Potential Fatty Acid as Antibacterial Agent Against Oral Bacteria of Streptococcus mutans and Streptococcus sanguinis from Basil (Ocimum americanum): In vitro and In silico Studies

BACKGROUND

Streptococcus mutans and Streptococcus sanguinis are Gram-positive bacteria that cause dental caries. MurA enzyme acts as a catalyst in the formation of peptidoglycan in bacterial cell walls, making it ideal as an antibacterial target. Basil (Ocimum americanum) is an edible plant that is diverse and has been used as a herbal medicine for a long time. It has been reported that basil has a pharmacological effect as well as antibacterial activity. The purpose of this study was to identify antibacterial compounds in O. americanum and analyze their inhibition activity on MurA enzyme.

METHODS

Fresh leaves from O. americanum were extracted with n-hexane and purified by a combination of column chromatography on normal and reverse phases together with in vitro bioactivity assay against S. mutans ATCC 25175 and S. sanguinis ATCC 10556, respectively, while in silico molecular docking simulation of lauric acid (1) was conducted using PyRx 0.8.

RESULTS

The structure determination of antibacterial compound by spectroscopic methods resulted in an active compound lauric acid (1). The in vitro evaluation of antibacterial activity in compound 1 showed Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) values of 78.13 and 156.3 ppm and 1250 and 2500 ppm against S. sanguinis and S. mutans, respectively. Further analysis and in silico evaluation determined lauric acid (1) as MurA Enzyme inhibitor. Lauric acid (1) showed a binding affinity of -5.2 Kcal/mol, which was higher than fosfomycin.

CONCLUSION

Lauric acid showed the potential as a new natural antibacterial agent through MurA inhibition in bacterial cell wall biosynthesis.

Organoarsenicals inhibit bacterial peptidoglycan biosynthesis by targeting the essential enzyme MurA

Trivalent organoarsenicals such as methylarsenite (MAs(III)) are considerably more toxic than inorganic arsenate (As(V)) or arsenite (As(III)). In microbial communities MAs(III) exhibits significant antimicrobial activity. Although MAs(III) and other organoarsenicals contribute to the global arsenic biogeocycle, how they exert antibiotic-like properties is largely unknown. To identify possible targets of MAs(III), a genomic library of the gram-negative bacterium, Shewanella putrefaciens 200, was expressed in Escherichia coli with selection for MAs(III) resistance. One clone contained the S. putrefaciens murA gene (SpmurA), which catalyzes the first committed step in peptidoglycan biosynthesis. Overexpression of SpmurA conferred MAs(III) resistance to E. coli. Purified SpMurA was inhibited by MAs(III), phenylarsenite (PhAs(III)) or the phosphonate antibiotic fosfomycin but not by inorganic As(III). Fosfomycin inhibits MurA by binding to a conserved residue that corresponds to Cys117 in SpMurA. A C117D mutant was resistant to fosfomycin but remained sensitive to MAs(III), indicating that the two compounds have different mechanisms of action. New inhibitors of peptidoglycan biosynthesis are highly sought after as antimicrobial drugs, and organoarsenicals represent a new area for the development of novel compounds for combating the threat of antibiotic resistance.

Potential Allylpyrocatechol Derivatives as Antibacterial Agent Against Oral Pathogen of S. sanguinis ATCC 10,556 and as Inhibitor of MurA Enzymes: in vitro and in silico Study

BACKGROUND

Streptococcus sanguinis is Gram-positive bacteria that contribute to caries. Many antibacterial agents are resistant against bacteria so that the discovery of new antibacterial agents is a crucial issue. Mechanism of antibacterial agents by disrupting cell wall bacteria is a promising target to be developed. One of the enzymes contributing to the cell wall is MurA enzyme. MurA is an enzyme catalyzing the first step of peptidoglycan biosynthesis in the cell wall formation. Inhibiting MurA is an effective and efficient way to kill the bacteria. Source of bioactive compounds including the antibacterial agent can be found in natural product such as herbal plant. Piper betle L. was reported to contain active antibacterial compounds. However, there is no more information on the antibacterial activity and molecular mechanism of P. betle's compound against S. sanguinis.

PURPOSE

The study aims to identify antibacterial constituents of P. betle L. and evaluate their activities through two different methods including in vitro and in silico analysis.

MATERIALS AND METHODS

The antibacterial agent was purified by bioactivity-guided isolation with combination chromatography methods and the chemical structure was determined by spectroscopic methods. The in vitro antibacterial activity was evaluated by disc diffusion and dilution methods while the in silico study of a compound binds on the MurA was determined using PyRx program.

RESULTS

The antibacterial compound identified as allylpyrocatechol showed inhibitory activity against S. sanguinis with an inhibition zone of 11.85 mm at 1%, together with MIC and MBC values of 39.1 and 78.1 μg/mL, respectively. Prediction for molecular inhibition mechanism of allylpyrocatechols against the MurA presented two allylpyrocatechol derivatives showing binding activity of -5.4, stronger than fosfomycin as a reference with the binding activity of -4.6.

CONCLUSION

Two allylpyrocatechol derivatives were predicted to have a good potency as a novel natural antibacterial agent against S. sanguinis through blocking MurA activity that causes disruption of bacterial cell wall.

Dual Farnesyl and Geranylgeranyl Transferase Inhibitor Thwarts Mutant KRAS-Driven Patient-Derived Pancreatic Tumors

PURPOSE

Mutant KRAS is a major driver of pancreatic oncogenesis and therapy resistance, yet KRAS inhibitors are lacking in the clinic. KRAS requires farnesylation for membrane localization and cancer-causing activity prompting the development of farnesyltransferase inhibitors (FTIs) as anticancer agents. However, KRAS becomes geranylgeranylated and active when cancer cells are treated with FTIs. To overcome this geranylgeranylation-dependent resistance to FTIs, we designed FGTI-2734, a RAS C-terminal mimetic dual FT and geranylgeranyltransferase-1 inhibitor (GGTI).

EXPERIMENTAL DESIGN

Immunofluorescence, cellular fractionation, and gel shift assays were used to assess RAS membrane association, Western blotting to evaluate FGTI-2734 effects on signaling, and mouse models to demonstrate its antitumor activity.

RESULTS

FGTI-2734, but not the selective FTI-2148 and GGTI-2418, inhibited membrane localization of KRAS in pancreatic, lung, and colon human cancer cells. FGTI-2734 induced apoptosis and inhibited the growth in mice of mutant KRAS-dependent but not mutant KRAS-independent human tumors. Importantly, FGTI-2734 inhibited the growth of xenografts derived from four patients with pancreatic cancer with mutant KRAS (2 G12D and 2 G12V) tumors. FGTI-2734 was also highly effective at inhibiting, in three-dimensional cocultures with resistance promoting pancreatic stellate cells, the viability of primary and metastatic mutant KRAS tumor cells derived from eight patients with pancreatic cancer. Finally, FGTI-2734 suppressed oncogenic pathways mediated by AKT, mTOR, and cMYC while upregulating p53 and inducing apoptosis in patient-derived xenografts in vivo.

CONCLUSIONS

The development of this novel dual FGTI overcomes a major hurdle in KRAS resistance, thwarting growth of patient-derived mutant KRAS-driven xenografts from patients with pancreatic cancer, and as such it warrants further preclinical and clinical studies.

