Semi-synthesis and anti-tumor activity of novel 25-OCH3-PPD derivatives incorporating aromatic moiety.

Previously we have reported that 25-OCH3-PPD could suppress the reproduction of cancer cells and cause apoptosis without obvious toxicity. Herein, we aimed to enhance its bioactivity by introducing aromatic groups to its dammarane-type skeleton. These synthesized derivatives were tested for their inhibitory activities against five cancer cell lines. Of them, compounds 3a, 14a and 18a had the strongest antiproliferative activities against tumor cells (IC50 < 15 µM, 5-fold to 10-fold increases than 25-OCH3-PPD). Especially compound 14a displayed the most potent activity against DU145, MCF-7 and HepG2 cells (IC50 = 6.7 ±â€¯0.8, 4.3 ±â€¯0.8 and 5.8 ±â€¯0.6 µM, respectively). Structure-activity relationships demonstrated that having aromatic ester at the C3 position could improve the bioactivity. The data provided new insights into exploring novel antiproliferative lead compounds.

Deletion of sigB Causes Increased Sensitivity to para-Aminosalicylic Acid and Sulfamethoxazole in Mycobacterium tuberculosis.

Although the de novo folate biosynthesis pathway has been well studied in bacteria, little is known about its regulation. In the present study, the sigB gene in Mycobacterium tuberculosis was deleted. Subsequent drug susceptibility tests revealed that the M. tuberculosis ΔsigB strain was more sensitive to para-aminosalicylic acid (PAS) and sulfamethoxazole. Comparative transcriptional analysis was performed, and downregulation of pabB was observed in the ΔsigB strain, which was further verified by a quantitative reverse transcription-PCR and Western blot assay. Then, the production levels of para-aminobenzoic acid (pABA) were compared between the sigB deletion mutant and wild-type strain, and the results showed that sigB deletion resulted in decreased production of pABA. In addition, SigB was able to recognize the promoter of pabB in vitro Furthermore, we found that deleting pabC also caused increased susceptibility to PAS. Taken together, our data revealed that, in M. tuberculosis, sigB affects susceptibility to antifolates through multiple ways, primarily by regulating the expression of pabB To our knowledge, this is the first report showing that SigB modulates pABA biosynthesis and thus affecting susceptibility to antifolates, which broadens our understanding of the regulation of bacterial folate metabolism and mechanisms of susceptibility to antifolates.

Deletion of nudB Causes Increased Susceptibility to Antifolates in Escherichia coli and Salmonella enterica.

Co-trimoxazole, a fixed-dose combination of sulfamethoxazole (SMX) and trimethoprim (TMP), has been used for the treatment of bacterial infections since the 1960s. Since it has long been assumed that the synergistic effects between SMX and TMP are the consequence of targeting 2 different enzymes of bacterial folate biosynthesis, 2 genes (pabB and nudB) involved in the folate biosynthesis of Escherichia coli were deleted, and their effects on the susceptibility to antifolates were tested. The results showed that the deletion of nudB resulted in a lag of growth in minimal medium and increased susceptibility to both SMX and TMP. Moreover, deletion of nudB also greatly enhanced the bactericidal effect of TMP. To elucidate the mechanism of how the deletion of nudB affects the bacterial growth and susceptibility to antifolates, 7,8-dihydroneopterin and 7,8-dihydropteroate were supplemented into the growth medium. Although those metabolites could restore bacterial growth, they had no effect on susceptibilities to the antifolates. Reverse mutants of the nudB deletion strain were isolated to further study the mechanism of how the deletion of nudB affects susceptibility to antifolates. Targeted sequencing and subsequent genetic studies revealed that the disruption of the tetrahydromonapterin biosynthesis pathway could reverse the phenotype caused by the nudB deletion. Meanwhile, overexpression of folM could also lead to increased susceptibility to both SMX and TMP. These data suggested that the deletion of nudB resulted in the excess production of tetrahydromonapterin, which then caused the increased susceptibility to antifolates. In addition, we found that the deletion of nudB also resulted in increased susceptibility to both SMX and TMP in Salmonella enterica Since dihydroneopterin triphosphate hydrolase is an important component of bacterial folate biosynthesis and the tetrahydromonapterin biosynthesis pathway also exists in a variety of bacteria, it will be interesting to design new compounds targeting dihydroneopterin triphosphate hydrolase, which may inhibit bacterial growth and simultaneously potentiate the antimicrobial activities of antifolates targeting other components of folate biosynthesis.

