Dimerization Mediated by a Divergent Forkhead-associated Domain Is Essential for the DNA Damage and Spindle Functions of Fission Yeast Mdb1

MDC1 is a key factor of DNA damage response in mammalian cells. It possesses two phospho-binding domains. In its C terminus, a tandem BRCA1 C-terminal domain binds phosphorylated histone H2AX, and in its N terminus, a forkhead-associated (FHA) domain mediates a phosphorylation-enhanced homodimerization. The FHA domain of the Drosophila homolog of MDC1, MU2, also forms a homodimer but utilizes a different dimer interface. The functional importance of the dimerization of MDC1 family proteins is uncertain. In the fission yeast Schizosaccharomyces pombe, a protein sharing homology with MDC1 in the tandem BRCA1 C-terminal domain, Mdb1, regulates DNA damage response and mitotic spindle functions. Here, we report the crystal structure of the N-terminal 91 amino acids of Mdb1. Despite a lack of obvious sequence conservation to the FHA domain of MDC1, this region of Mdb1 adopts an FHA-like fold and is therefore termed Mdb1-FHA. Unlike canonical FHA domains, Mdb1-FHA lacks all the conserved phospho-binding residues. It forms a stable homodimer through an interface distinct from those of MDC1 and MU2. Mdb1-FHA is important for the localization of Mdb1 to DNA damage sites and the spindle midzone, contributes to the roles of Mdb1 in cellular responses to genotoxins and an antimicrotubule drug, and promotes in vitro binding of Mdb1 to a phospho-H2A peptide. The defects caused by the loss of Mdb1-FHA can be rescued by fusion with either of two heterologous dimerization domains, suggesting that the main function of Mdb1-FHA is mediating dimerization. Our data support that FHA-mediated dimerization is conserved for MDC1 family proteins.     

The crystal structure of the MPN domain from the COP9 signalosome subunit CSN6

The COP9 signalosome (CSN) is a multiprotein complex containing eight subunits and is highly conserved from fungi to human. CSN is proposed to widely participate in many physiological processes, including protein degradation, DNA damage response and signal transduction. Among those subunits, only CSN5 and CSN6 belong to JAMM family. CSN5 possesses isopeptidase activity, but CSN6 lacks this ability. Here we report the 2.5 Å crystal structure of MPN domain from Drosophila melanogaster CSN6. Structural comparison with other MPN domains, along with bioinformation analysis, suggests that MPN domain from CSN6 may serve as a scaffold instead of a metalloprotease.Structured summary of protein interactionsCSN6 and CSN6 bind by x-ray crystallography (View interaction)CSN6 and CSN6 bind by x ray scattering (View interaction)     

Structure of a dimeric fungal α-type carbonic anhydrase

The crystal structure of Aspergillus oryzae carbonic anhydrase (AoCA) was determined at 2.7 Å resolution and it revealed a dimer, which only has precedents in the α class in two membrane and cancer-associated enzymes. α carbonic anhydrases are underrepresented in fungi compared to the β class, this being the first structural representative. The overall fold and zinc binding site resemble other well studied carbonic anhydrases. A major difference is that the histidine, thought to be the major proton shuttle residue in most mammalian enzymes, is replaced by a phenylalanine in AoCA. This finding poses intriguing questions as to the biological functions of fungal α carbonic anhydrases, which are promising candidates for biotechnological applications.Structured summaryAoCA binds to AoCA by molecular sieving (View interaction)AoCA binds to AoCA X-ray crystallography (View interaction)     

Design and biological testing of peptidic dimerization inhibitors of human Hsp90 that target the C-terminal domain

BackgroundSmall molecules targeting the dimerization interface of the C-terminal domain of Hsp90, a validated target for cancer treatment, have yet to be identified.MethodsThree peptides were designed with the aim to inhibit the dimerization of Hsp90. Computational and biophysical methods examined the α-helical structure for the three peptides. Based on the Autodisplay technology, a novel flow cytometer dimerization assay was developed to test inhibition of Hsp90 dimerization. Microscale thermophoresis was used to determine the K_D of the peptides towards the C-terminal domain of Hsp90.ResultsMD simulations and CD spectroscopy indicated an α-helical structure for two of the three peptides. By flow cytometer analysis, IC₅₀ values of 2.08 μM for peptide H2 and 8.96 μM for peptide H3 were determined. Dimer formation of the C-terminal dimerization domain was analyzed by microscale thermophoresis, and a K_D of 1.29 nM was determined. Furthermore, microscale thermophoresis studies demonstrated a high affinity binding of H2 and H3 to the C-terminal domain, with a K_D of 1.02 μM and 1.46 μM, respectively.ConclusionsThese results revealed the first peptidic inhibitors of Hsp90 dimerization targeting the C-terminal domain. Furthermore, it has been shown that these peptides bind to the C-terminal domain with a low micromolar affinity.General significanceThese results can be used to design and screen for small molecules that inhibit the dimerization of the C-terminal domain of Hsp90, which could open a new route for cancer therapy.     

