Optimisation of BACE1 inhibition of tripartite structures by modification of membrane anchors, spacers and pharmacophores - development of potential agents for the treatment of Alzheimer's disease

Peptide-Drug Conjugates: An Emerging Direction for the Next Generation of Peptide Therapeutics

Building on recent advances in peptide science, medicinal chemists have developed a hybrid class of bioconjugates, called peptide-drug conjugates, that demonstrate improved efficacy compared to peptides and small molecules independently. In this Perspective, we discuss how the conjugation of synergistic peptides and small molecules can be used to overcome complex disease states and resistance mechanisms that have eluded contemporary therapies because of their multi-component activity. We highlight how peptide-drug conjugates display a multi-factor therapeutic mechanism similar to that of antibody-drug conjugates but also demonstrate improved therapeutic properties such as less-severe off-target effects and conjugation strategies with greater site-specificity. The many considerations that go into peptide-drug conjugate design and optimization, such as peptide/small-molecule pairing and chemo-selective chemistries, are discussed. We also examine several peptide-drug conjugate series that demonstrate notable activity toward complex disease states such as neurodegenerative disorders and inflammation, as well as viral and bacterial targets with established resistance mechanisms.

Synergetic copper/TEMPO-catalysed benzylic C–H imidation with N-fluorobenzenesulfonimide at room temperature and tandem conversions with alcohols or arenes

A remote carbamate-directed benzylic C–H imidation with NFSI at room temperature through synergetic CuCl-TEMPO catalysis and tandem alkoxylation or arylation with alcohols or arenes are described.

A lipid-anchored neurokinin 1 receptor antagonist prolongs pain relief by a three-pronged mechanism of action targeting the receptor at the plasma membrane and in endosomes

G-protein-coupled receptors (GPCRs) are traditionally known for signaling at the plasma membrane, but they can also signal from endosomes after internalization to control important pathophysiological processes. In spinal neurons, sustained endosomal signaling of the neurokinin 1 receptor (NK1R) mediates nociception, as demonstrated in models of acute and neuropathic pain. An NK1R antagonist, Spantide I (Span), conjugated to cholestanol (Span-Chol), accumulates in endosomes, inhibits endosomal NK1R signaling, and causes prolonged antinociception. However, the extent to which the Chol-anchor influences long-term location and activity is poorly understood. Herein, we used fluorescent correlation spectroscopy and targeted biosensors to characterize Span-Chol over time. The Chol-anchor increased local concentration of probe at the plasma membrane. Over time we observed an increase in NK1R-binding affinity and more potent inhibition of NK1R-mediated calcium signaling. Span-Chol, but not Span, caused a persistent decrease in NK1R recruitment of β-arrestin and receptor internalization to early endosomes. Using targeted biosensors, we mapped the relative inhibition of NK1R signaling as the receptor moved into the cell. Span selectively inhibited cell surface signaling, whereas Span-Chol partitioned into endosomal membranes and blocked endosomal signaling. In a preclinical model of pain, Span-Chol caused prolonged antinociception (>9 h), which is attributable to a three-pronged mechanism of action: increased local concentration at membranes, a prolonged decrease in NK1R endocytosis, and persistent inhibition of signaling from endosomes. Identifying the mechanisms that contribute to the increased preclinical efficacy of lipid-anchored NK1R antagonists is an important step toward understanding how we can effectively target intracellular GPCRs in disease.

Pharmacological Inhibition of Amyloidogenic APP Processing and Knock-Down of APP in Primary Human Macrophages Impairs the Secretion of Cytokines

It has been previously shown that the amyloid precursor protein (APP) support the innate immune defense as an immune receptor. Amyloid β (Aβ) peptides seem to have properties of an antimicrobial peptide and can act as opsonines. In APP-deficient mouse models, a reduced secretion of cytokines has been observed. Still, it is unclear whether this can be attributed to the lack of APP or to the missing secretion of Aβ peptides. We inhibited the secretion of Aβ peptides in primary human monocyte derived macrophages with the γ-secretase inhibitor N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-S-phenylglycine-t-butyl-ester (DAPT) or the β-secretase inhibitor GL-189. Alternatively, we knocked down APP by transfection with siRNA. We measured tumor necrosis factor α (TNFα), interleukin 6 (IL-6) and interleukin (IL-10) by enzyme linked immunosorbent assay (ELISA) and evaluated the phagocytotic activity by flow cytometry. We observed reduced concentrations of TNFα and IL-6 in the media of APP^k/d macrophages and after inhibition of the β-, or γ-secretase, especially after additional immunological activation with lipopolysaccharide (LPS). Secretion of IL-10 was increased after pharmacological inhibition of APP processing when the macrophages were not immunologically activated but was decreased during LPS-induced inflammation in APP^k/d macrophages. No changes of the phagocytotic activity were observed. We conclude that macrophage APP and Aβ peptides support the initiation of an immune response and are involved in the regulation of TNFα, IL-6, and IL-10 secretion by human monocyte-derived macrophages.

