N-terminal-targeted anti-amyloid monoclonal antibodies illuminate the therapy for Alzheimer’s disease: a systematic review and comprehensive meta-analysis
Authors: Qiu Yu-Hui , Liu Ming , Zhan Jie , Liu Ling-Ling , Zheng Jia-Yi , Wu Dan , Wu Guang-Liang , Cai Ye-Feng , Zhang Shi-Jie 
Published: November 2023

Background

Recent clinical trials of anti-amyloid-beta (Aβ) monoclonal antibodies (mAbs) have demonstrated that the removal of Aβ in symptomatic patients can slow down the progression of Alzheimer’s disease (AD) and reinforce the “amyloid cascade” hypothesis. However, further investigation and analysis of integrated clinical data is needed to interpret the clinical efficacy of these mAbs. In this study, we aimed to estimate the effectiveness of mAbs for AD and firstly assessed the therapeutic efficacy from a perspective of mAbs targeting specific Aβ domains (N-terminal, C-terminal, central domain, and N-terminal+central domain) in pre-specified subgroups.

Methods

In this systematic review and meta-analysis, we searched on Pubmed, Embase, the Cochrane Library, andClinicalTrials.govfrom their inception until 31 August, 2023, and updated our search on 15 October, 2023, to identify all published randomised controlled trials (RCTs) on various clinical outcomes of anti-Aβ mAbs in AD. The primary outcomes of interest included Alzheimer’s Disease Assessment Scale-cognitive subscale (ADAS-cog), Mini Mental State Examination (MMSE), and Clinical Dementia Rating scale-Sum of Boxes (CDR-SB), as well as amyloid positron emission tomography (PET), the main biomarker. Additionally, we collected the data of volumetric Magnetic Resonance Imaging (vMRI), cerebrospinal fluid (CSF), plasma AD biomarkers, and the risks of amyloid-related imaging abnormalities (ARIA). Random-effects models to calculate pooled risk ratios (RRs) and standardized mean differences (SMDs) were employed to analyze the data across multiple studies of all mAbs. Furthermore, we also examined the interrelationships among changes in alterations of cognitive performance, Aβ deposition, variations in AD biomarkers, and the risks of ARIA both in all mAbs and N-terminal-targeted mAbs by calculating Pearson’s correlation coefficients. This study is registered with PROSPERO, No. CRD42023430637.

Findings

We identified a total of 37 eligible studies on quality assessment, of which 34 were included in the meta-analysis. The analysis revealed that eight monoclonal antibodies (aducanumab, lecanemab, donanemab, bapineuzumab, gantenerumab, crenezumab, solanezumab, and ponezumab) demonstrated statistical improvements in cognitive outcomes. Specifically, the ADAS-cog [(total mAbs: SMD: -0.08, 95% CI: -0.11 to -0.04); (N-terminal-targeted mAbs: SMD: -0.08, 95% CI: -0.13 to -0.03)], CDR-SB [(total mAbs: SMD: -0.06, 95% CI: -0.12 to -0.00); (N-terminal-targeted mAbs: SMD: -0.08, 95% CI: -0.16 to -0.01)], and MMSE [(total mAbs: SMD: 0.06, 95% CI: 0.02 to 0.10); (N-terminal-targeted mAbs: SMD: 0.05, 95% CI: -0.00 to 0.10)] demonstrated significant improvement. In addition, the meta-analyses indicated that mAbs also had a statistically significant impact on reducing amyloid PET [(total mAbs: SMD: -1.13, 95% CI: -1.66 to -0.61); (N-terminal-targeted mAbs: SMD: -1.64, 95% CI: -2.27 to -1.02)], accelerating ventricle enlargement [(total mAbs: SMD: 0.22, 95% CI: 0.06 to 0.38); (N-terminal-targeted mAbs: SMD: 0.44, 95% CI: 0.30 to 0.57)], and causing whole-brain atrophy [(total mAbs: SMD: -0.14, 95% CI: -0.26 to -0.03); (N-terminal-targeted mAbs: SMD: -0.24, 95% CI: -0.41 to -0.07)], while increased the risk ARIA-E (total mAbs: RR: 9.79, 95% CI 7.83 to 12.26); (N-terminal-targeted mAbs: RR: 10.79, 95% CI: 8.61 to 13.52)] and ARIA-H [(total mAbs: RR: 1.28, 95% CI 0.98 to 1.67); (N-terminal-targeted mAbs: RR: 1.94, 95% CI: 1.64 to 2.29)]. However, no significant hippocampal volume atrophy was observed [(total mAbs: SMD: 0.00, 95% CI: -0.07 to 0.07); (N-terminal-targeted mAbs: SMD: -0.03, 95% CI: -0.13 to 0.07)]. It should be noted that all above effects were more significant in AD patients treated with N-terminal-targeted mAbs, as observed in subgroup analyses. Additionally, we observed a negative association between ventricular enlargement and Aβ clearance (Pearson’s r: -0.76), especially with the administration of N-terminal-targeted mAbs (Pearson’s r: -0.79), indicating a stronger effect on Aβ clearance. Moreover, there was a strong negative correlation between the improvement in cognitive function and the preservation of hippocampal volume (Pearson’s r: -0.70), particularly in the case of N-terminal-targeted mAbs. Lastly, a strong correlation was also found between the risk of ARIA and Aβ reduction in amyloid PET (Pearson’s r: -0.60), brain atrophy (Pearson’s r: -0.83), and ventricle enlargement (Pearson’s r: 0.92).

