Kwang-su Park

In vitro solubility, stability and permeability of novel quercetin-amino acid conjugates.

In order to discover a quercetin prodrug with improved bioavailability, we synthesized nine quercetin-amion acid conjugates and estimated their pharmacokinetic properties including water solubility, stability against chemical or enzymatic hydrolysis, and cell permeability. Among the synthesized quercetin prodrugs, quercetin-glutamic acid conjugate Qu-E (4g/5g) showed remarkable increases in water solubility, stability, and cell permeability compared with quercetin, which warrants further development as a quercetin prodrug.

Enhanced Stability and Intracellular Accumulation of Quercetin by Protection of the Chemically or Metabolically Susceptible Hydroxyl Groups with a Pivaloxymethyl (POM) Promoiety

In order to increase stability of quercetin, its metabolically and chemically susceptible hydroxyl groups 7-OH and 3-OH respectively were transiently blocked with a pivaloxymethyl (POM) promoiety to provide two novel quercetin conjugates [7-O-POM-Q, 3-O-POM-Q]. In the absence of stabilizer (ascorbic acid), the synthesized conjugates showed significantly increased stability in cell culture media [t(½) = 4 h, 52 h] compared with quercetin (t(½) < 30 min) and quercetin prodrug 1 (t(½) = 0.8 h). In addition, the quercetin conjugate 2 underwent efficient cellular uptake and intracellular levels of its hydrolysis product, quercetin, were maintained up to 12 h. Stability and intracellular accumulation of were demonstrated by its stabilizer-independent cytostatic effect and induction of apoptotic cell death. Even though was more stable than, it failed to penetrate cell membranes. However, the remarkable stability of warrants further investigation of quercetin conjugates with various promoieties at the 3-OH position.

Benzimidazole Derivatives as Potent JAK1-Selective Inhibitors.

The Janus kinase (JAK) family comprises four members (JAK1, JAK2, JAK3, and Tyk2) that play a key role in mediating cytokine receptor signaling. JAK inhibition thus modulates cytokine-mediated effects. In particular, selective inhibition of JAK1 or JAK3 may provide an efficient therapeutic agent for the treatment of inflammatory diseases, with minimized side effects. In this study, as part of our continued efforts to develop a selective JAK1 inhibitor, a series of 1,2-disubstituted benzimidazole-5-carboxamide derivatives was prepared and their inhibitory activities against all four JAK isozymes were evaluated. A clear structure-activity relationship was observed with respect to JAK1 selectivity; this highlighted the importance of hydrogen bond donors at both N(1) and R2 positions located within a specific distance from the benzimidazole core. One of the synthesized compounds, 1-(2-aminoethyl)-2-(piperidin-4-yl)-1H-benzo[d]imidazole-5-carboxamide (5c), showed remarkable JAK1 selectivity (63-fold vs JAK2, 25-fold vs JAK3, and 74-fold vs Tyk2). Molecular docking revealed that the 2-aminoethyl and piperidin-4-yl substituents of 5c function as probes to differentiate the ATP-binding site of JAK1 from that of JAK2, resulting in preferential JAK1 binding. A kinase panel assay confirmed the JAK1 selectivity of 5c, which showed no appreciable inhibitory activity against 26 other protein kinases at 10 μM.

7-O-Arylmethylgalangin as a novel scaffold for anti-HCV agents

In spite of potent antiviral activity, suboptimal physicochemical properties of aryl diketo acids (ADKs) necessitates modification of the core 1,3-diketo acid functionality into a novel scaffold. As the metal-binding affinity of the diketo acid is the key to the antiviral activity of ADKs, we anticipated 3,5-dihydroxy-4-oxo arrangement of galangin scaffold would serve as an excellent mimic for the diketo acid functionality. In this study, through synthesis and biological evaluation of various galangin derivatives, we have shown that the diketo acid functionality can be successfully replaced with the galangin scaffold by specific combination of the substituents to result in identification of a novel galangin derivative (3s) with anti-HCV activity (EC(50)=0.9 μM) comparable to the ADK counterpart.

