Inhibition of protein prenylation by bisphosphonates causes sustained activation of Rac, Cdc42, and Rho GTPases

RhoB Mediates Phosphoantigen Recognition by Vγ9Vδ2 T Cell Receptor

Human Vγ9Vδ2 T cells respond to tumor cells by sensing elevated levels of phosphorylated intermediates of the dysregulated mevalonate pathway, which is translated into activating signals by the ubiquitously expressed butyrophilin A1 (BTN3A1) through yet unknown mechanisms. Here, we developed an unbiased, genome-wide screening method that identified RhoB as a critical mediator of Vγ9Vδ2 TCR activation in tumor cells. Our results show that Vγ9Vδ2 TCR activation is modulated by the GTPase activity of RhoB and its redistribution to BTN3A1. This is associated with cytoskeletal changes that directly stabilize BTN3A1 in the membrane, and the subsequent dissociation of RhoB from BTN3A1. Furthermore, phosphoantigen accumulation induces a conformational change in BTN3A1, rendering its extracellular domains recognizable by Vγ9Vδ2 TCRs. These complementary events provide further evidence for inside-out signaling as an essential step in the recognition of tumor cells by a Vγ9Vδ2 TCR.

Bone Tumor Environment as a Potential Therapeutic Target in Ewing Sarcoma

Ewing sarcoma is the second most common pediatric bone tumor, with three cases per million worldwide. In clinical terms, Ewing sarcoma is an aggressive, rapidly fatal malignancy that mainly develops not only in osseous sites (85%) but also in extra-skeletal soft tissue. It spreads naturally to the lungs, bones, and bone marrow with poor prognosis in the two latter cases. Bone lesions from primary or secondary (metastases) tumors are characterized by extensive bone remodeling, more often due to osteolysis. Osteoclast activation and subsequent bone resorption are responsible for the clinical features of bone tumors, including pain, vertebral collapse, and spinal cord compression. Based on the “vicious cycle” concept of tumor cells and bone resorbing cells, drugs, which target osteoclasts, may be promising agents as adjuvant setting for treating bone tumors, including Ewing sarcoma. There is also increasing evidence that cellular and molecular protagonists present in the bone microenvironment play a part in establishing a favorable “niche” for tumor initiation and progression. The purpose of this review is to discuss the potential therapeutic value of drugs targeting the bone tumor microenvironment in Ewing sarcoma. The first part of the review will focus on targeting the bone resorbing function of osteoclasts by means of bisphosphonates or drugs blocking the pro-resorbing cytokine receptor activator of NF-kappa B ligand. Second, the role of this peculiar hypoxic microenvironment will be discussed in the context of resistance to chemotherapy, escape from the immune system, or neo-angiogenesis. Therapeutic interventions based on these specificities could be then proposed in the context of Ewing sarcoma.

Dose-dependent inhibitory effects of zoledronic acid on osteoblast viability and function in vitro

Zoledronic acid (ZA), which is one of the most potent and efficacious bisphosphonates, has been commonly used in clinical practice for the treatment of various bone disorders. The extensive use of ZA has been associated with increasing occurrence of jaw complications, now known as bisphosphonate-associated osteonecrosis of the jaw (BRONJ). However, the mechanism underlying BRONJ remains to be fully elucidated. The aim of the present study was to investigate the effects of different concentrations of ZA on the MC3T3-E1 murine preosteoblast cell line cells and examine the possible pathogenesis of BRONJ. In the present study, the effect of ZA on the viability, apoptosis, differentiation and maturation of MC3T3-E1 cells, as well as its relevant molecular mechanism, were examined The results of a Cell Counting Kit 8 assay, a flow cytometric Annexin-V/propidium iodide assay and western blot analysis demonstrated that ZA exhibited a significant inhibition of cell viability and induction of apoptosis at concentrations >10 µM. Subsequently, the effect of ZA on cell differentiation at concentrations <1 µM were investigated. In this condition, ZA inhibited bone nodule formation and decreased the activity of alkaline phosphatase. The results of reverse transcription-quantitative polymerase chain reaction and western blot analyses indicated that ZA downregulated the expression levels of the marker genes and proteins associated with osteogenic differentiation. Further investigation revealed that the suppression of differentiation by ZA was associated with decreased expression of bone morphogenetic protein-2 (BMP-2) and downregulation of the phosphorylation levels in the downstream extracellular signal-regulated kinase 1/2 and p38 pathways. These adverse effects of ZA were observed to be concentration-dependent. The results from the present study suggested that ZA at higher concentrations induces cytotoxicity towards osteoblasts, and ZA at lower concentrations suppresses osteoblast differentiation by downregulation of BMP-2. These results assist in further understanding the mechanisms of BRONJ.

