Discovery of 4-((1-(1H-imidazol-2-yl)alkoxy)methyl)pyridines as a new class of Trypanosoma cruzi growth inhibitors.

The identification of a new series of growth inhibitors of Trypanosoma cruzi, the causative agent of Chagas' disease, is described. In vitro screening of a subset of compounds from our in-house compound collection against the parasite led to the identification of hit compound 1 with low micromolar inhibition of T. cruzi growth. SAR exploration on the hit compound led to the identification of compounds that show nanomolar parasite growth inhibition (T. cruzi EC50 ≤ 100 nM) and no cytotoxicity in human cells (HeLa CC50 > 50 µM). Further investigation identified CYP51 inhibition (compound 11 CYP51 IC50 52 nM) as a possible mechanism of action of this new class of anti-parasitic agents.

Improved Selective Class I HDAC and Novel Selective HDAC3 Inhibitors: Beyond Hydroxamic Acids and Benzamides.

The application of class I HDAC inhibitors as cancer therapies is well established, but more recently their development for nononcological indications has increased. We report here on the generation of improved class I selective human HDAC inhibitors based on an ethylketone zinc binding group (ZBG) in place of the hydroxamic acid that features the majority of HDAC inhibitors. We also describe a novel set of HDAC3 isoform selective inhibitors that show stronger potency and selectivity than the most commonly used HDAC3 selective tool compound RGFP966. These compounds are again based on an alternative ZBG with respect to the ortho-anilide that is featured in HDAC3 selective compounds reported to date.

Identification of novel multi-stage histone deacetylase (HDAC) inhibitors that impair Schistosoma mansoni viability and egg production.

BACKGROUND: Novel anti-schistosomal multi-stage drugs are needed because only a single drug, praziquantel, is available for the treatment of schistosomiasis and is poorly effective on larval and juvenile stages of the parasite. Schistosomes have a complex life-cycle and multiple developmental stages in the intermediate and definitive hosts. Acetylation and deacetylation of histones play pivotal roles in chromatin structure and in the regulation of transcription in eukaryotic cells. Histone deacetylase (HDAC) inhibitors modulate acetylation of several other proteins localized both in the nucleus and in the cytoplasm and therefore impact on many signaling networks and biological processes. Histone post-translational modifications may provide parasites with the ability to readily adapt to changes in gene expression required for their development and adaptation to the host environment. The aim of the present study was to screen a HDAC class I inhibitor library in order to identify and characterize novel multi-stage hit compounds. METHODS: We used a high-throughput assay based on the quantitation of ATP in the Schistosoma mansoni larval stage (schistosomula) and screened a library of 1500 class I HDAC inhibitors. Subsequently, a few hits were selected and further characterized by viability assays and phenotypic analyses on adult parasites by carmine red and confocal microscopy. RESULTS: Three compounds (SmI-124, SmI-148 and SmI-558) that had an effect on the viability of both the schistosomula larval stage and the adult worm were identified. Treatment with sub-lethal doses of SmI-148 and SmI-558 also decreased egg production. Moreover, treatment of adult parasites with SmI-148, and to a lesser extent Sm-124, was associated with histone hyperacetylation. Finally, SmI-148 and SmI-558 treatments of worm pairs caused a phenotype characterized by defects in the parasite reproductive system, with peculiar features in the ovary. In addition, SmI-558 induced oocyte- and vitelline cell-engulfment and signs of degeneration in the uterus and/or oviduct. CONCLUSIONS: We report the screening of a small HDAC inhibitor library and the identification of three novel compounds which impair viability of the S. mansoni larval stage and adult pairs. These compounds are useful tools for studying deacetylase activity during parasite development and for interfering with egg production. Characterization of their specificity for selected S. mansoni versus human HDAC could provide insights that can be used in optimization and compound design.

Peptidomimetic nitrile inhibitors of malarial protease falcipain-2 with high selectivity against human cathepsins.

