mouse model of cerebral amyloidosis was inhibited using sRAGE [15, 16]. These data suggest that RAGE is intimately involved in the pathogenesis of AD, and that sustained Aβ interaction with RAGE on blood brain barrier (BBB) and/or neuronal cells is an important element of amyloid plaque formation and chronic neuronal dysfunction.
TransTech Pharma, Inc. discovered TTP488, an orally active, centrally acting antagonist of RAGE-RAGE ligand interaction. Chronic oral dosing of TTP488 in AD transgenic mice led to a reduction of amyloid load in the brain, improved performance on behavioral testing and normalization of electrophysiological recordings from hippocampal slices .
This manuscript describes analyses of the effect of TTP488 5 mg/day, versus placebo, on the Alzheimer’s Disease Assessment Scale-Cognitive (ADAS-cog)  after 18 months of treatment, in patients on stable background therapy with acetylcholinesterase inhibitors and/or memantine, based on an “on-treatment” definition of the study population. Additionally, analysis of the ADAS-cog, Clinical Dementia Rating Sum of Boxes (CDR-sb)  and the Alzheimer’s Disease Cooperative Study – Activities of Daily Living scale (ADCS-ADL)  for mild sub-population and characterization of the pharmacokinetic/pharmacodynamic relationship of TTP488 to ADAS-cog are described.
This Phase 2, multicenter, randomized, double-blind, placebo-controlled, parallel, three-arm, multiple dose study was conducted at 40 study sites in the United States between January 2007 and December 2010 (ClinicalTrials.gov identifier NCT00566397.) The study was approved by each study site’s Local Institutional Review Board (see Additional file 1). Each patient provided written informed consent. If patients had impaired decisional capacity, caregivers provided consent and patients provided assent.
Eligible patients were aged ≥ 50; met the criteria for a diagnosis of probable AD ; had a MMSE  score between 14 and 26, had a modified Hachinski (Rosen) score ≤4, were receiving treatment with a stable dose of an acetylcholinesterase inhibitor and/or memantine for ≥ 4 months prior to randomization. Patients were excluded for clinically significant neurologic, psychiatric or other diseases contributing to his/her dementia, MRI and/or CT evidence of stroke or significant cerebrovascular disease, uncontrolled hypertension, unstable cardiac or pulmonary disease, diabetes (or hemoglobin A1c at screening > 6%).
Study design and treatment
Enrollment targeted 399 patients (133 per group), randomized (1:1:1) to placebo, or TTP488 20 mg daily (after a loading dose of 60 mg daily for 6 days), or 5 mg daily (after a loading dose of 15 mg daily for 6 days), for 18 months. An independent Data and Safety Monitoring Board (DSMB) monitored the safety of subjects in the trial.
Study visits occurred at screening, baseline, then at four weeks, 3, 6, 9, 12, 15, 18 months, with a safety follow-up visit at 21 months. Visits included clinical and safety evaluations, blood draw for plasma biomarker and pharmacokinetic analysis, and pill counts to assess compliance. Brain MRIs were obtained at baseline, 12 and 18 months. Lumbar punctures for CSF biomarkers were performed at baseline and 12 months on a subgroup of subjects.
The primary efficacy measure was the ADAS-cog . The ADAS-cog/12-item (scored 0–80) scale was administered before the first dose, and at 3, 6, 9, 12, 15 and 18 months with the pre-specified analyses being on the ADAS-cog/11-item scale (Scored 0–70). The key secondary clinical measure was the CDR-sb . The ADCS-ADL was included as a secondary measure . Both CDR-sb and ADCS-ADL were administered prior to dosing and at months 6, 12 and 18.
Blood samples for TTP488 PK analysis were collected prior to dosing at Week 1, at Months 1, 3, 6, 9, 12, 15, 18, and 21 and at Early Termination.
The full analysis set (FAS) consisted of all subjects who received at least 1 dose of study medication, and had a baseline (if applicable for the endpoint being analyzed) and post-baseline observation for the measurement of interest. The results of this analysis have been presented previously . The on-treatment analysis set was defined as all available on treatment data, where “on treatment” was defined as date of last dose plus 45 days (this definition was used because the drug has a long ½ life of 10–20 days).
