Biosynthetic Strategies for Macrocyclic Peptides

Considerations for the genotoxicity assessment of middle size peptide drugs containing non-canonical amino acid residues

BACKGROUND

Middle size peptides (MSPs) have emerged as a promising new pharmaceutical modality. We are seeking the best way to assess the non-clinical safety of MSPs.

CONSIDERATION

The requirements for assessing the genotoxicity of pharmaceuticals differ between small molecule drugs and biotherapeutics. Genotoxicity tests are necessary for small molecule drugs but not for biotherapeutics. MSPs, however, share similarities with both small molecule drugs and biotherapeutics. Here, we describe important points to consider in assessing the genotoxicity of MSP drugs. The current standard of genotoxicity assessment for small molecules may not be entirely appropriate for MSP drugs. MSP drugs need genotoxicity assessment mostly according to the current standard of small molecule drugs.

CONCLUSION

We propose a few modifications to the standard test battery of genotoxicity tests, specifically, the inclusion of an in vitro gene mutation test using mammalian cells, and exclusion of (Q)SAR assessment on MSP-related impurities.

Native and Engineered Cyclic Disulfide-Rich Peptides as Drug Leads

Bioactive peptides are a highly abundant and diverse group of molecules that exhibit a wide range of structural and functional variation. Despite their immense therapeutic potential, bioactive peptides have been traditionally perceived as poor drug candidates, largely due to intrinsic shortcomings that reflect their endogenous heritage, i.e., short biological half-lives and poor cell permeability. In this review, we examine the utility of molecular engineering to insert bioactive sequences into constrained scaffolds with desired pharmaceutical properties. Applying lessons learnt from nature, we focus on molecular grafting of cyclic disulfide-rich scaffolds (naturally derived or engineered), shown to be intrinsically stable and amenable to sequence modifications, and their utility as privileged frameworks in drug design.

Designing receptor agonists with enhanced pharmacokinetics by grafting macrocyclic peptides into fragment crystallizable regions

Short half-lives in circulation and poor transport across the blood-brain barrier limit the utility of cytokines and growth factors acting as receptor agonists. Here we show that surrogate receptor agonists with longer half-lives in circulation and enhanced transport rates across the blood-brain barrier can be generated by genetically inserting macrocyclic peptide pharmacophores into the structural loops of the fragment crystallizable (Fc) region of a human immunoglobulin. We used such 'lasso-grafting' approach, which preserves the expression levels of the Fc region and its affinity for the neonatal Fc receptor, to generate Fc-based protein scaffolds with macrocyclic peptides binding to the receptor tyrosine protein kinase Met. The Met agonists dimerized Met, inducing biological responses that were similar to those induced by its natural ligand. Moreover, lasso-grafting of the Fc region of the mouse anti-transferrin-receptor antibody with Met-binding macrocyclic peptides enhanced the accumulation of the resulting Met agonists in brain parenchyma in mice. Lasso-grafting may allow for designer protein therapeutics with enhanced stability and pharmacokinetics.

Lasso peptide microcin J25 variant containing RGD motif as a PET probe for integrin a v ß 3 in tumor imaging

Microcin J25 (MccJ25), a lasso peptide, has a unique 3-D interlocked structure that provides high stability under acidic conditions, at high temperatures, and in the presence of proteases. In this study, we generated a positron emission tomography (PET) probe based on MccJ25 analog with an RGD motif and investigated their pharmacokinetics and utility for integrin α_vβ₃ imaging in tumors. The MccJ25 variant with an RGD motif in the loop region and a lysine substitution at the C-terminus (MccJ25(RGDF)GtoK) was produced in E. coli transfected with plasmid DNA containing the MccJ25 biosynthetic gene cluster (mcjABCD). [⁶⁴Cu]Cu-MccJ25(RGDF)GtoK was synthesized using the C-terminal lysine labeled with copper-64 (t_1/2 = 12.7 h) via a bifunctional chelator; it showed stability in 90% mouse plasma for 45 min. Using PET imaging for integrin α_vβ₃ positive U87MG tumor bearing mice, [⁶⁴Cu]Cu-MccJ25(RGDF)GtoK could clearly distinguish the tumor, and its accumulation was significantly higher than that of MccJ25(GIGT)GtoK without the binding motif for integrin α_vβ₃. Furthermore, MccJ25(RGDF)GtoK enabled visualization of only U87MG tumors but not MCF-7 tumors with low integrin α_vβ₃ expression in double tumor-bearing mice. In ex vivo biodistribution analysis, the integrin α_vβ₃ non-specific accumulation of [⁶⁴Cu]Cu-MccJ25(RGDF)GtoK was significantly lower in various tissues, except for the kidneys, as compared to the control probe ([⁶⁴Cu]Cu-cyclic RGD peptide). These results of the present study indicate that ⁶⁴Cu-labeling methods are appropriate for the synthesis of MccJ25-based PET probes, and [⁶⁴Cu]Cu-MccJ25 variants are useful tools for cancer molecular imaging.

A comprehensive review of microorganism-derived cyclic peptides: Bioactive functions and food safety applications

Cyclic peptides possess advanced structural characteristics of stability and play a vital role in medical treatment and agriculture. However, the biological functions of microorganism-derived cyclic peptides (MDCPs) and their applications in food industry were relatively absent. MDCPs are derived from extensive fermented food or soil. In this review, the synthesis approaches and structural characteristics are overviewed, while the interrelationship between bioactivities and functions is emphasized. This review summarizes the bioactivities of MDCPs from in vitro to in vivo, including antimicrobial activities, immune regulation, and antiviral cell activation. Their multiple functions as well as applications during food product processing, packaging, and storage are also comprehensively reviewed. Remarkably, some potential risks and cytotoxicity of MDCPs are also critically discussed. Moreover, future applications of MDCPs in the development of novel food additives and bioengineering materials are organized. Based on this review of native MDCPs, it is noteworthy that expected improvements of synthetic cyclic peptides in bioactive properties present potential valuable applications in future food, including artificial meat.