Evolution of anti-HIV drug candidates. Part 3: Diarylpyrimidine (DAPY) analogues

Inhibition of human immunodeficiency virus type 1 infection by the candidate microbicide dapivirine, a nonnucleoside reverse transcriptase inhibitor

Heterosexual transmission of human immunodeficiency virus (HIV) remains the major route of infection worldwide; thus, there is an urgent need for additional prevention strategies, particularly strategies that could be controlled by women, such as topical microbicides. Potential microbicide candidates must be both safe and effective. Using cellular and tissue explant models, we have evaluated the activity of the nonnucleoside reverse transcriptase inhibitor (NNRTI) dapivirine as a vaginal microbicide. In tissue compatibility studies, dapivirine was well tolerated by epithelial cells, T cells, macrophages, and cervical tissue explants. Dapivirine demonstrated potent dose-dependent inhibitory effects against a broad panel of HIV type 1 isolates from different clades. Furthermore, dapivirine demonstrated potent activity against a wide range of NNRTI-resistant isolates. In human cervical explant cultures, dapivirine was able not only to inhibit direct infection of mucosal tissue but also to prevent the dissemination of the virus by migratory cells. Activity was retained in the presence of semen or a cervical mucus simulant. Furthermore, dapivirine demonstrated prolonged inhibitory effects: it was able to prevent both localized and disseminated infection for as long as 6 days posttreatment. The prolonged protection observed following pretreatment of genital tissue and the lack of observable toxicity suggest that dapivirine has considerable promise as a potential microbicide candidate.

Optimization of azoles as anti-human immunodeficiency virus agents guided by free-energy calculations

Efficient optimization of an inactive 2-anilinyl-5-benzyloxadiazole core has been guided by free energy perturbation (FEP) calculations to provide potent non-nucleoside inhibitors of human immunodeficiency virus (HIV) reverse transcriptase (NNRTIs). An FEP "chlorine scan" was performed to identify the most promising sites for substitution of aryl hydrogens. This yielded NNRTIs 8 and 10 with activities (EC50) of 820 and 310 nM for protection of human T-cells from infection by wild-type HIV-1. FEP calculations for additional substituent modifications and change of the core heterocycle readily led to oxazoles 28 and 29, which were confirmed as highly potent anti-HIV agents with activities in the 10-20 nM range. The designed compounds were also monitored for possession of desirable pharmacological properties by use of additional computational tools. Overall, the trends predicted by the FEP calculations were well borne out by the assay results. FEP-guided lead optimization is confirmed as a valuable tool for molecular design including drug discovery; chlorine scans are particularly attractive since they are both straightforward to perform and highly informative.

Etravirine has no effect on QT and corrected QT interval in HIV-negative volunteers

BACKGROUND

Etravirine (TMC125), a next-generation nonnucleoside reverse transcriptase inhibitor, has shown antiviral efficacy in 2 large Phase 3 trials. In vitro and in vivo studies have shown that etravirine is not associated with proarrhythmic potential. Electrocardiograms (ECGs) from healthy and HIV 1-infected volunteers showed no clinically relevant changes.

OBJECTIVE

To evaluate the effect of 2 etravirine dosing regimens on QT/corrected QT interval (QTc) in HIV-negative volunteers and assess pharmacokinetic and additional safety parameters.

METHODS

A double-blind, double-dummy, randomized, placebo- and active-controlled, 4-period crossover trial was conducted in 41 HIV-negative volunteers. Participants received 4 regimens: etravirine 200 mg twice daily, etravirine 400 mg once daily, moxifloxacin 400 mg once daily (positive control), and placebo in separate 8-day sessions, with each followed by a washout period of 14 or more days. On days -1, 1, and 8 of each session, ECGs were recorded at 11 time points over 12 hours. Pharmacokinetic profiles of etravirine regimens were evaluated and safety was assessed.

