Assay of mitochondrial functions by resazurin in vitro

AIM: To study the mechanism of resazurin as indicator of mitochondrial function and to develop a rapid and sensitive assay for measuring metabolic activity of isolated mitochondria from rat liver in vitro. METHODS: The screening was carried out on 96-well microtitre plates by monitoring fluorescence intensity of resazurin reduced by mitochondria. Experimental conditions were optimized and influences of several inhibitors on mitochondrial function were observed. RESULTS: Fluorescence intensity increased in a linear manner when the mitochondrial protein concentration from 5 to 50 μg protein per well was incubated with resazurin (5μmol/L) during 230 min period at 37℃. Edetic acid could promote the reduction of resazurin in mitochondria. The fluorescence intensity decreased greatly after pretreatment with NAN3, antimycin A, carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP),and oligomycin compared with the control. However, the typical complex I inhibitor, rotenone enhanced the fluorescence intensity without mitochondria. CONCLUSION: Using resazurin to determine mitochondrial function is sensitive, inexpensive and could be easily automated for high throughput screening.     

Discovery of a novel inhibitor of NAD（P）＋-dependent malic enzyme （ME2） by high-throughput screening

Aim： Malic enzymes are oxidative decarboxylases with NAD or NAD（P） as cofactor that catalyze the conversion of L-malate to pyruvate and CO2. The aim of this study was to discover and characterize a potent inhibitor of human NAD（P）＋-dependent malic enzyme 2 （ME2）. Methods： Recombinant human ME2-His-Tag fusion protein was overexpressed in E coil and purified with Ni-NTA resin. A high- throughput screening （HTS） assay was developed to find ME2 inhibitors. Detergent Brij-35 was used to exclude false positives. The characteristics of the inhibitor were analyzed with enzyme kinetics analysis. A thermal shift assay for ME2 was carried out to verify the binding of the inhibitor with the enzyme. Results： An HTS system for discovering ME2 inhibitors was established with a Z＇ factor value of 0.775 and a signal-to-noise ratio （S/N） of 9.80. A library containing 12 683 natural products was screened. From 47 hits, NPD387 was identified as an inhibitor of ME2. The primary structure-activity relationship study on NPD387 derivatives showed that one derivative NPD389 was more potent than the parent compound NPD387 （the ICso of NPD389 was 4.63±0.36 pmoVL or 5.59±0.38 pmoVL, respectively, in the absence or presence of 0.01% Brij-35 in the assay system）. The enzyme kinetics analysis showed that NPD389 was a fast-binding uncompetitive inhibitor with respect to the substrate NAD~ and a mixed-type inhibitor with respect to the substrate L-malate. Conclusion： NPD389 is a potent ME2 inhibitor that binds to the enzyme in a fast-binding mode, acting as an uncompetitive inhibitor with respect to the substrate NAD~ and a mixed-type inhibitor with respect to the substrate L-malate.     

Development of a quantitative, cell-based, high-content screening assay for epidermal growth factor receptor modulators

Aim： To develop a robust, cell-based, high-content screening （HCS） assay based on receptor internalization for the identification of novel modulators of the epidermal growth factor receptor （EGFR）. Methods： Agonist-induced receptor internalization is part of the signaling cascade of EGFR. Fluorescent-tagged epidermal growth factor （EGF） was used to visualize the internalized receptor- ligand complex. The fluorescent intracellular spots were detected and measured with an ArrayScan HCS reader. Compounds that can competitively bind to EGFR or interfere with EGFR internalization process would result in a reduced number and intensity of intracellular fluorescent spots. This assay was validated, optimized, and applied to a large-scale screening of a library containing 48 000 synthetic compounds. Results： The competition between fluorescent EGF and unlabeled EGF reveals the IC50 of unlabeled EGF is approximately 0.2 nmol/L, which is comparable with other published reports. Thirteen compounds with a relatively high degree of interference with EGFR internalization were identified. One of the compounds was proven to be agonist of the EGFR since it induced phosphorylation of the receptor and extracellular signal-regulated protein kinase （ERK）. Conclusion： This automated, objective, and easy-to-use assay provided abundant information, quantitative results, and demonstrated the potential use of HCS methods in searching membrane receptor modulators.     