A highly sensitive prenylation assay reveals in vivo effects of bisphosphonate drug on the Rab prenylome of macrophages outside the skeleton

Bisphosphonate drugs such as zoledronic acid (ZOL), used for the treatment of common bone disorders, target the skeleton and inhibit bone resorption by preventing the prenylation of small GTPases in bone-destroying osteoclasts. Increasing evidence indicates that bisphosphonates also have pleiotropic effects outside the skeleton, most likely via cells of the monocyte/macrophage lineage exposed to nanomolar circulating drug concentrations. However, no effects of such low concentrations of ZOL have been reported using existing approaches. We have optimized a highly sensitive in vitro prenylation assay utilizing recombinant geranylgeranyltransferases to enable the detection of subtle effects of ZOL on the prenylation of Rab- and Rho-family GTPases. Using this assay, we found for the first time that concentrations of ZOL as low as 10nM caused inhibition of Rab prenylation in J774 macrophages following prolonged cell culture. By combining the assay with quantitative mass spectrometry we identified an accumulation of 18 different unprenylated Rab proteins in J774 cells after nanomolar ZOL treatment, with a >7-fold increase in the unprenylated form of Rab proteins associated with the endophagosome pathway (Rab1, Rab5, Rab6, Rab7, Rab11, Rab14 and Rab21). Finally, we also detected a clear effect of subcutaneous ZOL administration in vivo on the prenylation of Rab1A, Rab5B, Rab7A and Rab14 in mouse peritoneal macrophages, confirming that systemic treatment with bisphosphonate drug can inhibit prenylation in myeloid cells in vivo outside the skeleton. These observations begin a new era in defining the precise pharmacological actions of bisphosphonate drugs on the prenylation of small GTPases in vivo.

Synthesis of new indole-based bisphosphonates and evaluation of their chelating ability in PE/CA-PJ15 cells

Bisphosphonates are the most important class of antiresorptive agents used against osteoclast-mediated bone loss, and, more recently, in oncology. These compounds have high affinity for calcium ions (Ca(2+)) and therefore target bone mineral, where they appear to be internalized selectively by bone-resorbing osteoclasts and inhibit osteoclast function. They are extensively used in healthcare, however they are affected by severe side effects; pharmacological properties of bisphosphonates depend on their molecular structure, which is frequently the cause of poor intestinal adsorption and low distribution. In this work we synthesized six novel bisphosphonate compounds having a variably substituted indole moiety to evaluate their extra- and intracellular calcium chelating ability in PE/CA-PJ15 cells. Preliminary in silico and in vitro ADME studies were also performed and the results suggested that the indole moiety plays an important role in cell permeability and metabolism properties.

Protein prenylation in islet β-cell function in health and diabetes: Putting the pieces of the puzzle together

Post-translational prenylation involves incorporation of 15-(farnesyl) or 20-(geranylgeranyl) carbon derivatives of mevalonic acid into highly conserved C-terminal cysteines of proteins. The farnesyl transferase (FTase) and the geranylgeranyl transferase (GGTase) mediate incorporation of farnesyl and geranylgeranyl groups, respectively. At least 300 proteins are prenylated in the human genome; the majority of these are implicated in cellular processes including growth, differentiation, cytoskeletal function and vesicle trafficking. From a functional standpoint, isoprenylation is requisite for targeting of modified proteins to relevant cellular compartments for regulation of effector proteins. Pharmacological and molecular biological studies have provided compelling evidence for key roles of this signaling pathway in physiological insulin secretion in normal rodent and human islets. Recent evidence indicates that inhibition of prenylation results in mislocalization of unprenylated proteins, and surprisingly, they remain in active (GTP-bound) conformation. Sustained activation of G proteins has been reported in mice lacking GGTase, suggesting alternate mechanisms for the activation of non-prenylated G proteins. These findings further raise an interesting question if mislocalized, non-prenylated and functionally active G proteins cause cellular pathology since aberrant protein prenylation has been implicated in the onset of cardiovascular disease and diabetes. Herein, we overview the existing evidence to implicate prenylation in islet function and potential defects in this signaling pathways in the diabetic β-cell. We will also identify critical knowledge gaps that need to be addressed for the development of therapeutics to halt defects in these signaling steps in β cells in models of impaired insulin secretion, metabolic stress and diabetes.

