Inhibitors of prenylation of Ras and other G-proteins and their application as therapeutics

Normalization of the tumor microenvironment by harnessing vascular and immune modulation to achieve enhanced cancer therapy

Solid tumors are complex entities that actively shape their microenvironment to create a supportive environment for their own growth. Angiogenesis and immune suppression are two key characteristics of this tumor microenvironment. Despite attempts to deplete tumor blood vessels using antiangiogenic drugs, extensive vessel pruning has shown limited efficacy. Instead, a targeted approach involving the judicious use of drugs at specific time points can normalize the function and structure of tumor vessels, leading to improved outcomes when combined with other anticancer therapies. Additionally, normalizing the immune microenvironment by suppressing immunosuppressive cells and activating immunostimulatory cells has shown promise in suppressing tumor growth and improving overall survival. Based on these findings, many studies have been conducted to normalize each component of the tumor microenvironment, leading to the development of a variety of strategies. In this review, we provide an overview of the concepts of vascular and immune normalization and discuss some of the strategies employed to achieve these goals.

Targeting protein modifications in metabolic diseases: molecular mechanisms and targeted therapies

The ever-increasing prevalence of noncommunicable diseases (NCDs) represents a major public health burden worldwide. The most common form of NCD is metabolic diseases, which affect people of all ages and usually manifest their pathobiology through life-threatening cardiovascular complications. A comprehensive understanding of the pathobiology of metabolic diseases will generate novel targets for improved therapies across the common metabolic spectrum. Protein posttranslational modification (PTM) is an important term that refers to biochemical modification of specific amino acid residues in target proteins, which immensely increases the functional diversity of the proteome. The range of PTMs includes phosphorylation, acetylation, methylation, ubiquitination, SUMOylation, neddylation, glycosylation, palmitoylation, myristoylation, prenylation, cholesterylation, glutathionylation, S-nitrosylation, sulfhydration, citrullination, ADP ribosylation, and several novel PTMs. Here, we offer a comprehensive review of PTMs and their roles in common metabolic diseases and pathological consequences, including diabetes, obesity, fatty liver diseases, hyperlipidemia, and atherosclerosis. Building upon this framework, we afford a through description of proteins and pathways involved in metabolic diseases by focusing on PTM-based protein modifications, showcase the pharmaceutical intervention of PTMs in preclinical studies and clinical trials, and offer future perspectives. Fundamental research defining the mechanisms whereby PTMs of proteins regulate metabolic diseases will open new avenues for therapeutic intervention.

Metabolic Regulation of Human Pluripotent Stem Cell-Derived Cardiomyocyte Maturation

PURPOSE OF REVIEW

This review summarizes the important role that metabolism plays in driving maturation of human pluripotent stem cell-derived cardiomyocytes.

RECENT FINDINGS

Human pluripotent stem cell-derived cardiomyocytes provide a model system for human cardiac biology. However, these models have been unable to fully recapitulate the maturity observed in the adult heart. By simulating the glucose to fatty acid transition observed in neonatal mammals, human pluripotent stem cell-derived cardiomyocytes undergo structural and functional maturation also accompanied by transcriptional changes and cell cycle arrest. The role of metabolism in energy production, signaling, and epigenetic modifications illustrates that metabolism and cellular phenotype are intimately linked. Further understanding of key metabolic factors driving cardiac maturation will facilitate the generation of more mature human pluripotent stem cell-derived cardiomyocyte models. This will increase our understanding of cardiac biology and potentially lead to novel therapeutics to enhance heart function.

BAI, a novel Cdk inhibitor, enhances farnesyltransferase inhibitor LB42708-mediated apoptosis in renal carcinoma cells through the downregulation of Bcl-2 and c-FLIP (L)

