geranylgeranyl-pyrophosphate and Neoplasms

The mevalonate synthesis inhibitors, statins, are mainstay therapeutics for cholesterol management and cardiovascular health. Thirty years of research have uncovered supportive roles for the mevalonate pathway in numerous cellular processes that support oncogenesis, most recently macropinocytosis. Central to the diverse mechanisms of statin sensitivity is an acquired dependence on one mevalonate pathway output, protein geranylgeranylation. New chemical prenylation probes and the discovery of a novel geranylgeranyl transferase hold promise to deepen our understanding of statin mechanisms of action. Further, insights into statin selection and the counterproductive role of dietary geranylgeraniol highlight how we should assess statins in the clinic. Lastly, rational combination strategies preview how statins will enter the oncology toolbox.

Topics: Alkyl and Aryl Transferases; Animals; Antineoplastic Combined Chemotherapy Protocols; Cell Line, Tumor; Cell Proliferation; Cell Survival; Disease Models, Animal; Diterpenes; Farnesyltranstransferase; Feeding Behavior; Food-Drug Interactions; Humans; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Metabolic Networks and Pathways; Mevalonic Acid; Mice; Neoplasms; Pinocytosis; Polyisoprenyl Phosphates; Prenylation

Dysregulation of isoprenoid biosynthesis is implicated in numerous biochemical disorders that play a role in the onset and/or progression of age-related diseases, such as hypercholesterolemia, osteoporosis, various cancers, and neurodegeneration. The mevalonate metabolic pathway is responsible for the biosynthesis of the two key isoprenoid metabolites, farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP). Post-translational prenylation of various proteins, including the small GTP-binding proteins (GTPases), with either FPP or GGPP is vital for proper localization and activation of these proteins. Prenylated GTPases play a critical role in cell signaling, proliferation, cellular plasticity, oncogenesis, and cancer metastasis. Pre-clinical and clinical studies strongly suggest that inhibition of protein prenylation can be an effective treatment for non-skeletal cancers. In this review, we summarize the most recent drug discovery efforts focusing on blocking protein farnesylation and/or geranylgeranylation and the biochemical and structural data available in guiding the current on-going studies in drug discovery. Furthermore, we provide a summary on the biochemical association between disruption of protein prenylation, endoplasmic reticulum (ER) stress, unfolded protein response (UPR) signaling, and cancer.

Topics: Animals; Antineoplastic Agents; Biosynthetic Pathways; Drug Discovery; Enzyme Inhibitors; Farnesyltranstransferase; Geranyltranstransferase; Humans; Mevalonic Acid; Models, Molecular; Neoplasms; Polyisoprenyl Phosphates; Protein Prenylation; Sesquiterpenes

The cholesterol biosynthesis pathway, also referred to as the mevalonate (MVA) pathway, is responsible for the biosynthesis of two key isoprenoids: farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP). Post-translational modification of small GTPases by FPP and GGPP has captured much attention due to their potential contribution to cancer, cardiovascular and neurodegenerative diseases. The enzyme 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (HMGCR) catalyzes the conversion of HMG-CoA to MVA, and is the rate-limiting step in the biosynthesis of cholesterol. Statins are HMGCR inhibitors that are used extensively in the treatment of hypercholesterolemia. Inhibitors of the MVA pathway exhibit anti-tumor effects and may reduce cancer incidence and cancer-related mortality in humans. In this review, we will focus on the mevalonate cascade and its regulation in cholesterol metabolism as well as polymorphisms of the MVA cascade in cancer development, infectious and cardiovascular disease (CVD).

Topics: Acyl Coenzyme A; Animals; Cardiovascular Diseases; Cholesterol; GTP Phosphohydrolases; Humans; Hydroxymethylglutaryl CoA Reductases; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Infections; Mevalonic Acid; Neoplasms; Polyisoprenyl Phosphates; Sesquiterpenes; Signal Transduction

