Protein farnesyltransferase inhibitors

Specific mutations in the ras gene impair the guanosine triphophatase (GTPase) activity of Ras proteins, which play a fundamental role in the signaling cascade, leading to uninterrupted growth signals and to the transformation of normal cells into malignant phenotypes. It has been shown that normal cells transfected with mutant ras gene become cancerous and that unfarnesylated, cytosolic mutant Ras protein does not anchor onto cell membranes and cannot induce this transformation. Posttranslational modification and plasma membrane association of mutant Ras is necessary for this transforming activity. Since its identification, the enzyme protein farnesyltransferase (FTase) that catalyzes the first and essential step of the three Ras-processing steps has emerged as the most promising target for therapeutic intervention. FTase has been implicated as a potential target in inhibiting the prenylation of a variety of proteins, thus in controlling varied disease states (e.g. cancer, neurofibromatosis, restenosis, viral hepatitis, bone resorption, parasitic infections, corneal inflammations, and diabetes) associated with prenyl modifications of Ras and other proteins. Furthermore, it has been suggested that FTase inhibitors indirectly help in inhibiting tumors via suppression of angiogenesis and induction of apoptosis. Major milestones have been achieved with small-molecule FTase inhibitors that show efficacy without toxicity in vitro, as well as in mouse models bearing ras-dependent tumors. With the determination of the crystal structure of mammalian FTase, existent leads have been fine-tuned and new potent molecules of diverse structural classes have been designed. A few of these molecules are currently in the clinic, with at least three drug candidates in Phase II studies and one in Phase III. This article will review the progress that has been reported with FTase inhibitors in drug discovery and in the clinic.     

Protein farnesyltransferase inhibitors exhibit potent antimalarial activity

New therapeutics to combat malaria are desperately needed. Here we show that the enzyme protein farnesyltransferase (PFT) from the malaria parasite Plasmodium falciparum (P. falciparum) is an ideal drug target. PFT inhibitors (PFTIs) are well tolerated in man, but are highly cytotoxic to P. falciparum. Because of their anticancer properties, PFTIs comprise a highly developed class of compounds. PFTIs are ideal for the rapid development of antimalarials, allowing "piggy-backing" on previously garnered information. Low nanomolar concentrations of tetrahydroquinoline (THQ)-based PFTIs inhibit P. falciparum PFT and are cytotoxic to cultured parasites. Biochemical studies suggest inhibition of parasite PFT as the mode of THQ cytotoxicity. Studies with malaria-infected mice show that THQ PFTIs dramatically reduce parasitemia and lead to parasite eradication in the majority of animals. These studies validate P. falciparum PFT as a target for the development of antimalarials and describe a potent new class of THQ PFTIs with antimalaria activity.     

Non-thiol farnesyltransferase inhibitors: FTase-inhibition and cellular activity of benzophenone-based bisubstrate analogue farnesyltransferase inhibitors

Some 5-acylaminoacylamino-benzophenone derivatives were designed as bisubstrate analogue farnesyltransferase inhibitors. These compounds turned out to be only weakly active against farnesyltransferase, but displayed an antiproliferative effect rendering them suitable for further development as a novel type of cytostatic agents.     

Protein farnesyltransferase and adenosine receptors

Many exciting advances in the treatment of cancer were presented at the symposium entitled 'Protein prenylation' which was chaired by Professor Richard A Gibbs (Wayne State University, Detroit, MI, USA). Prenylation, or the covalent attachment of isoprenoid lipids, is now recognized as an important component in the post-translational localization and functionalization of many cellular proteins. The majority of prenylated proteins are modified by one of two specific enzymes: protein farnesyl-transferase (FTase) and geranylgerany-ltransferase type I (GGTase-I). The finding that farnesylation of oncogenic forms of Ras proteins is required for expression of their transforming activity has led to FTase becoming an important target for anticancer drug design.     