RESULTS

Thirty-seven subjects completed the study. For etravirine, the upper limit of the 90% CIs of mean time-matched differences in QTc determined using Fridericia's formula (QTcF) was below 10 msec at all time points, the threshold for prolonged QT as defined by regulatory guidelines. The maximum mean (90% CI) difference of time-matched changes in QTcF versus placebo on day 1 was +0.1 msec (-2.6 to 2.9), -0.2 msec (-2.6 to 2.1), and +10.1 msec (7.3 to 12.8) for etravirine 200 mg twice daily, etravirine 400 mg once daily, and moxifloxacin, respectively. On day 8, these values were +0.6 msec (-2.1 to 3.3), -1.0 msec (-4.4 to 2.5), and +10.3 msec (6.8 to 13.9), respectively. Etravirine produced no clinically significant changes in other ECG parameters. No significant differences between males and females were observed. Both etravirine regimens had similar pharmacokinetic exposure and safety profiles.

CONCLUSIONS

Etravirine does not prolong the QTc interval. No clinically relevant ECG changes were observed in HIV-negative volunteers. Short-term dosing of etravirine in HIV-negative volunteers was generally safe and well tolerated.

High-resolution structures of HIV-1 reverse transcriptase/TMC278 complexes: strategic flexibility explains potency against resistance mutations

TMC278 is a diarylpyrimidine (DAPY) nonnucleoside reverse transcriptase inhibitor (NNRTI) that is highly effective in treating wild-type and drug-resistant HIV-1 infections in clinical trials at relatively low doses ( approximately 25-75 mg/day). We have determined the structure of wild-type HIV-1 RT complexed with TMC278 at 1.8 A resolution, using an RT crystal form engineered by systematic RT mutagenesis. This high-resolution structure reveals that the cyanovinyl group of TMC278 is positioned in a hydrophobic tunnel connecting the NNRTI-binding pocket to the nucleic acid-binding cleft. The crystal structures of TMC278 in complexes with the double mutant K103N/Y181C (2.1 A) and L100I/K103N HIV-1 RTs (2.9 A) demonstrated that TMC278 adapts to bind mutant RTs. In the K103N/Y181C RT/TMC278 structure, loss of the aromatic ring interaction caused by the Y181C mutation is counterbalanced by interactions between the cyanovinyl group of TMC278 and the aromatic side chain of Y183, which is facilitated by an approximately 1.5 A shift of the conserved Y(183)MDD motif. In the L100I/K103N RT/TMC278 structure, the binding mode of TMC278 is significantly altered so that the drug conforms to changes in the binding pocket primarily caused by the L100I mutation. The flexible binding pocket acts as a molecular "shrink wrap" that makes a shape complementary to the optimized TMC278 in wild-type and drug-resistant forms of HIV-1 RT. The crystal structures provide a better understanding of how the flexibility of an inhibitor can compensate for drug-resistance mutations.

Energetic effects for observed and unobserved HIV-1 reverse transcriptase mutations of residues L100, V106, and Y181 in the presence of nevirapine and efavirenz

The effect of mutations on amino acid residues L100, V106, and Y181 for unbound HIV-1 reverse transcriptase (RT) and RT bound to nevirapine and efavirenz was investigated using Monte Carlo/free energy perturbation calculations. Using both native and bound crystal structures of RT, mutation of the amino acid residues to both those observed and unobserved in patients was carried out. The results of the calculations revealed that the variant that survives in patients dosed with either nevirapine or efavirenz had a more positive Delta Delta G value than other variants that were not observed in patients. These data suggest that the mutation observed in patients is the most effective (the one that binds the drug most weakly) of all possible codon change mutations.

Crystal structures of HIV-1 reverse transcriptase complexes with thiocarbamate non-nucleoside inhibitors

O-Phthalimidoethyl-N-arylthiocarbamates (TCs) have been recently identified as a new class of potent HIV-1 reverse transcriptase (RT) non-nucleoside inhibitors (NNRTIs), by means of computer-aided drug design techniques [Ranise A. Spallarossa, S. Cesarini, F. Bondavalli, S. Schenone, O. Bruno, G. Menozzi, P. Fossa, L. Mosti, M. La Colla, et al., Structure-based design, parallel synthesis, structure-activity relationship, and molecular modeling studies of thiocarbamates, new potent non-nucleoside HIV-1 reverse transcriptase inhibitor isosteres of phenethylthiazolylthiourea derivatives, J. Med. Chem. 48 (2005) 3858-3873]. To elucidate the atomic details of RT/TC interaction and validate an earlier TC docking model, the structures of three RT/TC complexes were determined at 2.8-3.0A resolution by X-ray crystallography. The conformations adopted by the enzyme-bound TCs were analyzed and compared with those of bioisosterically related NNRTIs.

