Geranylgeranyl diphosphate synthase: an emerging therapeutic target

Characterisation of lepidopteran geranylgeranyl diphosphate synthase as a putative pesticide target

Geranylgeranyl pyrophosphate (diphosphate) synthase (GGPPS) plays an important role in various physiological processes in insects, such as isoprenoid biosynthesis and protein prenylation. Here, we functionally characterised the GGPPS from the major agricultural lepidopteran pests Spodoptera frugiperda and Helicoverpa armigera. Partial disruption of GGPPS by CRISPR in S. frugiperda decreased embryo hatching rate and larval survival, suggesting that this gene is essential. Functional expression in vitro of Helicoverpa armigera GGPPS in Escherichia coli revealed a catalytically active enzyme. Next, we developed and optimised an enzyme assay to screen for potential inhibitors, such as the zoledronate and the minodronate, which showed a dose-dependent inhibition. Phylogenetic analysis of GGPPS across insects showed that GGPPS is highly conserved but also revealed several residues likely to be involved in substrate binding, which were substantially different in bee pollinator and human GGPPS. Considering the essentiality of GGPPS and its putative binding residue variability qualifies a GGPPS as a novel pesticide target. The developed assay may contribute to the identification of novel insecticide leads.

Boosting synergism of chemo- and immuno-therapies via switching paclitaxel-induced apoptosis to mevalonate metabolism-triggered ferroptosis by bisphosphonate coordination lipid nanogranules

Conventional chemotherapy based on cytotoxic drugs is facing tough challenges recently following the advances of monoclonal antibodies and molecularly targeted drugs. It is critical to inspire new potential to remodel the value of this classical therapeutic strategy. Here, we fabricate bisphosphonate coordination lipid nanogranules (BC-LNPs) and load paclitaxel (PTX) to boost the chemo- and immuno-therapeutic synergism of cytotoxic drugs. Alendronate in BC-LNPs@PTX, a bisphosphonate to block mevalonate metabolism, works as both the structure and drug constituent in nanogranules, where alendronate coordinated with calcium ions to form the particle core. The synergy of alendronate enhances the efficacy of paclitaxel, suppresses tumor metastasis, and alters the cytotoxic mechanism. Differing from the paclitaxel-induced apoptosis, the involvement of alendronate inhibits the mevalonate metabolism, changes the mitochondrial morphology, disturbs the redox homeostasis, and causes the accumulation of mitochondrial ROS and lethal lipid peroxides (LPO). These factors finally trigger the ferroptosis of tumor cells, an immunogenic cell death mode, which remodels the suppressive tumor immune microenvironment and synergizes with immunotherapy. Therefore, by switching paclitaxel-induced apoptosis to mevalonate metabolism-triggered ferroptosis, BC-LNPs@PTX provides new insight into the development of cytotoxic drugs and highlights the potential of metabolism regulation in cancer therapy.

Mevalonate pathway and male reproductive aging

Male fertility declines with age. The mevalonate pathway, through which cholesterol and nonsteroidal isoprenoids are synthesized, plays key role in metabolic processes and is an essential pathway for cholesterol production and protein prenylation. Male reproductive aging is accompanied by dramatic changes in the metabolic microenvironment of the testis. Since the mevalonate pathway has an important role in spermatogenesis, we attempted to explore the association between male reproductive aging and the mevalonate pathway to explain the mechanism of male reproductive aging. Alterations in the mevalonate pathway may affect male reproductive aging by decreasing cholesterol synthesis and altering testis protein prenylation. Decreased cholesterol levels affect cholesterol modification, testosterone production, and remodeling of germ cell membranes. Aging-related metabolic disorders also affect the metabolic coupling between somatic cells and spermatogenic cells, leading to male fertility decline. Therefore, we hypothesized that alterations in the mevalonate pathway represent one of the metabolic causes of reproductive aging.

Production of Astaxanthin by Animal Cells via Introduction of an Entire Astaxanthin Biosynthetic Pathway

Astaxanthin is a fascinating molecule with powerful antioxidant activity, synthesized exclusively by specific microorganisms and higher plants. To expand astaxanthin production, numerous studies have employed metabolic engineering to introduce and optimize astaxanthin biosynthetic pathways in microorganisms and plant hosts. Here, we report the metabolic engineering of animal cells in vitro to biosynthesize astaxanthin. This was accomplished through a two-step study to introduce the entire astaxanthin pathway into human embryonic kidney cells (HEK293T). First, we introduced the astaxanthin biosynthesis sub-pathway (Ast subp) using several genes encoding β-carotene ketolase and β-carotene hydroxylase enzymes to synthesize astaxanthin directly from β-carotene. Next, we introduced a β-carotene biosynthesis sub-pathway (β-Car subp) with selected genes involved in Ast subp to synthesize astaxanthin from geranylgeranyl diphosphate (GGPP). As a result, we unprecedentedly enabled HEK293T cells to biosynthesize free astaxanthin from GGPP with a concentration of 41.86 µg/g dry weight (DW), which represented 66.19% of the total ketocarotenoids (63.24 µg/g DW). Through optimization steps using critical factors in the astaxanthin biosynthetic process, a remarkable 4.14-fold increase in total ketocarotenoids (262.10 µg/g DW) was achieved, with astaxanthin constituting over 88.82%. This pioneering study holds significant implications for transgenic animals, potentially revolutionizing the global demand for astaxanthin, particularly within the aquaculture sector.

Decoding the crosstalk between mevalonate metabolism and T cell function

The mevalonate pathway is an essential metabolic pathway in T cells regulating development, proliferation, survival, differentiation, and effector functions. The mevalonate pathway is a complex, branched pathway composed of many enzymes that ultimately generate cholesterol and nonsterol isoprenoids. T cells must tightly control metabolic flux through the branches of the mevalonate pathway to ensure sufficient isoprenoids and cholesterol are available to meet cellular demands. Unbalanced metabolite flux through the sterol or the nonsterol isoprenoid branch is metabolically inefficient and can have deleterious consequences for T cell fate and function. Accordingly, there is tight regulatory control over metabolic flux through the branches of this essential lipid synthetic pathway. In this review we provide an overview of how the branches of the mevalonate pathway are regulated in T cells and discuss our current understanding of the relationship between mevalonate metabolism, cholesterol homeostasis and T cell function.

