Piperidinylethyl, phenoxyethyl and fluoroethyl bromopyridyl thiourea compounds with potent anti-HIV activity

Novel tight binding PETT, HEPT and DABO-based non-nucleoside inhibitors of HIV-1 reverse transcriptase

Non-nucleoside reverse transcriptase (RT) inhibitors (NNRTIs) are a key component of effective combination antiretroviral therapies for HIV/AIDS. NNRTIs despite their chemical diversity, bind to a common allosteric site of HIV-1 RT, the primary target for anti-AIDS chemotherapy, and noncompetitively inhibit DNA polymerization. NNRTIs currently in clinical use have a low genetic barrier to resistance and therefore, the need for novel NNRTIs active against drug-resistant mutants selected by current therapies is of paramount importance. We describe the chemistry and biological evaluation of highly potent novel phenethylthiazolylthiourea (PETT), 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT) and dihydroalkoxybenzyloxopyrimidine (DABO) derivatives targeting the hydrophobic binding pocket of HIV-1 RT. These NNRTIs were rationally designed by molecular modeling and docking studies using a novel composite binding pocket that predicted how drug-resistant mutations would change the RT binding pocket shape, volume, and chemical make-up and how these changes could affect NNRTI binding. Several ligand derivatization sites were identified for docked NNRTIs that fit the composite binding pocket. The best fit was determined by calculating an inhibition constant (Ludi Ki) of the docked compound for the composite binding pocket. Compounds with a Ludi Ki of <1 microM were identified as the most promising tight binding NNRTIs. These NNRTIs displayed high selective indices with robust anti-HIV-1 activity against the wild-type and drug-resistant isolates carrying multiple RT gene mutations. The high rate of treatment failure due to the emergence of drug resistance mutations makes the discovery of broad-spectrum PETT, HEPT and DABO-based NNRTIs useful as a component of effective combination regimens.

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.

Potent dual anti-HIV and spermicidal activities of novel oxovanadium(V) complexes with thiourea non-nucleoside inhibitors of HIV-1 reverse transcriptase

We have previously demonstrated that tetrahedral bis(cyclopentadienyl)vanadium(IV) complexes and square pyramidal oxovanadium(IV) complexes of vanadium are rapid and selective spermicidal agents at low micromolar concentrations. This study investigated the potential utility of oxovanadium in combination with thiourea non-nucleoside inhibitors (NNIs) of HIV-1 reverse transcriptase (RT) for the development of an effective dual-function anti-HIV spermicide. Two rationally designed substituted phenyl-ring containing pyridyl thiourea NNIs, N-[2-(2-chlorophenethyl)]-N(')-[2-(5-bromopyridyl)-thiourea) [1] and N-[2-(2-methoxyphenethyl)]-N(')-[2-(pyridyl)-thiourea [2] that exhibited subnanomolar IC(50) values against the drug-sensitive, drug-resistant, and multidrug-resistant strains of HIV-1, were complexed with oxovanadium. The oxovanadium-thiourea [OVT] NNIs, C(29)H(27)Br(2)Cl(2)N(6)O(2)S(2)V [3], and C(31)H(35)N(6)O(4)S(2)V [4], were synthesized by reacting VOSO(4), a V(IV) compound, with the corresponding deprotonated thiourea NNI compounds as ligands. Elemental analysis showed that each OVT-NNI used two thiourea molecules as ligands. The existence of the Vz.dbnd6;O bond (968cm(-1)) was confirmed by IR spectroscopy. No d-d bands were observed in the visible spectra of OVT-NNIs and their EPR spectra were featureless, indicating that the vanadium centers were oxidized to V(V). The new OVT-NNIs as well as their thiourea NNI ligands were evaluated for (i) anti-HIV activity using the cell-free recombinant RT inhibition assays, (ii) cellular HIV replication assays, (iii) spermicidal activity against human sperm by computer-assisted sperm analysis (CASA), and (iv) cytotoxicity against normal human female genital tract epithelial cell using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) dye-reduction assays. Similar to thiourea NNIs 1 and 2, the OVT-NNIs 3 and 4, exhibited potent anti-HIV activity with submicromolar IC(50[p24]) values (0.08 and 0.128 microM, respectively) and submicromolar IC(50[RT]) values (2.1 and 0.87 microM, respectively). Notably, OVT-NNIs were spermicidal against human sperm at low micromolar concentrations (IC(50)=34 and 55 microM, respectively) and induced rapid sperm immobilization (T(1/2)=12 and 240s) when compared with their respective thiourea NNI ligands (EC(50)=>400 microM and T(1/2)=>180min). Moreover, OVT-NNIs displayed high selectivity indices against normal female genital tract epithelial cells (IC(50) values >250 microM) when compared to the detergent-type spermicide, nonoxynol-9, which was cytotoxic at spermicidal concentrations (IC(50) values 32-64 microM). This is the first report on the dual anti-HIV and spermicidal activities of a vanadium/oxovanadium complex. Our discovery of potent anti-HIV and rapid spermicidal activities of OVT-NNIs may be useful for the development of an effective and safe vaginal anti-HIV spermicide for women who are at high risk for acquiring HIV/AIDS by heterosexual transmission.

