Structural features of procyanidin interactions with salivary proteins

Procyanidin dimers and trimer C1 were synthesized, whereas (-)-epicatechin O-gallate and B2-3"-O-gallate were isolated from grape seeds. Human saliva was separated into two fractions. One of these was mainly alpha-amylase and the other mainly proline-rich proteins (PRPs). The procyanidin compounds were combined with each of the saliva protein fractions and with bovine serum albumin. The protein-polyphenol interactions were observed using nephelometry. (+)-Catechin had a higher tannin specific activity (TSA) for PRPs than (-)-epicatechin (1.45 versus 0.65 nephelos turbidity units/mg of polyphenol). This indicated the effect of the stereochemistry of flavan-3-ols on their interaction with proteins. Procyanidin dimers linked through a C(4)-C(8) interflavanoid bond had consistently greater TSA than their counterparts with a C(4)-C(6) linkage. Esterification of a galloyl group to the C(3) hydroxyl function of (-)-epicatechin or to the epicatechin moiety of procyanidin dimer B2 increased TSA. This was not as strong an effect for the dimer, probably as a result of the expected "closed" structure of B2-3"-O-gallate.

Peracetylation as a means of enhancing in vitro bioactivity and bioavailability of epigallocatechin-3-gallate

(-)-Epigallocatechin-3-gallate (EGCG) is the widely studied catechin in green tea (Camellia sinensis). Previously, we have reported the low bioavailability of EGCG in rats and mice. As a means of improving the bioavailability of EGCG, we have prepared a peracetylated EGCG derivative (AcEGCG) and herein report its growth inhibitory activity and cellular uptake in vitro, as well as bioavailability in mice. AcEGCG exhibited enhanced growth inhibitory activity relative to EGCG in both KYSE150 human esophageal (IC50 = 10 versus 20 microM) and HCT116 human colon cancer cells (IC50 = 32 versus 45 microM). AcEGCG was rapidly converted to EGCG by HCT116 cells, and treatment of cells with AcEGCG resulted in a 2.8- to 30-fold greater intracellular concentration of EGCG as compared with treatment with EGCG. AcEGCG was also more potent than EGCG at inhibiting nitric oxide production (4.4-fold) and arachidonic acid release (2.0-fold) from lipopolysaccharide-stimulated RAW264.7 murine macrophages. Intragastric administration of AcEGCG to CF-1 mice resulted in higher bioavailability compared with administration of equimolar doses of EGCG. The plasma area under the curve from 0 to infinity (AUC0-->infinity) of total EGCG was 465.0 and 194.6 [(microg/ml) . min] from the administration of AcEGCG and EGCG, respectively. The t1/2 of EGCG was also increased following administration of AcEGCG compared with EGCG (441.0 versus 200.3 min). The AUC0-->infinity and t1/2 were also increased in small intestinal (2.8- and 4.3-fold, respectively) and colonic tissues (2.4- and 6.0-fold, respectively). These data suggest that acetylation represents a means of increasing the biological potency in vitro, increasing the bioavailability of EGCG in vivo, and may improve cancer-preventive activity.

Studies in polyphenol chemistry and bioactivity. 4.(1) Synthesis of trimeric, tetrameric, pentameric, and higher oligomeric epicatechin-derived procyanidins having all-4beta,8-interflavan connectivity and their inhibition of cancer cell growth through cell cycle arrest

