A check on rational drug design: molecular simulation of the allosteric inhibition of HIV-1 reverse transcriptase

Use of allosteric targets in the discovery of safer drugs

The need for drugs with fewer side effects cannot be overemphasized. Today, most drugs modify the actions of enzymes, receptors, transporters and other molecules by directly binding to their active (orthosteric) sites. However, orthosteric site configuration is similar in several proteins performing related functions and this leads to a lower specificity of a drug for the desired protein. Consequently, such drugs may have adverse side effects. A new basis of drug discovery is emerging based on the binding of the drug molecules to sites away (allosteric) from the orthosteric sites. It is possible to find allosteric sites which are unique and hence more specific as targets for drug discovery. Of many available examples, two are highlighted here. The first is caloxins - a new class of highly specific inhibitors of plasma membrane Ca²⁺ pumps. The second concerns the modulation of receptors for the neurotransmitter acetylcholine, which binds to 12 types of receptors. Exploitation of allosteric sites has led to the discovery of drugs which can selectively modulate the activation of only 1 (M1 muscarinic) out of the 12 different types of acetylcholine receptors. These drugs are being tested for schizophrenia treatment. It is anticipated that the drug discovery exploiting allosteric sites will lead to more effective therapeutic agents with fewer side effects.

Study on the interaction between HIV reverse transcriptase and its non-nucleoside inhibitor nevirapine by capillary electrophoresis

The HIV reverse transcriptase (RT) is an important antiviral target for the chemotherapy of AIDS because of its key role in virus replication. Nevirapine is a first generation of non-nucleoside reverse transcriptase inhibitors (NNRTIs), which is usually used for the therapy of AIDS. In this study, a high-performance analytical method based on capillary electrophoresis (CE) to investigate interactions between HIV RT and nevirapine was developed. Samples containing HIV RT and nevirapine at various ratios were incubated at 37 degrees C for 45 min and then separated by CE with Tris-acetate buffer at pH 7.3 containing 0.15% SDS. Both qualitative and quantitative characterizations of the binding were determined by CE for the first time. The binding constants of the interactions between HIV RT and nevirapine were calculated as (3.25+/-0.16)x10(4) and (1.25+/-0.07)x10(2) M(-1) by Scatchard analysis. HIV RT and nevirapine have two binding sites. The presented methodology should be generally applicable to study the interactions between HIV RT and nevirapine quantitatively and qualitatively.

Molecular docking studies on 4-thiazolidinones as HIV-1 RT inhibitors

Flexible docking simulations were performed on two series of 4-thiazolidinones as HIV-1 reverse transcriptase (HIV-1 RT) inhibitors. This was done by analyzing the interaction of these compounds with the allosteric site of the HIV-1 reverse transcriptase enzyme. The binding scores for these compounds were also congruent with their anti-HIV activity. A good correlation between the predicted binding free energies and the experimentally observed inhibitory activities (EC(50)) suggest that the identified binding conformations of these inhibitors are reliable. The results of docking studies provide an insight into the pharmacophoric structural requirements for the HIV-1 RT inhibitory activity of this class of molecules.

Investigation on an Orientation and Interaction Energy of the Water Molecule in the HIV-1 Reverse Transcriptase Active Site by Quantum Chemical Calculations

To obtain basic information such as interaction between the water molecule and amino acids in the active site of HIV-1 Reverse Transcriptase (HIV-1 RT), ab initio molecular orbital calculations and the two-layer ONIOM method were performed. The energetic results from different methods show that the ONIOM2 (MP2/6-311G:HF/6-31G//HF/6-31G:HF/3-21G) can provide reliable results on the orientation of the water molecule in the HIV-1 RT active site. The interaction between the water molecule and Asp186 was found to be the most preferable. The obtained results from ONIOM2 calculations indicated that the active site model system included six amino acid residues (Asp186, Asp185, Met184, Tyr183, Leu187, and Tyr188) leading a preferable representation of the environment surrounding the water molecule in the more realistic model. The water molecule presented in the active site tends to form H-bonding with Asp186, Tyr183, and Tyr188 as indicated by the distances of O4-H2 = 1.91 A, O3-H7 = 2.36 A, and O3-H17 = 1.73 A, respectively. The stability of this complex system brings to the foundation of the estimated binding energy approximately -15.8 kcal/mol or -8.1 kcal/mol which is more stabilized relative to the smallest model complex. These observations revealed that the water molecule forms both a hydrogen bond donor and a hydrogen bond acceptor in the cavity and plays an important role in the specific conformation of the active site of HIV-1 RT. The H-bonding is a rather strong interaction; thus, the water might induce the conformation of the active site to fit the catalysis process and helpfully attract dNTP to elongate the viral DNA in the replication process of this enzyme.