Previously, we reported the potential of a novel Cdk inhibitor, 2-[1,1'-biphenyl]-4-yl-N-[5-(1,1-dioxo-1λ6-isothiazolidin-2-yl)-1H-indazol-3-yl]acetamide (BAI) as a cancer chemotherapeutic agent. In this study, we investigated mechanisms by which BAI modulates FTI-mediated apoptosis in human renal carcinoma Caki cells. BAI synergizes with FTI to activate DEVDase, cleavage of poly ADP-ribose polymerase (PARP), and degradation of various anti-apoptotic proteins in Caki cells. BAI plus LB42708-induced apoptosis was inhibited by pretreatment with pan-caspase inhibitor, z-VAD-fmk, but not by overexpression of CrmA. The ROS scavenger, N-acetylcysteine (NAC) did not reduce BAI plus LB4270-induced apoptosis. Co-treatment of BAI and LB42708 reduced the mitochondrial membrane potential (MMP, ∆Ψm) in a time-dependent manner, and induced release of AIF and cytochrome c from mitochondria in Caki cells. Furthermore, BAL plus LB42708 induced downregulation of anti-apoptotic proteins [c-FLIP (L), c-FLIP (s), Bcl-2, XIAP, and Mcl-1 (L)]. Especially, we found that BAI plus LB42708-induced apoptosis was significantly attenuated by overexpression of Bcl-2 and partially blocked by overexpression of c-FLIP (L). Taken together, our results show that the activity of BAI plus LB42708 modulate multiple components in apoptotic response of human renal Caki cells, and indicate a potential as combinational therapeutic agents for preventing cancer such as renal carcinoma.

Small G Proteins in the Cardiovascular System: Physiological and Pathological Aspects

Small G proteins exist in eukaryotes from yeast to human and constitute the Ras superfamily comprising more than 100 members. This superfamily is structurally classified into five families: the Ras, Rho, Rab, Arf, and Ran families that control a wide variety of cell and biological functions through highly coordinated regulation processes. Increasing evidence has accumulated to identify small G proteins and their regulators as key players of the cardiovascular physiology that control a large panel of cardiac (heart rhythm, contraction, hypertrophy) and vascular functions (angiogenesis, vascular permeability, vasoconstriction). Indeed, basal Ras protein activity is required for homeostatic functions in physiological conditions, but sustained overactivation of Ras proteins or spatiotemporal dysregulation of Ras signaling pathways has pathological consequences in the cardiovascular system. The primary object of this review is to provide a comprehensive overview of the current progress in our understanding of the role of small G proteins and their regulators in cardiovascular physiology and pathologies.

The role of 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibitors (statins) in modern rheumatology

Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase commonly known as statins are widely used for treating hypercholesterolemia. However, there is much evidence to suggest that statins may have other properties in addition to their cholesterol-lowering effect. In particular, statins may neutralize post-translational prenylation of vitally important regulatory small GTPases, which are involved in several processes such as tissue fibrosis, cell maturation, apoptosis, immune cell maturation, and immune response. The beneficial effect of statins has been reported in animal and in vitro models as well as in some clinical studies. As they have an acceptable safety profile, statins may be considered, in selected cases, as a valuable concomitant therapy in the treatment of rheumatic and autoimmune disorders.

Atorvastatin inhibits osteoclastogenesis by decreasing the expression of RANKL in the synoviocytes of rheumatoid arthritis

Introduction

Statins, hydroxymethylglutaryl-coenzyme A reductase inhibitors, have been reported to have antiinflammatory and/or immunomodulatory effects and prophylactic and therapeutic effects in collagen-induced arthritis, an experimental model of rheumatoid arthritis (RA). The authors undertook to determine the effect of atorvastatin on the expressions of osteoprotegerin (OPG) and receptor activator of nuclear factor κB ligand (RANKL) in RA fibroblast-like synoviocytes (FLSs), to identify the mechanisms responsible for these effects, and to determine whether the statin inhibits osteoclastogenesis.

Methods

FLSs isolated from five RA patients were cultured in the presence of 20 ng/ml of tumor necrosis factor-α (TNF-α) with or without atorvastatin. RANKL expressions were assayed with Western blotting and enzyme-linked immunosorbent assay. RANKL, RANK, and OPG expression were assayed with reverse transcription-polymerase chain reaction (RT-PCR). Osteoclast formation was assayed by counting cells after staining for tartrate-resistant acid phosphatase in cocultures of peripheral blood mononuclear cells (PBMCs) and RA FLSs.

Results

Atorvastatin inhibited the expression of RANKL in RA FLSs in a dose-dependent manner, and the suppression of RANKL was prevented by mevalonate. However, OPG expression was not affected by atorvastatin in RA FLSs, and atorvastatin did not affect RANK expression in CD14⁺ cells. Conversely, atorvastatin suppressed TNF-α-induced p38 phosphorylation in RA FLSs and significantly reduced TRAP-positive multinucleated osteoclast formation in the coculture of PBMCs and RA FLSs.

