Wang-Fun Fong

New Perspectives on How to Discover Drugs from Herbal Medicines: CAM's Outstanding Contribution to Modern Therapeutics

With tens of thousands of plant species on earth, we are endowed with an enormous wealth of medicinal remedies from Mother Nature. Natural products and their derivatives represent more than 50% of all the drugs in modern therapeutics. Because of the low success rate and huge capital investment need, the research and development of conventional drugs are very costly and difficult. Over the past few decades, researchers have focused on drug discovery from herbal medicines or botanical sources, an important group of complementary and alternative medicine (CAM) therapy. With a long history of herbal usage for the clinical management of a variety of diseases in indigenous cultures, the success rate of developing a new drug from herbal medicinal preparations should, in theory, be higher than that from chemical synthesis. While the endeavor for drug discovery from herbal medicines is “experience driven,” the search for a therapeutically useful synthetic drug, like “looking for a needle in a haystack,” is a daunting task. In this paper, we first illustrated various approaches of drug discovery from herbal medicines. Typical examples of successful drug discovery from botanical sources were given. In addition, problems in drug discovery from herbal medicines were described and possible solutions were proposed. The prospect of drug discovery from herbal medicines in the postgenomic era was made with the provision of future directions in this area of drug development.

Baicalein inhibits formation of α-Synuclein oligomers within living cells and prevents Aβ peptide fibrillation and oligomerisation

Abnormal protein aggregation in the brain is linked to the pathogenesis of neurodegenerative diseases, including Alzheimers disease (AD) and Parkinsons disease (PD). Recent studies revealed that the oligomeric form of aggregates is most likely the toxic species, and thus could be a good therapeutic target. To screen for potent inhibitors that can inhibit both oligomerisation and fibrillation of α‐synuclein (α‐syn), we systematically compared the antioligomeric and antifibrillar activities of eight compounds that were extracted from Chinese herbal medicines through three platforms that can monitor the formation of α‐syn fibrils and oligomers in cell‐free or cellular systems. Our results revealed that baicalein, a flavonoid extracted from the Chinese herbal medicine Scutellaria baicalensis Georgi (“huang qin” in Chinese), is a potent inhibitor of α‐syn oligomerisation both in cell‐free and cellular systems, and is also an effective inhibitor of α‐syn fibrillation in cell‐free systems. We further tested the protective effect of baicalein against α‐syn‐oligomer‐induced toxicity in neuronal cells. Our data showed that baicalein inhibited the formation of α‐syn oligomers in SH‐SY5Y and Hela cells, and protected SH‐SY5Y cells from α‐syn‐oligomer‐induced toxicity. We also explored the effect of baicalein on amyloid‐β peptide (Aβ) aggregation and toxicity. We found that baicalein can also inhibit Aβ fibrillation and oligomerisation, disaggregate pre‐formed Aβ amyloid fibrils and prevent Aβ fibril‐induced toxicity in PC12 cells. Our study indicates that baicalein is a good inhibitor of amyloid protein aggregation and toxicity. Given the role of these processes in neurodegenerative diseases such as AD and PD, our results suggest that baicalein has potential as a therapeutic agent for the treatment of these devastating disorders.

A highly selective, label-free, homogenous luminescent switch-on probe for the detection of nanomolar transcription factor NF-kappaB

Transcription factors are involved in a number of important cellular processes. The transcription factor NF-κB has been linked with a number of cancers, autoimmune and inflammatory diseases. As a result, monitoring transcription factors potentially represents a means for the early detection and prevention of diseases. Most methods for transcription factor detection tend to be tedious and laborious and involve complicated sample preparation, and are not practical for routine detection. We describe herein the first label-free luminescence switch-on detection method for transcription factor activity using Exonuclease III and a luminescent ruthenium complex, [Ru(phen)2(dppz)]2+. As a proof of concept for this novel assay, we have designed a double-stranded DNA sequence bearing two NF-κB binding sites. The results show that the luminescence response was proportional to the concentration of the NF-κB subunit p50 present in the sample within a wide concentration range, with a nanomolar detection limit. In the presence of a known NF-κB inhibitor, oridonin, a reduction in the luminescence response of the ruthenium complex was observed. The reduced luminescence response of the ruthenium complex in the presence of small molecule inhibitors allows the assay to be applied to the high-throughput screening of chemical libraries to identify new antagonists of transcription factor DNA binding activity. This will allow the rapid and low cost identification and development of novel scaffolds for the treatment of diseases caused by the deregulation of transcription factor activity.

