Secondary structure propensity and chirality of the amyloidophilic peptide p5 and its analogues impacts ligand binding - In vitro characterization

Development and characterization of a prototypic pan-amyloid clearing agent - a novel murine peptide-immunoglobulin fusion

Introduction

Systemic amyloidosis is a progressive disorder characterized by the extracellular deposition of amyloid fibrils and accessory proteins in visceral organs and tissues. Amyloid accumulation causes organ dysfunction and is not generally cleared by the immune system. Current treatment focuses on reducing amyloid precursor protein synthesis and slowing amyloid deposition. However, curative interventions will likely also require removal of preexisting amyloid deposits to restore organ function. Here we describe a prototypic pan-amyloid binding peptide-antibody fusion molecule (mIgp5) that enhances macrophage uptake of amyloid.

Methods

The murine IgG1-IgG2a hybrid immunoglobulin with a pan amyloid-reactive peptide, p5, fused genetically to the N-terminal of the immunoglobulin light chain was synthesized in HEK293T/17 cells. The binding of the p5 peptide moiety was assayed using synthetic amyloid-like fibrils, human amyloid extracts and amyloid-laden tissues as substrates. Binding of radioiodinated mIgp5 with amyloid deposits in vivo was evaluated in a murine model of AA amyloidosis using small animal imaging and microautoradiography. The bioactivity of mIgp5 was assessed in complement fixation and in vitro phagocytosis assays in the presence of patient-derived amyloid extracts and synthetic amyloid fibrils as substrates and in the presence or absence of human serum.

Results

Murine Igp5 exhibited highly potent binding to AL and ATTR amyloid extracts and diverse types of amyloid in formalin-fixed tissue sections. In the murine model of systemic AA amyloidosis, 125I-mIgp5 bound rapidly and specifically to amyloid deposits in all organs, including the heart, with no evidence of non-specific uptake in healthy tissues. The bioactivity of the immunoglobulin Fc domain was uncompromised in the context of mIgp5 and served as an effective opsonin. Macrophage-mediated uptake of amyloid extract and purified amyloid fibrils was enhanced by the addition of mIgp5. This effect was exaggerated in the presence of human serum coincident with deposition of complement C5b9.

Conclusion

Immunostimulatory, amyloid-clearing therapeutics can be developed by incorporating pan-amyloid-reactive peptides, such as p5, as a targeting moiety. The immunologic functionality of the IgG remains intact in the context of the fusion protein. These data highlight the potential use of peptide-antibody fusions as therapeutics for all types of systemic amyloidosis.

Anticytomegalovirus Peptides Point to New Insights for CMV Entry Mechanisms and the Limitations of In Vitro Screenings

In the absence of an effective vaccine to prevent HCMV infections, alternative interventions must be developed. Prevention of viral entry into susceptible cells is an attractive alternative strategy. Here we report that heparan sulfate-binding peptides effectively inhibit entry into fibroblasts of in vitro-derived CMVs and partially inhibit in vivo-derived CMVs. This includes the inhibition of urine-derived HCMV (uCMV), which is highly resistant to antibody neutralization. While these antiviral peptides are highly effective at inhibiting cell-free virus, they do not inhibit MCMV cell-to-cell spread. This underscores the need to understand the mechanism of cell-to-cell spread and differences between in vivo-derived versus in vitro-derived CMV entry to effectively prevent CMV’s spread.

Human cytomegalovirus (HCMV) is a ubiquitous betaherpesvirus that can cause severe disease following in utero exposure, during primary infection, or latent virus reactivation in immunocompromised populations. These complications lead to a 1- to 2-billion-dollar economic burden, making vaccine development and/or alternative treatments a high priority. Current treatments for HCMV include nucleoside analogues such as ganciclovir (GCV), foscarnet, and cidofovir. Recently, letermovir, a terminase complex inhibitor, was approved for prophylaxis after stem cell transplantation. These treatments have unwanted side effects, and HCMV is becoming resistant to them. Therefore, we sought to develop an alternative treatment that targets a different stage in viral infection. Currently, small antiviral peptides are being investigated as anti-influenza and anti-HIV treatments. We have developed heparan sulfate-binding peptides as tools for preventing CMV infections. These peptides are highly effective at stopping infection of fibroblasts with in vitro-derived HCMV and murine cytomegalovirus (MCMV). However, they do not prevent MCMV infection in vivo. Interestingly, these peptides inhibit infectivity of in vivo-derived CMVs, albeit not as well as tissue culture-grown CMVs. We further demonstrate that this class of heparan sulfate-binding peptides is incapable of inhibiting MCMV cell-to-cell spread, which is independent of heparan sulfate usage. These data indicate that inhibition of CMV infection can be achieved using synthetic polybasic peptides, but cell-to-cell spread and in vivo-grown CMVs require further investigation to design appropriate anti-CMV peptides.

