Wen-Shan Li

Preparation and Characterization of Amino-Linked Heterocyclic Carbene Palladium, Gold, and Silver Complexes and Their Use as Anticancer Agents That Act by Triggering Apoptotic Cell Death

Transition metal complexes bearing amino linked N-heterocyclic carbenes (NHC) were prepared and evaluated for their antiproliferative activities in human cancer cells. The optimum antiproliferative activity, observed for the gold complex 3 in U-87 MG cells, was found to involve S-phase arrest of the cell cycle. The results indicate that 3 induces apoptosis through a p53-bak pathway, a finding that could serve as a new strategy to reduce the resistance of cancer cells to p53-induced apoptosis.

A Novel Sialyltransferase Inhibitor Suppresses FAK/Paxillin Signaling and Cancer Angiogenesis and Metastasis Pathways

Increased sialyltransferase (ST) activity promotes cancer cell metastasis, and overexpression of cell surface sialic acid correlates with poor prognosis in cancer patients. To seek therapies targeting metastasis for cancer treatment, we developed a novel ST inhibitor, Lith-O-Asp, and investigated its antimetastatic and antiangiogenic effects and mechanisms. We found that cells treated with Lith-O-Asp showed a reduction of activity on various ST enzymes by in vitro and cell-based activity analyses. Lith-O-Asp inhibited migration and invasion abilities in various cancer cell lines and showed inhibitory effect on the angiogenic activity of human umbilical vein endothelial cells. Indeed, Lith-O-Asp treatment consequently delayed cancer cell metastasis in experimental and spontaneous metastasis assays in animal models. Importantly, Lith-O-Asp decreased the sialic acid modification of integrin-β1 and inhibited the expression of phospho-FAK, phospho-paxillin, and the matrix metalloprotease (MMP) 2 and MMP9. Lith-O-Asp attenuated the Rho GTPase activity leading to actin dynamic impairment. In addition, 2DE-MS/MS and immunoblotting analyses showed that Lith-O-Asp altered the protein expression level and phosphorylation status of various proteins involved in crucial metastasis and angiogenesis pathways such as vimentin and ribonuclease/angiogenin inhibitor RNH1. Furthermore, Lith-O-Asp treatment significantly inhibited the invasive ability exerted by ectopic overexpression of various ST enzymes catalyzing α-2,6- or α-2,3-sialylation. Our results provide compelling evidence that the potential pan-ST inhibitor, Lith-O-Asp, suppressed cancer cell metastasis likely by inhibiting FAK/paxillin signaling and expressing antiangiogenesis factors. Lith-O-Asp is worthy for further testing as a novel antimetastasis drug for cancer treatment.

Stereoselective detoxification of chiral sarin and soman analogues by phosphotriesterase

The catalytic activity of the bacterial phosphotriesterase (PTE) toward a series of chiral analogues of the chemical warfare agents sarin and soman was measured. Chemical procedures were developed for the chiral syntheses of the S(P)- and R(P)-enantiomers of O-isopropyl p-nitrophenyl methylphosphonate (sarin analogue) in high enantiomeric excess. The R(P)-enantiomer of the sarin analogue (k(cat)=2600 s(-1)) was the preferred substrate for the wild-type PTE relative to the corresponding S(P)-enantiomer (k(cat)=290 s(-1)). The observed stereoselectivity was reversed using the PTE mutant, I106A/F132A/H254Y where the k(cat) values for the R(P)- and S(P)-enantiomers were 410 and 4200 s(-1), respectively. A chemo-enzymatic procedure was developed for the chiral synthesis of the four stereoisomers of O-pinacolyl p-nitrophenyl methylphosphonate (soman analogue) with high diastereomeric excess. The R(P)R(C)-stereoisomer of the soman analogue was the preferred substrate for PTE. The k(cat) values for the soman analogues were measured as follows: R(P)R(C,) 48 s(-1); R(P)S(C), 4.8 s(-1); S(P)R(C), 0.3 s(-1), and S(P)S(C), 0.04 s(-1). With the I106A/F132A/H254Y mutant of PTE the stereoselectivity toward the chiral phosphorus center was reversed. With the triple mutant the k(cat) values for the soman analogues were found to be as follows: R(P)R(C,) 0.3 s(-1); R(P)S(C), 0.3 s(-1); S(P)R(C), 11s(-1), and S(P)S(C), 2.1 s(-1). Prior investigations have demonstrated that the S(P)-enantiomers of sarin and soman are significantly more toxic than the R(P)-enantiomers. This investigation has demonstrated that mutants of the wild-type PTE can be readily constructed with enhanced catalytic activities toward the most toxic stereoisomers of sarin and soman.

A novel sialyltransferase inhibitor AL10 suppresses invasion and metastasis of lung cancer cells by inhibiting integrin-mediated signaling

Aberrant sialylation catalyzed by sialyltransferases (STs) is frequently found in cancer cells and is associated with increased cancer metastasis. However, ST inhibitors developed till now are not applicable for clinical use because of their poor cell permeability. In this study, a novel ST inhibitor AL10 derived from the lead compound lithocholic acid identified in our previous study is synthesized and the anti‐cancer effect of this compound is studied. AL10 is cell‐permeable and effectively attenuates total sialylation on cell surface. This inhibitor shows no cytotoxicity but inhibits adhesion, migration, actin polymerization and invasion of α‐2,3‐ST‐overexpressing A549 and CL1.5 human lung cells. Inhibition of adhesion and migration by AL10 is associated with reduced sialylation of various integrin molecules and attenuated activation of the integrin downstream signaling mediator focal adhesion kinase. More importantly, AL10 significantly suppresses experimental lung metastasis in vivo without affecting liver and kidney function of experimental animals as determined by serum biochemical assays. Taken together, AL10 is the first ST inhibitor, which exhibits potent anti‐metastatic activity in vivo and may be useful for clinical cancer treatment. J. Cell. Physiol. 223: 492–499, 2010.

