Certification of the critical importance of L-3-(2-naphthyl)alanine at position 3 of a specific CXCR4 inhibitor, T140, leads to an exploratory performance of its downsizing study

Tetrahydroisoquinoline CXCR4 Antagonists Adopt a Hybrid Binding Mode within the Peptide Subpocket of the CXCR4 Receptor

The rationale for the structural and mechanistic basis of a tetrahydroisoquinoline (THIQ) based series of CXCR4 antagonists is presented. Using the previously reported crystal structures which reveal two distinct binding sites of CXCR4 defined as the small molecule (IT1t or minor) binding pocket and peptide (CVX15 or major) binding pocket, we hypothesized our THIQ small molecule series could bind like either molecule in these respective receptor configurations (IT1t versus CVX15 based poses). To this end, a thorough investigation was performed through a combination of receptor mutation studies, medicinal chemistry, biological testing, conformational analysis, and flexible docking. Our findings showed that the CVX15 peptide-based CXCR4 receptor complexes (red pose) were consistently favored over the small molecule IT1t based CXCR4 receptor configurations (blue pose) to correctly explain the computational and mutational studies as well as key structural components of activity for these small molecules.

Structure-activity relationship studies of the aromatic positions in cyclopentapeptide CXCR4 antagonists

The cyclopentapeptide CXCR4 antagonist FC131 (cyclo(-Arg(1)-Arg(2)-2-Nal(3)-Gly(4)-D-Tyr(5)-), 2; 2-Nal = 3-(2-naphthyl)alanine) represents an excellent starting point for development of novel drug-like ligands with therapeutic potential in HIV, cancer, stem-cell mobilization, inflammation, and autoimmune diseases. While the structure-activity relationships for Arg(1), Arg(2), and Gly(4) are well established, less is understood about the roles of the aromatic residues 2-Nal(3) and D-Tyr(5). Here we report further structure-activity relationship studies of these two positions, which showed that (i) the distal aromatic ring of the 2-Nal(3) side chain is required in order to maintain high potency and (ii) replacement of D-Tyr(5) with conformationally constrained analogues results in significantly reduced activity. However, a simplified analogue that contained Gly instead of D-Tyr(5) was only 13-fold less potent than 2, which means that the D-Tyr(5) side chain is dispensable. These findings were rationalized based on molecular docking, and the collective structure-activity data for the cyclopentapeptides suggest that appropriately designed Arg(2)-2-Nal(3) dipeptidomimetics have potential as CXCR4 antagonists.

Mechanisms and modifications of naturally occurring host defense peptides for anti-HIV microbicide development

Despite advances in the treatment of HIV infection, heterosexual transmission of HIV remains high, and vaccines to prevent HIV acquisition have been unfruitful. Vaginal microbicides, on the other hand, have demonstrated considerable potential for HIV prevention, and a variety of compounds have been screened for their activity and safety as anti-HIV microbicides. Among these are the naturally occurring host defense peptides, small peptides from diverse lineages with intrinsic antiviral activity. Naturally occurring host defense peptides with anti-HIV activity are promising candidates for vaginal microbicide development. Their structural variance and accompanying mechanistic diversity provide a wide range of inhibitors whose antiviral activity can be exerted at nearly every stage of the HIV lifecycle. Additionally, peptide modification has been explored as a method for improving the anti-HIV activity of host defense peptides. Structure- and sequence-based alterations have achieved varying success in improving the potency and specificity of anti-HIV peptides. Overall, peptides have been discovered or engineered to inhibit HIV with therapeutic indices of > 1000, encouraging their advancement toward clinical trials. Here we review the naturally occurring anti-HIV host defense peptides, demonstrating their breadth of mechanistic diversity, and exploring approaches to enhance and optimize their activity in order to expedite their development as safe and effective anti-HIV vaginal microbicides.

Role of chemokine network in the development and progression of ovarian cancer: a potential novel pharmacological target

Ovarian cancer is the most common type of gynecologic malignancy. Despite advances in surgery and chemotherapy, the survival rate is still low since most ovarian cancers relapse and become drug-resistant. Chemokines are small chemoattractant peptides mainly involved in the immune responses. More recently, chemokines were also demonstrated to regulate extra-immunological functions. It was shown that the chemokine network plays crucial functions in the tumorigenesis in several tissues. In particular the imbalanced or aberrant expression of CXCL12 and its receptor CXCR4 strongly affects cancer cell proliferation, recruitment of immunosuppressive cells, neovascularization, and metastasization. In the last years, several molecules able to target CXCR4 or CXCL12 have been developed to interfere with tumor growth, including pharmacological inhibitors, antagonists, and specific antibodies. This chemokine ligand/receptor pair was also proposed to represent an innovative therapeutic target for the treatment of ovarian cancer. Thus, a thorough understanding of ovarian cancer biology, and how chemokines may control these different biological activities might lead to the development of more effective therapies. This paper will focus on the current biology of CXCL12/CXCR4 axis in the context of understanding their potential role in ovarian cancer development.

Peptide bond mimicry by (E)-alkene and (Z)-fluoroalkene peptide isosteres: synthesis and bioevaluation of alpha-helical anti-HIV peptide analogues

The alpha-helix structures of the anti-HIV fusion inhibitory peptides are stabilized by the amino acid sequence and by intrachain hydrogen bonds. The study of peptide analogues using (E)-alkene and (Z)-fluoroalkene dipeptide isosteres demonstrated the substantial, yet position-dependent, contribution of hydrogen bonds to the alpha-helix stability and anti-HIV bioactivity.

