Pre-targeting amyloid-ß with antibodies for potential molecular imaging of Alzheimer's disease.

With the aim of developing the concept of pretargeted click chemistry for the diagnosis of Alzheimer's disease two antibodies specific for amyloid-ß were modified to incorporate trans-cyclooctene functional groups. Two bis(thiosemicarbazone) compounds with pendant 1,2,4,5-tetrazine functional groups were prepared and radiolabelled with positron emitting copper-64. The new copper-64 complexes rapidly react with the trans-cyclooctene functionalized antibodies in a bioorthogonal click reaction and cross the blood-brain barrier in mice.

Associations of plasma soluble CD22 levels with brain amyloid burden and cognitive decline in Alzheimer's disease.

CD22 has been suggested to contribute to Alzheimer's disease (AD) pathogenesis by inhibiting microglial amyloid ß (Aß) phagocytosis. Soluble CD22 (sCD22) generated by cleavage from cell membranes may be a marker of inflammation and microglial dysfunction; but alterations of sCD22 levels in AD and their correlation with AD biomarkers remain unclear. Plasma sCD22 levels were measured in cognitively normal non-AD participants and patients with preclinical AD and AD dementia from a Chinese cohort and the Australian Imaging, Biomarkers and Lifestyle Flagship Study of Ageing. Plasma sCD22 levels were elevated in patients with preclinical and dementia AD. Plasma sCD22 levels were negatively correlated with cerebrospinal fluid (CSF) Aß42 levels and Aß42/Aß40, and positively correlated with CSF phosphorylated tau levels and brain Aß burden, but negatively correlated with cognitive function. Moreover, higher plasma sCD22 levels were associated with faster cognitive decline during follow-up. These findings suggest that CD22 plays important roles in AD development, and that sCD22 is a potential biomarker for AD.

Genomics of Alzheimer's disease implicates the innate and adaptive immune systems.

Alzheimer's disease (AD) is a chronic neurodegenerative disease characterised by cognitive impairment, behavioural alteration, and functional decline. Over 130 AD-associated susceptibility loci have been identified by genome-wide association studies (GWAS), while whole genome sequencing (WGS) and whole exome sequencing (WES) studies have identified AD-associated rare variants. These variants are enriched in APOE, TREM2, CR1, CD33, CLU, BIN1, CD2AP, PILRA, SCIMP, PICALM, SORL1, SPI1, RIN3, and more genes. Given that aging is the single largest risk factor for late-onset AD (LOAD), the accumulation of somatic mutations in the brain and blood of AD patients have also been explored. Collectively, these genetic findings implicate the role of innate and adaptive immunity in LOAD pathogenesis and suggest that a systemic failure of cell-mediated amyloid-ß (Aß) clearance contributes to AD onset and progression. AD-associated variants are particularly enriched in myeloid-specific regulatory regions, implying that AD risk variants are likely to perturbate the expression of myeloid-specific AD-associated genes to interfere Aß clearance. Defective phagocytosis, endocytosis, and autophagy may drive Aß accumulation, which may be related to naturally-occurring antibodies to Aß (Nabs-Aß) produced by adaptive responses. Passive immunisation is providing efficiency in clearing Aß and slowing cognitive decline, such as aducanumab, donanemab, and lecanemab (ban2401). Causation of AD by impairment of the innate immunity and treatment using the tools of adaptive immunity is emerging as a new paradigm for AD, but immunotherapy that boosts the innate immune functions of myeloid cells is highly expected to modulate disease progression at asymptomatic stage.

Small Molecule Binding to Alzheimer Risk Factor CD33 Promotes Aß Phagocytosis.

Polymorphism in the microglial receptor CD33 gene has been linked to late-onset Alzheimer disease (AD), and reduced expression of the CD33 sialic acid-binding domain confers protection. Thus, CD33 inhibition might be an effective therapy against disease progression. Progress toward discovery of selective CD33 inhibitors has been hampered by the absence of an atomic resolution structure. We report here the crystal structures of CD33 alone and bound to a subtype-selective sialic acid mimetic called P22 and use them to identify key binding residues by site-directed mutagenesis and binding assays to reveal the molecular basis for its selectivity toward sialylated glycoproteins and glycolipids. We show that P22, when presented on microparticles, increases uptake of the toxic AD peptide, amyloid-ß (Aß), into microglial cells. Thus, the sialic acid-binding site on CD33 is a promising pharmacophore for developing therapeutics that promote clearance of the Aß peptide that is thought to cause AD.