Conclusion

These results suggest that atorvastatin inhibits osteoclastogenesis and bone destruction in RA patients.

Inflammatory breast cancer: what we know and what we need to learn

PURPOSE

We review the current status of multidisciplinary care for patients with inflammatory breast cancer (IBC) and discuss what further research is needed to advance the care of patients with this disease.

DESIGN

We performed a comprehensive review of the English-language literature on IBC through computerized literature searches.

RESULTS

Significant advances in imaging, including digital mammography, high-resolution ultrasonography with Doppler capabilities, magnetic resonance imaging, and positron emission tomography-computed tomography, have improved the diagnosis and staging of IBC. There are currently no established molecular criteria for distinguishing IBC from noninflammatory breast cancer. Such criteria would be helpful for the diagnosis and development of novel targeted therapies. Combinations of neoadjuvant systemic chemotherapy, surgery, and radiation therapy have led to an improved prognosis; however, the overall 5-year survival rate for patients with IBC remains very low (∼30%). Sentinel lymph node biopsy and skin-sparing mastectomy are not recommended for patients with IBC.

CONCLUSION

Optimal management of IBC requires close coordination among medical, surgical, and radiation oncologists, as well as radiologists and pathologists. There is a need to identify molecular changes that define the pathogenesis of IBC to enable eradication of IBC with the use of IBC-specific targeted therapies.

Inflammatory breast cancer: the disease, the biology, the treatment

Inflammatory breast cancer (IBC) is a rare and aggressive form of invasive breast cancer accounting for 2.5% of all breast cancer cases. It is characterized by rapid progression, local and distant metastases, younger age of onset, and lower overall survival compared with other breast cancers. Historically, IBC is a lethal disease with less than a 5% survival rate beyond 5 years when treated with surgery or radiation therapy. Because of its rarity, IBC is often misdiagnosed as mastitis or generalized dermatitis. This review examines IBC's unique clinical presentation, pathology, epidemiology, imaging, and biology and details current multidisciplinary management of the disease, which comprises systemic therapy, surgery, and radiation therapy.

Pleiotropic vasoprotective effects of statins: the chicken or the egg?

Statins (3-hydroxy-3-methyl glutaryl coenzyme A [HMG-CoA] reductase inhibitors) are the most commonly used lipid-lowering drugs. Their main lipid-lowering effect is achieved by an increase in the expression of low-density lipoprotein cholesterol receptors associated with inhibition of cholesterol synthesis through inhibition of HMG-CoA reductase - the first and rate-limiting step in cholesterol synthesis. However, beyond cholesterol synthesis inhibition, inhibition of the HMG-CoA reductase affects as well the synthesis of other molecules with significant roles in different, yet often intercalating, metabolic pathways. On this basis, and supported by an increasing series of advocating epidemiological and experimental data, an extended dialogue has been established over the last few years regarding the nonlipid or "pleiotropic" actions of statins.

Molecular targets for treatment of inflammatory breast cancer

Despite progress in combined-modality treatment with chemotherapy, surgery, and radiation therapy, the long-term outcome for patients with inflammatory breast cancer (IBC) remains poor. Therapies that target vasculolymphatic processes--angiogenesis, lymphangiogenesis, and vasculogenesis--have shown potential in the treatment for IBC, as represented by bevacizumab. Although the therapeutic effect of targeting lymphangiogenesis and vasculogenesis requires further investigation, targeting of angiogenesis has potential, not only through true antiangiogenic effects, but also through antitumor effects in concert with other pathways. Therapies that target cell proliferation pathways are the most promising targeted therapies for IBC. In particular, therapies that target human epidermal growth factor receptor 2 (for example, trastuzumab and lapatinib) have performed well in the clinical setting, leading to improved outcomes for patients with IBC. Metastatic pathways could have a unique, key role in the aggressiveness of the IBC phenotype. Further extensive work on the unique molecular characteristics of IBC is essential to ensure improved outcomes for patients with this disease. In this Review we discuss three pathways--vasculolymphatic, cell proliferation and metastatic--that could represent important targets in the treatment of IBC.

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.