Elucidating the inhibition of peptidoglycan biosynthesis in Staphylococcus aureus by albocycline, a macrolactone isolated from Streptomyces maizeus

Antibiotic resistance is a serious threat to global public health, and methicillin-resistant Staphylococcus aureus (MRSA) is a poignant example. The macrolactone natural product albocycline, derived from various Streptomyces strains, was recently identified as a promising antibiotic candidate for the treatment of both MRSA and vancomycin-resistant S. aureus (VRSA), which is another clinically relevant and antibiotic resistant strain. Moreover, it was hypothesized that albocycline's antimicrobial activity was derived from the inhibition of peptidoglycan (i.e., bacterial cell wall) biosynthesis. Herein, preliminary mechanistic studies are performed to test the hypothesis that albocycline inhibits MurA, the enzyme that catalyzes the first step of peptidoglycan biosynthesis, using a combination of biological assays alongside molecular modeling and simulation studies. Computational modeling suggests albocycline exists as two conformations in solution, and computational docking of these conformations to an ensemble of simulated receptor structures correctly predicted preferential binding to S. aureus MurA-the enzyme that catalyzes the first step of peptidoglycan biosynthesis-over Escherichia coli (E. coli) MurA. Albocycline isolated from the producing organism (Streptomyces maizeus) weakly inhibited S. aureus MurA (IC50 of 480 μM) but did not inhibit E. coli MurA. The antimicrobial activity of albocycline against resistant S. aureus strains was superior to that of vancomycin, preferentially inhibiting Gram-positive organisms. Albocycline was not toxic to human HepG2 cells in MTT assays. While these studies demonstrate that albocycline is a promising lead candidate against resistant S. aureus, taken together they suggest that MurA is not the primary target, and further work is necessary to identify the major biological target.

Farnesyltransferase Inhibitors and Their Role in the Treatment of Multiple Myeloma

BACKGROUND

Ras mutations are among the most common oncogene mutations found in multiple myeloma (MM). Patients with mutated Ras are less likely to respond to chemotherapy and have a shortened median survival. Therefore, targeting Ras farnesylation may be a valuable approach to treatment of MM. R115777 (tipifarnib) is a potent farnesyltransferase inhibitor (FTI) presently undergoing phase II/III clinical trials.

METHODS

We reviewed the preclinical and clinical experience of FTIs as antineoplastic agents and describe their potential role in the treatment of MM.

RESULTS

FTIs are a novel group of agents that selectively inhibit farnesyltransferase, an enzyme responsible for the posttranslational modification of several proteins including Ras. Since Ras is among the most commonly mutated oncogenes associated with cancer, this class of drugs has been evaluated in clinical trials in a diversity of tumors. R115777 has been evaluated in a phase II clinical trial in patients with advanced myeloma and found to be well tolerated. It induced disease stabilization in more than 60% of patients with advanced myeloma.

CONCLUSIONS

The drug selectively targets farnesyltransferase, but this effect did not correlate with disease stabilization, suggesting that these drugs may be targeting a survival pathway independent of Ras processing. Further studies will evaluate the use of FTI in maintenance therapy as well as in combination with other agents in advanced myeloma.

Novel long-chain compounds with both immunomodulatory and MenA inhibitory activities against Staphylococcus aureus and its biofilm

Menaquinone (MK) biosynthesis pathway is a potential target for evaluating antimicrobials in gram-positive bacteria. Here, 1,4-dihydroxy-2-naphthoate prenyltransferase (MenA) was targeted to reduce methicillin-resistant Staphylococcus aureus (MRSA) growth. MenA inhibiting, long chain-based compounds were designed, synthesized and evaluated against MRSA and menaquinone utilizing bacteria in aerobic conditions. The results showed that these bacteria were susceptible to most of the compounds. Menaquinone (MK-4) supplementation rescued MRSA growth, suggesting these compounds inhibit MK biosynthesis. 3a and 7c exhibited promising inhibitory activities with MICs ranging 1-8 μg/mL against MRSA strains. The compounds did not facilitate small colony variant formation. These compounds also inhibited the biofilm growth by MRSA at high concentration. Compounds 3a, 6b and 7c displayed a promising extracellular bactericidal activity against MRSA at concentrations equal to and four-fold less than their respective MICs. We also observed cytokines released from THP-1 macrophages treated with compounds 3a, 6b and 7c and found decreases in TNF-α and IL-6 release and increase in IL-1β. These data provide evidence that MenA inhibitors act as TNF-α and IL-6 inhibitors, raising the potential for development and application of these compounds as potential immunomodulatory agents.

Bacterial Cell Growth Inhibitors Targeting Undecaprenyl Diphosphate Synthase and Undecaprenyl Diphosphate Phosphatase

We synthesized a series of benzoic acids and phenylphosphonic acids and investigated their effects on the growth of Staphylococcus aureus and Bacillus subtilis. One of the most active compounds, 5-fluoro-2-(3-(octyloxy)benzamido)benzoic acid (7, ED50 ∼0.15 μg mL-1 ) acted synergistically with seven antibiotics known to target bacterial cell-wall biosynthesis (a fractional inhibitory concentration index (FICI) of ∼0.35, on average) but had indifferent effects in combinations with six non-cell-wall biosynthesis inhibitors (average FICI∼1.45). The most active compounds were found to inhibit two enzymes involved in isoprenoid/bacterial cell-wall biosynthesis: undecaprenyl diphosphate synthase (UPPS) and undecaprenyl diphosphate phosphatase (UPPP), but not farnesyl diphosphate synthase, and there were good correlations between bacterial cell growth inhibition, UPPS inhibition, and UPPP inhibition.

Mechanism-Based Post-Translational Modification and Inactivation in Terpene Synthases

Terpenes are ubiquitous natural chemicals with diverse biological functions spanning all three domains of life. In specialized metabolism, the active sites of terpene synthases (TPSs) evolve in shape and reactivity to direct the biosynthesis of a myriad of chemotypes for organismal fitness. As most terpene biosynthesis mechanistically involves highly reactive carbocationic intermediates, the protein surfaces catalyzing these cascade reactions possess reactive regions possibly prone to premature carbocation capture and potentially enzyme inactivation. Here, we show using proteomic and X-ray crystallographic analyses that cationic intermediates undergo capture by conserved active site residues leading to inhibitory self-alkylation. Moreover, the level of cation-mediated inactivation increases with mutation of the active site, upon changes in the size and structure of isoprenoid diphosphate substrates, and alongside increases in reaction temperatures. TPSs that individually synthesize multiple products are less prone to self-alkylation then TPSs possessing relatively high product specificity. In total, the results presented suggest that mechanism-based alkylation represents an overlooked mechanistic pressure during the evolution of cation-derived terpene biosynthesis.

Nanoformulation of Geranylgeranyltransferase-I Inhibitors for Cancer Therapy: Liposomal Encapsulation and pH-Dependent Delivery to Cancer Cells

Small molecule inhibitors against protein geranylgeranyltransferase-I such as P61A6 have been shown to inhibit proliferation of a variety of human cancer cells and exhibit antitumor activity in mouse models. Development of these inhibitors could be dramatically accelerated by conferring tumor targeting and controlled release capability. As a first step towards this goal, we have encapsulated P61A6 into a new type of liposomes that open and release cargos only under low pH condition. These low pH-release type liposomes were prepared by adjusting the ratio of two types of phospholipid derivatives. Loading of geranylgeranyltransferase-I inhibitor (GGTI) generated liposomes with average diameter of 50–100 nm. GGTI release in solution was sharply dependent on pH values, only showing release at pH lower than 6. Release of cargos in a pH-dependent manner inside the cell was demonstrated by the use of a proton pump inhibitor Bafilomycin A1 that Increased lysosomal pH and inhibited the release of a dye carried in the pH-liposome. Delivery of GGTI to human pancreatic cancer cells was demonstrated by the inhibition of protein geranylgeranylation inside the cell and this effect was blocked by Bafilomycin A1. In addition, GGTI delivered by pH-liposomes induced proliferation inhibition, G1 cell cycle arrest that is associated with the expression of cell cycle regulator p21^CIP1/WAF1. Proliferation inhibition was also observed with various lung cancer cell lines. Availability of nanoformulated GGTI opens up the possibility to combine with other types of inhibitors. To demonstrate this point, we combined the liposomal-GGTI with farnesyltransferase inhibitor (FTI) to inhibit K-Ras signaling in pancreatic cancer cells. Our results show that the activated K-Ras signaling in these cells can be effectively inhibited and that synergistic effect of the two drugs is observed. Our results suggest a new direction in the use of GGTI for cancer therapy.

