Stimuli-Responsive Conformational Transformation of Peptides for Tunable Cytotoxicity

Abstract

The stimuli-responsive conformational transformation of peptides possessing a constrained form triggered by specific biological microenvironment would provide an effective strategy for the development of highly specific peptide therapeutics. Here, we developed a peptide containing a cytotoxic helical KLA sequence with therapeutic specificity through the use of stimuli-responsive conformational transformation. The KLA peptide is modified to form a cyclic structure to allow for constrained helicity that confers low cytotoxicity. The modified KLA peptide is electrostatically complexed to hyaluronic acid to facilitate enhanced endocytosis into the cancer cells. After endocytosis, the peptide is released from the complex into the cellular cytoplasm by hyaluronidases on the surface of the cellular membrane. Specific intracellular stimuli then trigger the release of the strain that suppresses peptide helicity, and the inherent helical conformation of the KLA peptide is restored. Therefore, the stimuli-responsive conformational transformation of a peptide from low to high helicity selectively induces cell death by disruption of the plasma and mitochondrial membrane.

Strategies for Improving Peptide Stability and Delivery

“…Lee and coworkers developed a stimuli-responsive conformational transformation peptide in which the cytotoxicity could be controlled in response to a specific biological environment [ 75 ]. The authors considered a peptide from the honeybee venom which has a biological activity (KLAKLAK) 2 ( Figure 13 A).…”

“…Thus, it is also considered as a membrane-active peptide. The hydrophobic interaction between the hydrophobic alkyl chain of the membrane phospholipids and the Leu amino acid stabilizes the α-helical conformation of the peptide [ 75 ]. The peptide in its helical form can form pores on the cell membrane and induce cell death.…”

“…The HA is degraded by the upregulated hyaluronidases, the KLA-SS peptide is released into the cytoplasm of the cancerous cell, and the disulfide bond is reduced by the upregulated GSH into two thiol groups. Finally, the strain that suppresses the helicity is released and the original helicity is restored [ 75 ].…”

Tuning of Peptide Cytotoxicity with Cell Penetrating Motif Activatable by Matrix Metalloproteinase-2

“…The KLA peptide with the (KLAKLAK) 2 sequence is an antimicrobial peptide designed de novo from melittin, a major element of honey bee venom . The KLA peptide has an amphiphilic chemical structure that forms an α-helix on negatively charged cellular membranes. , Therefore, this peptide could form a helical pore on the mitochondrial or plasma membrane of prokaryotic microbial cells, leading to apoptotic or necrotic death of the microbe. − Although the KLA peptide could be used as an anticancer agent for several cancer cells with highly negatively charged lipid membranes, − targeting or cell penetrating motifs are typically required for the successful utilization of the KLA peptide as an effective anticancer agent owing to its low endocytic capability. ,,− …”

Induced cytotoxicity of peptides by intracellular native chemical ligation

“…18 The KLA peptide is known to induce cell death by forming helical pores in plasma or mitochondrial membranes. 18–22 The peptide with short KLAKLAK sequence does not kill cells because the helicity is too low and the thickness of lipid bilayer is higher than the length of its helical structure. 18 Therefore, we reasoned that elongation of the short amphiphilic helical peptide (NCL-Pep-1) having both N-terminal Cys(S t Bu) and C-terminal N -Hnb-Cys(S t Bu) via intracellular NCL reaction to form cyclic (CKKLAKL) n peptide with higher helicity and sufficient length could induce cell death selectively by formation of helical pore on plasma or mitochondrial membranes.…”