Peptide Bond Research Articles

C-C Bond Cleavage-Induced C- to N-Acyl Transfer for Synthesis of Amides.

A new approach for the preparation of amides was developed using C-C bond cleavage that initiates C- to N-acyl transfer, employing activated ketones as acylation reagents and amine nucleophiles. The reaction was operational under the coupling reagent system that is commonly utilized for peptide bond formations. The method enables practical preparation of amides using linear and cyclic ketone substrates under mild conditions.

Enhanced catalytic activity of Fe3O4-carbon dots complex in the Fenton reaction for enhanced immunotherapeutic and oxygenation effects

Tumor metastasis and recurrence are closely related to immune escape and hypoxia. Chemodynamic therapy (CDT), photodynamic therapy (PDT), and photothermal therapy (PTT) can induce immunogenic cell death (ICD), and their combination with immune checkpoint agents is a promising therapeutic strategy. Iron based nanomaterials have received more and more attention, but their low Fenton reaction efficiency has hindered their clinical application. In this study, Fe3O4-carbon dots complex (Fe3O4-CDs) was synthesized, which was modified with ferrocenedicarboxylic acid by amide bond, and crosslinked into Fe3O4-CDs@Fc nano complex. The CDs catalyzed the Fenton reaction activity of Fe3O4 by helping to improve the electron transfer efficiency, extended the reaction pH condition to 7.4. The Fe3O4-CDs@Fc exhibit exceptional optical activity, achieving a thermal conversion efficiency of 56.43 % under 808 nm light and a photosensitive single-line state oxygen quantum yield of 33 % under 660 nm light. Fe3O4-CDs@Fc improved intracellular oxygen level and inhibited hypoxia-inducing factor (HIF-1α) by in-situ oxygen production based on Fenton reaction. The multimodal combination of Fe3O4-CDs@Fc (CDT/PDT/PTT) strongly induced immune cell death (ICD). The expression of immune-related protein and HIF-1α was investigated by immunofluorescence method. In vivo, Fe3O4-CDs@Fc combined with immune checkpoint blocker (antibody PD-L1, αPD-L1) effectively ablated primary tumors and inhibited distal tumor growth. Fe3O4-CDs@Fc is a promising immune-antitumor drug.

Proline Peptide Bond Isomerization in Ubiquitin Under Folding and Denaturing Conditions by Pressure-Jump NMR

Proline isomerization is widely recognized as a kinetic bottleneck in protein folding, amplified for proteins rich in Pro residues. We introduced repeated hydrostatic pressure jumps between native and pressure-denaturing conditions inside an NMR sample cell to study proline isomerization in the pressure-sensitized L50A ubiquitin mutant. Whereas in two unfolded heptapeptides, X-Pro peptide bonds isomerized ca 1.6-fold faster at 1 bar than at 2.5 kbar, for ubiquitin ca eight-fold faster isomerization was observed for Pro-38 and ca two-fold for Pro-19 and Pro-37 relative to rates measured in the pressure-denatured state. Activation energies for isomerization in pressure-denatured ubiquitin were close to literature values of 20 kcal/mole for denatured polypeptides but showed a substantial drop to 12.7 kcal/mole for Pro-38 at atmospheric pressure. For ubiquitin isomers with a cis E18-P19 peptide bond, the 1-bar NMR spectrum showed sharp resonances with near random coil chemical shifts for the C-terminal half of the protein, characteristic of an unfolded chain, while most of the N-terminal residues were invisible due to exchange broadening, pointing to a metastable partially folded state for this previously recognized ‘folding nucleus’. For cis-P37 isomers, a drop in pressure resulted in the rapid loss of nearly all unfolded-state NMR resonances, while the recovery of native state intensity revealed a slow component attributed to cis → trans isomerization of P37. This result implies that the NMR-invisible cis-P37 isomer adopts a molten globule state that encompasses the entire length of the ubiquitin chain, suggestive of a structure that mostly resembles the folded state.