We report an improved synthesis of bis(5,7,3',4'-tetra-O-benzyl)epicatechin 4beta,8-dimer (3) from 5,7,3',4'-tetra-O-benzylepicatechin (1) and 5,7,3',4'-tetra-O-benzyl-4-(2-hydroxyethoxy)epicatechin (2) by replacing the previously employed Lewis acid, titanium tetrachloride, with the clay mineral Bentonite K-10. Under the same conditions, the benzyl-protected all-4beta,8-trimer, -tetramer, and -pentamer were obtained regioselectively from their lower homologues, albeit in rapidly decreasing yields. Reaction of 2 with an organoaluminum thiolate generated from 2-mercaptobenzothiazole and trimethylaluminum followed by acetylation produced 3-O-acetyl-4-[(2-benzothiazolyl)thio]-5,7,3',4'-tetra-O-benzylepicatechin (12). Medium-sized protected oligomers with 4beta,8-interflavan linkages are obtained in improved yields by using this compound as the electrophile and silver tetrafluoroborate as activator and are isolated by reversed-phase HPLC. Their deprotection by ester saponification followed by hydrogenolysis yielded the free procyanidins, which were characterized as their peracetates. The synthetic procyanidins are identical by normal-phase HPLC with fractions isolated from cocoa. The principle of chain extension by two members was demonstrated using a dimeric electrophile obtained by self-condensation of compound 12. Both the synthetic and natural pentamer 32 inhibit the growth of several breast cancer cell lines. Using the MDA MB 231 line, it was established that this outcome is based on the induction of cell cycle arrest in the G0/G1 phase. Subsequent cell death is more likely necrotic rather than apoptotic. Control experiments demonstrate that the polyphenol itself, rather than hydrogen peroxide potentially formed by its autoxidation, is the causative agent.

Enantioselective synthesis of epigallocatechin-3-gallate (EGCG), the active polyphenol component from green tea

[reaction: see text]. Enantioselective synthesis of epigallocatechin-3-gallate (EGCG, 3b), the active polyphenol component from green tea, has been achieved by using a stereospecific cyclization of the Sharpless asymmetric dihydroxylation product 7c as the key step.

Synthesis of (-)-[4-3H]epigallocatechin gallate and its metabolic fate in rats after intravenous administration

Because a great deal of attention has been focused on the metabolism of (-)-epigallocatechin gallate (EGCg), quantitative analysis of this compound is required. For this purpose we developed a method of chemical synthesis of [4-(3)H]EGCg. Synthesized [4-(3)H]EGCg showed 99.5% radiochemical purity and a specific activity of 13 Ci/mmol. To clarify the excretion route of EGCg, the radioactivity levels of bile and urine were quantified after intravenous administration of [4-(3)H]EGCg to bile-duct-cannulated rats. Results showed that the radioactivity of the bile sample excreted within 48 h accounted for 77.0% of the dose, whereas only 2.0% of the dose was recovered in the urine. The excretion ratio of bile to urine was calculated to be about 97:3. These results clearly showed that bile was the major excretion route of EGCg. Time-course analysis of the radioactivity in blood was also performed to estimate the pharmacokinetic parameters following intravenous administration of [4-(3)H]EGCg. In addition, EGCg metabolites excreted in the bile within 4 h after the intravenous dose of [4-(3)H]EGCg were analyzed by HPLC. The results showed that 4',4"-di-O-methyl-EGCg was present in the conjugated form and made up about 14.7% of the administered radioactivity.

Flavonoids: hemisynthesis, reactivity, characterization and free radical scavenging activity

Phenolic compounds form one of the main classes of secondary metabolites. They display a large range of structures and they are responsible for the major organoleptic characteristics of plant-derived-foods and beverages, particularly color and taste properties and they also contribute to the nutritional qualities of fruits and vegetables. Phenolic compounds are also highly unstable compounds which undergo numerous enzymatic and chemical reactions during postharvest food storage and processing thus adding to the complexity of plant polyphenol composition. Among these compounds flavonoids constitute one of the most ubiquitous groups of all plant phenolics. Owing to their importance in food organoleptic properties and in human health, a better understanding of their structures, their reactivity and chemical properties in addition to the mechanisms generating them appears essential to predict and control food quality. The purpose of this work is an overview of our findings concerning the hemisynthesis, the reactivity and the enzymatic oxidation of some flavonoids and shed light on the mechanisms involved in some of these processes and the structures of the resulting products. The free radical scavenging activity of some of the synthesized compounds is also presented and a structure-activity relationship is discussed. The first part of this review concerns the synthesis and structural characterization of modified monomeric flavanols. The use of these compounds as precursor for the preparation of natural and modified dimeric procyanidin derivatives was then explored through different coupling reactions. The full characterization of the synthesized compounds was achieved by concerted use of NMR and ESI-MS techniques. The free radical scavenging activity of some of the synthesized compounds was investigated. The second part of this review concerns the enzymatic oxidation of several flavonols by Trametes versicolor laccase. Most of the major oxidation products have been isolated as pure compounds and their structures unambiguously established through spectroscopic methods. Correlation between the structure of the oxidation product and the substitution pattern of the starting materials allows mechanistic features of this transformation to be elucidated.