High-Content Assay to Study Protein Prenylation

The mevalonate pathway leads to synthesis of cholesterol and isoprenoid lipids. Prenyltransferases attach the isoprenoid lipids to the C-terminus of several small guanosine triphosphate—binding proteins. The prenyl groups are essential for the biological activity of these proteins. The prenyltransferases and other components of the mevalonate pathway are either present or potential drug targets for cancer, osteoporosis, restenosis, or high serum cholesterol level. Until recently, cellular assays to study protein prenylation have been tedious, low-throughput assays. The authors have developed a high-content imaging-based assay to study protein prenylation. The assay is based on a green fluorescent protein (GFP) reporter, which is tagged with the prenylation motif of human H-Ras. The C-terminus of H-Ras targets GFP to the plasma membrane. When protein prenylation is inhibited, the tagged GFP cannot be localized to plasma membrane but is soluble in the cells. The localization of the GFP reporter can be analyzed in the 96- or 384-well format using automated microscopy and automated image analysis. Information about cell number and nuclear intensity can be obtained from the same images. In compound screening, these readouts provide valuable information about the toxicity of the compounds. The authors have validated their assay using several inhibitors of the mevalonate pathway as well as siRNA against farnesyl pyrophosphate synthase, a critical enzyme in the synthesis of the isoprenoid lipids. ( Journal of Biomolecular Screening 2008:456-467)

Potential benefit of statins for vascular disease in systemic sclerosis

PURPOSE OF REVIEW

Microvascular abnormality is a dominant feature of systemic sclerosis. There is increasing evidence that statins, developed as lipid-lowering drugs, yield profound benefits beyond their lipid-lowering effects. These 'pleiotropic' effects suggest that statins may be beneficial for treating SSc vasculopathy. This review focuses on the action of statins on endothelial functions and their potential use in treating SSc.

RECENT FINDINGS

The initial event in the pathogenesis of vascular involvement in SSc has been thought to be endothelial injury, but recent studies have led to another theory--that insufficient vascular repair due to defective vasculogenesis contributes to this process. Statins inhibit cholesterol synthesis, but they also suppress the synthesis of other lipid intermediates, resulting in protection of the endothelium through improvements in endothelial function, mobilization of endothelial precursors, suppression of the inflammatory response, and inhibition of fibrosis. Only a few studies evaluating the clinical benefits of statins have been conducted in SSc patients to date, but one open-label study showed that statins might be effective in improving vascular symptoms.

SUMMARY

Statins display numerous effects that may be of potential benefit in preventing endothelial dysfunction in SSc patients. Further clinical trials of statins in SSc patients are warranted.

Fluvastatin enhancement of trastuzumab and classical cytotoxic agents in defined breast cancer cell lines in vitro

The combination of anticancer drugs used in the clinic has been based upon empiricism, and the potential permutations of currently available drugs overwhelm the clinical trials system. Recently, investigators have suggested that the combination of a blockade of vital signal transduction pathways in combination with more standard therapy might enhance anticancer effect. Using a panel of breast cancer cell lines and isobologram median effect analysis, a method of determining synergism or antagonism of drugs, we have investigated in vitro potentially clinically useful combinations of agents with the human cell lines MCF7/wt, MCF7/adr, BT474, and SK-BR-3 grown in log phase. Results were confirmed by curve shift analysis. Cells were exposed to the agent(s) for 72 h and then analyzed for cytotoxicity using a MTT (3-(4,5-dimethylthiazolyl-2)-2,5-diphenyl-tetrazolium bromide) assay. Fluvastatin, an inhibitor of prenylation with excellent tolerability in man, was chosen to disrupt signal transduction pathways and thus potentially enhance the effect of more traditional anticancer agents. Anticancer agents tested were cytotoxics used in the treatment of breast cancer, trastuzumab, and rapamycin as an inhibitor of the AKT pathway. Fluvastatin combined with trastuzumab demonstrates global synergy of cytotoxic effect that is confirmed by apoptosis assay. These effects could only be partially reversed by adding farnesol or geranylgeraniol to restore prenylation. Epirubicin is also synergistic with fluvastatin in three of the four cell lines. Rapamycin, an inhibitor of MTOR, was synergistic with fluvastatin in two of the four cell lines and antagonistic in two other cell lines. The combination of fluvastatin or another inhibitor of prenylation and trastuzumab may be attractive for clinical development as the effect of trastuzumab in Her2/neu positive breast tumors is incomplete as a single agent.

Comparing antibody and small-molecule therapies for cancer

The 'magic bullet' concept of specifically targeting cancer cells at the same time as sparing normal tissues is now proven, as several monoclonal antibodies and targeted small-molecule compounds have been approved for cancer treatment. Both antibodies and small-molecule compounds are therefore promising tools for target-protein-based cancer therapy. We discuss and compare the distinctive properties of these two therapeutic strategies so as to provide a better view for the development of new drugs and the future direction of cancer therapy.