Structure-based optimization of FDA-approved drug methylene blue as a c-myc G-quadruplex DNA stabilizer

G-quadruplexes are non-canonical DNA secondary structures putatively present in the promoter regions of oncogenes in the human genome. The targeting of promoter G-quadruplex structures to repress oncogene transcription represents a potential anticancer strategy. Here, we have used high-throughput virtual screening to identify FDA-approved drug methylene blue (MB) as a promising scaffold for binding the c-myc oncogene G-quadruplex DNA. Based on molecular docking analysis of MB to the c-myc G-quadruplex, we designed and screened 50 MB derivatives containing side chains that could interact with the G-quadruplex grooves. As a proof-of-concept, the highest-scoring compounds were synthesized and the interactions with the c-myc G-quadruplex were investigated using the FID assay. The results showed that the methylene blue derivatives 6a-c were able to bind to the c-myc G-quadruplex with greater binding affinity compared to the known G-quadruplex binding ligand, crystal violet. The activity of the most potent compound identified from the FID assay, 6b, as an inhibitor for polymerase-drive DNA extension was examined using a PCR-stop assay and compared against that of the parent compound methylene blue. The results of the PCR-stop assay showed that the addition of the side chain improved the activity of the derivatives as an inhibitor compared to the parent compound. The MB derivative 6b was shown to be highly selective towards c-myc G-quadruplex over double-stranded DNA and other biologically relevant G-quadruplexes using UV-visible spectroscopy and mass spectrometry, respectively. The MB derivative 6b could induce or stabilize c-myc G-quadruplex formation in both cell-free and cellular biological models, and displayed higher cytoxicity against human hepatocarcinoma cells compared to the parent compound, MB.

Quercetin exerts anti-melanoma activities and inhibits STAT3 signaling

Melanoma is highly resistant to chemotherapy, and the mortality rate is increasing rapidly worldwide. STAT3 signaling has been implicated in the pathogenesis of melanoma and constitutive activated STAT3 has been validated can as a target for melanoma therapy. Quercetin, a noncarcinogenic dietary flavonoid with low toxicity, has been shown to exert anti-melanoma activity. However, the anti-melanoma mechanisms of quercetin are not fully understood. In this study, we sought to test the involvement of STAT3 signaling in the inhibitory effects of quercetin on melanoma cell growth, migration and invasion. Our results showed that exposure to quercetin resulted in inhibition of proliferation of melanoma cells, induction of cell apoptosis, and suppression of migratory and invasive properties. Mechanistic study indicated that quercetin inhibited the activation of STAT3 signaling by interfering with STAT3 phosphorylation, and reducing STAT3 nuclear localization. This inhibited STAT3 transcription activity and down-regulated STAT3 targeted genes Mcl-1, MMP-2, MMP-9 and VEGF, which are involved in cell growth, migration and invasion. Importantly, overexpression of constitutively active STAT3 partially rescued the growth inhibiting effects induced by quercetin. Furthermore, quercetin suppressed A375 tumor growth and STAT3 activities in xenografted mice model, and inhibited murine B16F10 cells lung metastasis in an animal model. Overall, these results indicate that the antitumor activity of quercetin is at least partially due to inhibition of STAT3 signaling in melanoma cells. Our findings provided new insight into the action of quercetin potently inhibits the STAT3 signaling pathway, suggesting it has a potential role in the prevention and treatment of melanoma.

Involvement of p38 MAPK signaling pathway in the anti-melanogenic effect of San-bai-tang, a Chinese herbal formula, in B16 cells

AIM OF THE STUDY San-bai-tang (SBT), a Chinese herbal formula, is traditionally used as a skin whitener in China. In our previous screening assays, SBT was identified as an effective tyrosinase inhibitor. In this study, we aim to investigate the anti-melanogenic effect and mechanisms of SBT in B16 cells. MATERIALS AND METHODS Cell viability was examined by the MTT assay. Cellular tyrosinase activity and melanin content were determined using spectrophotographic methods. Protein expression was analyzed by immunoblotting. RESULTS SBT inhibited tyrosinase activity with an IC(50) of 215.6 ± 10.3 μg/ml, and decreased cellular melanin content with an IC(50) of 254.8 ± 14.5 μg/ml at 48 h. MTT assay demonstrated that 48-h SBT (50-400 μg/ml) treatment did not show obvious cytotoxicity. Immunoblot analysis showed that SBT (100, 200 or 400 μg/ml) treatment for 48 h down-regulated the expression levels of phosphorylated-p38, MITF, tyrosinase, TRP-1 and TRP-2 in a dose-dependent manner. CONCLUSIONS SBT inhibited melanogenesis in B16 cells, and suppression of p38 MAPK signaling pathway contributed to the anti-melanogenic effect of SBT by down-regulating the expression of MITF and melanogenic enzymes. These novel findings demonstrated the anti-melanogenic effect and mechanisms of SBT, and provide pharmacological basis for the traditional use of SBT.

Schisandrin B from Schisandra chinensis reduces hepatic lipid contents in hypercholesterolaemic mice.

The effects of schisandrin B (Sch B) on liver and serum lipid contents were investigated in mice with experimentally‐induced hypercholesterolaemia. Hypercholesterolaemia was induced either by oral administration of a cholesterol/bile salts mixture (2/0.5 g kg−1) for four days or by feeding a high fat/cholesterol/bile salts (10/1/0.3%, w/w) diet for seven days. Daily co‐administration of Sch B (50–200 mg kg−1, i.g.) for four or six days, respectively, decreased hepatic total cholesterol (TC) and triglyceride (TG) levels (by up to 50% and 52%, respectively) in hypercholesterolaemic mice. Sch B treatment also increased hepatic indices (14–84%) in hypercholesterolaemic mice. The results indicated that Sch B treatment could decrease hepatic TC and TG levels, and increase liver weight, in mouse models of hypercholesterolaemia. Fenofibrate treatment (100 mg kg−1) produced effects similar to those of Sch B on the hepatic index and lipid levels of hypercholesterolaemic mice.