Positron emission tomography guided synergistic treatment of melanoma using multifunctional zirconium-hematoporphyrin nanosonosensitizers

Sonodynamic therapy (SDT) has emerged as a useful approach for tumor treatment. However, its widespread application is impeded by poor pharmacokinetics of existing sonosensitizers. Here we developed a metal-organic nanoplatform, wherein a small-molecule sonosensitizer (hematoporphyrin monomethyl ether, HMME) was ingeniously coordinated with zirconium, resulting in a multifunctional nanosonosensitizer termed Zr-HMME. Through post-synthetic modifications involving PEGylation and tumor-targeting peptide (F3) linkage, a nanoplatform capable of homing on melanoma was produced, which could elicit robust immune responses to suppress tumor lung metastasis in the host organism. Importantly, after seamless incorporation of positron-emitting 89Zr into this nanosonosensitizer, positron emission tomography (PET) could be used to monitor its in vivo pharmacokinetics. PET imaging studies revealed that this nanoplatform exhibited potent tumor accumulation and strong in vivo stability. Using intrinsic fluorescence from HMME, a dual-modal diagnostic capability (fluorescence and PET) was confirmed for this nanosonosensitizer. In addition, the mechanisms of how this nanoplatform interacted with immune system were also investigated. The collective data proved that the coordination structure between small-molecule drug cargos and metals may enhance the functions of each other while mitigating their weaknesses. This straightforward approach can expand the potential applications of suitable drug molecules.

Synthesis, In Silico and Kinetics Evaluation of N-(β-d-glucopyranosyl)-2-arylimidazole-4(5)-carboxamides and N-(β-d-glucopyranosyl)-4(5)-arylimidazole-2-carboxamides as Glycogen Phosphorylase Inhibitors.

Recently studied N-(β-d-glucopyranosyl)-3-aryl-1,2,4-triazole-5-carboxamides have proven to be low micromolar inhibitors of glycogen phosphorylase (GP), a validated target for the treatment of type 2 diabetes mellitus. Since in other settings, the bioisosteric replacement of the 1,2,4-triazole moiety with imidazole resulted in significantly more efficient GP inhibitors, in silico calculations using Glide molecular docking along with unbound state DFT calculations were performed on N-(β-d-glucopyranosyl)-arylimidazole-carboxamides, revealing their potential for strong GP inhibition. The syntheses of the target compounds involved the formation of an amide bond between per-O-acetylated β-d-glucopyranosylamine and the corresponding arylimidazole-carboxylic acids. Kinetics experiments on rabbit muscle GPb revealed low micromolar inhibitors, with the best inhibition constants (Kis) of ~3-4 µM obtained for 1- and 2-naphthyl-substituted N-(β-d-glucopyranosyl)-imidazolecarboxamides, 2b-c. The predicted protein-ligand interactions responsible for the observed potencies are discussed and will facilitate the structure-based design of other inhibitors targeting this important therapeutic target. Meanwhile, the importance of the careful consideration of ligand tautomeric states in binding calculations is highlighted, with the usefulness of DFT calculations in this regard proposed.

Highly defective ultra-small tetravalent MOF nanocrystals

The size and defects in crystalline inorganic materials are of importance in many applications, particularly catalysis, as it often results in enhanced/emerging properties. So far, applying the strategy of modulation chemistry has been unable to afford high-quality functional Metal–Organic Frameworks (MOFs) nanocrystals with minimized size while exhibiting maximized defects. We report here a general sustainable strategy for the design of highly defective and ultra-small tetravalent MOFs (Zr, Hf) crystals (ca. 35% missing linker, 4–6 nm). Advanced characterizations have been performed to shed light on the main factors governing the crystallization mechanism and to identify the nature of the defects. The ultra-small nanoMOFs showed exceptional performance in peptide hydrolysis reaction, including high reactivity, selectivity, diffusion, stability, and show emerging tailorable reactivity and selectivity towards peptide bond formation simply by changing the reaction solvent. Therefore, these highly defective ultra-small M(IV)-MOFs particles open new perspectives for the development of heterogeneous MOF catalysts with dual functions.