Interpretation

The administration of mAbs that specifically target the N-terminus of Aβ showed promising results in reducing Aβ burden and ameliorating cognitive decline. Furthermore, our preliminary findings shed light on the occurrence of brain atrophy, ventricular enlargement, and ARIA, might be attributed to the well clearance of Aβ deposits caused by mAb administration. In future anti-Aβ mAb development, our systematic review and meta-analysis indicated that N-terminal-targeted mAbs is an optimizing approach.

Funding

This work was supported by National Natural Science Foundation of China (No. 82004430, 82174310).

Research in context

Evidence before this study

The recent trials of lecanemab and donanemab have provided initial conclusive evidences that removal of Aβ from symptomatic patients’ brains can decelerate the progression of Alzheimer’s disease (AD). These findings offer clinical substantiation for the significance of aberrant Aβ in AD pathogenesis, thereby reinforcing the validity of the "amyloid cascade" hypothesis. While, the clinical benefit of the monoclonal antibodies (mAbs) is still limited and it is important to note that the treated subjects are still experienced disease progression, albeit at a slower rate. Targeting various forms of Aβ (monomers, oligomers, fibrils) is considered as the key mechanism of these mAbs’ efficacy. However, the results indicated that it is not crucial direction to explain the ideal antibody efficacy. In order to discover underlying mechanisms and formulate an enhanced immunotherapeutic regimen, it is essential to further analyze the integrated data of clinical trials.

Added value of this study

This comprehensive systematic review and meta-analysis not only encompassed all reported RCTs investigating the effects of anti-Aβ mAbs on various clinical outcomes in AD, but also firstly assessed the therapeutic efficacy of targeting specific Aβ domains (N-terminal, N-terminal+central-domain, central-domain, and C-terminal) by subgroup analyses. Enhanced data syntheses of all included 34 studies demonstrated significant enhancements in cognitive outcomes (ADAS-cog, CDR-SB and MMSE) with the utilization of mAbs. The meta-analysis also revealed that mAbs significantly reduced amyloid burden and certain AD biomarkers, expedited ventricle enlargement and whole-brain atrophy, concurrently increased the risk of ARIA. In addition, a notable efficacy was observed in AD patients by using the mAbs targeting the N-terminus of Aβ, as evidenced by subgroup analyses by employing different epitopes of Aβ.

Association analysis identified that there was a positive correlation between the extent of reduction in Aβ deposition after mAbs therapy and the degree of improvement in cognitive function, thereby supporting Aβ plaques as a pivotal driver of cognitive decline in AD and emphasizing the clinical advantages associated with Aβ elimination from the brain. Further, we observed a possible association between brain atrophy or ventricular enlargement and Aβ clearance, especially with the administration of N-terminal-targeted mAbs, which demonstrated a stronger Aβ clearance. Improvement in cognitive function seemed to be related to both Aβ clearance and preservation of hippocampal volume. Moreover, the risk of ARIA was strongly correlated with reductions in amyloid PET and brain atrophy, as well as ventricle enlargement. Hence, it is essential for us to recognize that the clinical efficacy of N-terminal-targeted mAbs in clearing Aβ is crucial. Nevertheless, the exacerbation of cerebral atrophy and the occurrence of ARIA of higher severity are both caused by the great abilities of Aβ clearance.

Implications of all the available evidence

The findings of this comprehensive meta-analysis provided a strong support for the efficacy of N-terminal-targeted Aβ antibodies in significantly reducing Aβ burden and ameliorating cognitive decline in AD patients, which represented a potentially groundbreaking therapeutic strategy. The principle of “structure dictates function” is a guiding tenet that targeting N-terminal region of Aβ to design superior mAbs is a promising direction for the future.