Promiscuous DNA-binding of a mutant zinc finger protein corrupts the transcriptome and diminishes cell viability.

The rules of engagement between zinc finger transcription factors and DNA have been partly defined by in vitro DNA-binding and structural studies, but less is known about how these rules apply in vivo. Here, we demonstrate how a missense mutation in the second zinc finger of Krüppel-like factor-1 (KLF1) leads to degenerate DNA-binding specificity in vivo, resulting in ectopic transcription and anemia in the Nan mouse model. We employed ChIP-seq and 4sU-RNA-seq to identify aberrant DNA-binding events genome wide and ectopic transcriptional consequences of this binding. We confirmed novel sequence specificity of the mutant recombinant zinc finger domain by performing biophysical measurements of in vitro DNA-binding affinity. Together, these results shed new light on the mechanisms by which missense mutations in DNA-binding domains of transcription factors can lead to autosomal dominant diseases.

Ex vivo 18O-labeling mass spectrometry identifies a peripheral amyloid ß clearance pathway.

BACKGROUND: Proteolytic degradation of amyloid ß (Aß) peptides has been intensely studied due to the central role of Aß in Alzheimer's disease (AD) pathogenesis. While several enzymes have been shown to degrade Aß peptides, the main pathway of Aß degradation in vivo is unknown. Cerebrospinal fluid (CSF) Aß42 is reduced in AD, reflecting aggregation and deposition in the brain, but low CSF Aß42 is, for unknown reasons, also found in some inflammatory brain disorders such as bacterial meningitis. METHOD: Using 18O-labeling mass spectrometry and immune-affinity purification, we examined endogenous proteolytic processing of Aß in human CSF. RESULTS: The Aß peptide profile was stable in CSF samples from healthy controls but in CSF samples from patients with bacterial meningitis, showing increased leukocyte cell count, 18O-labeling mass spectrometry identified proteolytic activities degrading Aß into several short fragments, including abundant Aß1-19 and 1-20. After antibiotic treatment, no degradation of Aß was detected. In vitro experiments located the source of the proteolytic activity to blood components, including leukocytes and erythrocytes, with insulin-degrading enzyme as the likely protease. A recombinant version of the mid-domain anti-Aß antibody solanezumab was found to inhibit insulin-degrading enzyme-mediated Aß degradation. CONCLUSION: 18O labeling-mass spectrometry can be used to detect endogenous proteolytic activity in human CSF. Using this technique, we found an enzymatic activity that was identified as insulin-degrading enzyme that cleaves Aß in the mid-domain of the peptide, and could be inhibited by a recombinant version of the mid-domain anti-Aß antibody solanezumab.

Transitional changes in the CRP structure lead to the exposure of proinflammatory binding sites.

C-reactive protein (CRP) concentrations rise in response to tissue injury or infection. Circulating pentameric CRP (pCRP) localizes to damaged tissue where it leads to complement activation and further tissue damage. In-depth knowledge of the pCRP activation mechanism is essential to develop therapeutic strategies to minimize tissue injury. Here we demonstrate that pCRP by binding to cell-derived microvesicles undergoes a structural change without disrupting the pentameric symmetry (pCRP*). pCRP* constitutes the major CRP species in human-inflamed tissue and allows binding of complement factor 1q (C1q) and activation of the classical complement pathway. pCRP*-microvesicle complexes lead to enhanced recruitment of leukocytes to inflamed tissue. A small-molecule inhibitor of pCRP (1,6-bis(phosphocholine)-hexane), which blocks the pCRP-microvesicle interactions, abrogates these proinflammatory effects. Reducing inflammation-mediated tissue injury by therapeutic inhibition might improve the outcome of myocardial infarction, stroke and other inflammatory conditions.