N-Oxide derivatives of 3-(3-pyridyl)-2-phosphonopropanoic acids as potential inhibitors of Rab geranylgeranylation

The N-oxide derivatives of [2-(3-pyridinyl)-1-hydroxyethylidene-1,1-phosphonocarboxylic acid (or PEHPC) and [2-(3-pyridinyl)-1-ethylidene-1,1-phosphonocarboxylic acid (or PEPC) have been prepared and evaluated for their activity against several enzymes which utilize isoprenoids. The parent pyridines are known inhibitors of GGTase II, but the N-oxide derivatives show no improvement in biological activity in assays with the isolated enzyme. However, the PEHPC N-oxide did induce significant accumulation of intracellular light chain in myeloma cells, consistent with inhibition of Rab geranylgeranylation.

Rab-NANOPS: FRET biosensors for Rab membrane nanoclustering and prenylation detection in mammalian cells

Rab proteins constitute the largest subfamily of Ras-like small GTPases. They are central to vesicular transport and organelle definition in eukaryotic cells. Unlike their Ras counterparts, they are not a hallmark of cancer. However, a number of diseases, including cancer, show a misregulation of Rab protein activity. As for all membrane-anchored signaling proteins, correct membrane organization is critical for Rabs to operate. In this chapter, we provide a detailed protocol for the use of a flow cytometry-based Fluorescence Resonance Energy Transfer (FRET)-biosensors assay, which allows to detect changes in membrane anchorage, subcellular distribution, and of the nanoscale organization of Rab-GTPases in mammalian cell lines. This assay is high-throughput amenable and can therefore be utilized in chemical-genomic and drug discovery efforts.

Impact of farnesylation inhibitors on survival in Hutchinson-Gilford progeria syndrome

BACKGROUND

Hutchinson-Gilford progeria syndrome is an ultrarare segmental premature aging disease resulting in early death from heart attack or stroke. There is no approved treatment, but starting in 2007, several recent single-arm clinical trials administered inhibitors of protein farnesylation aimed at reducing toxicity of the disease-producing protein progerin. No study assessed whether treatments influence patient survival. The key elements necessary for this analysis are a robust natural history of survival and comparison with a sufficiently large patient population that has been treated for a sufficient time period with disease-targeting medications.

METHODS AND RESULTS

We generated Kaplan-Meier survival analyses for the largest untreated Hutchinson-Gilford progeria syndrome cohort to date. Mean survival was 14.6 years. Comparing survival for treated versus age- and sex-matched untreated cohorts, hazard ratio was 0.13 (95% confidence interval, 0.04-0.37; P<0.001) with median follow-up of 5.3 years from time of treatment initiation. There were 21 of 43 deaths in untreated versus 5 of 43 deaths among treated subjects. Treatment increased mean survival by 1.6 years.

CONCLUSIONS

This study provides a robust untreated disease survival profile that can be used for comparisons now and in the future to assess changes in survival with treatments for Hutchinson-Gilford progeria syndrome. The current comparisons estimating increased survival with protein farnesylation inhibitors provide the first evidence of treatments influencing survival for this fatal disease.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique Indentifiers: NCT00425607, NCT00879034, and NCT00916747.

Ether lipid generating enzyme AGPS alters the balance of structural and signaling lipids to fuel cancer pathogenicity

Aberrant lipid metabolism is an established hallmark of cancer cells. In particular, ether lipid levels have been shown to be elevated in tumors, but their specific function in cancer remains elusive. We show here that the metabolic enzyme alkylglyceronephosphate synthase (AGPS), a critical step in the synthesis of ether lipids, is up-regulated across multiple types of aggressive human cancer cells and primary tumors. We demonstrate that ablation of AGPS in cancer cells results in reduced cell survival, cancer aggressiveness, and tumor growth through altering the balance of ether lipid, fatty acid, eicosanoid, and fatty acid-derived glycerophospholipid metabolism, resulting in an overall reduction in the levels of several oncogenic signaling lipids. Taken together, our results reveal that AGPS, in addition to maintaining ether lipids, also controls cellular utilization of fatty acids, favoring the generation of signaling lipids necessary for promoting the aggressive features of cancer.

A(2) expression and assembly regulates lysis in Qβ infections

The capsids of ssRNA phages comprise a single copy of an ~45 kDa maturation protein that serves to recognize the conjugative pilus as receptor, to protect the ends of the viral RNA and also to escort the genomic RNA into the host cytoplasm. In the Alloleviviridae, represented by the canonical phage Qβ, the maturation protein A(2) also causes lysis. This is achieved by inhibiting the activity of MurA, which catalyses the first committed step of murein biosynthesis. Previously, it was shown that Qβ virions, with a single copy of A(2), inhibit MurA activity. This led to a model for lysis timing in which, during phage infection, A(2) is not active as a MurA inhibitor until assembled into virion particles, thus preventing premature lysis before a sufficient yield of viable progeny has accumulated. Here we report that MurA inactivates purified Qβ particles, casting doubt on the notion that A(2) must assemble into particles prior to MurA inhibition. Furthermore, quantification of A(2) protein induced from a plasmid indicated that lysis is entrained when the amount of the lysis protein is approximately equimolar to that of cellular MurA. Qβ por mutants, isolated as suppressors that overcome a murA(rat) mutation that reduces the affinity of MurA for A(2), were shown to be missense mutations in A(2) that increase the translation of the maturation protein. Because of the increased production of A(2), the por mutants have an attenuated infection cycle and reduced burst size, indicating that a delicate balance between assembled and unassembled A(2) levels regulates lysis timing.

Triazole-based inhibitors of geranylgeranyltransferase II

A small set of triazole bisphosphonates has been prepared and tested for the ability to inhibit geranylgeranyltransferase II (GGTase II). The compounds were prepared through use of click chemistry to assemble a central triazole that links a polar head group to a hydrophobic tail. The resulting compounds were tested for their ability to inhibit GGTase II in an in vitro enzyme assay and also were tested for cytotoxic activity in an MTT assay with the human myeloma RPMI-8226 cell line. The most potent enzyme inhibitor was the triazole with a geranylgeranyl tail, which suggests that inhibitors that can access the enzyme region that holds the isoprenoid tail will display greater activity.

Rab-geranylgeranyl transferase regulates glucose-stimulated insulin secretion from pancreatic β cells

A growing body of evidence implicates essential roles for small molecular weight G-proteins (e.g., Cdc42, Rac1, Arf6 and Rab3A and Rab27A) in islet β-cell function including glucose-stimulated insulin secretion (GSIS). One of the known mechanisms for optimal activation of small G-proteins involves post-translational prenylation, which is mediated by farnesyltransferase (FTase) and geranylgeranyl transferases (GGTases I and II). The FTase catalyzes incorporation of a 15-carbon farnesyl group while the GGTase mediates incorporation of a 20-carbon geranylgeranyl group into the C-terminal cysteines of G-proteins. The FTase, GGTase I and GGTase II prenylate Ras, Cdc42/Rac1, and Rab G-proteins, respectively. While considerable evidence exists on FTase/GGTase I-mediated regulation of GSIS, very little is known about GGTase II (also referred to as Rab GGTase; RGGT) and its regulatory proteins in the cascade of events leading to GSIS. Herein, we provide the first immunological evidence to suggest expression of α- and β-subunits of RGGT in clonal INS 832/13 β-cells, normal rat islets and human islets. Furthermore, Rab escort protein1 (REP1), which has been shown to be critical for prenylation of Rab G-proteins, is also expressed in these cells. Furthermore, evidence is presented to suggest that siRNA-mediated knockdown of α- or β-subunits of RGGT and REP1 markedly attenuates GSIS in INS 832/13 cells. These findings provide the first evidence in support of key roles for RGGT and its regulatory proteins in GSIS.

Breast cancer cell targeting by prenylation inhibitors elucidated in living animals with a bioluminescence reporter

PURPOSE

Inhibitors of protein prenylation, including prenyltransferase inhibitors and aminobisphosphonates such as zoledronic acid, are being investigated intensively as therapeutics in cancer and other diseases. Determining whether prenylation inhibitors directly or indirectly target tumor and/or host cells is key to understanding therapeutic mechanisms.