Facilitation of polymerase chain reaction with thermostable inorganic pyrophosphatase from hyperthermophilic archaeon Pyrococcus horikoshii

An inorganic pyrophosphatase (PPases) was cloned from the hyperthermophilic archaeon Pyrococcus horikoshii and was expressed in and purified from Escherichia coli. The recombinant inorganic pyrophosphatase (PhPPase) exhibited robust catalytic activity of the hydrolysis of pyrophosphate into two orthophosphates at high temperatures (70°C to 95°C). Thermostable pyrophosphatase activity was applied into polymerase chain reaction (PCR) due to its ability to push chemical equilibrium toward the synthesis of DNA by removing pyrophosphate from the reaction. A colorimetric method using molybdate and reducing agents was used to measure PCR progress by detecting and quantifying inorganic phosphate in the PhPPase-coupled PCR mixture. Compared to PCR mixtures without PhPPase, the thermostable PhPPase enhanced the amount of PCR product in the same number of cycles. Thus, thermostable PPase may overcome the limitations of thermodynamically unfavorable DNA polymerization in PCR by yielding more products.

Effects of the aryl linker and the aromatic substituent on the anti-HCV activities of aryl diketoacid (ADK) analogues

Based on our pharmacophore model of the aryl diketoacids (ADKs), we designed and prepared a series of novel ADK analogues, which showed potent inhibitory activities against the NS5B polymerase in the submicromolar range. Pharmacophore-guided docking study revealed that the antiviral activities of the ADKs are highly dependent upon the aryl linker as well as the size and position of the aromatic substituent. It is of another importance that, unlike previously reported ADKs, three ADK analogues synthesized in this study effectively blocked Hepatitis C Virus (HCV) replication in the replicon systems.

Quercetin-POM (pivaloxymethyl) conjugates: Modulatory activity for P-glycoprotein-based multidrug resistance.

BACKGROUND We previously demonstrated that the bioactivity of quercetin could be improved through conjugation with a hydrolysable pivaloxymethyl (POM) group. PURPOSE Present study aimed to evaluate MDR (multidrug resistance)-modulatory activity of the quercetin-POM conjugates. STUDY DESIGN/METHODS MDR-modulatory activity was determined by measuring cytotoxicity of various anticancer agents to MDR MES-SA/Dx5 cell lines upon combination with the quercetin-POM conjugates. RESULTS The quercetin-7-O-POM conjugate (7-O-POM-Q) was significantly more potent than quercetin in reversing MDR, which recovered the cytotoxicity of various anticancer agents with EC50 values of 1.1-1.3 µM. A series of mechanistic studies revealed that 7-O-POM-Q competes with verapamil in binding to the same drug-binding site of the major MDR target, Pgp (P-glycoprotein), and inhibits Pgp-mediated drug efflux with a similar potency as verapamil. The physicochemical properties of 7-O-POM-Q were then evaluated, which confirmed that 7-O-POM-Q has remarkably enhanced cellular uptake and intracellular localization compared with quercetin. Additionally, it is noteworthy that 7-O-POM-Q undergoes slow hydrolysis to quercetin over a prolonged period of time. CONCLUSION The quercetin-POM conjugate showed significantly improved MDR-reversing activity compared with quercetin, which could be attributed to its capacity to maintain high intracellular concentrations.

Remarkable Stability and Cytostatic Effect of a Quercetin Conjugate, 3,7-Bis-O-Pivaloxymethyl (POM) Quercetin