Immunochemical determination of sulfamethazine in river water and medicinal preparations

A new variant of the immunochemical assay for determining sulfamethazine, an antimicrobial drug belonging to the class of sulfonamide derivatives, has been developed based on the fluorescence polarization technique. The immunoassay is carried out using a polyclonal antiserum against several sulfonamides (conjugated with bovine serum albumin) and a fluorescent label (tracer). The proposed fluorescence polarization immunoassay ensures sulfamethazine detection with a threshold of 6 ng/ml and has a dynamic range of linearity for drug concentrations from 0.05 to 25.7 μg/ml. The proposed method has been applied to the determination of sulfamethazine in river water and tablets. Various methods of tablet pretreatment using methanol, acetonitrile, potassium hydroxide solution, and hydrochloric acid have been tried and compared. The accuracy of the immunoassay was confirmed by the recovery test. The possibility of using the obtained antiserum and the proposed immunoassay scheme for the determination of some other sulfonamides is demonstrated. __________ Translated from Khimiko-Farmatsevticheskii Zhurnal, Vol. 39, No. 10, pp. 49–53, October, 2005.     

127例乙肝表面抗体ELISA检测与化学发光法的比较

Objective To compare the difference between ELISA and chemiluminescence assay in de-tecting hepatitis B surface antibody (HBsAb) serum valued in 5～100mIU/ml. Method 127 HBsAb serum samples that had valued by chemiluminescence were detected using 10 domestic ELISA kits. The correlation between the results of ELISA kits and chemiluminescence assay were analyzed. Coincidence between the results of ELISA kits and chemiluminescence at different OD value range were also analyzed. Results The detected results between 10 domestic ELISA kits and chemiluminescence assay are positive correlation (P<0.01); The optimal coincidence rates of the results of ELISA with those samples valued by chemiluminescence at more than 100mIU/ml was 99.4%; the coinci-dence rate is from 42% to 80% in cut-off±20%. The average coincidence rate is under 60%. Conclusions Though the detected results of 10 domestic ELISA reagents is related closely, the coincidence rate of the results at 5～10mIU/ ml in detecting anti-HBs is low. So it is important to make a positive standard in detecting anti-HBs.     

127例乙肝表面抗体ELISA检测与化学发光法的比较

Objective To compare the difference between ELISA and chemiluminescence assay in de-tecting hepatitis B surface antibody (HBsAb) serum valued in 5～100mIU/ml. Method 127 HBsAb serum samples that had valued by chemiluminescence were detected using 10 domestic ELISA kits. The correlation between the results of ELISA kits and chemiluminescence assay were analyzed. Coincidence between the results of ELISA kits and chemiluminescence at different OD value range were also analyzed. Results The detected results between 10 domestic ELISA kits and chemiluminescence assay are positive correlation (P<0.01); The optimal coincidence rates of the results of ELISA with those samples valued by chemiluminescence at more than 100mIU/ml was 99.4%; the coinci-dence rate is from 42% to 80% in cut-off±20%. The average coincidence rate is under 60%. Conclusions Though the detected results of 10 domestic ELISA reagents is related closely, the coincidence rate of the results at 5～10mIU/ ml in detecting anti-HBs is low. So it is important to make a positive standard in detecting anti-HBs.     

127例乙肝表面抗体ELISA检测与化学发光法的比较

Objective To compare the difference between ELISA and chemiluminescence assay in de-tecting hepatitis B surface antibody (HBsAb) serum valued in 5～100mIU/ml. Method 127 HBsAb serum samples that had valued by chemiluminescence were detected using 10 domestic ELISA kits. The correlation between the results of ELISA kits and chemiluminescence assay were analyzed. Coincidence between the results of ELISA kits and chemiluminescence at different OD value range were also analyzed. Results The detected results between 10 domestic ELISA kits and chemiluminescence assay are positive correlation (P<0.01); The optimal coincidence rates of the results of ELISA with those samples valued by chemiluminescence at more than 100mIU/ml was 99.4%; the coinci-dence rate is from 42% to 80% in cut-off±20%. The average coincidence rate is under 60%. Conclusions Though the detected results of 10 domestic ELISA reagents is related closely, the coincidence rate of the results at 5～10mIU/ ml in detecting anti-HBs is low. So it is important to make a positive standard in detecting anti-HBs.     

