Molecular mechanisms linking geranylgeranyl diphosphate synthase to cell survival and proliferation

α-Amino bisphosphonate triazoles serve as GGDPS inhibitors

Depletion of cellular levels of geranylgeranyl diphosphate by inhibition of the enzyme geranylgeranyl diphosphate synthase (GGDPS) is a potential strategy for disruption of protein transport by limiting the geranylgeranylation of the Rab proteins that regulate intracellular trafficking. As such, there is interest in the development of GGDPS inhibitors for the treatment of malignancies characterized by abnormal protein production, including multiple myeloma. Our previous work has explored the structure-function relationship of a series of isoprenoid triazole bisphosphonate-based GGDPS inhibitors, with modifications having impact on enzymatic, cellular and in vivo activities. We have synthesized a new series of α-amino bisphosphonates to understand the impact of modifying the alpha position with a moiety that is potentially linkable to other agents. Bioassays evaluating the enzymatic and cellular activities of these compounds demonstrate that incorporation of the α-amino group affords compounds with GGDPS inhibitory activity which is modulated by isoprenoid tail chain length and olefin stereochemistry. These studies provide further insight into the complexity of the structure-function relationship and will enable future efforts focused on tumor-specific drug delivery.

Anti-osteoporosis drugs reduce mortality in cancer patients: A national cohort study of elderly with vertebral fractures

Introduction

The most prevalent type of fragility fractures is osteoporotic vertebral fractures (OVFs). However, only a few studies have examined the relationship between anti-osteoporosis treatments and malignancy-related mortality following an OVF. The goal of this study is to determine the effect of anti-osteoporosis therapy on mortality in OVF patients with and without cancer.

Method

Data from older people over the age of 65 who were hospitalised for OVFs between 1 January 2003 and 31 December 2018 were analysed retrospectively. A total of 6139 persons getting osteoporosis treatment and 28,950 who did not receive treatment were analysed, together with 2 sets of patients, comprising cancer patients (794) and cancer-free patients (5342), using anti-osteoporosis medication or not, in 1:1 propensity score-matched analyses. The hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated.

Results

In all, 35,089 patients with OVFs were included in the population; 29,931 people (85.3%) were women, and the mean (standard deviation) age was 78.13 (9.27) years. Overall survival was considerably higher in those undergoing osteoporosis therapy. This was true both for those without cancer (adjusted HR 0.55; 95% CI 0.51-0.59; P<.0001) as well as those with cancer (adjusted HR 0.72; 95% CI 0.62-0.84; P<.0001). Even among cancer patients, those who received anti-osteoporotic drugs had a lower mortality rate than those who did not.

Conclusion

Our findings suggest that anti-osteoporosis therapy should be initiated regardless of the presence of cancer in the elderly, as it increases survival following OVFs.

Structural Insight into Geranylgeranyl Diphosphate Synthase (GGDPS) for Cancer Therapy

Geranylgeranyl diphosphate synthase (GGDPS), the source of the isoprenoid donor in protein geranylgeranylation reactions, has become an attractive target for anticancer therapy due to the reliance of cancers on geranylgeranylated proteins. Current GGDPS inhibitor development focuses on optimizing the drug-target enzyme interactions of nitrogen-containing bisphosphonate-based drugs. To advance GGDPS inhibitor development, understanding the enzyme structure, active site, and ligand/product interactions is essential. Here we provide a comprehensive structure-focused review of GGDPS. We reviewed available yeast and human GGDPS structures and then used AlphaFold modeling to complete unsolved structural aspects of these models. We delineate the elements of higher-order structure formation, product-substrate binding, the electrostatic surface, and small-molecule inhibitor binding. With the rise of structure-based drug design, the information provided here will serve as a valuable tool for rationally optimizing inhibitor selectivity and effectiveness.

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.