EXPERIMENTAL DESIGN

To determine which cell types can be targeted directly by distinct classes of prenylation inhibitors in vivo, we describe herein the development and implementation of a sensitive and pharmacologically specific bioluminescence-based imaging reporter that is inducible by prenylation inhibitors.

RESULTS

In mouse xenograft models of breast cancer, using reporter-bearing mammary fat pad- or bone-localized tumor cells, we show that a prenyltransferase inhibitor robustly induces reporter activity in vivo. In contrast, zoledronic acid, a bone-associated aminobisphosphonate that exerts adjuvant chemotherapeutic activity in patients with breast cancer, fails to induce reporter activity in tumor cells of either model.

CONCLUSIONS

Although a prenyltransferase inhibitor can directly target breast cancer cells in vivo, zoledronic acid and related aminobisphosphonates are likely to exert antitumor activity indirectly by targeting host cells. Accordingly, these findings shift attention toward the goal of determining which host cell types are targeted directly by aminobisphosphonates to exert adjuvant chemotherapeutic activity.

Preclinical metabolism of LB42908, a novel farnesyl transferase inhibitor, and its effects on the cytochrome P450 isozyme activities

Metabolism of LB42908, a novel farnesyl transferase inhibitor, was investigated for preclinical development. In vitro hepatic metabolism of LB42908 gave rise to at least 9 metabolites via phase I biotransformation pathways, which were characterized by HPLC-UV, LC-MS, and LC-MS/MS analyses. N-Dealkylation was shown to be a major phase I metabolic pathway. Species-specific in vitro metabolism of LB42908 was studied in liver fractions of rat, dog, monkey, and human. Order of metabolic stability is human≈dog>rat≈monkey in both S9 and microsomal fractions. Tissue-specific metabolism of LB42908 in various tissue homogenates of rats demonstrated that the liver was the major organ responsible for phase I metabolism of LB42908. The results from both qualitative and quantitative metabolism studies such as metabolic profiling and metabolic clearance indicated that dog would be the animal model of choice for preclinical toxicology studies. In addition, LB42908 was a potent CYP3A4 inhibitor in human liver microsomes and induced the activities of several CYP isozymes, implying that it has the potential for drug-drug interactions. Repeated dosing of LB42908 in rats did not significantly affect its own metabolism, indicating that long-term administration of LB42908 would not alter its pharmacokinetic profiles.

Targeting protein prenylation for cancer therapy

Protein farnesylation and geranylgeranylation, together referred to as prenylation, are lipid post-translational modifications that are required for the transforming activity of many oncogenic proteins, including some RAS family members. This observation prompted the development of inhibitors of farnesyltransferase (FT) and geranylgeranyl-transferase 1 (GGT1) as potential anticancer drugs. In this Review, we discuss the mechanisms by which FT and GGT1 inhibitors (FTIs and GGTIs, respectively) affect signal transduction pathways, cell cycle progression, proliferation and cell survival. In contrast to their preclinical efficacy, only a small subset of patients responds to FTIs. Identifying tumours that depend on farnesylation for survival remains a challenge, and strategies to overcome this are discussed. One GGTI has recently entered the clinic, and the safety and efficacy of GGTIs await results from clinical trials.

Identification and characterization of mechanism of action of P61-E7, a novel phosphine catalysis-based inhibitor of geranylgeranyltransferase-I

Small molecule inhibitors of protein geranylgeranyltransferase-I (GGTase-I) provide a promising type of anticancer drugs. Here, we first report the identification of a novel tetrahydropyridine scaffold compound, P61-E7, and define effects of this compound on pancreatic cancer cells. P61-E7 was identified from a library of allenoate-derived compounds made through phosphine-catalyzed annulation reactions. P61-E7 inhibits protein geranylgeranylation and blocks membrane association of geranylgeranylated proteins. P61-E7 is effective at inhibiting both cell proliferation and cell cycle progression, and it induces high p21(CIP1/WAF1) level in human cancer cells. P61-E7 also increases p27(Kip1) protein level and inhibits phosphorylation of p27(Kip1) on Thr187. We also report that P61-E7 treatment of Panc-1 cells causes cell rounding, disrupts actin cytoskeleton organization, abolishes focal adhesion assembly and inhibits anchorage independent growth. Because the cellular effects observed pointed to the involvement of RhoA, a geranylgeranylated small GTPase protein shown to influence a number of cellular processes including actin stress fiber organization, cell adhesion and cell proliferation, we have evaluated the significance of the inhibition of RhoA geranylgeranylation on the cellular effects of inhibitors of GGTase-I (GGTIs). Stable expression of farnesylated RhoA mutant (RhoA-F) results in partial resistance to the anti-proliferative effect of P61-E7 and prevents induction of p21(CIP1/WAF1) and p27(Kip1) by P61-E7 in Panc-1 cells. Moreover, stable expression of RhoA-F rescues Panc-1 cells from cell rounding and inhibition of focal adhesion formation caused by P61-E7. Taken together, these findings suggest that P61-E7 is a promising GGTI compound and that RhoA is an important target of P61-E7 in Panc-1 pancreatic cancer cells.

Inhibition of geranylgeranyl transferase-I decreases cell viability of HTLV-1-transformed cells

Human T-cell leukemia virus type-1 (HTLV-1) is the etiological agent of adult T-cell leukemia (ATL), an aggressive and highly chemoresistant malignancy. Rho family GTPases regulate multiple signaling pathways in tumorigenesis: cytoskeletal organization, transcription, cell cycle progression, and cell proliferation. Geranylgeranylation of Rho family GTPases is essential for cell membrane localization and activation of these proteins. It is currently unknown whether HTLV-1-transformed cells are preferentially sensitive to geranylgeranylation inhibitors, such as GGTI-298. In this report, we demonstrate that GGTI-298 decreased cell viability and induced G₂/M phase accumulation of HTLV-1-transformed cells, independent of p53 reactivation. HTLV-1-LTR transcriptional activity was inhibited and Tax protein levels decreased following treatment with GGTI-298. Furthermore, GGTI-298 decreased activation of NF-κB, a downstream target of Rho family GTPases. These studies suggest that protein geranylgeranylation contributes to dysregulation of cell survival pathways in HTLV-1-transformed cells.

Identification of inhibitors against Mycobacterium tuberculosis thiamin phosphate synthase, an important target for the development of anti-TB drugs

Tuberculosis (TB) continues to pose a serious challenge to human health afflicting a large number of people throughout the world. In spite of the availability of drugs for the treatment of TB, the non-compliance to 6–9 months long chemotherapeutic regimens often results in the emergence of multidrug resistant strains of Mycobacterium tuberculosis adding to the precariousness of the situation. This has necessitated the development of more effective drugs. Thiamin biosynthesis, an important metabolic pathway of M.tuberculosis, is shown to be essential for the intracellular growth of this pathogen and hence, it is believed that inhibition of this pathway would severely affect the growth of M.tuberculosis. In this study, a comparative homology model of M.tuberculosis thiamin phosphate synthase (MtTPS) was generated and employed for virtual screening of NCI diversity set II to select potential inhibitors. The best 39 compounds based on the docking results were evaluated for their potential to inhibit the MtTPS activity. Seven compounds inhibited MtTPS activity with IC₅₀ values ranging from 20 – 100 µg/ml and two of these exhibited weak inhibition of M.tuberculosis growth with MIC₉₉ values being 125 µg/ml and 162.5 µg/ml while one compound was identified as a very potent inhibitor of M.tuberculosis growth with an MIC₉₉ value of 6 µg/ml. This study establishes MtTPS as a novel drug target against M.tuberculosis leading to the identification of new lead molecules for the development of antitubercular drugs. Further optimization of these lead compounds could result in more potent therapeutic molecules against Tuberculosis.

