Identification of new benzofuran derivatives as STING agonists with broad-spectrum antiviral activity.

The Stimulator of Interferon Genes (STING) is involved in cytosolic DNA sensing and type I Interferons (IFN-I) induction. Aiming to identify new STING agonists with antiviral activity and given the known biological activity of benzothiazole and benzimidazole derivatives, a series of benzofuran derivatives were tested for their ability to act as STING agonists, induce IFN-I and inhibit viral replication. Compounds were firstly evaluated in a gene reporter assay measuring luciferase activity driven by the human IFN-ß promoter in cells expressing exogenous STING (HEK293T). Seven of them were able to induce IFN-ß transcription while no induction of the IFN promoter was observed in the presence of a mutated and inactive STING, showing specific protein-ligand interaction. Docking studies were performed to predict their putative binding mode. The best hit compounds were then tested on human coronavirus 229E replication in BEAS-2B and MRC-5 cells and three derivatives showed EC50 values in the µM range. Such compounds were also tested on SARS-CoV-2 replication in BEAS-2B cells and in Calu-3 showing they can inhibit SARS-CoV-2 replication at nanomolar concentrations. To further confirm their IFN-dependent antiviral activity, compounds were tested to verify their effect on phospho-IRF3 nuclear localization, that was found to be induced by benzofuran derivatives, and SARS-CoV-2 replication in Vero E6 cells, lacking IFN production, founding them to be inactive. In conclusion, we identified benzofurans as STING-dependent immunostimulatory compounds and host-targeting inhibitors of coronaviruses representing a novel chemical scaffold for the development of broad-spectrum antivirals.

Comparing the responses of countries and National Health Systems to the COVID-19 pandemic: a critical analysis with a case-report series.

This review aimed to compare the different responses of countries to the pandemic, their National Health Systems, and their impact on citizens' health. This work aimed to create a narrative plot that connects different discussion points and suggests organizational solutions and strategic choices in the face of the pandemic. In particular, this work focused on public health organizations, specifically the European Union and vaccination politics. It is also based on a case report series (about the United States, Germany, Vietnam, New Zealand, Cuba, and Italy), where each country has responded differently to the pandemic in terms of political decisions such as vaccination type, information to citizens, dealings with independent experts, and other specific country factors. In comparing the various models of care systems response to the pandemic, it emerges that: we have found some (few) good practices, but without global coordination, and this is obviously not enough. It is now quite clear that there cannot be a "good answer" in a single nation. Uncoordinated local responses cannot counter a global phenomenon. The second point is that the general context must be considered from a strategic point of view. With the threat of new pandemics (but also of health disasters linked to climate change, pollution, and wars), humanity finds itself at the crossroads between investing in a "democratic" management of international bodies but without power (and at the mercy of the need for funds with consequent conflicts) or in some new leadership proposals that advocate efficiency and problem-solving (and that would probably be able to implement it) but that would place processes totally outside of the public's control.

A new vinyl selenone-based domino approach to spirocyclopropyl oxindoles endowed with anti-HIV RT activity.

Herein, we disclose a general and flexible access to spirocyclopropyl oxindoles by a domino Michael/intramolecular nucleophilic substitution pathway with variously substituted vinyl selenones and enolizable oxindoles in aqueous sodium hydroxide solution. The spirocyclopropyl oxindole being a privileged scaffold, some of the synthesized compounds were selected for biological evaluation. Compound showed selective anti-HIV-1 activity thanks to its ability to inhibit the reverse transcriptase.

5-Arylaminouracil Derivatives as Potential Dual-Action Agents.

Several 5-aminouracil derivatives that have previously been shown to inhibit Mycobacterium tuberculosis growth at concentrations of 5-40 µg/mL are demonstrated to act also as noncompetitive non-nucleoside inhibitors of HIV-1 reverse transcriptase without causing toxicity in vitro (MT-4 cells) and ex vivo (human tonsillar tissue).

Effects of new quinizarin derivatives on both HCV NS5B RNA polymerase and HIV-1 reverse transcriptase associated ribonuclease H activities.

Human immunodeficiency virus 1 (HIV-1) and Hepatitis C virus (HCV) affect 60 and 170 million infected individuals worldwide, respectively, and co-infection by both pathogens is often observed. This represents a serious public health problem that requires the identification of new drugs targeting essential phases of the life cycle of these two viruses. In this report, the synthesis and inhibitory activity of quinizarin derivatives towards both HCV NS5B polymerase and HIV-1 reverse transcriptase associated functions are reported. Our results demonstrate that anthraquinone derivatives are promising anti-polymerase viral inhibitors.