Sulfamic and succinic acid derivatives of 25-OH-PPD and their activities to MCF-7, A-549, HCT-116, and BGC-823 cell lines.

In the search for new anti-tumor agents with higher potency than our previously identified compound 1 (25-OH-PPD, 25-hydroxyprotopanaxadiol), 12 novel sulfamic and succinic acid derivatives that could improve water solubility and contribute to good drug potency and pharmacokinetic profiles were designed and synthesized. Their in vitro anti-tumor activities in MCF-7, A-549, HCT-116, and BGC-823 cell lines and one normal cell line were tested by standard MTT assay. Results showed that compared with compound 1, compounds 2, 3, and 7 exhibited higher cytotoxic activity on A-549 and BGC-823 cell lines, together with lower toxicity in the normal cell. In particular, compound 2 exhibited the best anti-tumor activity in the in vitro assays, which may provide valuable data for the research and development of new anti-tumor agents.

Nanocomposites with gold nanorod/silica core-shell structure as saturable absorber for femtosecond pulse generation in a fiber laser.

Ultrafast fiber lasers play a significant role in our society with many aspects ranging from fundamental physics to industrial purposes. Searching for high-performance saturable absorbers (SAs) is vital to the developments of ultrafast fiber lasers. Gold nanorods (GNRs) have been discovered to possess saturable absorption effect. However, a major obstacle to make the GNRs as high-performance and practical SA is the low optical damage threshold. To overcome this drawback, herein we proposed the nanocomposites with gold nanorods/silica core-shell structure (GNRs@SiO(2)) as a high-performance SA for ultrashort pulse generation in a fiber laser. The GNRs@SiO(2) SA presents a modulation depth of 4.2% and nonsaturable loss of 45.6%. With the proposed GNRs@SiO(2) SA, 379 fs pulse was directly obtained from the fiber laser. The achieved results demonstrated that the GNR@SiO(2) could be indeed a good candidate of high-performance SA towards practical applications in the field of ultrafast photonics.

Novel dammarane-type triterpenes isolated from hydrolyzate of total Gynostemma pentaphyllum saponins.

In this study, five novel triterpenes were isolated from hydrolyzate of total saponins from Gynostemma pentaphyllum and identified as gypensapogenin H (1), gypensapogenin I (2), gypensapogenin L (3), gypensapogenin J (4) and gypensapogenin K (5), three of which (1-3) possess unprecedented ring A. All the isolated compounds were evaluated for cytotoxic activities in five cell lines and all the tested compounds showed significant anti-cancer activities against a series of human cancer cell lines, while having much weaker effect on the growth of normal cell. Among them, compound 1 showed strong inhibition toward MCF-7 human breast cancer cells (IC50 values 6.85 µM). Further mechanistic study demonstrated that compound 1 significantly induced MCF-7 cell apoptosis. Our results indicated that compound 1 may be a promising lead agent for further study.

Binding pocket alterations in dihydrofolate synthase confer resistance to para-aminosalicylic acid in clinical isolates of Mycobacterium tuberculosis.

The mechanistic basis for the resistance of Mycobacterium tuberculosis to para-aminosalicylic acid (PAS), an important agent in the treatment of multidrug-resistant tuberculosis, has yet to be fully defined. As a substrate analog of the folate precursor para-aminobenzoic acid, PAS is ultimately bioactivated to hydroxy dihydrofolate, which inhibits dihydrofolate reductase and disrupts the operation of folate-dependent metabolic pathways. As a result, the mutation of dihydrofolate synthase, an enzyme needed for the bioactivation of PAS, causes PAS resistance in M. tuberculosis strain H37Rv. Here, we demonstrate that various missense mutations within the coding sequence of the dihydropteroate (H2Pte) binding pocket of dihydrofolate synthase (FolC) confer PAS resistance in laboratory isolates of M. tuberculosis and Mycobacterium bovis. From a panel of 85 multidrug-resistant M. tuberculosis clinical isolates, 5 were found to harbor mutations in the folC gene within the H2Pte binding pocket, resulting in PAS resistance. While these alterations in the H2Pte binding pocket resulted in reduced dihydrofolate synthase activity, they also abolished the bioactivation of hydroxy dihydropteroate to hydroxy dihydrofolate. Consistent with this model for abolished bioactivation, the introduction of a wild-type copy of folC fully restored PAS susceptibility in folC mutant strains. Confirmation of this novel PAS resistance mechanism will be beneficial for the development of molecular method-based diagnostics for M. tuberculosis clinical isolates and for further defining the mode of action of this important tuberculosis drug.

