In vivo toxicity, pharmacokinetic features and tissue distribution of N-[2-(2,5-dimethoxyphenylethyl)]-N'-[2-(5-bromopyridyl)]-thiourea (HI-236), a potent non-nucleoside inhibitor of HIV-1 reverse transcriptase

Novel inhibitors of severe acute respiratory syndrome coronavirus entry that act by three distinct mechanisms

Severe acute respiratory syndrome (SARS) is an infectious and highly contagious disease that is caused by SARS coronavirus (SARS-CoV) and for which there are currently no approved treatments. We report the discovery and characterization of small-molecule inhibitors of SARS-CoV replication that block viral entry by three different mechanisms. The compounds were discovered by screening a chemical library of compounds for blocking of entry of HIV-1 pseudotyped with SARS-CoV surface glycoprotein S (SARS-S) but not that of HIV-1 pseudotyped with vesicular stomatitis virus surface glycoprotein G (VSV-G). Studies on their mechanisms of action revealed that the compounds act by three distinct mechanisms: (i) SSAA09E2 {N-[[4-(4-methylpiperazin-1-yl)phenyl]methyl]-1,2-oxazole-5-carboxamide} acts through a novel mechanism of action, by blocking early interactions of SARS-S with the receptor for SARS-CoV, angiotensin converting enzyme 2 (ACE2); (ii) SSAA09E1 {[(Z)-1-thiophen-2-ylethylideneamino]thiourea} acts later, by blocking cathepsin L, a host protease required for processing of SARS-S during viral entry; and (iii) SSAA09E3 [N-(9,10-dioxo-9,10-dihydroanthracen-2-yl)benzamide] also acts later and does not affect interactions of SARS-S with ACE2 or the enzymatic functions of cathepsin L but prevents fusion of the viral membrane with the host cellular membrane. Our work demonstrates that there are at least three independent strategies for blocking SARS-CoV entry, validates these mechanisms of inhibition, and introduces promising leads for the development of SARS therapeutics.

C-2-aryl O-substituted HI-236 derivatives as non-nucleoside HIV-1 reverse-transcriptase inhibitors

Several novel thiourea derivatives of the NNRTI HI-236 substituted at the C-2 oxygen of the phenyl ring have been synthesized and evaluated for their inhibitory activity against HIV-1 (IIIB) replication in MT-2 cell cultures. The compounds were synthesized in order to fine-tune the activity of HI-236 as well as to gain insight into spatial characteristics in the pocket pertaining to the positional choice of tether in the design of [NRTI]-tether-[HI-236] bifunctional inhibitors. Two of the thiourea derivatives bearing a butynyl (6c) or hydroxyethyl tether (6n) were endowed with improved anti-HIV activity compared to HI-236. NNRTI activity was confirmed by a cell-free RT assay on six of the derivatives in which 6c returned an IC(50) of 3.8 nM compared to 28 nM for HI-236, establishing it as an improved lead for HI-236. The structure-activity profile is discussed in terms of potential interactions in the NNRTI pocket as suggested by a docking model using AutoDock, which have a bearing on the bifunctional drug design.

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.