Effect of hydrogel matrix on binding kinetics of protein–protein interactions on sensor surface

Abstract Surface plasmon resonance (SPR) biosensor has become a standard technology for measuring kinetics of bimolecular interactions without the need for labeling. Sensor chips coated with a carboxymethylated dextran (CMD) hydrogel matrix are commonly used for immobilizing a protein binding partner in kinetic studies. The sensor chip provides a biocompatible surface with low non-specific binding, but it also presents some problems, such as steric effect and re-binding which may bias the kinetic measurement. In the present study, the effect of hydrogel matrix on protein–protein interaction was investigated. The insulin-like growth factors (IGFs) and their binding proteins were used as the model system. Kinetic parameters obtained with either of the binding partners immobilized on the matrix were compared to evaluate the effects of the matrix on the binding kinetics. The surface capacity and sensitivity of the hydrogel-modified sensor chip (CM5) and those of a sensor chip modified with a self-assembled monolayer (SAM) were measured and the performance of both chips was discussed.

20(S)-Protopanaxadiol, a metabolite of ginsenosides, induced cell apoptosis through endoplasmic reticulum stress in human hepatocarcinoma HepG2 cells.

20(S)-Protopanaxadiol (PPD), a metabolite of ginsenosides, has been demonstrated to possess cytotoxic effects on several cancer cell lines. The molecular mechanism is, however, not well understood. In this study, we have shown that PPD inhibits cell growth and induces apoptosis in human hepatocarcinoma HepG2 cells. PPD-treated cells showed a massive cytoplasmic vacuolization and a dramatic change of endoplasmic reticulum (ER) morphology. The induction of ER stress is associated with the upregulation of ER stress-associated genes and proteins. PPD activates the unfolded protein response (UPR) through the phosphorylation of PERK and eIF2α, the splicing of XBP1 mRNA, and the cleavage of AFT6. PPD also induces the intrinsic and extrinsic apoptotic pathways. It activates DR5, caspase-8, -9, -3, and promotes the cleavage of PARP while it downregulates Bcl-2, Bcl-x(L) and mitochondrial membrane potential. Knockdown of one of the three UPR limbs by specific siRNAs did not affect PPD-induced apoptosis, which was however, significantly suppressed by the downregulation of CHOP. Western blot analysis showed that PPD-stimulated downregulation of Bcl-2 protein, increase of DR5 protein, activation of caspase-8 and cleavage of PARP were significantly inhibited in CHOP siRNA-transfected cells. Taken together, we have identified ER as a molecular target of PPD and our data support the hypothesis that PPD induces HepG2 cell apoptosis through the ER stress pathway.

1α,25-Dihydroxyvitamin D3 inhibits transcriptional potential of nuclear factor kappa B in breast cancer cells

1alpha,25-Dihydroxyvitamin D(3) (VD(3)), the biologically active form of vitamin D, may have either pro- or anti-inflammatory activities because of its diverse actions on nuclear factor kappa B (NF-kappaB). Previous studies indicated that VD(3) can either activate or inhibit NF-kappaB via Akt-induced I kappaB alpha phosphorylation and increase in I kappaB alpha synthesis respectively. At present, the relevant contribution of each mechanism has not been fully explored. We observed a VD(3)-mediated NF-kappaB inhibitory effect in vitamin D receptor (VDR)-positive MCF-7 breast cancer cells. We showed that VD(3) induced VDR-dependent I kappaB alpha expression but still able to lead on transient NF-kappaB p65 nuclear translocation through Akt-induced I kappaB alpha phosphorylation. Upon TNFalpha stimulation, VD(3) was not capable to inhibit I kappaB alpha degradation, p65 nuclear translocation and p65/p50-DNA binding. Here, we found that VD(3) strongly repressed p65 transactivation in MCF-7 cells using Gal4-p65 chimeras system. VDR was required for the VD(3)-mediated transrepression and mutations in VDR affected its suppressive ability. We also demonstrated that neither inhibition of p65 phosphorylation nor acetylation was responsible for the transrepression. In fact, we found that treatment of MCF-7 cells with histone deacetylase inhibitors abrogated VD(3)-induced p65 transrepression. In addition, knockdown of two nuclear corepressors HDAC3 and SMRT relieved p65 transactivation and particular TNFalpha-triggered gene expression. In conclusion, the reduction of gene activation by VD(3) in breast cancer cells was caused by the interference of the transactivation potential of NF-kappaB p65 subunit. Our studies provide a scientific background for rational use of vitamin D in the prevention and treatment of inflammatory diseases.