Abeta targets of the biosimilar antibodies of Bapineuzumab, Crenezumab, Solanezumab in comparison to an antibody against N­truncated Abeta in sporadic Alzheimer disease cases and mouse models.

Solanezumab and Crenezumab are two humanized antibodies targeting Amyloid-ß (Aß) which are currently tested in multiple clinical trials for the prevention of Alzheimer's disease. However, there is a scientific discussion ongoing about the target engagement of these antibodies. Here, we report the immunohistochemical staining profiles of biosimilar antibodies of Solanezumab, Crenezumab and Bapineuzumab in human formalin-fixed, paraffin-embedded tissue and human fresh frozen tissue. Furthermore, we performed a direct comparative immunohistochemistry analysis of the biosimilar versions of the humanized antibodies in different mouse models including 5XFAD, Tg4-42, TBA42, APP/PS1KI, 3xTg. The staining pattern with these humanized antibodies revealed a surprisingly similar profile. All three antibodies detected plaques, cerebral amyloid angiopathy and intraneuronal Aß in a similar fashion. Remarkably, Solanezumab showed a strong binding affinity to plaques. We also reaffirmed that Bapineuzumab does not recognize N-truncated or modified Aß, while Solanezumab and Crenezumab do detect N-terminally modified Aß peptides Aß4-42 and pyroglutamate Aß3-42. In addition, we compared the results with the staining pattern of the mouse NT4X antibody that recognizes specifically Aß4-42 and pyroglutamate Aß3-42, but not full-length Aß1-42. In contrast to the biosimilar antibodies of Solanezumab, Crenezumab and Bapineuzumab, the murine NT4X antibody shows a unique target engagement. NT4X does barely cross-react with amyloid plaques in human tissue. It does, however, detect cerebral amyloid angiopathy in human tissue. In Alzheimer mouse models, NT4X detects intraneuronal Aß and plaques comparable to the humanized antibodies. In conclusion, the biosimilar antibodies Solanezumab, Crenezumab and Bapineuzumab strongly react with amyloid plaques, which are in contrast to the NT4X antibody that hardly recognizes plaques in human tissue. Therefore, NT4X is the first of a new class of therapeutic antibodies.

Molecular basis for mid-region amyloid-ß capture by leading Alzheimer's disease immunotherapies.

Solanezumab (Eli Lilly) and crenezumab (Genentech) are the leading clinical antibodies targeting Amyloid-ß (Aß) to be tested in multiple Phase III clinical trials for the prevention of Alzheimer's disease in at-risk individuals. Aß capture by these clinical antibodies is explained here with the first reported mid-region Aß-anti-Aß complex crystal structure. Solanezumab accommodates a large Aß epitope (960 Å(2) buried interface over residues 16 to 26) that forms extensive contacts and hydrogen bonds to the antibody, largely via main-chain Aß atoms and a deeply buried Phe19-Phe20 dipeptide core. The conformation of Aß captured is an intermediate between observed sheet and helical forms with intramolecular hydrogen bonds stabilising residues 20-26 in a helical conformation. Remarkably, Aß-binding residues are almost perfectly conserved in crenezumab. The structure explains the observed shared cross reactivity of solanezumab and crenezumab with proteins abundant in plasma that exhibit this Phe-Phe dipeptide.

Do current therapeutic anti-Aß antibodies for Alzheimer's disease engage the target?

Reducing amyloid-ß peptide (Aß) burden at the pre-symptomatic stages of Alzheimer's disease (AD) is currently the advocated clinical strategy for treating this disease. The most developed method for targeting Aß is the use of monoclonal antibodies including bapineuzumab, solanezumab and crenezumab. We have synthesized these antibodies and used surface plasmon resonance (SPR) and mass spectrometry to characterize and compare the ability of these antibodies to target Aß in transgenic mouse tissue as well as human AD tissue. SPR analysis showed that the antibodies were able to bind Aß with high affinity. All of the antibodies were able to bind Aß in mouse tissue. However, significant differences were observed in human brain tissue. While bapineuzumab was able to capture a variety of N-terminally truncated Aß species, the Aß detected using solanezumab was barely above detection limits while crenezumab did not detect any Aß. None of the antibodies were able to detect any Aß species in human blood. Immunoprecipitation experiments using plasma from AD subjects showed that both solanezumab and crenezumab have extensive cross-reactivity with non-Aß related proteins. Bapineuzumab demonstrated target engagement with brain Aß, consistent with published clinical data. Solanezumab and crenezumab did not, most likely as a result of a lack of specificity due to cross-reactivity with other proteins containing epitope overlap. This lack of target engagement raises questions as to whether solanezumab and crenezumab are suitable drug candidates for the preventative clinical trials for AD.