Implications on the Therapeutic Potential of Statins via Modulation of Autophagy

Statins, which are functionally known as 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) inhibitors, are lipid-lowering compounds widely prescribed in patients with cardiovascular diseases (CVD). Several biological and therapeutic functions have been attributed to statins, including neuroprotection, antioxidation, anti-inflammation, and anticancer effects. Pharmacological characteristics of statins have been attributed to their involvement in the modulation of several cellular signaling pathways. Over the past few years, the therapeutic role of statins has partially been attributed to the induction of autophagy, which is critical in maintaining cellular homeostasis and accounts for the removal of unfavorable cells or specific organelles within cells. Dysregulated mechanisms of the autophagy pathway have been attributed to the etiopathogenesis of various disorders, including neurodegenerative disorders, malignancies, infections, and even aging. Autophagy functions as a double-edged sword during tumor metastasis. On the one hand, it plays a role in inhibiting metastasis through restricting necrosis of tumor cells, suppressing the infiltration of the inflammatory cell to the tumor niche, and generating the release of mediators that induce potent immune responses against tumor cells. On the other hand, autophagy has also been associated with promoting tumor metastasis. Several anticancer medications which are aimed at inducing autophagy in the tumor cells are related to statins. This review article discusses the implications of statins in the induction of autophagy and, hence, the treatment of various disorders.

Dietary Geranylgeranyl Pyrophosphate Counteracts the Benefits of Statin Therapy in Experimental Pulmonary Hypertension

BACKGROUND

The mevalonate pathway generates endogenous cholesterol and intermediates including geranylgeranyl pyrophosphate (GGPP). By reducing GGPP production, statins exert pleiotropic or cholesterol-independent effects. The potential regulation of GGPP homeostasis through dietary intake and the interaction with concomitant statin therapy is unknown.

METHODS

We developed a sensitive high-pressure liquid chromatography technique to quantify dietary GGPP and conducted proteomics, qualitative real-time polymerase chain reaction screening, and Western blot to determine signaling cascades, gene expression, protein-protein interaction, and protein membrane trafficking in wild-type and transgenic rats.

RESULTS

GGPP contents were highly variable depending on food source that differentially regulated blood GGPP levels in rats. Diets containing intermediate and high GGPP reduced or abolished the effects of statins in rats with hypoxia- and monocrotaline-induced pulmonary hypertension: this was rescuable by methyl-allylthiosulfinate and methyl-allylthiosulfinate-rich garlic extracts. In human pulmonary artery smooth muscle cells treated with statins, hypoxia activated RhoA in an extracellular GGPP-dependent manner. Hypoxia-induced ROCK2 (Rho associated coiled-coil containing protein kinase 2)/Rab10 (Ras-related protein rab-10) signaling was prevented by statin and recovered by exogenous GGPP. The hypoxia-activated RhoA/ROCK2 pathway in rat and human pulmonary artery smooth muscle cells upregulated the expression of Ca²⁺-sensing receptor (CaSR) and HIMF (hypoxia-induced mitogenic factor), a mechanism attenuated by statin treatment and regained with exogenous GGPP. Rab10 knockdown almost abrogated hypoxia-promoted CaSR membrane trafficking, a process diminished by statin and resumed by exogenous GGPP. Hypoxia-induced pulmonary hypertension was reduced in rats with CaSR mutated at the binding motif of HIMF and the interaction between dietary GGPP and statin efficiency was abolished. In humans fed a high GGPP diet, blood GGPP levels were increased. This abolished statin-lowering effects on plasma GGPP, and also on hypoxia-enhanced RhoA activity of blood monocytes that was rescued by garlic extracts.

CONCLUSIONS

There is important dietary regulation of GGPP levels that interferes with the effects of statin therapy in experimental pulmonary hypertension. These observations rely on a key and central role of RhoA-ROCK2 cascade activation and Rab10-faciliated CaSR membrane trafficking with subsequent overexpression and binding of HIMF to CaSR. These findings warrant clinical investigation for the treatment of pulmonary hypertension and perhaps other diseases by combining statin with garlic-derived methyl-allylthiosulfinate or garlic extracts and thus circumventing dietary GGPP variations.

Synergistic effect of graphene oxide and zoledronic acid for osteoporosis and cancer treatment

Zoledronic acid (ZOL) is a third generation bisphosphonate which can be used as a drug for the treatment of osteoporosis and metastasis. In this study, graphene oxide (GO) is conjugated with ZOL, and the nanostructured material is evaluated in terms viability, proliferation and differentiation. Furthermore, the associated morphological changes of bone marrow-derived mesenchymal stem cells (BM-MSC), and Michigan Cancer Foundation-7 (MCF-7) breast cancer cells, as well as the effect of the drugs on mineralization of BM-MSCs are investigated using a variety of characterization techniques including Fourier Transform Infrared Spectroscopy (FTIR), scanning electron microscopy (SEM) as well as alamar blue, acridine orange, and alizarin red assays. Nanostructured ZOL-GO with an optimum performance is synthesized using ZOL and GO suspensions with the concentration of 50 µM and 2.91 ng/ml, respectively. ZOL-GO nanostructures can facilitate the mineralization of BM-MSC cells, demonstrated by the formation of clusters around the cells. The results obtained confirm the performance of ZOL-GO nanostructures as promising drug complexes for the treatment of osteoporosis and metastasis.

