Potent and orally bioavailable noncysteine-containing inhibitors of protein farnesyltransferase

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.

Solid-phase synthesis and pharmacological evaluation of a library of peptidomimetics as potential farnesyltransferase inhibitors: an approach to new lead compounds

Oncogenic Ras proteins whose activation is farnesylation by farnesyltransferase have been seen as important targets for novel anticancer drugs. Inhibitors of this enzyme have already been developed as potential anti-cancer drugs, particularly by rational design based on the structure of the CA(1)A(2)X carboxyl terminus of Ras. Synthesis of a peptidomimetics library via solid-phase synthesis using the Multipin method is described here. The most active hits on cellular assays were resynthesized and enzymatic activity was measured. Compounds A1, A5 and A7 present significant activity on the isolated enzyme (IC(50)=117, 57.3 and 28.5 nM) and their molecular docking in the active site of the enzyme provides details on key interactions with the protein.

Modeling of farnesyltransferase inhibition by some thiol and non-thiol peptidomimetic inhibitors using genetic neural networks and RDF approaches

Inhibition of farnesyltransferase (FT) enzyme by a set of 78 thiol and non-thiol peptidomimetic inhibitors was successfully modeled by a genetic neural network (GNN) approach, using radial distribution function descriptors. A linear model was unable to successfully fit the whole data set; however, the optimum Bayesian regularized neural network model described about 87% inhibitory activity variance with a relevant predictive power measured by q2 values of leave-one-out and leave-group-out cross-validations of about 0.7. According to their activity levels, thiol and non-thiol inhibitors were well-distributed in a topological map, built with the inputs of the optimum non-linear predictor. Furthermore, descriptors in the GNN model suggested the occurrence of a strong dependence of FT inhibition on the molecular shape and size rather than on electronegativity or polarizability characteristics of the studied compounds.

Non-Thiol Farnesyltransferase Inhibitors: Utilization of the Far Aryl Binding Site by Arylthienylacryloylaminobenzophenones

We recently described two novel aryl binding sites of farnesyltransferase. The 4- and 5-arylsubstituted thienylacryloyl moieties turned out as appropriate substituents for our benzophenone-based AAX-peptidomimetic capable for occupying the far aryl binding site.

Broad-Based Quantitative Structure−Activity Relationship Modeling of Potency and Selectivity of Farnesyltransferase Inhibitors Using a Bayesian Regularized Neural Network

Inhibitors of the enzyme farnesyltransferase show potential as novel anticancer agents. There are many known inhibitors, but efforts to build predictive SAR models have been hampered by the structural diversity and flexibility of inhibitors. We have undertaken for the first time a QSAR study of the potency and selectivity of a large, diverse data set of farnesyltransferase inhibitors. We used novel molecular descriptors based on binned atomic properties and invariants of molecular matrices and a robust, nonlinear QSAR mapping paradigm, the Bayesian regularized neural network. We have built robust QSAR models of farnesyltransferase inhibition, geranylgeranyltransferase inhibition, and in vivo data. We have derived a novel selectivity index that allows us to model potency and selectivity simultaneously and have built robust QSAR models using this index that have the potential to discover new potent and selective inhibitors.

Non-thiol farnesyltransferase inhibitors: N-(4-tolylacetylamino-3-benzoylphenyl)-3-arylfurylacrylic acid amides

We have designed arylfurylacryl-substituted benzophenones as non-thiol farnesyltransferase inhibitors utilizing a novel aryl binding site of farnesyltransferase. These compounds display activity in the low nanomolar range.

Preparation of polyhydroxyalkyl- and C-glycosylfuran derivatives from free sugars catalyzed by cerium(III) chloride in aqueous solution: an improvement of the Garcia González reaction

Unprotected aldose sugars react smoothly with 1,3-diones or beta-ketoesters in the presence of CeCl(3).7H(2)O in aqueous solution to produce polyhydroxylalkyl- and C-glycosylfuran derivatives in excellent yield. Operationally simple, mild neutral reaction conditions in aqueous solution is the key feature of this methodology.

Novel and selective imidazole-containing biphenyl inhibitors of protein farnesyltransferase

A series of imidazole-containing biphenyls was prepared and evaluated in vitro for inhibition of FTase and cellular Ras processing. Several of these analogues, such as 21, are potent inhibitors of FTase (<1nM), FTase/GGTase selective (>300-fold) and cellularly active (<or=80nM). An X-ray crystal structure of inhibitor 21 bound to rat farnesyltransferase is also presented.

Non-thiol farnesyltransferase inhibitors: N-(4-acylamino-3-benzoylphenyl)-3-[5-(4-nitrophenyl)-2-furyl]acrylic acid amides

We have designed the nitrophenylfurylacryl-substituted benzophenone 4f as a non-thiol farnesyltransferase inhibitor utilizing a novel aryl binding site of farnesyltransferase. Variation of the 2-acylamino substituent at the benzophenone core structure of our initial lead 4f yielded several non-thiol farnesyltransferase inhibitors with improved activity. These compounds display activity in the low nanomolar range.

