"Human and Mouse Cross-Reactive" Albumin-Binding Helix-Loop-Helix Peptide Tag for Prolonged Bioactivity of Therapeutic Proteins.

The effectiveness of protein and peptide pharmaceuticals depends essentially on their intrinsic pharmacokinetics. Small-sized pharmaceuticals in particular often suffer from short serum half-lives due to rapid renal clearance. To improve the pharmacokinetics by association with serum albumin (SA) in vivo, we generated an SA-binding tag of a helix-loop-helix (HLH) peptide to be linked with protein pharmaceuticals. For use in future preclinical studies, screening of yeast-displayed HLH peptide libraries against human SA (HSA) and mouse SA (MSA) was alternately repeated to give the SA-binding peptide AY-VE, which exhibited cross-binding activities to HSA and MSA with KD of 65 and 20 nM, respectively. As a proof of concept, we site-specifically conjugated peptide AY-VE with insulin to examine its bioactivity in vivo. In mouse bioassay monitoring the blood glucose level, the AY-VE conjugate was found to have a prolonged hypoglycemic effect for 12 h. The HLH peptide tag is a general platform for extending the bioactivity of therapeutic peptides or proteins.

A Cyclized Helix-Loop-Helix Peptide as a Molecular Scaffold for the Design of Inhibitors of Intracellular Protein-Protein Interactions by Epitope and Arginine Grafting.

The design of inhibitors of intracellular protein-protein interactions (PPIs) remains a challenge in chemical biology and drug discovery. We propose a cyclized helix-loop-helix (cHLH) peptide as a scaffold for generating cell-permeable PPI inhibitors through bifunctional grafting: epitope grafting to provide binding activity, and arginine grafting to endow cell-permeability. To inhibit p53-HDM2 interactions, the p53 epitope was grafted onto the C-terminal helix and six Arg residues were grafted onto another helix. The designed peptide cHLHp53-R showed high inhibitory activity for this interaction, and computational analysis suggested a binding mode for HDM2. Confocal microscopy of cells treated with fluorescently labeled cHLHp53-R revealed cell membrane penetration and cytosolic localization. The peptide inhibited the growth of HCT116 and LnCap cancer cells. This strategy of bifunctional grafting onto a well-structured peptide scaffold could facilitate the generation of inhibitors for intracellular PPIs.

Extracellular Microvesicles Modified with Arginine-Rich Peptides for Active Macropinocytosis Induction and Delivery of Therapeutic Molecules.

Extracellular vesicles (EVs), including exosomes and microvesicles (MVs), transfer bioactive molecules from donor to recipient cells in various pathophysiological settings, thereby mediating intercellular communication. Despite their significant roles in extracellular signaling, the cellular uptake mechanisms of different EV subpopulations remain unknown. In particular, plasma membrane-derived MVs are larger vesicles (100 nm to 1 µm in diameter) and may serve as efficient molecular delivery systems due to their large capacity; however, because of size limitations, receptor-mediated endocytosis is considered an inefficient means for cellular MV uptake. This study demonstrated that macropinocytosis (lamellipodia formation and plasma membrane ruffling, causing the engulfment of large fluid volumes outside cells) can enhance cellular MV uptake. We developed experimental techniques to induce macropinocytosis-mediated MV uptake by modifying MV membranes with arginine-rich cell-penetrating peptides for the intracellular delivery of therapeutic molecules.

T Cell-Association of Carboxy-Terminal Dendrimers with Different Bound Numbers of Phenylalanine and Their Application to Drug Delivery.

T cells play important roles in various immune reactions, and their activation is necessary for cancer immunotherapy. Previously, we showed that polyamidoamine (PAMAM) dendrimers modified with 1,2-cyclohexanedicarboxylic acid (CHex) and phenylalanine (Phe) underwent effective uptake by various immune cells, including T cells and their subsets. In this study, we synthesized various carboxy-terminal dendrimers modified with different bound numbers of Phe and investigated the association of these dendrimers with T cells to evaluate the influence of terminal Phe density. Carboxy-terminal dendrimers conjugating Phe at more than half of the termini exhibited a higher association with T cells and other immune cells. The carboxy-terminal Phe-modified dendrimers at 75% Phe density tended to exhibit the highest association with T cells and other immune cells, which was related to their association with liposomes. A model drug, protoporphyrin IX (PpIX), was encapsulated into carboxy-terminal Phe-modified dendrimers, which were then used for drug delivery into T cells. Our results suggest the carboxy-terminal Phe-modified dendrimers are useful for delivery into T cells.

Generation of molecular-targeting helix-loop-helix peptides for inhibition of the interaction between cytotoxic T-lymphocyte-associated protein 4 and B7 in the dog.

Blocking the interaction between CD28 and B7 by cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) is a potent immune checkpoint that prevents damage to host tissues from excessive immune responses. However, it also significantly diminishes immune responses against cancers and allows cancer cell growth. This study found that recombinant (r) human (h) CTLA-4 specifically binds to canine dendritic cells (DCs) and suppresses the responses of canine T cells to allogeneic DCs. ERY2-4, a peptide targeting rhCTLA-4 selected from a yeast-displayed library of helix-loop-helix (HLH) peptides and improved to have a binding affinity to rhCTLA-4 as strong as that of rhB7, inhibited the binding of rhCTLA-4 to canine DCs. Furthermore, the targeting peptide significantly enhanced the response of canine T cells to allogeneic DCs. These results suggest that the CTLA-4-targeting peptide enhances canine T cell activity by blocking the interaction between canine CTLA-4 on T cells and canine B7 on DCs. This study demonstrates the generation of a new type of immune checkpoint inhibitor, which may be applicable to cancer therapy in dogs.