New synthetic methodology for the construction of 7-substituted farnesyl diphosphate analogs

Through the use of a 1,2-metalate rearrangement, six 7-substituted farnesol analogs were generated in a concise manner. This new synthetic route allowed us to quickly prepare several diverse farnesyl diphosphate analogs with interesting biological activities against mammalian protein-farnesyl transferase.

The gunmetal mouse reveals Rab geranylgeranyl transferase to be the major molecular target of phosphonocarboxylate analogues of bisphosphonates

The described ability of phosphonocarboxylate analogues of bisphosphonates (BPs) to inhibit Rab geranylgeranyl transferase (RGGT) is thought to be the mechanism underlying their cellular effects, including their ability to reduce macrophage cell viability and to inhibit osteoclast-mediated resorption. However, until now the possibility that at least some of the effects of these drugs may be mediated through other targets has not been excluded. Since RGGT is the most distal enzyme in the process of Rab prenylation, it has not proved possible to confirm the mechanism underlying the effects of these drugs by adding back downstream intermediates of the mevalonate pathway, the approach used to demonstrate that bisphosphonates act through this pathway. We now confirm that RGGT is the major pharmacological target of phosphonocarboxylates by using several alternative approaches. Firstly, analysis of several different phosphonocarboxylate drugs demonstrates a very good correlation between the ability of these drugs to inhibit RGGT with their ability to: (a) reduce macrophage cell viability; (b) induce apoptosis; and (c) induce vacuolation in rabbit osteoclasts. Secondly, we have found that cells from the gunmetal (gm/gm) mouse, which bear a homozygous mutation in RGGT that results in ~80% reduced activity of this enzyme compared to wild-type or heterozygous mice, are more sensitive to the effects of active phosphonocarboxylates (including reducing macrophage cell viability, inhibiting osteoclast formation and inhibiting fluid-phase endocytosis), confirming that these effects are mediated through inhibition of RGGT. In conclusion, these data demonstrate that all of the pharmacological effects of phosphonocarboxylates found thus far appear to be mediated through the specific inhibition of RGGT, highlighting the potential therapeutic value of this class of drugs.

Contribution of Ras farnesyl transferase, MAP kinase and cytochrome P-450 metabolites to endothelin-1 induced hypertension

Endothelin 1 (ET-1) is vasoactive peptide that acts via ET-A receptors coupling inducing vascular smooth muscle cell proliferation and contraction. ET-1 is involved in the development and maintenance of hypertension. Aim of this study was to determine the contribution of Ras farnesyl transferase, mitogen activated protein kinase (MAP kinase) and cytochrome P¬450 (CYP450) metabolites to ET-1 induced hypertension. ET-1 (5 pmol/kg per minute) was chronically infused into to the jugular vein by use of mini-osmotic pump for 9 days in male Sprague-Dawley rats. Mean arterial blood pressure (MABP) in ET-1-treated rats was 154±2 mm Hg (hypertensive rats) compared with 98±3 mm Hg in control (normotensive) rats. Infusion of Ras farnesyl transferase inhibitor FPTIII (138 ng/min), MAP kinase inhibitor PD-98059 (694 ng/min) and CYP450 inhibitor 17-ODYA (189 ng/min) significantly attenuated MABP to 115±2.5 mm Hg, 109±3 mm Hg and 118±1.5 mm Hg, respectively. These results suggest that CYP-450 metabolites and Ras/MAP kinase pathway contribute to the development of ET-1 induced hypertension. Further investigation has to be done to confirm whether activation of RAS/MAP kinase pathway by arachidonic acid metabolites plays an important role in the development of ET-1 induced hypertension.

Inhibition of geranylgeranylation mediates sensitivity to CHOP-induced cell death of DLBCL cell lines

Prenylation is a post-translational hydrophobic modification of proteins, important for their membrane localization and biological function. The use of inhibitors of prenylation has proven to be a useful tool in the activation of apoptotic pathways in tumor cell lines. Rab geranylgeranyl transferase (Rab GGT) is responsible for the prenylation of the Rab family. Overexpression of Rab GGTbeta has been identified in CHOP refractory diffuse large B cell lymphoma (DLBCL). Using a cell line-based model for CHOP resistant DLBCL, we show that treatment with simvastatin, which inhibits protein farnesylation and geranylgeranylation, sensitizes DLBCL cells to cytotoxic treatment. Treatment with the farnesyl transferase inhibitor FTI-277 or the geranylgeranyl transferase I inhibitor GGTI-298 indicates that the reduction in cell viability was restricted to inhibition of geranylgeranylation. In addition, treatment with BMS1, a combined inhibitor of farnesyl transferase and Rab GGT, resulted in a high cytostatic effect in WSU-NHL cells, demonstrated by reduced cell viability and decreased proliferation. Co-treatment of BMS1 or GGTI-298 with CHOP showed synergistic effects with regard to markers of apoptosis. We propose that inhibition of protein geranylgeranylation together with conventional cytostatic therapy is a potential novel strategy for treating patients with CHOP refractory DLBCL.

Combining an FPTase inhibitor with cisplatin facilitates induction of apoptosis in human A549 lung cancer cells

Despite great efforts to develop efficacious curative treatments, the prognosis for lung cancer patients is poor. In the present study we compared the effects of cisplatin (CP), a strong DNA damaging compound, with those of roscovitine (ROSC), a selective inhibitor of cyclin-dependent kinases (CDKs), on wt p53-positive human A549 lung adenocarcinoma cells harboring a mutated K-RAS gene. Asynchronously growing A549 cells were relatively resistant to CP treatment for 24 h, but after exposure to CP at sufficiently high doses (> or = 20 microM) an accumulation of S-arrested cells was observed. However, after post-incubation of CP-treated cells in a drug-free medium for a further 48 h the number of living cells was markedly reduced. Combining CP with L-744,832, a small molecule FPTase inhibitor (FTI), slightly enhanced its anti-proliferative effect. Interestingly, FTI sensitized A549 cells to CP-induced apoptosis. ROSC inhibited A549 cells at the G/M transition, resulting in a marked decrease in the number of viable cells within 24 h, and prolonged treatment with ROSC for 48 h reduced the frequency of living cells by inducing apoptosis. The effects of ROSC (unlike those of CP) were more strongly enhanced by inhibition of the Ras protein processing pathway. Our preliminary results indicate that functional p53 contributes to the outcome of the therapy in human A549 cells by certain anti-cancer drugs.

Inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity and of Ras farnesylation mediate antitumor effects of anandamide in human breast cancer cells

The endocannabinoid system regulates cell proliferation in human breast cancer cells. Recently, we described that a metabolically stable anandamide analog, 2-methyl-2'-F-anandamide, by activation of CB1 receptors significantly inhibited cell proliferation of human breast cancer cell lines. In this study, we observed that the activation of the CB1 receptor, in two human mammary carcinoma cell lines, MDA-MB-231 and MCF7, caused the inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity due to a reduction of HMG-CoA reductase transcript levels. The decrease of HMG-CoA reductase activity induced the inhibition of the prenylation of proteins, in particular of the farnesylation of Ras oncogenic protein involved in cell proliferation of these cell lines. We suggest that the inhibitory effect of anandamide analog on tumor cell proliferation could be related to the inhibition of Ras farnesylation.

Inhibitory mechanism of novel inhibitors of UDP-N-acetylglucosamine enolpyruvyl transferase from Haemophilus influenzae

Bacterial UDP-N-acetylglucosamine enolpyruvyl transferase (MurA) catalyzes the transfer of enolpyruvate from phosphoenolphyruvate (PEP) to uridine diphospho-N-acetylglucosamine (UNAG), which is the first step of bacterial cell wall synthesis. We identified thimerosal, thiram, and ebselen as effective inhibitors of Heamophilus influenzae MurA by screening a chemical library that consisted of a wide range of bioactive compounds. When MurA was preincubated with these inhibitors, their 50% inhibitory concentrations (IC50s) were found to range from 0.1 to 0.7 microM. In particular, thimerosal suppressed the growth of several different Gram-negative bacteria such as Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium at a concentration range of 1-2 microg/ml. These inhibitors covalently modified the cysteine residue near the active site of MurA. This modification changed the open conformation of MurA to a more closed configuration, which may have prevented the necessary conformational change from occurring during the enzyme reaction.