Anticancer effects of zoledronic acid against human osteosarcoma cells

Based on neoadjuvant chemotherapy, the prognosis of osteosarcoma patients has improved dramatically. However, due to therapy resistance in patient subgroups, the development of new treatment strategies is still of utmost importance. The aim of our study was to test the effects of the nitrogen-containing bisphosphonate zoledronic acid (ZOL) on osteosarcoma cell lines (N = 9). Exposure to ZOL at low micromolar concentrations induced a dose- and time-dependent block of DNA synthesis and cell cycle progression followed by microfilament breakdown and apoptosis induction. The ZOL-induced cell cycle accumulation in S phase was accompanied by significant changes in the expression of cyclins and cyclin-dependent kinase inhibitors with a prominent loss of cyclin E and D1. ZOL not only inhibited growth but also migration of osteosarcoma cells. The mevalonate pathway intermediary geranyl-geraniol (GGOH) but not farnesol (FOH) significantly inhibited the anticancer effects of ZOL against osteosarcoma cells. Correspondingly, ZOL sensitivity correlated with the blockade of protein geranylgeranylation indicated by unprenylated Rap1. Overexpression of even high levels of P-glycoprotein, as frequently present in therapy-resistant osteosarcomas, did not impair the anticancer activity of ZOL. Summarizing, our data suggest that ZOL, which selectively accumulates in the bone, represents a promising agent to improve osteosarcoma therapy.

Phase I clinical trial of the farnesyltransferase inhibitor BMS-214662 administered as a weekly 24 h continuous intravenous infusion in patients with advanced solid tumors

PURPOSE

BMS-214662 is a novel farnesyltransferase (FT) inhibitor that has shown promising suggestions of single agent activity in patients with advanced solid tumors when administered as a 1 h intravenous (i.v.) infusion every 3 weeks. The degree of FT inhibition in peripheral blood mononuclear cells (PBMCs) was greatest at the end of the infusion and rapidly reversed as the concentration of the drug in the plasma decayed. A second phase I trial of BMS-214662 administered as a weekly 24 h i.v. infusion was initiated to determine if the duration of maximum FT inhibition could be significantly extended by prolonging the infusion time and increasing the frequency of administration.

PATIENTS AND METHODS

Infusion of BMS-214662 was prolonged from 2, 4, 8, 16, 24 h in single patient cohorts and repeated weekly for 3 out of 4 weeks. The initial dose was 56 mg/m(2). When the infusion duration reached 24 h, the dose was escalated at a constant multiples of 1.4 in single patient cohorts until the occurrence of toxicity greater than grade 1, upon which groups of at least three patients were evaluated at each dose level. The plasma pharmacokinetics and FT inhibition in PBMCs were measured in all patients at the prospective maximum tolerated dose.

RESULTS

Nineteen patients participated in the study (11 males/8 females) and the weekly dose was increased to a maximum of 300 mg/m(2) given as a 24 h i.v. infusion. Drug-related toxicity greater than grade 1 first occurred at 300 mg/m(2), with two patients experiencing dose-limiting toxicity. One patient developed a grade 3 hyponatremia and another developed reversible grade 3 diarrhea, grade 2 renal toxicity, and grade 3 transaminitis. A 275 mg/m(2) dose was then evaluated, where one of the three patients treated experienced reversible grade 4 renal toxicity and grade 3 diarrhea. In view of the identical renal toxicity at 275 mg/m(2) in another study and limited drug availability, there was no further accrual to this dose level and the study was closed. No evidence of antitumor activity was observed. The plasma pharmacokinetics of BMS-214662 was linear with high interpatient variability. In the three patients evaluated at the 275 mg/m(2) dose level, the maximum inhibition of FT activity in PBMCs was 47+/-23% of the baseline.

CONCLUSION

Administering BMS-214662 as a weekly 24 h continuous i.v. infusion permitted a considerably greater dose intensity to be delivered as compared to a single 1 h infusion given once every 3 weeks. The more prolonged infusion schedule resulted in a much lower degree of maximum FT inhibition in PBMCs than achieved with the 1 h infusion, although the duration of enzyme inhibition was longer, consistent with the lower peak plasma concentration of the drug provided by comparably tolerated doses when given as a 24 h infusion. Similarly, delivering the drug with increased dose intensity permitted by this weekly administration schedule did not appear to enhance its therapeutic benefit, at least in this phase I trial. Continued development of BMS-214662 may depend upon the potential for using it in combination with other anticancer drugs.