Non-thiol farnesyltransferase inhibitors: utilization of an aryl binding site by 5-arylacryloylaminobenzophenones

We recently described a novel aryl binding site of farnesyltransferase. The 2-naphthylacryloyl residue was developed as an appropriate substituent for our benzophenone-based AAX-peptidomimetic capable of occupying this binding site, resulting in a non-thiol farnesyltransferase inhibitor with nanomolar activity. The activity of this inhibitor is readily explained on the basis of docking studies which show the 2-naphthyl residue fitting into the aryl binding site.

Non-thiol farnesyltransferase inhibitors: N-(4-Acylamino-3-benzoylphenyl)-4-nitrocinnamic acid amides

We have developed the 4-nitrocinnamoyl substituted benzophenone 4a as a novel non-thiol farnesyltransferase inhibitor. Replacement of the p-tolyl moiety of our initial lead structure 4a by different para and ortho substituted phenyl residues as well as by 1-naphthyl resulted in derivatives with considerably enhanced activity displaying IC(50) values between 42 and 52 nM. These compounds represent novel, readily accessible non-thiol farnesyltransferase inhibitors being more active than the corresponding thiol-containing analogues.

Exploration of novel aryl binding sites of farnesyltransferase using molecular modeling and benzophenone-based farnesyltransferase inhibitors

Most non-thiol CAAX-peptidomimetic farnesyltransferase inhibitors bear nitrogen-containing heterocycles in place of the terminal cysteine which are supposed to coordinate the enzyme-bound zinc. However, it has been shown that those nitrogen-containing heterocycles can be replaced by carbocyclic aromatic moieties which are unable to coordinate the zinc ion, a conclusion that resulted in the postulation of one or two hitherto unknown aryl binding sites. No indication has been given about the spatial location of these novel binding sites. Employing flexible docking of several non-thiol farnesyltransferase inhibitors known from the literature and some model compounds based on our benzophenone scaffold as well as performing GRID searches, we have identified two regions in the farnesyltransferase's active site which we suggest being the postulated aryl binding sites. One aryl binding region is located in close proximity to the zinc ion and is defined by the aromatic side chains of Tyr 300beta, Trp 303beta, Tyr 361beta, and Tyr 365beta. The second aryl binding site is defined by the side chains of Tyr 300beta, Leu 295beta, Lys 294beta, Lys 353beta, and Lys 356beta. This second aryl binding site has been used for the design of a non-thiol farnesyltransferase inhibitor (9c) with an IC(50) of 35 nM.

Non-thiol farnesyltransferase inhibitors: structure-activity relationships of aralkylsubstituted benzophenones

We describe a novel class of benzophenone-based farnesyltransferase inhibitors exploiting a novel aryl binding region in the farnesyltransferase's active site. The present study was mainly focussed on structural modifications of the trimethylene spacer of the 4-phenyl butyroyl residue of our lead structure (IC50 = 530 nM). These modifications turned out to have little effect on activity as had the replacement of the terminal aryl by cyclohexyl (IC50 = 440 nM vs. IC50 = 530 nM).

Prenylation inhibitors in renal disease

Members of the superfamily of Ras GTPase signalling proteins (monomeric G proteins) require post-translational carboxy-terminal prenylation to function. Prenylation is the covalent attachment of a hydrophobic prenyl group (either farnesyl or geranylgeranyl), which localises the GTPase to cell membranes. Ras proteins exert substantial control on cell proliferation and gene-transcription events, and prenylation inhibitors are now included in clinical trials for cancer. Many renal diseases are highly proliferative and are driven by a range of profibrotic cytokines. We hypothesise that inhibition of prenylation could be of substantial therapeutic benefit in such diseases, providing greater selectivity against abnormal cytokine-driven proliferation and fibrogenesis than current treatments available to nephrologists.

Discovery of a series of cyclohexylethylamine-containing protein farnesyltransferase inhibitors exhibiting potent cellular activity

Synthesis of a library of secondary benzylic amines based on the Sebti-Hamilton type peptidomimetic farnesyltransferase (FTase) inhibitor FTI-276 (1) led to the identification of 6 as a potent enzyme inhibitor (IC(50) of 8 nM) which lacked the problematic thiol residue which had been a common theme in many of the more important FTase inhibitors reported to date. It has previously been disclosed that addition of o-tolyl substitution to FTase inhibitors of the general description 2 had a salutary effect on both FTase inhibition and inhibition of Ras prenylation in whole cells. Combination of these two observations led us to synthesize 7, a potent FTase inhibitor which displayed an IC(50) of 0.16 nM for in vitro inhibition of FTase and an EC(50) of 190 nM for inhibition of whole cell Ras prenylation. Modification of 7 by classical medicinal chemistry led to the discovery of a series of potent FTase inhibitors, culminating in the identification of 25 which exhibited an IC(50) of 0.20 nM and an EC(50) of 4.4 nM. In vivo tests in a nude mouse xenograft model of human pancreatic cancer (MiaPaCa cells) showed that oral dosing of 25 gave rise to impressive attenuation of the growth of this aggressive tumor cell line.