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.

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.

Altering the response to radiation: radiosensitizers and targeted therapies in pancreatic ductal adenocarcinoma: preclinical and emerging clinical evidence

Radiation therapy continues to have an evolving role in pancreatic ductal adenocarcinoma. While metastatic failure likely contributes to the majority of patient mortality, achieving local control through surgery and/or radiation appears to be important as certain studies suggest that mortality is contributed by local failure. Many studies support that pancreatic cancer is a relatively radiation resistant tumor type. In addition, the ability to further improve radiation through dose escalation strategies in the non-metastatic setting is hampered by closeness of normal organs, including small bowel and stomach, to the tumor. Thus subverting molecular pathways that promote radiation resistance will be critical to further success of radiation in this disease. There is a wealth of preclinical data supporting the targeting of various molecular pathways in combination with radiation therapy, including DNA repair, cell cycle checkpoint proteins, receptor tyrosine kinases, oncoproteins, stem cells, and immunomodulation. A number of clinical trials have been completed or are on-going with novel molecular inhibitors. In this review, we summarize existing preclinical and clinical molecular strategies for improving the efficacy of radiation in pancreatic cancer, and highlight recent and ongoing clinical trials combining radiation and various targeted therapies.

Preclinical investigation of a potent geranylgeranyl diphosphate synthase inhibitor

Geranylgeranyl diphosphate synthase (GGDPS) is the enzyme in the isoprenoid biosynthesis pathway that catalyzes the synthesis of the 20-carbon isoprenoid GGPP, which serves as the isoprenoid donor for protein geranylgeranylation reactions. Rab proteins mediate vesicle trafficking within the cell and their activity is dependent on geranylgeranylation. Our prior work has demonstrated that agents that disrupt Rab geranylgeranylation disrupt monoclonal protein trafficking in myeloma cells, resulting in induction of the unfolded protein response pathway and apoptosis. VSW1198 is a potent GGDPS inhibitor with measurable cellular activity at concentrations as low as 30 nM. Due to its potent activity against myeloma cells in vitro, we were interested in evaluating the toxicology profile, pharmacokinetic (PK) profile, tissue distribution pattern and metabolic stability of VSW1198 in preparation for in vivo efficacy studies. Single dose testing via IV administration in CD-1 mice revealed a maximum tolerated dose of 0.5 mg/kg. Doses ≥1 mg/kg resulted in liver toxicity that peaked around 6-7 days post-injection. Disruption of protein geranylgeranylation following repeat dosing of VSW1198 was confirmed via immunoblot analysis of unmodified Rap1a in multiple organs. The PK studies revealed a half-life of 47.7 ± 7.4 h. VSW1198 was present in all tested tissues with the highest levels in the liver. In both human liver microsomes and mouse S9 studies VSW1198 showed complete stability, suggesting no phase I or phase II metabolism. In summary, these studies demonstrate systemic distribution, on-target disruption of protein geranylgeranylation, and metabolic stability of a potent GGDPS inhibitor VSW1198 and form the basis for future efficacy studies in mouse models of myeloma.

Synthesis and Biological Evaluation of Imidazole-Bearing α-Phosphonocarboxylates as Inhibitors of Rab Geranylgeranyl Transferase (RGGT)

Rab geranylgeranyl transferase (RGGT) is an interesting therapeutic target, as it ensures proper functioning of Rab GTPases, a class of enzymes responsible for the regulation of vesicle trafficking. Relying on our previous studies, we synthesized a set of new α-phosphonocarboxylic acids as potential RGGT inhibitors, with emphasis on the elaboration of imidazole-containing analogues. We identified two compounds with activity similar to that of previously reported RGGT inhibitors, showing structural similarity to imidazo[1,2-a]pyridine-containing analogues in terms of their substitution pattern. Interestingly, analogues of the N-series, derived from another phosphonocarboxylate RGGT inhibitor, 2-fluoro-3-(1H-imidazol-1-yl)-2-phosphonopropanoic acid, turned out to be inactive in our model, indicating that an additional substituent localized at positions C2 or C4 of the imidazole ring, may adversely affect the potency against the targeted enzyme.