Enzymatic mechanism of MlrB for catalyzing linearized microcystins by Sphingopyxis sp. USTB-05.

Microcystins (MCs) are the most widespread cyanobacterial toxins in eutrophic water body. As high toxic intermediate metabolites, linearized MCs are further catalyzed by linearized microcystinase (MlrB) of Sphingopyxis sp. USTB-05. Here MlrB structure was studied by comprizing with a model representative of the penicillin-recognizing enzyme family via homology modeling. The key active sites of MlrB were predicted by molecular docking, and further verified by site-directed mutagenesis. A comprehensive enzymatic mechanism for linearized MCs biodegradation by MlrB was proposed: S77 transferred a proton to H307 to promote a nucleophilic attack on the peptide bond (Ala-Leu in MC-LR or Ala-Arg in MC-RR) of linearized MCs to form the amide intermediate. Then water was involved to break the peptide bond and produced the tetrapeptide as product. Meanwhile, four amino acid residues (K80, Y171, N173 and D245) acted synergistically to stabilize the substrate and intermediate transition states. This study firstly revealed the enzymatic mechanism of MlrB for biodegrading linearized MCs with both computer simulation and experimental verification.

N-Terminomic Identification of Intracellular MMP-2 Substrates in Cardiac Tissue.

Proteases are enzymes that induce irreversible post-translational modifications by hydrolyzing amide bonds in proteins. One of these proteases is matrix metalloproteinase-2 (MMP-2), which has been shown to modulate extracellular matrix remodeling and intracellular proteolysis during myocardial injury. However, the substrates of MMP-2 in heart tissue are limited, and lesser known are the cleavage sites. Here, we used degradomics to investigate the substrates of intracellular MMP-2 in rat ventricular extracts. First, we designed a novel, constitutively active MMP-2 fusion protein (MMP-2-Fc) that we expressed and purified from mammalian cells. Using this protease, we proteolyzed ventricular extracts and used subtiligase-mediated N-terminomic labeling which identified 95 putative MMP-2-Fc proteolytic cleavage sites using mass spectrometry. The intracellular MMP-2 cleavage sites identified in heart tissue extracts were enriched for proteins primarily involved in metabolism, as well as the breakdown of fatty acids and amino acids. We further characterized the cleavage of three of these MMP-2-Fc substrates based on the gene ontology analysis. We first characterized the cleavage of sarco/endoplasmic reticulum calcium ATPase (SERCA2a), a known MMP-2 substrate in myocardial injury. We then characterized the cleavage of malate dehydrogenase (MDHM) and phosphoglycerate kinase 1 (PGK1), representing new cardiac tissue substrates. Our findings provide insights into the intracellular substrates of MMP-2 in cardiac cells, suggesting that MMP-2 activation plays a role in cardiac metabolism.

Hydrophilic Modification of Polytetrafluoroethylene (PTFE) Capillary Membranes with Chemical Resistance by Constructing Three-Dimensional Hydrophilic Networks.

Polytetrafluoroethylene (PTFE) capillary membranes, known for the great chemical resistance and thermal stability, are commonly used in membrane separation technologies. However, the strong hydrophobic property of PTFE limits its application in water filtration. This study introduces a method whereby acrylamide (AM), N, N-methylene bisacrylamide (MBA), and vinyltriethoxysilane (VTES) undergo free radical copolymerization, followed by the hydrolysis-condensation of silane bonds, resulting in the formation of hydrophilic three-dimensional networks physically intertwined with the PTFE capillary membranes. The modified PTFE capillary membranes prepared through this method exhibit excellent hydrophilic properties, whose water contact angles are decreased by 24.3-61.2%, and increasing pure water flux from 0 to 1732.7-2666.0 L/m2·h. The enhancement in hydrophilicity of the modified PTFE capillary membranes is attributed to the introduction of hydrophilic groups such as amide bonds and siloxane bonds, along with an increase in surface roughness. Moreover, the modified PTFE capillary membranes exhibit chemical resistance, maintaining the hydrophilicity even after immersion in strong acidic (3 wt% HCl), alkaline (3 wt% NaOH), and oxidative (3 wt% NaClO) solutions for 2 weeks. In conclusion, this promising method yields modified PTFE capillary membranes with great hydrophilicity and chemical resistance, presenting substantial potential for applications in the field of water filtration.

