Ching-Chuan Kuo

4-Ketopinoresinol, a novel naturally occurring ARE activator, induces the Nrf2/HO-1 axis and protects against oxidative stress-induced cell injury via activation of PI3K/ AKT signaling

The Nrf2/ARE pathway plays an important role in inducing phase II detoxifying enzymes and antioxidant proteins and has been considered a potential target for cancer chemoprevention because it eliminates harmful reactive oxygen species or reactive intermediates generated from carcinogens. The objectives of this study were to identify novel Nrf2/ARE activators and to investigate the mechanistic signaling pathway involved in the activation of Nrf2-mediated cytoprotective effects against oxidative-induced cell injury. A stable ARE-driven luciferase reporter cell line was established to screen a potentially cytoprotective compound. 4-Ketopinoresinol (4-KPR), the (α-γ) double-cyclized type of lignan obtained from adlay (Coix lachryma-jobi L. var. ma-yuen Stapf), activates ARE-driven luciferase activity more effectively than the classical ARE activator tert-butylhydroquinone. 4-KPR treatment resulted in a transient increase in AKT phosphorylation and subsequent phosphorylation and nuclear translocation of Nrf2, along with increased expression of ARE-dependent cytoprotective genes, such as heme oxygenase-1 (HO-1), aldo-keto reductases, and glutathione synthetic enzyme. 4-KPR suppresses oxidative stress-induced DNA damage and cell death via upregulation of HO-1. Inhibition of PI3K/AKT signaling by chemical inhibitors or RNA interference not only suppressed 4-KPR-induced Nrf2/HO-1 activation, but also eliminated the cytoprotective effect against oxidative damage. These observations in an ARE-regulated gene system suggest that 4-KPR is a novel Nrf2/ARE-mediated transcription activator, activates the Nrf2/HO-1 axis, and protects against oxidative stress-induced cell injury via activation of PI3K/AKT signaling.

Generation of Ligand-Based Pharmacophore Model and Virtual Screening for Identification of Novel Tubulin Inhibitors with Potent Anticancer Activity

A pharmacophore model, Hypo1, was built on the basis of 21 training-set indole compounds with varying levels of antiproliferative activity. Hypo1 possessed important chemical features required for the inhibitors and demonstrated good predictive ability for biological activity, with high correlation coefficients of 0.96 and 0.89 for the training-set and test-set compounds, respectively. Further utilization of the Hypo1 pharmacophore model to screen chemical database in silico led to the identification of four compounds with antiproliferative activity. Among these four compounds, 43 showed potent antiproliferative activity against various cancer cell lines with the strongest inhibition on the proliferation of KB cells (IC(50) = 187 nM). Further biological characterization revealed that 43 effectively inhibited tubulin polymerization and significantly induced cell cycle arrest in G(2)-M phase. In addition, 43 also showed the in vivo-like anticancer effects. To our knowledge, 43 is the most potent antiproliferative compound with antitubulin activity discovered by computer-aided drug design. The chemical novelty of 43 and its anticancer activities make this compound worthy of further lead optimization.

D-501036, a novel selenophene-based triheterocycle derivative, exhibits potent in vitro and in vivo antitumoral activity which involves DNA damage and ataxia telangiectasia–mutated nuclear protein kinase activation

