A Vancomycin-Templated DNA-Encoded Library for Combating Drug-Resistant Bacteria.

It is an urgent need to tackle the global crisis of multidrug-resistant bacterial infections. We report here an innovative strategy for large-scale screening of new antibacterial agents using a whole bacteria-based DNA-encoded library (DEL) of vancomycin derivatives via peripheral modifications. A bacterial binding affinity assay was established to select the modification fragments in high-affinity compounds. The optimal resynthesized derivatives demonstrated excellently enhanced activity against various resistant bacterial strains and provided useful structures for vancomycin derivatization. This work presents the new concept in a natural product-templated DEL and in antibiotic discovery through bacterial affinity screening, which promotes the fight against drug-resistant bacteria.

Design, Synthesis, and Structure-Activity Relationship Studies of Novel GPR88 Agonists (4-Substituted-phenyl)acetamides Based on the Reversed Amide Scaffold.

The development of synthetic agonists for the orphan receptor GPR88 has recently attracted significant interest, given the promise of GPR88 as a novel drug target for psychiatric and neurodegenerative disorders. Examination of structure-activity relationships of two known agonist scaffolds 2-PCCA and 2-AMPP, as well as the recently resolved cryo-EM structure of 2-PCCA-bound GPR88, led to the design of a new scaffold based on the "reversed amide" strategy of 2-AMPP. A series of novel (4-substituted-phenyl)acetamides were synthesized and assessed in cAMP accumulation assays as GPR88 agonists, which led to the discovery of several compounds with better or comparable potencies to 2-AMPP. Computational docking studies suggest that these novel GPR88 agonists bind to the same allosteric site of GPR88 that 2-PCCA occupies. Collectively, our findings provide structural insight and SAR requirement at the allosteric site of GPR88 and a new scaffold for further development of GPR88 allosteric agonists.

Novel RXFP3 negative allosteric modulator RLX-33 reduces alcohol self-administration in rats.

There is much interest in identifying novel pharmacotherapeutic targets that improve clinical outcomes for the treatment of alcohol use disorder (AUD). One promising target for therapeutic intervention is the relaxin family peptide 3 (RXFP3) receptor, a cognate receptor for neuropeptide relaxin-3, which has previously been implicated in regulating alcohol drinking behavior. Recently, we developed the first small-molecule RXFP3-selective negative allosteric modulator (NAM) RLX-33. Therefore, the goal of the present work was to characterize the impact of this novel NAM on affective-related behaviors and alcohol self-administration in rats. First, the effects of RLX-33 were tested on alcohol and sucrose self-administration in Wistar and alcohol-preferring P rats to determine the dose-response profile and specificity for alcohol. Then, we assessed the effects of systemic RLX-33 injection in Wistar rats in a battery of behavioral assays (open-field test, elevated zero maze, acoustic startle response test, and prepulse inhibition) and tested for alcohol clearance. We found that the lowest effective dose (5 mg/kg) reduced alcohol self-administration in both male and female Wistar rats, while in alcohol-preferring P rats, this effect was restricted to males, and there were no effects on sucrose self-administration or general locomotor activity. The characterization of affective and metabolic effects in Wistar rats generally found few locomotor, affective, or alcohol clearance changes, particularly at the 5 mg/kg dose. Overall, these findings are promising and suggest that RXFP3 NAM has potential as a pharmacological target for treating AUD.

A facile and selective derivatization approach on kynurenine-NH2 in daptomycin, leading to the discovery of hexakynomycin to combat multidrug-resistant Gram-positive pathogens especially daptomycin-resistant bacteria.

Wide-spread use of daptomycin unavoidably resulted in the emergence of daptomycin-resistant pathogens. In the hunt for more active daptomycin derivatives through medicinal chemistry studies, we established a concise semisynthetic approach to modify the L-Kyn13 on daptomycin specifically and effectively. Here, 19 novel derivatives with certain diversity were designed and synthesized to perform a comprehensive SAR study on this underestimated position. The optimal compound, termed "hexakynomycin", as the new generation of daptomycin-based antibiotic candidate exhibited 4->125-fold higher activity against methicillin-susceptible S. aureus (MSSA), methicillin-resistant S. aureus (MRSA), vancomycin-intermediate resistant S. aureus (VISA), and vancomycin-resistant Enterococci (VRE), including daptomycin-resistant strains, compared with that of daptomycin. Greater membrane binding capacity rendered hexakynomycin better activity and special antibiotic property. Hexakynomycin also demonstrated a better pharmacokinetic profile, good safety features and good pharmacodynamics properties. This work provided an effective modification strategy aiming at daptomycin which provided significant insights and showed great promise for the next generation of daptomycin derivatives.

