Name: construction of cyclic cell-penetrating peptides for enhanced penetration of biological barriers
Uploaded: 2022-09-19T13:00:00
Description: Watch this Scientific Journal Video about Construction of Cyclic Cell-Penetrating Peptides for Enhanced Penetration of Biological Barriers at JoVE.com

This work is supported by the Natural Science Foundation of China (21708031), China Postdoctoral Science Foundation (BX20180264, 2018M643519), and the Fundamental Research Funds for the Central Universities (2682021ZTPY075).

1. Equipment preparation
NOTE: Carry out all the procedures in an operating fume hood with suitable personal protective equipment.
<ol>
	<li>Assemble the manual peptide synthesis apparatus in the fume hood (Figure 1). Place the three-way stopcocks (see Table of Materials) onto the vacuum manifold (see Table of Materials) and connect to the nitrogen (N2). Make sure to cap the unused inlets.</li>
	<li>A...

<ol>
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D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparative+&#945;-helicity+of+cyclic+pentapeptides+in+water.">Comparative &#945;-helicity of cyclic pentapeptides in water.</a> Angewandte Chemie International Edition. 53 (27), 6965-6969 (2014).</li><li>Chu, Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Towards+understanding+cell+penetration+by+stapled+peptides.">Towards understanding cell penetration by stapled peptides.</a> Medicinal Chemistry Communications. 6 (1), 111-119 (2015).</li><li>Bock, J. E., Gavenonis, J., Kritzer, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Getting+in+shape:+Controlling+peptide+bioactivity+and+bioavailability+using+conformational+constraints.">Getting in shape: Controlling peptide bioactivity and bioavailability using conformational constraints.</a> ACS Chemical Biology. 8 (3), 488-499 (2013).</li><li>Tian, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+stapling+architecture+on+physiochemical+properties+and+cell+permeability+of+stapled+&#945;-helical+peptides:+A+comparative+study.">Effect of stapling architecture on physiochemical properties and cell permeability of stapled &#945;-helical peptides: A comparative study.</a> ChemBioChem. 18 (21), 2087-2093 (2017).</li><li>White, C. J., Yudin, A. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Contemporary+strategies+for+peptide+macrocyclization.">Contemporary strategies for peptide macrocyclization.</a> Nature Chemistry. 3 (7), 509-524 (2011).</li><li>Jain, R. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Normalization+of+tumor+vasculature:+An+emerging+concept+in+antiangiogenic+therapy.">Normalization of tumor vasculature: An emerging concept in antiangiogenic therapy.</a> Science. 307 (5706), 58-62 (2005).</li><li>Patgiri, A., Menzenski, M. Z., Mahon, A. B., Arora, P. 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The chemical stabilization of peptides by incorporating conformational constraints has proven to be an effective strategy for improving the stability and cell permeability of the peptide26. In this protocol, a step-by-step procedure is described for the synthesis of cyclic CPPs with aromatic cross-links and the evaluation of their permeability across biological barriers. Compared to the hydrophilic lactam or triazole cross-links22,27, the ...