Alendronate inhalation ameliorates elastase-induced pulmonary emphysema in mice by induction of apoptosis of alveolar macrophages

Alveolar macrophages play a crucial role in the pathogenesis of emphysema, for which there is currently no effective treatment. Bisphosphonates are widely used to treat osteoclast-mediated bone diseases. Here we show that delivery of the nitrogen-containing bisphosphonate alendronate via aerosol inhalation ameliorates elastase-induced emphysema in mice. Inhaled, but not orally ingested, alendronate inhibits airspace enlargement after elastase instillation, and induces apoptosis of macrophages in bronchoalveolar fluid via caspase-3- and mevalonate-dependent pathways. Cytometric analysis indicates that the F4/80(+)CD11b(high)CD11c(mild) population characterizing inflammatory macrophages, and the F4/80(+)CD11b(mild)CD11c(high) population defining resident alveolar macrophages take up substantial amounts of the bisphosphonate imaging agent OsteoSense680 after aerosol inhalation. We further show that alendronate inhibits macrophage migratory and phagocytotic activities and blunts the inflammatory response of alveolar macrophages by inhibiting nuclear factor-κB signalling. Given that the alendronate inhalation effectively induces apoptosis in both recruited and resident alveolar macrophages, we suggest this strategy may have therapeutic potential for the treatment of emphysema.

Multiple myeloma-related bone disease: state-of-art and next future treatments

SUMMARY 

Multiple myeloma (MM) is a plasma cell malignancy associated with the development of life-threatening and/or severe osteolytic lesions, which significantly worsen the quality of life of affected patients. MM-related bone disease (BD) is the result of an overwhelming osteoclastic activity, while osteoblast-mediated bone formation is inhibited. Bisphosphonates are still the mainstay of therapy for BD. However, these drugs are associated with mid long-term sequelae. In this work, we review the pathogenesis and currently available therapies of MM-related BD. We describe the most recent and promising findings that may translate in changing the clinical practice in the next future.

The regulation of osteoclast function and bone resorption by small GTPases

Osteoclasts are multinucleated cells that are responsible for resorption of bone, and increased activity of these cells is associated with several common bone diseases, including postmenopausal osteoporosis. Upon adhesion to bone, osteoclasts become polarized and reorganise their cytoskeleton and membrane to form unique domains including the sealing zone (SZ), which is a dense ring of F-actin-rich podosomes delimiting the ruffled border (RB), where protons and proteases are secreted to demineralise and degrade the bone matrix, respectively. These processes are dependent on the activity of small GTPases. Rho GTPases are well known to control the organization of F-actin and adhesion structures of different cell types, affecting subsequently their migration. In osteoclasts, RhoA, Rac, Cdc42, RhoU and also Arf6 regulate podosome assembly and their organization into the SZ. By contrast, the formation of the RB involves vesicular trafficking pathways that are regulated by the Rab family of GTPases, in particular lysosomal Rab7. Finally, osteoclast survival is dependent on the activity of Ras GTPases. The correct function of almost all these GTPases is absolutely dependent on post-translational prenylation, which enables them to localize to specific target membranes. Bisphosphonate drugs, which are widely used in the treatment of bone diseases such as osteoporosis, act by preventing the prenylation of small GTPases, resulting in the loss of the SZ and RB and therefore inhibition of osteoclast activity, as well as inducing osteoclast apoptosis. In this review we summarize current understanding of the role of specific prenylated small GTPases in osteoclast polarization, function and survival.