抗肿瘤新药法尼基转移酶抑制剂的研究进展

肿瘤的发生与细胞信号转导系统异常密切相关,针地信号转导通路中的关键酶设计的抑制剂是当前抗肿瘤药物开发的热点.法尼基转移酶是细胞信号转导系统中Ras蛋白翻译后修饰的关键酶.综述了近年来法尼基转移酶抑制剂的研究状况,重点阐述了部分重要化合物的构效关系,指出了法尼基转移酶抑制剂的发展前景.     

Novel lead structures for antimalarial farnesyltransferase inhibitors

Through the combination of nitrophenylfurylacryloyl moiety which has been designed to occupy an aryl binding site of farnesyltransferase with several AA(X)-peptidomimetic substructures some novel farnesyltransferase inhibitors were obtained. Evaluation of their antimalarial activity and some initial modifications yielded a 4-benzophenone- and a sulfonamid-based novel lead for antimalarial farnesyltransferase inhibitors.     

Structure based design of benzophenone-based non-thiol farnesyltransferase inhibitors

Farnesyltransferase catalyzes the transfer of a farnesyl residue from farnesylpyrophosphate to the thiol of a cysteine side chain of proteins which carry at the C-terminus the so called CAAX-sequence. Although the exact cellular events affected by farnesyltransferase inhibiton remain to be determined, farnesyltransferase has become a major target in the development of potential anti-cancer drugs. Numerous farnesyltransferase inhibitors have been described from which the majority are CAAX-peptidomimetics possessing a free thiol group which coordinates the enzyme-bound zinc ion. The development of farnesyltransferase inhibitors is clearly directed towards the so-called non-thiol farnesyltransferase inhibitors because of adverse drug effects connected to free thiols. This review mainly deals with the efforts of the authers group towards the design of non-thiol-farnesyltransferase inhibitors. Our first step on the way to non-thiol farnesyltransferase inhibitors was the development of an CAAX-peptidomimetic based on a pharmacophore model. On the basis of this benzophenone core, bisubstrate analogues were developed as one class of non-thiol farnesyltransferase inhibitors. In most non-thiol farnesyltransferase inhibitors known in literature nitrogene containing heterocycles are used as cysteine replacements supposedly coordinating the enzyme bound zinc. However, we and others have shown that nitrogen heterocycles can be replaced by aryl residues lacking the ability to coordinate metal atoms, an observation which let to the postulation of two hitherto unknown aryl binding sites. Using flexible docking of model compounds and GRID analysis we were able to locate these postulated aryl binding sites. Subsequently, we used one of this aryl binding sites for the structure based design of highly active non-thiol farnesyltransferase inhibitors.     

Second generation tetrahydroquinoline-based protein farnesyltransferase inhibitors as antimalarials

Substituted tetrahydroquinolines (THQs) have been previously identified as inhibitors of mammalian protein farnesyltransferase (PFT). Previously we showed that blocking PFT in the malaria parasite led to cell death and that THQ-based inhibitors are the most potent among several structural classes of PFT inhibitors (PFTIs). We have prepared 266 THQ-based PFTIs and discovered several compounds that inhibit the malarial enzyme in the sub- to low-nanomolar range and that block the growth of the parasite (P. falciparum) in the low-nanomolar range. This body of structure-activity data can be rationalized in most cases by consideration of the X-ray structure of one of the THQs bound to mammalian PFT together with a homology structural model of the malarial enzyme. The results of this study provide the basis for selection of antimalarial PFTIs for further evaluation in preclinical drug discovery assays.     

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).     

Benzophenone-based farnesyltransferase inhibitors with high activity against Trypanosoma cruzi

Less toxic drugs are needed to combat the human parasite Trypanosoma cruzi (Chagas's disease). One novel target for antitrypanosomal drug design is farnesyltransferase. Several farnesyltransferase inhibitors based on the benzophenone scaffold were assayed in vitro and in vivo with the parasite. The common structural feature of all inhibitors is an amino function which can be protonated. Best in vitro activity (LC50 values 1 and 10 nM, respectively) was recorded for the R-phenylalanine derivative 4a and for the N-propylpiperazinyl derivative 2f. These inhibitors showed no cytotoxicity to cells. When tested in vivo, the survival rates of infected animals receiving the inhibitors at 7 mg/kg body weight/day were 80 and 60% at day 115 postinfection, respectively.     