Crystallization and preliminary X-ray diffraction analysis of the Fab portion of the Alzheimer's disease immunotherapy candidate bapineuzumab complexed with amyloid-ß.

Bapineuzumab (AAB-001) and its derivative (AAB-003) are humanized versions of the anti-Aß murine antibody 3D6 and are immunotherapy candidates in Alzheimer's disease. The common Fab fragment of these immunotherapies has been expressed, purified and crystallized in complex with ß-amyloid peptides (residues 1-8 and 1-28). Diffraction data at high resolution were acquired from crystals of Fab-Aß8 (2.0 Å) and Fab-Aß28 (2.2 Å) complexes at the Australian Synchrotron. Both crystal forms belonged to the primitive orthorhombic space group P21221.

Bapineuzumab captures the N-terminus of the Alzheimer's disease amyloid-beta peptide in a helical conformation.

Bapineuzumab is a humanized antibody developed by Pfizer and Johnson & Johnson targeting the amyloid (Aß) plaques that underlie Alzheimer's disease neuropathology. Here we report the crystal structure of a Fab-Aß peptide complex that reveals Bapineuzumab surprisingly captures Aß in a monomeric helical conformation at the N-terminus. Microscale thermophoresis suggests that the Fab binds soluble Aß(1-40) with a K(D) of 89 (±9) nM. The structure explains the antibody's exquisite selectivity for particular Aß species and why it cannot recognize N-terminally modified or truncated Aß peptides.

Structural approaches to probing metal interaction with proteins.

In this mini-review we focus on metal interactions with proteins with a particular emphasis on the evident synergism between different biophysical approaches toward understanding metallobiology. We highlight three recent examples from our own laboratory. Firstly, we describe metallodrug interactions with glutathione S-transferases, an enzyme family known to attack commonly used anti-cancer drugs. We then describe a protein target for memory enhancing drugs called insulin-regulated aminopeptidase in which zinc plays a role in catalysis and regulation. Finally we describe our studies on a protein, amyloid precursor protein, that appears to play a central role in Alzheimer's disease. Copper ions have been implicated in playing both beneficial and detrimental roles in the disease by binding to different regions of this protein.

An Escherichia coli cell-free system for recombinant protein synthesis on a milligram scale.

In vitro translation systems derived from a wide range of organisms have been described in the literature and are widely used in biomedical research laboratories. Perhaps the most robust and efficient of these cell-free systems is that derived from Escherichia coli. Over the past decade or so, experimental strategies have been developed which have enhanced the efficiency and stability of E. coli cell-free systems such that we can now prepare recombinant proteins on a scale suitable for purification and analysis by biophysical and structural biology techniques, which commonly require relatively large quantities of protein. This chapter describes in detail the protocols employed in our laboratory to prepare translationally active E. coli extracts and to synthesise proteins on a milligram scale from these extracts.

Solid-phase synthesis of homodimeric peptides: preparation of covalently-linked dimers of amyloid beta peptide.

Covalently cross-linked homodimeric Abeta peptides have been prepared by solid-phase peptide synthesis by exploiting 'site-site interactions', and exhibit substantially increased oligomerisation and fibrillisation properties compared with the corresponding monomers.

Cu2+ binding modes of recombinant alpha-synuclein--insights from EPR spectroscopy.