Regulation of protein prenylation

Prenyltransferases (PTases) are known to play a role in embryonic development, normal tissue homeostasis and cancer by posttranslationally modifying proteins involved in these processes. They are being discussed as potential drug targets in an increasing number of diseases, ranging from Alzheimer's disease to malaria. Protein prenylation and the development of specific PTase inhibitors (PTIs) have been subject to intense research in recent decades. Recently, the FDA approved lonafarnib, a specific farnesyltransferase inhibitor that acts directly on protein prenylation; and bempedoic acid, an ATP citrate lyase inhibitor that might alter intracellular isoprenoid composition, the relative concentrations of which can exert a decisive influence on protein prenylation. Both drugs represent the first approved agent in their respective substance class. Furthermore, an overwhelming number of processes and proteins that regulate protein prenylation have been identified over the years, many of which have been proposed as molecular targets for pharmacotherapy in their own right. However, certain aspects of protein prenylation, such as the regulation of PTase gene expression or the modulation of PTase activity by phosphorylation, have attracted less attention, despite their reported influence on tumor cell proliferation. Here, we want to summarize the advances regarding our understanding of the regulation of protein prenylation and the potential implications for drug development. Additionally, we want to suggest new lines of investigation that encompass the search for regulatory elements for PTases, especially at the genetic and epigenetic levels.

Geranylgeranyl diphosphate synthase: Role in human health, disease and potential therapeutic target

Geranylgeranyl diphosphate synthase (GGDPS), an enzyme in the isoprenoid biosynthesis pathway, is responsible for the production of geranylgeranyl pyrophosphate (GGPP). GGPP serves as a substrate for the post-translational modification (geranylgeranylation) of proteins, including those belonging to the Ras superfamily of small GTPases. These proteins play key roles in signalling pathways, cytoskeletal regulation and intracellular transport, and in the absence of the prenylation modification, cannot properly localise and function. Aberrant expression of GGDPS has been implicated in various human pathologies, including liver disease, type 2 diabetes, pulmonary disease and malignancy. Thus, this enzyme is of particular interest from a therapeutic perspective. Here, we review the physiological function of GGDPS as well as its role in pathophysiological processes. We discuss the current GGDPS inhibitors under development and the therapeutic implications of targeting this enzyme.

Pitavastatin Induces Apoptosis of Cutaneous Squamous Cell Carcinoma Cells through Geranylgeranyl Pyrophosphate-Dependent c-Jun N-Terminal Kinase Activation

BACKGROUND

Pitavastatin is a cholesterol-lowering drug and is widely used clinically. In addition to this effect, pitavastatin has shown the potential to induce apoptosis in cutaneous squamous cell carcinoma (SCC) cells.

OBJECTIVE

The purpose of this study is to investigate the effects and possible action mechanisms of pitavastatin.

METHODS

SCC cells (SCC12 and SCC13 cells) were treated with pitavastatin, and induction of apoptosis was confirmed by Western blot. To examine whether pitavastatin-induced apoptosis is related to a decrease in the amount of intermediate mediators in the cholesterol synthesis pathway, the changes in pitavastatin-induced apoptosis after supplementation with mevalonate, squalene, geranylgeranyl pyrophosphate (GGPP) and dolichol were investigated.

RESULTS

Pitavastatin dose-dependently induced apoptosis of cutaneous SCC cells, but the viability of normal keratinocytes was not affected by pitavastatin at the same concentrations. In supplementation experiments, pitavastatin-induced apoptosis was inhibited by the addition of mevalonate or downstream metabolite GGPP. As a result of examining the effect on intracellular signaling, pitavastatin decreased Yes1 associated transcriptional regulator and Ras homolog family member A and increased Rac family small GTPase 1 and c-Jun N-terminal kinase (JNK) activity. All these effects of pitavastatin on signaling molecules were restored when supplemented with either mevalonate or GGPP. Furthermore, pitavastatin-induced apoptosis of cutaneous SCC cells was inhibited by a JNK inhibitor.

CONCLUSION

These results suggest that pitavastatin induces apoptosis of cutaneous SCC cells through GGPP-dependent JNK activation.

Geranylgeranyl pyrophosphate depletion by statins compromises skeletal muscle insulin sensitivity

BACKGROUND

Statins are widely prescribed cholesterol-lowering drugs but have been shown to increase the risk of type 2 diabetes mellitus. However, the molecular mechanisms underlying the diabetogenic effect of statins are still not fully understood.

METHODS

The effects of geranylgeranyl transferase I and II (GGTase I and II) inhibition on insulin-stimulated glucose uptake and GLUT4 translocation, and the dependence of these effects on insulin signalling were investigated in skeletal muscle cells. The protective effects of geranylgeranyl pyrophosphate (GGPP) and its precursor geranylgeraniol (GGOH) on simvastatin-induced insulin resistance were evaluated in vitro and in vivo. The effect of GGTase II inhibition in skeletal muscle on insulin sensitivity in vivo was confirmed by adeno-associated virus serotype 9 (AAV9)-mediated knockdown of the specific subunit of GGTase II, RABGGTA. The regulatory mechanisms of GGTase I on insulin signalling and GGTase II on insulin-stimulated GLUT4 translocation were investigated by knockdown of RhoA, TAZ, IRS1, geranylgeranylation site mutation of RhoA, RAB8A, and RAB13.

RESULTS

Both inhibition of GGTase I and II mimicked simvastatin-induced insulin resistance in skeletal muscle cells. GGPP and GGOH were able to prevent simvastatin-induced skeletal muscle insulin resistance in vitro and in vivo. GGTase I inhibition suppressed the phosphorylation of AKT (Ser473) (-51.3%, P < 0.01), while GGTase II inhibition had no effect on it. AAV9-mediated knockdown of RABGGTA in skeletal muscle impaired glucose disposal without disrupting insulin signalling in vivo (-46.2% for gastrocnemius glucose uptake, P < 0.001; -52.5% for tibialis anterior glucose uptake, P < 0.001; -17.8% for soleus glucose uptake, P < 0.05; -31.4% for extensor digitorum longus glucose uptake, P < 0.01). Inhibition of RhoA, TAZ, IRS1, or geranylgeranylation deficiency of RhoA attenuated the beneficial effect of GGPP on insulin signalling in skeletal muscle cells. Geranylgeranylation deficiency of RAB8A inhibited insulin-stimulated GLUT4 translocation and concomitant glucose uptake in skeletal muscle cells (-42.8% for GLUT4 translocation, P < 0.01; -50.6% for glucose uptake, P < 0.001).

CONCLUSIONS

Geranylgeranyl pyrophosphate regulates glucose uptake via GGTase I-mediated insulin signalling-dependent way and GGTase II-mediated insulin signalling-independent way in skeletal muscle. Supplementation of GGPP/GGOH could be a potential therapeutic strategy for statin-induced insulin resistance.

Prenylation Defects and Oxidative Stress Trigger the Main Consequences of Neuroinflammation Linked to Mevalonate Pathway Deregulation

The cholesterol biosynthesis represents a crucial metabolic pathway for cellular homeostasis. The end products of this pathway are sterols, such as cholesterol, which are essential components of cell membranes, precursors of steroid hormones, bile acids, and other molecules such as ubiquinone. Furthermore, some intermediates of this metabolic system perform biological activity in specific cellular compartments, such as isoprenoid molecules that can modulate different signal proteins through the prenylation process. The defects of prenylation represent one of the main causes that promote the activation of inflammation. In particular, this mechanism, in association with oxidative stress, induces a dysfunction of the mitochondrial activity. The purpose of this review is to describe the pleiotropic role of prenylation in neuroinflammation and to highlight the consequence of the defects of prenylation.