Crystal structure of cce_0566 from Cyanothece 51142, a protein associated with nitrogen fixation in the DUF269 family

The crystal structure for cce_0566 (171 aa, 19.4 kDa), a DUF269 annotated protein from the diazotrophic cyanobacterium Cyanothece sp. ATCC 51142, was determined to 1.60 Å resolution. Cce_0566 is a homodimer with each molecule composed of eight α-helices folded on one side of a three strand anti-parallel β-sheet. Hydrophobic interactions between the side chains of largely conserved residues on the surface of each β-sheet hold the dimer together. The fold observed for cce_0566 may be unique to proteins in the DUF269 family, hence, the protein may also have a function unique to nitrogen fixation. A solvent accessible cleft containing conserved charged residues near the dimer interface could represent the active site or ligand-binding surface for the protein’s biological function.Structured summary of protein interactionsDUF269 and DUF269 bind by x-ray crystallography (View interaction)     

Structural insights into the dual substrate specificities of mammalian and Dictyostelium dihydropteridine reductases toward two stereoisomers of quinonoid dihydrobiopterin

Up to now, d-threo-tetrahydrobiopterin (DH₄, dictyopterin) was detected only in Dictyostelium discoideum, while the isomer l-erythro-tetrahydrobioterin (BH₄) is common in mammals. To elucidate the mechanism of DH₄ regeneration by D. discoideum dihydropteridine reductase (DicDHPR), we have determined the crystal structure of DicDHPR complexed with NAD⁺ at 2.16 Å resolution. Significant structural differences from mammalian DHPRs are found around the coenzyme binding site, resulting in a higher K_m value for NADH (K_m = 46.51 ± 0.4 μM) than mammals. In addition, we have found that rat DHPR as well as DicDHPR could bind to both substrates quinonoid-BH₂ and quinonoid-DH₂ by docking calculations and have confirmed their catalytic activity by in vitro assay.Structured summary of protein interactionsDHPR binds to DHPR by X-ray crystallography (View interaction)     

Does Availability of Reliable Home Blood Glucose Data at Diabetes Appointments Improve Glycemia?

ObjectiveTo establish the prevalence of reliable self-monitored blood glucose (r-SMBG) data at office visits for diabetes and to determine whether r-SMBG is associated with changes in glycemic control and other clinical parameters.MethodsWe conducted a chart review of 500 patients followed in an Endocrinology Faculty/Commercial Insurance Practice (FP) or a Managed Medicare/Medicaid Diabetes Clinic (MDC). Follow-up visits for patients with type 1 or type 2 diabetes from January 1, 2012 to June 30, 2012 were analyzed for anthropometric data, creatinine (Cr), glomerular filtration rate (GFR), low-density lipoprotein cholesterol (LDL-C), medications, hemoglobin A1C (A1C), change in A1C from the previous visit (ΔA1C), and availability of r-SMBG data at the visit.ResultsOur sample was composed of 215 MDC patients (43%) and 285 FP patients (57%). Overall, 151 patients (30%) provided r-SMBG data at their visit, with no difference between MDC or FP patients. Mean A1C at MDC was 9.1%, while mean A1C at FP was 7.9% (P < .001). MDC patients with A1C > 8.0% demonstrated an A1C reduction of 1.2% if they provided r-SMBG, compared to an increase of 0.1% for MDC patients who did not (P < .05). Providing r-SMBG did not affect A1C in FP patients in any A1C range.ConclusionOnly a minority of diabetes patients, mostly insulin-treated, made r-SMBG data available to their providers. Insulin-requiring Managed Medicare/ Medicaid patients with poorly controlled diabetes had an A1c reduction associated with r-SMBG. Prospective studies are needed to determine whether this patient population may be more likely to benefit from r-SMBG at their visits. (Endocr Pract. 2014;20:299-304)     

