Mingsheng Xie

An In-tether Chiral Center Modulates the Helicity, Cell Permeability, and Target Binding Affinity of a Peptide.

The addition of a precisely positioned chiral center in the tether of a constrained peptide is reported, yielding two separable peptide diastereomers with significantly different helicity, as supported by circular dichroism (CD) and NMR spectroscopy. Single crystal X-ray diffraction analysis suggests that the absolute configuration of the in-tether chiral center in helical form is R, which is in agreement with theoretical simulations. The relationship between the secondary structure of the short peptides and their biochemical/biophysical properties remains elusive, largely because of the lack of proper controls. The present strategy provides the only method for investigating the influence of solely conformational differences upon the biochemical/biophysical properties of peptides. The significant differences in permeability and target binding affinity between the peptide diastereomers demonstrate the importance of helical conformation.

Crosslinked Aspartic Acids as Helix‐Nucleating Templates

Described is a facile helix-nucleating template based on a tethered aspartic acid at the N-terminus [terminal aspartic acid (TD)]. The nucleating effect of the template is subtly influenced by the substituent at the end of the side-chain-end tether as indicated by circular dichroism, nuclear magnetic resonance, and molecular dynamics simulations. Unlike most nucleating strategies, the N-terminal amine is preserved, thus enabling further modification. Peptidomimetic estrogen receptor modulators (PERMs) constructed using this strategy show improved therapeutic properties. The current strategy can be regarded as a good complement to existing helix-stabilizing methods.

Black phosphorus quantum dot based novel siRNA delivery systems in human pluripotent teratoma PA-1 cells

As a novel semiconducting material, the inherent, direct, and appreciable band gap endows BP with preferable optical and electronic properties other than graphene and transition metal dichalcogenides. In addition, bio-related applications with equal importance also attract great attention thanks to several inherited advantages of BP including large drug loading capacity, high PDT efficiency, high biocompatibility and degradability. However, to date there is limited research about the biomedical applications of BP. In this study, we reported the engineering of polyelectrolyte polymers coated BP quantum dots (BP-QDs)-based nanocarriers to deliver small interfering RNA (siRNA) into human ovarian teratocarcinoma PA-1 cells. Compared to the commercial delivery reagents, superior transfection efficiency of BP-QD was detected. The expression of the LSD1 (lysine-specific demethylase 1) mRNA in PA-1 cells was significantly suppressed by BP-QDs-LSD1 siRNA complex. Notably, BP-QDs possess excellent biocompatibility and low cytotoxicity even at concentrations as high as 5 mg mL-1. The combination treatment of BP nanodots-LSD1 siRNA complex with NIR light could inhibit the cell growth rate by more than 80%. In conclusion, this is the first application of BP-QDs as gene delivery systems, which shows promising potential for siRNA delivery and photothermal effects in cancer therapy.

Structural Basis of Inhibition of ERα-Coactivator Interaction by High-Affinity N-Terminus Isoaspartic Acid Tethered Helical Peptides

Direct inhibition of the protein-protein interaction of ERα and its endogenous coactivators with a cell permeable stabilized peptide may offer a novel, promising strategy for combating ERα positive breast cancers. Here, we report the co-crystal structure of a helical peptide stabilized by a N-terminal unnatural cross-linked aspartic acid (TD) in complex with the ERα ligand binding domain (LBD). We designed a series of peptides and peptide 6 that showed direct and high-affinity binding to ERα with selective antiproliferative activity in ERα positive breast cancer cells. The co-crystal structure of the TD-stabilized peptide 6 in complex with ERα LBD further demonstrates that it forms an α helical conformation and directly binds at the coactivator binding site of ERα. Further studies showed that peptide 6W could potently inhibit cellular ERαs transcriptional activity. This approach demonstrates the potential of TD stabilized peptides to modulate various intracellular protein-protein interactions involved in a range of disorders.

Chiral Sulfoxide-Induced Single Turn Peptide α-Helicity

Inducing α-helicity through side-chain cross-linking is a strategy that has been pursued to improve peptide conformational rigidity and bio-availability. Here we describe the preparation of small peptides tethered to chiral sulfoxide-containing macrocyclic rings. Furthermore, a study of structure-activity relationships (SARs) disclosed properties with respect to ring size, sulfur position, oxidation state, and stereochemistry that show a propensity to induce α-helicity. Supporting data include circular dichroism spectroscopy (CD), NMR spectroscopy, and a single crystal X-ray structure for one such stabilized peptide. Finally, theoretical studies are presented to elucidate the effect of chiral sulfoxides in inducing backbone α-helicity.

