New farnesyltransferase inhibitors in the phenothiazine series

The biological screening of the chemical library of our Organic Chemistry Department, carried out on an automated fluorescence-based FTase assay, allowed us to discover that a phenothiazine derivative (1d) was an inhibitor of farnesyltransferase. Three new series of human farnesyltransferase inhibitors, based on a phenothiazine scaffold, were synthesized with protein farnesyltransferase inhibition potencies in the low micromolar range. Ester derivative 9d was the most active compound in these series. Four synthesized compounds were evaluated for their antiproliferative activity on a NCI-60 cancer cell line panel. The modest results obtained in this preliminary investigation showed that mixing the phenothiazine and the 1,2,3-triazole motif in the structure of a single compound can lead to new scaffolds in the field of farnesyltransferase inhibitors.     

Macrocyclic piperazinones as potent dual inhibitors of farnesyltransferase and geranylgeranyltransferase-I

A series of macrocyclic piperazinone compounds with dual farnesyltransferase/geranylgeranyltransferase-I inhibitory activity was prepared. These compounds were found to be potent inhibitors of protein prenylation in cell culture. A hypothesis for the binding mode of compound 3o in FPTase is proposed.     

Synthesis and evaluation of homofarnesoyl-substituted CAAX-peptidomimetics as farnesyltransferase inhibitors and antiproliferative agents

Several CAAX-peptidomimetics were linked to homofarnesoic acid via a beta-alanyl spacer with the intention to obtain a novel type of bisubstrate analogue farnesyltransferase inhibitors. However, the compounds were found to be only weakly active in the farnesyltransferase inhibition assay. Nevertheless, they displayed antiproliferative activity against different tumor cell lines in the low micromolar range. Replacement of the beta-alanine moiety by aspartic acid-1-methyl ester resulted in a compound which inhibited the farnesyltransferase with an IC50 of 860 nM. The corresponding free acid showed a eightfold loss in activity (IC50 = 6.9 microM).     

Peptidomimetic inhibitors of farnesyltransferase with high in vitro activity and significant cellular potency

2-o-Tolyl or 2-o-anisyl substituted 4-hydroxy- and 4-carboxybenzamides of methionine, etherified and amidified with 2-hydroxymethyl- and 2-aminomethylpyridodioxane, respectively, are described as inhibitors of Ras protein farnesyltransferase (FTase). Of the sixteen compounds, resulting from the substitution pattern of benzamide and the configuration of the two stereocenters, seven inhibited FTase activity with potencies in the nanomolar range. They were all 2-oxymethylpyridodioxane ethers and, among them, the four o-tolyl substituted stereoisomers also showed micromolar antiproliferative effect on human aortic smooth muscle cells interfering with Ras farnesylation. The docking analysis enlightened significant differences in enzyme interaction between oxymethylpyridodioxane and aminomethylpyridodioxane derivatives.     

Synthesis and biological evaluation of a new series of N-ylides as protein farnesyltransferase inhibitors

A new family of 30 benzoylated N-ylides 4 and 5 was synthesized and evaluated for the inhibitory activity on human protein farnesyltransferase. Most of these novel compounds possessed in vitro inhibition potencies in the micromolar range. The nature of the substituents on the pyridine and phenyl units proved to be important in determining inhibitory activity and generally, the replacement of the cyanoacrylonitrile function by a cyanoethylacrylate group decreased the biological potential on farnesyltransferase. These results completed our SAR study on this original class of N-ylides.     

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.     

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.     

A scaffold hopping approach to identify novel monoamine oxidase B inhibitors

Monoamine oxidase B (MAO-B) inhibitors are used to treat Parkinson's disease. In this study, we searched for novel MAO-B inhibitors using a scaffold hopping approach based on our experience with the thiazolidinedione (TZD) class of compounds as MAO-B inhibitors. Several novel compounds were identified, with potencies in the low nanomolar and low micromolar range. We also found that derivatives of the natural product sulfuretin are potent MAO-A and MAO-B inhibitors.     