Structural and SAXS analysis of the budding yeast SHU-complex proteins

In Saccharomyces cerevisiae, four proteins, Shu1, Shu2, Psy3 and Csm2, form a stable SHU-complex both in vivo and in vitro. These proteins are involved in the early stages of the homologous recombination DNA damage repair process. In this paper, the crystal structure of the Psy3–Csm2 sub-complex is presented at 1.8 Å resolution and successfully fitted into our small angle X-ray scattering (SAXS) data of the SHU-complex. Taken together with our electrophoretic mobility shift assay (EMSA) results, a model is proposed for the SHU–protein complex coupled with DNA.Structured summary of protein interactions:PSY3 and CSM2 bind by X-ray crystallography (View interaction) PSY3, CSM2, Shu 1 and Shu 2 physically interact by x ray scattering (View interaction)     

Structural mechanism of the phosphorylation-dependent dimerization of the MDC1 forkhead-associated domain

MDC1 is a key mediator of the DNA-damage response in mammals with several phosphorylation-dependent protein interaction domains. The function of its N-terminal forkhead-associated (FHA) domain remains elusive. Here, we show with structural, biochemical and cellular data that the FHA domain mediates phosphorylation-dependent dimerization of MDC1 in response to DNA damage. Crystal structures of the FHA domain reveal a face-to-face dimer with pseudo-dyad symmetry. We found that the FHA domain recognizes phosphothreonine 4 (pT4) at the N-terminus of MDC1 and determined its crystal structure in complex with a pT4 peptide. Biochemical analysis further revealed that in the dimer, the FHA domain binds in trans to pT4 from the other subunit, which greatly stabilizes the otherwise unstable dimer. We show that T4 is phosphorylated primarily by ATM upon DNA damage. MDC1 mutants with the FHA domain deleted or impaired in its ability to dimerize formed fewer foci at DNA-damage sites, but the localization defect was largely rescued by an artificial dimerization module, suggesting that dimerization is the primary function of the MDC1 FHA domain. Our results suggest a novel mechanism for the regulation of MDC1 function through T4 phosphorylation and FHA-mediated dimerization.     

Comparing anti-HIV,antibacterial, antifungal,micellar, and cytotoxic properties of tricarboxylato dendritic amphiphiles

Three series of homologous dendritic amphiphiles—RCONHC(CH₂CH₂COOH)₃, 1(n); ROCONHC(CH₂CH₂COOH)₃, 2(n); RNHCONHC(CH₂CH₂COOH)₃, 3(n), where R = n-C_nH_2n+1 and n = 13–22 carbon atoms—were assayed for their potential to serve as antimicrobial components in a topical vaginal formulation. Comparing epithelial cytotoxicities to the ability of these homologues to inhibit HIV, Neisseria gonorrhoeae, and Candida albicans provided a measure of their prophylactic/therapeutic potential. Measurements of the ability to inhibit Lactobacillus plantarum, a beneficial bacterium in the vagina, and critical micelle concentrations (CMCs), an indicator of the potential detergency of these amphiphiles, provided additional assessments of safety. Several amphiphiles from each homologous series had modest anti-HIV activity (EC₅₀ = 110–130 μM). Amphiphile 2(18) had the best anti-Neisseria activity (MIC = 65 μM), while 1(19) and 1(21) had MICs against C. albicans of 16 and 7.7 μM, respectively. Two measures of safety showed promise as all compounds had relatively low cytotoxic activity (EC₅₀ = 210–940 μM) against epithelial cells and low activity against L. plantarum, 1(n), 2(n), and 3(n) had MICs ? 490, 1300, and 940 μM, respectively. CMCs measured in aqueous triethanolamine and in aqueous potassium hydroxide showed linear dependences on chain length. As expected, the longest chain in each series had the lowest CMC—in triethanolamine: 1(21), 1500 μM; 2(22), 320 μM; 3(22), 340 μM, and in potassium hydroxide: 1(21), 130 μM; 3(22), 40 μM. The CMC in triethanolamine adjusted to pH 7.4 was 400 μM for 1(21) and 3900 μM for 3(16). The promising antifungal activity, low activity against L. plantarum, relatively high CMCs, and modest epithelial cytotoxicity in addition to their anti-Neisseria properties warrant further design studies with dendritic amphiphiles to improve their safety indices to produce suitable candidates for antimicrobial vaginal products.     