Binding kinetics of a fluorescently labeled bisphosphonate as a tool for dynamic monitoring of bone mineral deposition in vivo

Bone mineral deposition during the modeling of new bone and remodeling of old bone can be perturbed by several pathological conditions, including osteoporosis and skeletal metastases. A site-specific marker depicting the dynamics of bone mineral deposition would provide insight into skeletal disease location and severity, and prove useful in evaluating the efficacy of pharmacological interventions. Fluorescent labels may combine advantages of both radioisotope imaging and detailed microscopic analyses. The purpose of this study was to determine if the fluorescent bisphosphonate OsteoSense could detect localized changes in bone mineral deposition in established mouse models of accelerated bone loss (ovariectomy) (OVX) and anabolic bone gain resulting from parathyroid hormone (PTH) treatment. We hypothesized that the early rate of binding, as well as the total amount of bisphosphonate, which binds over long periods of time, could be useful in evaluating changes in bone metabolism. Evaluation of the kinetic uptake of bisphosphonates revealed a significant reduction in both the rate constant and plateau binding after OVX, whereas treatment with PTH resulted in a 36-fold increase in the bisphosphonate binding rate constant compared with untreated OVX controls. Localization of bisphosphonate binding revealed initial binding at sites of ossification adjacent to the growth plate and, to a lesser extent, along more distal trabecular and cortical elements. Micro-computed tomography (CT) was used to confirm that initial bisphosphonate binding is localized to sites of low tissue mineral density, associated with new bone mineral deposition. Our results suggest monitoring binding kinetics based on fluorescently labeled bisphosphonates represents a highly sensitive, site-specific method for monitoring changes in bone mineral deposition with the potential for translation into human applications in osteoporosis and bone metastatic processes and their treatment.

Phenotypic dissection of bone mineral density reveals skeletal site specificity and facilitates the identification of novel loci in the genetic regulation of bone mass attainment

Heritability of bone mineral density (BMD) varies across skeletal sites, reflecting different relative contributions of genetic and environmental influences. To quantify the degree to which common genetic variants tag and environmental factors influence BMD, at different sites, we estimated the genetic (rg) and residual (re) correlations between BMD measured at the upper limbs (UL-BMD), lower limbs (LL-BMD) and skull (SK-BMD), using total-body DXA scans of ∼ 4,890 participants recruited by the Avon Longitudinal Study of Parents and their Children (ALSPAC). Point estimates of rg indicated that appendicular sites have a greater proportion of shared genetic architecture (LL-/UL-BMD rg = 0.78) between them, than with the skull (UL-/SK-BMD rg = 0.58 and LL-/SK-BMD rg = 0.43). Likewise, the residual correlation between BMD at appendicular sites (r(e) = 0.55) was higher than the residual correlation between SK-BMD and BMD at appendicular sites (r(e) = 0.20-0.24). To explore the basis for the observed differences in rg and re, genome-wide association meta-analyses were performed (n ∼ 9,395), combining data from ALSPAC and the Generation R Study identifying 15 independent signals from 13 loci associated at genome-wide significant level across different skeletal regions. Results suggested that previously identified BMD-associated variants may exert site-specific effects (i.e. differ in the strength of their association and magnitude of effect across different skeletal sites). In particular, variants at CPED1 exerted a larger influence on SK-BMD and UL-BMD when compared to LL-BMD (P = 2.01 × 10(-37)), whilst variants at WNT16 influenced UL-BMD to a greater degree when compared to SK- and LL-BMD (P = 2.31 × 10(-14)). In addition, we report a novel association between RIN3 (previously associated with Paget's disease) and LL-BMD (rs754388: β = 0.13, SE = 0.02, P = 1.4 × 10(-10)). Our results suggest that BMD at different skeletal sites is under a mixture of shared and specific genetic and environmental influences. Allowing for these differences by performing genome-wide association at different skeletal sites may help uncover new genetic influences on BMD.

Follow-up of six patients with neurofibromatosis 1-related osteoporosis treated with alendronate for 23 months