The challenge of developing green tea polyphenols as therapeutic agents

The health benefits of green tea and its main constituent (-)-epigallocatechin gallate [(-)-EGCG] have been widely supported by results from epidemiological, cell culture, animal and clinical studies. On the other hand, there are a number of issues, such as stability, bioavailability and metabolic transformations under physiological conditions, facing the development of green tea polyphenols into therapeutic agents. We previously reported that the synthetic peracetate of (-)-EGCG has improved stability and better bioavailability than (-)-EGCG itself and can act as pro-drug under both in vitro and in vivo conditions. Analogs of catechins have been synthesized and their structure activity relationship provides an understanding to the mechanism of proteasome inhibition. Metabolic methylation of catechins leading to methylated (-)-EGCG may alter the biological activities of these compounds.

Targeted intracellular protein delivery based on hyaluronic acid-green tea catechin nanogels

A novel ternary nanogel based on the self-assembly of hyaluronic acid-epigallocatechin gallate conjugates (HA-EGCG), linear polyethylenimine (PEI) and Granzyme B (GzmB) in an aqueous environment was developed for the targeted intracellular delivery of GzmB into cancer cells. Lysozyme-encapsulated HA-EGCG nanogels were first prepared and characterized. HA-EGCG nanogels exhibited smaller particle sizes and a more homogeneous size distribution than the HA counterpart. Fluorescence quenching and lysozyme activity studies revealed that EGCG moieties facilitated protein binding through physical interactions and led to the formation of stable nanogels. When CD44-overexpressing HCT-116 colon cancer cells were treated with GzmB-encapsulated HA-EGCG nanogels in vitro, a significant cytotoxic effect was observed. Caspase assays and intracellular trafficking studies confirmed that cell death was due to apoptosis triggered by the delivery of GzmB to the cytosol of those cells. In comparison, little cytotoxic effect was observed in CD44-deficient cells treated with GzmB-encapsulated HA-EGCG nanogels. This study highlights the potential utility of HA-EGCG as effective intracellular protein carriers for targeted cancer therapy.

STATEMENT OF SIGNIFICANCE

Intracellularly activated cytotoxic proteins can be used to kill cancer cells but viable carriers for such proteins are lacking. In this work, we developed novel nanogels based on selfassembly of hyaluronic acid (HA)-(-)-epigallocatechin-3-gallate (EGCG) conjugates, linear polyethylenemine (PEI) and the cytotoxic protein Granzyme B (GzmB) for the intracellular delivery of GzmB for cancer therapy. HA was exploited for its ability to target CD44 which are overexpressed in many types of cancer cells, while EGCG, the main component of green tea catechins, was chosen for its ability to bind to proteins. Characterization studies showed that EGCG facilitated protein complexation through physical interactions and led to the formation of stable nanogels. HA-EGCG nanogels were able to achieve CD44 targeted killing of HCT-116 cancer cells by delivering GzmB into the cytosol of these cells. We believe that the applications of the HA-EGCG nanogels can be expanded to the intracellular delivery of other cytotoxic protein drugs for cancer therapy.

Oligomeric catechins: an enabling synthetic strategy by orthogonal activation and C(8) protection

Controlled formation of oligomeric catechins has become possible by an orthogonal synthetic strategy. Bromo-capping of the C(8) position of the flavan skeleton enabled the equimolar coupling of electrophilic and nucleophilic catechin derivatives, enabling an efficient synthetic strategy to complex catechin oligomers.