Synthesis,X-ray crystal structure,DNA/protein binding and cytotoxicity studies of five α-aminophosphonate N-derivatives

Five new α-aminophosphonates are synthesized and characterized by EA, FT-IR, ¹H NMR, ¹³C NMR, ³¹P NMR, ESI-MS and X-ray crystallography. The X-ray analyses reveal that the crystal structures of 1–5 are monoclinic or triclinic system with the space group P 21/c, P − 1, P − 1, P2(1)/c and P − 1, respectively. All P atoms of 1–5 have tetrahedral geometries involving two O-ethyl groups, one C_α atom, and a double bond O atom. The binding interaction of five new α-aminophosphonate N-derivatives (1–5) with calf thymus(CT)-DNA have been investigated by UV–visible and fluorescence emission spectrometry. The apparent binding constant (Kapp) values follows the order: 1 (3.38 × 10⁵ M⁻¹) > 2 (3.04 × 10⁵ M⁻¹) > 4 (2.52 × 10⁵ M⁻¹) > 5 (2.32 × 10⁵ M⁻¹) > 3 (2.10 × 10⁵ M⁻¹), suggesting moderate intercalative binding mode between the compounds and DNA. In addition, fluorescence spectrometry of bovine serum albumin (BSA) with the compounds 1–5 showed that the quenching mechanism might be a static quenching procedure. For the compounds 1–5, the number of binding sites were about one for BSA and the binding constants follow the order: 1 (2.72 × 10⁴ M⁻¹) > 2 (2.27 × 10⁴ M⁻¹) > 4 (2.08 × 10⁴ M⁻¹) > 5 (1.79 × 10⁴ M⁻¹) > 3 (1.17 × 10⁴ M⁻¹). Moreover, the DNA cleavage abilities of 1 exhibit remarkable changes and the in vitro cytotoxicity of 1 on tumor cells lines (MCF-7, HepG2 and HT29) have been examined by MTT and shown antitumor effect on the tested cells.     

Synthesis,crystal structure and magnetic properties of the spin crossover system [Fe(pq)3]2+

Three new compounds formulated (ClO₄)₂[Fe(pq)₃] (1), (BF₄)₂[Fe(pq)₃] · EtOH (2) and {(ClO₄)[MnCr(C₂O₄)₃][Fe(pq)₂(H₂O)₂]} (3), where pq is 2,2′-pyridylquinoline, have been synthesised and characterised. Despite the different crystal packing exhibited by 1 and 2, the cationic species [Fe(pq)₃]²⁺ are structurally quite similar. At 293 K, the Fe–N bond lengths are characteristic of the iron(II) in the high-spin state. In contrast to 1, 2 undergoes a continuous spin transition. Indeed, at 95 K its structure experiences a noticeable change in the Fe–N bonds and angles, i.e. the Fe–N bonds shorten by 0.194 Å on the average. The magnetic behaviour confirms that 1 is fully high-spin in the 4–300 K temperature range while 2 shows a spin transition centred at T_1/2 = 150 K. The corresponding enthalpy, entropy and interaction parameter are ΔH = 7.49 kJ mol^?1, ΔS = 50 J K^?1 mol^?1and Γ = 1.35 kJ mol^?1. Compound 3 has been obtained as a microcrystalline powder. The magnetic properties of 3 point at the occurrence of ferromagnetic coupling below 100 K and the onset of a ferromagnetic ordering below 10 K (Weiss constant equal to 6.8 K). The Mössbauer spectra of 3 show the occurrence of a magnetic order at T ? 4.2 K.     

Synthesis and antioxidant evaluation of (S,S)- and (R,R)-secoisolariciresinol diglucosides (SDGs)