IMPORTANCE In the absence of an effective vaccine to prevent HCMV infections, alternative interventions must be developed. Prevention of viral entry into susceptible cells is an attractive alternative strategy. Here we report that heparan sulfate-binding peptides effectively inhibit entry into fibroblasts of in vitro-derived CMVs and partially inhibit in vivo-derived CMVs. This includes the inhibition of urine-derived HCMV (uCMV), which is highly resistant to antibody neutralization. While these antiviral peptides are highly effective at inhibiting cell-free virus, they do not inhibit MCMV cell-to-cell spread. This underscores the need to understand the mechanism of cell-to-cell spread and differences between in vivo-derived versus in vitro-derived CMV entry to effectively prevent CMV’s spread.

Novel Antibacterial Peptides Isolated from the Maillard Reaction Products of Half-Fin Anchovy (Setipinna taty) Hydrolysates/Glucose and Their Mode of Action in Escherichia coli

The Maillard reaction products (MRPs) of half-fin anchovy hydrolysates and glucose, named as HAHp(9.0)-G MRPs, were fractionated by size exclusion chromatography into three major fractions (F1⁻F3). F2, which demonstrated the strongest antibacterial activity against Escherichia coli (E. coli) and showed self-production of hydrogen peroxide (H₂O₂), was extracted by solid phase extraction. The hydrophobic extract of F2 was further isolated by reverse phase-high performance liquid chromatography into sub-fractions HE-F2-1 and HE-F2-2. Nine peptides were identified from HE-F2-1, and two peptides from HE-F2-2 using liquid chromatography-electrospray ionization/multi-stage mass spectrometry. Three peptides, FEDQLR (HGM-Hp1), ALERTF (HGM-Hp2), and RHPEYAVSVLLR (HGM-Hp3), with net charges of -1, 0, and +1, respectively, were synthesized. The minimal inhibitory concentration of these synthetic peptides was 2 mg/mL against E. coli. Once incubated with logarithmic growth phase of E. coli, HGM-Hp1 and HGM-Hp2 induced significant increases of both extracellular and intracellular H₂O₂ formation. However, HGM-Hp3 only dramatically enhanced intracellular H₂O₂ production in E. coli. The increased potassium ions in E. coli suspension after addition of HGM-Hp1 or HGM-Hp2 indicated the destruction of cell integrity via irreversible membrane damage. It is the first report of hydrolysates MRPs-derived peptides that might perform the antibacterial activity via inducing intracellular H₂O2 production.

Specific Amyloid Binding of Polybasic Peptides In Vivo Is Retained by β-Sheet Conformers but Lost in the Disrupted Coil and All D-Amino Acid Variants

PURPOSE

The heparin-reactive, helical peptide p5 is an effective amyloid imaging agent in mice with systemic amyloidosis. Analogs of p5 with modified secondary structure characteristics exhibited altered binding to heparin, synthetic amyloid fibrils, and amyloid extracts in vitro. Herein, we further study the effects of peptide helicity and chirality on specific amyloid binding using a mouse model of systemic inflammation-associated (AA) amyloidosis.

PROCEDURES

Peptides with disrupted helical structure [p5_(coil) and p5_(Pro3)], with an extended sheet conformation [p5_(sheet)] or an all-D enantiomer [p5_(D)], were chemically synthesized, radioiodinated, and their biodistribution studied in WT mice as well as transgenic animals with severe systemic AA amyloidosis. Peptide binding was assessed qualitatively by using small animal single-photon emission computed tomography/x-ray computed tomography imaging and microautoradiography and quantitatively using tissue counting.

RESULTS

Peptides with reduced helical propensity, p5_(coil) and p5_(Pro3), exhibited significantly reduced binding to AA amyloid-laden organs. In contrast, peptide p5_(D) was retained by non-amyloid-related ligands in the liver and kidneys of both WT and AA mice, but it also bound AA amyloid in the spleen. The p5_(sheet) peptide specifically bound AA amyloid in vivo and was not retained by healthy tissues in WT animals.