127例乙肝表面抗体ELISA检测与化学发光法的比较

Objective To compare the difference between ELISA and chemiluminescence assay in de-tecting hepatitis B surface antibody (HBsAb) serum valued in 5～100mIU/ml. Method 127 HBsAb serum samples that had valued by chemiluminescence were detected using 10 domestic ELISA kits. The correlation between the results of ELISA kits and chemiluminescence assay were analyzed. Coincidence between the results of ELISA kits and chemiluminescence at different OD value range were also analyzed. Results The detected results between 10 domestic ELISA kits and chemiluminescence assay are positive correlation (P<0.01); The optimal coincidence rates of the results of ELISA with those samples valued by chemiluminescence at more than 100mIU/ml was 99.4%; the coinci-dence rate is from 42% to 80% in cut-off±20%. The average coincidence rate is under 60%. Conclusions Though the detected results of 10 domestic ELISA reagents is related closely, the coincidence rate of the results at 5～10mIU/ ml in detecting anti-HBs is low. So it is important to make a positive standard in detecting anti-HBs.     

127例乙肝表面抗体ELISA检测与化学发光法的比较

Objective To compare the difference between ELISA and chemiluminescence assay in de-tecting hepatitis B surface antibody (HBsAb) serum valued in 5～100mIU/ml. Method 127 HBsAb serum samples that had valued by chemiluminescence were detected using 10 domestic ELISA kits. The correlation between the results of ELISA kits and chemiluminescence assay were analyzed. Coincidence between the results of ELISA kits and chemiluminescence at different OD value range were also analyzed. Results The detected results between 10 domestic ELISA kits and chemiluminescence assay are positive correlation (P<0.01); The optimal coincidence rates of the results of ELISA with those samples valued by chemiluminescence at more than 100mIU/ml was 99.4%; the coinci-dence rate is from 42% to 80% in cut-off±20%. The average coincidence rate is under 60%. Conclusions Though the detected results of 10 domestic ELISA reagents is related closely, the coincidence rate of the results at 5～10mIU/ ml in detecting anti-HBs is low. So it is important to make a positive standard in detecting anti-HBs.     

127例乙肝表面抗体ELISA检测与化学发光法的比较

Objective To compare the difference between ELISA and chemiluminescence assay in de-tecting hepatitis B surface antibody (HBsAb) serum valued in 5～100mIU/ml. Method 127 HBsAb serum samples that had valued by chemiluminescence were detected using 10 domestic ELISA kits. The correlation between the results of ELISA kits and chemiluminescence assay were analyzed. Coincidence between the results of ELISA kits and chemiluminescence at different OD value range were also analyzed. Results The detected results between 10 domestic ELISA kits and chemiluminescence assay are positive correlation (P<0.01); The optimal coincidence rates of the results of ELISA with those samples valued by chemiluminescence at more than 100mIU/ml was 99.4%; the coinci-dence rate is from 42% to 80% in cut-off±20%. The average coincidence rate is under 60%. Conclusions Though the detected results of 10 domestic ELISA reagents is related closely, the coincidence rate of the results at 5～10mIU/ ml in detecting anti-HBs is low. So it is important to make a positive standard in detecting anti-HBs.     

Mechanism of HIV-1 integrase inhibition by styrylquinoline derivatives in vitro

Styrylquinoline derivatives (SQ) efficiently inhibit the 3'-processing activity of integrase (IN) with IC50 values of between 0.5 and 5 microM. We studied the mechanism of action of these compounds in vitro. First, we used steady-state fluorescence anisotropy to assay the effects of the SQ derivatives on the formation of IN-viral DNA complexes independently of the catalytic process. The IC50 values obtained in activity and DNA-binding tests were similar, suggesting that the inhibition of 3'-processing can be fully explained by the prevention of IN-DNA recognition. SQ compounds act in a competitive manner, with Ki values of between 400 and 900 nM. In contrast, SQs did not inhibit 3'-processing when IN-DNA complexes were preassembled. Computational docking followed or not by molecular dynamics using the catalytic core of HIV-1 IN suggested a competitive inhibition mechanism, which is consistent with our previous data obtained with the corresponding Rous sarcoma virus domain. Second, we used preassembled IN-preprocessed DNA complexes to assay the potency of SQs against the strand transfer reaction, independently of 3'-processing. Inhibition occurred even if the efficiency was decreased by about 5- to 10-fold. Our results suggest that two inhibitor-binding modes exist: the first one prevents the binding of the viral DNA and then the two subsequent reactions (i.e., 3'-processing and strand transfer), whereas the second one prevents the binding of target DNA, thus inhibiting strand transfer. SQ derivatives have a higher affinity for the first site, in contrast to that observed for the diketo acids, which preferentially bind to the second one.     