A novel inhibitor of farnesyltransferase with a zinc site recognition moiety and a farnesyl group

Protein prenylation such as farnesylation and geranylgeranylation is associated with various diseases. Thus, many inhibitors of prenyltransferase have been developed. We report novel inhibitors of farnesyltransferase with a zinc-site recognition moiety and a farnesyl/dodecyl group. Molecular docking analysis showed that both parts of the inhibitor fit well into the catalytic domain of farnesyltransferase. The synthesized inhibitors showed activity against farnesyltransferase in vitro and inhibited proliferation of the pancreatic cell line AsPC-1. Among the compounds with farnesyl and dodecyl groups, the inhibitor with a farnesyl group was found to have stronger and more selective activity.     

Isothiazole dioxides: synthesis and inhibition of Trypanosoma brucei protein farnesyltransferase

A series of isothiazole dioxides was synthesized and evaluated as inhibitors of protein farnesyltransferase from the parasite that causes African sleeping sickness (Trypanosoma brucei). The most potent compound in the series inhibited the parasite enzyme with an IC(50) of 2 microM and blocked the growth of the bloodstream parasite in vitro with an ED(50) of 10 microM. The same compound inhibited rat protein farnesyltransferase and protein geranylgeranyltransferase type I only at much higher concentration.     

Identification and characterisation of Toxoplasma gondii protein farnesyltransferase

Prenylated proteins are involved in the regulation of DNA replication and cell cycling and have important roles in the regulation of cell proliferation. Protein farnesyltransferase and protein geranylgeranyltransferase are the two enzymes responsible for catalysing isoprene lipid modifications. Recently these enzymes have been targets for the development of cancer chemotherapeutics. Using metabolic labelling we identified isoprenylated proteins which suggests the presence of protein farnesyltransferase in Toxoplasma gondii. T. gondii protein farnesyltransferase is heat-labile and requires Mg(2+) and Zn(2+) ions for full activity. Peptidomimetic analogues as well as short synthetic peptides were tested in vitro as possible competitors for farnesyltransferase substrates. We found that the synthetic peptide (KTSCVIA) specifically inhibited T. gondiiprotein farnesyltransferase but not mammalian (HeLa cells) farnesyltransferase. Therefore this study suggests the possible development of specific inhibitors of T. gondiiprotein farnesyltransferase as an approach to parasitic protozoa therapy.     

α-Substituted norstatines as the transition-state mimic in inhibitors of multiple digestive vacuole malaria aspartic proteases

The impact of moving the P1 side-chain from the β-position to the α-position in norstatine-containing plasmepsin inhibitors was investigated, generating two new classes of tertiary alcohol-comprising α-benzylnorstatines and α-phenylnorstatines. Twelve α-substituted norstatines were designed, synthesized and evaluated for their inhibitory potencies against plasmepsin II and the plasmepsin IV orthologues (PM4) present in the digestive vacuole of all four Plasmodium species causing malaria in man. New synthetic routes were developed for producing the desired α-substituted norstatines as pure stereoisomers. The best compounds provided K_i values in the nanomolar range for all PM4, with a best value of 110 nM in PM4 from Plasmodium ovale. In addition, excellent selectivity over the closely related human aspartic protease Cathepsin D was achieved. The loss of affinity to Plasmodium falciparum PM4, which was experienced upon the move of the P1 substituent, was rationalized by the calculation of inhibitor–protein binding affinities using the linear interaction energy method (LIE).     

Non-thiol farnesyltransferase inhibitors: structure-activity relationships of benzophenone-based bisubstrate analogue farnesyltransferase inhibitors

Investigations on the structure-activity relationships of benzophenone-based bisubstrate analogue farnesyltransferase inhibitors yielded a bisubstrate analogue farnesyltransferase inhibitor lacking any prenylic or peptidic substructures with nanomolar activity. This represents a considerable progress in comparison to those non-prenylic, non-peptidic bisubstrate analogue farnesyltransferase inhibitors we have described before which utilized AAX-peptidomimetic substructures different from the benzophenone since those inhibitors displayed activity only in the micromolar range.     

Non-peptidic, non-prenylic inhibitors of the prenyl protein-specific protease Rce1

Several compounds designed as bisubstrate analogues of protein farnesyltransferase inhibited the prenyl protein-specific protease Rce1, qualifying them as lead structures for a novel class of non-peptidic, non-prenylic inhibitors of this protease.     