From docking false-positive to active anti-HIV agent

Virtual screening of the Maybridge library of ca. 70 000 compounds was performed using a similarity filter, docking, and molecular mechanics-generalized Born/surface area postprocessing to seek potential non-nucleoside inhibitors of human immunodeficiency virus-1 (HIV-1) reverse transcriptase (NNRTIs). Although known NNRTIs were retrieved well, purchase and assaying of representative, top-scoring compounds from the library failed to yield any active anti-HIV agents. However, the highest-ranked library compound, oxadiazole 1, was pursued as a potential "near-miss" with the BOMB program to seek constructive modifications. Subsequent synthesis and assaying of several polychloro-analogs did yield anti-HIV agents with EC50 values as low as 310 nM. The study demonstrates that it is possible to learn from a formally unsuccessful virtual-screening exercise and, with the aid of computational analyses, to efficiently evolve a false positive into a true active.

Synthesis of novel diarylpyrimidine analogues of TMC278 and their antiviral activity against HIV-1 wild-type and mutant strains

Novel diarylpyrimidines (DAPY), which represent next generation of non-nucleoside reverse transcriptase inhibitors (NNRTIs), were synthesized and their activities against human immunodeficiency virus type I (HIV-1) assessed. Modulations at positions 2 and 6 of the left phenyl ring generated interesting derivatives of TMC278 displaying high potency against wild-type and mutant viruses compared to nevirapine and efavirenz. The pharmacokinetic profile of the best newly synthesized DAPY was evaluated and compared with TMC278 now in phase II clinical trials.

Synthesis and biological activity of imidazopyridine anticoccidial agents: part I

Coccidiosis is the major cause of morbidity and mortality in the poultry industry. Protozoan parasites of the genus Eimeria invade the intestinal lining of the avian host causing tissue pathology, poor weight gain, and in some cases mortality. Resistance to current anticoccidials has prompted the search for new therapeutic agents with potent in vitro and in vivo activity against Eimeria. Antiparasitic activity is due to inhibition of a parasite specific cGMP-dependent protein kinase (PKG). In this study, we present the synthesis and biological activity of imidazo[1,2-a]pyridine anticoccidial agents. From this series, several compounds showed subnanomolar in vitro activity and commercial levels of in vivo activity. However, the potential genotoxicity of these compounds precludes them from further development.

Impact of EGFR point mutations on the sensitivity to gefitinib: insights from comparative structural analyses and molecular dynamics simulations

Emergence of resistant mutations in drug targets represents a serious problem in the targeted chemotherapy. One challenging issue is to understand the atomic-detailed effect of the mutation on the target. Another intriguing issue is how to predict specific mutations that would show up in the clinical setting, leading to drug resistance. By computational approaches, we have investigated structural, dynamics and energetic effects of a series of EGFR mutations identified from the lung cancer patients. We demonstrated mutation L858R caused gefitinib move closer to the hinge region, whereas T790M caused the ligand escape from the binding pocket. In particular, the T790M decreased the size of the hydrophobic slot formed by L718 and G796. This suggests that, to be effective against the T790M mutant, the inhibitors should avoid interactions with the hydrophobic slot. Mutations T790M, L858R, and their combinations are found to cause different conformational redistribution and to perturb the electrostatic potential at the ATP-binding pocket. Normal mode analysis revealed the mutations resulted in changes in the correlated movements in the protein. In an attempt to develop a computational descriptor for predicting the functional effect of EGFR mutations, we have developed a Plarm algorithm, and the Plarm score was found to be an excellent predictor of the functional impact of six clinical relevant mutations in EGFR tyrosine kinase domains, including T790M, L858R, G719C, L861Q, T790M + L858R double mutant, and delL747-P753insS. The Plarm algorithm could be readily extended to investigate other drug targets.

