Macrocyclization

All forms of cellular processing depend heavily on interactions between proteins and proteins and peptides. Proteins and peptides are each other's natural companions, and because peptides may adapt to the frequently changeable protein surface, they attach to proteins with high affinity when used as ligands. Due to their protein-like nature, peptides are biocompatible; but, as medication candidates, they have a number of disadvantages, such as limited plasma bioavailability, instability from proteolytic enzymes, and poor passive membrane permeability. With linear peptides, especially those that preserve -helical secondary structures, some success has been attained. By using conventional "peptide-stapling" techniques, these motifs can be added to stable -helical motifs, however stapled peptides may have low bioactivity and poor solubility. The modification of peptides through macrocyclization has been one method to increase peptide stability.

Macrocyclization Chemistry

CPC Scientific has the know-how to execute a range of ring-closure procedures and specializes in the synthesis of complicated peptide macrocycles. We regularly create peptide macrocycles with the following types of bonds:

• Disulfide bridges that are numerous and site-specific (Cys-Cys, Pen-Cys, and Pen-Pen)

• Cyclizations of amide bonds (lactam)

• Sidechain-to-sidechain, sidechain-to-tail, head-to-sidechain, and head-to-sidechain

• Hydrocarbon-stapled peptides are connected by backbone-to-backbone, backbone-to-sidechain, backbone-to-head, and backbone-to-tail thioether bridges.

• Azide-alkyne cycloaddition catalyzed by copper (Click Chemistry)

X = S-S (disulfide bridge)

X = NH-CO (lactam bridge, amide bond)

X = S (thioether bridge, sulfide bridge)

X = O-CO (lactone bridge, depsipeptide)

X = CH=CH (alkene bridge, hydrocarbon stapled)

Y = NH (lactam bridge, amide bond)

Y = O (depsipeptide)

Cyclized RGD Motif

More attention is being paid to localization and cellular absorption as research into medication delivery platforms progresses. Targeting cancer cells that overexpress specific receptor proteins that may recognize and internalize CTPs through receptor-mediated endocytosis has become possible thanks to the development of cell-targeting peptides (CTPs). Cell adhesion receptors control the process of angiogenesis, which is reliant on vascular endothelial cell migration and infiltration in tumor spread. Integrins are a significant group of heterodimeric transmembrane proteins that are essential for cell adhesion, cell signaling, and apoptosis[1]. The v3 integrins are the members of the integrin family that have undergone the most research because of their significance in tumor angiogenesis and metastasis. V3 integrins are an appealing target for cancer therapies (e.g., radiotracers, cancer medicines), as they are overexpressed in a variety of tumor cell types (such as breast, prostate, and ovarian malignancies) but missing in healthy tissue types. By inhibiting angiogenesis, inhibition of v3 integrin receptors has been linked to tumor prevention and decreased tumor growth. It has been created and synthesized to make antagonists based on peptides that bind to v3 integrins. Kessler and colleagues created cyclo[Arg-Gly-Asp-D-Phe-Val] (c[RGDfV]), one of the most effective and selective of these peptide antagonists.[2]

Numerous RGD motif peptides have been created by CPC Scientific and are intended for use in multivalent molecular structures and as conjugates with chelating moieties (such as DOTA, NOTA, etc.). For therapeutic usage, cyclic RGD (cRGD) peptide-based nanomedicines have been created. A brain glioma cascade delivery method using dual targeting liposomal systems made up of cRGD and transferrin (TF) mixed with a liposome (cRGD/TF-LP) has been established. The finding that cRGD peptide coupled with TF permits distribution across the blood-brain barrier (BBB), permitting RGD-targeting in the brain, was crucial to this approach. When paired with paclitaxel, cRGD/TF-LP creates a novel system that can specifically target brain-based gliomas, which are challenging to treat with chemotherapeutic drugs alone.[3]

cRGD Nanomedicine

Mesoporous silica nanoparticles (MSNs), a platform that has mostly been researched for controlled drug release, are another nanoparticle (NP)-based cRGD targeting method. MDA-MB 435 metastatic breast cancer cell lines have been successfully targeted and subjected to apoptosis using MSN-cRGD loaded with camptothecin (CPT). It was shown that this cell line had increased localisation and cellular absorption using the MSN-cRGD platform in combination with a fluorescent tag.[4]

Figure. MDA-MB 435 cell line with 20ug/mL (left) NP (control), (middle) cRGD-NP overlay images showing cellular membrane (red) and cell nucleus (blue), and (right) cRGD-NP dye (green).

Figure. Nanoparticle (NP)-based cRGD targeting system is mesoporous silica nanoparticles (MSNs).[3]

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References

1. Van der Flier, Arjan, and Arnoud Sonnenberg. “Function and interactions of integrins.” Cell and tissue research 305, no. 3 (2001): 285-298.

2. Wermuth, J., S. L. Goodman, A. Jonczyk, and H. Kessler. “Stereoisomerism and biological activity of the selective and superactive αvβ3 integrin inhibitor cyclo (-RGDfV-) and its retro-inverso peptide.” Journal of the American Chemical Society 119, no. 6 (1997): 1328-1335.

3. Ferris, Daniel P., Jie Lu, Chris Gothard, Rolando Yanes, Courtney R. Thomas, John‐Carl Olsen, J. Fraser Stoddart, Fuyuhiko Tamanoi, and Jeffrey I. Zink. “Synthesis of biomolecule‐modified mesoporous silica nanoparticles for targeted hydrophobic drug delivery to cancer cells.” Small 7, no. 13 (2011): 1816-1826.