Exploring the Utility of Cell-Penetrating Peptides as Vehicles for the Delivery of Distinct Antimalarial Drug Cargoes.

The devastating impact of malaria includes significant mortality and illness worldwide. Increasing resistance of the causative parasite, Plasmodium, to existing antimalarial drugs underscores a need for additional compounds with distinct modes of action in the therapeutic development pipeline. Here we showcase peptide-drug conjugates (PDCs) as an attractive compound class, in which therapeutic or lead antimalarials are chemically conjugated to cell-penetrating peptides.

Total Synthesis of a Peptide Diatom Sex Pheromone Bearing a Sulfated Aspartic Acid.

The peptide sex-inducing pheromone SIP () bearing an unusual sulfated aspartic acid residue induces sexual reproduction in diatom populations. Herein, we report the first total synthesis of SIP using both a sulfated building block approach and a solid-phase peptide synthesis (SPPS)-compatible late-stage sulfation strategy to assemble the natural product. The modular approaches provide concise routes to useful quantities of the natural product for future structure activity relationship studies examining the role of SIP in diatom biology.

Chemical synthesis of grafted cyclotides using a "plug and play" approach.

Cyclotides are a diverse class of plant-derived cyclic, disulfide-rich peptides with a unique cyclic cystine knot topology. Their remarkable structural stability and resistance to proteolytic degradation can lead to improved pharmacokinetics and oral activity as well as selectivity and high enzymatic stability. Thus, cyclotides have emerged as powerful scaffold molecules for designing peptide-based therapeutics.

Development of Melanocortin 4 Receptor Agonists by Exploiting Animal-Derived Macrocyclic, Disulfide-Rich Peptide Scaffolds.

G protein-coupled receptors are among the most widely studied classes of drug targets. A major challenge in this field is to develop ligands that will selectively modulate a single receptor subtype to overcome the disadvantages of undesired "off target" effects caused by lack of target and thus signaling specificity. In the current study, we explored ligand design for the melanocortin 4 receptor (MC4R) since it is an attractive target for developing antiobesity drugs.

Development of a Selective Peptide κ-Opioid Receptor Antagonist by Late-Stage Functionalization with Cysteine Staples.

The κ-opioid receptor (KOR) is an attractive target for the development of novel drugs. KOR agonists are potentially safer pain medications, whereas KOR antagonists are promising drug candidates for the treatment of neuropsychiatric disorders. Hitherto, the vast majority of selective drug leads that have been developed for KOR are small molecules.

Development of Antiplasmodial Peptide-Drug Conjugates Using a Human Protein-Derived Cell-Penetrating Peptide with Selectivity for Infected Cells.

Malaria continues to impose a global health burden. Drug-resistant parasites have emerged to each introduced small-molecule therapy, highlighting the need for novel treatment approaches for the future eradication of malaria. Herein, targeted drug delivery with peptide-drug conjugates (PDCs) was investigated as an alternative antimalarial therapy, inspired by the success of emerging antibody-drug conjugates utilized in cancer treatment.

Neoadjuvant enoblituzumab in localized prostate cancer: a single-arm, phase 2 trial.

B7 homolog 3 (B7-H3; CD276), a tumor-associated antigen and possible immune checkpoint, is highly expressed in prostate cancer (PCa) and is associated with early recurrence and metastasis. Enoblituzumab is a humanized, Fc-engineered, B7-H3-targeting antibody that mediates antibody-dependent cellular cytotoxicity. In this phase 2, biomarker-rich neoadjuvant trial, 32 biological males with operable intermediate to high-risk localized PCa were enrolled to evaluate the safety, anti-tumor activity and immunogenicity of enoblituzumab when given before prostatectomy.

Late-Stage Functionalization with Cysteine Staples Generates Potent and Selective Melanocortin Receptor-1 Agonists.

In this work, cysteine staples were used as a late-stage functionalization strategy to diversify peptides and build conjugates targeting the melanocortin G-protein-coupled receptors [melanocortin receptor-1 (MC1R) and MC3R-MC5R]. Monocyclic and bicyclic agonists based on sunflower trypsin inhibitor-1 were used to generate a selection of stapled peptides that were evaluated for binding (p) and functional activation (pEC) of the melanocortin receptor subtypes. Stapled peptides generally had improved activity, with aromatic stapled peptides yielding selective MC1R agonists, including a xylene-stapled peptide () with an EC of 1.

Umpolung strategies for the functionalization of peptides and proteins.

Umpolung strategies, defined as synthetic approaches which reverse commonly accepted reactivity patterns, are broadly recognized as enabling tools for small molecule synthesis and catalysis. However, methods which exploit this logic for peptide and protein functionalizations are comparatively rare, with the overwhelming majority of existing bioconjugation approaches relying on the well-established reactivity profiles of a handful of amino acids. This perspective serves to highlight a small but growing body of recent work that masterfully capitalizes on the concept of polarity reversal for the selective modification of proteinogenic functionalities.