Carbohydrate Strengthens the Immunotherapeutic Effect of Small-Molecule PD-L1 Inhibitors.

PD-1/PD-L1 checkpoint blockade has demonstrated great success in cancer immunotherapy. Small-molecule PD-L1 inhibitors also attract significant research interests but remain challenging in the efficacy and safety. Carbohydrate moiety and carbohydrate-binding proteins (lectins) play important roles in immune modulation including antigen recognition and presenting. Herein, we reported a novel strategy to strengthen the immunotherapeutic effect of small-molecule PD-L1 inhibitors by introducing sugar motifs, which may utilize the carbohydrate-mediated immune enhancement for cancer treatment. The data revealed that glycoside compounds containing mannose or N-acetylglucosamine exhibited the best results in IFN-γ secretion. Moreover, compared to the nonglycosylated compounds, glycosides C3 and C15 demonstrated significant lower cytotoxicity and effective in vivo antitumor potency in the CT26 and melanoma B16-F10 tumor models with good tolerance. Notably, tumor-infiltrating lymphocyte (TIL) analysis validated increased CD3+, CD4+, CD8+, and granzyme B+ T cells after glycoside treatments. This work presents a new concept to improve the immunotherapy.

Single Modification at the N-Terminus of Norvancomycin to Combat Drug-Resistant Gram-Positive Bacteria.

In the arsenal of glycopeptide antibiotics, norvancomycin, which differs from vancomycin by a single methyl group, has received much less attention. Facing the risks of serious antibiotic resistance and even the collapse of last-line defenses, we designed and synthesized 40 novel norvancomycin derivatives to combat the threat. 32 compounds are single N-terminally modified derivatives generated through simple and efficient methods. Diversity at the N-terminus was greatly enriched, mainly by lipophilic attachment and strategies for the introduction of lipo-sulfonium moieties for extensive structure-activity relationship analysis. The first incorporation of a sulfonium moiety into the norvancomycin structure gave rise to compounds that exhibited 4- to 2048-fold higher activity against vancomycin-resistant bacteria VISA and VRE. This N-terminal modification for norvancomycin provides an alternatively useful and promising strategy to restore the antibacterial activity of glycopeptide antibiotics against resistant bacteria, highlighting the same importance of the N-terminal site as well as the vancosamine position, which is worth further study and development.

Potentiation of Vancomycin: Creating Cooperative Membrane Lysis through a "Derivatization-for-Sensitization" Approach.

Gram-negative bacteria, especially the ones with multidrug resistance, post dire challenges to antibiotic treatments due to the presence of the outer membrane (OM), which blocks the entry of many antibiotics. Current solutions for such permeability issues, namely lipophilic-cationic derivatization of antibiotics and sensitization with membrane-active agents, cannot effectively potentiate the large, globular, and hydrophilic antibiotics such as vancomycin, due to ineffective disruption of the OM. Here, we present our solution for high-degree OM binding of vancomycin via a hybrid "derivatization-for-sensitization" approach, which features a combination of LPS-targeting lipo-cationic modifications on vancomycin and OM disruption activity from a sensitizing adjuvant. 106- to 107-fold potentiation of vancomycin and 20-fold increase of the sensitizer's effectiveness were achieved with a combination of a vancomycin derivative and its sensitizer. Such potentiation is the result of direct membrane lysis through cooperative membrane binding for the sensitizer-antibiotic complex, which strongly promotes the uptake of vancomycin and adds to the extensive antiresistance effectiveness. The potential of such derivatization-for-sensitization approach was also supported by the combination's potent in vivo antimicrobial efficacy in mouse model studies, and the expanded application of such strategy on other antibiotics and sensitizer structures.

Discovery and Characterization of the First Nonpeptide Antagonists for the Relaxin-3/RXFP3 System.

The neuropeptide relaxin-3/RXFP3 system is involved in many important physiological processes such as stress responses, appetite control, and motivation for reward. To date, pharmacological studies of RXFP3 have been limited to peptide ligands. In this study, we report the discovery of the first small-molecule antagonists of RXFP3 through a high-throughput screening campaign. Focused structure-activity relationship studies of the hit compound resulted in RLX-33 (33) that was able to inhibit relaxin-3 activity in a battery of functional assays. RLX-33 is selective for RXFP3 over RXFP1 and RXFP4, two related members in the relaxin/insulin superfamily, and has favorable pharmacokinetic properties for behavioral assessment. When administered to rats intraperitoneally, RLX-33 blocked food intake induced by the RXFP3-selective agonist R3/I5. Collectively, our findings demonstrated that RLX-33 represents a promising antagonist scaffold for the development of drugs targeting the relaxin-3/RXFP3 system.

