Design and biological activity of (S)-4-(5-([1-(3-chlorobenzyl)-2-oxopyrrolidin-3-ylamino]methyl)imidazol-1-ylmethyl)benzonitrile, a 3-aminopyrrolidinone farnesyltransferase inhibitor with excellent cell potency

Design and discovery of C2-fluoroalkyl iminothiazine dioxides as BACE inhibitors

This paper describes the structure-activity-relationships of novel fluoroalkyl substituents at the C2 position of iminothiazine dioxide beta secretase inhibitors. Key discoveries include reduced amidine basicity and its effect on Pgp, cell potency, and efficacy in various preclinical in vivo efficacy animal models. Findings from these structure-activity-relationships are discussed.

Core Replacements in a Potent Series of VEGFR-2 Inhibitors and Their Impact on Potency, Solubility, and hERG

Anti-VEGF therapy has been a clinically validated treatment of age-related macular degeneration (AMD). We have recently reported the discovery of indole based oral VEGFR-2 inhibitors that provide sustained ocular retention and efficacy in models of wet-AMD. We disclose herein the synthesis and the biological evaluation of a series of novel core replacements as an expansion of the reported indole based VEGFR-2 inhibitor series. Addition of heteroatoms to the existing core and/or rearranging the heteroatoms around the 6-5 bicyclic ring structure produced a series of compounds that generally retained good on-target potency and an improved solubility profile. The hERG affinity was proven not be dependent on the change in lipophilicity through alteration of the core structure. A serendipitous discovery led to the identification of a new indole-pyrimidine connectivity: from 5-hydroxy to 6-hydroxyindole with potentially vast implication on the in vitro/in vivo properties of this class of compounds.

Expanding the scope of oligo-pyrrolinone-pyrrolidines as protein-protein interface mimics

Oligo-pyrrolinone-pyrrolidines (generic structure 1) have the potential to interfere with protein-protein interactions (PPIs), but to reduce this to practice it is necessary to be able to synthesize these structures with a variety of different side chains corresponding to genetically encoded proteins. This paper describes expansion of the synthetic scope of 1, the difficulties encountered in this process, particularly issues with epimerization and slow coupling rates, and methods to overcome them. Finally, spectroscopic and physicochemical properties as well as proteolytic stabilities of molecules in this series were measured; these data highlight the suitability of oligo-pyrrolinone-pyrrolidines for the development of pharmacological probes or pharmaceutical leads.

The discovery of tricyclic pyridone JAK2 inhibitors. Part 1: hit to lead

This paper describes the discovery and design of a novel class of JAK2 inhibitors. Furthermore, we detail the optimization of a screening hit using ligand binding efficiency and log D. These efforts led to the identification of compound 41, which demonstrates in vivo activity in our study.

Allosteric inhibitors of Akt1 and Akt2: discovery of [1,2,4]triazolo[3,4-f][1,6]naphthyridines with potent and balanced activity

A series of [1,2,4]triazolo[3,4-f][1,6]naphthyridine allosteric dual inhibitors of Akt1 and 2 have been developed. These compounds have been shown to have potent dual Akt1 and 2 cell potency. The representative compound 13 provided potent inhibitory activity against Akt1 and 2 in vivo in a mouse model.

Strategies to reduce the risk of drug-induced QT interval prolongation: a pharmaceutical company perspective

Drug-induced prolongation of the QT interval is having a significant impact on the ability of the pharmaceutical industry to develop new drugs. The development implications for a compound causing a significant effect in the 'Thorough QT/QTc Study' -- as defined in the clinical regulatory guidance (ICH E14) -- are substantial. In view of this, and the fact that QT interval prolongation is linked to direct inhibition of the hERG channel, in the early stages of drug discovery the focus is on testing for and screening out hERG activity. This has led to understanding of how to produce low potency hERG blockers whilst retaining desirable properties. Despite this, a number of factors mean that when an integrated risk assessment is generated towards the end of the discovery phase (by conducting at least an in vivo QT assessment) a QT interval prolongation risk is still often apparent; inhibition of hERG channel trafficking and partitioning into cardiac tissue are just two confounding factors. However, emerging information suggests that hERG safety margins have high predictive value and that when hERG and in vivo non-clinical data are combined, their predictive value to man, whilst not perfect, is >80%. Although understanding the anomalies is important and is being addressed, of greater importance is developing a better understanding of TdP, with the aim of being able to predict TdP rather than using an imperfect surrogate marker (QT interval prolongation). Without an understanding of how to predict TdP risk, high-benefit drugs for serious indications may never be marketed.

The design and synthesis of potent and cell-active allosteric dual Akt 1 and 2 inhibitors devoid of hERG activity

This letter details the attenuation of hERG in a class of Akt inhibitors through heteroatom insertions into aromatic rings. The development of a cell-active dual Akt 1 and 2 inhibitors devoid of hERG activity is discussed using structure-activity relationships.