This is the first prospective follow-up study to describe the effects of oral alendronate medication on neurofibromatosis 1 (NF1)-related osteoporosis. NF1 is a neurocutaneous skeletal syndrome associated with increased fracture risk and high frequency of osteopenia and osteoporosis. Alendronate is a bisphosphonate drug which inhibits the function of bone-resorbing osteoclasts, ultimately leading to an increase in bone mineral density (BMD) and reduction in fracture risk. However, in vitro studies have shown that NF1 osteoclasts display insensitivity to apoptotic signals caused by bisphosphonates. Our aim was to monitor the effects of alendronate medication in patients with NF1. Five men and one woman, aged 28-76 years, with NF1-related osteoporosis were enrolled to the study. Study participants did not have other conditions and were not taking any medication known to affect bone. The medication included a weekly dose of 70 mg alendronate and a daily 20 μg vitamin D supplementation. After 23 months of follow-up, BMD was increased in five out of six patients, but the increase was not statistically significant. Serum levels of the bone turnover markers CTX and PINP were reduced, suggesting slower bone remodeling, as expected. An unexpected result was that serum levels of the osteoclast activity marker TRAP5b did not change during the follow-up. One new stress fracture of the tibia was documented during the alendronate therapy. Even though the study group was small, the findings of the current study (one new fracture and one patient with decreased BMD) call for a larger study to assess the efficacy of bisphosphonates in NF1-related osteoporosis.

Modulation of osteoclast differentiation and bone resorption by Rho GTPases

Bone is a dynamic tissue constantly renewed through a regulated balance between bone formation and resorption. Excessive bone degradation by osteoclasts leads to pathological decreased bone density characteristic of osteolytic diseases such as post-menopausal osteoporosis or bone metastasis. Osteoclasts are multinucleated cells derived from hematopoietic stem cells via a complex differentiation process. Their unique ability to resorb bone is dependent on the formation of the actin-rich sealing zone. Within this adhesion structure, the plasma membrane differentiates into the ruffled border where protons and proteases are secreted to demineralize and degrade bone, respectively. On the bone surface, mature osteoclasts alternate between stationary resorptive and migratory phases. These are associated with profound actin cytoskeleton reorganization, until osteoclasts die of apoptosis. In this review, we highlight the role of Rho GTPases in all the steps of osteoclasts differentiation, function, and death and conclude on their interest as targets for treatment of osteolytic pathologies.

The Roles of Small GTPases in Osteoclast Biology

The adult skeleton undergoes bone remodeling that consists of bone formation by osteoblasts and bone resorption by osteoclasts. When the amount of bone resorbed is greater than the amount of new bone formed, low bone mass results, putting individuals at increased risk for osteoporosis and osteoporotic bone fracture. Nitrogenous bisphosphonates (NBPs) are the most common first line treatment for conditions of low bone mass. NBPs reduce osteoclast bone resorption by impairing the post-translational modification of small GTPases. Small GTPases play crucial roles in the differentiation, function, and survival of osteoclasts. Understanding the roles of individual small GTPases in osteoclast biology may lead to more targeted therapies for the treatment of low bone mass. In this review, we discuss recent investigations into the in vivo effects of individual GTPase deletion in osteoclasts and the molecular roles for small GTPases in osteoclast biology.

Differential impact of the Bisphosphonate Alendronate on undifferentiated and terminally differentiated human myogenic cells

Objectives

Alendronate, a nitrogen-containing bisphosphonate, is well established as a treatment for osteoporosis through regulation of osteoclast activity. Previously, the pharmacological effects of bisphosphonates on cells outside the bone environment have been considered irrelevant because of the bone-targeting property of bisphosphonates. However, the chronic effects of bisphosphonates on tissue-neighbouring bone, in particular skeletal muscles, should not be ignored because patients are treated with bisphosphonates for long periods.

Methods

Here, we show that the impact of alendronate on immortalized human myogenic cells depends on growth and differentiation-inducing conditions.

Key findings

Alendronate disrupted cytoskeletal structures and prevented migration, proliferation and differentiation of undifferentiated human myogenic cells that are involved in muscle regeneration. In contrast, alendronate did not affect the morphology, gene expression or survival of terminally differentiated human myotubes.

Conclusions

The present results suggest that the muscle regeneration capacity of osteoporosis patients treated with bisphosphonates for long periods may be attenuated. The present research on the pharmacological effects of alendronate on cultured human myogenic cells will contribute to improvement of therapeutic strategies and optimization of rehabilitation programmes for locomotive activity in osteoporosis patients treated with bisphosphonates.