HIV-1 RT-associated RNase H function inhibitors: Recent advances in drug development.

The HIV-1 genomic RNA reverse transcription is an essential step in the virus cycle carried out by the viral-coded reverse transcriptase (RT), which has two associated functions: the RNA- and DNA-dependent DNA polymerase (RDDP and DDDP) function and the ribonuclease H (RNase H) function. The RNase H function catalyzes the selective hydrolysis of the RNA strand of the RNA:DNA heteroduplex replication intermediate. The RT associated activities are both essential for HIV-1 replication and validated targets for drug development, but only the polymerase function has been widely investigated as drug target. In fact, either nucleoside or non-nucleoside RT inhibitors currently used in therapy act on the polymerase associated activity. In this review, we describe the compounds, reported up to today, which inhibit the HIV-1 RNase H function, their chemical structures, the structure-activity relationships and the mechanism of action.

Plant low-molecular-weight phospholipase A2S (PLA2s) are structurally related to the animal secretory PLA2s and are present as a family of isoforms in rice (Oryza sativa).

Recently, we purified to homogeneity and characterized a low-molecular-weight calcium-dependent phospholipase A2 (PLA2) from developing elm seed endosperm. This represented the first purified and characterized PLA2 from a plant tissue. The full sequences of two distinct but homologous rice (Oryza sativa) cDNAs are given here. These encode mature proteins of 1 19 amino acids (PLA2-I, preceded by a 19 amino acid signal peptide) and 128 amino acids (PLA2-II. preceded by a 25 amino acid signal peptide), and were derived from four expressed sequence tag (EST) clones. Both proteins were homologous to the N-terminal amino acid sequence of the elm PLA2. They contained twelve conserved cysteine residues and sequences that are likely to represent the Ca(2+)-binding loop and active-site motif, which are characteristic of animal secretory PLA2s. A soluble PLA2s activity was purified 145 000-fold from green rice shoots. This had the same biochemical characteristics as the elm and animal secretory PLA2s. The purified rice PLA2 consisted of two proteins, with a molecular weight of 12 440 and 12 920, that had identical N-terminal amino acid sequences. This sequence was different from but homologous to the PLA2-I and PLA2-II sequences. Taken together, the results suggest that at least three different low-molecular-weight PLA2s are expressed in green rice shoots. Southern blot analysis suggested that multiple copies of such genes are likely to occur in the rice and in other plant genomes.

Effect of acyclic nucleoside phosphonates on the HIV-1 integrase in vitro.

Integrase (IN) is an essential enzyme in the human immunodeficiency virus type-1 (HIV-1) replication cycle and, thus, a potential target for chemotherapeutic agents. Because various nucleotide analogues have been reported to inhibit IN in vitro, we investigated the effect of acyclic nucleoside phosphonates. Both unphosphorylated and diphosphorylated derivatives were inhibitory to IN at concentrations ranging between 60 and 800 microM, with diphosphorylated derivatives being 5- to 8-fold more potent than unphosphorylated counterparts.

5-Alkyl-2-(alkylthio)-6-(2,6-dihalophenylmethyl)-3, 4-dihydropyrimidin-4(3H)-ones: novel potent and selective dihydro-alkoxy-benzyl-oxopyrimidine derivatives.

Molecular modeling analysis of compounds belonging to the recently published series of dihydro-alkoxy-benzyl-oxopyrimidines (DABOs), such as S-DABOs and DATNOs, gave support to the design of new 2, 6-disubstituted benzyl-DABO derivatives as highly potent and specific inhibitors of the HIV-1 reverse transcriptase (RT). To follow up on the novel DABO derivatives, we decided to investigate the effect of electron-withdrawing substituents in the benzyl unit of the S-DABO skeleton versus their anti-HIV-1 activity. Such chemical modifications impacted the inhibitory activity, especially when two halogen units were introduced at positions 2 and 6 in the phenyl portion of the benzyl group bound to C-6 of the pyrimidine ring. Various 5-alkyl-2-(alkyl(or cycloalkyl)thio)-6-(2, 6-dichloro(or 2,6-difluoro)phenylmethyl)-3, 4-dihydropyrimidin-4(3H)-ones were then synthesized and tested as anti-HIV-1 agents in both cell-based and enzyme (recombinant reverse transcriptase, rRT) assays. Among the various mono- and disubstituted phenyl derivatives, the most potent were those containing a 6-(2,6-difluorophenylmethyl) substituent (F-DABOs), which showed EC50's ranging between 40 and 90 nM and selectivity indexes up to >/=5000. An excellent correlation was found between EC50 and IC50 values which confirmed that these compounds act as inhibitors of the HIV-1 RT. The structure-activity relationships of the newly synthesized pyrimidinones are presented herein.