Farnesyl transferase inhibitors have emerged as bona fide anticancer agents whereas the development of geranylgeranyl transferase inhibitors has been mitigated by overt systemic toxicities. Evidence suggests that the therapeutic value of farnesyl transferase inhibitors is an indirect result of perturbations in the function of geranylgeranylated Rho proteins. To address this question, we used inhibitors of the mevalonate synthesis pathway to decrease cellular levels of farnesly and geranylgeranly isoprenoids and supplemented our culture systems with exogenous isoprenoids accordingly. Using a murine lung alveolar carcinoma cell line (Line 1), we report a dose-dependent inhibition of tumor cell proliferation, adhesion and invasiveness, in response to alendronate (3-30 micromol/L) and mevastatin (1-10 micromol/L). Supplementation of cultures with geranylgeranyl pyrophosphates (100 micromol/L) was observed to rescue drug-induced phenotypic changes whereas farnesyl pyrophosphate (100 micromol/L) had a minimal effect. Our observations highlight the mevalonate synthesis pathway as a target for anticancer therapies and suggest a greater role for geranylgeranylated proteins in cellular processes germane to cancer.

Topics: Acute-Phase Proteins; Alendronate; Alkyl and Aryl Transferases; Animals; Dose-Response Relationship, Drug; Drug Screening Assays, Antitumor; Farnesyltranstransferase; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Lovastatin; Mevalonic Acid; Mice; Neoplasms; Polyisoprenyl Phosphates; Tumor Cells, Cultured

The statin family of drugs preferentially triggers tumor cell apoptosis by depleting mevalonate pathway metabolites farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP), which are used for protein prenylation, including the oncoproteins of the RAS superfamily. However, accumulating data indicate that activation of the RAS superfamily are poor biomarkers of statin sensitivity, and the mechanism of statin-induced tumor-specific apoptosis remains unclear. Here we demonstrate that cancer cell death triggered by statins can be uncoupled from prenylation of the RAS superfamily of oncoproteins. Ectopic expression of different members of the RAS superfamily did not uniformly sensitize cells to fluvastatin, indicating that increased cellular demand for protein prenylation cannot explain increased statin sensitivity. Although ectopic expression of HRAS increased statin sensitivity, expression of myristoylated HRAS did not rescue this effect. HRAS-induced epithelial-to-mesenchymal transition (EMT) through activation of zinc finger E-box binding homeobox 1 (ZEB1) sensitized tumor cells to the antiproliferative activity of statins, and induction of EMT by ZEB1 was sufficient to phenocopy the increase in fluvastatin sensitivity; knocking out ZEB1 reversed this effect. Publicly available gene expression and statin sensitivity data indicated that enrichment of EMT features was associated with increased sensitivity to statins in a large panel of cancer cell lines across multiple cancer types. These results indicate that the anticancer effect of statins is independent from prenylation of RAS family proteins and is associated with a cancer cell EMT phenotype.

Topics: Apoptosis; Biomarkers, Tumor; Cell Proliferation; Drug Resistance, Neoplasm; Epithelial-Mesenchymal Transition; Fluvastatin; Humans; Mevalonic Acid; Neoplasms; Polyisoprenyl Phosphates; Protein Prenylation; ras Proteins; Sesquiterpenes; Tumor Cells, Cultured; Zinc Finger E-box-Binding Homeobox 1

Statins, such as lovastatin, can induce a cell cycle arrest in the G1 phase. This robust antiproliferative activity remains intact in many cancer cells that are deficient in cell cycle checkpoints and leads to an increased expression of CDK inhibitor proteins p27Kip1 and p21Cip1. The molecular details of this statin-induced growth arrest remains unclear. Here we present evidence that lovastatin can induce the degradation of Skp2, a subunit of the SCFSkp2 ubiquitin ligase that targets p27Kip1 and p21Cip1 for proteasomal destruction. The statin-induced degradation of Skp2 is cell cycle phase independent and does not require its well characterised degradation pathway mediated by APC/CCdh1- or Skp2 autoubiquitination. An N-terminal domain preceding the F-box of Skp2 is both necessary and sufficient for its statin mediated degradation. The degradation of Skp2 results from statin induced depletion of geranylgeranyl isoprenoid intermediates of cholesterol biosynthesis. Inhibition of geranylgeranyl-transferase-I also promotes APC/CCdh1- independent degradation of Skp2, indicating that de-modification of a geranylgeranylated protein triggers this novel pathway of Skp2 degradation.