Cyclic Peptides from Graspetide Biosynthesis and Native Chemical Ligation.

The ribosomally synthesized and post-translationally modified peptide (RiPP) superfamily of natural products includes many examples of cyclic peptides with diverse macrocyclization chemistries. The graspetides, one family of macrocyclized RiPPs, harbor side chain-side chain ester or amide linkages. We recently reported the structure and biosynthesis of the graspetide pre-fuscimiditide, a 22-amino-acid (aa) peptide with two ester cross-links forming a stem-loop structure. These cross-links are introduced by a single graspetide synthetase, the ATP-grasp enzyme ThfB. Here we show that ThfB can also catalyze the formation of amide or thioester cross-links in prefuscimiditide, with thioester formation being especially efficient. We further show that upon proteolysis to reveal an N-terminal cysteine residue, the thioester-linked peptide rapidly and quantitatively rearranges via native chemical ligation into an isopeptide-bonded head-to-tail cyclic peptide. The solution structure of this rearranged peptide was determined by using 2D NMR spectroscopy experiments. Our methodology offers a straightforward recombinant route to head-to-tail cyclic peptides.

Exploring and Synthesis of bio-active natural product coupling reactions

Utilizing natural products in drug discovery research are very comment practice and they lead to more than fifty percent of current medicines in the market. However, there are still needed in new therapeutic entities that can improve the efficiency of drugs against the enzymes. We are hoping this and future study lead to combat unmet needs among healthcare. Having said that, we would like to explore the coupling reactions to make bio-active natural products similar to capsaicin natural product and its chemical synthetic optimization before the its kinetic study. Currently, we are exploring two distinctive coupling reaction conditions to optimize the reaction condition and will present current status of our research project of coupling reaction. Furthermore, we would like to carry on enzymatic profile against resinaase HT enzyme to see how stable amide bond is.

Endophthalmitis therapy revolution: Proof of concept based on in vivo evaluation of maleic acid modified chitosan

The aim was to develop chitosan-maleic acid (CS-MA) based ocular inserts with enhanced mucoadhesiveness for prevention of endophthalmitis caused by Escherichia coli. Therefore, chitosan (CS) and maleic acid (MA) were conjugated via formation of amide bond. Characterization via proton nuclear magnetic resonance and infrared spectroscopy was carried out and attached maleic acid groups were quantified by free amino groups assay. Biocompatibility of the conjugate was assessed following resazurin assay on fibroblasts, membrane damage on human erythrocytes and Hen's Egg-Chorioallantoic membrane tests. Inserts were pressed and characterized in terms of swelling behavior, pH, hardness, in vitro drug release and disintegration. To test mucoadhesive properties of CS-MA inserts, rheometer, rotating cylinder, inclined plane, and texture analyzer were the instruments utilized. Furthermore, antibacterial efficacy of the conjugate was established by direct agar diffusion method and in vivo Draize test was carried out to determine tolerability of the inserts. Results exhibited successful synthesis of the biomaterial, maintaining the great biocompatibility of native chitosan even though a 68.81 % of modification was achieved. Additionally, mucoadhesive studies showed improved properties of CS-MA compared to native polymer, with 2.42-fold, 4-fold, 3.42-fold and 4.05-fold increase in dynamic viscosity, retention time, overall attachment work and peak force of detachment, respectively. Finally, antibacterial activity was enhanced in 1.77-fold and in vivo experiments showed no irritation and good tolerability of CS-MA inserts. In conclusion, CS-MA ocular inserts effectively developed exhibiting promising features capable of revolutionizing the endophthalmitis therapy field.

Magnetic Nanoparticle Support with an Ultra-Thin Chitosan Layer Preserves the Catalytic Activity of the Immobilized Glucose Oxidase.

