Binding modes of two novel dinucleotide inhibitors of HIV-1 integrase

Insights into the binding modes on HIV-1 integrase of our novel dinucleotide inhibitors (pisodApdC and pdCpisodU) have been obtained using molecular docking experiments. In contrast to their base-stacked unbound state, these dinucleotides in their integrase-bound state prefer unstacked conformations for a more extensive interaction with the active site. The calculated free energies of binding are in concert with the experimentally acquired anti-HIV-1 integrase data.     

A novel diketo phosphonic acid that exhibits specific, strand-transfer inhibition of HIV integrase and anti-HIV activity

We have synthesized novel phosphonic acid analogues of beta-diketo acids. Interestingly, the phosphonic acid isostere, 2, of our anti-HIV compound, 1, was an inhibitor of only the strand transfer step, in stark contrast to 1. Compound 2 had lower anti-HIV activity than 1, but was more active and less toxic than the phosphonic acid analogue of L-708906. These isosteric compounds represent the first examples of beta-diketo phosphonic acids of structural, synthetic, and antiviral interest.     

Modeling, analysis, and validation of a novel HIV integrase structure provide insights into the binding modes of potent integrase inhibitors

It has been shown that L-731988, a potent integrase inhibitor, targets a conformation of the integrase enzyme formed when complexed to viral DNA, with the 3′-end dinucleotide already cleaved. It has also been shown that diketo acid inhibitors bind to the strand transfer complex of integrase and are competitive with the host target DNA. However, published X-ray structures of HIV integrase do not include the DNA; thus, there is a need to develop a model representing the strand transfer complex. In this study, we have constructed an active-site model of the HIV-1 integrase complexed with viral DNA using the crystal structure of DNA-bound transposase and have identified a binding mode for inhibitors. This proposed binding mechanism for integrase inhibitors involves interaction with a specific Mg^2 + in the active site, accentuated by a hydrophobic interaction in a cavity formed by a flexible loop upon DNA binding. We further validated the integrase active-site model by selectively mutating key residues predicted to play an important role in the binding of inhibitors. Thus, we have a binding model that is applicable to a wide range of potent integrase inhibitors and is consistent with the available resistant mutation data.     

Discovery of a nuclease-resistant, non-natural dinucleotide that inhibits HIV-1 integrase

Integration of HIV viral DNA into human chromosomal DNA catalyzed by HIV integrase is essential for the replication of HIV. Discovery of novel inhibitors of HIV integrase is of considerable significance in approaches to the development of therapeutic agents against AIDS. We have synthesized a new dinucleotide 1 with an internucleotide phosphate bond that is unusually resistant to exonucleases. This compound exhibits potent anti-HIV-1 integrase activity.     

Potential inhibitors of HIV integrase.

In the search for inhibitors of HIV integrase, the enzyme involved in the integration of viral DNA into host DNA, we have synthesized and studied a number of analogs of the heterocyclic molecule, chloroquine.     

A platform for designing HIV integrase inhibitors. Part 2: a two-metal binding model as a potential mechanism of HIV integrase inhibitors

We propose a two-metal binding model as a potential mechanism of chelating inhibitors against HIV integrase (HIV IN) represented by 2-hydroxy-3-heteroaryl acrylic acids (HHAAs). Potential inhibitors would bind to two metal ions in the active site of HIV IN to prevent human DNA from undergoing the integration reaction. Correlation of the results of metal (Mg²⁺ and Mn²⁺) titration studies with HIV IN inhibition for a series of active and inactive compounds provides support for the model. Results suggest Mg²⁺ is an essential cofactor for chelating inhibitors.     

Design, synthesis, and SAR studies of novel and highly active tri-cyclic HIV integrase inhibitors

A novel class of tri-cyclic HIV integrase inhibitors were designed based on conformational analysis of 1,6-naphthyridine carboxamide compound L-870810 and docking the designed inhibitor into the active site of our integrase enzyme model. The efficient syntheses of pyrroloquinoline tri-cyclic analogs are described. The SAR studies resulted in the identification of a lead compound that is more potent and more soluble than L-870810.     

Methylphosphonodiester substitution near the conserved CA dinucleotide in the HIV LTR alters both extent of 3'-processing and choice of nucleophile by HIV-1 integrase.