D-501036 [2,5-bis(5-hydroxymethyl-2-selenienyl)-3-hydroxymethyl-N-methylpyrrole] is herein identified as a novel antineoplastic agent with a broad spectrum of antitumoral activity against several human cancer cells and an IC50 value in the nanomolar range. The IC50 values for D-501036 in the renal proximal tubule, normal bronchial epithelial, and fibroblast cells were >10 μmol/L. D-501036 exhibited no cross-resistance with vincristine- and paclitaxel-resistant cell lines, whereas a low level of resistance toward the etoposide-resistant KB variant was observed. Cell cycle analysis established that D-501036 treatment resulted in a dose-dependent accumulation in S phase with concomitant loss of both the G0-G1 and G2-M phase in both Hep 3B and A-498 cells. Pulsed-field gel electrophoresis showed D-501036–induced, concentration-dependent DNA breaks in both Hep 3B and A-498 cells. These breaks did not involve interference with either topoisomerase-I and topoisomerase-II function or DNA binding. Rapid reactive oxygen species production and formation of Se-DNA adducts were evident following exposure of cells to D-501036, indicating that D-501036–mediated DNA breaks were attributable to the induction of reactive oxygen species and DNA adduct formation. Moreover, D-501036–induced DNA damage activated ataxia telangiectasia–mutated nuclear protein kinase, leading to hyperphosphorylation of Chk1, Chk2, and p53, decreased expression of CDC25A, and up-regulation of p21WAF1 in both p53-proficient and p53-deficient cells. Collectively, the results indicate that D-501036–induced cell death was associated with DNA damage–mediated induction of ataxia telangiectasia–mutated activation, and p53-dependent and -independent apoptosis pathways. Notably, D-501036 shows potent activity against the growth of xenograft tumors of human renal carcinoma A-498 cells. Thus, D-501036 is a promising anticancer compound that has strong potential for the management of human cancers. [Mol Cancer Ther 2007;6(1):193–202]

Combined modalities of resistance in an oxaliplatin-resistant human gastric cancer cell line with enhanced sensitivity to 5-fluorouracil

To identify mechanisms underlying oxaliplatin resistance, a subline of the human gastric adenocarcinoma TSGH cell line, S3, was made resistant to oxaliplatin by continuous selection against increasing drug concentrations. Compared with the parental TSGH cells, the S3 subline showed 58-fold resistance to oxaliplatin; it also displayed 11-, 2-, and 4.7-fold resistance to cis-diammine-dichloroplatinum (II) (CDDP), copper sulphate, and arsenic trioxide, respectively. Interestingly, S3 cells were fourfold more susceptible to 5-fluorouracil-induced cytotoxicity due to downregulation of thymidylate synthase. Despite elevated glutathione levels in S3 cells, there was no alteration of resistant phenotype to oxaliplatin or CDDP when cells were co-treated with glutathione-depleting agent, l-buthionine-(S,R)-sulphoximine. Cellular CDDP and oxaliplatin accumulation was decreased in S3 cells. In addition, amounts of oxaliplatin- and CDDP–DNA adducts in S3 cells were about 15 and 40% of those seen with TSGH cells, respectively. Western blot analysis showed increased the expression level of copper transporter ATP7A in S3 cells compared with TSGH cells. Partial reversal of the resistance of S3 cells to oxaliplatin and CDDP was observed by treating cell with ATP7A-targeted siRNA oligonucleotides or P-type ATPase-inhibitor sodium orthovanadate. Besides, host reactivation assay revealed enhanced repair of oxaliplatin- or CDDP-damaged DNA in S3 cells compared with TSGH cells. Together, our results show that the mechanism responsible for oxaliplatin and CDDP resistance in S3 cells is the combination of increased DNA repair and overexpression of ATP7A. Downregulation of thymidylate synthase in S3 cells renders them more susceptible to 5-fluorouracil-induced cytotoxicity. These findings could pave ways for future efforts to overcome oxaliplatin resistance.

Cytotoxic steroidal saponins from Agave sisalana

Two new steroidal saponins, 8 and 10, along with 7 known steroidal sapogenins and saponins (1-7) and a furostanol saponin (9) were isolated from Agave sisalana Perrine ex Engelm. The structures of these two new compounds were identified and characterized by 1D and 2D NMR spectroscopy and mass spectrometry. In addition, acid hydrolysis and GC-FID were used to confirm the sugar moieties of 8 and 10. The cytotoxic effects of 1-10 on MCF-7, NCI-H460, and SF-268 cancer cells were evaluated, and among them, compound 10 proved to be the most cytotoxic with IC₅₀ values of 1.2, 3.8, and 1.5 µM, respectively.