The primary analysis planned in the study protocol compared differences in mean treatment effect using 5 statistical methodologies that cope with missing data in different ways, with multiple-imputation methods demarked as primary and others as supportive (supportive methods included endpoint analysis, observed cases, generalized estimating equations (GEE), and mixed-models repeated measures on the longitudinal data). Point estimates, standard errors, confidence intervals, and p-values were computed using the statistical models as planned. For all analyses alpha = 0.05, as the supportive analyses were planned to ensure robustness against missing data.
Baseline measures of the variable of analysis are recommended covariables for statistical modeling . Subgroup analysis for covariables of baseline severity of AD can be based on MMSE or ADAS-cog, the latter of which is the variable of analysis. Use of the baseline ADAS-cog can reduce heterogeneity, thereby increasing the sensitivity of detecting delineation between treatments.
Blood samples (5 mL) for TTP488 plasma concentrations were collected in dipotassium (K2) EDTA tubes prior to dosing at Week 1, months 1, 3, 6, 9, 12, 15, 18, 21 and at Early Termination. Samples were centrifuged at approximately 1700 g for about 10 minutes at 4°C with plasma stored in polypropylene tubes at approximately -20°C within 1 hour of collection. Plasma samples were analyzed for TTP488 concentrations using a validated HPLC-MS/MS method.
Exploratory analyses relating TTP488 plasma concentration (including the 20 mg/day and 5 mg/day dose groups) to ADAS-cog values, and changes over time, utilized deriving a subject-level value by two methods: (1) deriving the subject level value by the maximum of the trough concentration values for that subject over the 18-month period, and (2) deriving the subject level value by taking the median concentration value for that individual. Analyses were done at the subject level.
Subjects were classified into concentration groups according to quintile cut-points in the distribution of concentration values ignoring administered dose.
Analysis of mild vs. moderate subgroups
Protocol-planned analyses included subgroup analysis based on baseline severity of AD. ADAS-cog and CDR-sb changes from baseline were analyzed (ANCOVA adjusted for baseline main effects) by baseline disease severity using an MMSE based definition of mild AD (MMSE ≥ 20). ADAS-cog, CDR-sb and ADCS-ADL were additionally evaluated (2-sample t-test) using an ADAS-cog based definition of mild AD (ADAS-cog ≤ 19). An ADAS-cog value of 19 was selected based on conversion of a traditional cut-off of an MMSE value of 20, used in the analyses reported above, to a corresponding ADAS-cog value using the previously described linear relationship between ADAS-cog and MMSE (ADAS-cog = 56.4-1.86*MMSE) .
With approximately 133 subjects per group, the primary study had 80% power to detect a 3 point difference in change from baseline to 18 months in ADAS-cog scores between a TTP488 dose group and placebo, allowing for 25% missing data and two interim analyses. ADAS-cog 18- month changes from baseline were assumed to have a standard deviation of 6.5 points for all treatment groups. A total experiment-wise Type 1 error rate of α= 0.05 was targeted.