We present evidence suggesting that the 3'-processing activity of HIV-1 integrase is dramatically affected by electrostatic and/or steric perturbations 3' to the conserved CA dinucleotide. When the phosphodiester bond 3' to the scissile phosphodiester is replaced by a methylphosphonodiester linkage, 3'-processing decreases by two orders of magnitude. This block of cleavage can be somewhat overcome by increasing the pH of the reaction. Labeling of the substrates at the 3'-end revealed blockage of water and glycerol, but stimulation of the viral DNA 3'-hydroxyl, acting as the nucleophile with the methylphosphonodiester substrate. Interestingly, a circular trinucleotide was formed using the phosphodiester and methylphosphonodiester substrates when the terminal nucleotide was 3'-deoxyadenosine but not 2'-deoxyadenosine. Mutagenesis of the enzyme active site has previously been shown to alter the choice of nucleophile in the 3'-processing reaction. Taken together, the results in this study suggest that 'mutagenesis' of the DNA backbone can also alter the choice of nucleophile.     

A platform for designing HIV integrase inhibitors. Part 1: 2-hydroxy-3-heteroaryl acrylic acid derivatives as novel HIV integrase inhibitor and modeling of hydrophilic and hydrophobic pharmacophores

We present a novel series of HIV integrase inhibitors, showing IC₅₀s ranging from 0.01 to over 370 μM in an enzymatic assay. Furthermore, pharmacophore modeling study for the inhibitors was carried out to elucidate the structure–activity relationships. Finally, we found a 3D-pharmacophore model, which is composed of a hydrophilic and a hydrophobic domain, providing valuable information for designing other novel types of integrase inhibitors.     

Structure-activity of inhibition of HIV-1 integrase and virus replication by G-quartet oligonucleotides

As novel anti-HIV agents, the G-tetrad-forming oligonucleotides have been explored for their structure-activity relations with regard to inhibition of integrase (IN) (N. Jing, Expert Opin. Investig. Drugs (2000) 9, 1777-1785). We have now developed two families of G-quartet oligonucleotides: T40217-T40222, with potential formation of a tail-to-tail G-quartet dimer, and T40224-T40227, with phosphorothioate (PT) linkages in the guanine loops. The results obtained from biophysical measurements and the assays of the inhibition of HIV-1 IN and virus replication demonstrated that an increase in the length of the G-quartet structure from a monomer (15A) to a tail-to-tail dimer (47A) does not distinctly disrupt the inhibition of HIV-1 IN activity or the inhibition of HIV-1 replication in cell cultures. G-quartet oligonucleotides were observed to induce molecular aggregation of HIV-1 IN and interrupt the binding of viral DNA to HIV-1 IN. Also, PT substitutions did not confer any advantages compared with the regular phosphodiesters for the inhibition of HIV-1 replication by intramolecular G-quartets. The G-quartet motif is the primary requirement for the remarkable nuclease resistance and pronounced biological efficacy of these oligonucleotides.     

Correlation between shiftide activity and HIV-1 integrase inhibition by a peptide selected from a combinatorial library

The human immunodeficiency virus type 1 (HIV-1) integrase (IN) protein is an emerging target for the development of anti-HIV drugs. We recently described a new approach for inhibiting IN by “shiftides”—peptides that inhibit the protein by shifting its oligomerization equilibrium from the active dimer to the inactive tetramer. In this study, we used the yeast two-hybrid system with the HIV-1 IN as a bait and a combinatorial peptide aptamer library as a prey to select peptides of 20 amino acids that specifically bind IN. Five non-homologous peptides, designated as IN-1 to IN-5, were selected. ELISA studies confirmed that IN binds the free peptides. All the five peptides interact with IN with comparable affinity (K_d≈10 μM), as was revealed by fluorescence anisotropy studies. Only one peptide, IN-1, inhibited the enzymatic activity of IN in vitro and the HIV-1 replication in cultured cells. In correlation, fluorescence anisotropy binding experiments revealed that of the five peptides, only the inhibitory IN-1 inhibited the DNA binding of IN. Analytical gel filtration experiments revealed that only the IN-1 and not the four other peptides shifted the oligomerization equilibrium of IN towards the tetramer. Thus, the results show a distinct correlation between the ability of the selected peptides to inhibit IN activity and that to shift its oligomerization equilibrium.     

