Bioactive tetrahydrofuran lignans from roots, stems, leaves and twigs of Anogeissus rivularis.

Four previously undescribed tetrahydrofuran lignans, named anorisols A-D (1-4) and fourteen known compounds (5-18) were isolated from the roots, stems, leaves and twigs of Anogeissus rivularis. The chemical structures were elucidated on the basis of their spectroscopic data and by comparison with the literature data. The absolute configurations of 1-4 were established by comparison of the experimental ECD spectra with the calculated ECD spectra. Some isolated compounds were evaluated for their cytotoxic activity as well as anti-HIV-1 activity employing reverse transcriptase (RT) and syncytium reduction assays using the ΔTat/RevMC99 virus in 1A2 cell line systems. Compound 6 displayed the most potent activity in syncytium inhibition assay with effective concentration at 50% (EC50) value of 13.3 µM (SI >3.0). In the reverse transcriptase assay, compound 1 exhibited moderate activity with IC50 value of 213.9 µM.

Flavonoids and Acid-Hydrolysis derivatives of Neo-Clerodane diterpenes from Teucrium flavum subsp. glaucum as inhibitors of the HIV-1 reverse transcriptase-associated RNase H function.

Bioassay-guided fractionation of the ethyl acetate extract from Teucrium flavum subsp. glaucum, endowed with inhibitory activity towards the HIV-1 reverse transcriptase-associated RNase H function, led to the isolation of salvigenin (1), cirsimaritin (2) and cirsiliol (3) along with the neo-clerodanes teuflavin (4) and teuflavoside (5). Acid hydrolysis of the inactive teuflavoside provided three undescribed neo-clerodanes, flavuglaucins A-C (7-9) and one known neo-clerodane (10). Among all neo-clerodanes, flavuglaucin B showed the highest inhibitory activity towards RNase H function with a IC50 value of 9.1 µM. Molecular modelling and site-directed mutagenesis analysis suggested that flavuglaucin B binds into an allosteric pocket close to RNase H catalytic site. This is the first report of clerodane diterpenoids endowed with anti-reverse transcriptase activity. Neo-clerodanes represent a valid scaffold for the development of a new class of HIV-1 RNase H inhibitors.

Potent Inhibitor of Drug-Resistant HIV-1 Strains Identified from the Medicinal Plant Justicia gendarussa.

Justicia gendarussa, a medicinal plant collected in Vietnam, was identified as a potent anti-HIV-1 active lead from the evaluation of over 4500 plant extracts. Bioassay-guided separation of the extracts of the stems and roots of this plant led to the isolation of an anti-HIV arylnaphthalene lignan (ANL) glycoside, patentiflorin A (1). Evaluation of the compound against both the M- and T-tropic HIV-1 isolates showed it to possess a significantly higher inhibition effect than the clinically used anti-HIV drug AZT. Patentiflorin A and two congeners were synthesized, de novo, as an efficient strategy for resupply as well as for further structural modification of the anti-HIV ANL glycosides in the search for drug leads. Subsequently, it was determined that the presence of a quinovopyranosyloxy group in the structure is likely essential to retain the high degree of anti-HIV activity of this type of compounds. Patentiflorin A was further investigated against the HIV-1 gene expression of the R/U5 and U5/gag transcripts, and the data showed that the compound acts as a potential inhibitor of HIV-1 reverse transcription. Importantly, the compound displayed potent inhibitory activity against drug-resistant HIV-1 isolates of both the nucleotide analogue (AZT) and non-nucleotide analogue (nevaripine). Thus, the ANL glycosides have the potential to be developed as novel anti-HIV drugs.

Polyoxygenated cyclohexene derivatives isolated from Dasymaschalon sootepense and their biological activities.

Six new naturally occurring polyoxygenated cyclohexene derivatives together with eight related known derivatives, two known alkaloids, and two known flavonoid derivatives were isolated from bioassay-guided fractionation of the ethyl acetate extract of the leaves and twigs of Dasymaschalon sootepense. The structure elucidation and determination of absolute configurations were established by various spectroscopic methods, X-ray diffraction techniques as well as comparison with the literature data. Several isolated compounds were evaluated for their cytotoxic, anti-HIV-1 RT and anti-inflammatory activities.

A novel, cell-free PCR-based assay for evaluating the inhibitory activity of antiretroviral compounds against HIV reverse transcriptase.

