Combined molecular dynamics and experimental approach to understand the impact of the oxetane and azetidine modification on peptides

Peptide-based drugs are promising as therapeutics, but they are limited by unfavourable pharmacokinetic properties. Modifying or cyclising the peptide backbone increases their biological activity in many cases. However, cyclic peptides remain challenging to make, and no single backbone modification is universally tolerated. Both oxetanes and azetidines have previously been used in medicinal chemistry, and previous work suggests that oxetane modification of the peptide backbone may bring the termini in close proximity, enhancing efficiency of cyclisation. In order to realise the potential of oxetane and azetidine modification in medicinal chemistry, an investigation into the effects of these modifications on the backbone of peptides is needed. In this work, linear and cyclic oxetane-modified peptides were characterised using CD, NMR spectroscopy and molecular dynamics (MD) simulations. In linear peptides, oxetane modification induces the formation of a turn, as evidenced by the presence of medium-range NOEs observed in NMR experiments. In cyclic peptides, MD simulations reveal that the oxetane-modified peptide is more rigid and the structure is stabilised by the formation of a new hydrogen bond that is absent in the parent peptide. The effect of oxetane modification on _-helicity was also explored. CD spectroscopy revealed that oxetane modification drastically reduces the helical content of a well-characterised sequence. Furthermore, steered MD simulations revealed the molecular determinants of this destabilisation|that oxetane modification introduces a kink in the helical axis, which disrupts the dihedral angles and hydrogen bonding pattern in both directions. NMR experiments showed that, like oxetane, azetidine induces a turn in a short linear peptide. Finally, the impact of azetidine modification on the activity of antimicrobial peptides (AMPs) was assessed using microbiological assays. Following confirmation of activity, a known AMP sequence was modified and/or cyclised, and the activity was measured. It was found that azetidine modification increases the activity of this AMP without increasing its toxicity. Overall, this work may help direct future design of peptide-based drugs

P1266: Flow cytometry combined with systems biology enables rational targeting of NFKB in DLBCL

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Impact of oxetane incorporation on the structure and stability of alpha-helical peptides

Peptide-based drugs combine advantages of larger biological therapeutics with those of small molecule drugs, but they generally display poor permeability and metabolic stability. Recently, we introduced a new type of peptide bond isostere, in which the backbone carbonyl is replaced with a 3-amino oxetane heterocycle, into short linear peptides with the aim of improving their therapeutic potential. In this study, we have explored the impact of oxetane modification on α-helical peptides to establish whether or not this modification is tolerated in this biologically important structural motif. The oxetane modification was introduced at two positions in a well-characterised helical peptide sequence, and circular dichroism and NMR spectroscopy were used to measure the resulting secondary structure content under different experimental conditions. Our data demonstrated that introduction of an oxetane into the peptide backbone results in a significant loss of helicity, regardless of where in the sequence the modification is placed. The molecular determinants of this destabilisation were then explored using steered molecular dynamics simulations, a computational method analogous to single molecule spectroscopy. Our simulations indicated that oxetane modification introduces a kink in the helical axis, alters the dihedral angles of residues up to three positions away from the modification, and disrupts the (i, i + 4) hydrogen bonding pattern characteristic of α-helices in favour of new, short-range hydrogen bonds. The detailed structural understanding provided in this work can direct future design of chemically modified peptides

Synthesis and functionalization of azetidine‐containing small macrocyclic peptides

Cyclic peptides are increasingly important structures in drugs but their development can be impeded by difficulties associated with their synthesis. Here, we introduce the 3-aminoazetidine (3-AAz) subunit as a new turn-inducing element for the efficient synthesis of small head-to-tail cyclic peptides. Greatly improved cyclizations of tetra-, penta- and hexapeptides (28 examples) under standard reaction conditions are achieved by introduction of this element within the linear peptide precursor. Post-cyclization deprotection of the amino acid side chains with strong acid is realized without degradation of the strained four-membered azetidine. An special feature of this chemistry is that further late-stage modification of the resultant macrocyclic peptides can be achieved via the 3-AAz unit. This is done by: (i) chemoselective deprotection and substitution at the azetidine nitrogen, or by (ii) a click-based approach employing a 2-propynyl carbamate on the azetidine nitrogen. In this way, a range of dye and biotin tagged macrocycles are readily produced. Structural insights gained by XRD analysis of a cyclic tetrapeptide indicate that the azetidine ring encourages access to the less stable, all-trans conformation. Moreover, introduction of a 3-AAz into a representative cyclohexapeptide improves stability towards proteases compared to the homodetic macrocycle

Synthesis and Functionalization of Azetidine‐Containing Small Macrocyclic Peptides

Cyclic peptides are increasingly important structures in drugs but their development can be impeded by difficulties associated with their synthesis. Here, we introduce the 3-aminoazetidine (3-AAz) subunit as a new turn-inducing element for the efficient synthesis of small head-to-tail cyclic peptides. Greatly improved cyclizations of tetra-, penta- and hexapeptides (28 examples) under standard reaction conditions are achieved by introduction of this element within the linear peptide precursor. Post-cyclization deprotection of the amino acid side chains with strong acid is realized without degradation of the strained four-membered azetidine. A special feature of this chemistry is that further late-stage modification of the resultant macrocyclic peptides can be achieved via the 3-AAz unit. This is done by: (i) chemoselective deprotection and substitution at the azetidine nitrogen, or by (ii) a click-based approach employing a 2-propynyl carbamate on the azetidine nitrogen. In this way, a range of dye and biotin tagged macrocycles are readily produced. Structural insights gained by XRD analysis of a cyclic tetrapeptide indicate that the azetidine ring encourages access to the less stable, all-trans conformation. Moreover, introduction of a 3-AAz into a representative cyclohexapeptide improves stability towards proteases compared to the homodetic macrocycle