Proteomic analysis of bovine brain G protein gamma subunit processing heterogeneity

We characterized the variable processing of the G protein gamma subunit isoforms associated with bovine brain G proteins, a primary mediator of cellular communication. Ggamma subunits were isolated from purified brain G proteins and characterized by Edman sequencing, by MALDI MS, by chemical and/or enzymatic fragmentation assayed by MALDI MS, and by MS/MS fragmentation and sequencing. Multiple forms of six different Ggamma isoforms were detected. Significant variation in processing was found at both the amino termini and particularly the carboxyl termini of the proteins. All Ggamma isoforms contain a carboxyl-terminal CAAX motif for prenylation, carboxyl-terminal proteolysis, and carboxymethylation. Characterization of these proteins indicates significant variability in the normal processing of all of these steps in the prenylation reaction, including a new variation of prenyl processing resulting from cysteinylation of the carboxyl terminus. These results have multiple implications for intracellular signaling mechanisms by G proteins, for the role of prenyl processing variation in cell signaling, and for the site of action and consequences of drugs that target the prenylation modification.

A combinatorial approach toward the generation of ambiphilic peptide-based inhibitors of protein:geranylgeranyl transferase-1

A combinatorial synthesis of oligopeptide analogues and their evaluation as protein:geranylgeranyl transferase inhibitors is presented. The combinatorial strategy is based on the random mutation, in each new generation, of one of any of the four amino acid building blocks of which the most effective compounds of the previous generation are assembled. In this way, a progressive improvement of the average inhibitory activity was observed until the fifth generation. The most active inhibitors were found to inhibit PGGT-1 in the low micromolar range (IC(50): 3.8-8.1 microM).

Stable analogues of geranylgeranyl diphosphate possessing improved geranylgeranyl versus farnesyl protein transferase inhibitory selectivity

Phosphonoacetamido(oxy) groups have proven to be good mimics of the diphosphate portion in geranylgeranyl protein transferase I (GGTase I) inhibitors. The introduction of small alkyl groups (Me, Et) into the diphosphate mimic moiety caused a further decrease in collateral farnesyl protein transferase (FTase) inhibitory activity, thereby improving GGTase I over FTase selectivity.

Modulation of RhoA-Rho kinase-mediated Ca2+ sensitization of rabbit myometrium during pregnancy - role of Rnd3

During pregnancy, the uterus undergoes major functional and structural remodelling. It is well known that during the major part of pregnancy, the myometrium normally remains relatively quiescent but is able to generate powerful contractions at the time of parturition. However, the intracellular molecular events regulating myometrial contractility during pregnancy still remain poorly understood. We applied differential gene expression screening using cDNA array technology to probe myometrium samples from non-pregnant and mid-pregnant (15 days) rabbits. Among the differentially expressed genes, the farnesylated small G-protein of the Rho family, Rnd3, was found to be upregulated (3.6-fold) at mid-pregnancy. Upregulation of Rnd3 was confirmed at the protein level by a 3.4-fold increase in Rnd3 expression in mid-pregnant myometrium. Measurements of contractile properties of beta-escin permeabilized smooth muscle strips revealed that the upregulation of Rnd3 correlated with an inhibition of RhoA-Rho kinase-mediated Ca2+ sensitization at mid-pregnancy. Treatment of muscle strips from mid-pregnant myometrium with the farnesyl-transferase inhibitor manumycin A (10 muM) led to the recovery of RhoA-Rho kinase-dependent Ca2+ sensitization. At late pregnancy (31 days), upregulation of RhoA and Rho kinase expression was associated with an increase in Ca2+ sensitivity of contractile proteins that was inhibited by the Rho kinase inhibitor Y-27632 (10 muM). These data thus demonstrate the time-dependent regulation of the RhoA-Rho kinase-mediated Ca2+ sensitization during the course of pregnancy. The depression of this mechanism at mid-pregnancy followed by its constitutive activation near term is associated with a co-ordinated modulation of Rnd3, RhoA and Rho kinase expression. The RhoA-Rho kinase signalling pathway and its regulators might thus represent potential targets for the development of new treatments for pre-term labour.