This study describes a novel, PCR-based assay that evaluates the ability of compounds to inhibit cDNA generation by HIV reverse transcriptase (RT), of both commercial and viral lysate origin, from a known RNA template. The template consisted of RNA from stable transfectants ectopically expressing the US6 gene of herpes simplex virus-1, coding for glycoprotein D. Controls were carried out to demonstrate that no residual DNA polymerase activity or DNA contamination was responsible for the amplified DNA in the tested, control samples. In this assay, 0.1 µM nevirapine totally inhibited the RT activity of 0.5 U commercial HIV RT, while 10 nM inhibited it by only 10%. Conversely, 10 pM efavirenz completely inhibited 0.5 U HIV RT. Similar results were obtained when a self-prepared viral lysate was used as a source of HIV RT. A reference commercial kit directly measuring HIV RT activity, without amplification, was less sensitive than the new assay. As a consequence, the HIV RT 50% inhibitory concentration of nevirapine and efavirenz in the newly described assay was 8 and 5 × 10(3) times lower, respectively, than in the commercial assay. In conclusion, this novel method was sensitive, reproducible, and sufficiently rapid for screening in vitro the functional activity of known or potential antiretroviral compounds against HIV RT.

Diaryltriazine non-nucleoside reverse transcriptase inhibitors are potent candidates for pre-exposure prophylaxis in the prevention of sexual HIV transmission.

OBJECTIVES: Pre-exposure prophylaxis and topical microbicides are important strategies in the prevention of sexual HIV transmission, especially since partial protection has been shown in proof-of-concept studies. In search of new candidate drugs with an improved toxicity profile and with activity against common non-nucleoside reverse transcriptase inhibitor (NNRTI)-resistant HIV, we have synthesized and investigated a library of 60 new diaryltriazine analogues. METHODS: From this library, 15 compounds were evaluated in depth using a broad armamentarium of in vitro assays that are part of a preclinical testing algorithm for microbicide development. Antiviral activity was assessed in a cell line, and in primary human cells, against both subtype B and subtype C HIV-1 and against viruses resistant to therapeutic NNRTIs and the candidate NNRTI microbicide dapivirine. Toxicity towards primary blood-derived cells, cell lines originating from the female reproductive tract and female genital microflora was also studied. RESULTS AND CONCLUSIONS: We identified several compounds with highly potent antiviral activity and toxicity profiles that are superior to that of dapivirine. In particular, compound UAMC01398 is an interesting new candidate that warrants further investigation because of its superior toxicity profile and potent activity against dapivirine-resistant viruses.

[Shizukaol F: a new structural type inhibitor of HIV-1 reverse transcriptase RNase H].

This study is to investigate the mechanism of action of lindenane disesquiterpenoid shizukaol F on HIV-1 replication. Real time quantity PCR, ELISA assay and fluorescence methods were used to test HIV-1 reverse transcription process, RNA-dependent DNA polymerase activity, and RNase H activity, respectively. It showed that shizukaol F inhibited LTR/Gag production of HIV-1 reverse transcription with an IC50 of 9.11 micromol x L(-1). This result is consistent with its inhibitory effect on HIV-1 replication (IC50 of 6.12 micromol x L(-1)). Mechanism studies showed that compound shizukaol F inhibited HIV-1 RT-RNase H with IC50 of 26.4 micromol x L(-1), but had no effect on HIV-1 RT RNA-dependent DNA polymerase activity. In conclusion, shizukaol F is a new structural type HIV-1 RNase H inhibitor. This discovery will provide a clue for new type of reverse transcriptase inhibitors development.

Identification of anti-HIV and anti-reverse transcriptase activity from Tetracera scandens.

We report here that an ethanol extract of Tetracera scandens, a Vietnamese medicinal plant, has anti-HIV activity and possesses strong inhibitory activity against HIV-1 reverse transcriptase (RTase). Using a MT-4 cell-based assay, we found that the T. scandens extract inhibited effectively HIV virus replication with an IC(50) value in the range of 2.0-2.5 µg/ml while the cellular toxicity value (CC50) was more than 40-50 µg/ml concentration, thus yielding a minimum specificity index of 20-fold. Moreover, the anti-HIV efficacy of the T. scandens extract was determined to be due, in part, to its potent inhibitory activity against HIV-1 RTase activity in vitro. The inhibitory activity against the RTase was further confirmed by probing viral cDNA production, an intermediate of viral reverse transcription, in virus-infected cells using quantitative DNA-PCR analysis. Thus, these results suggest that T. scandens can be a useful source for the isolation and development of new anti- HIV-1 inhibitor(s). [BMB reports 2012; 45(3): 165-170].