Metronomic chemotherapy dosing-schedules with estramustine and temozolomide act synergistically with anti-VEGFR-2 antibody to cause inhibition of human umbilical venous endothelial cell growth

The effects of 'metronomic' or extended chemotherapy dosing schedules (ECS) are mediated through poorly understood anti-angiogenic mechanisms. ECS combined with biological anti-angiogenic agents have produced promising pre-clinical results.

MATERIALS AND METHODS

We have expanded the list of agents with an in vitro ECS profile to include the methylating agent temozolomide (Temodal) and the anti-mitotic agent estramustine (Estracyt). These agents were also combined with a specific anti-angiogenic inhibitor IMC-1C11 and a non-specific agent with anti-angiogenic properties, Compound 5h. The in vitro HUVEC ECS model system was optimised and cell proliferation assays undertaken.

RESULTS

As a single agent, estramustine inhibited endothelial cell proliferation with an IC50 of 4.5 microM and was active at 10-33% of the maximum tolerated dose (MTD) from clinical schedules, whilst temozolomide had IC50 of 6.6 microM and was active at 1-6% of MTD. In combination, significant synergy was seen with IMC-1C11 in combination with either drug, whilst modest additive effects were observed with Compound 5h. None of the combinations resulted in significant cytotoxicity or apoptosis.

DISCUSSION

The results show that ECS of temozolomide and estramustine can be significantly enhanced when combined with specific anti-angiogenic inhibitors in an in vitro HUVEC system.

2-Amino-N-pyrimidin-4-ylacetamides as A2A receptor antagonists: 2. Reduction of hERG activity, observed species selectivity, and structure-activity relationships

Previously we have described a series of novel A 2A receptor antagonists with excellent water solubility. As described in the accompanying paper, the antagonists were first optimized to remove an unsubstituted furyl moiety, with the aim of avoiding the potential metabolic liabilities that can arise from the presence of an unsubstituted furan. This effort identified a series of potent and selective methylfuryl derivatives. Herein, we describe the further optimization of this series to increase potency, maintain selectivity for the human A 2A vs the human A 1 receptor, and minimize activity against the hERG channel. In addition, the observed structure-activity relationships against both the human and the rat A 2A receptor are reported.

Insights into the structural requirements of farnesyltransferase inhibitors as potential anti-tumor agents based on 3D-QSAR CoMFA and CoMSIA models

A three-dimensional quantitative structure-activity relationship (3D-QSAR) study was performed on three different chemical series reported as selective farnesyltransferase (FTase) inhibitors employing comparative molecular field analysis (CoMFA) and comparative molecular similarity indices (CoMSIA) techniques to investigate the structural requirements for substrates and derive a predictive model that may be used for the design of novel FTase inhibitors. Removal of outliers improved the predictive power of models developed for all three structurally diverse classes of compounds. 3D-QSAR models were derived for 3-aminopyrrolidinone derivatives (training set N=38, test set N=7), 2-amino-nicotinonitriles (training set N=46, test set N=13) and 1-aryl-1'-imidazolyl methyl ethers (training set N=35, test set N=5). The CoMFA models with steric and electrostatic fields exhibited r(2)(cv) 0.479-0.803, r(2)(ncv) 0.945-0.993, r(2)(pred) 0.686-0.811. The CoMSIA models displayed r(2)(cv) 0.411-0.814, r(2)(ncv) 0.923-0.984, r(2)(pred) 0.399-0.787. 3D contour maps generated from these models were analyzed individually, which provide the regions in space where interactive fields may influence the activity. The superimposition of contour maps on the active site of farnesyltransferase additionally helps in understanding the structural requirements of these inhibitors. 3D-QSAR models developed may guide our efforts in designing and predicting the FTase inhibitory activity of novel molecules.

Optimisation and validation of a medium-throughput electrophysiology-based hERG assay using IonWorks™ HT

INTRODUCTION

Regulatory and competitive pressure to reduce the QT interval prolongation risk of potential new drugs has led to focus on methods to test for inhibition of the human ether-a-go-go-related gene (hERG)-encoded K+ channel, the primary molecular target underlying this safety issue. Here we describe the validation of a method that combines medium-throughput with direct assessment of channel function.

METHODS

The electrophysiological and pharmacological properties of hERG were compared using two methods: conventional, low-throughput electrophysiology and planar-array-based, medium-throughput electrophysiology (IonWorks HT). A pharmacological comparison was also made between IonWorks HT and an indirect assay (Rb+ efflux).