Potent nonnucleoside reverse transcriptase inhibitors target HIV-1 Gag-Pol

Nonnucleoside reverse transcriptase inhibitors (NNRTIs) target HIV-1 reverse transcriptase (RT) by binding to a pocket in RT that is close to, but distinct, from the DNA polymerase active site and prevent the synthesis of viral cDNA. NNRTIs, in particular, those that are potent inhibitors of RT polymerase activity, can also act as chemical enhancers of the enzyme's inter-subunit interactions. However, the consequences of this chemical enhancement effect on HIV-1 replication are not understood. Here, we show that the potent NNRTIs efavirenz, TMC120, and TMC125, but not nevirapine or delavirdine, inhibit the late stages of HIV-1 replication. These potent NNRTIs enhanced the intracellular processing of Gag and Gag-Pol polyproteins, and this was associated with a decrease in viral particle production from HIV-1-transfected cells. The increased polyprotein processing is consistent with premature activation of the HIV-1 protease by NNRTI-enhanced Gag-Pol multimerization through the embedded RT sequence. These findings support the view that Gag-Pol multimerization is an important step in viral assembly and demonstrate that regulation of Gag-Pol/Gag-Pol interactions is a novel target for small molecule inhibitors of HIV-1 production. Furthermore, these drugs can serve as useful probes to further understand processes involved in HIV-1 particle assembly and maturation.

HIV-1 encodes reverse transcriptase (RT), an enzyme that is essential for virus replication. Nonnucleoside reverse transcriptase inhibitors (NNRTIs) are allosteric inhibitors of the HIV-1 RT. In HIV-1-infected cells NNRTIs block the RT-catalyzed synthesis of a double-stranded DNA copy of the viral genomic RNA, which is an early step in the virus life cycle. Potent NNRTIs have the novel feature of promoting the interaction between the two RT subunits. However, the importance of this effect on the inhibition of HIV-1 replication has not been defined. In this study, the authors show that potent NNRTIs block an additional step in the virus life cycle. NNRTIs increase the intracellular processing of viral polyproteins called Gag and Gag-Pol that express the HIV-1 structural proteins and viral enzymes. Enhanced polyprotein processing is associated with a decrease in viral particles released from NNRTI-treated cells. NNRTI enhanced polyprotein processing is likely due to the drug binding to RT, expressed as part of the Gag-Pol polyprotein and promoting the interaction between separate Gag-Pol polyproteins. This leads to premature activation of the Gag-Pol embedded HIV-1 protease, resulting in a decrease in full-length viral polyproteins available for assembly and budding from the host cell membrane. This study provides proof-of-concept that small molecules can modulate the interactions between Gag-Pol polyproteins and suggests a new target for the development of HIV-1 antiviral drugs.

Current developments in HIV chemotherapy

HIV infection is the leading cause of death worldwide and despite major advances in treatment, more new cases were diagnosed in 2004 than any previous year. Current treatment regimens are based on the use of two or more drugs from two or more classes of inhibitors termed highly active antiretroviral therapy (HAART). Although HAART is capable of suppressing viral loads to undetectable levels, problems of toxicity, patient adherence, and particularly the emergence of drug-resistant viruses continues to spur the development of new chemotherapeutics to combat HIV. Clinical candidates from the four existing classes of inhibitors are presented in this review along with lead compounds against new viral targets, with special emphasis on HIV integrase.

Aspects of successful drug discovery and development

Despite landmark achievements (e.g. >20 new anti-HIV drugs), a number of important therapeutic challenges remain. Although an expanding array of new drug discovery technologies has become available, drug research and development (R&D) productivity in general is still low. The establishment of close functional links between specialists active in early discovery, development and the clinic can thereby contribute to overall efficiency and higher success rates of new drug candidates. One of the more qualitative discovery challenges is to improve the predictability of early stage research models in term of in vivo drug efficacy. A cell-based model using viral replication in human T cells (MT-4) is used as an example from the HIV field to highlight the role of cell-based assays as tools for new target discovery, lead finding and optimization. The development of the next generation HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs) TMC125 and TMC278 and the protease inhibitor (PI) TMC114 (Prezista), further point to new fundamental strategies to combat and prevent antiviral drug resistance and to the importance of incorporating clinical and pharmaceutical aspects into lead finding and optimization, drug design and drug candidate selection. A more parallel-oriented drug discovery strategy is thus portrayed that harnesses some 'evolutionary' principles in combination with technologies that are currently rationalizing drug discovery.