The past few decades have witnessed rapid advances in the development of cell-penetrating peptides (CPPs) for drug delivery. CPPs have been widely used as molecular transporters for the treatment of a range of life-threatening diseases, including neurological disorders1,2, heart diseases3, diabetes4, dermatosis5, and cancer6,7. Cancer remains a global health burden accompanied by a high rate of morbidity and mortality despite widespread research efforts8. A serious obstacle to treating cancer is the limited access of therapeutics to deeper tumor cells due to physiological barriers such as compact extracellular matrix (ECM), abnormal tumor vasculature, multiple membrane barriers, and high interstitial fluid pressure (IFP)9. Thus, developing novel CPPs with superior ability to deliver cargoes across biological barriers is considered an essential strategy for cancer treatment10,11.
CPPs can be categorized into cationic, amphipathic, and hydrophobic CPPs in terms of their physicochemical properties12. Among these, the positively charged HIV-TAT peptide and the synthetic polyarginine are of considerable importance in biomedical research and have been extensively studied to facilitate intracellular drug delivery13. Tunnemann et al. reported that a minimum length of eight arginines is essential for efficient cell penetration of the synthetic polyarginine peptides, based on a cell permeability study conducted using R3 to R12 peptides14. However, these CPPs generally have short plasma half-lives due to their rapid hydrolysis in vivo. In addition, little is known regarding the optimization of the chemical structure of CPPs to increase their trans-barrier ability as it is challenging to penetrate multiple cell membranes15. Thus, the development of novel molecular transporters capable of penetrating biological barriers is strongly desired to enhance drug delivery efficiency. In 2020, Komin et al.16 discovered a CPP called CL peptide, which contains a helix motif (RLLRLLR) and a polyarginine tail (R7) for crossing the epithelial monolayer. A set of CL peptide variants were also synthesized by altering the helical pattern. This exploration could be a significant guide for the development of novel CPPs for the delivery of cargoes across biological barriers. Moreover, Dietrich et al. optimized the cell permeability of the StAX peptide, inhibiting the Wnt/&#946;-catenin signaling pathway by increasing the overall hydrophobicity of the peptides17.
Conformational restriction of unstructured linear peptides by cyclization is an effective way to enhance their proteolytic stability and permeablity18,19,20. The structural reinforcement increases the protease resistance of cyclic peptides, making them more stable in vivo compared to their linear counterparts. In addition, the cyclization of peptides can potentially mask the polar peptide backbone by promoting intramolecular hydrogen bonding, thus increasing the membrane permeability of the peptides21. In the past two decades, chemoselective cyclization methods have become effective strategies for the construction of cyclic peptides with different architectures, such as all-hydrocarbon, lactam, triazole, m-xylene, perfluoroaryl, and other cross-links22,23. The biological barrier imposed by the sophisticated tumor microenvironment could reduce the penetration of drugs in solid tumors24. We have previously found that the cyclic CPPs displayed superior resistance to enzymatic digestion over their linear counterparts20. Furthermore, the overall hydrophobicity of the peptides is critical for their enhanced cell permeability22. Based on the studies discussed above, the combination of a positively charged pattern, elevated overall hydrophobicity, and enhanced proteolysis stability can be hypothesized to increase the permeability of CPPs across biological barriers. In a recent study, we identified two cyclic CPPs with aromatic crosslinks at positions i and i+7 that exhibit improved permeability in tumor cells and tissues compared to their linear counterparts15. Here, a concise synthetic protocol for the synthesis of fluorescently labeled cyclic CPPs and the key steps to investigate their permeability are presented.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1,2-ethanedithiol</td>
			<td>Aladdin</td>
			<td>K1722093</td>
			<td>stench</td>
		</tr>
		<tr>
			<td>2-(7-Azobenzotriazole)-N,N,N&#39;,N&#39;-tetramethyluronium hexafluorophosphate (HATU)</td>
			<td>HEOWNS</td>
			<td>A-0443697</td>
			<td></td>
		</tr>
		<tr>
			<td>4,4&#39;-bis(bromomethyl)biphenyl</td>
			<td>TCI</td>
			<td>B1921</td>
			<td></td>
		</tr>
		<tr>
			<td>4T1 cells</td>
			<td>ATCC</td>
			<td></td>
			<td>4T1 cells were cultured in DMEM medium supplemented with 10% FBS (Hyclone) in a 37 &#176;C humidified incubator containing 5% CO2.</td>
		</tr>
		<tr>
			<td>Acetonitrile&#160;</td>
			<td>Adamas</td>
			<td>1484971</td>
			<td>toxicity</td>
		</tr>
		<tr>
			<td>Dichloromethane</td>
			<td>Energy</td>
			<td>W330229</td>
			<td>skin harmful</td>
		</tr>
		<tr>
			<td>Diethyl ether</td>
			<td>Aldrich</td>
			<td>673811</td>
			<td>flammable</td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide</td>
			<td>Beyotime</td>
			<td>ST038</td>
			<td>skin harmful</td>
		</tr>
		<tr>
			<td>Dulbecco&#8217;s Modified Eagle Medium (DMEM)</td>
			<td>Gibco</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Electrospray Ionization Mass Spectrometer</td>
			<td>Waters</td>
			<td>G2-S Tof</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethylene Diamine Tetraacetic Acid (EDTA)</td>
			<td>BioFroxx</td>
			<td>1340</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum (FBS)</td>
			<td>HyClone</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Flow cytometer</td>
			<td>Beckman Coulter</td>
			<td>CytoFLEX</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescein isothiocyanate isomer (FITC)</td>
			<td>Energy</td>
			<td>E0801812500</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescent microscope</td>
			<td>Carl Zeiss</td>
			<td>Axio Observer 7</td>
			<td></td>
		</tr>
		<tr>
			<td>Fmoc-Arg(Pbf)-OH</td>
			<td>HEOWNS</td>
			<td>F-81070</td>
			<td></td>
		</tr>
		<tr>
			<td>Fmoc-Cys(Trt)-OH</td>
			<td>GL Biochem</td>
			<td>GLS201115-35202</td>
			<td></td>
		</tr>
		<tr>
			<td>Fmoc-&#946;Ala-OH</td>
			<td>Adamas</td>
			<td>51341C</td>
			<td></td>
		</tr>
		<tr>
			<td>HeLa cells</td>
			<td>ATCC</td>
			<td></td>
			<td>HeLa cells were cultured in DMEM supplemented with 10% FBS (Hyclone) in a 37 &#176;C humidified incubator containing 5% CO2.</td>
		</tr>
		<tr>
			<td>High-Performance Liquid Chromatography</td>
			<td>Agilent</td>
			<td>Agilent 1260</td>
			<td></td>
		</tr>
		<tr>
			<td>High-Performance Liquid Chromatography column</td>
			<td>Agilent</td>
			<td>Poroshell EC-C18 120, 4.6 &#215; 150 mm (pore size 120 &#197;, particle size 4 &#956;m)</td>
			<td></td>
		</tr>
		<tr>
			<td>Lyophilizer</td>
			<td>SP Scientific</td>
			<td>Vir Tis</td>
			<td></td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Aldrich</td>
			<td>9758</td>
			<td>toxicity</td>
		</tr>
		<tr>
			<td>Microtiter plate</td>
			<td>Thermo &#956;drop plate</td>
			<td>N12391</td>
			<td></td>
		</tr>
		<tr>
			<td>Morpholine</td>
			<td>HEOWNS</td>
			<td>M99040</td>
			<td>irritant</td>
		</tr>
		<tr>
			<td>Multi-technology microplate reader</td>
			<td>Thermo</td>
			<td>VARIOSKAN LUX</td>
			<td></td>
		</tr>
		<tr>
			<td>N,N-Diisopropylethylamine</td>
			<td>HEOWNS</td>
			<td>E-81416</td>
			<td>irritant</td>
		</tr>
		<tr>
			<td>N,N-Dimethyl formamide</td>
			<td>Energy</td>
			<td>B020051</td>
			<td>harmful to skin</td>
		</tr>
		<tr>
			<td>Poly-Prep column</td>
			<td>Bio-Rad</td>
			<td>7321010</td>
			<td>polypropylene chromatography columns</td>
		</tr>
		<tr>
			<td>Rink Amide MBHA resin (0.572 mmol/g)</td>
			<td>GL Biochem</td>
			<td>GLS180301-49101</td>
			<td></td>
		</tr>
		<tr>
			<td>Three-way stopcocks</td>
			<td>Bio-Rad</td>
			<td>7328107</td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue culture plate insert</td>
			<td>LABSELECT</td>
			<td>14211</td>
			<td></td>
		</tr>
		<tr>
			<td>Trifluoroacetic acid</td>
			<td>HEOWNS</td>
			<td>T63278</td>
			<td>corrosive</td>
		</tr>
		<tr>
			<td>Triisopropylsilane</td>
			<td>HEOWNS</td>
			<td>T-0284475</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin</td>
			<td>BioFroxx</td>
			<td>1004</td>
			<td></td>
		</tr>
		<tr>
			<td>Vacuum manifold</td>
			<td>Promega</td>
			<td>A7231</td>
			<td></td>
		</tr>
	</tbody>
</table>

