Isoprenoid pyrophosphate analogues regulate expression of Ras-related proteins

Statins enhances antitumor effect of oxaliplatin in KRAS-mutated colorectal cancer cells and inhibits oxaliplatin-induced neuropathy

BACKGROUND

KRAS mutations are fraught with the progression of colorectal cancer and resistance to chemotherapy. There are pathways such as extracellular regulated protein kinase 1/2 (ERK1/2) and Akt downstream and farnesylation and geranylgeranylation upstream that are activated upon mutated KRAS. Previous studies have shown that statins, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, are effective to treat KRAS mutated colorectal cancer cells. Increased doses of oxaliplatin (L-OHP), a well-known alkylating chemotherapeutic drug, causes side effects such as peripheral neuropathy due to ERK1/2 activation in spinal cords. Hence, we examined the combinatorial therapeutic efficacy of statins and L-OHP to reduce colorectal cancer cell growth and abrogate neuropathy in mice.

METHODS

Cell survival and confirmed apoptosis was assessed using WST-8 assay and Annexin V detection kit. Detection of phosphorylated and total proteins was analyzed the western blotting. Combined effect of simvastatin and L-OHP was examined the allograft mouse model and L-OHP-induced neuropathy was assessed using cold plate and von Frey filament test.

RESULTS

In this study, we examined the effect of combining statins with L-OHP on induction of cell death in colorectal cancer cell lines and improvement of L-OHP-induced neuropathy in vivo. We demonstrated that combined administration with statins and L-OHP significantly induced apoptosis and elevated the sensitivity of KRAS-mutated colorectal cancer cells to L-OHP. In addition, simvastatin suppressed KRAS prenylation, thereby enhancing antitumor effect of L-OHP through downregulation of survivin, XIAP, Bcl-xL, and Bcl-2, and upregulation of p53 and PUMA via inhibition of nuclear factor of κB (NF-κB) and Akt activation, and induction of c-Jun N-terminal kinase (JNK) activation in KRAS-mutated colorectal cancer cells. Moreover, simvastatin enhanced the antitumor effects of L-OHP and suppressed L-OHP-induced neuropathy via ERK1/2 activation in vivo.

CONCLUSION

Therefore, statins may be therapeutically useful as adjuvants to L-OHP in KRAS-mutated colorectal cancer and may also be useful in the treatment of L-OHP-induced neuropathy.

Chemical Proteomic Profiling of the Interacting Proteins of Isoprenoid Pyrophosphates

Isoprenoid pyrophosphates are involved in protein prenylation and assume regulatory roles in cells; however, little is known about the cellular proteins that can interact with isoprenoid pyrophosphates. Here, we devised a chemical proteomic strategy, capitalizing on the use of a desthiobiotin-geranyl pyrophosphate (GPP) acyl phosphate probe for the enrichment and subsequent identification of GPP-binding proteins using liquid chromatography-tandem mass spectrometry (LC-MS/MS). By combining stable isotope labeling by amino acids in cell culture (SILAC) and competitive labeling with low vs high concentrations of GPP probe, with ATP vs GPP acyl phosphate probes, or with the GPP probe in the presence of different concentrations of free GPP, we uncovered a number of candidate GPP-binding proteins. We also discovered, for the first time, histone deacetylase 1 (HDAC1) as a GPP-binding protein. Furthermore, we found that the enzymatic activity of HDAC1 could be modulated by isoprenoid pyrophosphates. Together, we developed a novel chemical proteomic method for the proteome-wide discovery of GPP-binding proteins, which sets the stage for a better understanding about the biological functions of isoprenoids.

Reduced esophageal cancer incidence in statin users, particularly with cyclo-oxygenase inhibition

AIM: To examine the association between statin use and the development of esophageal cancer

METHODS: We performed a systematic review and meta-analysis. Multiple databases (Pubmed, EMBASE, Cochrane Library, Web of Science, Wiley Interscience and Google Scholar) were systematically searched for studies reporting the association of statin use and the development of esophageal cancer. Literature searching and data abstraction were performed independently by two separate researchers. The quality of studies reviewed was evaluated using the Newcastle-Ottawa Quality assessment scale. Meta-analysis on the relationship between statin use and cancer incidence was performed. The effect of the combination of statin plus a cyclo-oxygenase inhibitor was also examined.