Structural and functional analysis of the human cone-rod homeobox transcription factor.

The cone-rod homeobox (CRX) protein is a critical K50 homeodomain transcription factor responsible for the differentiation and maintenance of photoreceptor neurons in the vertebrate retina. Mutant alleles in the human gene encoding CRX result in a variety of distinct blinding retinopathies, including retinitis pigmentosa, cone-rod dystrophy, and Leber congenital amaurosis. Despite the success of using in vitro biochemistry, animal models, and genomics approaches to study this clinically relevant transcription factor over the past 25 years since its initial characterization, there are no high-resolution structures in the published literature for the CRX protein.

Phage display-based discovery of cyclic peptides against the broad spectrum bacterial anti-virulence target CsrA.

Small macrocyclic peptides are promising candidates for new anti-infective drugs. To date, such peptides have been poorly studied in the context of anti-virulence targets. Using phage display and a self-designed peptide library, we identified a cyclic heptapeptide that can bind the carbon storage regulator A (CsrA) from Yersinia pseudotuberculosis and displace bound RNA.

Weapons or deterrents? Nudibranch molluscs use distinct ecological modes of chemical defence against predators.

Defensive chemicals are used by plants and animals to reduce the risk of predation through different mechanisms, including toxins that cause injury and harm (weapons) and unpalatable or odiferous compounds that prevent attacks (deterrents). However, whether effective defences are both toxins and deterrents, or work in just one modality is often unclear. In this study, our primary aim was to determine whether defensive compounds stored by nudibranch molluscs acted as weapons (in terms of being toxic), deterrents (in terms of being distasteful) or both.

The tumor immune microenvironment of primary and metastatic HER2- positive breast cancers utilizing gene expression and spatial proteomic profiling.

Background: The characterization of the immune component of the tumor microenvironment (TME) of human epidermal growth factor receptor 2 positive (HER2+) breast cancer has been limited. Molecular and spatial characterization of HER2+ TME of primary, recurrent, and metastatic breast tumors has the potential to identify immune mediated mechanisms and biomarker targets that could be used to guide selection of therapies.

Methods: We examined 15 specimens from eight patients with HER2+ breast cancer: 10 primary breast tumors (PBT), two soft tissue, one lung, and two brain metastases (BM).

Melanocortin 1 Receptor Agonists Based on a Bivalent, Bicyclic Peptide Framework.

We have designed a new class of highly potent bivalent melanocortin receptor ligands based on the nature-derived bicyclic peptide sunflower trypsin inhibitor 1 (SFTI-1). Incorporation of melanotropin pharmacophores in each of the two turn regions of SFTI-1 resulted in substantial gains in agonist activity particularly at human melanocortin receptors 1 and 3 (hMC1R/hMC3R) compared to monovalent analogues. In binding and functional assays, the most potent molecule, compound , displayed low picomolar agonist activity at hMC1R (pEC > 10.

Sunflower Trypsin Inhibitor-1 (SFTI-1): Sowing Seeds in the Fields of Chemistry and Biology.

Nature-derived cyclic peptides have proven to be a vast source of inspiration for advancing modern pharmaceutical design and synthetic chemistry. The focus of this Review is sunflower trypsin inhibitor-1 (SFTI-1), one of the smallest disulfide-bridged cyclic peptides found in nature. SFTI-1 has an unusual biosynthetic pathway that begins with a dual-purpose albumin precursor and ends with the production of a high-affinity serine protease inhibitor that rivals other inhibitors much larger in size.

Application and Structural Analysis of Triazole-Bridged Disulfide Mimetics in Cyclic Peptides.

Ruthenium-catalysed azide-alkyne cycloaddition (RuAAC) provides access to 1,5-disubstituted 1,2,3-triazole motifs in peptide engineering applications. However, investigation of this motif as a disulfide mimetic in cyclic peptides has been limited, and the structural consequences remain to be studied. We report synthetic strategies to install various triazole linkages into cyclic peptides through backbone cyclisation and RuAAC cross-linking reactions.

Effects of a potassium channel opener on brain injury and neurologic outcomes in an animal model of neonatal hypoxic-ischemic injury.

Background: Hypoxia-ischemia (HI) is the most common cause of brain injury in newborns and the survivors often develop cognitive and sensorimotor disabilities that undermine the quality of life. In the current study, we examined the effectiveness of flupirtine, a potassium channel opener, shown previously in an animal model to have strong anti-neonatal-seizure efficacy, to provide neuroprotection and alleviate later-life disabilities caused by neonatal hypoxic-ischemic injury.