Mutation of a prenyltransferase results in accumulation of subglutinols and destruxins and enhanced virulence in the insect pathogen, Metarhizium anisopliae

The insect pathogenic fungus, Metarhizium anisopliae is a commercialized microbial agent used in biological control efforts targeting a diverse range of agricultural and other insect pests. The second step in the synthesis of a group of M. anisopliae α-pyrone diterpenoids (termed subglutinols) involves the activity of a prenyltransferase family geranylgeranyl diphosphate synthase (product of the subD/MaGGPPS5 gene). Here, we show that targeted gene disruption of MaGGPPS5 results in earlier conidial germination and faster greater vegetative growth compared to the wild type (WT) parent and complemented strains. In addition, insect bioassays revealed that the ΔMaGGPPS5 mutant strain displayed significantly increased virulence, with a ~50% decrease in the mean lethal time (LT₅₀ , from 6 to 3 days) to kill (50% of) target insects, and an ~15-40-fold decrease in the mean lethal dose (LC₅₀ ). Metabolite profiling indicated increased accumulation in the ΔMaGGPPS5 mutant of select subglutinols (A, B and C) and destruxins (A, A2, B and B2), the latter a set of fungal secondary metabolites that act as insect toxins, with a concomitant loss of production of subglutinol 'analogue 45'. These data suggest that the increased virulence phenotype seen for the ΔMaGGPPS5 strain can, at least in part, be attributed to a combination of faster growth and increased insect toxin production, linking the production of two different secondary metabolite pathways, and represent a novel approach for the screening of isolates with enhanced virulence via modulation of terpenoid secondary metabolite biosynthesis.

Key Enzymes for the Mevalonate Pathway in the Cardiovascular System

ABSTRACT

Isoprenylation is an important post-transcriptional modification of small GTPases required for their activation and function. Isoprenoids, including farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate, are indispensable for isoprenylation by serving as donors of a prenyl moiety to small G proteins. In the human body, isoprenoids are mainly generated by the mevalonate pathway (also known as the cholesterol-synthesis pathway). The hydroxymethylglutaryl coenzyme A reductase catalyzes the first rate-limiting steps of the mevalonate pathway, and its inhibitor (statins) are widely used as lipid-lowering agents. In addition, the FPP synthase is also of critical importance for the regulation of the isoprenoids production, for which the inhibitor is mainly used in the treatment of osteoporosis. Synthetic FPP can be further used to generate geranylgeranyl pyrophosphate and cholesterol. Recent studies suggest a role for isoprenoids in the genesis and development of cardiovascular disorders, such as pathological cardiac hypertrophy, fibrosis, endothelial dysfunction, and fibrotic responses of smooth-muscle cells. Furthermore, statins and FPP synthase inhibitors have also been applied for the management of heart failure and other cardiovascular diseases rather than their clinical use for hyperlipidemia or bone diseases. In this review, we focus on the function of several critical enzymes, including hydroxymethylglutaryl coenzyme A reductase, FPP synthase, farnesyltransferase, and geranylgeranyltransferase in the mevalonate pathway which are involved in regulating the generation of isoprenoids and isoprenylation of small GTPases, and their pathophysiological role in the cardiovascular system. Moreover, we summarize recent research into applications of statins and the FPP synthase inhibitors to treat cardiovascular diseases, rather than for their traditional indications respectively.

Inhibition of zoledronic acid derivatives with extended methylene linkers on osteoclastogenesis involve downregulation of JNK and Akt pathways

Bisphosphonates (BPs), especially zoledronic acid (ZOL), are clinically used to treat osteolytic bone lesions. However, serious side-effects may be also induced during the therapeutic process. To improve the BPs drugs, here, we investigated the effects of a series of ZOL derivatives with increasing number of methylene linker between the imidazole ring and the P-C-P backbone named IPrDP, IBDP, IPeDP, and IHDP on cell viability and receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast differentiation, function and apoptosis induction in mouse bone marrow-derived macrophages (BMMs). Our results suggested that IPeDP and IHDP, which contains 4 and 5 methylene linkers, respectively, exerted lower toxicity on BMMs compared with ZOL, IPrDP, and IBDP, which contains 1, 2, and 3 methylene linkers respectively. At concentrations below cytotoxicity threshold, IPeDP and IHDP possessed strong abilities of antiosteoclast formation, antibone absorption, and inducing osteoclast apoptosis, which were similar to ZOL and more powerful than IPrDP and IBDP. The mechanism behind these effects of IPeDP and IHDP might involve the interference of small GTPases prenylation through suppression of mevalonate pathway. The downregulation of JNK and Akt phosphorylation and subsequent inhibition of the expression of c-Fos and NFATc1 might also be involved. Our results supported the potential usage of IPeDP and IHDP to treat bone-related disorders involving increased osteoclastogenesis. Our attempt to extend the methylene linker between the imidazole ring and the P-C-P backbone of ZOL also reveals some regularities between the structure and properties of the BPs drugs.

Nuclear Morphological Remodeling in Human Granulocytes Is Linked to Prenylation Independently from Cytoskeleton

Nuclear shape modulates cell behavior and function, while aberrant nuclear morphologies correlate with pathological phenotype severity. Nevertheless, functions of specific nuclear morphological features and underlying molecular mechanisms remain poorly understood. Here, we investigate a nucleus-intrinsic mechanism driving nuclear lobulation and segmentation concurrent with granulocyte specification, independently from extracellular forces and cytosolic cytoskeleton contributions. Transcriptomic regulation of cholesterol biosynthesis is equally concurrent with nuclear remodeling. Its putative role as a regulatory element is supported by morphological aberrations observed upon pharmacological impairment of several enzymatic steps of the pathway, most prominently the sterol ∆14-reductase activity of laminB-receptor and protein prenylation. Thus, we support the hypothesis of a nuclear-intrinsic mechanism for nuclear shape control with the putative involvement of the recently discovered GGTase III complex. Such process could be independent from or complementary to the better studied cytoskeleton-based nuclear remodeling essential for cell migration in both physiological and pathological contexts such as immune system function and cancer metastasis.

Phosphonate prodrugs: an overview and recent advances

Phosphonates, often used as isosteric replacements for phosphates, can provide important interactions with an enzyme. Due to their high charge at physiological pH, however, permeation into cells can be a challenge. Protecting phosphonates as prodrugs has shown promise in drug delivery. Thus, a variety of structures and cleavage/activation mechanisms exist, enabling release of the active compound. This review describes the structural diversity of these pro-moieties, relevant cleavage mechanisms and recent advances in the design of phosphonate prodrugs.