Inhibition of HIV-1 and M-MLV reverse transcriptases by a major polyphenol (3,4,5 tri-O-galloylquinic acid) present in the leaves of the South African resurrection plant, Myrothamnus flabellifolia.

A polyphenol-rich extract of the medicinal resurrection plant Myrothamnus flabellifolia was shown to inhibit viral (M-MLV and HIV-1) reverse transcriptases. Fractionation and purification of this extract yielded the major polyphenol, 3,4,5 tri-O-galloylquinic acid, as the main active compound. A sensitive, ethidium bromide based fluorescent assay, was developed and used to monitor the kinetics of M-MLV and HIV-1 reverse transcriptases in the presence and absence of 3,4,5 tri-O-galloylquinic acid. Kinetic monitoring of these enzymes in the presence of 3,4,5 tri-O-galloylquinic acid revealed non-competitive inhibition with IC(50) values of 5 µM and 34 µM for the M-MLV and HIV-1 enzymes, respectively. We propose that 3,4,5 tri-O-galloylquinic acid and related polymers have potential as indigenous drugs for anti-viral therapy.

Isolation and characterization of a French bean hemagglutinin with antitumor, antifungal, and anti-HIV-1 reverse transcriptase activities and an exceptionally high yield.

A dimeric 64-kDa hemagglutinin was isolated with a high yield from dried Phaseolus vulgaris cultivar "French bean number 35" seeds using a chromatographic protocol that involved Blue-Sepharose, Q-Sepharose, and Superdex 75. The yield was exceptionally high (1.1g hemagglutinin per 100g seed), which is around 10-85 times higher than other Phaseolus cultivars. Its N-terminal sequence resembled those of other Phaseolus hemagglutinins. The hemagglutinating activity of the hemagglutinin was stable in the pH range 6-8, and in the temperature range 0 degrees C-50 degrees C. It inhibited HIV-1 reverse transcriptase with an IC50 of 2microM. It suppressed mycelial growth in Valsa mali with an IC50 of 10microM. It inhibited proliferation of hepatoma HepG2 cells and breast cancer MCF-7 cells with an IC50 of 100 and 2microM, respectively. It had no antiproliferative effect on normal embryonic liver WRL68 cells.

A trypsin-chymotrypsin inhibitor with antiproliferative activity from small glossy black soybeans.

A trypsin inhibitor with a molecular mass of about 19 kDa was isolated from seeds of Chinese black soybean Glycine max cv. "Small Glossy Black". It was isolated using a protocol that comprised ion exchange chromatography on Q-Sepharose, SP-Sepharose and DEAE-cellulose. It was adsorbed on all three ion exchangers. It inhibited trypsin with an IC(50) of 19 microM and chymotrypsin with an IC(50) of 14.3 microM. Its trypsin inhibitory activity was stable in the pH range pH 3-pH 13 and in the temperature range 0 degree C-60 degrees C. The trypsin inhibitor was inhibited by dithiothreitol (from 5 to 25 mM) in a dose-dependent manner. It exhibited an N-terminal sequence highly homologous to Kunitz-type trypsin inhibitors. It inhibited HIV-1 reverse transcriptase with an IC(50) of 0.16 microM, and suppressed proliferation of MCF-7 breast cancer cells with an IC(50) of 4.3 microM and HepG2 hepatoma cells with an IC(50) higher than 25 microM. The trypsin inhibitor lacked antifungal activity and mitogenic activity towards mouse splenocytes.

Inhibition of HIV-1 protease and RNase H of HIV-1 reverse transcriptase activities by long chain phenols from the sarcotestas of Ginkgo biloba.

Nine long-chain phenols: four cardanols (1-4), two bilobols (5, 6) and three alkylsalicylic acids (7-9) [corrected] were isolated from the CH(2)Cl(2) extracts of the sarcotestas of Ginkgo biloba as HIV-1 protease (PR) inhibitors. From these phenols, the bilobols (IC (50), 2.6 - 5.8 microM) and alkylsalicylic acids (IC (50), 10.2 - 24.9 microM) exhibited dose-dependent potent inhibitory activities on HIV-1 PR, while the cardanols did not. On the other hand, only the alkylsalicylic acids (IC (50), 33.7 - 170.3 microM) inhibited the activities of RNase H of HIV-1 reverse transcriptase (RT), while all of the compounds failed to affect the RNA dependent DNA polymerase (RDDP) of HIV-1 RT. Therefore, we regard bilobols as a new class and selective inhibitors of HIV-1 PR; in addition, alkylsalicylic acids are elucidated as a new class of inhibitors against HIV-1 PR and RNase H of HIV-1 RT.