Meroterpenes from Dichrostachys cinerea inhibit protein farnesyl transferase activity

Eighteen new meroterpene derivatives, dichrostachines A-R (1-18), have been isolated from the root and stem barks of Dichrostachys cinerea, and their structures determined by spectroscopic means and molecular modeling. From a biosynthetic standpoint these compounds arise from a Diels-Alder reaction between a labdane diene of the raimonol type and a flavonoid B-ring-derived quinone. The hypothesis was tested by the partial synthesis of similar compounds by simply mixing methyl communate and a synthetic flavonoid quinone. The hemisynthetic compounds were shown by NMR to have configurations different from those of the natural products, thus allowing a refinement of the biosynthesis hypothesis. Most of the compounds were assayed for their ability to inhibit the enzyme protein farnesyl transferase. The most active compounds exhibited IC50 and cytotoxicity values in the 1 microM range.

Farnesyl Transferase Inhibitors for Patients with Lung Cancer

The ras family of genes have been identified as potential targets for therapeutic intervention because of somatic mutations in different human cancers. They are mutated in non-small cell lung cancer (NSCLC) approximately 20% of the time. The enzyme farnesyl transferase is involved in posttranslational modification of the ras proteins by covalently linking a farnesyl group to the ras protein. This permits the ras protein to be translocated to the surface membrane, allowing the protein to be involved in signaling for increased proliferation and inhibition of apoptosis. The class of farnesyl transferase inhibitors is designed to block farnesylation and prevent the mature ras signaling and thus inhibit cell proliferation and facilitate apoptosis. Multiple agents that inhibit farnesylation have been developed, and two farnesyl transferase inhibitors have been tested in patients with lung cancer in three Phase II trials. R115777 has been studied in patients with NSCLC and in patients with relapsed small cell lung cancer (SCLC) after chemotherapy. There has been a single trial of L-778,123 in patients with untreated NSCLC. No objective tumor responses in patients with stage IIIB/IV NSCLC were seen in these studies. There were also no objective responses among the 22 patients with relapsed SCLC treated with R115777. The median survival for the 44 patients with NSCLC treated with R115777 was approximately 8 months, whereas it was 11 months for the 23 patients treated with L-778,123. R115777 and L-778,123 were well tolerated in these studies but showed no significant activity as single-agent therapy in relapsed SCLC or untreated NSLC.

Farnesyltransferase inhibitors as radiation sensitizers

PURPOSE

The inhibition of activated Ras combined with radiotherapy was identified as a potential method for radiosensitization.

MATERIALS AND METHODS

Immunoblotting was used to control for prenylation inhibition of the respective Ras isoforms and for changes in activity of downstream proteins. Clonogenic assays with human and rodent tumour cell lines and transfected cell lines served for the testing of radiosensitivity. Xenograft tumours were treated with farnesyl transferase inhibitors and radiation and assayed for ex vivo plating efficiency, regrowth of tumours and EF5 staining for detection of hypoxia. Concurrent treatment with L-778,123 and radiotherapy was performed in non-small cell lung cancer (NSCLC) and head and neck cancer (HNC) patients.

RESULTS

Blocking the prenylation of Ras proteins in cell lines with Ras activated by mutations or receptor signalling resulted in radiation sensitization in in vitro and in vivo. The PI3 kinase downstream pathway was identified as a contributor to Ras-mediated radiation resistance. Additionally, increased oxygenation of xenograft tumours was observed after FTI treatment. Combined treatment in a phase I study was safe and effective in NSCLC and HNC.

CONCLUSIONS

Tumour cells with activated Ras were sensitized to radiation. Unravelling the underlying mechanisms promises to lead to even more specific drugs with higher potency and safety.

Farnesyl Transferase Inhibitors Enhance Death Receptor Signals and Induce Apoptosis in Multiple Myeloma Cells

Multiple myeloma is an incurable plasma cell malignancy in which Ras may be constitutively active either via interleukin-6 (IL-6) receptor signaling or by mutation. Inactivation of Ras may be achieved with farnesyl transferase (FTase) inhibitors a class of drugs which have shown promise in clinical trials particularly in patients with acute leukemia. This report investigates the efficacy of two distinct classes of FTase inhibitors in diverse myeloma cell lines and primary isolates. While Ras signaling has traditionally been linked to myeloma cell growth, we found that these compounds also potently triggered cell death. Death induced by perillic acid (PA) was caspase dependent without evidence of death receptor activation. Apoptosis was associated with mitochondrial membrane depolarization and activation of caspase-9 and 3 but proceeded despite over-expression of Bcl-XL a known correlate of relapsed and chemorefractory myeloma. In addition, Fas ligand and TRAIL mediated apoptosis was potentiated in death receptor resistant (U266) and sensitive (RPMI 8226/S) cell lines. Of clinical relevance, the FTase inhibitor R115777 induced cell death in myeloma lines at doses observed in clinical trials. Furthermore, both R115777 and PA induced cell death in primary isolates with relative specificity. Taken together these preclinical data provide evidence that FTase inhibitors may be an effective therapeutic modality for the treatment of multiple myeloma.

Rho GTPase signaling and PTH 3-34, but not PTH 1-34, maintain the actin cytoskeleton and antagonize bisphosphonate effects in mouse osteoblastic MC3T3-E1 cells

Cytoskeletal elements are critical for cell morphology and signal transduction, and are involved in many cellular processes including motility, intracellular transport, and differentiation. Small GTP-binding proteins (G proteins) of the Ras family, such as RhoA, influence various elements of the cytoskeleton. RhoA stabilizes the actin cytoskeleton and promotes formation of focal adhesions. We found previously that RhoA is expressed in osteoblastic cells and is translocated to the plasma membrane and activated by PTH 1-34 as well as by Nleu(8,18) Tyr(34) PTH 3-34 amide, a PTH analog that does not increase cAMP. We therefore investigated effects of manipulating RhoA on the actin cytoskeleton of osteoblastic MC3T3-E1 cells. Three inhibitors were used: 1) GGTI-2166, a geranylgeranyl transferase I inhibitor that prevents the isoprenylation and membrane translocation of RhoA, 2) Y-27632, a Rho kinase inhibitor, and 3) alendronate, a nitrogen (N)-containing bisphosphonate that reduces intracellular geranylgeranylpyrophosphate through inhibiting farnesyl pyrophosphate synthase. To increase RhoA activity, we used the geranylgeranyl group donor geranylgeraniol (GGOH), and a constitutively active RhoA. The F-actin cytoskeleton and focal adhesions (FA) were visualized with rhodamine-phalloidin and fluorescent anti-vinculin antibodies, respectively. Cells were imaged with confocal microscopy. Actin stress fiber density, edge actin bundle density, focal adhesion density, cellular area and circularity (a morphological descriptor relating area and perimeter) were quantified by a program developed with Matlab software. GGTI-2166, Y-27632, and alendronate reduced actin stress fibers, FA density, and FA size, but had no effect on edge actin bundle density, cellular area, or circularity. GGOH completely antagonized the effects of alendronate, but did not significantly affect responses to GGTI-2166 or Y-27632. Constitutively active RhoA antagonized the effects of alendronate and GGTI-2166, but not those of Y-27632. The effects of alendronate were also antagonized by Nleu(8,18) Tyr(34) PTH 3-34 amide, but not by PTH 1-34. The results indicate that RhoA is involved in the maintenance of stress fibers and focal adhesions in osteoblastic cells, that PTH can affect this pathway independently of cAMP, and that a N-containing bisphosphonate can affect the actin cytoskeleton and focal adhesions through actions on geranylgeranyl groups and potentially through RhoA. In view of the importance of the actin cytoskeleton, the findings constitute evidence that N-containing bisphosphonates, when they attain certain concentrations, have effects on osteoblasts that could influence bone remodeling.

