Direct-to-biology platform: From synthesis to biological evaluation of SHP2 allosteric inhibitors.

Tyrosine phosphatase SHP2 is a proto-oncogenic protein involved in cell growth and differentiation via diverse intracellular signaling pathways. With the scope of identifying new SHP2 allosteric inhibitors, we report here the development and optimization of a high-throughput "Direct-to-Biology" (D2B) workflow including the synthesis and the biological evaluation of the reaction crude, thus eliminating the need for purification. During this labor-saving procedure, the structural diversity was introduced through a SNAr reaction. A wide array of analogues with good chemical purity was generated, allowing the obtention of reliable biological data which validated this efficient technique. This approach enabled the fast evaluation of a variety of structurally diverse fragments leading to nanomolar SHP2 allosteric inhibitors and a new series bearing a novel bicyclo[3.1.0]hexane moiety.

Discovery of a Novel Series of Imidazopyrazine Derivatives as Potent SHP2 Allosteric Inhibitors.

Protein tyrosine phosphatase SHP2 is an oncogenic protein that can regulate different cytokine receptor and receptor tyrosine kinase signaling pathways. We report here the identification of a novel series of SHP2 allosteric inhibitors having an imidazopyrazine 6,5-fused heterocyclic system as the central scaffold that displays good potency in enzymatic and cellular assays. SAR studies led to the identification of compound 8, a highly potent SHP2 allosteric inhibitor. X-ray studies showed novel stabilizing interactions with respect to known SHP2 inhibitors. Subsequent optimization allowed us to identify analogue 10, which possesses excellent potency and a promising PK profile in rodents.

SAR evolution towards potent C-terminal carboxamide peptide inhibitors of Zika virus NS2B-NS3 protease.

Zika virus (ZIKV) is a member of the Flaviviridae family that can cause neurological disorders and congenital malformations. The NS2B-NS3 viral serine protease is an attractive target for the development of new antiviral agents against ZIKV. We report here a SAR study on a series of substrate-like linear tripeptides that inhibit in a non-covalent manner the NS2B-NS3 protease. Optimization of the residues at positions P1, P2, P3 and of the N-terminal and C-terminal portions of the tripeptide allowed the identification of inhibitors with sub-micromolar potency with phenylglycine as arginine-mimicking group and benzylamide as C-terminal fragment. Further SAR exploration and application of these structural changes to a series of peptides having a 4-substituted phenylglycine residue at the P1 position led to potent compounds showing double digit nanomolar inhibition of the Zika protease (IC50 = 30 nM) with high selectivity against trypsin-like proteases and the proteases of other flavivirus, such as Dengue 2 virus (DEN2V) and West Nile virus (WNV).

Combined Peptide and Small-Molecule Approach toward Nonacidic THIQ Inhibitors of the KEAP1/NRF2 Interaction.

The NRF2-ARE pathway is an intrinsic mechanism of defense against oxidative stress. Inhibition of the interaction between NRF2 and its main negative regulator KEAP1 is an attractive strategy toward neuroprotective agents. We report here the identification of nonacidic tetrahydroisoquinolines (THIQs) that inhibit the KEAP1/NRF2 protein-protein interaction. Peptide SAR at one residue is utilized as a tool to probe structural changes within a specific pocket of the KEAP1 binding site. We used structural information from peptide screening at the P2 pocket, noncovalent small-molecules inhibitors, and the outcome from an explorative SAR at position 5 of THIQs to identify a series of neutral THIQ analogs that bind to KEAP1 in the low micromolar range. These analogs establish new H-bond interactions at the P3 and P2 pockets allowing the replacement of the carboxylic acid functionality by a neutral primary carboxamide. X-ray crystallographic studies reveal the novel binding mode of these molecules to KEAP1.

Optimization of 2-(1H-imidazo-2-yl)piperazines series of Trypanosoma brucei growth inhibitors as potential treatment for the second stage of HAT.

A previous publication from our laboratory reported the identification of a new class of 2-(1H-imidazo-2-yl)piperazines as potent T. brucei growth inhibitors as potential treatment for Human African Trypanosomiasis (HAT). This work describes the structure-activity relationship (SAR) around the hit compound 1, which led to the identification of the optimized compound 18, a single digit nanomolar inhibitor (EC50 7 nM), not cytotoxic and with optimal in vivo profile that made it a suitable candidate for efficacy studies in a mouse model mimicking the second stage of disease.

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.

Discovery of 2-(1H-imidazo-2-yl)piperazines as a new class of potent and non-cytotoxic inhibitors of Trypanosoma brucei growth in vitro.