Operational daily evapotranspiration mapping at field scale based on SSEBop model and spatiotemporal fusion of multi-source remote sensing data.

Accurate understanding of daily evapotranspiration (ET) at field scale is of great significance for agricultural water resources management. The operational simplified surface energy balance (SSEBop) model has been applied to estimate field scale ET with Landsat satellite imagery. However, there is still uncertainty in the ET time reconstruction for cloudy days based on limited clear days' Landsat ET fraction (ETf) computed by SSEBop. The Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing data can provide daily surface observation over clear-sky areas. This paper presented an enhanced gap-filling scheme for the SSEBop ET model, which improved the temporal resolution of Landsat ETf through the spatio-temporal fusion with SSEBop MODIS ETf on clear days and increased the time reconstruction accuracy of field-scale ET. The results were validated with the eddy covariance (EC) measurements over cropland in northwestern China. It indicated that the improved scheme performed better than the original SSEBop Landsat approach in daily ET estimation, with higher Nash-Sutcliffe efficiency (NSE, 0.75 vs. 0.70), lower root mean square error (RMSE, 0.95 mm·d-1 vs. 1.05 mm·d-1), and percent bias (PBias, 16.5% vs. 25.0%). This fusion method reduced the proportion of deviation (13.3% vs. 25.5%) in the total errors and made the random error the main proportion, which can be reduced over time and space in regional ET estimation. It also evidently improved the underestimation of crop ET by the SSEBop Landsat scheme during irrigation before sowing and could more accurately describe the synergistic changes of soil moisture and cropland ET. The proposed MODIS and Landsat ETf fusion can significantly improve the accuracy of SSEBop in estimating field-scale ET.

Indole-Containing Amidinohydrazones as Nonpeptide, Dual RXFP3/4 Agonists: Synthesis, Structure-Activity Relationship, and Molecular Modeling Studies.

The central relaxin-3/RXFP3 system plays important roles in stress responses, feeding, and motivation for reward. However, exploration of its therapeutic applications has been hampered by the lack of small molecule ligands and the cross-activation of RXFP1 in the brain and RXFP4 in the periphery. Herein, we report the first structure-activity relationship studies of a series of novel nonpeptide amidinohydrazone-based agonists, which were characterized by RXFP3 functional and radioligand binding assays. Several potent and efficacious RXFP3 agonists (e.g., 10d) were identified with EC50 values <10 nM. These compounds also had high potency at RXFP4 but no agonist activity at RXFP1, demonstrating > 100-fold selectivity for RXFP3/4 over RXFP1. In vitro ADME and pharmacokinetic assessments revealed that the amidinohydrazone derivatives may have limited brain permeability. Collectively, our findings provide the basis for further optimization of lead compounds to develop a suitable agonist to probe RXFP3 functions in the brain.

Total and Semisyntheses of Polymyxin Analogues with 2-Thr or 10-Thr Modifications to Decipher the Structure-Activity Relationship and Improve the Antibacterial Activity.

Herein, we report the total and semisyntheses of a series of polymyxin analogues with 2-Thr and 10-Thr modifications to reveal the structure-activity relationship (SAR), which has not been fully elucidated previously. We employed two total-synthetic strategies to facilitate the diversified replacements on 2-Thr or 10-Thr, respectively. Moreover, semisynthetic approaches were utilized to achieve selective esterification of 2-Thr or dual esterification of both 2- and 10-Thr. Based on the results of in vitro antibacterial assays, SAR analysis implicated that the replacement of 2-/10-Thr with amino acids carrying hydrophobic side chains can maintain the activity against Pseudomonas aeruginosa but had varied effects on other tested Gram-negative bacteria. The aminoacetyl esterification on 2-/10-Thr achieved excellent antibacterial activity, and the compound 76 exhibited 2-8-fold higher activity against different strains and lower toxicity toward the HK-2 cell line. This work explored the SAR of polymyxin 2-/10-Thr and provided a promising strategy for the development of novel polymyxin derivatives.

Selective N-glycan editing on living cell surfaces to probe glycoconjugate function.

Cell surfaces are glycosylated in various ways with high heterogeneity, which usually leads to ambiguous conclusions about glycan-involved biological functions. Here, we describe a two-step chemoenzymatic approach for N-glycan-subtype-selective editing on the surface of living cells that consists of a first 'delete' step to remove heterogeneous N-glycoforms of a certain subclass and a second 'insert' step to assemble a well-defined N-glycan back onto the pretreated glyco-sites. Such glyco-edited cells, carrying more homogeneous oligosaccharide structures, could enable precise understanding of carbohydrate-mediated functions. In particular, N-glycan-subtype-selective remodeling and imaging with different monosaccharide motifs at the non-reducing end were successfully achieved. Using a combination of the expression system of the Lec4 CHO cell line and this two-step glycan-editing approach, opioid receptor delta 1 (OPRD1) was investigated to correlate its glycostructures with the biological functions of receptor dimerization, agonist-induced signaling and internalization.

