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 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.     

Increasing complexity of farnesyltransferase inhibitors activity: role in chromosome instability

Oncogenic Ras proteins have been seen as an important target for novel anticancer drugs. Due to the functional role of Ras farnesylation, fanesyltransferase (FTase) inhibition was thought to be a strategy for interfering with Ras-dependent transformation. When farnesylation is blocked, the function of Ras protein is severely impaired because of the inability of the nonfarnesylated protein to anchor to the membrane. Although it has been clearly demonstrated that FTase inhibitors (FTIs) inhibit Ras farnesylation, it is uncertain whether the antiproliferative effects of these compounds result exclusively from the effects on Ras. Moreover, no consensus has been reached as to the relevant targets(s) of FTIs that can explain their mosaic pharmacology. In searching for downstream targets for FTIs effects, CENP-E and CENP-F/mitosin were identified. Different studies showed that the inhibition of farnesylation interferes with CENP-E-microtubule association. In the presence of FTIs, chromosome alignment to the metaphase plate is delayed, suggesting that farnesylated proteins are involved in a step critical to bipolar spindle formation and chromosome alignment. An important question is whether these biological effects might contribute to the chemotherapeutic effects of the FTIs. However, FTIs, triggering the spindle checkpoint, might elevate the rate of cellular missegregation to levels that are incompatible with cell viability, as well as have a reduced (but still significant?) effect on checkpoint-proficient normal cells. As an example, RPR-115135 induced micronuclei (MN) increase in cancer cells displaying high chromosome instability (CIN) levels, whereas in normal cells it is devoid of activity. Cancer cells showing high CIN level might represent an ideal target for the activity of some FTIs.     

Anticancer activity of farnesyltransferase and geranylgeranyltransferase i inhibitors: prospects for drug development

Inhibition of Farnesyltransferase (FTase) has been thoroughly investigated as a strategy to discover novel anticancer drugs because the oncoprotein Ras, requires farnesylation for its cancer-causing activity. Several highly potent and selective FTase inhibitors have been made and show excellent antitumour activity against human tumours in animal models without toxicity to normal cells. However, resistance of the most frequently mutated form of Ras, K-Ras, to FTase inhibitors and its alternative prenylation by geranylgeranyltransferase I (GGTase I), has cast doubts on whether K-Ras is the target for FTase inhibitors. This monthly update focuses on issues of critical importance to the further development of FTase inhibitors as anticancer agents. Alternative prenylation of K-Ras by GGTase I as a mechanism of resistance to FTase inhibitors, targets for FTase inhibitors other than K-Ras and the relevance of GGTase I inhibitors as antitumour agents will be discussed.     

Anticancer activity of farnesyltransferase and geranylgeranyltransferase I inhibitors: prospects for drug development

Inhibition of farnesyltransferase (FTase) has been thoroughly investigated as a strategy to discover novel anticancer drugs because the oncoprotein Ras, requires farnesylation for its cancer-causing activity. Several highly potent and selective FTase inhibitors have been made and show excellent antitumour activity against human tumours in animal models without toxicity to normal cells. However, resistance of the most frequently mutated form of Ras, K-Ras, to FTase inhibitors and its alternative prenylation by geranylgeranyltransferase I (GGTase I), has cast doubts on whether K-Ras is the target for FTase inhibitors. This monthly update focuses on issues of critical importance to the further development of FTase inhibitors as anticancer agents. Alternative prenylation of K-Ras by GGTase I as a mechanism of resistance to FTase inhibitors, targets for FTase inhibitors other than K-Ras and the relevance of GGTase I inhibitors as antitumour agents will be discussed.     

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.     

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.     

2'-Chloropentostatin: discovery, fermentation and biological activity

2'-Chloropentostatin (2-CP) is a new nucleoside antibiotic produced by Actinomadura sp. ATCC 39365. A selectively sensitive assay organism, Enterococcus faecalis PD 05045 (MIC 0.005 micrograms/ml) was instrumental in the discovery of this compound. 2-CP is a tight-binding inhibitor of adenosine deaminase (Ki = 1.1 X 10(-10) M).     