Development of Stabilized Peptide-Based PROTACs against Estrogen Receptor α

Peptide modulators targeting protein-protein interactions (PPIs) exhibit greater potential than small-molecule drugs in several important aspects including facile modification and relative large contact surface area. Stabilized peptides constructed by variable chemistry methods exhibit improved peptide stability and cell permeability compared to that of the linears. Herein, we designed a stabilized peptide-based proteolysis-targeting chimera (PROTAC) targeting estrogen receptor α (ERα) by tethering an N-terminal aspartic acid cross-linked stabilized peptide ERα modulator (TD-PERM) with a pentapeptide that binds the Von Hippel-Lindau (VHL) E3 ubiquitin ligase complex. The resulting heterobifunctional peptide (TD-PROTAC) selectively recruits ERα to the VHL E3 ligase complex, leading to the degradation of ERα in a proteasome-dependent manner. Compared with the control peptides, TD-PROTAC shows significantly enhanced activities in reducing the transcription of the ERα-downstream genes and inhibiting the proliferation of ERα-positive breast cancer cells. In addition, in vivo experiments indicate that TD-PROTAC leads to tumor regression in the MCF-7 mouse xenograft model. This work is a successful attempt to construct PROTACs based on cell-permeable stabilized peptides, which significantly broadens the chemical space of PROTACs and stabilized peptides.

In-Tether Chiral Center Induced Helical Peptide Modulators Target p53-MDM2/MDMX and Inhibit Tumor Growth in Stem-Like Cancer Cell

Inhibition of the interaction between p53 and MDM2/MDMX has attracted significant attention in anticancer therapy development. We designed a series of in-tether chiral center-induced helical stabilized peptides, among which MeR/PhR effectively reactivated p53. The activation of p53 inhibits cell proliferation and induces apoptosis in both the MCF-7 normal tumor cell line and the PA-1 pluripotent cancer cell line with only minimal cellular toxicity towards normal cells or cancer cell lines with p53 mutations. The in vivo bioactivity study of the peptide in the ovarian teratocarcinoma (PA-1) xenograft model showed a tumor growth rate inhibition of 70% with a dosage of 10 mg/kg (one injection every other day). This is the first application of a stabilized peptide modulator targeting stem-like cancer cell both in vitro and in vivo and provides references to cancer stem cell therapy.

Stabilized β-Hairpin Peptide Inhibits Insulin Degrading Enzyme

Insulin-degrading enzyme (IDE) plays a critical role in both the proteolytic degradation and inactivation of insulin. The exploration of novel IDE inhibitors could aid in the study of novel therapeutics for type-2 diabetes. Herein, we report a hypothesized stabilized β-hairpin peptide that can efficiently inhibit the enzymatic activity of IDE. The resulting stabilized peptide B35 is demonstrated to activate the AKT phosphorylation pathway in skeletal muscle cells and is shown to slow insulin degradation. An 80 mg kg-1 intraperitoneal (i.p.) injection of the stabilized β-hairpin peptide B35 is demonstrated to improve glucose tolerance during an oral glucose tolerance test in obese mouse model. We note that this stabilized peptide exhibited negligible cytotoxicity in both in vitro and in vivo assays, even at high concentrations (300 μM). This study suggests that IDE peptide inhibitors could function as potentially meaningful candidates for the development of type-2 diabetes therapeutics.

Recent advances in peptidomimetics antagonists targeting estrogen receptor α-coactivator interaction in cancer therapy

Estrogen receptor α (ERα) is a crucial target for ERα positive breast cancer treatment. Previous drug discovery efforts were focused on developing inhibitors that targeted the canonical ligand binding pockets of the ligand binding domain (LBD) of ERα. However, significant percentage of patients developed cancer relapse with drug-resistance. ERα peptidomimetic modulators have been considered as promising treatments for drug resistant breast cancers as they are targeting ERα-coactivator interacting interface instead of the ligand binding pocket of ERα. Herein, we reviewed the recent development of ERα peptidomimetics antagonists.