Novel 25-hydroxyprotopanaxadiol derivatives incorporating chloroacetyl chloride and their anti-tumor evaluation.

In the current work, 12 novel 25-hydroxyprotopanaxadiol (25-OH-PPD) derivatives were synthesized by reacting with chloroacetyl chloride. And their in vitro antitumor activities were evaluated on six human tumor cell lines by MTT assay. The results demonstrated that, as compared with 25-OH-PPD, compounds 4, 6 and 7 exhibited higher cytotoxic activity on all tested cell lines. Of them, compound 4 showed strongly inhibition against MCF-7, HCT-116 and Lovo cells with IC50 values of 1.7, 1.6 and 2.1 µM, respectively. The IC50 values of compound 6 against HCT-116 and 7 against MCF-7 were the lowest (1.2 and 1.6 µM, respectively). It was also noted that compound 4 showed a 20- to 100-fold greater growth inhibition than ginsenoside-Rg3 (an anti-cancer regular drug in China). In conclusion, the data revealed that compounds 4, 6 and 7 were potential candidates for anti-tumor treatment and may be useful for the development of novel antiproliferative agents.

[Measurement of atmospheric NO3 radical with long path differential optical absorption spectroscopy based on red light emitting diodes].

Nitrate radical (NO3) is the most important oxidant in the tropospheric nighttime chemistry. Due to its high reactivity and low atmospheric concentrations, modern red light emitting diodes (LEDs) was proposed as light source in long path differential optical absorption spectroscopy (LP-DOAS) to measure NO3 radical in the atmosphere. The spectral properties of Luxeon LXHL-MD1D LEDs were analyzed in the present paper. The principle of LEDs-DOAS system to measure nitrate radical was studied in this paper. The experimental setup and retrieval method of NO3 radical were discussed in this paper. The retrieved example of NO3 was given and the time series of NO3 concentrations was performed for a week. The results showed that the detection limits of LEDs-DOAS system were 12 ppt for atmospheric NO3 radical when the optical path of LEDs-DOAS system was 2.8 km.

Polyketides with anti-inflammatory activity isolated from Rhodiola tibetica endophytic fungus Penicillium sp. HJT-A-10.

Seven undescribed polyketide compounds (1-4, 9-11) and six known polyketide compounds (5-8,12, 13) were isolated from Rhodiola tibetica endophytic Penicillium sp. HJT-A-10. The structural of seven undescribed polyketides metabolites were established on the basis of spectroscopic methods. The results of anti-inflammatory activity showed that compounds 1-8，10-13 had significant inhibitory effects on LPS-induced NO production in RAW 264.7 cells.

Comparative analysis of mycobacterial NADH pyrophosphatase isoforms reveals a novel mechanism for isoniazid and ethionamide inactivation.

NADH pyrophosphatase (NudC) catalyses the hydrolysis of NAD(H) to AMP and NMN(H) [nicotinamide mononucleotide (reduced form)]. NudC multiple sequence alignment reveals that homologues from most Mycobacterium tuberculosis isolates, but not other mycobacterial species, have a polymorphism at the highly conserved residue 237. To elucidate the functional significance of this polymorphism, comparative analyses were performed using representative NudC isoforms from M. tuberculosis H37Rv (NudC(Rv)) and M. bovis BCG (NudC(BCG)). Biochemical analysis showed that the P237Q polymorphism prevents dimer formation, and results in a loss of enzymatic activity. Importantly, NudC(BCG) was found to degrade the active forms of isoniazid (INH), INH-NAD and ethionamide (ETH), ETH-NAD. Consequently, overexpression of NudC(BCG) in Mycobacterium smegmatis mc(2)155 and M. bovis BCG resulted in a high level of resistance to both INH and ETH. Further genetic studies showed that deletion of the nudC gene in M. smegmatis mc(2)155 and M. bovis BCG resulted in increased susceptibility to INH and ETH. Moreover, inactivation of NudC in both strains caused a defect in drug tolerance phenotype for both drugs in exposure assays. Taken together, these data suggest that mycobacterial NudC plays an important role in the inactivation of INH and ETH.