Falcipain-2 (FP2) is an essential enzyme in the lifecycle of malaria parasites such as Plasmodium falciparum, and its inhibition is viewed as an attractive mechanism of action for new anti-malarial agents. Selective inhibition of FP2 with respect to a family of human cysteine proteases (that include cathepsins B, K, L and S) is likely to be required for the development of agents targeting FP2. Here we describe a series of P2-modified aminonitrile based inhibitors of FP2 that provide a clear strategy toward addressing selectivity for the P. falciparum and show that it can provide potent FP2 inhibitors with strong selectivity against all four of these human cathepsin isoforms.

Discovery by organism based high-throughput screening of new multi-stage compounds affecting Schistosoma mansoni viability, egg formation and production.

Schistosomiasis, one of the most prevalent neglected parasitic diseases affecting humans and animals, is caused by the Platyhelminthes of the genus Schistosoma. Schistosomes are the only trematodes to have evolved sexual dimorphism and the constant pairing with a male is essential for the sexual maturation of the female. Pairing is required for the full development of the two major female organs, ovary and vitellarium that are involved in the production of different cell types such as oocytes and vitellocytes, which represent the core elements of the whole egg machinery. Sexually mature females can produce a large number of eggs each day. Due to the importance of egg production for both life cycle and pathogenesis, there is significant interest in the search for new strategies and compounds not only affecting parasite viability but also egg production. Here we use a recently developed high-throughput organism-based approach, based on ATP quantitation in the schistosomula larval stage of Schistosoma mansoni for the screening of a large compound library, and describe a pharmacophore-based drug selection approach and phenotypic analyses to identify novel multi-stage schistosomicidal compounds. Interestingly, worm pairs treated with seven of the eight compounds identified show a phenotype characterized by defects in eggshell assemblage within the ootype and egg formation with degenerated oocytes and vitelline cells engulfment in the uterus and/or oviduct. We describe promising new molecules that not only impair the schistosomula larval stage but also impact juvenile and adult worm viability and egg formation and production in vitro.

Discovery of a Selective Series of Inhibitors of Plasmodium falciparum HDACs.

The identification of a new series of P. falciparum growth inhibitors is described. Starting from a series of known human class I HDAC inhibitors a SAR exploration based on growth inhibitory activity in parasite and human cells-based assays led to the identification of compounds with submicromolar inhibition of P. falciparum growth (EC50 < 500 nM) and good selectivity over the activity of human HDAC in cells (up to >50-fold). Inhibition of parasital HDACs as the mechanism of action of this new class of selective growth inhibitors is supported by hyperacetylation studies.

Discovery of MK-5172, a Macrocyclic Hepatitis C Virus NS3/4a Protease Inhibitor.

A new class of HCV NS3/4a protease inhibitors containing a P2 to P4 macrocyclic constraint was designed using a molecular modeling-derived strategy. Building on the profile of previous clinical compounds and exploring the P2 and linker regions of the series allowed for optimization of broad genotype and mutant enzyme potency, cellular activity, and rat liver exposure following oral dosing. These studies led to the identification of clinical candidate 15 (MK-5172), which is active against genotype 1-3 NS3/4a and clinically relevant mutant enzymes and has good plasma exposure and excellent liver exposure in multiple species.

Novel macrocyclic inhibitors of hepatitis C NS3/4A protease featuring a 2-amino-1,3-thiazole as a P4 carbamate replacement.

Our laboratories recently reported the discovery of P2-P4 macrocyclic inhibitors of HCV NS3/4A protease, characterized by high levels of potency and liver exposure. Within this novel class of inhibitors, we here describe the identification of a structurally diverse series of compounds featuring a 2-amino-1,3-thiazole as replacement of the carbamate in P4. Optimization studies focused on structural modifications in the P3, P2, and P1 regions of the macrocycle as well as on the linker chain and resulted in the discovery of several analogues characterized by excellent levels of enzyme and cellular activity. Among these, compound 59 displayed an attractive pharmacokinetic profile in preclinical species and showed sustained liver levels following oral administration in rats.