New Class of Drug Modalities: Directed Evolution of a De Novo Designed Helix-Loop-Helix Peptide to Bind VEGF for Tumor Growth Inhibition.

As a small affinity molecule to serve as an alternative to antibodies, we have developed a conformationally constrained peptide with a de novo designed helix-loop-helix (HLH) scaffold. To evaluate its potential for biomedical applications, we performed directed evolution of HLH peptides to obtain an inhibitor for vascular endothelial growth factor-A (VEGF). A phage-displayed library of HLH peptides was constructed and screened against VEGF, giving the peptide VS42 that inhibits the VEGF/VEGF receptor-2 interaction (IC50 = 210 nM), which was further improved by in vitro affinity maturation using a yeast-displayed library. An identified HLH peptide, VS42-LR3, exhibited improved inhibitory activity (IC50 = 37 nM), high thermal stability, and excellent resistance against chemical denaturation. In biological activity tests, the HLH peptide was found to block VEGF-induced proliferation of human umbilical vein endothelial cells and suppress tumor growth in a murine xenograft model of human colorectal cancer.

Carboxy-terminal dendrimers with phenylalanine for a pH-sensitive delivery system into immune cells including T cells.

Although T cells play important roles in various immune reactions, there are only a few reports on delivery systems into T cells. Our previous study showed that carboxy-terminal phenylalanine (Phe)-modified polyamidoamine (PAMAM) dendrimers have both temperature- and pH-sensitive properties, which are affected by the chemical structure. The self-assembled structures of Phe, observed in phenylketonuria, enhance the protein aggregation, the association with the cell membrane and the membrane permeability. In this study, we applied the Phe-modified dendrimers to a pH-sensitive drug delivery system into T cells. Dendrimers with different amino acids and acid anhydrides were synthesized, and their pH-responsive association with T cells and their subsets was investigated. The dendrimers modified with Phe and cyclohexanedicarboxylic acid (CHex) showed higher uptake into various cells, including Jurkat cells, CD3+ T cells, CD3 + CD4+ helper T cells and CD3 + CD8+ killer T cells. These dendrimers were internalized into T cells via endocytosis, and their cellular uptake was enhanced under weak acidic conditions (pH 6.5). Our results showed that Phe- and CHex-modified dendrimers have a delivery potential to T cells and their subsets, which may be useful for cancer immunotherapy.

A "ligand-targeting" peptide-drug conjugate: Targeted intracellular drug delivery by VEGF-binding helix-loop-helix peptides via receptor-mediated endocytosis.

As a new alternative to antibody-drug conjugates, we generated "ligand-targeting" peptide-drug conjugates (PDCs), which utilize receptor-mediated endocytosis for targeted intracellular drug delivery. The PDC makes a complex with an extracellular ligand and then binds to the receptor on the cell surface to stimulate intracellular uptake via the endocytic pathway. A helix-loop-helix (HLH) peptide was designed as the drug carrier and randomized to give a conformationally constrained peptide library. The phage-displayed library was screened against vascular endothelial growth factor (VEGF) to yield the binding peptide M49, which exhibited strong binding affinity (KD = 0.87 nM). The confocal fluorescence microscopy revealed that peptide M49 formed a ternary complex with VEGF and its receptor, which was then internalized into human umbilical vein endothelial cells (HUVECs) via VEGF receptor-mediated endocytosis. The backbone-cyclized peptide M49K was conjugated with a drug, monomethyl auristatin E, to afford a PDC, which inhibited VEGF-induced HUVEC proliferation. HLH peptides and their PDCs have great potential as a new modality for targeted molecular therapy.

An Immune-Stimulatory Helix-Loop-Helix Peptide: Selective Inhibition of CTLA-4-B7 Interaction.

Molecular-targeting peptides and mini-proteins are promising alternatives to antibodies in a wide range of applications in bioscience and medicine. We have developed a helix-loop-helix (HLH) peptide as an alternative to antibodies to inhibit specific protein interactions. Cytotoxic T lymphocyte antigen-4 (CTLA-4) downregulates immune responses of cytotoxic T-cells by interaction with B7-1, a co-stimulatory molecule expressed on antigen presenting cells (APCs). To induce immune stimulatory activity, we used directed evolution methods to generate a HLH peptide that binds to CTLA-4, inhibiting the CTLA-4-B7-1 interaction and inducing immune stimulatory activity. Yeast-displayed libraries of HLH peptides were constructed and screened against CTLA-4 and identified the binding peptide Y-2, which exhibits a moderate affinity. The affinity of Y-2 was improved by in vitro affinity maturation to afford a stronger binder, ERY2-4. Peptide ERY2-4 specifically bound to CTLA-4 with a KD of 196.8 ± 2.3 nM, comparable to the affinity of the CTLA-4-B7-1 interaction. Furthermore, ERY2-4 inhibited the CTLA-4-B7-1 interaction with an IC50 of 1.1 ± 0.03 µM and blocked the interaction between CTLA-4 and dendritic cells (DCs) presenting B7 on their surface. Importantly, ERY2-4 showed no cross-reactivity against CD28, suggesting it does not suppress T-cell activation. Finally, in a mixed lymphocyte reaction assay with DCs and T cells, ERY2-4 enhanced an allogeneic lymphocyte response. Since CTLA-4 is a critical immune checkpoint for restricting the cancer immune response, this inhibitory HLH peptide represents a new class of drug candidates for immunotherapy.