The interaction of the small (140 amino acid) protein, alpha-synuclein (alphaS), with Cu(2+) has been proposed to play a role in Parkinson's disease (PD). While some insight from truncated model complexes has been gained, the nature of the corresponding Cu(2+) binding modes in the full length protein remains comparatively less well characterized. This work examined the Cu(2+) binding of recombinant human alphaS using Electron Paramagnetic Resonance (EPR) spectroscopy. Wild type (wt) alphaS was shown to bind stoichiometric Cu(2+) via two N-terminal binding modes at physiological pH. An H50N mutation isolated one binding mode, whose g parallel, A parallel, and metal-ligand hyperfine parameters correlated well with a {NH2, N(-), beta-COO(-), H2O} mode previously identified in truncated model fragments. Electron spin-echo envelope modulation (ESEEM) studies of wt alphaS confirmed the second binding mode at pH 7.4 involved coordination of His50 and its g parallel and A parallel parameters correlated with either {NH2, N(-), beta-COO(-), N(Im)} or {N(Im), 2 N(-)} coordination observed in alphaS fragments. At pH 5.0, His50-anchored Cu(2+) binding was greatly diminished, while {NH2, N(-), beta-COO(-), H2O} binding persisted in conjunction with another two binding modes. Metal-ligand hyperfine interactions from one of these indicated a 1N3O coordination sphere, which was ascribed to a {NH2, CO} binding mode. The other was characterized by a spectrum similar to that previously observed for diethylpyrocarbonate-treated alphaS and was attributed to C-terminal binding centered on Asp121. In total, four Cu(2+) binding modes were identified within pH 5.0-7.4, providing a more comprehensive picture of the Cu(2+) binding properties of recombinant alphaS.

Crystallization and preliminary X-ray diffraction analysis of the Fab fragment of WO2, an antibody specific for the Abeta peptides associated with Alzheimer's disease.

The murine monoclonal antibody WO2 specifically binds the N-terminal region of the amyloid beta peptide (Abeta) associated with Alzheimer's disease. This region of Abeta has been shown to be the immunodominant B-cell epitope of the peptide and hence is considered to be a basis for the development of immunotherapeutic strategies against this prevalent cause of dementia. Structural studies have been undertaken in order to characterize the molecular basis for antibody recognition of this important epitope. Here, details of the crystallization and X-ray analysis of the Fab fragment of the unliganded WO2 antibody in two crystal forms and of the complexes that it forms with the truncated Abeta peptides Abeta(1-16) and Abeta(1-28) are presented. These crystals were all obtained using the hanging-drop vapour-diffusion method at 295 K. Crystals of WO2 Fab were grown in polyethylene glycol solutions containing ZnSO(4); they belonged to the orthorhombic space group P2(1)2(1)2(1) and diffracted to 1.6 A resolution. The complexes of WO2 Fab with either Abeta(1-16) or Abeta(1-28) were cocrystallized from polyethylene glycol solutions. These two complex crystals grew in the same space group, P2(1)2(1)2(1), and diffracted to 1.6 A resolution. A second crystal form of WO2 Fab was grown in the presence of the sparingly soluble Abeta(1-42) in PEG 550 MME. This second form belonged to space group P2(1) and diffracted to 1.9 A resolution.

Amyloid-beta-anti-amyloid-beta complex structure reveals an extended conformation in the immunodominant B-cell epitope.

Alzheimer's disease (AD) is the most common form of dementia. Amyloid-beta (A beta) peptide, generated by proteolytic cleavage of the amyloid precursor protein, is central to AD pathogenesis. Most pharmaceutical activity in AD research has focused on A beta, its generation and clearance from the brain. In particular, there is much interest in immunotherapy approaches with a number of anti-A beta antibodies in clinical trials. We have developed a monoclonal antibody, called WO2, which recognises the A beta peptide. To this end, we have determined the three-dimensional structure, to near atomic resolution, of both the antibody and the complex with its antigen, the A beta peptide. The structures reveal the molecular basis for WO2 recognition and binding of A beta. The A beta peptide adopts an extended, coil-like conformation across its major immunodominant B-cell epitope between residues 2 and 8. We have also studied the antibody-bound A beta peptide in the presence of metals known to affect its aggregation state and show that WO2 inhibits these interactions. Thus, antibodies that target the N-terminal region of A beta, such as WO2, hold promise for therapeutic development.