Secoisolariciresinol diglucosides (SDGs) (S,S)-SDG-1 (major isomer in flaxseed) and (R,R)-SDG-2 (minor isomer in flaxseed) were synthesized from vanillin via secoisolariciresinol (6) and glucosyl donor 7 through a concise route that involved chromatographic separation of diastereomeric diglucoside derivatives (S,S)-8 and (R,R)-9. Synthetic (S,S)-SDG-1 and (R,R)-SDG-2 exhibited potent antioxidant properties (EC₅₀ = 292.17 ± 27.71 μM and 331.94 ± 21.21 μM, respectively), which compared well with that of natural (S,S)-SDG-1 (EC₅₀ = 275.24 ± 13.15 μM). These values are significantly lower than those of ascorbic acid (EC₅₀ = 1129.32 ± 88.79 μM) and α-tocopherol (EC₅₀ = 944.62 ± 148.00 μM). Compounds (S,S)-SDG-1 and (R,R)-SDG-2 also demonstrated powerful scavenging activities against hydroxyl [natural (S,S)-SDG-1: 3.68 ± 0.27; synthetic (S,S)-SDG-1: 2.09 ± 0.16; synthetic (R,R)-SDG-2: 1.96 ± 0.27], peroxyl [natural (S,S)-SDG-1: 2.55 ± 0.11; synthetic (S,S)-SDG-1: 2.20 ± 0.10; synthetic (R,R)-SDG-2: 3.03 ± 0.04] and DPPH [natural (S,S)-SDG-1: EC₅₀ = 83.94 ± 2.80 μM; synthetic (S,S)-SDG-1: EC₅₀ = 157.54 ± 21.30 μM; synthetic (R,R)-SDG-2: EC₅₀ = 123.63 ± 8.67 μM] radicals. These results confirm previous studies with naturally occurring (S,S)-SDG-1 and establish both (S,S)-SDG-1 and (R,R)-SDG-2 as potent antioxidants and free radical scavengers for potential in vivo use.     

Subunit CydX of Escherichia coli cytochrome bd ubiquinol oxidase is essential for assembly and stability of the di-heme active site

Cytochrome bd ubiquinol oxidase uses the electron transport from ubiquinol to oxygen to establish a proton gradient across the membrane. The enzyme complex consists of subunits CydA and B and contains two b- and one d-type hemes as cofactors. Recently, it was proposed that a third subunit named CydX is essential for the function of the complex. Here, we show that CydX is indeed a subunit of purified Escherichia coli cytochrome bd oxidase and that the small protein is needed either for the assembly or the stability of the active site di-heme center and, thus, is essential for oxidase activity.Structured summary of protein interactionscydA physically interacts with cydB by affinity technology (View interaction)cydA physically interacts with cydB by molecular sieving (View interaction)cydB, cydA and cydX physically interact by molecular sieving (View interaction)cydB, cydA, and cydX physically interacts by affinity technology (1, 2)     

Design,synthesis, and DNA binding characteristics of a group of orthogonally positioned diamino,N-formamido,pyrrole- and imidazole-containing polyamides

Orthogonally positioned diamino/dicationic polyamides (PAs) have good water solubility and enhanced binding affinity, whilst retaining DNA minor groove and sequence specificity compared to their monoamino/monocationic counterparts. The synthesis and DNA binding properties of the following diamino PAs: f-IPI (3a), f-IPP (4), f-PIP (5), and f-PPP (6) are described. P denotes the site where a 1-propylamino group is attached to the N1-position of the heterocycle. Binding of the diamino PAs to DNA was assessed by DNase I footprinting, thermal denaturation, circular dichroism titration, biosensor surface plasmon resonance (SPR), and isothermal titration calorimetry (ITC) studies. According to SPR studies, f-IPI (3a) bound more strongly (K_eq = 2.4 × 10⁸ M^?1) and with comparable sequence selectivity to its cognate sequence 5′-ACGCGT-3′ when compared to its monoamino analog f-IPI (1). The binding of f-IPI (3a) to 5′-ACGCGT-3′ via the stacked dimer motif was balanced between enthalpy and entropy, and that was quite different from the enthalpy-driven binding of its monoamino parent f-IPI (1). f-IPP (4) also bound more strongly to its cognate sequence 5′-ATGCAT-3′ (K_eq = 7.4 × 10⁶ M^?1) via the side-by-side stacked motif than its monoamino analog f-IPP (2a). Although f-PPP (6) bound via a 1:1 motif, it bound strongly to its cognate sequence 5′-AAATTT-3′ (K_eq = 4.8 × 10⁷ M^?1), 15-times higher than the binding of its monoamino analog f-PPP (2c), albeit f-PPP bound via the stacked motif. Finally, f-PIP (5) bound to its target sequence 5′-ATCGAT-3′ as a stacked dimer and it has the lowest affinity among the diamino PAs tested (K_eq <1 × 10⁵ M^?1). This was about two times lower in affinity than the binding of its monoamino analog f-PIP (2b). The results further demonstrated that the ‘core rules’ of DNA recognition by monoamino PAs also apply to their diamino analogs. Specifically, PAs that contain a stacked IP core structure bind most strongly (highest binding constants) to their cognate GC doublet, followed by the binding of PAs with a stacked PP structure to two degenerate AT base pairs, and finally the binding of PAs with a PI core to their cognate CG doublet.     