Synthesis and anti-human immunodeficiency virus type 1 integrase activity of hydroxybenzoic and hydroxycinnamic acid flavon-3-yl esters.

A series of new hydroxybenzoic and hydroxycinnamic acid flavon-3-yl esters were synthesized in order to obtain compounds targeting the human immunodeficiency virus (HIV) type 1 integrase (IN). The esters were tested for anti-IN and anti-reverse transcriptase (RT) activity in enzyme assays and for anti-HIV-1, anti-proliferative and anti-topoisomerase activity in cell-based assays. In enzyme assays, the two gallic acid flavon-3-yl esters showed a notable IN inhibition (IC50 values were 8.3 and 9.1 microM, respectively), while the two caffeic acid flavon-3-yl esters exhibited a modest activity (IC50 75 and 60 microM, respectively). Replacement of hydroxyl groups resulted in loss of potency. Caffeic acid 3',4'-dichloroflavon-3-yl ester also inhibited the RT activity whereas it was not active on human topoisomerases. It therefore represents an interesting example of a compound specifically targeting more than one step of the virus replication cycle.

Geometrically and conformationally restrained cinnamoyl compounds as inhibitors of HIV-1 integrase: synthesis, biological evaluation, and molecular modeling.

Various cinnammoyl-based structures were synthesized and tested in enzyme assays as inhibitors of the HIV-1 integrase (IN). The majority of compounds were designed as geometrically or conformationally constrained analogues of caffeic acid phenethyl ester (CAPE) and were characterized by a syn disposition of the carbonyl group with respect to the vinylic double bond. Since the cinnamoyl moiety present in flavones such as quercetin (inactive on HIV-1-infected cells) is frozen in an anti arrangement, it was hoped that fixing our compounds in a syn disposition could favor anti-HIV-1 activity in cell-based assays. Geometrical and conformational properties of the designed compounds were taken into account through analysis of X-ray structures available from the Cambridge Structural Database. The polyhydroxylated analogues were prepared by reacting 3,4-bis(tetrahydropyran-2-yloxy)benzaldehyde with various compounds having active methylene groups such as 2-propanone, cyclopentanone, cyclohexanone, 1,3-diacetylbenzene, 2, 4-dihydroxyacetophenone, 2,3-dihydro-1-indanone, 2,3-dihydro-1, 3-indandione, and others. While active against both 3'-processing and strand-transfer reactions, the new compounds, curcumin included, failed to inhibit the HIV-1 multiplication in acutely infected MT-4 cells. Nevertheless, they specifically inhibited the enzymatic reactions associated with IN, being totally inactive against other viral (HIV-1 reverse transcriptase) and cellular (RNA polymerase II) nucleic acid-processing enzymes. On the other hand, title compounds were endowed with remarkable antiproliferative activity, whose potency correlated neither with the presence of catechols (possible source of reactive quinones) nor with inhibition of topoisomerases. The SARs developed for our compounds led to novel findings concerning the molecular determinants of IN inhibitory activity within the class of cinnamoyl-based structures. We hypothesize that these compounds bind to IN featuring the cinnamoyl residue C=C-C=O in a syn disposition, differently from flavone derivatives characterized by an anti arrangement about the same fragment. Certain inhibitors, lacking one of the two pharmacophoric catechol hydroxyls, retain moderate potency thanks to nonpharmacophoric fragments (i.e., a m-methoxy group in curcumin) which favorably interact with an "accessory" region of IN. This region is supposed to be located adjacent to the binding site accommodating the pharmacophoric dihydroxycinnamoyl moiety. Disruption of coplanarity in the inhibitor structure abolishes activity owing to poor shape complementarity with the target or an exceedingly high strain energy of the coplanar conformation.

Biochemical characterization of the HIV-1 integrase 3'-processing activity and its inhibition by phosphorothioate oligonucleotides.

