Elongation of the C-terminal domain of an anti-amyloid β single-chain variable fragment increases its thermodynamic stability and decreases its aggregation tendency

Both Amyloid-β Peptide and Tau Protein Are Affected by an Anti-Amyloid-β Antibody Fragment in Elderly 3xTg-AD Mice

Alzheimer's disease (AD) is the most common dementia worldwide. According to the amyloid hypothesis, the early accumulation of the Aβ-peptide triggers tau phosphorylation, synaptic dysfunction, and eventually neuronal death leading to cognitive impairment, as well as behavioral and psychological symptoms of dementia. ScFv-h3D6 is a single-chain variable fragment that has already shown its ability to diminish the amyloid burden in 5-month-old 3xTg-AD mice. However, tau pathology is not evident at this early stage of the disease in this mouse model. In this study, the effects of scFv-h3D6 on Aβ and tau pathologies have been assessed in 22-month-old 3xTg-AD mice. Briefly, 3xTg-AD female mice were treated for 2 weeks with scFv-h3D6 and compared with 3xTg-AD and non-transgenic (NTg) mice treated with PBS. The treatment with scFv-h3D6 was unequivocally effective in reducing the area of Aβ staining. Furthermore, a tendency for a reduction in tau levels was also observed after treatment that points to the interplay between Aβ and tau pathologies. The pro-inflammatory state observed in the 3xTg-AD mice did not progress after scFv-h3D6 treatment. In addition, the treatment did not alter the levels of apolipoprotein E or apolipoprotein J. Thus, a 2-week treatment with scFv-h3D6 was able to reduce AD-like pathology in elderly 3xTg-AD female mice.

Progression of Alzheimer's disease and effect of scFv-h3D6 immunotherapy in the 3xTg-AD mouse model: An in vivo longitudinal study using Magnetic Resonance Imaging and Spectroscopy

Alzheimer's disease (AD) is an incurable disease that affects most of the 47 million people estimated as living with dementia worldwide. The main histopathological hallmarks of AD are extracellular β-amyloid (Aβ) plaques and intracellular neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau protein. In recent years, Aβ-immunotherapy has been revealed as a potential tool in AD treatment. One strategy consists of using single-chain variable fragments (scFvs), which avoids the fragment crystallizable (Fc) effects that are supposed to trigger a microglial response, leading to microhemorrhages and vasogenic edemas, as evidenced in clinical trials with bapineuzumab. The scFv-h3D6 generated by our research group derives from this monoclonal antibody, which targets the N-terminal of the Aβ peptide and recognizes monomers, oligomers and fibrils. In this study, 3xTg-AD mice were intraperitoneally and monthly treated with 100 μg of scFv-h3D6 (a dose of ~3.3 mg/kg) or PBS, from 5 to 12 months of age (-mo), the age at which the mice were sacrificed and samples collected for histological and biochemical analyses. During treatments, four monitoring sessions using magnetic resonance imaging and spectroscopy (MRI/MRS) were performed at 5, 7, 9, and 12 months of age. MRI/MRS techniques are widely used in both human and mouse research, allowing to draw an in vivo picture of concrete aspects of the pathology in a non-invasive manner and allowing to monitor its development across time. Compared with the genetic background, 3xTg-AD mice presented a smaller volume in almost all cerebral regions and ages examined, an increase in both the intra and extracellular Aβ_1-42 at 12-mo, and an inflammation process at this age, in both the hippocampus (IL-6 and mIns) and cortex (IL-6). In addition, treatment with scFv-h3D6 partially recovered the values in brain volume, and Aβ, IL-6, and mIns concentrations, among others, encouraging further studies with this antibody fragment.

Pharmacokinetic parameters and mechanism of action of an efficient anti-Aβ single chain antibody fragment