Here, we developed magnetically recoverable biocatalysts based on magnetite nanoparticles coated with an ultra-thin layer (about 0.9 nm) of chitosan (CS) ionically cross-linked by sodium tripolyphosphate (TPP). Excessive CS amounts were removed by multiple washings combined with magnetic separation. Glucose oxidase (GOx) was attached to the magnetic support via the interaction with N-hydroxysuccinimide (NHS) in the presence of carbodiimide (EDC) leading to a covalent amide bond. These steps result in the formation of the biocatalyst for D-glucose oxidation to D-gluconic acid to be used in the preparation of pharmaceuticals due to the benign character of the biocatalyst components. To choose the catalyst with the best catalytic performance, the amounts of CS, TPP, NHS, EDC, and GOx were varied. The optimal biocatalyst allowed for 100% relative catalytic activity. The immobilization of GOx and the magnetic character of the support prevents GOx and biocatalyst loss and allows for repeated use.

General Installation of (4H)-Imidazolone cis-Amide Bioisosteres Along the Peptide Backbone.

Imidazolones represent an important class of heterocycles present in a wide range of pharmaceuticals, metabolites, and bioactive natural products and serve as the active chromophore in green fluorescent protein. Recently, imidazolones have received attention for their ability to act as a nonaromatic amide bond bioisotere which improves pharmacological properties. Herein, we present a tandem amidine installation and cyclization with an adjacent ester to yield (4H)-imidazolone products. Using amino acid building blocks, we can access the first examples of α-chiral imidazolones that have been previously inaccessible. Additionally, our method is amenable to on-resin installation which can be seamlessly integrated into existing solid-phase peptide synthesis protocols. Finally, we show that peptide imidazolones are potent cis-amide bond surrogates that preorganize linear peptides for head-to-tail macrocyclization. This work represents the first general approach to the backbone and side-chain insertion of imidazolone bioisosteres at various positions in linear and cyclic peptides.

Mechanisms of acrylamide biosorption by Lactobacillus plantarum ATCC8014 peptidoglycan

This study extracted peptidoglycan (PG) from Lactobacillus plantarum ATCC8014, its acrylamide (AA) adsorption behavior was evaluated by creating adsorption models, and its binding characterizations were investigated by physicochemical methods. The kinetics and isothermal model revealed that the biosorption of AA by PG conformed to Langmuir, Freundlich equations, and the second-order kinetic model, confirming that the adsorption process involved both physisorption and chemisorption. Fourier transform infrared spectroscopy and chemical blocking of functional groups confirmed that carboxyl, amino and hydroxyl groups were involved. Meanwhile, a new peak was generated in the proton nuclear magnetic resonance spectrum of PG upon adsorption, and the water contact angle was significantly reduced, indicating that hydrogen bonds and hydrophobic force were involved in the biosorption. Besides, energy dispersive spectroscopy and X-ray photoelectron spectroscopy results have important findings, suggesting that amide bonds might be formed during the adsorption process. Subsequently, this speculation was confirmed by the identification results of amidase. Overall, our results indicated that the mechanism of adsorption is complex and involves hydrogen bonding, hydrophobic forces and the formation of chemical bonds.