Activity of three cytotoxic isoflavonoids from Erythrina excelsa and Erythrina senegalensis (neobavaisoflavone,sigmoidin H and isoneorautenol) toward multi-factorial drug resistant cancer cells

IntroductionResistance of cancer cells to chemotherapy has become a worldwide concern. Naturally occuring isoflavonoids possess a variety of biological activities including anti-cancer effects. The present study was aimed at investigating the cytotoxicity and the modes of action of three naturally occuring isoflavonoids, neobavaisoflavone (1), sigmoidin H (2) and a pterocarpan that is a special type of isoflavonoid, isoneorautenol (3) against a panel of nine cancer cell lines, including various sensitive and drug-resistant phenotypes.MethodsThe cytotoxicity of the compounds was determined using a resazurin reduction assay, whereas the caspase-Glo assay was used to detect the activation of caspases 3/7, caspase 8 and caspase 9 in cells treated with compounds 3. Flow cytometry was used for cell cycle analysis and detection of apoptotic cells, analysis of mitochondrial membrane potential (MMP) as well as measurement of reactive oxygen species (ROS).ResultsCompounds 3 showed significant cytotoxicity toward sensitive and drug-resistant cancer cell lines. Compounds 1 and 2 were selectively active, and IC50 values below 115 μM were obtained on 6/9 and 4/9 cell lines respectively with values ranging from 42.93 μM (toward CCRF-CEM cells) to 114.64 μM [against HCT116 (p53^+/+) cells] for 1 and 25.59 μM (toward U87MG) to 110.51 μM [against HCT116 (p53^+/+) cells] for 2. IC50 values ranging from 2.67 μM (against MDA-MB 237BCRP cells) to 21.84 (toward U87MG) were measured for compound 3 and between 0.20 μM (toward CCRF-CEM cells) and 195.12 μM (toward CEM/ADR5000 cells) for doxorubicin as control drug. BCRP-transfected MDA-MB-231 cells, HCT116 (p53^+/+) and U87MG.ΔEGFR cells were hypersensitive (collateral sensitive) to compound 3 as compared to their counterpart cell lines. Compound 3 induced apoptosis in CCRF-CEM cells via activation of caspases 3/7, 8 and 9 as well as the loss of MMP and increased ROS production.ConclusionsThe cytotoxicity of the studied isoflavonoids and especially the pterocarpan 3 deserve more detailed exploration in the future to develop novel anticancer drugs against sensitive and otherwise drug-resistant phenotypes.     

Rheediinosides A and B,two antiproliferative and antioxidant triterpene saponins from Entada rheedii

Two triterpenoid saponins have been isolated from the seed kernels of Entada rheedii. Their structures have been established using 1D- and 2D-NMR and mass spectrometry as 3-O-β-d-xylopyranosyl-(1 → 3)-O-α-l-arabinopyranosyl-(1 → 6)-2-acetylamino-2-deoxy-β-d-glucopyranosylentagenic acid 28-O-β-apiofuranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 2)-β-d-glucopyranoside (Rheediinoside A, 1) and 3-O-β-d-glucopyranosyl-(1 → 3)-O-[β-d-xylopyranosyl-(1 → 3)-α-l-arabinopyranosyl-(1 → 6)]-2-acetylamino-2-deoxy-β-d-glucopyranosylentagenic acid 28-O-β-apiofuranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 2)-β-d-glucopyranoside (Rheediinoside B, 2). Compounds 1 and 2 were tested for their antiproliferative activity against T98G, A431, PC3 and B16-F1 cell lines, and further for their antioxidant properties. Moderate cytotoxic potency and antioxidant properties were found for these compounds whereas Rheediinoside B was in all assays more active than Rheediinoside A.     