Evolution of anti-HIV drug candidates. Part 1: From alpha-anilinophenylacetamide (alpha-APA) to imidoyl thiourea (ITU)

Stemming from work on a previous clinical candidate, loviride, and other alpha-APA derivatives, a new series of potent non-nucleoside reverse transcriptase inhibitors (NNRTIs) has been synthesized. The ITU analogues, which contain a unique diarylated imidoyl thiourea, are very active in inhibiting both wild-type and clinically important mutant strains of HIV-1.

Three-dimensional quantitative structure-activity relationships study on HIV-1 reverse transcriptase inhibitors in the class of dipyridodiazepinone derivatives, using comparative molecular field analysis

A three-dimensional quantitative structure-activity relationships (3D QSAR) method, Comparative Molecular Field Analysis (CoMFA), was applied to a set of dipyridodiazepinone (nevirapine) derivatives active against wild-type (WT) and mutant-type (Y181C) HIV-1 reverse transcriptase. The starting geometry of dipyridodiazepinone was taken from X-ray crystallographic data. All 75 derivatives, divided into a training set of 53 compounds and a test set of 22 molecules, were then constructed and full geometrical optimizations were performed, based on a semiempirical molecular orbital method (AM1). CoMFA was used to discriminate between structural requirements for WT and Y181C inhibitory activities. The resulting CoMFA models yield satisfactory predictive ability regarding WT and Y181C inhibitions, with r2 cv = 0.624 and 0.726, respectively. CoMFA contour maps reveal that steric and electrostatic interactions corresponding to the WT inhibition amount to 58.5% and 41.5%, respectively, while steric and electrostatic effects have approximately equal contributions for the explanation of inhibitory activities against Y181C. The contour maps high-light different characteristics for different types of wild-type and mutant-type HIV-1 RT. In addition, these contour maps agree with experimental data for the binding topology. Consequently, the results obtained provide information for a better understanding of the inhibitor-receptor interactions of dipyridodiazepinone analogs.

Comparative molecular field analysis (CoMFA) and docking studies of non-nucleoside HIV-1 RT inhibitors (NNIs)

A set of TIBO derivatives endowed with reverse transcriptase (RT) inhibitory activity were analyzed by comparative molecular field analysis (CoMFA). Besides conventional steric and electrostatic fields, molecular lipophilicity potential (MLP) was also used as a third field in CoMFA. An informative and statistically significant model (q2 = 0.70, r2 = 0.90, s = 0.46) was obtained by taking into account the three field types together. The key molecular determinants governing the RT inhibition by TIBO congeners were detected at the 3-D level by a careful analysis of the CoMFA isocontour maps. To challenge the predictive ability of the CoMFA model, an external set of thiazolobenzimidazole (TBZ) derivatives were examined. Good predictions, suggesting a similar binding mode for TIBO and TBZ derivatives, emerged. Flexible docking experiments on TBZ, TIBO and other NNIs confirmed common binding characteristics, as found out also by CoMFA, and moreover a good correlation between calculated binding energies and inhibitory potency was found.

Novel spironucleosides: 1",3"-thiazolidine-2"-spiro-3'-3'-deoxyuridine derivatives

Reaction of 2',5'-di-O-TBDMS-3'-ketouridine 1 with L-cysteine yielded in good yield a resolvable mixture of the two expected epimeric spironucleosides 2 and 3. Amidification of their carboxylic group took place readily and the ribo carboxamide 4 was oxidized to the corresponding sulfoxide 6. Despite their similarity to TSAO derivatives these compounds did not exhibit usable anti-HIV activity.