Emerging reverse transcriptase inhibitors for the treatment of HIV infection in adults

A combination of three or more antiretroviral drugs, commonly called 'highly active antiretroviral therapy' (HAART), has become the standard-of-care treatment for HIV-infected patients in the developed world. There are now 21 licensed anti-HIV drugs to choose from when starting a HAART regimen. The currently approved antiretroviral drugs fall into four categories: nucleoside/nucleotide reverse transcriptase inhibitors, non-nucleoside reverse transcriptase inhibitors, protease inhibitors and fusion inhibitors. Novel compounds currently in preclinical or clinical development are either focusing on new viral proteins or the same specific viral elements targeted by the available drugs. When developing new anti-HIV drugs of an already existing class, focus should be held on maximising potency, minimising toxicity, diminishing the risk for resistance development and producing effective drugs for patients who already have resistance to currently available drugs. In addition, pill burden should be ideally reduced to once-daily dosing, thereby enhancing a patient's adherence and reducing treatment costs. The present review focuses on emerging drugs to inhibit the reverse transcriptase of HIV.

Dawn of non-nucleoside inhibitor-based anti-HIV microbicides

The emergence of HIV/AIDS as a disease spread through sexual intercourse has prompted the search for safe and effective vaginal and rectal microbicides for curbing mucosal viral transmission via semen. Since endogenous reverse transcription is implicated in augmenting the sexual transmission of HIV-1 infection, potential microbicides should have the inherent ability to optimally inhibit both wild-type and drug-escape mutants. The non-nucleoside reverse transcriptase inhibitors (NNRTIs), which bind to an allosteric site on RT, are an important arsenal of drugs against HIV-1. The clinical success of NNRTI-based HIV/AIDS therapies has led to extensive structural and molecular modelling studies of enzyme complexes and chemical synthesis of second- and third-generation NNRTIs. Rationally designed NNRTIs deduced from changes in binding pocket size, shape and residue character that result from clinically observed NNRTI resistance-associated mutations exhibit high binding affinity for HIV-1 RT and robust anti-HIV activity against the wild-type and drug-escape mutants without cytotoxicity. Notably, membrane permeable tight binding NNRTIs have the ability to inactivate cell-free as well as cell-associated HIV-1 in semen without metabolic activation. Consequently, NNRTIs currently under development as experimental microbicides include thiourea-PETT (where PETT stands for phenethylthiazolylthiourea) derivatives (PHI-236, PHI-346 and PHI-443), urea-PETT derivatives (MIV-150), oxypyrimidines (S-DABOs), thiocarboxanilides (UC-781) and diarylpyrimidines (TMC-120). Mucoadhesive formulations of these NNRTIs have been studied for safety and efficacy in animal models and some have entered Phase I safety testing in humans. This review focuses on the structural, biological and preclinical studies relevant to the clinical development of these NNRTIs as molecular virucides intended to prevent the sexual transmission of HIV-1.

Resistance to New Anti-HIV Agents: Problems in the Pathway of Drug Registration

Resistance data are now requested by the regulatory agencies as an integral part of the approval process of new antiretroviral drugs. We examined the means by which resistance data was gathered during pre-clinical and clinical Phases I, II and III of drug development, and how the public and academic experts access these proprietary data. The analysis identified various opportunities for improvement of the current process, in particular the need for standards in generating and reporting resistance data on new antiretroviral drugs, and the need to enforce warnings in the product labelling on the drug combinations that can potentially lead to resistance and treatment failure.

New antiretroviral agents for the treatment of HIV infection

Issues, such as complexity, tolerability, and drug resistance and cross-resistance, limit the effectiveness of current antiretroviral regimens and make the continued development of newer agents important, despite the availability of 20 approved drugs for the treatment of HIV infection. Many new compounds are in development in existing classes: nucleoside and nucleotide analogue reverse transcriptase inhibitors (eg, D-d4FC and SPD754), non-nucleoside analogue reverse transcriptase inhibitors (eg, capravirine and TMC125), and protease inhibitors (eg, tipranavir and TMC114). In addition, newer classes of antiretroviral drugs, such as HIV entry inhibitors (eg, TNX-355, SCH 417690, UK-427,857, AMD 11070), that target the first step in the HIV life cycle are under development. Continued improvement in the treatment of HIV infection will result from the availability of convenient, well-tolerated, and affordable drugs with potent and durable antiretroviral activity.