Quercetin (Q, 1) is a polyphenolic flavonoid that is readily found in human diet. The tremendous growth in the study of this bioactive compound has revealed numerous health-promoting effects, such as antioxidant, antiviral, 3] and anticancer activities. However, quercetin is unstable and undergoes oxidative decomposition in aqueous solution. As a result, the bioactivity of quercetin is often limited by its stability, and it is desirable to develop a method to increase quercetin stability. Many studies support the critical role of the free hydroxy group in the 3 position in the oxidative decomposition of quercetin. In our previous study, we introduced a pivaloxymethyl (POM) group to quercetin at this position and observed remarkable stability of the resulting 3-O-POM-Q (2). Quercetin–POM conjugate 2 showed very slow decomposition (t1/2=52 h) in a cell culture medium under conditions of high oxidative stress. This remarkably stable quercetin–POM conjugate, however, failed to show cytostatic effects against various cancer cell lines due to its inability to permeate the cell membrane. Conversely, 7-O-POM-Q (3) with the POM group attached to the hydroxy group in the 7 position of quercetin showed much faster hydrolysis and/or decomposition in cell culture medium (t1/2=4 h) compared with 3-O-POM-Q (2). However, unlike 3-O-POM-Q (2), 7-O-POM-Q (3) showed efficient cellular uptake and intracellular conversion to quercetin and its metabolites, which resulted in enhanced cytostatic effects against cancer cell lines compared with the parent compound, quercetin. We reasoned that the introduction of POM groups at both the 3and 7-hydroxys of quercetin would produce synergistic effects to provide a stable quercetin–POM conjugate with efficient cellular uptake and thereby significant cytostatic activity. Herein, we report the synthesis and biological evaluation of 3,7-bis-O-POM-Q (4). The synthesis of 4 was accomplished by nucleophilic substitution of the selectively protected quercetin, quercetin diphenylmethylketal (5), with excess amount of pivaloxymethyl iodide (POM-I) (Scheme 1). The stability of the quercetin–POM conjugates 2–4 was assessed in phosphate buffered saline (PBS; pH 7.4) and Dulbecco’s modified eagle medium supplemented with fetal bovine serum (cDMEM), and the results are summarized in Table 1 and Figure 1. The instability of quercetin in aerobic aqueous media such as PBS (t1/2=10 h, Table 1) and cDMEM (t1/2<30 min, Table 1) is well known. In contrast, 3,7-bis-O-POM-Q (4) is as stable as the previously reported quercetin–POM conjugates 2 and 3 (Table 1) against hydrolytic cleavage or oxidative decomposition in PBS. More intriguingly, in cDMEM, 3,7-bis-O-POM-Q (4) was even more stable (t1/2=100 h, Table 1) than conjugates 2 (t1/2=52 h, Table 1) and 3 (t1/2=4 h, Table 1). [10] High-performance liquid chromatography (HPLC) analysis of the cell culScheme 1. Synthesis of 3,7-bis-O-POM-Q (4). Reagents and conditions : a) Ph2CCl2, 180 8C, 30 min, 35%; b) POM-I, K2CO3, acetone, RT, 4 h; c) H2, Pd/ C, THF/MeOH (1:1), RT, 12 h, 63%.

Quercetin-POC conjugates: Differential stability and bioactivity profiles between breast cancer (MCF-7) and colorectal carcinoma (HCT116) cell lines.

In the course of our ongoing efforts to develop novel quercetin conjugates with enhanced stability profiles, we introduced an isopropyloxycarbonylmethoxy (POC) group to 7-OH and/or 3-OH of quercetin and prepared three novel quercetin conjugates. The quercetin-POC conjugates were stable up to 96 h in PBS but slowly hydrolyzed with half-lives of 1-54 h in cell-free culture medium, which is reminiscent of the stability profiles of the previously reported quercetin-POM (pivaloxymethyl) conjugates. However, the quercetin-POC conjugates were more susceptible to passive transport, intracellular hydrolysis, and metabolism in breast cancer (MCF-7) cell line compared with their POM congeners to result in low concentration of quercetin in this cell line and thereby low antiproliferative effect. In contrast, upon incubation with colorectal carcinoma HCT116 cells, the quercetin-POC conjugates were shown to undergo slow hydrolysis and metabolism to maintain concentrations of the active quercetin species high enough to exert enhanced cytotoxicity. Taken together, the quercetin-POC conjugates synthesized in this study exhibited cell type-specific stability as well as bioactivity profiles, which warrants further investigation into the underlying mechanisms and therapeutic potential.

Myricetin: biological activity related to human health

Myricetin (3,5,7,3′,4′,5′-hexahydroxyflavone) is one of the natural flavonols from fruit, vegetable, tea, and medicinal plants. A great deal of attention has been paid to this compound owing to its various health-promoting effects. In this review, we provide a comprehensive discussion of the therapeutic potential of myricetin by focusing on its biological activity and pharmacokinetic properties.