Patient demographic and baseline clinical characteristics (including all on- and off-drug data)
TTP488 20 mg/day
TTP488 5 mg/day
(n = 135)
(n = 131)
(n = 133)
73.0 ± 9.0
73.6 ± 8.8
72.2 ± 9.6
Sex (% women)
15.0 ± 3.0
14.8 ± 2.8
15.3 ± 2.8
19.9 ± 3.6
20.8 ± 3.5
20.5 ± 3.4
Mild (MMSE ≥20), n(%)
Moderate (MMSE < 20), n(%)
24.9 ± 9.7
24.4 ± 9.8
24.1 ± 9.6
5.7 ± 2.9
5.6 ± 2.7
6.0 ± 2.8
61.3 ± 12.9
61.4 ± 12.3
59.9 ± 12.8
7.9 ± 10.5
7.7 ± 10.3
8.6 ± 10.4
APOE e4+status, n (%)
AchEI use, n(%)
Memantine use, n (%)
Changes from baseline in ADAS-cog for on-treatment population
1.43 ± 0.50
3.02 ± 0.62
5.14 ± 0.75
7.18 ± 0.81
8.96 ± 1.07
(n = 126)
(n = 118)
(n = 106)
(n = 95)
(n = 83)
(n = 63)
1.58 ± 0.44
3.16 ± 0.54
3.99 ± 0.68
6.26 ± 0.69
8.74 ± 0.91
11.63 ± 1.15
(n = 127)
(n = 114)
(n = 109)
(n = 101)
(n = 86)
(n = 59)
p = 0.03
Exploratory analysis by disease severity
TTP488 Plasma concentration driven analysis
TTP488 median and mean trough concentrations associated with the 5 mg/day and 20 mg/day dose groups
TTP488 dose group
TTP488 mean concentrationa
TTP488 median concentrationb
95% confidence interval of the mean
Median of subjects’ trough values
5 mg/day (n = 131)
20 mg/day (n = 134)
Mean of subjects’ trough values
5 mg/day (n = 131)
20 mg/day (n = 134)
Changes from baseline in ADAS-cog for each quintile TTP488 concentration range over 18 months of treatment
n = 129
n = 50
n = 51
n = 52
n = 47
n = 48
n = 115
n = 48
n = 49
n = 48
n = 37
n = 46
n = 112
n = 39
n = 46
n = 42
n = 27
n = 40
n = 105
n = 32
n = 42
n = 37
n = 22
n = 31
n = 89
n = 30
n = 37
n = 30
n = 21
n = 24
n = 64
n = 25
n = 26
n = 25
n = 15
n = 19
This Phase 2 trial explored the safety and efficacy of 2 doses levels of TTP488, compared to placebo, in patients with mild-to-moderate AD. Post-futility, protocol-specified analyses of changes in ADAS-cog showed a favorable effect in the 5 mg/day dose group compared to placebo at month 18. Sensitivity analyses using methodologies that cope with missing data differently indicated that conclusions were invariant to statistical model or methodology, thereby supporting the robustness of the result. Post-hoc analyses of subjects “on treatment” also demonstrated significant treatment effects for the 5 mg/day dose group.
Effects on the ADAS and CDR-SB were slightly greater and similar in magnitude, respectively, in mild versus moderate subjects defining each subgroup based on MMSE. Given the MMSE is a brief screening test, analyses based on an ADAS-cog based definition of mild AD (consistent with recommended statistical methodologies for accommodating baseline measures of the variable of analysis as a covariable) provide additional confirmation of the effect of TTP488 in patients with mild AD. The inability to demonstrate a significant effect on the ADAS-cog and CDR-sb, despite clinically meaningful numerical effect sizes, in moderate subjects is presumably due the smaller group size and increased variability. While a 5 mg dose of TTP488 may impart beneficial effects in both mild and moderate subjects, enrichment of a study population for mild subjects may allow for not only a greater magnitude of effect but early demonstration of clinical effects.
The results of analyses of ADAS-cog, based on plasma concentrations suggest 5 mg/day, associated with plasma concentrations of 7.6-16.8 ng/mL, as a dose that would be associated with beneficial effects on cognition relative to placebo. While concentrations above 46.8 ng/mL were associated with reversible worsening of cognition in TTP488 treated subjects, the ability to safely dose subjects in the concentration range of 17.0-46.3 ng/mL provides an adequate safety margin for the 5 mg/day dose thereby allowing for accommodation of increased intersubject variability that may be seen in an expanded Phase 3 population.
This Phase 2 trial demonstrated a 3.1 point difference in ADAS-cog at 18 months for the 5 mg/day dose relative to placebo in patients with mild-to-moderate AD; an effect supported by “on-treatment” analyses of the data. Secondary analyses evaluating the effect in mild patients demonstrated a significant effect on ADAS-cog and trend on CDR-sb and ADCS-ADL at 18 months. This finding supports the enrichment of future TTP488 trials with mild subjects, to allow for demonstration of effects with a dose of 5 mg/day plus standard of care.
Funding was provided by Pfizer, Inc. and by the National Institute on Aging (grant AG10483).
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