N1,N10-Ethylene-bridged high-potential flavins: synthesis, characterization, and reactivity

N1,N10-Ethyleneisoalloxazinium chloride and its 8-Cl-, 7-CF3-, and 3-CH3-7-CF3-substituted analogs were synthesized for the purpose of exhibiting thermal reactivity with organic substrates. The new flavins were characterized spectroscopically and electrochemically, and were found to react with amines, thiols, and phenylhydrazine, the latter case exhibiting catalytic aerobic recycling. Reactions of aliphatic benzylic and cyclopropyl amines with the 7-CF3 analog were also compared to their oxidations by tris(phenanthroline)iron(III). All reactions of the flavinium salts appear to occur through heterolytic rather than homolytic mechanisms.

Isomalyngamide A, A-1 and their analogs suppress cancer cell migration in vitro

Isomalyngamide A (1) and A-1 (2) were isolated from the Taiwanese Lyngbya majuscule and the latter structure was elucidated by a combination of NMR spectroscopic analysis and HRESIMS measurement. We report the isolation of isomalyngamide A (1), discovery of isomalyngamide A-1 (2) and their synthetic analogs (3-9), which are further demonstrated to have therapeutic potential against tumor cell migration at the level of nanomolar to micromolar ranges, perhaps, by inactivating the expression of p-FAK, FAK, p-Akt and Akt through β1 integrin-mediated antimetastatic pathway.

Photoswitchable alkoxy-bridged binuclear rhenium(I) complexes – a potential probe for biomolecules and optical cell imaging

We describe the solvothermal synthesis, structural characterization, photophysics and potential applications as probes of two alkoxy-bridged binuclear Re(I) complexes, [{Re(CO)3(1,4-NVP)}2(μ2-OR)2] (1, R = C4H9; 2, R = C10H21; 1,4-NVP = 4-(1-naphthylvinyl)pyridine). Irradiation of 1 and 2 at 365 nm leads to an interesting trans-cis photoisomerization process, which was examined by 1H NMR, UV-vis, emission and time-resolved techniques. Compounds 1 and 2 exhibit photoswitchable luminescence enhancement arising from photoinduced intramolecular energy transfer from the 3MLCT state of the Re(I) chromophore to the triplet excited state of the ligand 1,4-NVP. In addition, these Re(I) complexes serve as excellent probes for the ultrasensitive detection of biological molecules, including bovine serum albumin (BSA) and a platelet derived growth factor (PDGF) binding aptamer. Our results also suggest that, since these Re(I) complexes have low cytotoxicity and fluorescence properties under physiological conditions, they could be a useful probe for optical imaging of cancer cells by confocal laser scanning microscopy.

Lithocholic acid analogues, new and potent α-2,3-sialyltransferase inhibitors

A new type of noncompetitive α-2,3-sialyltransferase inhibitor has been synthesized; we report the discovery, preparation and inhibitory activity of sixteen lithocholic acid analogues.

Oxidations of N-(3-Indoleethyl) Cyclic Aliphatic Amines by Horseradish Peroxidase : The Indole Ring Binds to the Enzyme and Mediates Electron-Transfer Amine Oxidation

Although oxidations of aromatic amines by horseradish peroxidase (HRP) are well-known, typical aliphatic amines are not substrates of HRP. In this study, the reactions of N-benzyl and N-methyl cyclic amines with HRP were found to be slow, but reactions of N-(3-indoleethyl) cyclic amines were 2-3 orders of magnitude faster. Analyses of pH-rate profiles revealed a dominant contribution to reaction by the amine-free base forms, the only species found to bind to the enzyme. A metabolic study on a family of congeneric N-(3-indoleethyl) cyclic amines indicated competition between amine and indole oxidation pathways. Amine oxidation dominated for the seven- and eight-membered azacycles, where ring size supports the change in hybridization from sp3 to sp2 that occurs upon one-electron amine nitrogen oxidation, whereas only indole oxidation was observed for the six-membered ring congener. Optical difference spectroscopic binding data and computational docking simulations suggest that all the arylalkylamine substrates bind to the enzyme through their aromatic termini with similar binding modes and binding affinities. Kinetic saturation was observed for a particularly soluble substrate, consistent with an obligatory role of an enzyme-substrate complexation preceding electron transfer. The significant rate enhancements seen for the indoleethylamine substrates suggest the ability of the bound indole ring to mediate what amounts to medium long-range electron-transfer oxidation of the tertiary amine center by the HRP oxidants. This is the first systematic investigation to document aliphatic amine oxidation by HRP at rates consistent with normal metabolic turnover, and the demonstration that this is facilitated by an auxiliary electron-rich aromatic ring.

reaction of amines with n1,n10-ethylene-bridged flavinium salts: the first nmr spectroscopic evidence of c10a tetrahedral amine adducts.

Abstract Two different 13C-labeled 7-trifluoromethyl-N1,N10-ethyleneisoalloxazinium chlorides were utilized to examine the mechanism of amine dehydrogenation. 1H NMR studies in CD3CN (13C NMR in DMSO-d6), as confirmed using 15N-labeled benzylamine, indicate that primary and secondary amines add to give tetrahedral C10a adducts that persist for hours at 25°C. Upon heating, the C10a amine adducts partition between rearrangement to C4a spirohydantoin amidines, and, in the case of benzylic amines, β-elimination to give reduced flavin and imine dehydrogenation product. A C10a tetrahedral hydroxy adduct, generated under basic conditions when water was present, was also confirmed by 1H/13C NMR.