Structural requirements for potent anti-human immunodeficiency virus (HIV) and sperm-immobilizing activities of cyclohexenyl thiourea and urea non-nucleoside inhibitors of HIV-1 reverse transcriptase

The current pandemic of sexually transmitted human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) has created an urgent need for a new type of microbicide, one that is both a spermicide and a virucide. In a systematic effort to identify a non-detergent-type antiviral spermicide, we have rationally designed and synthesized a series of cyclohexenyl thiourea (CHET) nonnucleoside inhibitors (NNIs) of HIV-1 reverse transcriptase (RT) with sperm-immobilizing activity (SIA). To gain further insight into the structural requirements for the optimal activity of these dual-function NNIs, we compared the effects of thiazolyl, benzothiazolyl, and pyridyl ring substitutions and functionalization with electron-donating and electron-withdrawing groups as well as the importance of thiourea and urea moieties of 15 heterocyclic ring-substituted NNIs. RT activity and p24 antigen production in HIV-infected peripheral blood mononuclear cells were used as markers of viral replication. Computer-assisted sperm analysis was used for evaluating SIA of CHET compounds. The rabbit model was used for evaluation of in vivo mucosal toxicity and contraceptive activity of the lead NNIs. Three CHET-NNIs with a bromo, chloro, or methyl substitution at the 5 position of the pyridyl ring exhibited potent anti-HIV activity at nanomolar concentrations (IC(50) = 3-5 nM) and SIA at micromolar concentrations (EC(50) = 45-96 micro M). The dual-function CHET-NNIs were potent inhibitors of drug-resistant HIV-1 strains with genotypic and phenotypic NNI resistance. Upon substitution of the sulfur atom of the thiourea moiety with an oxygen atom, the most striking difference noted was a 38-fold reduction in time required for 50% sperm immobilization (T(1/2)). A quantitative structure-activity relationship (QSAR) analysis was used in deriving regression equations between 20 physicochemical properties and SIA of NNIs. QSAR analysis showed that the T(1/2) values positively correlated with values for molecular refractivity (r = 0.88), hydrophobicity (r = 0.72), atomic polarizability (r = 0.70), and principal moment of inertia (r = 0.63) of spermicidal NNIs. A stepwise multiple regression model to describe the relationship of T(1/2) values with these four regressors provided excellent predictability (r = 0.93). Exposure of semen to thiourea/urea NNIs either alone or in combination at the time of artificial insemination led to marked or complete inhibition of pregnancy in rabbits as assessed by the number of embryo implants versus corpora lutea on Day 8 of pregnancy. Repeated intravaginal application of a gel-microemulsion with and without 0.5%, 1%, and 2% CHET-NNI or its urea analog either alone or in combination did not induce mucosal toxicity. We hypothesize that the gain of spermicidal function by CHET-NNIs is due to their metabolic oxidation to urea analogs by sperm. Three reaction pathways are discussed. The extremely rapid SIA of the urea analog as well as the broad-spectrum anti-HIV activity of spermicidal CHET-NNIs together with their lack of mucosal toxicity and the marked ability to reduce in vivo fertility is particularly useful for the clinical development of a dual-function spermicidal microbicide. The cyclohexenyl pyridyl NNIs, especially N-[2-(1-cyclohexenyl)ethyl] N'-[2-(5-bromopyridyl)]-thiourea in combination with the urea analog, show unique clinical potential as anti-HIV spermicides aimed at curbing the sexual transmission of multidrug-resistant HIV-1 while providing effective fertility control for women.

Stereochemistry as a major determinant of the anti-HIV activity of chiral naphthyl thiourea compounds

Eleven chiral naphthyl thiourea (CNT) compounds were synthesized as non-nucleoside inhibitors (NNI) of the reverse transcriptase (RT) enzyme of HIV-1. Molecular modelling studies indicated that, because of the asymmetric geometry of the NNI binding pocket, the 'R' stereoisomers would fit the NNI binding pocket of the HIV-1 RT much better than the corresponding 'S' stereoisomers, as reflected by their 10(4)-fold lower Ki values. The 'R' stereoisomers of all 11 compounds inhibited the recombinant RT in vitro with lower IC50 values than their enantiomers. Of seven CNT compounds whose 'R' stereoisomers exhibited nanomolar IC50 values against recombinant RT, five were further evaluated for their ability to inhibit HIV-1 replication in human peripheral blood mononuclear cells (PBMC). All five 'R' stereoisomers were active anti-HIV agents and inhibited the replication of the HIV-1 strains HTLV-IIIB (NNI-sensitive), A17 (NNI-resistant, Y181C mutant RT) and A17Var (NNI-resistant, Y181C plus K103N mutant RT), as well as primary HIV-1 isolates from AIDS patients in human PBMC at nanomolar concentrations, whereas their enantiomers were inactive. The lead compounds, 1R and 5R, were 3 log more potent than the standard NNI drug nevirapine against the NNI-resistant HIV-1 strains. Our data establish the stereochemistry as a major determinant of the potency of this new class of NNI.