Chemokine receptor CXCR4 as a therapeutic target for neuroectodermal tumors

Chemokines (chemotactic cytokines) are a family of proteins associated with the trafficking and activation of leukocytes and other cell types in immune surveillance and inflammatory response. Besides their roles in the immune system, they play pleiotropic roles in tumor initiation, promotion, and progression. Chemokines can be classified into four subfamilies of chemokines, CXC, CC, C, or CX3C, based on their number and spacing of conserved cysteine residues near the N-terminus. This CXC subfamily can be further subclassified into two groups, depending on the presence or absence of a tripeptide motif glutamic acid-leucine-arginine (ELR) in the N-terminal domain. ELR(-)CXCL12, which binds to CXCR4 has been frequently implicated in various cancers. Over the past several years, studies have increasingly shown that the CXCR4/CXCL12 axis plays critical roles in tumor progression, such as invasion, angiogenesis, survival, homing to metastatic sites. This review focuses on involvement of CXCR4/CXCL12 interaction in neuroectodermal cancers and their therapeutic potentials. As an attractive therapeutic target of CXCR4/CXCL12 axis for cancer chemotherapy, development history and application of CXCR4 antagonists are described.

CXCR4, inhibitors and mechanisms of action

In this review, the author discusses recent advances in anti-HIV inhibitors, targeting CXCR4, including natural and modified chemokines, peptides and organic compounds, their mechanisms of action, and the molecular process of virus invasion of immune cells. Peptides with strong anti-HIV activity exhibit several common features, such as electrostatic charges, cyclization, beta-turns and dimerization induced by a sulphide bond. Organic compounds, such as cyclams, display a unique metal-mediated mechanism in the binding process to its target CXCR4. Understanding of their mechanisms of action may be useful for the design of more effective drugs. Consecutive interactions of viral glycoprotein gp120 with CD4 and the co-receptor, CXCR4 or another co-receptor CCR5 on the cell surface leads to virus invasion into host cells. The molecular details of the binding between HIV glycoproteins and the co-receptors also provide a basis for anti-HIV therapy.

Development of a 111In-labeled peptide derivative targeting a chemokine receptor, CXCR4, for imaging tumors

The chemokine receptor CXCR4 is highly expressed in tumor cells and plays an important role in tumor metastasis. The aim of this study was to develop a radiopharmaceutical for the imaging of CXCR4-expressing tumors in vivo. Based on structure-activity relationships, we designed a 14-residue peptidic CXCR4 inhibitor, Ac-TZ14011, as a precursor for radiolabeled peptides. For 111In-labeling, diethylenetriaminepentaacetic acid (DTPA) was attached to the side chain of d-Lys(8) which is distant from the residues indispensable for the antagonistic activity. In-DTPA-Ac-TZ14011 inhibited the binding of a natural ligand, stromal cell-derived factor-1alpha, to CXCR4 in a concentration-dependent manner with an IC50 of 7.9 nM (Ac-TZ14011: 1.2 nM). In biodistribution experiments, more 111In-DTPA-Ac-TZ14011 accumulated in the CXCR4-expressing tumor than in blood or muscle. Furthermore, the tumor-to-blood and tumor-to-muscle ratios were significantly reduced by coinjection of Ac-TZ14011, indicating a CXCR4-mediated accumulation in tumor. These findings suggested that 111In-DTPA-Ac-TZ14011 would be a potential agent for the imaging of CXCR4 expression in metastatic tumors in vivo.

Four-base codon mediated mRNA display to construct peptide libraries that contain multiple nonnatural amino acids

In vitro selection and directed evolution of peptides from mRNA display are powerful strategies to find novel peptide ligands that bind to target biomolecules. In this study, we expanded the mRNA display method to include multiple nonnatural amino acids by introducing three different four-base codons at a randomly selected single position on the mRNA. Another nonnatural amino acid may be introduced by suppressing an amber codon that may appear from a (NNK)_n nucleotide sequence on the mRNA. The mRNA display was expressed in an Escherichia coli in vitro translation system in the presence of three types of tRNAs carrying different four-base anticodons and a tRNA carrying an amber anticodon, the tRNAs being chemically aminoacylated with different nonnatural amino acids. The complexity of the starting mRNA-displayed peptide library was estimated to be 1.1 × 10¹² molecules. The effectiveness of the four-base codon mediated mRNA display method was demonstrated in the selection of biocytin-containing peptides on streptavidin-coated beads. Moreover, a novel streptavidin-binding nonnatural peptide containing benzoylphenylalanine was obtained from the nonnatural peptide library. The nonnatural peptide library from the four-base codon mediated mRNA display provides much wider functional and structural diversity than conventional peptide libraries that are constituted from 20 naturally occurring amino acids.

A single treatment with microcapsules containing a CXCR4 antagonist suppresses pulmonary metastasis of murine melanoma

Biodegradable poly D,L-lactic acid (PLA, molecular weight: ca. 5000) microcapsules containing a CXCR4 antagonist (4F-benzoyl-TE14011) were prepared (4F-benzoyl-TE14011-PLA), and their anti-metastatic activity was evaluated in mice. A single subcutaneous administration of 4F-benzoyl-TE14011-PLA significantly reduced the number of colonies formed by pulmonary metastasis of B16-BL6 melanoma cells expressing CXCR4. The same dose of 4F-benzoyl-TE14011 in a single or a series of treatments affected little. The substance 4F-benzoyl-TE14011 dose-dependently suppressed B16-BL6 cell growth. In the cells cultured with SDF-1, a more potent suppression was observed. 4F-Benzoyl-TE14011 was rapidly released from 4F-benzoyl-TE14011-PLA for an initial period, both in vitro and in vivo. A steady release was thereafter observed. Therefore, this drug release profile might contribute to prevention of melanoma metastasis at the steps involving the migration and cell growth. These results also show that a sustained drug release formulation could be a useful drug delivery system for CXCR4 antagonists.