Design and Synthesis of α-Ketoamides as Cathepsin S Inhibitors with Potential Applications against Tumor Invasion and Angiogenesis

A series of small molecules bearing an alpha-ketoamide warhead were synthesized and evaluated for their ability to inhibit cathepsin S, a key proteolytic enzyme upregulated in many cancers during tumor progression and metastasis. Most of the synthetic compounds were noncytotoxic, but several robustly inhibited cathepsin S (IC(50) < 10 nM) and potently suppressed cell migration, invasion, and capillary tube formation. These results highlight the potential of alpha-ketoamide therapy for preventing or delaying cancer spread.

Synthesis and Structure-Activity Relationships of 2-Amino-1-aroylnaphthalene and 2-Hydroxy-1-aroylnaphthalenes as Potent Antitubulin Agents §

A series of aroylnaphthalene derivatives were prepared as bioisosteres of combrestatin A-4 and evaluated for anticancer activity. 2-Amino-1-aroylnaphthalene and 2-hydroxy-1-aroylnaphthalene, 9 and 8, respectively, showed strong antiproliferative activity with IC(50) values of 2.1-26.3 nM against a panel of human cancer cell lines including multiple-drug resistant cell line. Compound 9 demonstrated better antiproliferative activity and has a comparable tubulin binding efficacy as that of colchicine.

Furanylazaindoles: potent anticancer agents in vitro and in vivo.

Preliminary biological data on 7-anilino-6-azaindoles (8-11) suggested that hydrophobic substituents at C7 contribute to enhancement of antiproliferative activity. A novel series of 7-aryl-6-azaindole-1-benzenesulfonamides (12-22) were developed and showed improved cytotoxicity compared to ABT751 (5). The conversion of C7 phenyl rings into C7 heterocycles led to a remarkable improvement of antiproliferative activity. Among all the synthetic products, 7-(2-furanyl)-1-(4-methoxybenzenesulfonyl)-6-azaindole (21) exhibited the most potent anticancer activity against KB, HT29, MKN45, and H460 cancer cell lines with IC50 values of 21.1, 32.0, 27.5, and 40.0 nM, respectively. Bioassays indicated that 21 not only inhibits tubulin polymerization by binding to tubulin at the colchicine binding site but also arrests the cell cycle at the G2/M phase with slight arrest at the sub-G1 phase. Compound 21 also functions as a vascular disrupting agent and dose-dependently inhibits tumor growth without significant change of body weight in an HT29 xenograft mouse model. Taken together, compound 21 has potential for further development as a novel class of anticancer agents.

Concise syntheses of N-aryl-5,6,7-trimethoxyindoles as antimitotic and vascular disrupting agents: application of the copper-mediated Ullmann-type arylation

In an attempt to mimic the 3,4,5-trimethoxyphenyl-Z-stilbene moiety of combretastatin A-4, a series of N-aryl-5,6,7-trimethoxyindoles were synthesized via copper-catalyzed Ullmann-type N-arylation through the corresponding 5,6,7-trimethoxyindole and aryl halides. These synthesized compounds demonstrated potent antiproliferative activity providing a novel skeleton for potent tubulin polymerization inhibitors.

Cytotoxic C35 Terpenoid Cryptotrione from the Bark of Cryptomeria japonica

A novel C(35)-terpene, designated as cryptotrione (1), with an unprecedented skeleton possessing an abietane diterpene with a unique bicyclic sesquiterpene, is identified from the bark of Cryptomeria japonica. The carbon skeleton of 1 represents a new structural entity, and this is an intriguing addition to the structurally diverse diterpene-sesquiterpene class. A unique biosynthetic pathway is proposed to support the production of this phytocompound. Notably, 1 exhibits anticancer activity with an IC(50) value of 6.44 +/- 2.23 microM.