Structure-Activity Relationships of Butyrophilin 3 Ligands

Phosphoantigens (pAgs) are small phosphorus-containing molecules that stimulate Vγ9Vδ2 T cells with sub-nanomolar cellular potency. Recent work has revealed that these compounds work through binding to the transmembrane immunoglobulin butyrophilin 3A1 (BTN3A1) within its intracellular B30.2 domain. Engagement of BTN3A1 is critical to the formation of an immune synapse between cells that contain pAgs and the Vγ9Vδ2 T cells. This minireview summarizes the structure-activity relationships of pAgs and their implications to the mechanisms of butyrophilin 3 activation leading to Vγ9Vδ2 T cell response.

Characterization of the Geranylgeranyl Diphosphate Synthase Gene in Acyrthosiphon pisum (Hemiptera: Aphididae) and Its Association With Carotenoid Biosynthesis

Carotenoids play many crucial roles in organisms. Recently, the de novo synthesis of carotenoids has been reported in pea aphid (Acyrthosiphon pisum) through horizontally transferred genes. However, their upstream pathway in the pea aphid is poorly understood. Geranylgeranyl diphosphate synthase (GGPPS) is the functional enzyme in the synthesis of geranylgeranyl diphosphate (GGPP) which is a precursor for the biosynthesis of many biological metabolites, including carotenoid synthesis. In this study, we performed a series of experiments to characterize GGPPS gene and its association with carotenoid biosynthesis. (1) determining the transcript abundance and carotenoid content in two geographical strain with red and green morphs, and (2) examining the abundance of carotenoid related genes and carotenoid levels after silencing of GGPPS in both red and green morphs. We observed that GGPPS was more highly expressed in the green morph than in the red morph of two strains of the pea aphid. The total level of carotenoids was also higher in green morphs than in red morphs in both strains. In addition to the total carotenoid difference, the carotenoids found in the two morphs also differed. There were α-carotene, β-carotene, and γ-carotene in the green morphs, but three additional carotenoids, including cis-torulene^∗, trans-torulene^∗, and 3,4-didehydrolycopene^∗, were present in the red morphs. Silencing the GGPPS by RNAi in both the red and green morphs decreased the expression of some carotenoid biosynthesis-related genes, including carotenoid synthase/cyclase genes and carotenoid desaturase genes in green morphs. Carotenoid levels were decreased in both green and red morphs. However, the specific carotenoids present were not changed after silencing GGPPS. These results demonstrated that GGPPS may act as the upstream enzyme to influence the synthesis of the total amount of carotenoids. The present study provided important molecular evidence for the conserved roles of GGPPS associated with carotenoids biosynthesis and will enhance further investigation on the mechanisms of carotenoid biosynthesis in pea aphid.

Regulation of the Notch-ATM-abl axis by geranylgeranyl diphosphate synthase inhibition

Notch proteins drive oncogenesis of many cancers, most prominently T-cell acute lymphoblastic leukemia (T-ALL). Because geranylgeranylated Rab proteins regulate Notch processing, we hypothesized that inhibition of geranylgeranyl diphosphate synthase (GGDPS) would impair Notch processing and reduce viability of T-ALL cells that express Notch. Here, we show that GGDPS inhibition reduces Notch1 expression and impairs the proliferation of T-ALL cells. GGDPS inhibition also reduces Rab7 membrane association and depletes Notch1 mRNA. GGDPS inhibition increases phosphorylation of histone H2A.X, and inhibitors of ataxia telangiectasia-mutated kinase (ATM) mitigate GGDPS inhibitor-induced apoptosis. GGDPS inhibition also influences c-abl activity downstream of caspases, and inhibitors of these enzymes prevent GGDPS inhibitor-induced apoptosis. Surprisingly, induction of apoptosis by GGDPS inhibition is reduced by co-treatment with γ-secretase inhibitors. While inhibitors of γ-secretase deplete one specific form of the Notch1 intracellular domain (NICD), they also increase Notch1 mRNA expression and increase alternate forms of Notch1 protein expression in cells treated with a GGDPS inhibitor. Furthermore, inhibitors of γ-secretase and ATM increase Notch1 mRNA stability independent of GGDPS inhibition. These results provide a model by which T-ALL cells use Notch1 to avoid DNA-damage-induced apoptosis, and can be overcome by inhibition of GGDPS through effects on Notch1 expression and its subsequent response.

The role of cholesterol metabolism in leukemia

Leukemia is a common hematological malignancy with overall poor prognosis. Novel therapies are needed to improve the outcome of leukemia patients. Cholesterol metabolism reprogramming is a featured alteration in leukemia. Many metabolic-related genes and metabolites are essential to the progress and drug resistance of leukemia. Exploring potential therapeutical targets related to cholesterol homeostasis is a promising area. This review summarized the functions of cholesterol and its derived intermediate metabolites, and also discussed potential agents targeting this metabolic vulnerability in leukemia.

ω-Hydroxy isoprenoid bisphosphonates as linkable GGDPS inhibitors

The enzyme geranylgeranyl diphosphate synthase (GGDPS) is a potential therapeutic target for multiple myeloma. Malignant plasma cells produce and secrete large amounts of monoclonal protein, and inhibition of GGDPS results in disruption of protein geranylgeranylation which in turn impairs intracellular protein trafficking. Our previous work has demonstrated that some isoprenoid triazole bisphosphonates are potent and selective inhibitors of GGDPS. To explore the possibility of selective delivery of such compounds to plasma cells, new analogues with an ω-hydroxy group have been synthesized and examined for their enzymatic and cellular activity. These studies demonstrate that incorporation of the ω-hydroxy group minimally impairs GGDPS inhibitory activity. Furthermore conjugation of one of the novel ω-hydroxy GGDPS inhibitors to hyaluronic acid resulted in enhanced cellular activity. These results will allow future studies to focus on the in vivo biodistribution of HA-conjugated GGDPS inhibitors.

S-Geranylgeranyl-L-glutathione is a ligand for human B cell-confinement receptor P2RY8

Germinal centres are important sites for antibody diversification and affinity maturation, and are also a common origin of B cell malignancies. Despite being made up of motile cells, germinal centres are tightly confined within B cell follicles. The cues that promote this confinement are incompletely understood. P2RY8 is a Gα₁₃-coupled receptor that mediates the inhibition of migration and regulates the growth of B cells in lymphoid tissues^1,2. P2RY8 is frequently mutated in germinal-centre B cell-like diffuse large B cell lymphoma (GCB-DLBCL) and Burkitt lymphoma^1,3-6, and the ligand for this receptor has not yet been identified. Here we perform a search for P2RY8 ligands and find P2RY8 bioactivity in bile and in culture supernatants of several mouse and human cell lines. Using a seven-step biochemical fractionation procedure and a drop-out mass spectrometry approach, we show that a previously undescribed biomolecule, S-geranylgeranyl-L-glutathione (GGG), is a potent P2RY8 ligand that is detectable in lymphoid tissues at the nanomolar level. GGG inhibited the chemokine-mediated migration of human germinal-centre B cells and T follicular helper cells, and antagonized the induction of phosphorylated AKT in germinal-centre B cells. We also found that the enzyme gamma-glutamyltransferase-5 (GGT5), which was highly expressed by follicular dendritic cells, metabolized GGG to a form that did not activate the receptor. Overexpression of GGT5 disrupted the ability of P2RY8 to promote B cell confinement to germinal centres, which indicates that GGT5 establishes a GGG gradient in lymphoid tissues. This work defines GGG as an intercellular signalling molecule that is involved in organizing and controlling germinal-centre responses. As the P2RY8 locus is modified in several other types of cancer in addition to GCB-DLBCL and Burkitt lymphoma, we speculate that GGG might have organizing and growth-regulatory roles in multiple human tissues.