Novel enzymatic approach to the synthesis of flavonoid glycosides and their esters

Flavonoids such as (+)catechin can be efficiently solubilised in supersaturated solutions prepared with donor glycosides, e.g., p-nitrophenyl glycosides, di- and higher oligosaccharides, and poly(ethylene glycol) dimethyl ether in sufficiently high concentration for their efficient enzymatic glycosylation. Under these conditions several glycosidases readily accept (+)catechin as substrate and the target glycosides were prepared in one step in up to 26% yields. The regioselectivity of the reaction depends on the enzyme and substrate combination used; three positions, 5, 7, and 4', in the flavonoid can be glycosylated. The resulting and similar flavonoid glycosides were further modified by regioselective acylation with vinyl esters of arylpropenoic acids using lipases as biocatalyst. The efficiency of acylation was found to diminish in the order of vinyl cinnamate > vinyl ferulate > vinyl coumarate. This work demonstrates the feasibility of assembling complex flavonoid glycoside esters in just two steps by sequential use of commercially available glycosidases and lipases.

Planar Catechin Analogues with Alkyl Side Chains: A Potent Antioxidant and an α-Glucosidase Inhibitor

Planar catechin analogues having various alkyl side chain lengths were synthesized, and their remarkable antioxidative abilities and alpha-glucosidase inhibitory activities are shown.

Enzymatic synthesis and antioxidant property of gelatin-catechin conjugates

Gelatin-catechin conjugate was synthesized by the laccase-catalyzed oxidation of catechin in the presence of gelatin. The conjugate had a good scavenging activity against superoxide anion radicals. Moreover, the conjugate showed an amplified inhibition effect on human low density lipoprotein oxidation initiated by 2,2'-azobis(2-amidinopropane)dihydrochloride as a radical generator.

Study of the green tea polyphenols catechin-3-gallate (CG) and epicatechin-3-gallate (ECG) as proteasome inhibitors

The green tea polyphenol catechin-3-gallate (CG) and epicatechin-3-gallate (ECG) were synthesized enantioselectively via a Sharpless hydroxylation reaction followed by a diastereoselective cyclization. Their potencies to inhibit the proteasome activity were measured. The unnatural enantiomers were found to be equally potent to the natural compounds.

Synthesis of a 3,4,5-trimethoxybenzoyl ester analogue of epigallocatechin-3-gallate (EGCG): a potential route to the natural product green tea catechin, EGCG

The synthesis of a trimethoxybenzoyl ester (D-ring) analogue of epigallocatechin-3-gallate (EGCG) is described. The versatile synthesis route can be used to synthesize A, B, and D ring analogues of EGCG and involves a key cyclization of the chalcone to the 3-flavene. This synthesis provides a possible route to the polyphenolic green tea natural product EGCG.

Chemical studies of the antioxidant mechanism of tea catechins: radical reaction products of epicatechin with peroxyl radicals

Tea catechins, an important class of polyphenols, have been shown to have antioxidant activity and are thought to act as antioxidants in biological systems. However, the mechanisms of their antioxidant reactions remain unclear. The objective of this study was to characterize the reaction products of epicatechin with peroxyl radicals generated by thermolysis of the azo initiator azo-bisisobutyrylnitrile (AIBN). Structural elucidation of these products can provide insights into specific mechanisms of antioxidant reactions. Eight reaction products were isolated and identified using high-field 1D and 2D NMR spectral analysis. The observation of these compounds confirmed that the B-ring is the initial site for formation of reaction products in the peroxyl radical oxidant system.