To better understand HIV-1 integrase (IN) functions, we determined the kinetic parameters of the 3'-processing reaction. Steady-state kinetic analysis performed using Dixon plots indicated that the concentration of active enzyme was 10-fold lower than that calculated by protein determination. The turnover number was low, suggesting that IN remained bound to DNA after cleavage. The catalytic efficiency increased 10-fold from 30 to 37 degrees C and 2-fold from 37 to 42 degrees C. In enzyme assays carried out at 37 degrees C, both single- and double-stranded phosphorothioate oligos bound to IN with an efficiency comparable to that of the phosphodiester duplex substrate. The competition efficiency of single-stranded oligos was directly related to the sequence length. On the other hand, phosphorothioate duplex U5 LTRs modified in the plus strand were capable of both competing with the substrate and directly inhibiting the 3'-processing activity. These results suggest that, in addition to other modes of action (inhibition of gp120-CD4 interaction and reverse transcriptase), phosphorothioate hetero- and homopolimeric oligos also potently inhibit the IN activity.

Biochemical characterization of HIV-1 reverse transcriptases encoding mutations at amino acid residues 161 and 208 involved in resistance to phosphonoformate.

Mutations at amino acid residues 161 (Q161L) and 208 (H208Y) of the reverse transcriptase (RT) have been identified in HIV-1 variants which are resistant to phosphonoformate (PFA). In the present study, we report on the biochemical properties of recombinant RTs (rRTs) carrying either one or both of the above mutations. We also report on their susceptibility to PFA and to nucleoside (NRTI) and non-nucleoside (NNRTI) RT inhibitors. Like the wild-type (wt) enzyme, mutant rRTs H208Y and Q161L/H208Y showed a preference for Mg2+ over Mn2+, whereas the Q161L rRT preferred Mn2+. The three mutant rRTs showed degrees of PFA resistance which differed according to the template-primer used, and steady-state kinetic studies revealed an inverse correlation between their degree of PFA resistance, affinity for deoxynucleoside triphosphates (dNTPs) and catalytic efficiency (kcat/Km ratio). These results indicated that HIV-1 rRTs bearing mutations at codons 161 and/or 208 had altered dNTP binding sites which led to a PFA-resistant phenotype. However, unlike the corresponding mutant viruses, which are hypersensitive to 3'-azido-3'-deoxythymidine (AZT), 11-cyclopropyl-5,-11-dihydro-4-methyl-6H-dipyridol[3,2-b:2',3',-e] diazepin-6-one (Nevirapine) and (+)-(5S)-4,5,6,7-tetrahydro-5-methyl-6-(3-methyl-2-butenyl)-imidazo[4,5, 1-jk][1,4]benzodiazepin-2(1H)-thione. (TIBO R82150), the mutant RTs Q161L and Q161L/H208Y were resistant to 3'-azido-3'-deoxythymidine triphosphate (AZTTP) and as susceptible as the wt enzyme to Nevirapine and TIBO R82150. Overall, these results suggest that codons 161 and 208 of the HIV-1 RT gene are involved in substrate binding as well as in NRTI recognition, and provide more insights into the mechanism by which HIV-1 becomes resistant to PFA.

Synthesis and anti-HIV-1 activity of thio analogues of dihydroalkoxybenzyloxopyrimidines.

Various thio analogues of dihydroalkoxybenzyloxopyrimidines (DABOs), a new class of non-nucleoside reverse transcriptase inhibitors, were found to selectively inhibit the HIV-1 multiplication in vitro. Among the C-5 H-substituted 6-benzyl-3,4-dihydro-4-oxopyrimidines, the introduction of alkylthio or cycloalkylthio substituents at C-2 of the pyrimidine ring led to derivatives (S-DABOs) which were up to 10-fold more potent than the alkyloxy or cycloalkyloxy counterparts. The further introduction of a methyl group at the 3'-position of the benzyl portion of 2-(alkylthio)-6-benzyluracils reduced the cytotoxicity leading to more selective compounds. Among C-5 methyl-substituted S-DABOs, numerous derivatives showed EC50 values as low as 0.6 microM and lacked cytotoxicity at doses as high as 300 microM. In the C-5 double methyl-substituted series, a more pronounced cytotoxicity was observed and the further introduction of a methyl at the 3'-position in the benzylidene group resulted in total loss of antiviral activity. S-DABOs, namely 2-(alkylthio)-6-benzyl-3,4-dihydro-4-oxopyrimidines, were synthesized by reacting proper methyl (phenylacetyl)acetates or their 2-methyl compounds with thiourea to afford 6-benzyl-4-oxo-1,2,3,4-tetrahydro-2-thiaoxopyrimidines or the related 5-methyl derivatives. Treatment of the latter derivatives with alkyl or cycloalkyl halides in alkaline medium gave the required title compounds.