Metabolomics investigation of dietary effects on flesh quality in grass carp (Ctenopharyngodon idellus)

Background

The ultrahigh density intensive farming model of grass carp (Ctenopharyngodon idellus) may elicit growth inhibition, decrease flesh quality, and increase disease susceptibility of fish. The degradation in quality and excessive fat accumulation in cultured C. idellus have long been attributed to possible alterations in the lipid metabolism of fish muscle tissues as a result of overnutrition from artificial diets. To investigate the effects of different diets on fish muscle quality, a large-scale metabolomics study was performed on 250 tails of C. idellus.

Findings

The experimental fish were divided into four groups based on sex and diet—female artificial feed (FAF), female grass feed, male artificial feed (MAF), and male grass feed (MGF). After a 113-day rearing period, the artificial feed (AF) group showed a significantly higher total mass of muscle fat (P < 0.01), with the FAF group being the highest. Metabolomics profiling based on liquid chromatography-mass spectrometry revealed distinctive patterns of clustering according to the four groups. Overall, artificial feeding was associated with higher concentrations of docosapentaenoic acid, dihomo-gamma-linolenic acid, and arachidonic acid, whereas grass feeding was associated with elevated n-3 unsaturated fatty acids (UFAs) such as eicosapentaenoic acid, alpha-linolenic acid, and gamma-linolenic acid. Artificial feeding also resulted in significant increased docosahexaenoic acid in MAF muscle than in MGF fish, whereas there was no significance in the comparison of female samples. Metabolic pathway analyses using both targeted and untargeted approaches consistently revealed that arachidonic acid metabolism and steroid hormone biosynthesis pathways were significantly different between AF and grass fed groups.

Conclusions

Our results suggest that grass is a better source of dietary fatty acid and protein when compared to artificial feed. Grass feeding could effectively lower triglycerides in serum, reduce fat accumulation, and alter lipid compositions in fish muscle by increasing the concentrations of n-3 UFAs, leading to better nutrition and health.

Reduced Activity of Geranylgeranyl Diphosphate Synthase Mutant Is Involved in Bisphosphonate-Induced Atypical Fractures

Bisphosphonates are widely used for treating osteoporosis, a common disorder in which bone strength is reduced, increasing the risk for fractures. Rarely, bisphosphonates can paradoxically lead to atypical fractures occurring spontaneously or with trivial trauma. Recently, a novel missense mutation (D188Y) in the GGPS1 gene, encoding for geranylgeranyl diphosphate synthase (GGPPS), was associated with bisphosphonate-induced atypical fractures. However, the molecular basis for GGPPS involvement in this devastating condition remains elusive. Here, we show that while maintaining an overall unperturbed global enzyme structure, the D188Y mutation leads to ∼4-fold catalytic activity decrease. Furthermore, GGPPS-D188Y is unable to support cross-species complementation, highlighting the functional significance of the reduced catalytic activity observed in vitro. We next determined the crystal structure of apo-GGPPS-D188Y, revealing that while Y188 does not alter the protein fold, its bulky side chain sterically interferes with substrate binding. In agreement, we show that GGPPS-D188Y exhibits ∼3-fold reduction in the binding affinity of zoledronate, a commonly used bisphosphonate. However, inhibition of the mutated enzyme by zoledronate, in pharmacologically relevant concentrations, is maintained. Finally, we determined the crystal structure of zoledronate-bound GGPPS-D188Y, revealing large ligand-induced binding pocket rearrangements, revising the previous model for GGPPS-bisphosphonate interactions. In conclusion, we propose that among heterozygotes residual GGPPS activity is sufficient to support physiologic cellular function, concealing any pathologic phenotype. However, under bisphosphonate treatment, GGPPS activity is reduced below a crucial threshold for osteoclast function, leading to impaired bone remodeling and increased susceptibility to atypical fractures.

Expression of key enzymes in the mevalonate pathway are altered in monocrotaline-induced pulmonary arterial hypertension in rats

Pulmonary arterial hypertension (PAH) is a serious pulmonary vascular disease. The changes in the structure, function and metabolism of endothelial cells are some of the important features of PAH. Previous studies have demonstrated that the mevalonate pathway is important in cardiovascular remodeling. However, whether the mevalonate pathway is involved in the development of PAH remains to be elucidated. The present study aimed to investigate the expression pattern of mevalonate pathway-related enzymes in monocrotaline (MCT)-induced PAH. F344 rats were randomly divided into two groups (n=6/group): Control group rats were injected with a single dose of saline, and MCT group rats were injected with a single dose of MCT (60 mg/kg). After 4 weeks, the right ventricular systolic pressure (RVSP) was measured, and lung and pulmonary artery tissue samples were collected. It was demonstrated that the RVSP increased and pulmonary vascular remodeling was detected in the PAH group. The expression levels of the enzymes farnesyldiphosphate synthase farnesyltransferase α and geranylgeranyltransferase type I increased in the PAH group, which suggested that the mevalonate pathway may be involved in the pathological development of PAH.

Geranylgeranyl diphosphate synthase inhibition induces apoptosis that is dependent upon GGPP depletion, ERK phosphorylation and caspase activation

Bisphosphonates are diphosphate analogs that inhibit the intermediate enzymes of the mevalonate pathway. Here, we compared the effects of a farnesyl diphosphate synthase inhibitor, zoledronate, and a geranylgeranyl diphosphate synthase (GGDPS) inhibitor, digeranyl bisphosphonate (DGBP), on lymphocytic leukemia cell proliferation and apoptosis. Both zoledronate and DGBP inhibited proliferation with DGBP doing so more potently. DGBP was markedly less toxic than zoledronate toward the viability of healthy human peripheral blood mononuclear cells. Addition of GGPP, but not farnesyl diphosphate (FPP), prevented the anti-proliferative effects of DGBP. Both GGPP and FPP partially rescued the effects of zoledronate. Co-treatment with DGBP and zoledronate was antagonistic. To further assess the effects of the bisphosphonates, we analyzed annexin V and propidium iodide staining via flow cytometry and found that DGBP induced apoptosis more potently than zoledronate. Western blots show that DGBP treatment altered expression and membrane affinity of some but not all geranylgeranylated small GTPases, activated caspases and increased ERK phosphorylation. Importantly, the anti-proliferative effects of DGBP were blocked by treatment with a caspase inhibitor and by treatment with a MEK inhibitor. Together, our findings indicate that DGBP is a more potent and selective compound than zoledronate in inducing apoptosis mediated through pathways that include caspases and MEK/ERK. These findings support the further development of GGDPS inhibitors as anticancer therapeutics.