RESULTS: Eleven studies met eligibility criteria, 9 high and 2 medium quality. All were observational studies. Studies examining adenocarcinoma development in Barrett’s oesophagus included 317 cancers and 1999 controls, population-based studies examining all esophageal cancers included 371203 cancers and 6083150 controls. In the Barrett’s population the use of statins (OR = 0.57; 95%CI: 0.43-0.75) and cyclo-oxygenase inhibitors (OR = 0.59; 95%CI: 0.45-0.77) were independently associated with a reduced incidence of adenocarcinoma. Combined use of a statin plus cyclo-oxygenase inhibitor was associated with an even lower adenocarcinoma incidence (OR = 0.26; 95%CI: 0.1-0.68). There was more heterogeneity in the population-based studies but pooled adjusted data showed that statin use was associated with a lower incidence of all combined esophageal cancers (OR = 0.81; 95%CI: 0.75-0.88).

CONCLUSION: Statin use in patients with Barrett’s oesophagus is associated with a significantly lower incidence of adenocarcinoma. The chemopreventive actions of statins, especially combined with cyclo-oxygenase inhibitors deserve further exploration.

Statin use is associated with a reduction in the incidence of esophageal adenocarcinoma: a case control study

The incidence of esophageal adenocarcinoma (EAC) is increasing significantly throughout the developed world. As yet, there are no proven chemopreventive strategies. In laboratory studies, aspirin, non-steroidal anti-inflammatory drugs and statins have promising chemopreventive actions. Several observational studies support a protective effect of aspirin and non-steroidal anti-inflammatory drugs, but there are only limited clinical data exploring the potential protective effect of statins. We conducted a case-control study examining aspirin and statin use in patients with EAC. Cancer cases were compared against age-sex-matched controls attending for diagnostic upper gastrointestinal endoscopy. Risk factor and drug exposure were established using standardized interviews. Logistic regression was used to compare statin exposure and correct for confounding factors. A total of 112 cases and 448 controls were enrolled. Statin use was associated with a significantly lower incidence of EAC (odds ratio 0.52, 95% confidence interval 0.27-0.92). Aspirin use was also associated with apparent protection against EAC (odds ratio 0.68, 95% confidence interval 0.28-0.92), and a significantly greater effect was seen with the combination of statin plus aspirin (odds ratio 0.27, 95% confidence interval 0.05-0.67). There was a significant trend for greater risk reduction with longer duration and higher doses of statin use. Simvastatin comprised the majority of statin use, but similar effects were seen with simvastatin and non-simvastatin agents. In this observational study, patients regularly using statins or aspirin had a lower incidence of EAC. Statins may have clinically useful effects in preventing the development of EAC.

Regular statin and aspirin use in patients with Barrett's oesophagus is associated with a reduced incidence of oesophageal adenocarcinoma

BACKGROUND

Oesophageal adenocarcinoma (OAC) has a poor prognosis, and chemoprevention is an attractive option to reduce the burden of the disease. Hydroxyl-methyl-CoA reductase inhibitors (statins) have been shown to exert potentially useful anticancer effects against OAC cell lines, but there are only limited clinical data examining the effects of statins on the incidence of OAC.

AIM

To examine the association between statin use and the incidence of OAC.

METHODS

We have carried out a case-control study comparing statin use between patients with an incident diagnosis of OAC and controls with nonprogressive Barrett's oesophagus. Eighty-five cancer cases were compared with 170 age-matched and sex-matched controls. Risk factors and drug exposure were established using standardized interviews. Logistic regression was used to compare statin exposure and correct for confounding factors.

RESULTS

Regular statin use was associated with a significantly lower incidence of OAC [uncorrected odds ratio (OR) 0.45, 95% confidence intervals 0.24-0.84)]. After correction for confounding variables including aspirin and NSAID use, statin use was still associated with a reduced incidence of OAC (OR 0.57, 0.28-0.94). Longer duration of statin use and higher doses were both associated with a significantly greater reduction in OAC. The combination of regular statin and aspirin use was associated with a significantly further reduced incidence of OAC (OR 0.31, 0.04-0.69).

CONCLUSION

In this observational case-control study, the regular use of statins was associated with a reduced incidence of OAC. The chemopreventative actions of statins, especially in conjunction with aspirin, deserve further study.