多羟基芳香族化合物对HIV-1整合酶的抑制作用

目的研究HIV-1整合酶抑制剂,为艾滋病的治疗提供新作用靶位的抗HIV药物。方法用HIV-1整合酶ELISA法检测3种萘醌类化合物,10种白藜芦醇及其衍生物和7种吡喃香豆素类化合物对整合酶的抑制作用。结果双羟基-1,4-萘醌(NQ-2)对HIV-1整合酶有抑制活性,IC₅₀为78.5 μmol·L^-1,发现萘醌类新化合物NQ-3对HIV-1整合酶的抑制作用优于NQ-2,IC₅₀为37.2 μmol·L^-1。用分步测定法发现NQ-2主要抑制HIV-1整合酶的链转移活性,而NQ-3则对装配和链转移都有较强的抑制。结论萘醌类化合物(NQ-2,3)对HIV-1整合酶有抑制作用,NQ-3为新化合物值得进一步研究。     

Novel quinolinonyl diketo acid derivatives as HIV-1 integrase inhibitors: design, synthesis, and biological activities

Novel quinolinonyl diketo acids were designed to obtain integrase (IN) inhibitors selectively active against the strand transfer (ST) step of the HIV integration process. Those new compounds are characterized by a single aryl diketo acid (DKA) chain in comparison to 4, a bifunctional diketo acid reported by our group as an anti-IN agent highly potent against both the 3'-processing and ST steps. Compound 6d was the most potent derivative in IN enzyme assays, while 6i showed the highest potency against HIV-1 in acutely infected cells. The selective inhibition of ST suggested the newly designed monofunctional DKAs bind the IN-DNA acceptor site without affecting the DNA donor site.     

HIV integrase inhibitors with nucleobase scaffolds: discovery of a highly potent anti-HIV agent

HIV integrase is essential for HIV replication. However, there are currently no integrase inhibitors in clinical use for AIDS. We have discovered a conceptually new beta-diketo acid that is a powerful inhibitor of both the 3'-processing and strand transfer steps of HIV-1 integrase. The in vitro anti-HIV data of this inhibitor were remarkable as exemplified by its highly potent antiviral therapeutic efficacy against HIV(TEKI) and HIV-1(NL4)(-)(3) replication in PBMC (TI >4,000 and >10,000, respectively).     

The use of a new in vitro reaction substrate reproducing both U3 and U5 regions of the HIV-1 3'-ends increases the correlation between the in vitro and in vivo effects of the HIV-1 integrase inhibitors

Human Immunodeficiency Virus type 1 (HIV-1) integrase (IN) is an attractive target for the development of new antiviral therapies. Recently, several HIV-1 recombinant IN (rIN) in vitro inhibitors have been described. However, the great majority of them failed to block the virus replication in cell-based assays, suggesting the inadequacy of the in vitro assay systems used for inhibitor screening. To improve these systems, we designed a 40(mer) duplex DNA reaction substrate consisting of recognition sequences from both U3 and U5 HIV-1 long terminal repeat (LTR) termini. The HIV-1 rIN was able to catalyze its enzyme activities recognizing both ends of the 40(mer) dsDNA. Using this substrate we assayed the effects on rIN catalysis of different classes of compounds which inhibit the HIV-1 rIN in vitro when the reaction substrate is the standard 21(mer) U5 dsDNA, and that are either active or inactive on the HIV-1 replication. We also compared the efficacy of these compounds when added to the reaction before or after the formation of the rIN-dsDNA complex. In this system, the enzyme preincubation with the two-ended 40(mer) dsDNA before the addition of the compounds allowed a strong correlation between the effects of hydroxylated aromatics derivatives on rIN activity in cell-free assays and their effects on viral replication in cell-culture assays. This increase in drug selectivity of the rIN in vitro assay was explored by investigating whether it was due to the length of the 40(mer), longer than the standard 21(mer), or to presence of both viral ends, versus only one viral end. To this purpose we designed four 40(mer) oligonucleotides containing either only one viral end or two-repetitive ends, finding that the architecture of the rIN-dsDNA complex and its compound susceptibility is significantly influenced by the sequence of the dsDNA substrate.     