Olefin Isomers of a Triazole Bisphosphonate Synergistically Inhibit Geranylgeranyl Diphosphate Synthase

The isoprenoid donor for protein geranylgeranylation reactions, geranylgeranyl diphosphate (GGDP), is the product of the enzyme GGDP synthase (GGDPS) that condenses farnesyl diphosphate (FDP) and isopentenyl pyrophosphate. GGDPS inhibition is of interest from a therapeutic perspective for multiple myeloma because we have shown that targeting Rab GTPase geranylgeranylation impairs monoclonal protein trafficking, leading to endoplasmic reticulum stress and apoptosis. We reported a series of triazole bisphosphonate GGDPS inhibitors, of which the most potent was a 3:1 mixture of homogeranyl (HG) and homoneryl (HN) isomers. Here we determined the activity of the individual olefin isomers. Enzymatic and cellular assays revealed that although HN is approximately threefold more potent than HG, HN is not more potent than the original mixture. Studies in which cells were treated with varying concentrations of each isomer alone and in different combinations revealed that the two isomers potentiate the induced-inhibition of protein geranylgeranylation when used in a 3:1 HG:HN combination. A synergistic interaction was observed between the two isomers in the GGDPS enzyme assay. These results suggested that the two isomers bind simultaneously to the enzyme but within different domains. Computational modeling studies revealed that HN is preferred at the FDP site, that HG is preferred at the GGDP site, and that both isomers may bind to the enzyme simultaneously. These studies are the first to report a set of olefin isomers that synergistically inhibit GGDPS, thus establishing a new paradigm for the future development of GGDPS inhibitors.

The interplay between cell signalling and the mevalonate pathway in cancer

The mevalonate (MVA) pathway is an essential metabolic pathway that uses acetyl-CoA to produce sterols and isoprenoids that are integral to tumour growth and progression. In recent years, many oncogenic signalling pathways have been shown to increase the activity and/or the expression of MVA pathway enzymes. This Review summarizes recent advances and discusses unique opportunities for immediately targeting this metabolic vulnerability in cancer with agents that have been approved for other therapeutic uses, such as the statin family of drugs, to improve outcomes for cancer patients.

How to Target Activated Ras Proteins: Direct Inhibition vs. Induced Mislocalization

Oncogenic Ras proteins are a driving force in a significant set of human cancers and wildtype, unmutated Ras proteins likely contribute to the malignant phenotype of many more. The overall challenge of targeting activated Ras proteins has great promise to treat cancer, but this goal has yet to be achieved. Significant efforts and resources have been committed to inhibiting Ras, but these energies have so far made little impact in the clinic. Direct attempts to target activated Ras proteins have faced many obstacles, including the fundamental nature of the gain-of-function oncogenic activity being produced by a loss-of-function at the biochemical level. Nevertheless, there has been very promising recent pre-clinical progress. The major strategy that has so far reached the clinic aimed to inhibit activated Ras indirectly through blocking its post-translational modification and inducing its mislocalization. While these efforts to indirectly target Ras through inhibition of farnesyl transferase (FTase) were rationally designed, this strategy suffered from insufficient attention to the distinctions between the isoforms of Ras. This led to subsequent failures in large-scale clinical trials targeting K-Ras driven lung, colon, and pancreatic cancers. Despite these setbacks, efforts to indirectly target activated Ras through inducing its mislocalization have persisted. It is plausible that FTase inhibitors may still have some utility in the clinic, perhaps in combination with statins or other agents. Alternative approaches for inducing mislocalization of Ras through disruption of its palmitoylation cycle or interaction with chaperone proteins are in early stages of development.

Stereoselective Synthesis of Homoneryl and Homogeranyl Triazole Bisphosphonates

Isoprenoid-substituted bisphosphonates are known to serve as inhibitors of the enzyme geranylgeranyl diphosphate synthase, and their activity can be highly sensitive to olefin stereochemistry. A mixture of homogeranyl and homoneryl triazole bisphosphonates has previously demonstrated potent activity, and thus stereocontrolled syntheses of the individual isomers have been developed.

Genome-wide RNAi analysis reveals that simultaneous inhibition of specific mevalonate pathway genes potentiates tumor cell death

The mevalonate (MVA) pathway is often dysregulated or overexpressed in many cancers suggesting tumor dependency on this classic metabolic pathway. Statins, which target the rate-limiting enzyme of this pathway, 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), are promising agents currently being evaluated in clinical trials for anti-cancer efficacy. To uncover novel targets that potentiate statin-induced apoptosis when knocked down, we carried out a pooled genome-wide short hairpin RNA (shRNA) screen. Genes of the MVA pathway were amongst the top-scoring targets, including sterol regulatory element binding transcription factor 2 (SREBP2), 3-hydroxy-3-methylglutaryl-coenzyme A synthase 1 (HMGCS1) and geranylgeranyl diphosphate synthase 1 (GGPS1). Each gene was independently validated and shown to significantly sensitize A549 cells to statin-induced apoptosis when knocked down. SREBP2 knockdown in lung and breast cancer cells completely abrogated the fluvastatin-induced upregulation of sterol-responsive genes HMGCR and HMGCS1. Knockdown of SREBP2 alone did not affect three-dimensional growth of lung and breast cancer cells, yet in combination with fluvastatin cell growth was disrupted. Taken together, these results show that directly targeting multiple levels of the MVA pathway, including blocking the sterol-feedback loop initiated by statin treatment, is an effective and targetable anti-tumor strategy.

Molecular mechanisms linking geranylgeranyl diphosphate synthase to cell survival and proliferation

Geranylgeranyl diphosphate is a 20-carbon isoprenoid phospholipid whose lipid moiety can be post-translationally incorporated into proteins to promote membrane association. The process of geranylgeranylation has been implicated in anti-proliferative effects of clinical agents that inhibit enzymes of the mevalonate pathway (i.e. statins and nitrogenous bisphosphonates) as well as experimental agents that deplete geranylgeranyl diphosphate. Inhibitors of geranylgeranyl diphosphate synthase are an attractive way to block geranylgeranylation because they possess a calcium-chelating substructure to allow localization to bone and take advantage of a unique position of the enzyme within the biosynthetic pathway. Here, we describe recent advances in geranylgeranyl diphosphate synthase expression and inhibitor development with a particular focus on the molecular mechanisms that link geranylgeranyl diphosphate to cell proliferation via geranylgeranylated small GTPases.