Topics: Alkyl and Aryl Transferases; Animals; Antigens, CD; Antineoplastic Agents; Cadherins; Cdh1 Proteins; Cell Proliferation; Cyclin-Dependent Kinase Inhibitor p21; Cyclin-Dependent Kinase Inhibitor p27; Down-Regulation; Genes, APC; HeLa Cells; Humans; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Lovastatin; Mice; Neoplasms; NIH 3T3 Cells; Polyisoprenyl Phosphates; Proteasome Endopeptidase Complex; Proteolysis; S-Phase Kinase-Associated Proteins; Signal Transduction; Time Factors; Transfection; U937 Cells

The schweinfurthins, a family of natural products derived from the isoprenoid biosynthetic pathway (IBP), have marked growth inhibitory activity. However, the biochemical basis for the schweinfurthins cellular effects has remained ill-defined. Here, the effects of the synthetic schweinfurthin, 3-deoxyschweinfurthin (3dSB) on multiple aspects of isoprenoid homeostasis are explored. Cytotoxicity assays demonstrate a synergistic interaction between 3dSB and the HMG-CoA reductase inhibitor lovastatin but not with other IBP inhibitors in a variety of human cancer cell lines. The cytotoxic effects of 3dSB were enhanced in cells incubated in lipid-depleted serum. 3dSB was found to enhance the lovastatin-induced decrease in protein prenylation. In addition, 3dSB decreases intracellular farnesyl pyrophosphate and geranylgeranyl pyrophosphate levels in both established cell lines and primary cells. To determine whether 3dSB alters the regulation of expression of genes involved in isoprenoid homeostasis, real-time PCR studies were performed in human cell lines cultured in either lipid-replete or -deplete conditions. These studies demonstrate that 3dSB abrogates lovastatin-induced upregulation of sterol regulatory element-containing genes and lovastatin-induced downregulation of ABCA1. In aggregate, these studies are the first to demonstrate that a schweinfurthin exerts pleiotropic effects on isoprenoid homeostasis.

Topics: Animals; Antineoplastic Agents; ATP Binding Cassette Transporter 1; ATP-Binding Cassette Transporters; Cell Line, Tumor; Cell Survival; Down-Regulation; Drug Synergism; Humans; Lovastatin; Neoplasms; Polyisoprenyl Phosphates; Prenylation; Sesquiterpenes; Stilbenes; Terpenes

This study emphasizes the importance of Rho/ROCK pathway in lovastatin-induced apoptosis as replenishment with exogenous isoprenoid, geranylgeranylpyrophosphate (GGPP), resulted in inhibition of apoptosis in cultured tumor cells. Treatment of C6 glioma cells with Toxin B and exoenzyme C3 resulted in cell death suggesting the role of geranylgeranylated protein(s) in the survival of glioma cells. Relative apoptotic death observed in cells transfected with dominant negative constructs of RhoA, Rac, and cdc42 imply Rho A as playing the major role in cell survival. Furthermore, the inhibition of Rho A kinase (ROCK), a direct downstream effector of Rho A, by Y-27632 or dominant negative of ROCK, induced apoptosis in glioma cells. These findings indicate that RhoA/ROCK pathway is involved negatively in the regulation of glioma cell death pathway. Moreover, in vivo studies of lovastatin treatment in animals implanted with C6 glioma cell tumors also resulted in smaller tumor size and induced apoptosis in the tumor tissue. The implantation of stably transfected C6 glioma cells with expression vector of C3 exoenzyme, dominant negative of RhoA and ROCK, resulted in significant smaller tumor mass, further establishing the importance of geranylgeranylated proteins, specifically RhoA and its downstream effecter ROCK, in cell survival and tumor genesis.

Topics: Amides; Animals; Antineoplastic Agents; Apoptosis; Blotting, Southern; Blotting, Western; Caspases; Cell Survival; Disease Models, Animal; DNA Fragmentation; Dose-Response Relationship, Drug; Drug Interactions; Enzyme Inhibitors; Flow Cytometry; Humans; Immunohistochemistry; In Situ Nick-End Labeling; Intracellular Signaling Peptides and Proteins; Lovastatin; Male; Mevalonic Acid; Mice; Neoplasms; Neoplasms, Experimental; Polyisoprenyl Phosphates; Protein Serine-Threonine Kinases; Pyridines; Rats; Rats, Wistar; rho-Associated Kinases; rhoA GTP-Binding Protein; Signal Transduction; Tetrazolium Salts; Thiazoles; Time Factors; Tumor Cells, Cultured