Bicyclic hydroxy-1H-pyrrolopyridine-trione containing HIV-1 integrase inhibitors

HIV-1 integrase (IN) is a validated therapeutic target for the treatment of AIDS. However, the emergence of resistance to raltegravir, the sole marketed FDA-approved IN inhibitor, emphasizes the need to develop second-generation inhibitors that retain efficacy against clinically relevant IN mutants. We report herein bicyclic hydroxy-1H-pyrrolopyridine-triones as a new family of HIV-1 integrase inhibitors that were efficiently prepared using a key 'Pummerer cyclization deprotonation cycloaddition' cascade of imidosulfoxides. In in vitro HIV-1 integrase assays, the analogs showed low micromolar inhibitory potencies with selectivity for strand transfer reactions as compared with 3'-processing inhibition. A representative inhibitor (5e) retained most of its inhibitory potency against the three major raltegravir-resistant IN mutant enzymes, G140S/Q148H, Y143R, and N155H. In antiviral assays employing viral vectors coding these IN mutants, compound 5e was approximately 200- and 20-fold less affected than raltegravir against the G140S/Q148H and Y143R mutations, respectively. Against the N155H mutation, 5e was approximately 10-fold less affected than raltegravir. Thus, our new compounds represent a novel structural class that may be further developed to overcome resistance to raltegravir, particularly in the case of the G140S/Q148H mutations.     

Dynamic receptor-based pharmacophore model development and its application in designing novel HIV-1 integrase inhibitors

We present here a dynamic receptor-based pharmacophore model representing the complementary features of the active site region of HIV-1 integrase (IN), which was developed from a series of representative conformations of IN. Conformations of IN were sampled through a molecular dynamics study of the catalytic domain of an IN monomer, and an ensemble of representative IN structures were collected via a probability-based representative conformer sampling method that considers both the potential energy and the structural similarity of the protein conformations. The dynamic pharmacophore model was validated by a set of 128 known inhibitors, and the results showed that over 72% of the active inhibitors (IC(50) lower than 20 microM) could be successfully identified by the dynamic model. Therefore, we screened our in-house database of commercially available compounds against this model and successfully identified a set of structurally novel IN inhibitors. Compounds 7 and 18 with IC(50)s of 8 microM and 15 microM, respectively, against the strand transfer reaction were the most potent. Moreover, 7, 8 and 20 showed a 5-fold selectivity for the strand transfer reaction over 3'-processing.     

Chromone and chromanone derivatives as strand transfer inhibitors of HIV-1 integrase

HIV-1 integrase catalyzes terminal cleavage at the 3′ end of the proviral DNA, removing a pair of bases and causing strand transfer by joining the 3′ end to 5′-phosphates in the target DNA. Several aryl 1,3-diketo acids that can inhibit the strand transfer reaction of HIV-1 IN have been identified. Here we synthesized a new series of compounds with a chromone or chromanone ring as conformationally constrained scaffolds of 1,3-diketo acids, and then tested their ability to inhibit HIV-1 IN-mediated strand transfer. All compounds moderately inhibited HIV-1 IN activity, indicating that the conformational restriction of one keto group into a chromone or chromanone ring decreases inhibition of the HIV-1 IN strand transfer.     

Design and synthesis of novel N-hydroxy-dihydronaphthyridinones as potent and orally bioavailable HIV-1 integrase inhibitors

HIV-1 integrase (IN) is one of three enzymes encoded by the HIV genome and is essential for viral replication, and HIV-1 IN inhibitors have emerged as a new promising class of therapeutics. Recently, we reported the synthesis of orally bioavailable azaindole hydroxamic acids that were potent inhibitors of the HIV-1 IN enzyme. Here we disclose the design and synthesis of novel tricyclic N-hydroxy-dihydronaphthyridinones as potent, orally bioavailable HIV-1 integrase inhibitors displaying excellent ligand and lipophilic efficiencies.