The identification of a new series of growth inhibitors of Trypanosoma brucei rhodesiense, causative agent of Human African Trypanosomiasis (HAT), is described. A selection of compounds from our in-house compound collection was screened in vitro against the parasite leading to the identification of compounds with nanomolar inhibition of T. brucei growth. Preliminary SAR on the hit compound led to the identification of compound 34 that shows low nanomolar parasite growth inhibition (T. brucei EC50 5 nM), is not cytotoxic (HeLa CC50 > 25,000 nM) and is selective over other parasites, such as Trypanosoma cruzi and Plasmodium falciparum (T. cruzi EC50 8120 nM, P. falciparum EC50 3624 nM).

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.

N-(2-alkylaminoethyl)-4-(1,2,4-oxadiazol-5-yl)piperazine-1-carboxamides as highly potent smoothened antagonists.

Smoothened (Smo) antagonists are emerging as new therapies for the treatment of neoplasias with aberrantly reactivated hedgehog (Hh) signaling pathway. A novel series of 4-[3-(quinolin-2-yl)-1,2,4-oxadiazol-5-yl]piperazinyl ureas as smoothened antagonists was recently described, herein the series has been further optimized through the incorporation of a basic amine into the urea. This development resulted in identification of some exceptionally potent smoothened antagonists with low serum shifts, however, reductive ring opening on the 1,2,4-oxadiazole in rats limits the applicability of these compounds in in vivo studies.

Identification of a series of 4-[3-(quinolin-2-yl)-1,2,4-oxadiazol-5-yl]piperazinyl ureas as potent smoothened antagonist hedgehog pathway inhibitors.

The Hedgehog (Hh-) signalling pathway is a key developmental pathway and there is a growing body of evidence showing that this pathway is aberrantly reactivated in a number of human tumors. Novel agents capable of inhibiting this pathway are sought, and an entirely novel series of smoothened (Smo) antagonists capable of inhibiting the pathway have been identified through uHTS screening. Extensive exploration of the scaffold identified the key functionalities necessary for potency, enabling potent nanomolar Smo antagonists like 91 and 94 to be developed. Optimization resulted in the most advanced compounds displaying low serum shift, clean off-targets profile, and moderate clearance in both rats and dogs. These compounds are valuable tools with which to probe the biology of the Hh-pathway.

Allosteric inhibitors of hepatitis C virus NS5B polymerase thumb domain site II: structure-based design and synthesis of new templates.

Chronic hepatitis C virus (HCV) infections are a significant medical problem worldwide. The NS5B Polymerase of HCV plays a central role in virus replication and is a prime target for the discovery of new treatment options. We recently disclosed 1H-benzo[de]isoquinoline-1,3(2H)-diones as allosteric inhibitors of NS5B Polymerase. Structural and SAR information guided us in the modification of the core structure leading to new templates with improved activity and toxicity/activity window.

Synthesis and biological evaluation of substituted 2-phenyl-2H-indazole-7-carboxamides as potent poly(ADP-ribose) polymerase (PARP) inhibitors.

A potent series of substituted 2-phenyl-2H-indazole-7-carboxamides were synthesized and evaluated as inhibitors of poly (ADP-ribose) polymerase (PARP). This extensive SAR exploration culminated with the identification of substituted 5-fluoro-2-phenyl-2H-indazole-7-carboxamide analog 48 which displayed excellent PARP enzyme inhibition with IC(50)=4nM, inhibited proliferation of cancer cell lines deficient in BRCA-1 with CC(50)=42nM and showed encouraging pharmacokinetic properties in rats compared to the lead 6.

Discovery and SAR of novel, potent and selective hexahydrobenzonaphthyridinone inhibitors of poly(ADP-ribose)polymerase-1 (PARP-1).

A novel hexahydrobenzonaphthyridinone PARP-1 pharmacophore is reported, subsequent SAR exploration around this scaffold led to selective PARP-1 inhibitors with low nanomolar enzyme potency, displaying good cellular activity and promising rat PK properties.

Identification of novel, selective, and stable inhibitors of class II histone deacetylases. Validation studies of the inhibition of the enzymatic activity of HDAC4 by small molecules as a novel approach for cancer therapy.

5-Aryl-2-(trifluoroacetyl)thiophenes were identified as a new series of class II HDAC inhibitors (HDACi). Further development of this new series led to compounds such as 6h, a potent inhibitor of HDAC4 and HDAC6 (HDAC4 WT IC(50) = 310 nM, HDAC6 IC(50) = 70 nM) that displays 40-fold selectivity over HDAC1 and improved stability in HCT116 cancer cells (t(1/2) = 11 h). Compounds 6h and 2 show inhibition of alpha-tubulin deacetylation in HCT116 cells at 1 microM concentration and antiproliferation effects only at concentrations where inhibition of histone H3 deacetylation is observed.