Synthesis and biological activity of a CXCR4-targeting bis(cyclam) lipid

A bis(cyclam)-capped cholesterol lipid designed to bind C-X-C chemokine receptor type 4 (CXCR4) was synthesised in good overall yield from 4-methoxyphenol through a seven step synthetic route, which also provided a bis(cyclam) intermediate bearing an octaethyleneglycol-primary amine that can be easily derivatised. This bis(cyclam)-capped cholesterol lipid was water soluble and self-assembled into micellar and non-micellar aggregates in water at concentrations above 8 μM. The bioactivity of the bis(cyclam)-capped cholesterol lipid was assessed using primary chronic lymphocytic leukaemia (CLL) cells, first with a competition binding assay then with a chemotaxis assay along a C-X-C motif chemokine ligand 12 (CXCL12) concentration gradient. At 20 μM, the bis(cyclam)-capped cholesterol lipid was as effective as the commercial drug AMD3100 for preventing the migration of CLL cells, despite a lower affinity for CXCR4 than AMD3100.

Design and characterization of bivalent compounds as potential neuroprotectants for Alzheimer's disease: Impact of the spacer on biological activity

In our continuing efforts to develop bivalent compounds as potential neuroprotectants for Alzheimer's disease, a series of bivalent compounds that contain cholesterylamine and an extended spacer were synthesized and biologically characterized. Our results demonstrated that incorporation of a piperazine ring into the spacer composition significantly improved the protective potency in MC65 cell models. Our results also suggested that the optimal spacer length for such bivalent compounds ranges from 17 to 21 atoms, and further spacer extension beyond 21 atoms results no further optimization. Notably, incorporation of a piperazine ring into the spacer diminished the biometal chelating capacity for these bivalent compounds, thus suggesting structural flexibility of these compounds in interactions with metals. Collectively, the results provided valuable guidance to develop new bivalent compounds as neuroprotectants for Alzheimer's disease.

Insights into the Impact of a Membrane-Anchoring Moiety on the Biological Activities of Bivalent Compounds As Potential Neuroprotectants for Alzheimer's Disease

Bivalent compounds anchoring in different manners to the membrane were designed and biologically characterized to understand the contribution of the anchor moiety to their biological activity as neuroprotectants for Alzheimer's disease. Our results established that the anchor moiety is essential, and we identified a preference for diosgenin, as evidenced by 17MD. Studies in primary neurons and mouse brain mitochondria also identified 17MD as exhibiting activity on neuritic outgrowth and the state 3 oxidative rate of glutamate while preserving the coupling capacity of the mitochondria. Significantly, our studies demonstrated that the integrated bivalent structure is essential to the observed biological activities. Further studies employing bivalent compounds as probes in a model membrane also revealed the influence of the anchor moiety on how they interact with the membrane. Collectively, our results suggest diosgenin to be an optimal anchor moiety, providing bivalent compounds with promising pharmacology that have potential applications for Alzheimer's disease.

Presumed LRP1-targeting transport peptide delivers β-secretase inhibitor to neurons in vitro with limited efficiency

Interfering with the activity of β-secretase to reduce the production of Aβ peptides is a conceivable therapeutic strategy for Alzheimer’s disease. However, the development of efficient yet safe inhibitors is hampered by secondary effects, usually linked to the indiscriminate inhibition of other substrates’ processing by the targeted enzyme. Based on the spatial compartmentalization of the cleavage of the amyloid precursor protein by β-secretase, we hypothesized that by exploiting the endocytosis receptor low-density lipoprotein receptor-related protein it would be possible to direct an otherwise cell-impermeable inhibitor to the endosomes of neurons, boosting the drug’s efficacy and importantly, sparing the off-target effects. We used the transport peptide Angiopep to build an endocytosis-competent conjugate and found that although the peptide facilitated the inhibitor’s internalization into neurons and delivered it to the endosomes, the delivery was not efficient enough to potently reduce β-secretase activity at the cellular level. This is likely connected to the finding that in the cell lines we used, Angiopep’s internalization was not mediated by its presumed receptor to a significant extent. Additionally, Angiopep exploited different internalization mechanisms when applied alone or when conjugated to the inhibitor, highlighting the impact that drug conjugation can have on transport peptides.

Solid-Phase Synthesis and Characterization of N-Terminally Elongated Aβ-3-x -Peptides

In addition to the prototypic amyloid-β (Aβ) peptides Aβ1-40 and Aβ1-42 , several Aβ variants differing in their amino and carboxy termini have been described. Synthetic availability of an Aβ variant is often the key to study its role under physiological or pathological conditions. Herein, we report a protocol for the efficient solid-phase peptide synthesis of the N-terminally elongated Aβ-peptides Aβ-3-38 , Aβ-3-40 , and Aβ-3-42 . Biophysical characterization by NMR spectroscopy, CD spectroscopy, an aggregation assay, and electron microscopy revealed that all three peptides were prone to aggregation into amyloid fibrils. Immunoprecipitation, followed by mass spectrometry, indicated that Aβ-3-38 and Aβ-3-40 are generated by transfected cells even in the presence of a tripartite β-site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibitor. The elongated Aβ peptides starting at Val(-3) can be separated from N-terminally-truncated Aβ forms by high-resolution isoelectric-focusing techniques, despite virtually identical isoelectric points. The synthetic Aβ variants and the methods presented here are providing tools to advance our understanding of the potential roles of N-terminally elongated Aβ variants in Alzheimer's disease.