Characterization of the anti-HIV-1 activity of 3,4-dihydro-2-alkoxy-6-benzyl-4-oxopyrimidines (DABOs), new non-nucleoside reverse transcriptase inhibitors.

Novel 3,4-dihydro-6-benzyl-4-oxopyrimidines (DABOs), variously substituted at both the C-2 and C-5 positions of the pyrimidine ring, proved to be specific inhibitors of the human immunodeficiency virus type 1 (HIV-1) in vitro. Some compounds showed potency at micromolar doses, no cytotoxicity at the maximum testable doses and selectivity indexes comparable to that of 2'-3'-dideoxyinosine (ddI). Mode of action studies suggested that DABOs interfered with a step of the virus multiplication cycle following adsorption and preceding integration. Enzyme assays indicated that DABOs targeted HIV-1 reverse transcriptase: they inhibited the RNA-dependent DNA polymerase activity in a template-dependent manner and, to a lesser extent, the DNA-dependent DNA polymerase activity. No inhibition of the RNase-H associated activity was observed. When DABOs were assayed in combination with 3'-azido-3'-dideoxythymidine (AZT) or ddI against HIV-1 in cell cultures, a slightly synergistic inhibitory effect was observed. The combination of DABO 546 and AZTTP in enzyme assays showed that the two compounds were kinetically mutually exclusive.

Synthesis and evaluation of the anti-HIV activity of aza and deaza analogues of isoddA and their phosphates as prodrugs.

Some aza and deaza analogues of the anti-HIV agent 2',3'-dideoxy-3'-oxoadenosine (isoddA) (8-aza-, 8-aza-1-deaza, 8-aza-3-deaza-, 1-deaza-, and 3-deaza-isoddA) were synthesized and found inactive against HIV in vitro. The hypothesis that the inactivity of these isonucleosides might be due to their poor affinity for cellular nucleoside kinases was checked by the synthesis of a series of 5'-[bis(2,2,2-trichloroethyl) phosphate] triesters and 5'-phenyl phosphoramidate derivatives which, acting as membrane soluble prodrugs, could release the free phosphate form inside the cell. The 5'-(phenylmethoxy)alaninyl phosphate derived from 8-aza-isoddA was found active against HIV-1 and HIV-2 with a potency similar to that of isoddA, while the anti-HIV potency of 5'-(phenylmethoxy)alaninyl phosphate of isoddA proved remarkably higher than that of isoddA, in particular against HIV-2, being similar to that of AZT. Further evidence that 8-aza-isoddA could behave as anti-HIV agent, provided that it is activated as phosphate, was obtained by the synthesis of its 5'-triphosphate derivative, which proved to be an active inhibitor of HIV-1 recombinant reverse transcriptase.

Identification of the amino acid in the human immunodeficiency virus type 1 reverse transcriptase involved in the pyrophosphate binding of antiviral nucleoside triphosphate analogs and phosphonoformate. Implications for multiple drug resistance.

A recombinant clone of human immunodeficiency virus type 1 reverse transcriptase (HIV-1 RT) with reduced sensitivity to 3'-azido-3'-deoxythymidine 5'-triphosphate (AZTTP) and phosphonoformate (PFA), a pyrophosphate analog, has been obtained from the RNA of HTLV-IIIB infected cells using the polymerase chain reaction. The mutant HIV-1 RT retained polymerase activity and was cross-resistant to triphosphate forms of other nucleoside analogs including 2',3'-dideoxycytidine 5'-triphosphate, 2',3'-dideoxyadenosine 5'-triphosphate, and 3'-deoxy-2',3'-didehydrothymidine 5'-triphosphate (D4TTP), but remained sensitive to the non-nucleoside HIV-1 RT inhibitors, such as nevirapine and TIBO R82150. Sequence analysis of the mutant HIV-1 RT revealed a single amino acid substitution (Val-->Ala) at amino acid 90. The substitution of amino acid 90 by the closely related amino acids, such as Thr and Gly, also showed decreased sensitivity to AZTTP, D4TTP, and PFA. All these mutations at amino acid 90 also caused an alteration of Km for thymidine triphosphate. These results suggest that Val at this site plays a role in determining the interaction of the HIV-1 RT enzyme with the pyrophosphate group of deoxynucleoside triphosphate (dNTP) and that the hydrophobicity of the amino acid at this position was the most important determinant in the binding of HIV-1 RT to dNTP.