CobB regulates Escherichia coli chemotaxis by deacetylating the response regulator CheY.

The silent information regulator (Sir2) family proteins are NAD+-dependent deacetylases. Although a few substrates have been identified, functions of the bacteria Sir2-like protein (CobB) still remain unclear. Here the role of CobB on Escherichia coli chemotaxis was investigated. We used Western blotting and mass spectrometry to show that the response regulator CheY is a substrate of CobB. Surface plasmon resonance (SPR) indicated that acetylation affects the interaction between CheY and the flagellar switch protein FliM. The presence of intact flagella in knockout strains DeltacobB, Deltaacs, Delta(cobB) Delta(acs), Delta(cheA) Delta(cheZ), Delta(cheA) Delta(cheZ) Delta(cobB) and Delta(cheA) Delta(cheZ) Delta(acs) was confirmed by electron microscopy. Genetic analysis of these knockout strains showed that: (i) the DeltacobB mutant exhibited reduced responses to chemotactic stimuli in chemotactic assays, whereas the Deltaacs mutant was indistinguishable from the parental strain, (ii) CheY from the DeltacobB mutant showed a higher level of acetylation, indicating that CobB can mediate the deacetylation of CheY in vivo, and (iii) deletion of cobB reversed the phenotype of Delta(cheA) Delta(cheZ). Our findings suggest that CobB regulates E. coli chemotaxis by deacetylating CheY. Thus a new function of bacterial cobB was identified and also new insights of regulation of bacterial chemotaxis were provided.

Biochemical characterization and mutational improvement of a thermophilic esterase from Sulfolobus solfataricus P2.

A thermophilic esterase, SsoPEst, from Sulfolobus solfataricus P2 was cloned and expressed in E. coli AD494 (DE3). Gene sequencing indicated the encoded 353 amino acids had less than 32% identity with reported esterases. The recombinant enzyme hydrolyzed p-nitrophenyl esters but not tributyrin or tricaprylin, exhibiting the highest specific activity (1.1 U/mg) with p-nitrophenyl caprylate. The enzyme was optimally active at pH 5.5 and 80 degrees C. It retained 50% activity after 1 h incubation at 80 degrees C. Activity was significantly inhibited by PMSF. Five SsoPEst mutants were generated by site-directed mutagenesis. One mutant had a higher specific activity of 2.8 U/mg at 37 degrees C and 14 U/mg at 80 degrees C than the wild-type enzyme which exhibited 0.7 U/mg at 37 degrees C and 3.8 U/mg at 80 degrees C against p-nitrophenyl butyrate.

Characterization of glycerol dehydratase expressed by fusing its alpha- and beta-subunits.

The gdh and gdhr genes, encoding B(12)-dependent glycerol dehydratase (GDH) and glycerol dehydratase reactivase (GDHR), respectively, in Klebsiella pneumoniae, were cloned and expressed in E. coli. Part of the beta-subunit was lost during GDH purification when co-expressing alpha, beta and gamma subunit. This was overcome by fusing the beta-subunit to alpha- or gamma-subunit with/without the insertion of a linker peptide between the fusion moieties. The kinetic properties of the fusion enzymes were characterized and compared with wild type enzyme. The results demonstrated that the fusion protein GDHALB/C, constructed by linking the N-terminal of beta-subunit to the C-terminal of alpha subunit through a (Gly(4)Ser)(4) linker peptide, had the greatest catalytic activity. Similar to the wild-type enzyme, GDHALB/C underwent mechanism-based inactivation by glycerol during catalysis and could be reactivated by GDHR.

4-XL-PPD, a novel ginsenoside derivative, as potential therapeutic agents for gastric cancer shows anti-cancer activity via inducing cell apoptosis medicated generation of reactive oxygen species and inhibiting migratory and invasive.