The success of the targeting of amyloid-β (Aβ) oligomers through immunotherapy in Alzheimer’s disease (AD) mouse models has not been translated into the clinics. The use of single-chain variable fragments (scFvs) has been proposed to prevent the potential severe effects of full-length mAbs by precluding crystallizable fraction-mediated microglia activation. The efficacy of scFv-h3D6, a bapineuzumab-derived anti-Aβ scFv, has been extensively proven. In this work, we compared scFv-h3D6-EL, an elongated variant of the scFv-h3D6, with its original version to assess whether its characteristic higher thermodynamic stability improved its pharmacokinetic parameters. Although scFv-h3D6-EL had a longer half-life than its original version, its absorption from the peritoneal cavity into the systemic compartment was lower than that of the original version. Moreover, we attempted to determine the mechanism underlying the protective effect of scFv-h3D6. We found that scFv-h3D6 showed compartmental distribution and more interestingly crossed the blood–brain barrier. In the brain, scFv-h3D6 was engulfed by glial cells or internalized by Aβ peptide-containing neurons in the early phase post-injection, and was colocalized with the Aβ peptide almost exclusively in glial cells in the late phase post-injection. Aβ peptide levels in the brain decreased simultaneously with an increase in scFv-h3D6 levels. This observation in addition to the increased tumor necrosis factor-α levels in the late phase post-injection suggested that the engulfment of Aβ peptide/scFv-h3D6 complex extruded from large neurons by phagocytic cells was the mechanism underlying Aβ peptide withdrawal. The mechanism of action of scFv-h3D6 demonstrates the effectivity of Aβ-immunotherapy and lays the background for other studies focused on the finding of a treatment for AD.

Effects of an Aβ-antibody fragment on Aβ aggregation and astrocytic uptake are modulated by apolipoprotein E and J mimetic peptides

Aβ-Immunotherapy has long been studied in the treatment of Alzheimer’s disease (AD), but not how other molecules involved in the disease can affect antibody performance. We previously designed an antibody fragment, scFv-h3D6, and showed that it precludes Aβ-induced cytotoxicity by withdrawing Aβ oligomers from the amyloid pathway towards a non-toxic, worm-like pathway. ScFv-h3D6 was effective at the behavioral, cellular, and molecular levels in the 3xTg-AD mouse model. Because scFv-h3D6 treatment restored apolipoprotein E (apoE) and J (apoJ) concentrations to non-pathological values, and Aβ internalization by glial cells was found to be decreased in the presence of these apolipoproteins, we now aimed to test the influence of scFv-h3D6 on Aβ aggregation and cellular uptake by primary human astrocytes in the presence of therapeutic apoE and apoJ mimetic peptides (MPs). Firstly, we demonstrated by CD and FTIR that the molecules used in this work were well folded. Next, interactions between apoE or apoJ-MP, scFv-h3D6 and Aβ were studied by CD. The conformational change induced by the interaction of Aβ with apoE-MP was much bigger than the induced with apoJ-MP, in line with the observed formation of protective worm-like fibrils by the scFv-h3D6/Aβ complex in the presence of apoJ-MP, but not of apoE-MP. ScFv-h3D6, apoJ-MP, and apoE-MP to a different extent reduced Aβ uptake by astrocytes, and apoE-MP partially interfered with the dramatic reduction by scFv-h3D6 while apoJ-MP had no effect on scFv-h3D6 action. As sustained Aβ uptake by astrocytes may impair their normal functions, and ultimately neuronal viability, this work shows another beneficence of scFv-h3D6 treatment, which is not further improved by the use of apoE or apoJ mimetic peptides.

Towards the improvement in stability of an anti-Aβ single-chain variable fragment, scFv-h3D6, as a way to enhance its therapeutic potential

ScFv-h3D6 is a single-chain variable fragment derived from the monoclonal antibody bapineuzumab that prevents Aβ-induced cytotoxicity by capturing Aβ oligomers. The benefits of scFv-h3D6 treatment in Alzheimer's disease are known at the behavioural, cellular and molecular levels in the 3xTg-AD mouse model. Antibody-based therapeutics are only stable in a limited temperature range, so their benefit in vivo depends on their capability for maintaining the proper fold. Here, we have stabilized the scFv-h3D6 folding by introducing the mutation V_H-K64R and combining it with the previously described elongation of the V_L domain (C3). The stabilities of the different scFv-h3D6 constructs were calculated from urea and thermal denaturation followed by Trp-fluorescence, CD and DSC and resulted in the order C3 > K64R/C3 > V_H-K64R ≥ scFv-h3D6; showing that the combination of both mutations was not additive, instead they partially cancelled each other. The three mutants assayed showed a decreased aggregation tendency but maintained their capability to aggregate in the form of worm-like fibrils, basis of the protective effect of scFv-h3D6. Cytotoxicity assays showed that all the mutants recovered cell viability of Aβ-treated neuroblastoma cell cultures in a dose-dependent manner and with efficiencies that correlated with stability, therefore improving the therapeutic ability of this antibody.