Three new derivatives of anti-HIV-1 polyphenols isolated from Salvia yunnanensis.

During the study of anti-HIV-1 active components of the aqueous extracts of the roots of Salvia yunnanensis, three new derivatives of polyphenols, namely: methyl salvianolate A (2), ethyl salvianolate A (3) and cis-lithospermic acid (5) were isolated along with two known polyphenols, salvianolic acid A (1) and lithospermic acid (4) their structures were elucidated on the basis of NMR and MS spectral analyses. The anti-HIV-1 activities of the 5 polyphenols were tested for the inhibition of P24 antigen in HIV-1 infected MT-4 cell cultures and HIV-1 replicative enzymes in vitro.

Compounds from rose (Rosa rugosa) flowers with human immunodeficiency virus type 1 reverse transcriptase inhibitory activity.

The aqueous extracts and ethanol precipitates of aqueous extracts of 18 medicinal herbs traditionally used in China were screened for their ability to inhibit human immunodeficiency virus type-1 reverse transcriptase (HIV-1 RT) in-vitro. Among the samples screened at a concentration of 500 microg mL-1, dried rose (Rosa rugosa) flowers showed the strongest inhibition. The ethanol precipitate of the aqueous extract of R. rugosa was processed and two components (P1 and P2) were obtained after ion exchange chromatography on DEAE-cellulose. Then, P1-a (Mr 150 kDa) and P1-b (Mr 8 kDa) were isolated from P1 by gel filtration on Sephadex G-200. They inhibited the activity of HIV-1 RT with an IC50 of 158 nM and 148.16 microg mL-1 (18.5 microM), respectively. Further structural analyses revealed that P1-a was a polysaccharide-peptide complex, and P1-b was a polymer consisting of acteoside and acteoside derivatives identified by Fourier transform infrared spectroscopy, nuclear magnetic resonance, assays of carbohydrate and protein contents and high-performance liquid chromatography electrospray ionization mass spectrometry.

Effects of diterpenes isolated from the Brazilian marine alga Dictyota menstrualis on HIV-1 reverse transcriptase.

It has been recently demonstrated that HIV-1 reverse transcriptase is the target of two diterpenes, (6 R)-6-hydroxydichotoma-3,14-diene-1,17-dial (compound 1) and (6 R)-6-acetoxydichotoma-3,14-diene-1,17-dial (compound 2), that inhibit HIV-1 replication in vitro. In this work, the effects of both diterpenes on the kinetic properties of the recombinant HIV-1 reverse transcriptase (RT) enzyme were evaluated. RNA-dependent DNA-polymerase (RDDP) activity assays demonstrated that both diterpenes behave as non-competitive inhibitors with respect to dTTP and uncompetitive inhibitors with respect to poly(rA).oligo(dT) template primers. The K(i) values obtained for compounds 1 and 2 were 10 and 35 microM, respectively. Neither of these diterpenes affected the DNA-dependent DNA-polymerase (DDDP) activity of the HIV-1 RT. The RDDP activities of AMV-RT and MMLV-RT enzymes were also inhibited by compounds 1 and 2. In contrast to the HIV-1 enzyme, the DDDP activities of AMV-RT and MMLV-RT enzymes were significantly reduced by compound 1. Taken together, our results demonstrate that compound 1 is a more effective inhibitor of the viral reverse transcriptases from HIV-1, AMV and MMLV than compound 2. The kinetic behavior analyses of the HIV-1 RT demonstrate that both diterpenes have similar mechanisms of inhibition of RDDP activity.

Evaluation of selected South African medicinal plants for inhibitory properties against human immunodeficiency virus type 1 reverse transcriptase and integrase.