Dihydroxy-pyrimidine and N-methylpyrimidone HIV-integrase inhibitors: improving cell based activity by the quaternarization of a chiral center.

In the context of HIV-integrase, dihydroxypyrimidine and N-methyl pyrimidone inhibitors the cellular activity of this class of compounds has been optimized by the introduction of a simple methyl substituent in the alpha-position of the C-2 side chains. Enhanced passive membrane permeability has been identified as the key factor driving the observed cell-based activity improvement. The rat PK profile of the alpha-methyl derivative 26a was also improved over its des-methyl exact analog.

Novel peptidomimetics containing a vinyl ester moiety as highly potent and selective falcipain-2 inhibitors.

This paper describes the synthesis and biological evaluation of a new class of peptidomimetic falcipain-2 inhibitors based on a 1,4-benzodiazepine scaffold combined with various alpha,beta-unsaturated electrophilic functions such as vinyl-ketone, -amide, -ester, and -nitrile. The profile of reactivity of this class of derivatives has been evaluated and 4c, containing a vinyl ester warhead, proved to be a highly potent and selective falcipain-2 inhibitor.

Discovery of raltegravir, a potent, selective orally bioavailable HIV-integrase inhibitor for the treatment of HIV-AIDS infection.

Human immunodeficiency virus type-1 (HIV-1) integrase is one of the three virally encoded enzymes required for replication and therefore a rational target for chemotherapeutic intervention in the treatment of HIV-1 infection. We report here the discovery of Raltegravir, the first HIV-integrase inhibitor approved by FDA for the treatment of HIV infection. It derives from the evolution of 5,6-dihydroxypyrimidine-4-carboxamides and N-methyl-4-hydroxypyrimidinone-carboxamides, which exhibited potent inhibition of the HIV-integrase catalyzed strand transfer process. Structural modifications on these molecules were made in order to maximize potency as HIV-integrase inhibitors against the wild type virus, a selection of mutants, and optimize the selectivity, pharmacokinetic, and metabolic profiles in preclinical species. The good profile of Raltegravir has enabled its progression toward the end of phase III clinical trials for the treatment of HIV-1 infection and culminated with the FDA approval as the first HIV-integrase inhibitor for the treatment of HIV-1 infection.

Development of peptidomimetics with a vinyl sulfone warhead as irreversible falcipain-2 inhibitors.

This paper describes the synthesis of a new class of peptidomimetic cysteine protease inhibitors based on a 1,4-benzodiazepine scaffold and on an electrophilic vinyl sulfone moiety. The former was introduced internally to a peptide sequence that mimics the fragment D-Ser-Gly; the latter was built on the P1-P1' site and reacts as a classical "Michael acceptor", leading to an alkylated enzyme by irreversible addition of the thiol group of the active site cysteine. The introduction of the vinyl sulfone moiety has been accomplished by olefin cross-metathesis, a powerful tool for the formation of carbon-carbon double bonds. New compounds 2-3 have been proven to be potent and selective inhibitors of falcipain-2, a cysteine protease isolated from Plasmodium falciparum, displaying antiplasmodial activity.

Design and synthesis of bicyclic pyrimidinones as potent and orally bioavailable HIV-1 integrase inhibitors.

HIV integrase is one of the three enzymes encoded by HIV genome and is essential for viral replication, but integrase inhibitors as marketed drugs have just very recently started to emerge. In this study, we show the evolution from the N-methylpyrimidinone structure to bicyclic pyrimidinones. Introduction of a suitably substituted amino moiety modulated the physical-chemical properties of the molecules and conferred nanomolar activity in the inhibition of spread of HIV-1 infection in cell culture. An extensive SAR study led to sulfamide (R)- 22b, which inhibited the strand transfer with an IC50 of 7 nM and HIV infection in MT4 cells with a CIC95 of 44 nM, and ketoamide (S)- 28c that inhibited strand transfer with an IC50 of 12 nM and the HIV infection in MT4 cells with a CIC95 of 13 nM and exhibited a good pharmacokinetic profile when dosed orally to preclinical species.