Crystallography and the design of anti-AIDS drugs: conformational flexibility and positional adaptability are important in the design of non-nucleoside HIV-1 reverse transcriptase inhibitors

Drug resistance is a key cause of failure for treatment of HIV infection. The efficacy of non-nucleoside reverse transcriptase inhibiting (NNRTI) drugs is impaired by rapid emergence of drug-resistance mutations. A multidisciplinary effort led to the discovery of the potent NNRTIs dapivirine and etravirine, both of which are diarylpyrimidine (DAPY) derivatives. Systematic structural and molecular modeling studies of HIV-1 reverse transcriptase (RT)/NNRTI complexes revealed different modes of inhibitor binding, and some of the DAPY inhibitors can bind to RT in different conformations. The torsional flexibility ("wiggling") of the inhibitors can generate numerous conformational variants and the compactness of the inhibitors permits significant repositioning and reorientation (translation and rotation) within the pocket ("jiggling"). Such adaptations appear to be critical for the ability of the diarylpyrimidine NNRTIs to retain their potency against a wide range of drug-resistant HIV-1 RTs. Exploitation of inhibitor conformational flexibility (such as torsional flexibility about strategically located chemical bonds) can be a powerful element of drug design, especially for the design of drugs that will be effective against rapidly mutating targets (which is a collection of related targets).

TMC125, a novel next-generation nonnucleoside reverse transcriptase inhibitor active against nonnucleoside reverse transcriptase inhibitor-resistant human immunodeficiency virus type 1

Nonnucleoside reverse transcriptase inhibitors (NNRTIs) are potent inhibitors of human immunodeficiency virus type 1 (HIV-1); however, currently marketed NNRTIs rapidly select resistant virus, and cross-resistance within the class is extensive. A parallel screening strategy was applied to test candidates from a series of diarylpyrimidines against wild-type and resistant HIV strains carrying clinically relevant mutations. Serum protein binding and metabolic stability were addressed early in the selection process. The emerging clinical candidate, TMC125, was highly active against wild-type HIV-1 (50% effective concentration [EC50] = 1.4 to 4.8 nM) and showed some activity against HIV-2 (EC50 = 3.5 microM). TMC125 also inhibited a series of HIV-1 group M subtypes and circulating recombinant forms and a group O virus. Incubation of TMC125 with human liver microsomal fractions suggested good metabolic stability (15% decrease in drug concentration and 7% decrease in antiviral activity after 120 min). Although TMC125 is highly protein bound, its antiviral effect was not reduced by the presence of 45 mg of human serum albumin/ml, 1 mg of alpha1-acid glycoprotein/ml, or 50% human serum. In an initial screen for activity against a panel of 25 viruses carrying single and double reverse transcriptase amino acid substitutions associated with NNRTI resistance, the EC50 of TMC125 was <5 nM for 19 viruses, including the double mutants K101E+K103N and K103N+Y181C. TMC125 also retained activity (EC50 < 100 nM) against 97% of 1,081 recent clinically derived recombinant viruses resistant to at least one of the currently marketed NNRTIs. TMC125 is a potent next generation NNRTI, with the potential for use in individuals infected with NNRTI-resistant virus.

A series of diaryltriazines and diarylpyrimidines are highly potent nonnucleoside reverse transcriptase inhibitors with possible applications as microbicides

An in vitro model of monocyte-derived dendritic cells (MO-DC) and CD4(+) T cells, representing the primary targets of sexual human immunodeficiency virus (HIV) transmission, was used to evaluate the antiviral and immune suppressive activity of new classes of nonnucleoside reverse transcriptase inhibitors, diaryltriazines (DATAs) and diarylpyrimidines (DAPYs), compared to the reference compounds UC-781 and PMPA. Antiviral activity (as reflected by the 50% effective concentration [EC(50)]) was determined by treating HIV-infected MO-DC/CD4(+)-T-cell cocultures with a dose range of a compound during 14 days, followed by analysis of supernatants in HIV p24 antigen enzyme-linked immunosorbent assay. A limited, 24-h treatment evaluated the compounds as microbicides. Viral rescue was evaluated in a PCR by monitoring proviral DNA in secondary cultures with phytohemagglutinin-interleukin-2 blasts. We determined 50% immunosuppressive concentrations in mixed leukocyte cultures of MO-DC and allogeneic T cells, with compound either continuously present or present only during the first 24 h. The EC(50) values of DATA and DAPY compounds ranged from 0.05 to 3 nM compared to 50 nM for UC-781 and 89 nM for PMPA. When evaluated in the "microbicide" setting, the most potent compounds completely blocked HIV infection at 10 to 100 nM. The immunosuppressive concentrations were well above the EC(50), resulting in favorable therapeutic indices for all compounds tested. The DATA and DAPY compounds described here are more potent than earlier reverse transcriptase inhibitors and show favorable pharmacological profiles in vitro. They could strengthen the antiretroviral armamentarium and might be useful as microbicides.