(20R)-Dammarane-3ß, 12ß, 20, 25-tetrol (25-OH-PPD) is a ginsenoside isolated from Panax ginseng (C. A. Meyer). Previous research shows that the compound exhibits anti-cancer activities on many human cancer cell lines. In an attempt to enhance 25-OH-PPD activity, some derivatives were synthesized. Through screening of the derivative compounds for anti-cancer activity against gastric carcinoma cells, 12ß-O-(L-Chloracetyl)-dammar-20(22)-ene-3ß, 25-diol (4-XL-PPD) was selected as a strong anti-cancer agent. In this study, the anti-cancer mechanisms of 4-XL-PPD were investigated. The results showed that compound 4-XL-PPD resulted in a concentration-dependent inhibition of cells viability in gastric cancer cells, without affecting the viability of normal cell (human gastric epithelial cell line-GES-1). In BGC-803 cancer cells, 4-XL-PPD triggered apoptosis, and stimulated reactive oxygen species production. Apoptosis can be attenuated by the reactive oxygen species scavenger N-acetylcysteine. Meantime, 4-XL-PPD effectively suppressed the migratory and invasive capabilities of BGC-803 cancer cell and inhibited the expression levels of proteins associated with migratory and invasive capabilities (MMP-2, MMP-9, E-cadherin and CD34). All the results suggest that 4-XL-PPD exhibited remarkable anticancer activity base on inducing apoptosis via generating reactive oxygen species and inhibiting migratory and invasive, which support development of 4-XL-PPD as a potential agent for cancer therapy.

Anticancer activity and potential mechanisms of 1C, a ginseng saponin derivative, on prostate cancer cells.

BACKGROUND: AD-2 (20(R)-dammarane-3b, 12b, 20, 25-tetrol; 25-OH-PPD) is a ginsenoside and isolated from Panax ginseng, showing anticancer activity against extensive human cancer cell lines. In this study, effects and mechanisms of 1C ((20R)-3b-O-(L-alanyl)-dammarane-12b, 20, 25-triol), a modified version of AD-2, were evaluated for its development as a novel anticancer drug. METHODS: MTT assay was performed to evaluate cell cytotoxic activity. Cell cycle and levels of reactive oxygen species (ROS) were determined using flow cytometry analysis. Western blotting was employed to analyze signaling pathways. RESULTS: 1C concentration-dependently reduces prostate cancer cell viability without affecting normal human gastric epithelial cell line-1 viability. In LNCaP prostate cancer cells, 1C triggered apoptosis via Bcl-2 family-mediated mitochondria pathway, downregulated expression of mouse double minute 2, upregulated expression of p53 and stimulated ROS production. ROS scavenger, N-acetylcysteine, can attenuate 1C-induced apoptosis. 1C also inhibited the proliferation of LNCaP cells through inhibition on Wnt/ß-catenin signaling pathway. CONCLUSION: 1C shows obvious anticancer activity based on inducing cell apoptosis by Bcl-2 family-mediated mitochondria pathway and ROS production, inhibiting Wnt/ß-catenin signaling pathway. These findings demonstrate that 1C may provide leads as a potential agent for cancer therapy.

Identification of Serine 119 as an Effective Inhibitor Binding Site of M. tuberculosis Ubiquitin-like Protein Ligase PafA Using Purified Proteins and M. smegmatis.

Owing to the spread of multidrug resistance (MDR) and extensive drug resistance (XDR), there is a pressing need to identify potential targets for the development of more-effective anti-M. tuberculosis (Mtb) drugs. PafA, as the sole Prokaryotic Ubiquitin-like Protein ligase in the Pup-proteasome System (PPS) of Mtb, is an attractive drug target. Here, we show that the activity of purified Mtb PafA is significantly inhibited upon the association of AEBSF (4-(2-aminoethyl) benzenesulfonyl fluoride) to PafA residue Serine 119 (S119). Mutation of S119 to amino acids that resemble AEBSF has similar inhibitory effects on the activity of purified Mtb PafA. Structural analysis reveals that although S119 is distant from the PafA catalytic site, it is located at a critical position in the groove where PafA binds the C-terminal region of Pup. Phenotypic studies demonstrate that S119 plays critical roles in the function of Mtb PafA when tested in M. smegmatis. Our study suggests that targeting S119 is a promising direction for developing an inhibitor of M. tuberculosis PafA.