Discovery and synthesis of HIV integrase inhibitors: development of potent and orally bioavailable N-methyl pyrimidones.

The human immunodeficiency virus type-1 (HIV-1) encodes three enzymes essential for viral replication: a reverse transcriptase, a protease, and an integrase. The latter is responsible for the integration of the viral genome into the human genome and, therefore, represents an attractive target for chemotherapeutic intervention against AIDS. A drug based on this mechanism has not yet been approved. Benzyl-dihydroxypyrimidine-carboxamides were discovered in our laboratories as a novel and metabolically stable class of agents that exhibits potent inhibition of the HIV integrase strand transfer step. Further efforts led to very potent compounds based on the structurally related N-Me pyrimidone scaffold. One of the more interesting compounds in this series is the 2-N-Me-morpholino derivative 27a, which shows a CIC95 of 65 nM in the cell in the presence of serum. The compound has favorable pharmacokinetic properties in three preclinical species and shows no liabilities in several counterscreening assays.

Dihydroxypyrimidine-4-carboxamides as novel potent and selective HIV integrase inhibitors.

Human immunodeficiency virus type-1 (HIV-1) integrase, one of the three constitutive viral enzymes required for replication, is a rational target for chemotherapeutic intervention in the treatment of AIDS that has also recently been confirmed in the clinical setting. We report here on the design and synthesis of N-benzyl-5,6-dihydroxypyrimidine-4-carboxamides as a class of agents which exhibits potent inhibition of the HIV-integrase-catalyzed strand transfer process. In the current study, structural modifications on these molecules were made in order to examine effects on HIV-integrase inhibitory potencies. One of the most interesting compounds for this series is 2-[1-(dimethylamino)-1-methylethyl]-N-(4-fluorobenzyl)-5,6-dihydroxypyrimidine-4-carboxamide 38, with a CIC95 of 78 nM in the cell-based assay in the presence of serum proteins. The compound has favorable pharmacokinetic properties in preclinical species (rats, dogs, and monkeys) and shows no liabilities in several counterscreening assays, highlighting its potential as a clinically useful antiviral agent.

The monoethyl ester of meconic acid is an active site inhibitor of HCV NS5B RNA-dependent RNA polymerase.

Screening of the in-house sample collection for compounds with HCV NS5B RNA dependent RNA polymerase inhibition led to the identification of a new lead. Afterwards, we discovered that the screening lead, rather than containing the expected structure 1, was comprised of roughly a 1:1 mixture of meconic acid 2 and its monoethyl ester 3, with all inhibitory potency residing with 3. We propose that this compound shares critical common features for activity with alpha,gamma-diketoacids inhibitors previously discovered by our group. SAR around this molecule will be presented to provide an improved basis for structure-based ligand design.

Capped dipeptide phenethylamide inhibitors of the HCV NS3 protease.

The N-terminal aminoacid of phenethylamide tripeptide inhibitors of the hepatitis C virus NS3 protease can be replaced with an alpha-hydroxy acid to obtain more 'drug like' inhibitors with low micromolar activity. The preferred S-configuration of the capping residue can be explained by molecular modeling studies.

Capped dipeptide alpha-ketoacid inhibitors of the HCV NS3 protease.

The N-terminal aminoacid of alpha-ketotripeptide inhibitors of the hepatitis C virus NS3 protease can be replaced with an alpha-hydroxy acid, leading to capped dipeptide inhibitors such as 20 with an IC(50) value of 3.0 microM. The importance of the lipophilic side chain interactions at S3 of the protease and the requirement of the capping residue with R configuration have been explained by molecular modeling studies.