New Antiretroviral Agents for the Treatment of HIV Infection

Issues, such as complexity, tolerability, and drug resistance and cross-resistance, limit the effectiveness of current antiretroviral regimens and make the continued development of newer agents important, despite the availability of 20 approved drugs for the treatment of HIV infection. Many new compounds are in development in existing classes: nucleoside and nucleotide analogue reverse transcriptase inhibitors (eg, D-d4FC and SPD754), non-nucleoside analogue reverse transcriptase inhibitors (eg, capravirine and TMC125), and protease inhibitors (eg, tipranavir and TMC114). In addition, newer classes of antiretroviral drugs, such as HIV entry inhibitors (eg, TNX-355, SCH 417690, UK-427,857, AMD 11070), that target the first step in the HIV life cycle are under development. Continued improvement in the treatment of HIV infection will result from the availability of convenient, well-tolerated, and affordable drugs with potent and durable antiretroviral activity.

Paul Janssen (1926-2003)

Paul Janssen (1926-2003) performed during fifty Years an intense pharmaceutical research activity. From 1953 to 2003, he discovered numerous new drugs in various fields of pharmacology. He widened the neuroleptic spectrum with haloperidol and risperidone, the opioid one with dextromoramide, fentanyl and its short-life derivates, constipating agents like loperamide, hypnotics, anaesthetics. In the field of anti-infectious agents, he discovered azole antifungals, parasiticides among which levamisole and mebendazole. Other therapeutic classes have been enriched by JANSSEN's works: vasodilatating agents, antihypertensive and anti-allergic drugs, etc. More recently, his research was oriented towards virology namely anti-HIV drugs. When Paul JANSSEN's life ended, his scientific production seemed to be one of the most eminent in the XXth century.

Effect of stereo and regiochemistry towards wild and multidrug resistant HIV-1 virus: viral potency of chiral PETT derivatives

Chiral derivatives of several substituted halopyridyl and thiazolyl PETT compounds were synthesized as non-nucleoside inhibitors of the reverse transcriptase (RT) enzyme of the human immunodeficiency virus (HIV-1). Molecular modeling studies indicated that because of the asymmetric geometry of the non-nucleoside inhibitors (NNRTI) binding pocket, the "R" stereoisomers would fit the NNRTI binding pocket of the HIV-1 RT much better than the corresponding "S" stereoisomers, as reflected by their 10(4)-fold lower K(i) values. The "R" stereoisomers of several PETT derivatives inhibited the recombinant RT in vitro with lower IC(50) values than their enantiomers. The active compounds were further evaluated for their ability to inhibit HIV-1 replication in human peripheral blood mononuclear cells (PBMCs). All the "R" isomers again showed potent anti-HIV activity and inhibited the replication of the HIV-1 strains HTLV(IIIB) in PBMCs at nanomolar concentrations whereas their enantiomers were less potent. The lead compounds for the respective groups were further tested against A17 (NNRTI-resistant, Y181C mutant RT), and A17Var (NNI-resistant Y181C +/- K103N mutant RT) as well as multidrug resistant viral strains. The results indicated that the lead compounds were several logs more potent than the standard NNRTI drug nevirapine. Structure-activity relationship among the derivatives showed preference of pyridyl unit with halo substitutions primarily at 5-position demonstrating the importance of both the stereochemistry as well as regiochemistry. Our data provides experimental evidence that the stereochemistry and the regiochemistry of non-nucleoside inhibitors can profoundly affect their anti-HIV activity.