CONCLUSIONS

Modification of amyloid-targeting peptides using D-amino acids should be performed cautiously due to the introduction of unexpected secondary pharmacologic effects. Peptides that adopt a helical structure, to align charged amino acid side chains along one face, exhibit specific reactivity with amyloid; however, polybasic peptides with a propensity for β-sheet conformation are also amyloid-reactive and may yield a novel class of amyloid-targeting agents for imaging and therapy.

Evaluation of the effect of D-amino acid incorporation into amyloid-reactive peptides

BACKGROUND

Systemic amyloidoses comprise diseases characterized by the deposition of proteinaceous material known as amyloid. Currently, without performing multiple biopsies, there is no way to ascertain the extent of amyloid deposition in patients-a critical piece of information that informs prognosis and therapeutic strategies. We have developed pan-amyloid-targeting peptides for imaging amyloid and recently have adapted these for use as pre-targeting agents in conjunction with immunotherapy. Incorporation of D-amino acids in these peptides may enhance serum half-life, which is an important characteristic of effective peptide therapeutics. Herein, we assess the effects of partial incorporation of D-amino acids into the amyloidophilic peptide p5 on in vivo amyloid reactivity.

METHODS

Peptides, referred to as ^AQAp5 _(d) , ^aqap5, and ^AQAp5, were radiolabeled with iodine-125 and the tissue biodistribution (% injected dose/gram) measured in healthy mice at multiple time points post-injection. Microscopic distribution of the peptides was further visualized using microautoradiography (ARG). Peptides ^aqap5 and ^AQAp5 were injected into healthy and amyloid-laden mice and evaluated by using SPECT/CT imaging at 1, 4 and 24 h post injection.

RESULTS

Biodistribution data and ARG revealed persistent retention of [¹²⁵I]^AQAp5 _(d) in the liver and kidneys of healthy mice for at least 24 h. In contrast, peptides [¹²⁵I]^aqap5 and [¹²⁵I]^AQAp5 did not bind these organs and was significantly lower than [¹²⁵I]^AQAp5 _(d) at 24 h post injection (p < 0.0001). SPECT/CT imaging of amyloid-laden mice revealed accumulation of both [¹²⁵I]^aqap5 and [¹²⁵I]^AQAp5 in amyloid-affected organs; whereas, in healthy mice, [¹²⁵I]^aqap5 was observed in the kidneys and liver at early time points, and free radioiodide liberated during catabolism of [¹²⁵I]^AQAp5 was seen in the stomach and thyroid. Autoradiography confirmed that both [¹²⁵I]^aqap5 and [¹²⁵I]^AQAp5 peptides specifically bound amyloid with no off-target binding to healthy organs.

CONCLUSION

Incorporation of D-amino acids in amyloid-binding regions of amyloidophilic peptides resulted in off-target binding; however, N-terminus placement retained amyloid-specificity and evasion of deiodinases. Peptide ^aqap5, or similar reagents, may prove useful in novel immunotherapy strategies as well as for imaging renal, gastric and pancreatic amyloidosis.

A Peptide-Fc Opsonin with Pan-Amyloid Reactivity

There is a continuing need for therapeutic interventions for patients with the protein misfolding disorders that result in systemic amyloidosis. Recently, specific antibodies have been employed to treat AL amyloidosis by opsonizing tissue amyloid deposits thereby inducing cell-mediated dissolution and organ improvement. To develop a pan-amyloid therapeutic agent, we have produced an Fc-fusion product incorporating a peptide, p5, which binds many if not all forms of amyloid. This protein, designated Fcp5, expressed in mammalian cells, forms the desired bivalent dimer structure and retains pan-amyloid reactivity similar to the p5 peptide as measured by immunosorbent assays, immunohistochemistry, surface plasmon resonance, and pulldown assays using radioiodinated Fcp5. Additionally, Fcp5 was capable of opsonizing amyloid fibrils in vitro using a pH-sensitive fluorescence assay of phagocytosis. In mice,¹²⁵ I-labeled Fcp5 exhibited an extended serum circulation time, relative to the p5 peptide. It specifically bound AA amyloid deposits in diseased mice, as evidenced by biodistribution and microautoradiographic methods, which coincided with an increase in active, Iba-1-positive macrophages in the liver at 48 h postinjection of Fcp5. In healthy mice, no specific tissue accumulation was observed. The data indicate that polybasic, pan-amyloid-targeting peptides, in the context of an Fc fusion, can yield amyloid reactive, opsonizing reagents that may serve as next-generation immunotherapeutics.