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.     

Dihydroxynitrobenzaldehydes and hydroxymethoxynitrobenzaldehydes: synthesis and biological activity as catechol-O-methyltransferase inhibitors.

A series of nitro derivatives of dihydroxy- and hydroxymethoxybenzaldehyde was synthesized and tested as potential inhibitors of partially purified pig liver catechol-O-methyltransferase (COMT). All the dihydroxynitrobenzaldehydes prepared were potent inhibitors of COMT, but only one hydroxymethoxynitrobenzaldehyde (3-hydroxy-4-methoxy-5-nitrobenzaldehyde) showed activity as a COMT inhibitor. Although previously reported data showed that the presence of electron-withdrawing substituents at position 5 seemed to be very important for activity as COMT inhibitor, our results suggest that the requirement necessary to enhance the activity of the dihydroxyni-trobenzaldehyde derivatives toward COMT is the presence of the nitro group in a position ortho with respect to one hydroxyl group. The assayed compounds showed a reversible inhibition of COMT, which was mixed for all the dihydroxynitro derivatives but noncompetitive for 3-hydroxy-4-methoxy-5-nitrobenzaldehyde when pyrocatechol was the variable substrate and uncompetitive in all the inhibitors with respect to S-adenosyl-L-methionine.     

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).     

Inhibitors of farnesyltransferase and geranylgeranyltransferase-I for antitumor therapy: substrate-based design,conformational constraint and biological activity

The development of farnesyltransferase inhibitors, a novel approach to non-cytotoxic anticancer therapy, has been an active area of research over the past decade. Compounds that have advanced to clinical trials were evolved both from substrate-based design efforts and from compound library screening hits. This review focuses on the effort at Merck to evolve inhibitors from the protein substrate of farnesyltransferase, which resulted in the identification of a non-peptide inhibitor for clinical evaluation. X-ray crystal structures of farnesyltransferase complexed with early peptidomimetic as well as later non-peptide inhibitors have validated this design approach. NMR spectroscopic methods for studying enzyme-bound inhibitor structure, in conjunction with the use of conformational constraints, were critical components of subsequent efforts to provide potent inhibitors with varying levels of farnesyltransferase and geranylgeranyltransferase-I inhibitory specificity. Several of these compounds were important tools for investigating the use of prenyltransferase inhibitors to target Ki-Ras-mediated tumor growth.     

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.     

Synthesis and biological activity of pyridinium-type acetylcholinesterase inhibitors

A novel series of bispyridinium-type acetylcholinesterase (AChE) inhibitors derived from obidoxime, being active in the lower micromolar range, has been reported recently. According to the hypothesis that shorter pyridinium compounds should exhibit higher activity, a new series of compounds was synthesized that has 2,6-dichlorobenzyl, 2-chlorobenzyl and phthalimidomethyl moieties, respectively, at one end of the molecule and that are systematically shortened from the contralateral end. The concentration inhibiting the AChE and butyrylcholinesterase (BChE) by 50% (IC50) was evaluated by means of Ellman's test. Compounds characterized by a phenylpropyl residue at the contralateral end (3) were found to have IC50 values comparable with tacrine. In addition, the affinity of 3c toward the BChE was lower, indicating a lower degree of side effects.     

1,3,5-Triazine inhibitors of histone deacetylases: synthesis and biological activity

A series of 1,3,5-triazine-based hydroximic acids 6a–6i were designed and synthesized, and they were found to be potent inhibitors of human histone deacetylases. These compounds were evaluated for their antiproliferative activity by MTT assay, and most of them exhibited significant antiproliferative effect on HCT-116, MCF-7, and HeLa cancer cell lines. DNA flow cytometric analysis revealed that compound 6i induced apoptosis and cell cycle arrest at G2/M phase in HCT-116 cells.