Macrocyclisation of small peptides enabled by oxetane incorporation

Cyclic peptides are an important source of new drugs but are challenging to produce synthetically. We show that head-to-tail peptide macrocyclisations are greatly improved, as measured by isolated yields, reaction rates and product distribution, by substitution of one of the backbone amide C=O bonds with an oxetane ring. The cyclisation precursors are easily made by standard solution- or solid-phase peptide synthesis techniques. Macrocyclisations across a range of challenging ring sizes (tetra-, penta- and hexapeptides) are enabled by incorporation of this turn-inducing element. Oxetane incorporation is shown to be superior to other established amino acid modifications such as N-methylation. The positional dependence of the modification on cyclisation efficiency is mapped using a cyclic peptide of sequence LAGAY. We provide the first direct experimental evidence that oxetane modification induces a turn in linear peptide backbones, through the observation of dNN (i, i+2) and dαN (i, i+2) NOEs, which offers an explanation for these improvements. For cyclic peptide, cLAGAY, a combination of NMR derived distance restraints and molecular dynamics simulations are used to show that this modification alters the backbone conformation in proximity to the oxetane, with the flexibility of the ring reduced and a new intramolecular H-bond established. Finally, we incorporated an oxetane into a cyclic pentapeptide inhibitor of Aminopeptidase N, a transmembrane metalloprotease overexpressed on the surface of cancer cells. The inhibitor, cCNGRC, displayed similar IC50 values in the presence or absence of an oxetane at the Gly residue, indicating that bioactivity is fully retained upon amide C=O bond replacement

NF-κB fingerprinting reveals heterogeneous NF-κB composition in diffuse large B-cell lymphoma

IntroductionImproving treatments for Diffuse Large B-Cell Lymphoma (DLBCL) is challenged by the vast heterogeneity of the disease. Nuclear factor-κB (NF-κB) is frequently aberrantly activated in DLBCL. Transcriptionally active NF-κB is a dimer containing either RelA, RelB or cRel, but the variability in the composition of NF-κB between and within DLBCL cell populations is not known.ResultsHere we describe a new flow cytometry-based analysis technique termed “NF-κB fingerprinting” and demonstrate its applicability to DLBCL cell lines, DLBCL core-needle biopsy samples, and healthy donor blood samples. We find each of these cell populations has a unique NF-κB fingerprint and that widely used cell-of-origin classifications are inadequate to capture NF-κB heterogeneity in DLBCL. Computational modeling predicts that RelA is a key determinant of response to microenvironmental stimuli, and we experimentally identify substantial variability in RelA between and within ABC-DLBCL cell lines. We find that when we incorporate NF-κB fingerprints and mutational information into computational models we can predict how heterogeneous DLBCL cell populations respond to microenvironmental stimuli, and we validate these predictions experimentally.DiscussionOur results show that the composition of NF-κB is highly heterogeneous in DLBCL and predictive of how DLBCL cells will respond to microenvironmental stimuli. We find that commonly occurring mutations in the NF-κB signaling pathway reduce DLBCL’s response to microenvironmental stimuli. NF-κB fingerprinting is a widely applicable analysis technique to quantify NF-κB heterogeneity in B cell malignancies that reveals functionally significant differences in NF-κB composition within and between cell populations

Molecular Basis of Selectivity and Activity for the Antimicrobial Peptide Lynronne‐1 Informs Rational Design of Peptide with Improved Activity

Antibiotic resistance is a significant threat to human health, with natural products remaining the best source for new antimicrobial compounds. Antimicrobial peptides (AMPs) are natural products with great potential for clinical use as they are small, amenable to customization, and show broad-spectrum activities. Lynronne-1 is a promising AMP identified in the rumen microbiome that shows broad-spectrum activity against pathogens such as methicillin-resistant Staphylococcus aureus and Acinetobacter baumannii. Here we investigated the structure of Lynronne-1 using solution NMR spectroscopy and identified a 13-residue amphipathic helix containing all six cationic residues. We used biophysical approaches to observe folding, membrane partitioning and membrane lysis selective to the presence of anionic lipids. We translated our understanding of Lynronne-1 structure to design peptides which varied in the size of their hydrophobic helical face. These peptides displayed the predicted continuum of membrane-lysis activities in vitro and in vivo, and yielded a new AMP with 4-fold improved activity against A. baumannii and 32-fold improved activity against S. aureus

Homozygous mutations in the SCN1A gene associated with genetic epilepsy with febrile seizures plus and Dravet syndrome in 2 families

Background Mutations in the gene encoding the alpha subunit of the voltage-gated sodium channel SCN1A are associated with several epilepsy syndromes. These range from severe phenotypes including Dravet syndrome to milder phenotypes such as genetic epilepsy with febrile seizures plus (GEFS+). To date the sequence variants identified have been heterozygous in nature as one would expect for a disorder that occurs de novo or is dominantly inherited. Methods and Results We report the association of two novel homozygous missense mutations of the SCN1A gene in four children with infantile epilepsies from two consanguineous pedigrees. We suggest that the nature and location of the identified amino acid changes allows heterozygous carriers to remain unaffected. However, having such changes on both alleles may have a cumulative and detrimental effect. Conclusion The presented cases illustrate how better understanding of the nature and location of SCN1A missense mutations may aid the interpretation of genotype–phenotype associations. SCN1A related epilepsies should be considered in children with infantile onset epilepsies even when an autosomal recessive neurological disorder is suspected