A human scFv antibody that targets and neutralizes high molecular weight pathogenic amyloid-β oligomers

Brain accumulation of soluble oligomers of the amyloid-β peptide (AβOs) is increasingly considered a key early event in the pathogenesis of Alzheimer's disease (AD). A variety of AβO species have been identified, both in vitro and in vivo, ranging from dimers to 24mers and higher order oligomers. However, there is no consensus in the literature regarding which AβO species are most germane to AD pathogenesis. Antibodies capable of specifically recognizing defined subpopulations of AβOs would be a valuable asset in the identification, isolation, and characterization of AD-relevant AβO species. Here, we report the characterization of a human single chain antibody fragment (scFv) denoted NUsc1, one of a number of scFvs we have identified that stringently distinguish AβOs from both monomeric and fibrillar Aβ. NUsc1 readily detected AβOs previously bound to dendrites in cultured hippocampal neurons. In addition, NUsc1 blocked AβO binding and reduced AβO-induced neuronal oxidative stress and tau hyperphosphorylation in cultured neurons. NUsc1 further distinguished brain extracts from AD-transgenic mice from wild type (WT) mice, and detected endogenous AβOs in fixed AD brain tissue and AD brain extracts. Biochemical analyses indicated that NUsc1 targets a subpopulation of AβOs with apparent molecular mass greater than 50 kDa. Results indicate that NUsc1 targets a particular AβO species relevant to AD pathogenesis, and suggest that NUsc1 may constitute an effective tool for AD diagnostics and therapeutics.

Production of an anti-Aβ antibody fragment in Pichia pastoris and in vitro and in vivo validation of its therapeutic effect

ScFv-h3D6 has been shown as an efficient therapy in the 3xTg-AD mouse model of Alzheimer's Disease. Because one of the major bottlenecks for the therapeutic uses of proteins produced in Escherichia coli is their potential contamination with endotoxins, LPS were extensively removed by a rather low-efficient, expensive, and time-consuming purification step. In addition, disulfide scrambling is favored in the reducing bacterial cytoplasm albeit the use of reductase deficient strains. To overcome these hurdles, as well as to improve the yield, the yeast Pichia pastoris, an endotoxin-free host system for recombinant protein production, has been used to produce scFv-h3D6, both in flask and in a fed-batch bioreactor. Comparison of the thermal stability of the obtained protein with that from E. coli showed no differences. Opposite to the case of the protein obtained from E. coli, no disulfide scrambled conformations or LPS traces were detected in that produced in P. pastoris. Cytotoxicity assays in SH-SY5Y neuroblastoma cell-cultures demonstrated that proteins from both expression systems were similarly efficient in precluding Aβ-induced toxicity. Finally, the 3xTg-AD mouse model was used to test the therapeutic effect of both proteins. Quantification of Aβ levels from cortex and hippocampus protein extracts by ELISA, and Aβ-immunohistochemistry, showed that both proteins reduced Aβ burden. This work demonstrates that scFv-h3D6 obtained from P. pastoris shows the same benefits as those already known for that obtained from E. coli, with multiple advantages in terms of recombinant production and safety.

Understanding the contribution of disulfide bridges to the folding and misfolding of an anti-Aβ scFv

ScFv-h3D6 is a single chain variable fragment that precludes Aβ peptide-induced cytotoxicity by withdrawing Aβ oligomers from the amyloid pathway to the worm-like pathway. Production of scFv molecules is not a straightforward procedure because of the occurrence of disulfide scrambled conformations generated in the refolding process. Here, we separately removed the disulfide bond of each domain and solved the scrambling problem; and then, we intended to compensate the loss of thermodynamic stability by adding three C-terminal elongation mutations, previously described to stabilize the native fold of scFv-h3D6. Such stabilization occurred through stabilization of the intermediate state in the folding pathway and destabilization of a different, β-rich, intermediate state driving to worm-like fibrils. Elimination of the disulfide bridge of the less stable domain, V_L , deeply compromised the yield and increased the aggregation tendency, but elimination of the disulfide bridge of the more stable domain, V_H , solved the scrambling problem and doubled the production yield. Notably, it also changed the aggregation pathway from the protective worm-like morphology to an amyloid one. This was so because a partially unfolded intermediate driving to amyloid aggregation was present, instead of the β-rich intermediate driving to worm-like fibrils. When combining with the elongation mutants, stabilization of the partially unfolded intermediate driving to amyloid fibrils was the only effect observed. Therefore, the same mutations drove to completely different scenarios depending on the presence of disulfide bridges and this illustrates the relevance of such linkages in the stability of different intermediate states for folding and misfolding.