Zoledronic acid for adjuvant use in patients with breast cancer

Zoledronic acid, a nitrogen-containing bisphosphonate, is firmly established in the management of metastatic bone disease. It inhibits farnesyl diphosphonate synthase within the mevalonate pathway and, through this mechanism, is a potent inhibitor of osteoclast-mediated bone resorption. In addition, there are preclinical data suggesting that farnesyl diphosphonate synthase inhibition by zoledronic acid has anti-tumor effects in breast cancer. Adjuvant therapies for early breast cancer are associated with substantial decreases in bone mineral density. Results from three clinical trials, ABCSG-12, Z-FAST and ZO-FAST, indicate that the addition of twice-yearly zoledronic acid to standard adjuvant endocrine therapy in premenopausal and postmenopausal patients with hormone receptor-positive breast cancer prevents cancer treatment-induced bone loss. Moreover, it is becoming evident that it may also exert anticancer effects in an estrogen-deprived state in the adjuvant and neoadjuvant setting. However, long-term side effects need to be taken into consideration for treatment decisions.

Synergistic actions of atorvastatin with gamma-tocotrienol and celecoxib against human colon cancer HT29 and HCT116 cells

The synergistic actions of atorvastatin (ATST) with gamma-tocotrienol (gamma-TT) and celecoxib (CXIB) were studied in human colon cancer cell lines HT29 and HCT116. The synergistic inhibition of cell growth by ATST and gamma-TT was demonstrated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and isobologram analysis. delta-TT exhibited a similar inhibitory action when combined with ATST. Mevalonate and geranylgeranyl pyrophosphate eliminated most of the growth inhibitory effect of ATST, but only marginally decreased that of gamma-TT; whereas farnesyl pyrophosphate and squalene exhibited little effect on the inhibitory action of ATST and gamma-TT, indicating protein geranylgeranylation, but not farnesylation are involved in the inhibition of colon cancer cell growth. Both mevalonate and squalene restored the cellular cholesterol level that was reduced by ATST treatment, but only mevalonate eliminated the cell growth inhibitory effect, suggesting that the cholesterol level in cells does not play an essential role in inhibiting cancer cell growth. Protein level of HMG-CoA reductase increased after ATST treatment, and the presence of gamma-TT attenuated the elevated level of HMG-CoA reductase. ATST also decreased membrane-bound RhoA, possibly due to a reduced level of protein geranylgeranylation; addition of gamma-TT enhanced this effect. The mediation of HMG-CoA reductase and RhoA provides a possible mechanism for the synergistic action of ATST and gamma-TT. The triple combination of ATST, gamma-TT and CXIB showed a synergistic inhibition of cancer cell growth in MTT assays. The synergistic action of these three compounds was also illustrated by their induction of G(0)/G(1) phase cell cycle arrest and apoptosis.

Rosuvastatin induces delayed preconditioning against oxygen-glucose deprivation in cultured cortical neurons

We tested whether rosuvastatin (RST) protected against oxygen-glucose deprivation (OGD)-induced cell death in primary rat cortical neuronal cultures. OGD reduced neuronal viability (%naive controls, mean +/- SE, n = 24-96, P < 0.05) to 44 +/- 1%, but 3-day pretreatment with RST (5 microM) increased survival to 82 +/- 2% (P < 0.05). One-day RST treatment was not protective. RST-induced neuroprotection was abolished by mevalonate or geranylgeranyl pyrophosphate (GGPP), but not by cholesterol coapplication. Furthermore, RST-induced decreases in neuronal cholesterol levels were abolished by mevalonate but not by GGPP. Reactive oxygen species (ROS) levels were reduced in RST-preconditioned neurons after OGD, and this effect was also reversed by both mevalonate and GGPP. These data suggested that GGPP, but not cholesterol depletion, were responsible for the induction of neuroprotection. Therefore, we tested whether 3-day treatments with perillic acid, a nonspecific inhibitor of both geranylgeranyl transferase (GGT) GGT 1 and Rab GGT, and the GGT 1-specific inhibitor GGTI-286 would reproduce the effects of RST. Perillic acid, but not GGTI-286, elicited robust neuronal preconditioning against OGD. RST, GGTI-286, and perillic acid all decreased mitochondrial membrane potential and lactate dehydrogenase activity in the cultured neurons, but only RST and perillic acid reduced neuronal ATP and membrane Rab3a protein levels. In conclusion, RST preconditions cultured neurons against OGD via depletion of GGPP, leading to decreased geranylgeranylation of proteins that are probably not isoprenylated by GGT 1. Reduced neuronal ATP levels and ROS production after OGD may be directly involved in the mechanism of neuroprotection.