On the detection of multiple-binding modes of ligands to proteins, from biological, structural, and modeling data

There are several indications that a given compound or a set of related compounds can bind in different modes to a specific binding site of a protein. This is especially evident from X-ray crystallographic structures of ligand-protein complexes. The availability of multiple binding modes of a ligand in a binding site may present an advantage in drug design when simultaneously optimizing several criteria. In the case of the design of anti-HIV compounds we observed that the more active compounds that are also resilient against mutation of the non-nucleoside binding site of HIV1-reverse transcriptase make use of more binding modes than the less active and resilient compounds.

In vitro evaluation of nonnucleoside reverse transcriptase inhibitors UC-781 and TMC120-R147681 as human immunodeficiency virus microbicides

The nonnucleoside reverse transcriptase inhibitors UC-781 and TMC120-R147681 (Dapivirine) effectively prevented human immunodeficiency virus (HIV) infection in cocultures of monocyte-derived dendritic cells and T cells, representing primary targets in sexual transmission. Both drugs had a favorable therapeutic index. A 24-h treatment with 1,000 nM UC-781 or 100 nM TMC120-R147681 prevented cell-free HIV infection, whereas 10-fold-higher concentrations blocked cell-associated HIV.

Correlations between Factors Determining the Pharmacokinetics and Antiviral Activity of HIV-1 Non-Nucleoside Reverse Transcriptase Inhibitors of the Diaryltriazine and Diarylpyrimidine Classes of Compounds

OBJECTIVE

To investigate the important factors that determine the bioavailability and the antiviral activity of the diaryltriazine (DATA) and diarylpyrimidine (DAPY) non-nucleoside reverse transcriptase inhibitors (NNRTIs) of HIV-1 in animal species and humans using cell-based assays, physicochemical and computed parameters.

METHODS

This naturalistic study included 15 parameters ranging from molecular mechanics calculations to phase I clinical trials. The calculated parameters were solvent-accessible surface area (SASA), polar surface area and Gibbs free energy of solvation. Physicochemical parameters comprised lipophilicity (octanol/water partition coefficient [cLogP]), ionisation constant (pKa), solubility and aggregate radius. Cell-based assays included human colonic adenocarcinoma cell (Caco-2) permeability (transepithelial transport), drug metabolism and antiviral activity (negative logarithm of the molar effective concentration inhibiting viral replication by 50% [pEC50]). Exposure was tested in rats, dogs and human volunteers.

RESULTS

Of the 15 parameters, eight correlated consistently among one another. Exposure (area under the plasma concentration-time curve [AUC]) in humans correlated positively with that in rats (r = 1.00), with transepithelial transport (r = 0.83), lipophilicity (r = 0.60), ionisability (r = 0.89), hydrodynamic radius of aggregates (r = 0.66) and with antiviral activity (r = 0.61). Exposure in humans was also seen to correlate negatively with SASA (r = -0.89). No consistent correlation was found between exposure in dogs and the eight parameters. Of the 14 DATA/DAPY molecules, 11 form aggregates with radii between 34 and 100 nm.

CONCLUSIONS

We observed correlations between exposure in humans with exposure in rats, transepithelial transport (Caco-2 cells), ionisability, lipophilicity, aggregate radius and SASA in the class of DATA/DAPY NNRTI compounds. The lipophilic DATA/DAPY compounds form aggregates. It can be assumed that absorption in the intestinal tract and endocytosis in infected cells of these lipophilic compounds are governed by the common phenomenon of aggregate formation. As the lymphatic system offers a pathway for intestinal uptake of aggregates, this may offer a therapeutic advantage in the treatment of HIV-1 infection. Although it was not the objective of the study, we found that the rat was a better in vivo model than the dog for the prediction of systemic exposure in this particular set of compounds.

Evolution of anti-HIV drug candidates. Part 2: Diaryltriazine (DATA) analogues

A synthesis program directed toward improving the stability of imidoyl thiourea based non-nucleoside reverse transcriptase inhibitors (NNRTIs) led to the discovery of diaryltriazines (DATAs), a new class of potent NNRTIs. The synthesis and anti-HIV structure-activity relationship (SAR) studies of a series of DATA derivatives are described.