Mutations can cause light chains to be too stable or too unstable to form amyloid fibrils

Light chain (AL) amyloidosis is an incurable human disease, where the amyloid precursor is a misfolding-prone immunoglobulin light-chain. Here, we identify the role of somatic mutations in the structure, stability and in vitro fibril formation for an amyloidogenic AL-12 protein by restoring four nonconservative mutations to their germline (wild-type) sequence. The single restorative mutations do not affect significantly the native structure, the unfolding pathway, and the reversibility of the protein. However, certain mutations either decrease (H32Y and H70D) or increase (R65S and Q96Y) the protein thermal stability. Interestingly, the most and the least stable mutants, Q96Y and H32Y, do not form amyloid fibrils under physiological conditions. Thus, Q96 and H32 are key residues for AL-12 stability and fibril formation and restoring them to the wild-type residues preclude amyloid formation. The mutants whose equilibrium is shifted to either the native or unfolded states barely sample transient partially folded states, and therefore do not form fibrils. These results agree with previous observations by our laboratory and others that amyloid formation occurs because of the sampling of partially folded states found within the unfolding transition (Blancas-Mejia and Ramirez-Alvarado, Ann Rev Biochem 2013;82:745-774). Here we provide a new insight on the AL amyloidosis mechanism by demonstrating that AL-12 does not follow the established thermodynamic hypothesis of amyloid formation. In this hypothesis, thermodynamically unstable proteins are more prone to amyloid formation. Here we show that within a thermal stability range, the most stable protein in this study is the most amyloidogenic protein.

[Alzheimer's disease: New therapeutic strategies]

The rapid increase in prevalence rates of Alzheimer's disease means that treatments to prevent, stop or reverse this devastating disease are urgently needed. Despite advances in understanding its molecular pathology, there are no drugs that can halt its progression. This review takes a tour through phase 2, or higher studies, probing receptor agonist agents interfering with aggregation, inhibitors/modulators of secretases, lipid-lowering agents, and, finally and most extensively, immunotherapy. The fact that phase 3 studies with bapineuzumab and solaneuzumab have recently failed does not invalidate the potential of immunotherapy, as more information is available and new clinical trials are being initiated.

Early intervention in the 3xTg-AD mice with an amyloid β-antibody fragment ameliorates first hallmarks of Alzheimer disease

The single-chain variable fragment, scFv-h3D6, has been shown to prevent in vitro toxicity induced by the amyloid β (Aβ) peptide in neuroblastoma cell cultures by withdrawing Aβ oligomers from the amyloid pathway. Present study examined the in vivo effects of scFv-h3D6 in the triple-transgenic 3xTg-AD mouse model of Alzheimer disease. Prior to the treatment, five-month-old female animals, corresponding to early stages of the disease, showed the first behavioral and psychological symptoms of dementia -like behaviors. Cognitive deficits included long- and short-term learning and memory deficits and high swimming navigation speed. After a single intraperitoneal dose of scFv-h3D6, the swimming speed was reversed to normal levels and the learning and memory deficits were ameliorated. Brain tissues of these animals revealed a global decrease of Aβ oligomers in the cortex and olfactory bulb after treatment, but this was not seen in the hippocampus and cerebellum. In the untreated 3xTg-AD animals, we observed an increase of both apoJ and apoE concentrations in the cortex, as well as an increase of apoE in the hippocampus. Treatment significantly recovered the non-pathological levels of these apolipoproteins. Our results suggest that the benefit of scFv-h3D6 occurs at both behavioral and molecular levels.

Loss of deep cerebellar nuclei neurons in the 3xTg-AD mice and protection by an anti-amyloid β antibody fragment

The therapeutic potential of scFv-h3D6 has recently been shown in the 3xTg-AD mice. A clear effect on amyloid β (Aβ) oligomers and certain apolipoproteins in the brain was found, but no effect was seen in the cerebellum. Here, cellular vulnerability of the 3xTg-AD cerebellum is described for the first time, together with its protection by scFv-h3D6. Neuron depletion in the DCN was regionally variable and followed a mediolateral axis of involvement that was greatest in the fastigial nucleus, lesser in the interpositus and negligible in the dentate nucleus. A sole and low intraperitoneal dose of scFv-h3D6 protected 3xTg-AD DCN neurons from death. Further studies might provide interesting information about both the potential of scFv-h3D6 as a therapeutic agent and the role of the cerebellum in AD.