Identification and biological evaluation of a series of 1H-benzo[de]isoquinoline-1,3(2H)-diones as hepatitis C virus NS5B polymerase inhibitors.

The hepatitis C virus (HCV) NS5B RNA-dependent RNA polymerase (RdRp) plays a central role in virus replication. NS5B has no functional equivalent in mammalian cells and, as a consequence, is an attractive target for inhibition. Herein, we present 1H-benzo[de]isoquinoline-1,3(2H)-diones as a new series of selective inhibitors of HCV NS5B polymerase. The HTS hit 1 shows submicromolar potency in two different HCV replicons (1b and 2b) and displays no activity on other polymerases (HIV-RT, Polio-pol, GBV-b-pol). These inhibitors act during the pre-elongation phase by binding to NS5B non-nucleoside binding site Thumb Site II as demonstrated by crystal structure of compound 1 with the DeltaC55-1b and DeltaC21-2b enzymes and by mutagenesis studies. SAR in this new series reveals inhibitors, such as 20, with low micromolar activity in the HCV replicon and with good activity/toxicity window in cells.

Discovery of 2-{4-[(3S)-piperidin-3-yl]phenyl}-2H-indazole-7-carboxamide (MK-4827): a novel oral poly(ADP-ribose)polymerase (PARP) inhibitor efficacious in BRCA-1 and -2 mutant tumors.

We disclose the development of a novel series of 2-phenyl-2H-indazole-7-carboxamides as poly(ADP-ribose)polymerase (PARP) 1 and 2 inhibitors. This series was optimized to improve enzyme and cellular activity, and the resulting PARP inhibitors display antiproliferation activities against BRCA-1 and BRCA-2 deficient cancer cells, with high selectivity over BRCA proficient cells. Extrahepatic oxidation by CYP450 1A1 and 1A2 was identified as a metabolic concern, and strategies to improve pharmacokinetic properties are reported. These efforts culminated in the identification of 2-{4-[(3S)-piperidin-3-yl]phenyl}-2H-indazole-7-carboxamide 56 (MK-4827), which displays good pharmacokinetic properties and is currently in phase I clinical trials. This compound displays excellent PARP 1 and 2 inhibition with IC(50) = 3.8 and 2.1 nM, respectively, and in a whole cell assay, it inhibited PARP activity with EC(50) = 4 nM and inhibited proliferation of cancer cells with mutant BRCA-1 and BRCA-2 with CC(50) in the 10-100 nM range. Compound 56 was well tolerated in vivo and demonstrated efficacy as a single agent in a xenograft model of BRCA-1 deficient cancer.

Identification of substituted pyrazolo[1,5-a]quinazolin-5(4H)-one as potent poly(ADP-ribose)polymerase-1 (PARP-1) inhibitors.

A novel series of pyrazolo[1,5-a]quinazolin-5(4H)-one derivatives proved to be a potent class of PARP-1 inhibitors. An extensive SAR around the 3-position of pyrazole in the scaffold led to the discovery of amides derivatives as low nanomolar PARP-1 inhibitors.

Histone deacetylase inhibitors with a primary amide zinc binding group display antitumor activity in xenograft model.

Histone deacetylase (HDAC) inhibition causes hyperacetylation of histones leading to differentiation, growth arrest and apoptosis of malignant cells, representing a new strategy in cancer therapy. Many of the known HDAC inhibitors (HDACi) that are in clinical trials possess a hydroxamic acid, that is a strong Zn(2+) binding group, thereby inhibiting some of the class I and class II isoforms. Herein we describe the identification of a selective class I HDAC inhibitor bearing a primary carboxamide moiety as zinc binding group. This HDACi displays good antiproliferative activity against multiple cancer cell lines, and demonstrates efficacy in a xenograft model comparable to vorinostat.

Studies of the metabolic stability in cells of 5-(trifluoroacetyl)thiophene-2-carboxamides and identification of more stable class II histone deacetylase (HDAC) inhibitors.

5-(Trifluoroacetyl)thiophene-2-carboxamides were found to be potent and selective class II HDAC inhibitors. This paper describes their further development and the investigation on the cause for the lack of cell-based activity. A rapid screening assay was set up which enabled the identification of more metabolic stable compounds as potent and selective class II HDAC inhibitors.