Biological evaluation of anti-influenza viral activity of semi-synthetic catechin derivatives

Catechin derivatives with different alkyl chain length and aromatic ring substitutions at the 3-hydroxyl group were synthesized from epigallocatechin (EGC) and (+)-catechin (C) and their anti-influenza viral activity were evaluated in vitro and in ovo. Pronounced antiviral activity was observed for derivatives carrying moderate chain length (7-9 carbons) as compared to those with aromatic rings, whereas the 5'-hydroxyl group of the trihydroxy benzyl moiety did not significantly contribute to antiviral activity. The derivatives exerted inhibitory effects for all six influenza subtypes tested including three major types of currently circulating human influenza viruses (A/H1N1, A/H3N2 and B type), H2N2 and H9N2 avian influenza virus. The compounds strongly inhibited adsorption of the viruses on red blood cell (RBC). They also restricted the growth of avian influenza virus in ovo with minimum inhibition concentration (MIC) of 5-10 microM far exceeding the neuraminidase (NA) inhibitor oseltamivir or M2 proton channel inhibitor amantadine. The antiviral activity appears to be mediated by interaction with hemagglutinin (HA)/viral membrane rendering HA less fusogenic at the initial stage of infection. The broad spectrum activity against various subtypes of influenza viruses may complement the limitations of current antivirals and contribute for managing potentially emerging influenza pandemic. The structure-activity data of catechin derivatives may usefully guideline future research endeavors for applying green tea catechins as alternative anti-viral agents.

Preparation and characterization of catechin sulfates, glucuronides, and methylethers with metabolic interest

Catechins are major polyphenols in many plant foods that have been related to health promotion. In the human organism they are largely metabolized to different conjugates (sulfates, glucuronides, and methylethers), which are further found in plasma and would contribute to the biological effects associated with the intake of the parent compounds. Circulating metabolites are likely to possess biological properties different from those of the original compounds, and therefore, it is important to evaluate their activity, for which sufficient amounts of them are required that cannot be obtained by isolation from biological fluids. This paper describes the preparation of the methyl, sulfate, and glucuronide derivatives of catechins using different chemical syntheses and their characterization by HPLC-DAD-ESI/MS. MS2 fragmentation of the compounds was also described that allowed the determination of the location of the different substituents on the catechin aglycones. The procedures optimized allowed the preparation of (epi)catechin sulfates, glucuronides, and methylethers conjugated at positions 3' and 4', as well as the sulfates at positions 5 and 7 with satisfactory yields for their further isolation by semipreparative-HPLC in view of their use in in vitro/ex vivo assays.

Systematic synthesis of four epicatechin series procyanidin trimers and their inhibitory activity on the Maillard reaction and antioxidant activity

A systematic synthesis of four natural epicatechin series procyanidin trimers [[4,8:4",8"]-2,3-cis-3,4-trans: 2",3"-cis-3",4"-trans: 2,3-trans-(-)-epi-catechin-(-)-epicatechin-(+)-catechin, [4,8:4",8"]-2,3-cis-3,4-trans: 2",3"-cis-3",4"-trans: 2,3-cis-tri-(-)-epicatechin: procyanidin C1, [4,8:4",8"]-2,3-cis-3,4-trans: 2",3"-trans-3",4"-trans: 2,3-trans-(-)-epicatechin-(+)-catechin-(+)-catechin: procyanidin C4, and [4,8:4",8"]-2,3-cis-3,4-trans: 2",3"-trans-3",4"-trans: 2,3-cis-(-)-epicatechin-(+)-catechin-(-)-epicatechin] is described. Condensation of (2R,3R,4S)-5,7,3'4'-tetra-O-benzyl-4-(2"-ethoxyethyloxy)flavan derived from (-)-epicatechin as an electrophile with the dimeric nucleophiles in the presence of TMSOTf followed by deprotection yielded trimers. Inhibitory activities on the Maillard reaction and antioxidant activity on lipid peroxide of the synthesized oligomers were also investigated.