Protein Farnesyltransferase Inhibitor (SCH 66336) Abolishes NF-κB Activation Induced by Various Carcinogens and Inflammatory Stimuli Leading to Suppression of NF-κB-regulated Gene Expression and Up-regulation of Apoptosis

Ras farnesyltransferase inhibitor (FTI) exhibit antiproliferative and antiangiogenic effects through a mechanism that is poorly understood. Because of the known role of Ras in the activation of transcription factor NF-kappaB and because NF-kappaB-regulated genes can control cell survival and angiogenesis, we postulated that FTI mediates its effects in part by modulating NF-kappaB activation. Therefore, in the present study we investigated the effect of FTI, SCH 66336, on NF-kappaB and NF-kappaB-regulated gene expression activated by a variety of inflammatory and carcinogenic agents. We demonstrate by DNA-binding assay that NF-kappaB activation induced by tumor necrosis factor (TNF), phorbol 12-myristate 13-acetate, cigarette smoke, okadaic acid, and H(2)O(2) was completely suppressed by SCH 66336; the suppression was not cell type-specific. This FTI suppressed the activation of IkappaBalpha kinase (IKK), thus abrogating the phosphorylation and degradation of IkappaBalpha. Additionally, TNF-activated Ras and SCH 66336 inhibited the activation. Also, overexpression of Ras (V12) enhanced TNF-induced NF-kappaB activation, and adenoviral dominant-negative Ras (N17) suppressed the activation, thus suggesting the critical role of Ras in TNF signaling. SCH 66336 also inhibited the NF-kappaB-dependent reporter gene expression activated by TNF, TNFR1, TRADD, TRAF2, NIK, and IKK but not that activated by the p65 subunit of NF-kappaB. The TNF-induced NF-kappaB-regulated gene products cyclin D1, COX-2, MMP-9, survivin, IAP1, IAP2, XIAP, Bcl-2, Bfl-1/A1, TRAF1, and FLIP were all down-regulated by SCH 66336, which potentiated apoptosis induced by TNF and doxorubicin. Overall, our results indicate that SCH 66336 inhibited activation of NF-kappaB and NF-kappaB-regulated gene expressions induced by carcinogens and inflammatory stimuli, which may provide a molecular basis for the ability of SCH 66336 to suppress proliferation and angiogenesis.

The lipid and non-lipid effects of statins

The 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors, more commonly known as statins, are a class of drug widely used for the treatment of hypercholesterolaemia in patients with established cardiovascular disease as well as those at high risk of developing atherosclerosis. Their predominant action is to reduce circulating levels of low-density lipoprotein (LDL) cholesterol; to a smaller degree, they also increase high-density lipoprotein (HDL) cholesterol and reduce triglyceride concentrations. In recent years, however, there has been an increasing body of evidence that their effects on lipid profile cannot fully account for their cardiovascular protective actions: their beneficial effects are too rapid to be easily explained by their relatively slow effects on atherogenesis and too large to be accounted for by their relatively small effects on plaque regression. Experimental models have revealed that statins exert a variety of other cardiovascular effects, which would be predicted to be of clinical benefit: they possess anti-inflammatory properties, as evidenced by their ability to reduce the accumulation of inflammatory cells in atherosclerotic plaques; they inhibit vascular smooth muscle cell proliferation, a key event in atherogenesis; they inhibit platelet function, thereby limiting both atherosclerosis and superadded thrombosis; and they improve vascular endothelial function, largely through augmentation of nitric oxide (NO) generation. The relative importance of the lipid- and non-lipid-related effects of the statins in the clinical situation remains the subject of much continuing research.

Therapeutic approaches to bladder cancer: identifying targets and mechanisms

Transitional cell carcinoma is the second most common genitourinary malignancy in US and third most common cause of death among genitourinary tumors. Treatment options for bladder cancer include surgery, often combined with chemotherapy, radiation, and/or immunotherapy. The MVAC adjuvant chemotherapy regimen has been most widely used in locally invasive as well as metastatic disease. Only a proportion of patients at risk will respond to therapy. There is thus need to identify good responder patients for adjuvant therapy and to identify new targets to treat a greater range of patients. Based upon patient-specific aberrations in pathways or known markers, both existing and new therapies can be tailored to benefit patients based on the risk of progression and molecular alterations specific to a patient's tumor. Targeted therapy, therefore, is defined as therapy that targets mechanism and risk. Utilizing the available knowledge of the molecular biology of cell-cycle regulation, signal transduction, apoptosis, and angiogenesis in bladder cancer, we review the potential therapeutic targets for rational drug development. Finally, using bladder cancer as a model for translational research, requirements for a desired clinical trial are presented.