Interaction of melanoidins, proline, and valine with sorbents of various nature

The isolation of pure amino acids from industrial solutions is one of the important tasks of production. Solutions of amino acids obtained as a result of chemical or microbiological treatment contain a number of impurities, mostly organic ones. The microbiological synthesis of proline is accompanied by the presence of valine, leucine, alanine, and coloured high-molecular components in the culture liquid that belong to the melanoidin group. Melanoidins of proline acid production are high-molecular compounds containing amino acid fragments, heterocyclic structures, and amide bonds. Melanoidins in solutions can exist in cationic, bipolar, and anionic forms. They have different molecular weights, molecular sizes, and isoelectric states. Various ion exchange methods can be used to isolate the target amino acid. It should be noted that the interaction of amino acids with ion-exchange materials is a complex process depending on the electrolytic properties of the sorbate and sorbent and accompanied by multiple side effects. It is necessary to know the specific features of interaction in the “amino acid - sorbent” system and the factors that affect the transport of sorbate ions in the sorbent phase when choosing an isolation method for the target product. The goal of this work was to determine the impact of pH on the sorption process of proline and valine by high-basic ion exchangers, to identify the features of their interactions, and to use the obtained results to optimise the conditions for the separation of amino acids. We studied the process of interaction of bipolar ions and anions of proline (Pro±, Pro-) and valine (Val±, Val-) with anionites AV-17-8 and AV-17-2P. It was established that the mechanism of amino acid ion exchange in granular sorbents depended on the рН value in the “anionite - external solution” system. Based on the studied interactions, we suggested the methods of the anion-exchange separation of proline and valine. The selected conditions of separation of proline and valine were on anionite AV-17-2P in ОН-form (рН of the initial solution was 6.6-6.7; the solution flow rate was 2 cm3/min). The results of separation of proline and valine indicated that even in a one-step sorption process, five to seven fractions with proline contained no valine ions, while the concentration of proline was 2.0-2.7 times higher as compared to the original solution.

Photodynamic anticancer activity evaluation of novel 5-aminolevulinic acid and 3-hydroxypyridinone conjugates

5-Aminolevulinic acid (ALA) and its derivatives, serving as the endogenous precursor of the photosensitizer (PS) protoporphyrin IX (PpIX), successfully applied in tumor imaging and photodynamic therapy (PDT). ALA and its derivatives have been used to treat actinic keratosis (AK), basal cell carcinoma (BCC), and improve the detection of superficial bladder cancer. However, the high hydrophilicity of ALA and the conversion of PpIX to heme have limited the accumulation of PpIX, hindering the efficiency and potential application of ALA-PDT. This study aims to evaluate the PDT activity of three rationally designed series of ALA-HPO prodrugs, which were based on enhancing the lipophilicity of the prodrugs and reducing the labile iron pool (LIP) through HPO iron chelators to promote PpIX accumulation. Twenty-four ALA-HPO conjugates, incorporating amide, amino acid, and ester linkages, were synthesized. Most of the conjugates, exhibited no dark-toxicity to cells, according to bioactivity evaluation. Ester conjugates 19a-g showed promoted phototoxicity when tested on tumor cell lines, and this increased phototoxicity was strongly correlated with elevated PpIX levels. Among them, conjugate 19c emerged as the most promising (HeLa, IC50 = 24.25 ± 1.43 μM; MCF-7, IC50 = 43.30 ± 1.76 μM; A375, IC50 = 28.03 ± 1.00 μM), displaying superior photodynamic anticancer activity to ALA (IC50 > 100 μM). At a concentration of 80 μM, the fluorescence intensity of PpIX induced by compound 19c in HeLa, MCF-7, and A375 cells was 18.9, 5.3, and 2.8 times higher, respectively, than that induced by ALA. In conclusion, cellular phototoxicity showed a strong correlation with intracellular PpIX fluorescence levels, indicating the potential application of ALA-HPO conjugates in ALA-PDT.

Recent Advances in Polymers Bearing Activated Esters for the Synthesis of Glycopolymers by Postpolymerization Modification.

Glycopolymers are functional polymers with saccharide moieties on their side chains and are attractive candidates for biomaterials. Postpolymerization modification can be employed for the synthesis of glycopolymers. Activated esters are useful in various fields, including polymer chemistry and biochemistry, because of their high reactivity and ease of reaction. In particular, the formation of amide bonds caused by the reaction of activated esters with amino groups is of high synthetic chemical value owing to its high selectivity. It has been employed in the synthesis of various functional polymers, including glycopolymers. This paper reviews the recent advances in polymers bearing activated esters for the synthesis of glycopolymers by postpolymerization modification. The development of polymers bearing hydrophobic and hydrophilic activated esters is described. Although water-soluble activated esters are generally unstable and hydrolyzed in water, novel polymer backbones bearing water-soluble activated esters are stable and useful for postpolymerization modification for synthesizing glycopolymers in water. Dual postpolymerization modification can be employed to modify polymer side chains using two different molecules. Thiolactone and glycine propargyl esters on the polymer backbone are described as activated esters for dual postpolymerization modification.