Methods: The rats were treated with a single dose of flupirtine for 4 days following HI induction in 7-day-old rats.

Amino Acid Scanning at P5' within the Bowman-Birk Inhibitory Loop Reveals Specificity Trends for Diverse Serine Proteases.

Sunflower trypsin inhibitor-1 (SFTI-1) is a 14-amino acid cyclic peptide that shares an inhibitory loop with a sequence and structure similar to a larger family of serine protease inhibitors, the Bowman-Birk inhibitors. Here, we focus on the P5' residue in the Bowman-Birk inhibitory loop and produce a library of SFTI variants to characterize the P5' specificity of 11 different proteases. We identify seven amino acids that are generally preferred by these enzymes and also correlate with P5' sequence diversity in naturally occurring Bowman-Birk inhibitors.

Cytotoxic Spiroepoxide Lactone and Its Putative Biosynthetic Precursor from .

Epoxygoniolide-1 (), possessing spiroepoxide lactone, enal, and masked dialdehyde functionalities, has been characterized from the conspicuously patterned mollusc . Its relative configuration was investigated by spectroscopic analyses, molecular modeling, and density functional theory calculations. The biosynthesis of may involve rearrangement of a diterpene framework, providing a precursor to cometabolite gonioline (), followed by C-C bond cleavage (via Grob or P450 mechanism).

Toxicity and taste: unequal chemical defences in a mimicry ring.

Mimicry of warning signals is common, and can be mutualistic when mimetic species harbour equal levels of defence (Müllerian), or parasitic when mimics are undefended but still gain protection from their resemblance to the model (Batesian). However, whether chemically defended mimics should be similar in terms of toxicity (i.e.

Development of Novel Melanocortin Receptor Agonists Based on the Cyclic Peptide Framework of Sunflower Trypsin Inhibitor-1.

Ultrastable cyclic peptide frameworks offer great potential for drug design due to their improved bioavailability compared to their linear analogues. Using the sunflower trypsin inhibitor-1 (SFTI-1) peptide scaffold in combination with systematic N-methylation of the grafted pharmacophore led to the identification of novel subtype selective melanocortin receptor (MCR) agonists. Multiple bicyclic peptides were synthesized and tested toward their activity at MC1R and MC3-5R.

Distribution of Defensive Metabolites in Nudibranch Molluscs.

Many plants and animals store toxic or unpalatable compounds in tissues that are easily encountered by predators during attack. Defensive compounds can be produced de novo, or obtained from dietary sources and stored directly without selection or modification, or can be selectively sequestered or biotransformed. Storage strategies should be optimized to produce effective defence mechanisms but also prevent autotoxicity of the host.

Catalyst-Controlled Stereoselective Synthesis Secures the Structure of the Antimalarial Isocyanoterpene Pustulosaisonitrile-1.

Three new isocyanoditerpenes (5-7) have been characterized from Australian specimens of the nudibranch Phyllidiella pustulosa. The planar structure and (3R,6S,7R) absolute configuration of pustulosaisonitrile-1 were deduced by spectroscopic analyses at 900 MHz informed by molecular modeling, DFT calculations, and computational NMR chemical shift predictions and by comparison of experimental electronic circular dichroism (ECD) data with TDDFT-ECD calculations for the truncated model compound 8. A catalyst-controlled enantio- and diastereoselective total synthesis of the two most likely diastereomeric candidates for the structure of 5 solidified its (3R,6S,7R,10S,11R,14R) absolute configuration.

New sesquiterpenoid isonitriles from three species of phyllidid nudibranchs.

Chemical investigation of the two nudibranch species Phyllidiella pustulosa and Phyllidia ocellata collected in Queensland, Australia, provided new stereoisomers of 4-isocyano-9-amorphene (1) and of 10-isocyano-4-amorphene (2), respectively. A specimen of Phyllidia picta collected from Bali, Indonesia, contained the axane sesquiterpenoids pictaisonitrile-1 (3) and pictaisonitrile-2 (4). The planar structures were elucidated using 1D and 2D NMR spectroscopy, while relative configurations were established using NOESY correlations, coupling constant data, and comparison with literature data.

Anticonvulsant effect of flupirtine in an animal model of neonatal hypoxic-ischemic encephalopathy.

Research studies suggest that neonatal seizures, which are most commonly associated with hypoxic-ischemic injury, may contribute to brain injury and adverse neurologic outcome. Unfortunately, neonatal seizures are often resistant to treatment with current anticonvulsants. In the present study, we evaluated the efficacy of flupirtine, administered at clinically relevant time-points, for the treatment of neonatal seizures in an animal model of hypoxic-ischemic injury that closely replicates features of the human syndrome.