Inhibition by apple polyphenols of ADP-ribosyltransferase activity of cholera toxin and toxin-induced fluid accumulation in mice

The effects of crude polyphenol extracted from immature apples on the enzymatic and biological activities of a cholera toxin (CT) were investigated. When the apple polyphenol extract (APE) was examined for properties to inhibit CT-catalyzed ADP-ribosylation of agmatine, it was found that APE inhibited it in a dose-dependent manner. The concentration of APE to inhibit 50% of the enzymatic activity of CT (15 microg/ml) was approximately 8.7 microg/ml. The APE also diminished CT-induced fluid accumulation in two diarrhea models for in vivo mice. In the ligated ileum loops, 25 microg of APE significantly inhibited fluid accumulation induced by 500 ng of CT. In a sealed mouse model, even when APE was administered orally 10 min after a toxin injection, fluid accumulation was significantly inhibited at a comparable dosage. Lineweaver-Burk analysis demonstrated that APE had negative allosteric effects on CT-catalyzed NAD: agmatine ADP-ribosyltransferase. We fractionated the APE into four fractions using LH-20 Sephadex resin. One of the fractions, FAP (fraction from apple polyphenol) 1, which contains non-catechin polyphenols, did not significantly inhibit the CT-catalyzed ADP-ribosylation of agmatine. FAP2, which contains compounds with monomeric, dimeric, and trimeric catechins, inhibited the ADP-ribosylation only partially, but significantly. FAP3 and FAP4, which consist of highly polymerized catechin compounds, strongly inhibited the ADP-ribosylation, indicating that the polymerized structure of catechin is responsible for the inhibitory effect that resides in APE. The results suggest that polymerized catechin compounds in APE inhibit the biological and enzymatic activities of CT and can be used in a precautionary and therapeutic manner in the treatment of cholera patients.

Systematic synthesis of galloyl-substituted procyanidin B1 and B2, and their ability of DPPH radical scavenging activity and inhibitory activity of DNA polymerases

Six galloyl-substituted procyanidin B1 and B2, 3-O-gallate, 3''-O-gallate, and 3,3''-di-O-gallate, were systematically synthesized with the condensation method using TMSOTf as a catalyst. Their ability of DPPH radical scavenging activity and DNA polymerase inhibitory activity were also investigated. The results indicated that the galloyl group of these compounds is very important for both activities. 3,3''-Di-O-gallate dimers acted as strong inhibitor against DNA polymerase alpha and beta, whereas the desgalloyl and monogalloyl compounds did not exhibit any appreciable inhibitory activity against the DNA polymerase beta.

Synthesis and antioxidant activity of novel amphipathic derivatives of tea polyphenol

Hydrophobic derivatives of a tea polyphenol have been synthesized. 6, 8-Bis(octylthiomethyl)-epigallocatechin 3-O-gallate, 6, 8-bis(octylthiomethyl)-4 beta-(2-hydroxyethylthio)epigallocatechin 3-O-gallate and epigallocatechin 3-O-[4-O-(N-octadecylcarbamoyl)gallate] showed strong inhibition activity against lipid peroxidation of liposome caused by both lipid-soluble and water-soluble radical generators.

Proteasome inhibition in human breast cancer cells with high catechol-O-methyltransferase activity by green tea polyphenol EGCG analogs

A pro-drug 8 of a synthetic analog 7 is more active in its antiproliferative activity against human breast cancer MDA-MB-231 cells possessing high catechol-O-methyltransferase (COMT) activity than the pro-drugs of EGCG and the analog 5. The higher activity of 8 is attributed to it not being a substrate of COMT.

Designing small, nonsugar activators of antithrombin using hydropathic interaction analyses

Conformational activation of antithrombin is a critical mechanism for the inhibition of factor Xa, a proteinase of the blood coagulation cascade, and is typically achieved with heparin, a polyanionic polysaccharide clinically used for anticoagulation. Although numerous efforts have been directed toward the design of better activators, a fundamental tenet of these studies has been the assumed requirement of an oligo- or a polysaccharide backbone. We demonstrate here a concept that small nonsaccharidic nonpolymeric molecules may be rationally designed to interact with and activate antithrombin for enhanced inhibition of factor Xa. The rational design strategy is based on a study of complexes of natural and mutant antithrombins with heparin-based oligosaccharides using hydropathic interaction (HINT) technique, a quantitative computerized tool for analysis of molecular interactions. A linear correlation was observed between the free energy of binding for antithrombinminus signoligosaccharide complexes and the HINT score over a wide range of approximately 13 kcal/mol, indicating strong predictive capability of the HINT technique. Using this approach, a small, nonsugar, aromatic molecule, (minus sign)-epicatechin sulfate (ECS), was designed to mimic the nonreducing end trisaccharide unit DEF of the sequence specific heparin pentasaccharide DEFGH. HINT suggested a comparable antithrombin-binding geometry and interaction profile for ECS and trisaccharide DEF. Biochemical studies indicated that ECS binds antithrombin with equilibrium dissociation constants of 10.5 and 66 microM at pH 6.0, I 0.025, and pH 7.4, I 0.035, respectively, that compare favorably with 2 and 80 microM observed for the natural activator DEF. ECS accelerates the antithrombin inhibition of factor Xa nearly 8-fold demonstrating for the first time that conformational activation of antithrombin is feasible with appropriately designed small nonsugar organic molecules. The results present unique opportunities for de novo activator design based on this first-generation lead.