Molecular Insights into Sequence-Specific Protein Hydrolysis by a Soluble Zirconium-Oxo Cluster Catalyst.

The development of catalysts for controlled fragmentation of proteins is a critical undertaking in modern proteomics and biotechnology. {Zr6O8}-based metal-organic frameworks (MOFs) have emerged as promising candidates for catalysis of peptide bond hydrolysis due to their high reactivity, stability, and recyclability. However, emerging evidence suggests that protein hydrolysis mainly occurs on the MOF surface, thereby questioning the need for their highly porous 3D nature. In this work, we show that the discrete and water-soluble [Zr6O4(OH)4(CH3CO2)8(H2O)2Cl3]+ (Zr6) metal-oxo cluster (MOC), which is based on the same hexamer motif found in various {Zr6O8}-based MOFs, shows excellent activity toward selective hydrolysis of equine skeletal muscle myoglobin. Compared to related Zr-MOFs, Zr6 exhibits superior reactivity, with near-complete protein hydrolysis after 24 h of incubation at 60 °C, producing seven selective fragments with a molecular weight in the range of 3-15 kDa, which are of ideal size for middle-down proteomics. The high solubility and molecular nature of Zr6 allow detailed solution-based mechanistic/interaction studies, which revealed that cluster-induced protein unfolding is a key step that facilitates hydrolysis. A combination of multinuclear nuclear magnetic resonance spectroscopy and pair distribution function analysis provided insight into the speciation of Zr6 and the ligand exchange processes occurring on the surface of the cluster, which results in the dimerization of two Zr6 clusters via bridging oxygen atoms. Considering the relevance of discrete Zr-oxo clusters as building blocks of MOFs, the molecular-level understanding reported in this work contributes to the further development of novel catalysts based on Zr-MOFs.

Lysine-Polydopamine Nanocrystals Loaded with the Codrug Abemaciclib-Flurbiprofen for Oral Treatment of Cancer.

Nonsteroidal anti-inflammatory drugs (NSAIDs) combined with chemotherapeutic agents for the treatment of colorectal cancer (CRC) are a promising therapeutic strategy. NSAIDs can effectively boost the antitumor efficacy of chemotherapeutic agents by inhibiting the synthesis of COX-2. However, hazardous side effects and barriers to oral drug absorption are the main challenges for combination therapy with chemotherapeutics and NSAIDs. To address these issues, a safe and effective lysine-polydopamine@abemaciclib-flurbiprofen (Flu) codrug nanocrystal (Lys-PDA@AF NCs) was designed. Abemaciclib (Abe), a novel and effective inhibitor of the CDK4/6 enzyme, and Flu were joined to prepare Abemaciclib-Flu codrug (AF) by amide bonds, and then the AF was made into nanocrystals. Lysine-modified polydopamine was selected as a shell to encapsulate nanocrystals to enhance intestinal adhesion and penetration and lengthen the duration time of drugs in vivo. Nuclear magnetic resonance, Fourier transform infrared, Massspectrometry, X-ray photoelectron spectroscopy, Transmission electron microscopy, and drug loading were used to evaluate the physicochemical characteristics of the nanocrystals. In our study, Abe and Flu were released to exert their synergistic effect when the amide bond of AF was broken and the amide bond was sensitive to cathepsin B which is overexpressed in most tumor tissues, thus increasing the selectivity of the drug to the tumor. The results showed that Lys-PDA@AF NCs had higher cytotoxicity for CRC cell with an IC50 of 4.86 μg/mL. Additionally, pharmacokinetics showed that Abe and Flu had similar absorption rates in the Lys-PDA@AF NCs group, improving the safety of combination therapy. Meanwhile, in vivo experiments showed that Lys-PDA@AF NCs had excellent antitumor effects and safety. Overall, it was anticipated that the created Lys-PDA@AF NCs would be a potential method for treating cancer.