Expression, regulation, and activity of ABCA1 in human cell lines

Mutations in the ATP-binding cassette transporter A1 (ABCA1) gene cause familial high-density lipoprotein deficiency and Tangier disease. ABCA1 plays a crucial role in active apolipoprotein A-I (apoA-I) lipidation, a key step in reverse cholesterol transport. We compared ABCA1 transcriptional regulation and cholesterol efflux in human skin fibroblasts, monocyte-derived macrophages and hepatocytes (HepG2). 8-Br-cAMP did not increase ABCA1 transcription in these tissues compared to mouse macrophages. We found that ABCA1 is differentially regulated among tissues. While transcription in HepG2 appears to be constitutive, sterols stimulate ABCA1 transcription in fibroblasts and monocyte-derived macrophages. ApoA-I promoted cholesterol efflux in fibroblasts, macrophages, and HepG2. Cholesterol homeostasis in fibroblasts is tightly regulated, and ABCA1 mRNA closely follows the cellular mass of free cholesterol (dose- and time-dependent manner). To further determine the mechanism used by fibroblasts to maintain sterol balance, we used a competitive inhibition approach with geranylgeranyl pyrophosphate (GGPP) to block the LXR induction pathway. GGPP blocked basal, 22-(R)-hydroxycholesterol- and cholesterol-induced ABCA1 expression. Taken together, these results demonstrate that: (1) ABCA1 expression varies among tissues, and (2) cholesterol conversion to hydroxycholesterol is an important mechanism for the maintenance of cholesterol homeostasis in fibroblasts.

Structure, mechanism and function of prenyltransferases

In this review, we summarize recent progress in studying three main classes of prenyltransferases: (a) isoprenyl pyrophosphate synthases (IPPSs), which catalyze chain elongation of allylic pyrophosphate substrates via consecutive condensation reactions with isopentenyl pyrophosphate (IPP) to generate linear polymers with defined chain lengths; (b) protein prenyltransferases, which catalyze the transfer of an isoprenyl pyrophosphate (e.g. farnesyl pyrophosphate) to a protein or a peptide; (c) prenyltransferases, which catalyze the cyclization of isoprenyl pyrophosphates. The prenyltransferase products are widely distributed in nature and serve a variety of important biological functions. The catalytic mechanism deduced from the 3D structure and other biochemical studies of these prenyltransferases as well as how the protein functions are related to their reaction mechanism and structure are discussed. In the IPPS reaction, we focus on the mechanism that controls product chain length and the reaction kinetics of IPP condensation in the cis-type and trans-type enzymes. For protein prenyltransferases, the structures of Ras farnesyltransferase and Rab geranylgeranyltransferase are used to elucidate the reaction mechanism of this group of enzymes. For the enzymes involved in cyclic terpene biosynthesis, the structures and mechanisms of squalene cyclase, 5-epi-aristolochene synthase, pentalenene synthase, and trichodiene synthase are summarized.

Evolving therapies: farnesyltransferase inhibitors

Farnesyltransferase inhibitors (FTIs) are compounds designed to interfere with the signal transduction of cancer cells containing ras gene mutations. Specifically, FTIs were designed to prevent the farnesylation of Ras and other intracellular proteins, and they have been shown to have an effect on malignant cell proliferation and survival. However, the actual intracellular target of FTIs and the cellular determinants of drug action that correlate with antitumor effects currently are unknown. The following are key questions relating to FTI cell biology and clinical development: 1) Are ras gene mutations required for FTIs to be effective? 2) Does the effect of FTI therapy depend on which ras isoform is active (ie, H-ras, K-ras4A/B, or N-ras) in cancer cells? 3) What level of farnesyltransferase inhibition is required for clinical effect? 4) What surrogate biomarkers can be used to evaluate the biologic effect of FTIs in ongoing clinical trials? 5) What is the mechanism of FTI antitumor activity? Although the preliminary results are encouraging, more understanding of the intracellular mechanism of the FTIs is needed to determine how best to administer them in patients with cancer and to test their antitumor effects.