Discovery and structure-activity relationships of novel piperidine inhibitors of farnesyltransferase

A novel piperidine series of farnesyltransferase (FTase) inhibitors is described. Systematic medicinal chemistry studies starting with the lead compound, discovered from a 5-nitropiperidin-2-one combinatorial library, resulted in a potent series of novel FTase inhibitors. We found that all of four substituents of the piperidine core played an important role for FTase inhibition. A 10-fold increase in potency was observed by changing the piperidine-2-one core to the corresponding piperidine core. This class of compounds was found to inhibit farnesyltransferase in a Ras competitive manner. Optical resolution of several potent inhibitors revealed that the (+)-enantiomers showed potent farnesyltransferase inhibition. (+)-8 inhibited FTase with an IC(50) of 1.9 nM.     

Discovery and structure-activity relationships of imidazole-containing tetrahydrobenzodiazepine inhibitors of farnesyltransferase

2,3,4,5-Tetrahydro-1-(imidazol-4-ylalkyl)-1,4-benzodiazepines were found to be potent inhibitors of farnesyltransferase (FT). A hydrophobic substituent at the 4-position of the benzodiazepine, linked via a hydrogen bond acceptor, was important to enzyme inhibitory activity. An aryl ring at position 7 or a hydrophobic group linked to the 8-position through an amide, carbamate, or urea linkage was also important for potent inhibition. 2,3,4, 5-Tetrahydro-1-(1H-imidazol-4-ylmethyl)-7-(4-pyridinyl)-4-[2-(t rifluo romethoxy)benzoyl]-1H-1,4-benzodiazepine (36), with an FT IC(50) value of 24 nM, produced 85% phenotypic reversion of Ras transformed NIH 3T3 cells at 1.25 microM and had an EC(50) of 160 nM for inhibition of anchorage-independent growth in soft agar of H-Ras transformed Rat-1 cells. Selected analogues demonstrated ip antitumor activity against an ip Rat-1 tumor in mice.     

Binding mode of conformations and structure-based pharmacophore development for farnesyltransferase inhibitors

Farnesyltransferase (FTase) is one of the prenyltransferase family enzymes that catalyse the transfer of 15-membered isoprenoid (farnesyl) moiety to the cysteine of CAAX motif-containing proteins including Rho and Ras family of G proteins. Inhibitors of FTase act as drugs for cancer, malaria, progeria and other diseases. In the present investigation, we have developed two structure-based pharmacophore models from protein–ligand complex (3E33 and 3E37) obtained from the protein data bank. Molecular dynamics (MD) simulations were performed on the complexes, and different conformers of the same complex were generated. These conformers were undergone protein–ligand interaction fingerprint (PLIF) analysis, and the fingerprint bits have been used for structure-based pharmacophore model development. The PLIF results showed that Lys164, Tyr166, TrpB106 and TyrB361 are the major interacting residues in both the complexes. The RMSD and RMSF analyses on the MD-simulated systems showed that the absence of FPP in the complex 3E37 has significant effect in the conformational changes of the ligands. During this conformational change, some interactions between the protein and the ligands are lost, but regained after some simulations (after 2 ns). The structure-based pharmacophore models showed that the hydrophobic and acceptor contours are predominantly present in the models. The pharmacophore models were validated using reference compounds, which significantly identified as HITs with smaller RMSD values. The developed structure-based pharmacophore models are significant, and the methodology used in this study is novel from the existing methods (the original X-ray crystallographic coordination of the ligands is used for the model building). In our study, along with the original coordination of the ligand, different conformers of the same complex (protein–ligand) are used. It concluded that the developed methodology is significant for the virtual screening of novel molecules on different targets.