construction of cyclic cell-penetrating peptides for enhanced penetration of biological barriers

Cancer has been a grand challenge in global health. However, the complex tumor microenvironment generally limits the access of therapeutics to deeper tumor cells, leading to tumor recurrence. To conquer the limited penetration of biological barriers, cell-penetrating peptides (CPPs) have been discovered with excellent membrane translocation ability and have emerged as useful molecular transporters for delivering various cargoes into cells. However, conventional linear CPPs generally show compromised proteolytic stability, which limits their permeability across biological barriers. Thus, the development of novel molecular transporters that can penetrate biological barriers and exhibit enhanced proteolytic stability is highly desired to promote drug delivery efficiency in biomedical applications. We have previously synthesized a panel of short cyclic CPPs with aromatic crosslinks, which exhibited superior permeability in cancer cells and tissues compared to their linear counterparts. Here, a concise protocol is described for the synthesis of the fluorescently labeled cyclic polyarginine R8 peptide and its linear counterpart, as well as key steps for investigating their cell permeability.

In this protocol, a synthetic procedure to constrain the linear polyarginine R8 into its cyclic form was presented. The SPPS was conducted manually using a simple apparatus (Figure 1). The detailed synthetic process of SPPS is shown in Figure 2. Briefly, the resin was sufficiently swelled, followed by deprotection of the N&#945;-Fmoc protecting group. Then, the N&#945;-Fmoc-protected amino acid was anchored on the resin unt...

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Construction of Cyclic Cell-Penetrating Peptides for Enhanced Penetration of Biological Barriers

This protocol describes the synthesis of cyclic cell-penetrating peptides with aromatic cross-links and the evaluation of their permeability across biological barriers.

Cancer has been a grand challenge in global health. However, the complex tumor microenvironment generally limits the access of therapeutics to deeper ...

Research

JoVE Journal

Chemistry

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