A new motif for inhibitors of geranylgeranyl diphosphate synthase

The enzyme geranylgeranyl diphosphate synthase (GGDPS) is believed to receive the substrate farnesyl diphosphate through one lipophilic channel and release the product geranylgeranyl diphosphate through another. Bisphosphonates with two isoprenoid chains positioned on the α-carbon have proven to be effective inhibitors of this enzyme. Now a new motif has been prepared with one isoprenoid chain on the α-carbon, a second included as a phosphonate ester, and the potential for a third at the α-carbon. The pivaloyloxymethyl prodrugs of several compounds based on this motif have been prepared and the resulting compounds have been tested for their ability to disrupt protein geranylgeranylation and induce cytotoxicity in myeloma cells. The initial biological studies reveal activity consistent with GGDPS inhibition, and demonstrate a structure-function relationship which is dependent on the nature of the alkyl group at the α-carbon.

P53- and mevalonate pathway-driven malignancies require Arf6 for metastasis and drug resistance

Drug resistance, metastasis, and a mesenchymal transcriptional program are central features of aggressive breast tumors. The GTPase Arf6, often overexpressed in tumors, is critical to promote epithelial-mesenchymal transition and invasiveness. The metabolic mevalonate pathway (MVP) is associated with tumor invasiveness and known to prenylate proteins, but which prenylated proteins are critical for MVP-driven cancers is unknown. We show here that MVP requires the Arf6-dependent mesenchymal program. The MVP enzyme geranylgeranyl transferase II (GGT-II) and its substrate Rab11b are critical for Arf6 trafficking to the plasma membrane, where it is activated by receptor tyrosine kinases. Consistently, mutant p53, which is known to support tumorigenesis via MVP, promotes Arf6 activation via GGT-II and Rab11b. Inhibition of MVP and GGT-II blocked invasion and metastasis and reduced cancer cell resistance against chemotherapy agents, but only in cells overexpressing Arf6 and components of the mesenchymal program. Overexpression of Arf6 and mesenchymal proteins as well as enhanced MVP activity correlated with poor patient survival. These results provide insights into the molecular basis of MVP-driven malignancy.

Potent Triazole Bisphosphonate Inhibitor of Geranylgeranyl Diphosphate Synthase

Studies of triazole bisphosphonates have resulted in identification of a potent inhibitor of geranylgeranyl diphosphate synthase (IC50 = 45 nM) with very good selectivity for this enzyme over farnesyl diphosphate synthase (IC50 = 28 μM). This compound also potently disrupts geranylgeranylation and induces cytotoxicity in human myeloma cells at submicromolar levels, suggesting that it may serve as a lead compound for treatment of malignancies characterized by excessive protein secretion.

Novel Activities of Select NSAID R-Enantiomers against Rac1 and Cdc42 GTPases

Rho family GTPases (including Rac, Rho and Cdc42) collectively control cell proliferation, adhesion and migration and are of interest as functional therapeutic targets in numerous epithelial cancers. Based on high throughput screening of the Prestwick Chemical Library^® and cheminformatics we identified the R-enantiomers of two approved drugs (naproxen and ketorolac) as inhibitors of Rac1 and Cdc42. The corresponding S-enantiomers are considered the active component in racemic drug formulations, acting as non-steroidal anti-inflammatory drugs (NSAIDs) with selective activity against cyclooxygenases. Here, we show that the S-enantiomers of naproxen and ketorolac are inactive against the GTPases. Additionally, more than twenty other NSAIDs lacked inhibitory action against the GTPases, establishing the selectivity of the two identified NSAIDs. R-naproxen was first identified as a lead compound and tested in parallel with its S-enantiomer and the non-chiral 6-methoxy-naphthalene acetic acid (active metabolite of nabumetone, another NSAID) as a structural series. Cheminformatics-based substructure analyses—using the rotationally constrained carboxylate in R-naproxen—led to identification of racemic [R/S] ketorolac as a suitable FDA-approved candidate. Cell based measurement of GTPase activity (in animal and human cell lines) demonstrated that the R-enantiomers specifically inhibit epidermal growth factor stimulated Rac1 and Cdc42 activation. The GTPase inhibitory effects of the R-enantiomers in cells largely mimic those of established Rac1 (NSC23766) and Cdc42 (CID2950007/ML141) specific inhibitors. Docking predicts that rotational constraints position the carboxylate moieties of the R-enantiomers to preferentially coordinate the magnesium ion, thereby destabilizing nucleotide binding to Rac1 and Cdc42. The S-enantiomers can be docked but are less favorably positioned in proximity to the magnesium. R-naproxen and R-ketorolac have potential for rapid translation and efficacy in the treatment of several epithelial cancer types on account of established human toxicity profiles and novel activities against Rho-family GTPases.

Correlation of changes in the mandible and retina/choroid vasculature of a rat model of BRONJ

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) causes bones of the mandible and maxilla to become necrotic and protrude into the oral cavity. Compromised blood supply to bone is also a feature of BRONJ. The design of this study was first to use our established technique of molar extraction and IV bisphosphonate injection to produce features of BRONJ in rats that mimic the human disease; second to confirm vascular changes in the mandible and eye using micro-CT of vascular casts, and image analysis of retina/choroid images; and third to show parallel bisphosphonate-induced changes in the structure and markers of the vasculature of the bone and eye. The results of this study show structural changes in the eye and mandible as well as biochemical changes including the up-regulation of VEGF in response to the bisphosphonate-associated ischemia. These changes are not associated with angiogenesis in either the eye or mandible as determined by reduced vascular complexity. These results suggest that observations of direct changes to the vasculature in the retina/choroid structures of the eye in patients taking bisphosphonates could serve as a window to the progression of debilitating changes occurring as a result of bisphosphonate therapy.

In vitro studies in a myelogenous leukemia cell line suggest an organized binding of geranylgeranyl diphosphate synthase inhibitors

A small set of isoprenoid bisphosphonates ethers has been tested in the K562 chronic myelogenous leukemia cell line to determine their impact on isoprenoid biosynthesis. Five of these compounds inhibit geranylgeranyl diphosphate synthase (GGDPS) with IC50 values below 1 μM in enzyme assays, but in cells their apparent activity is more varied. In particular, the isomeric C-geranyl-O-prenyl and C-prenyl-O-geranyl bisphosphonates are quite different in their activity with the former consistently demonstrating greater impairment of geranylgeranylation in cells but the latter showing greater impact in the enzyme assays with GGDPS. Together, these findings suggest an organized binding of these inhibitors in the two hydrophobic channels of the geranylgeranyl diphosphate synthase enzyme.