Mono- and dialkyl isoprenoid bisphosphonates as geranylgeranyl diphosphate synthase inhibitors

Nitrogenous bisphosphonates are used clinically to reduce bone resorption associated with osteoporosis or metastatic bone disease, and are recognized as inhibitors of farnesyl diphosphate synthase. Inhibition of this enzyme decreases cellular levels of both farnesyl diphosphate and geranylgeranyl diphosphate which results in a variety of downstream biological effects including inhibition of protein geranylgeranylation. Our lab recently has prepared several isoprenoid bisphosphonates that inhibit protein geranylgeranylation and showed that one selectively inhibits geranylgeranyl diphosphate synthase. This results in depletion of intracellular geranylgeranyl diphosphate and impacts protein geranylgeranylation but does not affect protein farnesylation. To clarify the structural features of isoprenoid bisphosphonates that account for their geranylgeranyl diphosphate synthase inhibition, we have prepared a new group of isoprenoid bisphosphonates. The complete set of compounds has been tested for in vitro inhibition of human recombinant geranylgeranyl diphosphate synthase and cellular inhibition of protein geranylgeranylation. These results show some surprising relationships between in vitro and cellular activity, and will guide development of clinical agents directed at geranylgeranyl diphosphate synthase.

Farnesyl phosphates are endogenous ligands of lysophosphatidic acid receptors: inhibition of LPA GPCR and activation of PPARs

Oligoprenyl phosphates are key metabolic intermediates for the biosynthesis of steroids, the side chain of ubiquinones, and dolichols and the posttranslational isoprenylation of proteins. Farnesyl phosphates are isoprenoid phosphates that resemble polyunsaturated fatty alcohol phosphates, which we have recently shown to be the minimal pharmacophores of lysophosphatidic acid (LPA) receptors. Here we examine whether farnesyl phosphates can interact with the cell surface and nuclear receptors for LPA. Both farnesyl phosphate and farnesyl diphosphate potently and specifically antagonized LPA-elicited intracellular Ca(2+)-mobilization mediated through the LPA(3) receptor, while causing only modest inhibition at the LPA(2) receptor and no measurable effect at the LPA(1) receptor. Farnesol also inhibited LPA(3) but was much less effective. The estimated dissociation constant of LPA(3) for farnesyl phosphate is 48+/-12 nM and 155+/-30 nM for farnesyl diphosphate. The transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma) binds to and is activated by LPA and its analogs including fatty alcohol phosphates. We found that both farnesyl phosphate and diphosphate, but not farnesol, compete with the binding of the synthetic PPARgamma agonist [(3)H]rosiglitazone and activate the PPARgamma-mediated gene transcription. Farnesyl monophosphate at 1 microM, but not diphosphate, activated PPARalpha and PPARbeta/delta reporter gene expression. These results indicate new potential roles for the oligoprenyl phosphates as potential endogenous modulators of LPA targets and show that the polyisoprenoid chain is recognized by some LPA receptors.

Stable propylphosphonic acid analogues of geranylgeranyl diphosphate possessing inhibitory activity on geranylgeranyl protein transferase

Stable analogues of geranylgeranyl diphosphate, possessing 3-(phosphono)propionamido moieties in the place of the metabolically unstable diphosphate portion, were prepared and submitted to prenyltransferase (GGTase and FTase) inhibition assays. In one case, an excellent GGTase inhibitory activity was obtained (IC(50) = 39 nM), accompanied by a certain degree of GGTase vs. FTase selectivity.

Studies of the isoprenoid-mediated inhibition of mevalonate synthesis applied to cancer chemotherapy and chemoprevention

