Hiroshi Tsutsumi

Structure–activity relationship studies on CXCR4 antagonists having cyclic pentapeptide scaffolds

Structure-activity relationship studies on CXCR4 antagonists, which were previously found by using cyclic pentapeptide libraries, were performed to optimize side-chain functional groups, involving conformationally constrained analogues. In addition, a new lead of cyclic pentapeptides with the introduction of a novel pharmacophore was developed.

Cell penetration and cell-selective drug delivery using α-helix peptides conjugated with gold nanoparticles

Cell penetrating peptides (CPPs) have been developed as vectors for molecular delivery into various cells for use in drug delivery, gene therapy and cancer treatment by their property transporting various molecules into cytoplasm. CPPs with high internalization, cell specificity, and low cytotoxicity have been considered to increase the applicability for cell engineering. Gold nanospheres (GNSs) are a useful tool for molecular imaging, because they are non-cytotoxic and have high solubility, ease of synthesis and excellent light scattering property. Here, we investigated the cell penetrability using α-helix peptides of 17-amino acids conjugated to gold nanospheres (P-GNS). Depending on the peptide sequence had the different cell penetrating (CP) activity for three kinds of cell lines. P-GNS showed low cytotoxicity and high selectivity against three cell types, despite just one amino acid difference between the peptide. We studied the cytotoxic activity of an anti-cancer drug doxorubicin (DOX) conjugated to the P-GNS. They showed different cytotoxicity against the three cell lines, depending on the peptide sequence, with a higher efficiency than free DOX at the same concentration. The cytotoxicity by DOX was correlated with the CP activity of the peptides against the three cell lines. These results demonstrated that P-GNS would be a useful tool for the development of a new cell-selective drug delivery system.

Fluorophore Labeling Enables Imaging and Evaluation of Specific CXCR4−Ligand Interaction at the Cell Membrane for Fluorescence-Based Screening

Development of CXCR4-specific ligands is an important issue in chemotherapy of HIV infection, cancer metastasis, and rheumatoid arthritis, and numerous potential ligands have been developed to date. However, it is difficult to assess their binding mode and specificity because of uncertainties in the structure of the CXCR4-ligand complexes. To address this problem, we have synthesized fluorophore labeled Ac-TZ14011, which is derived from T140, a powerful CXCR4 antagonist. Binding of Ac-TZ14011 to CXCR4 on the cell membrane was observed by fluorescence microscope, and analysis of the binding data produced IC 50 values of several ligands comparable to those obtained in RI-based assays. This fluorescence-based assay is applicable to explore new pharmacophores of CXCR4-specific ligands with high-throughput screening and also to screening of the other GPCR binding ligands.

Development of Low Molecular Weight CXCR4 Antagonists by Exploratory Structural Tuning of Cyclic Tetra- and Pentapeptide-Scaffolds Towards the Treatment of HIV Infection, Cancer Metastasis and Rheumatoid Arthritis

The chemokine receptor, CXCR4, is a GPCR that transduces signals of its endogenous ligand, CXCL12 (stromal cell-derived factor-1, SDF-1). The CXCL12-CXCR4 system plays an important role in the migration of progenitors during embryologic development of the cardiovascular, hemopoietic, central nervous systems, etc. This system has recently been proven to be involved in several problematic diseases, including HIV infection, cancer cell metastasis, leukemia cell progression, rheumatoid arthritis (RA) and pulmonary fibrosis. Thus, CXCR4 is thought to be an important therapeutic target to overcome the above diseases. Fourteen-mer peptides, T140 and its analogs, were previously found to be specific CXCR4 antagonists that were characterized as HIV-entry inhibitors, anti-cancer-metastatic agents, anti-chronic lymphocytic/acute lymphoblastic leukemia agents and anti-RA agents. Based on our knowledge of pharmacophores of T140, CXCR4 antagonists, such as FC131, were previously found by the efficient utilization of cyclic pentapeptide libraries. This review article focuses on our recent research on the development of low molecular weight CXCR4 antagonists including FC131 analogs, in which structural tuning of the cyclic peptide ring and chemical modifications were performed for an increase in potency and a reduction of the peptide character.

Development of a linear type of low molecular weight CXCR4 antagonists based on T140 analogs

A linear type of several low molecular weight CXCR4 antagonists were developed based on T140 analogs, which were previously found to be strong CXCR4 antagonists that block X4-HIV-1 entry and have inhibitory activities against cancer metastasis/progression and rheumatoid arthritis.

Fluorogenically Active Leucine Zipper Peptides as Tag–Probe Pairs for Protein Imaging in Living Cells†

Artificial functional peptides are valuable tools in variousfields of chemical biology. Small peptides, such as anoligohistidine tag (His tag), can be genetically incorporatedinto target proteins and used for purification of recombinantproteins, immobilization of proteins on microplates, andbioimaging of proteins on the surface of living cells with theircomplementary partner molecules, such as Ni

A monosaccharide-modified peptide phage library for screening of ligands to carbohydrate-binding proteins.

A monosaccharide-modified β-loop peptide library displayed on phage has been constructed and used for the screening of glycopeptide ligands against a carbohydrate-binding protein. The β-loop peptide library was designed and modified with a mannose derivative on phage. The glycopeptide ligands to concanavalin A (ConA), a mannose-binding protein, were obtained from the mannose-modified peptide phage library. The amino acids neighboring the mannose unit of glycopeptides not only reinforced the binding affinity but also gave diverse binding characteristics.

The Chemokine Receptor CXCR4 as a Therapeutic Target for Several Diseases

CXCR4 is the receptor for a chemokine, CXCL12 (stromal cell-derived factor-1, SDF-1). The CXCL12-CXCR4 axis has been proven to be involved in several problematic diseases, including AIDS, cancer cell metastasis, leukemia cell progression and rheumatoid arthritis (RA). Thus, CXCR4 is thought to be an important therapeutic target to overcome the above diseases. We have developed several specific CXCR4 antagonists.

Cyclodextrin-peptide hybrid as a hydrolytic catalyst having multiple functional groups

A designed cyclodextrin peptide hybrid, which has multiple functional groups on its alpha-helix peptide backbone, has been synthesized as a catalyst for ester hydrolysis. Kinetic study revealed that the carboxylate group plays a key role in this system.

Cell-selective intracellular drug delivery using doxorubicin and α-helical peptides conjugated to gold nanoparticles.

Cell penetrating peptides (CPPs), which can enter a cell through the cell membrane, have potential research applications in the fields of drug delivery, gene therapy, and cancer therapy. However, CPPs are associated with problems such as low cell selectivity, low cell penetrating activity, and cell toxicity. To overcome the disadvantages of CPPs, we constructed a drug delivery system by developing 25 nm gold nanospheres (GNSs) conjugated to four α-helical CPPs from our peptide library. We examined the applicability of this cell-selective drug delivery system by evaluating its cell-penetrating and cell death activities and comparing them with those activities of the TAT peptide. Using the 25 nm GNS, we obtained higher cell death induction activity by the anti-cancer drug doxorubicin compared with our previous study using a 41 nm GNS. After entering the cell, the peptide-conjugated 25 nm GNS accumulated around the cell nucleus. High cell selectivity by α-helical CPP sequences was also demonstrated. Our results indicate that these α-helical peptide and 25 nm GNS conjugates are useful elements in an efficient cell-selective drug delivery system.