HIV-1 integrase inhibition by dimeric bisbenzimidazoles with different spacer structures

HIV-1 integrase is responsible for one of the key stages in virus replication, namely, integration of viral cDNA into the host cell genome. Integration inhibition leads to a complete block of the virus replication. We studied the integration inhibition by dimeric bisbenzimidazoles DBBI(7) with heptamethylene and DBBI(8) with tri(ethylene glycol) spacers and found that IC₅₀ for DBBI(7) was approximately 0.03 μM and for DBBI(8) it was approximately 10 μM. Cross-linking assays demonstrated that both compounds interfered with a proper positioning of the DNA substrate in the active centre of integrase. To clarify the inhibition mechanism, dissociation constants were determined for the complexes between DBBI and integrase DNA substrate. Calculated K _d values for the complexes formed by DBBI(7) and DBBI(8) were 270 and 140 nM, respectively. Thus, the integration inhibition is not directly connected with DBBI binding to DNA. The dependence of initial enzymatic reaction rate on DNA substrate concentration in the presence of different concentrations of inhibitors was found, and inhibition constants were determined. These data suggest that different inhibition activity of DBBI(7) and DBBI (8) is determined by different mechanisms underlying their action, namely, competitive inhibition of integrase by DBBI(7) and a more complex mechanism assumed for DBBI(8).     

Mechanism of inhibition of HIV-1 integrase by G-tetrad-forming oligonucleotides in Vitro

The G-tetrad-forming oligonucleotides and have been identified as potent inhibitors of human immunodeficiency virus type 1 integrase (HIV-1 IN) activity (Rando, R. F., Ojwang, J., Elbaggari, A., Reyes, G. R., Tinder, R., McGrath, M. S., and Hogan, M. E. (1995) J. Biol. Chem. 270, 1754-1760; Mazumder, A., Neamati, N., Ojwang, J. O., Sunder, S., Rando, R. F., and Pommier, Y. (1996) Biochemistry 35, 13762-13771; Jing, N., and Hogan, M. E. (1998) J. Biol. Chem. 273, 34992-34999). To understand the inhibition of HIV-1 IN activity by the G-quartet inhibitors, we have designed the oligonucleotides and, composed of three and four G-quartets with stem lengths of 19 and 24 A, respectively. The fact that increasing the G-quartet stem length from 15 to 24 A kept inhibition of HIV-1 IN activity unchanged suggests that the binding interaction occurs between a GTGT loop domain of the G-quartet inhibitors and a catalytic site of HIV-1 IN, referred to as a face-to-face interaction. Docking the NMR structure of (Jing and Hogan (1998)) into the x-ray structure of the core domain of HIV-1 IN, HIV-1 IN-(51-209) (Maignan, S., Guilloteau, J.-P. , Qing, Z.-L., Clement-Mella, C., and Mikol, V. (1998) J. Mol. Biol. 282, 359-368), was performed using the GRAMM program. The statistical distributions of hydrogen bonding between HIV-1 IN and were obtained from the analyses of 1000 random docking structures. The docking results show a high probability of interaction between the GTGT loop residues of the G-quartet inhibitors and the catalytic site of HIV-1 IN, in agreement with the experimental observation.     

Changes to the HIV long terminal repeat and to HIV integrase differentially impact HIV integrase assembly, activity, and the binding of strand transfer inhibitors

Human immunodeficiency virus (HIV) integrase enzyme is required for the integration of viral DNA into the host cell chromosome. Integrase complex assembly and subsequent strand transfer catalysis are mediated by specific interactions between integrase and bases at the end of the viral long terminal repeat (LTR). The strand transfer reaction can be blocked by the action of small molecule inhibitors, thought to bind in the vicinity of the viral LTR termini. This study examines the contributions of the terminal four bases of the nonprocessed strand (G(2)T(1)C(-1)A(-2)) of the HIV LTR on complex assembly, specific strand transfer activity, and inhibitor binding. Base substitutions and abasic replacements at the LTR terminus provided a means to probe the importance of each nucleotide on the different functions. An approach is described wherein the specific strand transfer activity for each integrase/LTR variant is derived by normalizing strand transfer activity to the concentration of active sites. The key findings of this study are as follows. 1) The G(2):C(2) base pair is necessary for efficient assembly of the complex and for maintenance of an active site architecture, which has high affinity for strand transfer inhibitors. 2) Inhibitor-resistant enzymes exhibit greatly increased sensitivity to LTR changes. 3) The strand transfer and inhibitor binding defects of a Q148R mutant are due to a decreased affinity of the complex for magnesium. 4) Gln(148) interacts with G(2), T(1), and C(-1) at the 5' end of the viral LTR, with these four determinants playing important and overlapping roles in assembly, strand transfer catalysis and high affinity inhibitor binding.