Probing the hydrophobic pocket of farnesyltransferase: aromatic substitution of CAAX peptidomimetics leads to highly potent inhibitors

Cysteine farnesylation at the carboxylate terminal tetrapeptide CAAX of Ras protein is catalyzed by farnesyltransferase. This lipid modification is necessary for regulatory function of both normal and oncogenic Ras. The high frequency of Ras mutation in human cancers has prompted an intensive study on finding ways of controlling oncogenic Ras function. Inhibition of farnesyltransferase is among the most sought after targets for cancer chemotherapy. We report here the design, synthesis and biological characterization of a series of peptidomimetics as farnesyltransferase inhibitors. These compounds are extremely potent towards farnesyltransferase with IC₅₀ values ranging from subnanomolar to low nanomolar concentrations. They have a high selectivity for farnesyltransferase over the closely related geranylgeranyltransferase-I. Structure–activity relationship studies demonstrated that a properly positioned hydrophobic group significantly enhanced inhibition potency, reflecting an improved complementarity to the large hydrophobic pocket in the CAAX binding site.     

Synthesis and activity of 1-aryl-1'-imidazolyl methyl ethers as non-thiol farnesyltransferase inhibitors

A series of imidazole-containing methyl ethers (4-5) have been designed and synthesized as potent and selective farnesyltransferase inhibitors (FTIs) by transposition of the D-ring to the methyl group on the imidazole of the previously reported FTIs 3. Several compounds such as 4h and 5b demonstrate superior enzymatic activity to the current benchmark compound tipifarnib (1) with IC(50) values in the lower subnanomolar range, while maintaining excellent cellular activity comparable to tipifarnib. The compounds are characterized as being simple, easier to make, and possess no chiral center involved.     

Generation and screening of pseudostatic hydrazone libraries derived from 5-substituted nipecotic acid derivatives at the GABA transporter mGAT4

The γ-aminobutyric acid (GABA) transporter mGAT4 represents a promising drug target for the treatment of epilepsy and other neurological disorders; however, the lack of highly potent and selective inhibitors for mGAT4 still retards its pharmacological elucidation. Herein, the generation and screening of pseudostatic combinatorial hydrazone libraries at the murine GABA transporter mGAT4 for the search of novel GABA uptake inhibitors is described. The hydrazone libraries contained more than 1100 compounds derived from nipecotic acid derivatives substituted at the 5-position instead, as common, at the 1-position of the core structure. Two hits were found and evaluated, which display potencies in the lower micromolar range at mGAT4 and its human equivalent hGAT3. These compounds possess a lipophilic moiety derived from a biphenyl residue attached to the 5-position of the hydrophilic nipecotic acid moiety via a three-atom spacer. Thus, the novel structures with potencies close to that of the bench mark mGAT4 inhibitor (S)-SNAP-5114 add new insights into the structure–activity relationship of mGAT4 inhibitors and could provide a promising starting point for the development of new mGAT4 inhibitors with even higher potencies.     

Naphthylisopropylamine and N-benzylamphetamine derivatives as monoamine oxidase inhibitors

A series of naphthylisopropylamine and N-benzyl-4-methylthioamphetamine derivatives were evaluated as monoamine oxidase inhibitors. Their potencies were compared with those of a series of amphetamine derivatives, to test if the increase of electron richness of the aromatic ring and overall size of the molecule might improve their potency as enzyme inhibitors. Molecular dockings were performed to gain insight regarding the binding mode of these inhibitors and rationalize their different potencies. In the case of naphthylisopropylamine derivatives, the increased electron-donating capacity and size of the aromatic moiety resulting from replacement of the phenyl ring of amphetamine derivatives by a naphthalene system resulted in more potent compounds. In the other case, extension of the arylisopropylamine molecule by N-benzylation of the amino group led to a decrease in potency as monoamine oxidase inhibitors.     

Aryloxy substituted N-arylpiperazinones as dual inhibitors of farnesyltransferase and geranylgeranyltransferase-I

A series of aryloxy substituted piperazinones with dual farnesyltransferase/geranylgeranyltransferase-I inhibitory activity was prepared. These compounds were found to have potent inhibitory activity in vitro and are promising agents for the inhibition of Ki-Ras signaling.