Anti-folates potentiate bactericidal effects of other antimicrobial agents.

Synergies between sulfonamides and other antimicrobial agents have long been reported, but the reason still remains unclear. Previously, Vilchèze et al. found that, sulfamethoxazole (SMX) could potentiate the bacterialcidal activity of isoniazid (INH) and rifampin (RIF) in Mycobacterium tuberculosis. To test if this was also the case in other bacteria, the ability to potentiate bactericidal effect of RIF by SMX was evaluated in Escherichia coli, Staphylococcus aureus, Salmonella typhimurium and Mycobacterium smegmatis. And the ability to potentiate bactericidal effect of streptomycin (SM) by SMX was also evaluated in E. coli and M. Smegmatis. Susceptibility tests and drug exposure experiments were performed for RIF and SM in the presence of sub-ICs of SMX. In drug exposure experiments, 10 mg l-1 of 7,8-dihydropteroic acid (DHP) was used to reverse the effect of SMX. In the presence of sub-ICs of SMX, MIC of RIF for E. coli and M. smegmatis decreased 2 and 16 fold, respectively. In the drug exposure experiments, addition of sub-ICs of SMX suppressed the growth of RIF and SM resistant population in a pool of susceptible bacteria, and the effects of SMX could be reversed by DHP. Besides, we also found that, sub-ICs of para-aminosalicylic acid (PAS) could bactericidal effects of INH, RIF and SM in M. tuberculosis. Taken together, our data suggest that, sub-ICs of anti-folates can potentiate bactericidal effects of other antimicrobial agents in various bacteria.

12-Chloracetyl-PPD, a novel dammarane derivative, shows anti-cancer activity via delay the progression of cell cycle G2/M phase and reactive oxygen species-mediate cell apoptosis.

(20R)-Dammarane-3ß, 12ß, 20, 25-tetrol (25-OH-PPD) is a ginsenoside isolated from Panax ginseng (C. A. Meyer). This compound exhibits anti-cancer activities on many human cancer cell lines. In this study, we investigated anti-cancer mechanisms of 12ß-O-(L-Chloracetyl)-dammar-20(22)-ene-3ß,25-diol(12-Chloracetyl-PPD), a modified 25-OH-PPD. We found that compound 12-Chloracetyl-PPD resulted in a concentration-dependent inhibition of viability in prostate, breast, and gastric cancer cells, without affecting the viability of normal cell (human gastric epithelial cell line-GES-1, hair follicle dermal papilla cell line-HHDPC and rat myocardial cell line-H9C2). In MDA-MB-435 and C4-2B cancer cells, 12-Chloracetyl-PPD induced G2/M cell cycle arrest, down-regulated mouse double minute 2 (MDM2) expression, up-regulated p53 expression, triggered apoptosis, and stimulated reactive oxygen species production. Apoptosis can be attenuated by the reactive oxygen species scavenger N-acetylcysteine. Our results suggested that compound 12-Chloracetyl-PPD showed obvious anti-cancer activity based on delaying cell cycle arrest and inducing cell apoptosis by reactive oxygen species production, which supported development of 12-Chloracetyl-PPD as a potential agent for cancer chemotherapy.

Reversibly acetylated lysine residues play important roles in the enzymatic activity of Escherichia coli N-hydroxyarylamine O-acetyltransferase.

CobB is a bacterial NAD(+)-dependent protein deacetylase. Although progress has been made in functional studies of this protein in recent years, its substrates and biological functions are still largely unclear. Using proteome microarray technology, potential substrates of Escherichia coli CobB were screened and nine proteins were identified, including N-hydroxyarylamine O-acetyltransferase (NhoA). In vitro acetylation/deacetylation of NhoA was verified by western blotting and mass spectrometry, and two acetylated lysine residues were identified. Site-specific mutagenesis experiments showed that mutation of each acetylated lysine decreased the acetylation level of NhoA in vitro. Further analysis showed that variant NhoA proteins carrying substitutions at the two acetylated lysine residues are involved in both the O-acetyltransferase and N-acetyltransferase activity of NhoA. Structural analyses were also performed to explore the effects of the acetylated lysine residues on the activity of NhoA. These results suggest that reversible acetylation may play a role in the activity of Escherichia coli NhoA.