RESULTS

Basic electrophysiological properties of hERG were similar whether recorded conventionally (HEK cells) or using IonWorks HT (CHO cells): for example, tail current V1/2 -12.1+/-5.0 mV (32) for conventional and -9.5+/-6.0 mV (46) for IonWorks HT (mean+/-S.D. (n)). A key finding was that as the number of cells per well was increased in IonWorks HT, the potency reported for a given compound decreased. Using the lowest possible cell concentration (250,000 cells/ml) and 89 compounds spanning a broad potency range, the pIC50 values from IonWorks HT (CHO-hERG) were found to correlate well with those obtained using conventional methodology (HEK-hERG)(r=0.90; p<0.001). Further validation using CHO-hERG cells with both methods confirmed the correlation (r=0.94; p<0.001). In contrast, a comparison of IonWorks HT and Rb+ efflux data with 649 compounds using CHO-hERG cells showed that the indirect assay consistently reported compounds as being, on average, 6-fold less potent, though the differences varied depending on chemical series.

DISCUSSION

The main finding of this work is that providing a relatively low cell concentration is used in IonWorks HT, the potency information generated correlates well with that determined using conventional electrophysiology. The effect on potency of increasing cell concentration may relate to a reduced free concentration of test compound owing to partitioning into cell membranes. In summary, the IonWorks HT hERG assay can generate pIC50 values based on a direct assessment of channel function in a timeframe short enough to influence chemical design.

The role of the medicinal chemist in drug discovery--then and now

The role of the medicinal chemist in drug discovery has undergone major changes in the past 25 years, mainly because of the introduction of technologies such as combinatorial chemistry and structure-based drug design. As medicinal chemists with more than 50 years of combined experience spanning the past four decades, we discuss this changing role using examples from our own and others' experience. This historical perspective could provide insights in to how to improve the current model for drug discovery by helping the medicinal chemist regain the creative role that contributed to past successes.

An efficient route to novel 4,5-di- and 2,4,5-tri substituted imidazoles from imidazo[1,5-a]-1,3,5-triazine (5,8-diaza-7,9-dideazapurine) derivatives

Two new types of imidazole derivatives: N-(2-R1-5-R2-1H-imidazol-4-yl) thioureas 7a-g and N-(2-R1-5-R2-1H-imidazol-4-yl) formamides 8b,c,g were obtained in high yields by the hydrolytic degradation of 6-R1-8-R2-2-thioxo-2,3-dihydroimidazo[1,5-a]-1,3,5-triazin-4(1H)-ones 5a-g and 6-R1-8-R2-imidazo[1,5-a]-1,3,5-triazin-4(3H)-ones 6b,c,d, respectively. The tautomeric preferences of the new imidazoles were determined.

A cell-based radioligand binding assay for farnesyl: protein transferase inhibitors

Farnesyl:protein transferase (FPTase) catalyzes the covalent addition of the isoprenyl moiety of farnesylpyrophosphate to the C-terminus of the Ras oncoprotein and other cellular proteins. Inhibitors of FPTase (FTIs) have been developed as potential anticancer agents, and several compounds have been evaluated in clinical trials. To facilitate the identification of cell-active FTIs with high potency, the authors developed a method that uses a radiolabeled FTI that serves as a ligand in competitive displacement assays. Using high-affinity [(3)H]-labeled or [(125)I]-labeled FTI radioligands, they show that specific binding to FPTase can be detected in intact cells. Binding of these labeled FTI radioligands can be competed with a variety of structurally diverse FTIs, and the authors show that inhibition of FTI radioligand binding correlates well with inhibition of FPTase substrate prenylation in cells. This method provides a rapid and quantitative means of assessing FTI potency in cells and is useful for guiding the discovery of potent, novel inhibitors of FPTase. Similar methods could be employed in the optimization of inhibitors for other intracellular drug targets.

The synthesis and biological evaluation of a series of potent dual inhibitors of farnesyl and geranyl-Geranyl protein transferases

We have prepared a series of potent, dual inhibitors of the prenyl transferases farnesyl protein transferase (FPTase) and geranyl-geranyl protein transferase I (GGPTase). The compounds were shown to possess potent activity against both enzymes in cell culture. Mechanistic analysis has shown that the compounds are CAAX competitive for FPTase inhibition but geranyl-geranyl pyrophosphate (GGPP) competitive for GGPTase inhibiton.

Potent inhibitors of farnesyltransferase and geranylgeranyltransferase-I

Compound 1 has been shown to be a dual prenylation inhibitor with FPTase (IC50=2 nM) and GGPTase-I (IC50=95 nM). Analogues of 1, which replaced the cyanophenyl group with various biaryls, led to the discovery of highly potent dual FPTase/GGPTase-I inhibitors. 4-trifluoromethylphenyl, trifluoropentynyl, and trifluoropentyl were identified as good p-cyano replacements.