Alteration of mevalonate pathway in proliferated vascular smooth muscle from diabetic mice: possible role in high-glucose-induced atherogenic process

The proliferation of vascular smooth muscle cells (VSMCs) is one of the main features of atherosclerosis induced by high glucose. Mevalonate pathway is an important metabolic pathway that plays a key role in multiple cellular processes. The aim of this study was to define whether the enzyme expression in mevalonate pathway is changed in proliferated VSMCs during atherogenic process in diabetic mice. Diabetes was induced in BALB/c mice with streptozotocin (STZ, 50 mg/kg/day for 5 days). Induction of diabetes with STZ was associated with an increase of lesion area and media thickness after 8 and 16 weeks of diabetes. In aorta, there were overexpressions of some enzymes, including 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR), farnesyl pyrophosphate synthase (FPPS), geranylgeranyl pyrophosphate synthase (GGPPS), farnesyltransferase (FNT), and geranylgeranyltransferase-1 (GGT-1), and unchanged expression of squalene synthase (SQS) and phosphor-3-hydroxy-3-methylglutaryl-coenzyme A reductase (P-HMGR) in 8 and 16 weeks of diabetes. In vitro, VSMCs were cultured and treated with different glucose concentrations for 48 h. High glucose (22.2 mM) induced VSMC proliferation and upregulation of HMGR, FPPS, GGPPS, FNT, and GGT-1 but did not change the expressions of SQS and P-HMGR. In conclusion, altered expression of several key enzymes in the mevalonate pathway may play a potential pathophysiological role in atherogenic process of diabetes macrovascular complication.

Prodrugs of phosphonates and phosphates: crossing the membrane barrier

A substantial portion of metabolism involves transformation of phosphate esters, including pathways leading to nucleotides and oligonucleotides, carbohydrates, isoprenoids and steroids, and phosphorylated proteins. Because the natural substrates bear one or more negative charges, drugs that target these enzymes generally must be charged as well, but small charged molecules can have difficulty traversing the cell membrane by means other than endocytosis. The resulting dichotomy has stimulated a great deal of effort to develop effective prodrugs, compounds that carry little or no charge to enable them to transit biological membranes, but able to release the parent drug once inside the target cell. This chapter presents recent studies on advances in prodrug forms, along with representative examples of their application to marketed and developmental drugs.

Efficient methods for enol phosphate synthesis using carbon-centred magnesium bases

Efficient conversion of ketones into enol phosphates under mild and accessible conditions has been realised using the developed methods with di-tert-butylmagnesium and bismesitylmagnesium. Optimisation of the quench protocol resulted in high yields of enol phosphates from a range of cyclohexanones and aryl methyl ketones.

Synthesis of isoprenoid bisphosphonate ethers through C-P bond formations: Potential inhibitors of geranylgeranyl diphosphate synthase

A set of bisphosphonate ethers has been prepared through sequential phosphonylation and alkylation of monophosphonate ethers. After formation of the corresponding phosphonic acid salts, these compounds were tested for their ability to inhibit the enzyme geranylgeranyl diphosphate synthase (GGDPS). Five of the new compounds show IC₅₀ values of less than 1 μM against GGDPS with little to no activity against the related enzyme farnesyl diphosphate synthase (FDPS). The most active compound displayed an IC₅₀ value of 82 nM when assayed with GGDPS, and no activity against FDPS even at a 10 μM concentration.

Synthetic Routes to Methylerythritol Phosphate Pathway Intermediates and Downstream Isoprenoids

Isoprenoids constitute the largest class of natural products with greater than 55,000 identified members. They play essential roles in maintaining proper cellular function leading to maintenance of human health, plant defense mechanisms against predators, and are often exploited for their beneficial properties in the pharmaceutical and nutraceutical industries. Most impressively, all known isoprenoids are derived from one of two C5-precursors, isopentenyl diphosphate (IPP) or dimethylallyl diphosphate (DMAPP). In order to study the enzyme transformations leading to the extensive structural diversity found within this class of compounds there must be access to the substrates. Sometimes, intermediates within a biological pathway can be isolated and used directly to study enzyme/pathway function. However, the primary route to most of the isoprenoid intermediates is through chemical catalysis. As such, this review provides the first exhaustive examination of synthetic routes to isoprenoid and isoprenoid precursors with particular emphasis on the syntheses of intermediates found as part of the 2C-methylerythritol 4-phosphate (MEP) pathway. In addition, representative syntheses are presented for the monoterpenes (C10), sesquiterpenes (C15), diterpenes (C20), triterpenes (C30) and tetraterpenes (C40). Finally, in some instances, the synthetic routes to substrate analogs found both within the MEP pathway and downstream isoprenoids are examined.

Geranyl and neryl triazole bisphosphonates as inhibitors of geranylgeranyl diphosphate synthase

When inhibitors of enzymes that utilize isoprenoid pyrophosphates are based on the natural substrates, a significant challenge can be to achieve selective inhibition of a specific enzyme. One element in the design process is the stereochemistry of the isoprenoid olefins. We recently reported preparation of a series of isoprenoid triazoles as potential inhibitors of geranylgeranyl transferase II but these compounds were obtained as a mixture of olefin isomers. We now have accomplished the stereoselective synthesis of these triazoles through the use of epoxy azides for the cycloaddition reaction followed by regeneration of the desired olefin. Both geranyl and neryl derivatives have been prepared as single olefin isomers through parallel reaction sequences. The products were assayed against multiple enzymes as well as in cell culture studies and surprisingly a Z-olefin isomer was found to be a potent and selective inhibitor of geranylgeranyl diphosphate synthase.

Rho-kinase: regulation, (dys)function, and inhibition

In a variety of normal and pathological cell types, Rho-kinases I and II (ROCKI/II) play a pivotal role in the organization of the nonmuscle and smooth muscle cytoskeleton and adhesion plaques as well as in the regulation of transcription factors. Thus, ROCKI/II activity regulates cellular contraction, motility, morphology, polarity, cell division, and gene expression. Emerging evidence suggests that dysregulation of the Rho-ROCK pathways at different stages is linked to cardiovascular, metabolic, and neurodegenerative diseases as well as cancer. This review focuses on the current status of understanding the multiple functions of Rho-ROCK signaling pathways and various modes of regulation of Rho-ROCK activity, thereby orchestrating a concerted functional response.

Low toxicity and unprecedented anti-osteoclast activity of a simple sulfur-containing gem-bisphosphonate: a comparative study

Bisphosphonates (BPs) are key drugs for the treatment of bone resorption diseases like osteoporosis, Paget's disease and some forms of tumors. Recent findings underlined the importance of lipophilic N-containing BPs to ensure high biological activity. Herein we present some unprecedented results concerning the low toxicity and good anti-osteoclast activity of low molecular weight hydrophilic S-containing BPs. A series of S and N-containing BPs bearing aromatic and aliphatic substitution were prepared through Michael addition reaction between vinylidenebisphosphonate tetraethyl ester and the proper nucleophile under basic catalysis. S-containing BPs showed a generally low toxicity, determined with the neutral-red assay using the L929 cell line, and, in particular for an aliphatic one, a good biological activity assessed on primary cultures of human osteoclasts.

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.