A single conservative amino acid substitution in the reverse transcriptase of human immunodeficiency virus-1 confers resistance to (+)-(5S)-4,5,6,7-tetrahydro-5-methyl-6-(3-methyl-2-butenyl)imidazo[4,5, 1- jk][1,4]benzodiazepin-2(1H)-thione (TIBO R82150).

Tetrahydroimidazo[4,5,1-jk][1,4]benzodiazepin-2(1H)-one and -thione (TIBO) derivatives (e.g., R82150) are potent, human immunodeficiency virus-1 (HIV-1)-specific, inhibitors of reverse transcriptase (RT) that are undergoing initial evaluation in clinical trials. Because HIV-1 has become resistant to other RT inhibitors, we investigated the potential for viral resistance to TIBO R82150 by serial in vitro passage of HIV-1IIIB in the presence of drug. R82150-resistant variants (> 100-fold increase in IC50) dominated the replicating virus population after only three or four passages. R82150-resistant virus was partially cross-resistant to other HIV-1-specific RT inhibitors, including nevirapine (approximately 10-fold increase in IC50) and 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (approximately 3.5-fold increase) but remained susceptible to 2',3'-dideoxynucleosides and phosphonoformate. DNA sequencing of cloned resistant RT, combined with site-specific mutational analyses and construction of mutant recombinant proviruses, demonstrated that a single, conservative amino acid substitution (Leu100 to Ile) in HIV-1 RT is responsible for high level R82150 resistance and partial nevirapine resistance. These studies indicate that a subtle mutation in HIV-1 RT can dramatically affect viral susceptibility to an HIV-1-specific RT inhibitor. The clinical efficacy of TIBO derivatives and other HIV-1-specific RT inhibitors may be limited by the emergence of drug-resistant viral strains.

Anti-aids agents, 6. Salaspermic acid, an anti-HIV principle from Tripterygium wilfordii, and the structure-activity correlation with its related compounds.

Salaspermic acid [1], an inhibitor of HIV reverse transcriptase and HIV replication in H9 lymphocyte cells, was isolated from the roots of Tripterygium wilfordii for the first time. The structure of 1 derived from spectral data was established unequivocally by an X-ray analysis of crystals of the monohydrate. A structure-activity correlation of 1 with ten related compounds indicated that the acetal linkage in ring A and the carboxyl group in ring E of 1 may be required for the anti-HIV activity.

HIV-1 reverse transcriptase inhibition by a dipyridodiazepinone derivative: BI-RG-587.

The dipyridodiazepinone derivative 6,11-dihydro-11-cyclopropyl-4-methyldipyrido[2,3-b:2',3'-e]-[1,4] diazepin-6-one (BI-RG-587) selectively inhibits human immunodeficiency virus type 1 (HIV-1) replication by suppressing HIV-1 reverse transcriptase activity. Both RNA- and DNA-dependent polymerase associated activities of this enzyme were found to be inhibited by BI-RG-587 in a pattern dependent on the template used. The lowest IC50 values were obtained using poly(rC)-oligo(dG)12-18 and poly(dA)-oligo(dT)12-18 as template-primer. For the RNA-dependent activity poly(rC)-oligo(dG)12-18 and dGTP appeared to enhance the inhibition of the RNA-dependent enzyme activity by BI-RG-587, with the effect of poly(rC)-oligo(dG)12-18 dominating that of dGTP. Poly(rA)-oligo(dT)10 seemed to decrease the inhibition whereas poly(rU)-oligo(dA)12-18 or poly(rG)-oligo-(dC)12-18 had no effect. dATP, dTTP and dCTP, three nucleotide triphosphates, also had no impact on the inhibition. Differences were observed for the template-dependent action of BI-RG-587 against the DNA-dependent enzyme activity. Both substrates were required to allow the inhibition by BI-RG-587 in the poly(dC)-oligo(dG)12-18 and dGTP reaction, whereas only the template and enzyme interaction seemed to be necessary for the poly(dA)-oligo(dT)12-18 and dTTP reaction. The different behaviors of DNA- and RNA-dependent DNA polymerase activities could indicate either the presence of different active sites for distinct activities or the presence of a unique active site with different configurations depending upon the template used. Also, BI-RG-587 showed a mutually exclusive inhibition when combined with two other classes of HIV-1 RT inhibitors represented by phosphonoformic acid and 3'-azido-3'-dideoxythymidine triphosphate.