Sulfonium, an Underestimated Moiety for Structural Modification, Alters the Antibacterial Profile of Vancomycin Against Multidrug-Resistant Bacteria.

In the antibiotics arsenal, vancomycin is a last resort for the treatment of intractable infections. However, this situation is under threat because of the increasing appearance of vancomycin-resistant bacteria (VRB). Herein, we report a series of novel vancomycin derivatives carrying a sulfonium moiety. The sulfonium-vancomycin derivatives exhibited enhanced antibacterial activity against VRB both in vitro and in vivo. These derivatives also exhibited activity against some Gram-negative bacteria. The sulfonium modification enhanced the interaction of vancomycin with the bacterial cell membrane and disrupts membrane integrity. Furthermore, the in vivo pharmacokinetic profile, stability, and toxicity of these derivatives demonstrated good druggability of the sulfonium-vancomycin analogues. This work provides a promising strategy for combating drug-resistant bacterial infection, and advances the knowledge on sulfonium derivatives for structural optimization and drug development.

Design and synthesis of novel dual-cyclic RGD peptides for αvß3 integrin targeting.

The specific binding of RGD cyclic peptide with integrin αvß3 attracts great research interest for tumor-targeting drug delivery. Herein, we designed and synthesized a series of dual-ring RGD-peptide derivatives as a drug carrier for αvß3 targeting. Three novel peptides showed excellent cell adhesion inhibition effect, in which, P3 exhibited 7-fold enhancement in IC50 compared with cyclo(RGDfK). Drug-loaded cytotoxicity experiment and imaging experiment indicated that such dual-cyclic RGD peptides have good tumor targeting effects. This work provides a new strategy for the design of novel RGD peptides.

Design and Synthesis of Pyrophosphate-Targeting Vancomycin Derivatives for Combating Vancomycin-Resistant Enterococci.

As the last resort for intractable Gram-positive bacterial infections, vancomycin is losing efficacy with the emergence of vancomycin-resistant bacteria, especially vancomycin-resistant Enterococci (VRE). To combat this threat, we rationally designed and synthesized 39 novel vancomycin derivatives by respective or combined modifications using metal-chelating, lipophilic, and galactose-attachment strategies for extensive structure-activity relationship (SAR) analysis. In a proposed mechanism, the conjugation of dipicolylamine on the seventh amino acid resorcinol position or C-terminus endowed the vancomycin backbone with binding capacity for the pyrophosphate moiety in lipid II while maintaining the intrinsic binding affinity for the dipeptide terminus of the bacterial cell wall peptidoglycan precursor. The in vitro antibacterial activities were evaluated, and the optimal compounds indicated 16- to 1024-fold higher activity against VRE than that of vancomycin. Compound 11 b (3',5'-bis(dipicolylaminomethyl)tyrosine [1,2,3]triazolylmethoxylethyoxyl ethylaminomethyl-N-decylvancomycin) was found to have particularly potent activity against VRE through synergistic effects brought about by combining two peripheral modifications.

Extra Sugar on Vancomycin: New Analogues for Combating Multidrug-Resistant Staphylococcus aureus and Vancomycin-Resistant Enterococci.

Lipophilic substitution on vancomycin is an effective strategy for the development of novel vancomycin analogues against drug-resistant bacteria by enhancing bacterial cell wall interactions. However, hydrophobic structures usually lead to long elimination half-life and accumulative toxicity; therefore, hydrophilic fragments were also introduced to the lipo-vancomycin to regulate their pharmacokinetic/pharmacodynamic properties. Here, we synthesized a series of new vancomycin analogues carrying various sugar moieties on the seventh-amino acid phenyl ring and lipophilic substitutions on vancosamine with extensive structure-activity relationship analysis. The optimal analogues indicated 128-1024-fold higher activity against methicillin-susceptible S. aureus, vancomycin-intermediate resistant S. aureus (VISA), and vancomycin-resistant Enterococci (VRE) compared with that of vancomycin. In vivo pharmacokinetics studies demonstrated the effective regulation of extra sugar motifs, which shortened the half-life and addressed concerns of accumulative toxicity of lipo-vancomycin. This work presents an effective strategy for lipo-vancomycin derivative design by introducing extra sugars, which leads to better antibiotic-like properties of enhanced efficacy, optimal pharmacokinetics, and lower toxicity.