Clinical Activity of Farnesyl Transferase Inhibitors in Hematologic Malignancies: Possible Mechanisms of Action

Farnesyl transferase inhibitors (FTIs) are a novel class of anti-cancer agents that competitively inhibit farnesyl protein transferase (FTase). Initially developed to inhibit the prenylation necessary for Ras activation, their mechanism of action seems to be more complex, involving other proteins unrelated to Ras. FTIs have been developed and tested across a wide range of human cancers. At least 3 agents within this family have been investigated in hematologic malignancies. These are tipifarnib (R115777, Zarnestra), lonafarnib (SCH66336, Sarasar), both of which are orally administered, and BMS-214662, which is given intravenously. Preliminary results from clinical trials demonstrate enzyme target inhibition, a favorable toxicity profile and promising efficacy. Ongoing studies will better determine their mechanism of action and the role of combination with other agents, defining their place in the therapeutic arsenal of hematologic disorders.

Gibberellin precursor is involved in spore germination in the moss Physcomitrella patens

Gibberellins are ent-kaurene derived phytohormones that are involved in seed germination, stem elongation, and flower induction in seed plants, as well as in antheridia formation and spore germination in ferns. Although ubiquitous in vascular plants, the occurrence and potential function(s) of gibberellins in bryophytes have not yet been resolved. To determine the potential role of gibberellin and/or gibberellin-like compounds in mosses, the effect of AMO-1618 on spores of Physcomitrella patens (Hedw.) B.S.G. was tested. AMO-1618, which inhibited ent-kaurene and gibberellin biosynthesis in angiosperms, also inhibited the bifunctional copalyl diphosphate synthase (E.C. 5.5.1.13)/ent-kaurene synthase (E.C. 4.2.3.19) of P. patens. AMO-1618 also caused a decrease in spore germination rates of P. patens, and this inhibitory effect was less pronounced in the presence of ent-kaurene. These results suggest that ent-kaurene biosynthesis is required by P. patens spores to germinate, implying the presence of gibberellin-like phytohormones in mosses.

Novel approaches in anti-angiogenic treatment targeting endothelial F-actin: a new anti-angiogenic strategy?

As a functional blood supply is crucial for growth of solid tumors, the development of anticancer agents to inhibit the formation of new tumor blood vessels is an area of extensive research. Endothelial cell motility driven by the dynamics of the cytoskeleton is a key feature of angiogenesis. Agents that preferentially target endothelial tubulin are well established, and inhibition of the endothelial actin dynamics appears to be another promising anti-angiogenic strategy. Remodeling of the actin cytoskeleton is regulated by several pathways involving a large number of signaling proteins. Therefore, therapeutic strategies for the modulation of actin dynamics include agents that target the actin cytoskeleton directly, as well as inhibitors of actin binding proteins and regulators in upstream pathways. This review provides an overview of the regulation of the actin cytoskeleton and proteins that could potentially be targeted by therapeutic agents. In addition, an outline of promising agents, which includes recombinant proteins, endogenous effectors and treatment regimes that exert anti-angiogenic effects partly mediated by affecting endothelial actin dynamics is provided.

Mass spectrometric studies of potent inhibitors of farnesyl protein transferase--detection of pentameric noncovalent complexes

Farnesyl protein transferase (FPT) inhibition is an interesting and promising approach to noncytotoxic anticancer therapy. Research in this area has resulted in several orally active compounds that are in clinical trials. Electrospray ionization (ESI) time-of-flight mass spectrometry (TOF-MS) was used for the direct detection of a 95 182 Da pentameric noncovalent complex of alpha/beta subunits of FPT containing Zn, farnesyl pyrophosphate (FPP) and SCH 66336, a compound currently undergoing phase III clinical trials as an anticancer agent. It was noted that the desalting of protein samples was an important factor in the detection of the complex. This study demonstrated that the presence of FPP in the system was necessary for the detection of the FPT-inhibitor complex. No pentameric complex was detected in the spectrum when the experiment was carried out in the absence of the FPP. An indirect approach was also applied to confirm the noncovalent binding of SCH 66336 to FPT by the use of an off-line size exclusion chromatography followed by liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) for the detection of the inhibitor.

A combined treatment of HeLa cells with the farnesyl protein transferase inhibitor L-744,832 and cisplatin significantly increases the therapeutic effect as compared to cisplatin monotherapy

Activating mutations of Ras that frequently occur during malignant transformation, enhance growth-promoting signal transduction, allowing cells to bypass stringent control of cell cycle progression, thereby rendering them highly proliferative. Abundantly expressed c-Ha-ras protein in human cervical HeLa cells is farnesylated and attached to the plasma membrane, inducing enhanced signal transduction. Exposure of HeLa cells to cisplatin very efficiently inhibits cell proliferation and induces apoptosis. Unfortunately, high doses of cisplatin are strongly cytotoxic, therefore, an alternative therapeutic strategy allowing dose reduction of cisplatin by inhibition of farnesylation could increase the curative effects of cisplatin, thereby benefiting cancer patients. We used two inhibitors of farnesyl protein transferase (FPTase), FTI, and L-744,832, to sensitize HeLa cells to the action of cisplatin. The combined administration of cisplatin and inhibitors of FPTase increased the cytostatic potency of cisplatin. L-744,832 exhibited a stronger synergistic effect in combination with cisplatin than FTI. Moreover, the efficiency of the combined therapy strongly depended on the treatment regimen: The highest efficiency was achieved after combined treatment for 24 h and post-incubation with an inhibitor of FPTase for 48 h. Following this optimized treatment, apoptosis was induced in approximately 50% of HeLa cells treated with 1 microM cisplatin, representing approximately a threefold increase as compared to cisplatin monotherapy. Combined treatment of HeLa cells with cisplatin and inhibitors of FPTase significantly increases the efficacy of the therapy and allows to reduce the dose of cisplatin. Importantly, best therapeutic effects can be achieved by post-treatment with inhibitors of FPTase.

Alisiaquinones and alisiaquinol, dual inhibitors of Plasmodium falciparum enzyme targets from a New Caledonian deep water sponge

Four new meroterpenes, alisiaquinones A-C (1-3) and alisiaquinol (4), were isolated from a New Caledonian deep water sponge. Their structures and relative stereochemistry were elucidated by spectroscopic data analysis. They are related to xestoquinone, but showed unusual substitution on a tetrahydrofuran junction. They displayed micromolar range activity on two enzymatic targets of importance for the control of malaria, the plasmodial kinase Pfnek-1 and a protein farnesyl transferase, as well as on different chloroquine-sensitive and -resistant strains of Plasmodium falciparum. Alisiaquinone C displayed a submicromolar activity on P. falciparum and a competitive selectivity index on the different plasmodial strains.

Regulation of carotenoid biosynthetic genes expression and carotenoid accumulation in the green alga Haematococcus pluvialis under nutrient stress conditions

Haematococcus pluvialis, a green alga, accumulates carotenoids, predominantly astaxanthin, when exposed to stress conditions. In the present work, changes in the pigment profile and expression of carotenogenic genes under various nutrient stress conditions and their regulation were studied. Nutrient stress and higher light intensity in combination with NaCl/sodium acetate (SA) enhanced total carotenoid and total astaxanthin content to 32.0 and 24.5 mg g(-1) of dry biomass, respectively. Expression of carotenogenic genes, phytoene synthase (PSY), phytoene desaturase (PDS), lycopene cyclase (LCY), beta-carotene ketolase (BKT), and beta-carotene hydroxylase (CHY) were up-regulated under all the stress conditions studied. However, the extent of expression of carotenogenic genes varied with stress conditions. Nutrient stress and high light intensity induced expression of astaxanthin biosynthetic genes, BKT and CHY, transiently. Enhanced expression of these genes was observed with SA and NaCl/SA, while expression was delayed with NaCl. The maximum content of astaxanthin recorded in cells grown in medium with SA and NaCl/SA correlated with the expression profile of the astaxanthin biosynthetic genes. Studies using various inhibitors indicated that general carotenogenesis and secondary carotenoid induction were regulated at both the transcriptional and the cytoplasmic translational levels. The induction of general carotenoid synthesis genes was independent of cytoplasmic protein synthesis while BKT gene expression was dependent on de novo protein synthesis.

