Macrocyclic peptides that inhibit Wnt signalling via interaction with Wnt3a

A macrocyclic peptide inhibitor traps MRP1 in a catalytically incompetent conformation

Adenosine triphosphate-binding cassette (ABC) transporters, such as multidrug resistance protein 1 (MRP1), protect against cellular toxicity by exporting xenobiotic compounds across the plasma membrane. However, constitutive MRP1 function hinders drug delivery across the blood-brain barrier, and MRP1 overexpression in certain cancers leads to acquired multidrug resistance and chemotherapy failure. Small-molecule inhibitors have the potential to block substrate transport, but few show specificity for MRP1. Here we identify a macrocyclic peptide, named CPI1, which inhibits MRP1 with nanomolar potency but shows minimal inhibition of a related multidrug transporter P-glycoprotein. A cryoelectron microscopy (cryo-EM) structure at 3.27 Å resolution shows that CPI1 binds MRP1 at the same location as the physiological substrate leukotriene C4 (LTC4). Residues that interact with both ligands contain large, flexible sidechains that can form a variety of interactions, revealing how MRP1 recognizes multiple structurally unrelated molecules. CPI1 binding prevents the conformational changes necessary for adenosine triphosphate (ATP) hydrolysis and substrate transport, suggesting it may have potential as a therapeutic candidate.

Discovery of De Novo Macrocyclic Peptides by Messenger RNA Display

Macrocyclic peptides are a promising class of compounds that can often engage challenging therapeutic targets. Display technologies, such as mRNA display, allow for the efficient discovery of macrocyclic peptides. This article reviews the current approaches for generating macrocyclic peptide libraries using mRNA display and highlights some recent examples of ribosomal incorporation of nonproteinogenic amino acids into macrocyclic peptides.

Controlling Wnt Signaling Specificity and Implications for Targeting WNTs Pharmacologically

Wnt signaling is critical for proper development of the embryo and for tissue homeostasis in the adult. Activation of this signaling cascade is initiated by binding of the secreted Wnts to their receptors. With the mammalian genome encoding multiple Wnts and Wnt receptors, a longstanding question in the field has been how Wnt-receptor specificities are achieved. Emerging from these studies is a picture of exquisite control over Wnt protein production, secretion, distribution, and receptor interactions, culminating in activation of downstream signaling cascades that control a myriad of biological processes. Here we discuss mechanisms by which Wnt protein activities are tuned and illustrate how the multiple layers of regulation can be leveraged for therapeutic interventions in disease.

Targeting and therapeutic peptide-based strategies for polycystic kidney disease

Polycystic kidney disease (PKD) is characterized by progressive cyst growth and is a leading cause of renal failure worldwide. Currently, there are limited therapeutic options available to PKD patients, and only one drug, tolvaptan, has been FDA-approved to slow cyst progression. Similar to other small molecule drugs, however, tolvaptan is costly, only moderately effective, and causes adverse events leading to high patient dropout rates. Peptides may mitigate many drawbacks of small molecule drugs, as they can be highly tissue-specific, biocompatible, and economically scaled-up. Peptides can function as targeting ligands that direct therapies to diseased renal tissue, or be potent as therapeutic agents themselves. This review discusses various aberrant signaling pathways in PKD and renal receptors that can be potential targets of peptide-mediated strategies. Additionally, peptides utilized in other kidney applications, but may prove useful in the context of PKD, are highlighted. Insights into novel peptide-based solutions that have potential to improve clinical management of PKD are provided.