Syntheses,structures, and magnetic properties of heterobimetallic complexes based on tetracyanometallic building blocks

Two tetracyanometalate building blocks, [Fe(5,5′-dmbipy)(CN)₄]^? (2) and [Fe(4,4′-dmbipy)(CN)₄]^? (3) (5,5′-dmbipy = 5,5′-dimethyl-2,2′-bipyridine; 4,4′-dmbipy = 4,4′-dimethyl-2,2′-bipyridine), and two cyano-bridged heterobimetallic complexes, [Cu₂(bpca)₂(H₂O)₂Fe₂(5,5′-dmbipy)₂(CN)₈] · 2[Cu(bpca)Fe(5,5′-dmbipy)(CN)₄] · 4H₂O (4) and [Cu(bpca)Fe(4,4′-dmbipy)(CN)₄]_n (5) (bpca = bis(2-pyridylcarbonyl)amidate), have been synthesized and structurally characterized. Complex 4 contains two dinuclear and one tetranuclear heterobimetallic clusters in an asymmetric unit whereas the structure of complex 5 features a one-dimensional heterobimetallic zigzag chain. The Cu(II) ion is penta-coordinated in the form of a distorted square-based pyramid. Magnetic studies show ferromagnetic coupling between Cu(II) and Fe(III) ions with g = 2.28, J₁ = 2.64 cm^?1, J₂ = 5.40 cm^?1 and TIP = ?2.36 × 10^?3 for complex 4, and g = 2.17, J = 4.82 cm^?1 and zJ′ = 0.029 cm^?1 for complex 5.     

Coumarin-thiazole and -oxadiazole derivatives: Synthesis,bioactivity and docking studies for aldose/aldehyde reductase inhibitors

In continuation of our previous efforts directed towards the development of potent and selective inhibitors of aldose reductase (ALR2), and to control the diabetes mellitus (DM), a chronic metabolic disease, we synthesized novel coumarin-thiazole 6(a–o) and coumarin-oxadiazole 11(a–h) hybrids and screened for their inhibitory activity against aldose reductase (ALR2), for the selectivity against aldehyde reductase (ALR1). Compounds were also screened against ALR1. Among the newly designed compounds, 6c, 11d, and 11g were selective inhibitors of ALR2. Whereas, (E)-3-(2-(2-(2-bromobenzylidene)hydrazinyl)thiazol-4-yl)-2H-chromen-2-one 6c yielded the lowest IC₅₀ value of 0.16 ± 0.06 μM for ALR2. Moreover, compounds (E)-3-(2-(2-benzylidenehydrazinyl)thiazol-4-yl)-2H-chromen-2-one (6a; IC₅₀ = 2.94 ± 1.23 μM for ARL1 and 0.12 ± 0.05 μM for ARL2) and (E)-3-(2-(2-(1-(4-bromophenyl)ethylidene)hydrazinyl)thiazol-4-yl)-2H-chromen-2-one (6e; IC₅₀ = 1.71 ± 0.01 μM for ARL1 and 0.11 ± 0.001 μM for ARL2) were confirmed as dual inhibitors. Furthermore, compounds 6i, 6k, 6m, and 11b were found to be selective inhibitors for ALR1, among which (E)-3-(2-(2-((2-amino-4-chlorophenyl)(phenyl)methylene)hydrazinyl)thiazol-4-yl)-2H-chromen-2-one (6m) was most potent (IC₅₀ = 0.459 ± 0.001 μM). Docking studies performed using X-ray structures of ALR1 and ALR2 with the given synthesized inhibitors showed that coumarinyl thiazole series lacks the carboxylate function that could interact with the anionic binding site being a common ALR1/ALR2 inhibitors trait. Molecular docking study with dual inhibitor 6e also suggested plausible binding modes for the ALR1 and ALR2 enzymes. Hence, the results of this study revealed that coumarinyl thiazole and oxadiazole derivatives could act as potential ALR1/ALR2 inhibitors.     

Discovery of thioether-bridged cyclic pentapeptides binding to Grb2-SH2 domain with high affinity

Blocking the interaction between phosphotyrosine (pTyr)-containing activated receptors and the Src homology 2 (SH2) domain of the growth factor receptor-bound protein 2 (Grb 2) is considered to be an effective and non-cytotoxic strategy to develop new anti-proliferate agents due to its potential to shut down the Ras activation pathway. In this study, a series of phosphotyrosine containing cyclic pentapeptides were designed and synthesized based upon the phage library derived cyclopeptide, G1TE. A comprehensive SAR study was also carried out to develop potent Grb2-SH2 domain antagonists based upon this novel template. With both the peptidomimetic optimization of the amino acid side-chains and the constraint of the backbone conformation guided by molecular modeling, we developed several potent antagonists with low micromolar range binding affinity, such as cyclic peptide 15 with an K_d = 0.359 μM, which is providing a novel template for the development of Grb2-SH2 domain antagonists as potential therapeutics for certain cancers.