Pools of farnesyl diphosphate and other phosphorylated products of the mevalonate pathway are essential to the post-translational processing and physiological function of small G proteins, nuclear lamins, and growth factor receptors. Inhibitors of enzyme activities providing those pools, namely, 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase and mevalonic acid-pyrophosphate decarboxylase, and of activities requiring substrates from the pools, the prenyl protein transferases, have potential for development as novel chemotherapeutic agents. Their potentials as suggested by the clinical responses recorded in Phase I and II investigations of inhibitors of HMG CoA reductase (the statins), of mevalonic acid-pyrophosphate decarboxylase (sodium phenylacetate and sodium phenylbutyrate), and of farnesyl protein transferase (R115777, SCH66336, BMS-214662, Tipifarnib, L-778,123, and, prematurely, perillyl alcohol) are dimmed by dose-limiting toxicities. These nondiscriminant growth-suppressive agents induce G1 arrest and initiate apoptosis and differentiation, effects attributed to modulation of cell signaling pathways either by modulating gene expression, suppressing the post-translational processing of signaling proteins and growth factor receptors, or altering diacylglycerol signaling. Diverse isoprenoids and the HMG CoA reductase inhibitor, lovastatin, modulate cell growth, induce cell cycle arrest, initiate apoptosis, and suppress cellular signaling activities. Perillyl alcohol, the isoprenoid of greatest clinical interest, initially was considered to inhibit farnesyl protein transferase; follow-up studies revealed that perillyl alcohol suppresses the synthesis of small G proteins and HMG CoA reductase. In sterologenic tissues, sterol feedback control, mediated by sterol regulatory element binding proteins (SREBPs) 1a and 2, exerts the primary regulation on HMG CoA reductase activity at the transcriptional level. Secondary regulation, a nonsterol isoprenoid-mediated fine-tuning of reductase activity, occurs at the levels of reductase translation and degradation. HMG CoA reductase activity in tumors is elevated and resistant to sterol feedback regulation, possibly as a consequence of aberrant SREBP activities. Nonetheless, tumor reductase remains sensitive to isoprenoid-mediated post-transcriptional downregulation. Farnesol, an acyclic sesquiterpene, and farnesyl homologs, gamma-tocotrienol and various farnesyl derivatives, inhibit reductase synthesis and accelerate reductase degradation. Cyclic monoterpenes, d-limonene, menthol and perillyl alcohol and beta-ionone, a carotenoid fragment, lower reductase mass; perillyl alcohol and d-limonene lower reductase mass by modulating translational efficiency. The elevated reductase expression and greater demand for nonsterol products to maintain growth amplify the susceptibility of tumor reductase to isoprenoids, therein rendering tumor cells more responsive than normal cells to isoprenoid-mediated growth suppression. Blends of lovastatin, a potent nondiscriminant inhibitor of HMG CoA reductase, and gamma-tocotrienol, a potent isoprenoid shown to post-transcription-ally attenuate reductase activity with specificity for tumors, synergistically affect the growth of human DU145 and LNCaP prostate carcinoma cells and pending extensive preclinical evaluation, potentially offer a novel chemotherapeutic strategy free of the dose-limiting toxicity associated with high-dose lovastatin and other nondiscriminant mevalonate pathway inhibitors.

Isoprenoids: Remarkable diversity of form and function

The isoprenoid biosynthetic pathway is the source of a wide array of products. The pathway has been highly conserved throughout evolution, and isoprenoids are some of the most ancient biomolecules ever identified, playing key roles in many life forms. In this review we focus on C-10 mono-, C-15 sesqui-, and C-20 diterpenes. Evidence for interconversion between the pathway intermediates farnesyl pyrophosphate and geranylgeranyl pyrophosphate and their respective metabolites is examined. The diverse functions of these molecules are discussed in detail, including their ability to regulate expression of the beta-HMG-CoA reductase and Ras-related proteins. Additional topics include the mechanisms underlying the apoptotic effects of select isoprenoids, antiulcer activities, and the disposition and degradation of isoprenoids in the environment. Finally, the significance of pharmacological manipulation of the isoprenoid pathway and clinical correlations are discussed.

Structural basis for bisphosphonate-mediated inhibition of isoprenoid biosynthesis

Farnesyl pyrophosphate synthetase (FPPS) synthesizes farnesyl pyrophosphate through successive condensations of isopentyl pyrophosphate with dimethylallyl pyrophosphate and geranyl pyrophosphate. Nitrogen-containing bisphosphonate drugs used to treat osteoclast-mediated bone resorption and tumor-induced hypercalcemia are potent inhibitors of the enzyme. Here we present crystal structures of substrate and bisphosphonate complexes of FPPS. The structures reveal how enzyme conformational changes organize conserved active site residues to exploit metal-induced ionization and substrate positioning for catalysis. The structures further demonstrate how nitrogen-containing bisphosphonates mimic a carbocation intermediate to inhibit the enzyme. Together, these FPPS complexes provide a structural template for the design of novel inhibitors that may prove useful for the treatment of osteoporosis and other clinical indications including cancer.