Geranylgeranyltransferase I inhibitors target RalB to inhibit anchorage-dependent growth and induce apoptosis and RalA to inhibit anchorage-independent growth

Geranylgeranyltransferase I inhibitors (GGTIs) are presently undergoing advanced preclinical studies and have been shown to disrupt oncogenic and tumor survival pathways, to inhibit anchorage-dependent and -independent growth, and to induce apoptosis. However, the geranylgeranylated proteins that are targeted by GGTIs to induce these effects are not known. Here we provide evidence that the Ras-like small GTPases RalA and RalB are exclusively geranylgeranylated and that inhibition of their geranylgeranylation mediates, at least in part, the effects of GGTIs on anchorage-dependent and -independent growth and tumor apoptosis. To this end, we have created the corresponding carboxyl-terminal mutants that are exclusively farnesylated and verified that they retain the subcellular localization and signaling activities of the wild-type geranylgeranylated proteins and that Ral GTPases do not undergo alternative prenylation in response to GGTI treatment. By expressing farnesylated, GGTI-resistant RalA and RalB in Cos7 cells and human pancreatic MiaPaCa2 cancer cells followed by GGTI-2417 treatment, we demonstrated that farnesylated RalB, but not RalA, confers resistance to the proapoptotic and anti-anchorage-dependent growth effects of GGTI-2417. Conversely, farnesylated RalA but not RalB expression renders MiaPaCa2 cells less sensitive to inhibition of anchorage-independent growth. Furthermore, farnesylated RalB, but not RalA, inhibits the ability of GGTI-2417 to suppress survivin and induce p27(Kip1) protein levels. We conclude that RalA and RalB are important, functionally distinct targets for GGTI-mediated tumor apoptosis and growth inhibition.

[Acute lymphoblastic leukemia with Philadelphia chromosome: treatment with kinase inhibitors]

Distinct clinicopathologic acute lymphoblastic leukemia (ALL) entities have been identified, resulting in the adoption of risk-oriented treatment approaches. In Philadelphia chromosome-positive ALL, the optimal treatment requires the addition of BCR-ABL tyrosine kinase inhibitors, as imatinib. Despite advances, the outcome remains poor, and novel agents are desperately required. The emergence of resistance to the Bcr-Abl inhibitor imatinib mesylate in patients with Philadelphia chromosome-positive (Ph+) ALL has prompted the development of second-generation compounds active against mutant forms, including dasatinib and nilotinib.

New approaches to progeria

Progeria (Hutchinson-Gilford progeria syndrome) is a rare genetic disorder that offers considerable insight into the biology of premature aging. This review summarizes the clinical characteristics of this disease and the underlying mutation in the lamin A (LMNA) gene that results in this phenotype. Modifications in the processing of prelamin A through alterations in farnesylation are detailed, because this pathway offers a possible drug target. Finally, discussion of an ongoing clinical trial for these children, including possible parameters for evaluation, are discussed. In the span of less than a decade, this disease has progressed from an interesting phenotype to one in which the gene defect has been identified, animal models have been created and tested with drugs that target the primary disease pathway, and significant clinical baseline data for the support of a clinical trial have been obtained.

16-Aza-ent-beyerane and 16-Aza-ent-trachylobane: potent mechanism-based inhibitors of recombinant ent-kaurene synthase from Arabidopsis thaliana

The secondary ent-beyeran-16-yl carbocation (7) is a key branch point intermediate in mechanistic schemes to rationalize the cyclic structures of many tetra- and pentacyclic diterpenes, including ent-beyerene, ent-kaurene, ent-trachylobane, and ent-atiserene, presumed precursors to >1000 known diterpenes. To evaluate these mechanistic hypotheses, we synthesized the heterocyclic analogues 16-aza-ent-beyerane (12) and 16-aza-ent-trachylobane (13) by means of Hg(II)- and Pb(IV)-induced cyclizations onto the Delta12 double bonds of tricyclic intermediates bearing carbamoylmethyl and aminomethyl groups at C-8. The 13,16-seco-16-norcarbamate (20a) was obtained from ent-beyeran-16-one oxime (17) by Beckmann fragmentation, hydrolysis, and Curtius rearrangement. The aza analogues inhibited recombinant ent-kaurene synthase from Arabidopsis thaliana (GST-rAtKS) with inhibition constants (IC50 = 1 x 10-7 and 1 x 10-6 M) similar in magnitude to the pseudo-binding constant of the bicyclic ent-copalyl diphosphate substrate (Km = 3 x 10-7 M). Large enhancements of binding affinities (IC50 = 4 x 10-9 and 2 x 10-8 M) were observed in the presence of 1 mM pyrophosphate, which is consistent with a tightly bound ent-beyeranyl+/pyrophosphate- ion pair intermediate in the cyclization-rearrangement catalyzed by this diterpene synthase. The weak inhibition (IC50 = 1 x 10-5 M) exhibited by ent-beyeran-16-exo-yl diphosphate (11) and its failure to undergo bridge rearrangement to kaurene appear to rule out the covalent diphosphate as a free intermediate. 16-Aza-ent-beyerane is proposed as an effective mimic for the ent-beyeran-16-yl carbocation with potential applications as an active site probe for the various ent-diterpene cyclases and as a novel, selective inhibitor of gibberellin biosynthesis in plants.

Discovery of 1,4-dihydroxy-2-naphthoate [corrected] prenyltransferase inhibitors: new drug leads for multidrug-resistant gram-positive pathogens

Since utilization of menaquinone in the electron transport system is a characteristic of Gram-positive organisms, the 1,4-dihydroxy-2-naphthoate prenyltransferase (MenA) inhibitors 1a and 2a act as selective antibacterial agents against organisms such as methicillin-resistant Stapylococcus aureus (MRSA), Staphylococcus epidermidis (MRSE), and Mycobacterium spp. Growth of drug-resistant Gram-positive organisms was sensitive to the MenA inhibitors, indicating that menaquinone synthesis is a valid new drug target in Gram-positive organisms.

GGTase-I deficiency reduces tumor formation and improves survival in mice with K-RAS-induced lung cancer

Protein geranylgeranyltransferase type I (GGTase-I) is responsible for the posttranslational lipidation of CAAX proteins such as RHOA, RAC1, and cell division cycle 42 (CDC42). Inhibition of GGTase-I has been suggested as a strategy to treat cancer and a host of other diseases. Although several GGTase-I inhibitors (GGTIs) have been synthesized, they have very different properties, and the effects of GGTIs and GGTase-I deficiency are unclear. One concern is that inhibiting GGTase-I might lead to severe toxicity. In this study, we determined the effects of GGTase-I deficiency on cell viability and K-RAS-induced cancer development in mice. Inactivating the gene for the critical beta subunit of GGTase-I eliminated GGTase-I activity, disrupted the actin cytoskeleton, reduced cell migration, and blocked the proliferation of fibroblasts expressing oncogenic K-RAS. Moreover, the absence of GGTase-I activity reduced lung tumor formation, eliminated myeloproliferative phenotypes, and increased survival of mice in which expression of oncogenic K-RAS was switched on in lung cells and myeloid cells. Interestingly, several cell types remained viable in the absence of GGTase-I, and myelopoiesis appeared to function normally. These findings suggest that inhibiting GGTase-I may be a useful strategy to treat K-RAS-induced malignancies.

Farnesyl protein transferase and tumor cell growth inhibitory activities of lipiferolide isolated from Liriodendron tulipifera

The methanolic extract of the leaves of Liriodendron tulipifera was found to show inhibitory activity towards farnesyl protein transferase (FPTase). Bioassay-guided fractionation of the methanolic extract resulted in the isolation of lipiferolide, an inhibitor of FPTase. This compound inhibited the FPTase activity in a dose-dependent manner, and showed cell growth inhibitory activity against several tumor cells.