Seventeen aqueous and methanol extracts from nine South African medicinal plants, ethnobotanically selected, were screened for inhibitory properties against HIV-1 reverse transcriptase (RT). Isolated compounds were additionally evaluated on HIV-1 integrase (IN). The strongest inhibition against the RNA-dependent-DNA polymerase (RDDP) activity of RT was observed with the methanol extract of the stem-bark of Peltophorum africanum Sond. (Fabaceae) (IC(50) 3.5 microg/ml), while the methanol extract of the roots of Combretum molle R.Br. ex G. Don (Combretaceae) was the most inhibitory on the ribonuclease H (RNase H) activity (IC(50) 9.7 microg/ml). The known compounds bergenin and catechin, and a red coloured gallotannin composed of meta-depside chains of gallic and protocatechuic acids esterified to a 1-O-isobutyroly-beta-D-glucopyranose core, were isolated from the methanol extract of the roots and stem-bark of Peltophorum africanum. The gallotannin inhibited the RDDP and RNase H functions of RT with IC(50) values of 6.0 and 5.0 microM, respectively, and abolished the 3'-end processing activity of IN at 100 microM. Catechin showed no effect on RT but had a moderate activity on HIV-1 IN. Bergenin was inactive on both enzymes. The aqueous and methanol extracts were non-toxic in a HeLaP4 cell line at a concentration of 400 microg/ml.

HIV-1 inhibitory compounds from Calophyllum brasiliense leaves.

The hexane, acetone and methanol extracts of Calophyllum brasiliense leaves were fractionated following a three bioassay guide: high HIV-1 RT inhibition, low cytotoxicity on MT2 cells and high inhibition of HIV-1 IIIb/LAV replication. This led to the isolation of three anti HIV-1 dipyranocoumarins: calanolides A and B and soulattrolide. In contrast, other isolated compounds such as apetalic acid, isoapetalic acid, a structural isomer of isoapetalic acid, friedelin, canophyllol and amentoflavone were devoid of HIV-1 RT inhibitory activity. Calanolide C was also obtained as a natural product and showed moderate inhibitory properties.

Purification of a trypsin-stable lectin with antiproliferative and HIV-1 reverse transcriptase inhibitory activity.

A lectin, with a molecular mass of approximately 60 kDa and two different subunits exhibiting an N-terminal sequence manifesting considerable homology to phytohemagglutinin from Phaseolus species, was isolated from the ground bean (Vigna sesquipedalis cv ground bean). The lectin was unique in hemagglutinating activity was inhibited by polygalacturonic acid and not by galacturonic acid and other simple monosaccharides. The lectin was isolated by affinity chromatography on Affi-gel blue gel, ion exchange chromatography by fast protein liquid chromatography (FPLC) on Mono S, and gel filtration by FPLC on Superdex 75. It was adsorbed on both Affi-gel blue gel and Mono S. Ground bean lectin exhibited mitogenic activity on murine splenocytes with the maximal response achieved at a concentration of 156 nM, as similar to the dose required for Con A. The viability of hepatoma (HepG2), leukemia (L1210), and leukemia (M1) cells was reduced in the presence of ground bean lectin, which also exerted an inhibitory activity toward HIV-1 reverse transcriptase IC(50) of 73 microM. The hemagglutinating activity of the lectin was unaffected by trypsinization and the presence of a number of divalent cations, but was augmented by 500 mM K(+) ions. The activity was unstable above 40 degrees C although some activity remained after heating and at 100 degrees C for 30s.

New Rev-transport inhibitor with anti-HIV activity from Valerianae Radix.

Bioassay-guided separation by use of the fission yeast expressing NES of Rev, a HIV-1 viral regulatory protein, resulted in isolation of valtrate (1) as a new Rev-transport inhibitor from the nucleus to cytoplasm from Valerianae Radix. Valtrate (1) also inhibited the p-24 production of HIV-1 virus without showing any cytotoxicity against the host MT-4 cells.

HIV inhibitor from Thai bitter gourd.

Thai bitter gourd protein (MRK29) was isolated from Momordica charantia ripe fruit and seed. The purification was performed by ammonium sulfate fractionation and gel filtration chromatography. MRK29 possessed one isoelectric point of (pI) > or = 9, and the time of flight mass spectrum (TOFMS) indicated its molecular weight at 28.6 kD. The twenty amino acid sequence from the N-terminus was in the following order: 1Asp Val Asn Phe Arg Leu Ser Gly Ala 10Asp Pro Arg X Tyr Gly Met Phe Ile Glu 20Asp. MRK29 inhibited the HIV-1 reverse transcriptase with 50% IR at the concentration of 18 micrograms/ml. MRK29 was concentrated in the 30-60% salt precipitated fraction, at which the concentration of 0.175 microgram/ml exerted 82% reduction of viral core protein p24 expression in HIV-infected cells. MRK29 might have modulatory role on immune cells, because it increased 3-fold TNF activity.