Quantitative determination of a potent geranylgeranyl diphosphate synthase inhibitor using LC-MS/MS: Derivatization and application

An isomeric mixture of homogeranyl/homoneryl triazole bisphosphonates (VSW1198) has previously been shown to be a potent inhibitor of geranylgeranyl diphosphate (GGDP) synthase (GGDPS) and of therapeutic interest for the treatment of multiple myeloma. We have developed and validated a selective and sensitive liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method for the simultaneous quantitation of both the E- and Z- isomers of VSW1198 in cell culture media, mouse plasma and tissues. VSW1198 and internal standard are extracted from the bio-matrices by solid-phase extraction, followed by derivatization using trimethylsilyldiazomethane. The chromatographic separation of analytes was achieved on a Phenomenex Gemini NX column (150 mm * 2.0 mm, 5 μ) with gradient elution using 0.1% acetic acid and methanol/acetonitrile (1:1) as the mobile phase at a flow rate of 0.2 mL/min. Derivatized analytes were ionized with an electrospray ionization source in positive multiple reaction monitoring (MRM) mode and quantitated using MS/MS. The MS/MS response was linear over the concentration range from 0.38-1500 and 0.13-500 ng/mL for the E- and Z-isomers, respectively. The within- and between-day precision (relative standard deviation, % RSD) and accuracy were within the acceptable limits per FDA guidelines. The validated method was used for quantitative determination of the compounds in preclinical studies focused on the development of VSW1198 as a novel anti-cancer agent.

α-Methylation enhances the potency of isoprenoid triazole bisphosphonates as geranylgeranyl diphosphate synthase inhibitors

Disruption of protein geranylgeranylation via inhibition of geranylgeranyl diphosphate synthase (GGDPS) represents a novel therapeutic strategy for a variety of malignancies, especially those characterized by excessive protein secretion such as multiple myeloma. Our work has demonstrated that some isoprenoid triazole bisphosphonates are potent and selective inhibitors of GGDPS. Here we present the synthesis and biological evaluation of a new series of isoprenoid triazoles modified by incorporation of a methyl group at the α-carbon. These studies reveal that incorporation of an α-methyl substituent enhances the potency of these compounds as GGDPS inhibitors, and, in the case of the homogeranyl/homoneryl series, abrogates the effects of olefin stereochemistry on inhibitory activity. The incorporation of the methyl group allowed preparation of a POM-prodrug, which displayed a 10-fold increase in cellular activity compared to the corresponding salt. These studies form the basis for future preclinical studies investigating the anti-myeloma activity of these novel α-methyl triazole bisphosphonates.

Identification of the Privileged Position in the Imidazo[1,2-a]pyridine Ring of Phosphonocarboxylates for Development of Rab Geranylgeranyl Transferase (RGGT) Inhibitors

Members of the Rab GTPase family are master regulators of vesicle trafficking. When disregulated, they are associated with a number of pathological states. The inhibition of RGGT, an enzyme responsible for post-translational geranylgeranylation of Rab GTPases represents one way to control the activity of these proteins. Because the number of molecules modulating RGGT is limited, we combined molecular modeling with biological assays to ascertain how modifications of phosphonocarboxylates, the first reported RGGT inhibitors, rationally improve understanding of their structure-activity relationship. We have identified the privileged position in the core scaffold of the imidazo[1,2-a]pyridine ring, which can be modified without compromising compounds' potency. Thus modified compounds are micromolar inhibitors of Rab11A prenylation, simultaneously being inactive against Rap1A/Rap1B modification, with the ability to inhibit proliferation of the HeLa cancer cell line. These findings were rationalized by molecular docking, which recognized interaction of phosphonic and carboxylic groups as decisive in phosphonocarboxylate localization in the RGGT binding site.

Recent Advances in the Development of Mammalian Geranylgeranyl Diphosphate Synthase Inhibitors

The enzyme geranylgeranyl diphosphate synthase (GGDPS) catalyzes the synthesis of the 20-carbon isoprenoid geranylgeranyl diphosphate (GGPP). GGPP is the isoprenoid donor for protein geranylgeranylation reactions catalyzed by the enzymes geranylgeranyl transferase (GGTase) I and II. Inhibitors of GGDPS result in diminution of protein geranylgeranylation through depletion of cellular GGPP levels, and there has been interest in GGDPS inhibitors as potential anti-cancer agents. Here we discuss recent advances in the development of GGDPS inhibitors, including insights gained by structure-function relationships, and review the preclinical data that support the continued development of this novel class of drugs.

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.