Mg(II)-Catechin nanoparticles delivering siRNA targeting EIF5A2 inhibit bladder cancer cell growth in vitro and in vivo

Emerging evidence indicates that combination of two or more therapeutic strategies can synergistically enhance antitumor activity in cancer therapy. Here, we established a green method of generating nanocomposite particles that can be fabricated using catechin, a natural anti-cancer compound from green tea, and Mg(2+) in an easy one-step approach at room temperature. We show that Mg(II)-Catechin nanocomposite particles (Mg(II)-Cat NPs) have good biocompatibility and high cellular uptake also can load and effectively deliver small interfering RNA (siRNA) into cells in vitro and to tumor site in vivo. Mg(II)-Cat NPs by themselves had tumor-suppression effects. When complexed with siRNA that targets oncogene eukaryotic translation initiation factor 5A2 (EIF5A2), Mg(II)-Cat/siEIF5A2 complex had further enhanced anti-tumor activity. Mechanistically, we show that Mg(II)-Cat/siEIF5A2 inhibits oncogenic PI3K/Akt signal pathway. More importantly, Mg(II)-Cat/siEIF5A2 had tumor suppression effect in a clinically-relevant rat in-situ bladder cancer model. Our studies demonstrated that combination of Mg(II)-Cat NPs and siRNA is a promising therapeutic modality of combining chemotherapy with gene therapy in order to afford higher therapeutic efficacy and provided a proof of principle for such modality in a pre-clinical setting.

Duo of (-)-epigallocatechin-3-gallate and doxorubicin loaded by polydopamine coating ZIF-8 in the regulation of autophagy for chemo-photothermal synergistic therapy

To achieve highly systemic therapeutic efficacy, chemotherapy is combined with photothermal therapy for chemo-photothermal synergistic therapy; however, this strategy suffers from high toxicity and unsatisfactory sensitivity for cancer cells. Herein, we developed a pH- and photothermal-responsive zeolitic imidazolate framework (ZIF-8) compound for loading a dual-drug in the tumor site and improving their curative effects. Since autophagy always accompanies tumor progression and metastasis, there is an unmet need for an anticancer treatment related to the regulation of autophagy. Green tea polyphenols, namely, (-)-epigallocatechin-3-gallate (EGCG) and doxorubicin (DOX), both of which exhibit anticancer activity, were dual-loaded via polydopamine (PDA) coating ZIF-8 (EGCG@ZIF-PDA-PEG-DOX, EZPPD for short) through hierarchical self-assembly. PDA could transfer photothermal energy to increase the temperature under near-infrared (NIR) laser irradiation. Due to its pH-response, EZPPD released EGCG and DOX in the tumor microenvironment, wherein the temperature increased with the help of PDA and NIR laser irradiation. The duo of DOX and EGCG induced autophagic flux and accelerated the formation of autophagosomes. In a mouse HeLa tumor model, photothermal-chemotherapy could ablate the tumor with a significant synergistic effect and potentiate the anticancer efficacy. Thus, the results indicate that EZPPD renders the key traits of a clinically promising candidate to address the challenges associated with synergistic chemotherapy and photothermal utilization in antitumor therapy.