Alendronate promotes bone formation by inhibiting protein prenylation in osteoblasts in rat tooth replantation model

Bisphosphonates (BPs) are a major class of antiresorptive drug, and their molecular mechanisms of antiresorptive action have been extensively studied. Recent studies have suggested that BPs target bone-forming cells as well as bone-resorbing cells. We previously demonstrated that local application of a nitrogen-containing BP (N-BP), alendronate (ALN), for a short period of time increased bone tissue in a rat tooth replantation model. Here, we investigated cellular mechanisms of bone formation by ALN. Bone histomorphometry confirmed that bone formation was increased by local application of ALN. ALN increased proliferation of bone-forming cells residing on the bone surface, whereas it suppressed the number of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts in vivo. Moreover, ALN treatment induced more alkaline phosphatase-positive and osteocalcin-positive cells on the bone surface than PBS treatment. In vitro studies revealed that pulse treatment with ALN promoted osteocalcin expression. To track the target cells of N-BPs, we applied fluorescence-labeled ALN (F-ALN) in vivo and in vitro. F-ALN was taken into bone-forming cells both in vivo and in vitro. This intracellular uptake was inhibited by endocytosis inhibitors. Furthermore, the endocytosis inhibitor dansylcadaverine (DC) suppressed ALN-stimulated osteoblastic differentiation in vitro and it suppressed the increase in alkaline phosphatase-positive bone-forming cells and subsequent bone formation in vivo. DC also blocked the inhibition of Rap1A prenylation by ALN in the osteoblastic cells. These data suggest that local application of ALN promotes bone formation by stimulating proliferation and differentiation of bone-forming cells as well as inhibiting osteoclast function. These effects may occur through endocytic incorporation of ALN and subsequent inhibition of protein prenylation.

Acquired resistance to zoledronic acid and the parallel acquisition of an aggressive phenotype are mediated by p38-MAP kinase activation in prostate cancer cells

The nitrogen-containing bisphosphonates (N-BP) zoledronic acid (ZOL) inhibits osteoclast-mediated bone resorption, and it is used to prevent skeletal complications from bone metastases. ZOL has also demonstrated anticancer activities in preclinical models and, recently, in cancer patients, highlighting the interest in determining eventual mechanisms of resistance against this agent. In our study, we selected and characterised a resistant subline of prostate cancer (PCa) cells to better understand the mechanisms, by which tumour cells can escape the antitumour effect of ZOL. DU145R80-resistant cells were selected in about 5 months using stepwise increasing concentrations of ZOL from DU145 parental cells. DU145R80 cells showed a resistance index value of 5.5 and cross-resistance to another N-BP, pamidronate, but not to the non-nitrogen containing BP clodronate. Notably, compared with DU145 parental cells, DU145R80 developed resistance to apoptosis and anoikis, as well as overexpressed the anti-apoptotic protein Bcl-2 and oncoprotein c-Myc. Moreover, DU145R80 cells underwent epithelial to mesenchymal transition (EMT) and showed increased expression of the metalloproteases MMP-2/9, as well as increased invading capability. Interestingly, compared with DU145, DU145R80 cells also increased the gene expression and protein secretion of VEGF and the cytokines Eotaxin-1 and IL-12. At the molecular level, DU145R80 cells showed strong activation of the p38-MAPK-dependent survival pathway compared with parental sensitive cells. Moreover, using the p38-inhibitor SB203580, we completely reversed the resistance to ZOL, as well as EMT marker expression and invasion. Furthermore, SB203580 treatment reduced the expression of VEGF, Eotaxin-1, IL-12, MMP-9, Bcl-2 and c-Myc. Thus, for the first time, we demonstrate that the p38-MAPK pathway can be activated under continuous extensive exposure to ZOL in PCa cells and that the p38-MAPK pathway has a critical role in the induction of resistance, as well as in the acquisition of a more aggressive and invasive phenotype.

An in vitro assessment of fibroblast and osteoblast response to alendronate-modified titanium and the potential for decreasing fibrous encapsulation

Fibrous encapsulation can impair implant osseointegration and cause implant failure but currently there are limited strategies to address this problem. Since bisphosphonates (BPs), a class of drugs widely used to treat bone diseases, was recently found to induce fibroblast apoptosis, we hypothesize that by loading BPs on titanium (Ti) implant surface, fibrous encapsulation may be inhibited with simultaneous enhancement of implant osseointegration. This strategy of local administration can also be expected to minimize the adverse side effects of BPs, which are associated with intravenous injections. To verify this hypothesis, alendronate was loaded on Ti surface via a hydroxyapatite (CaP) coating, and the effects of the loaded alendronate on fibroblast proliferation and apoptosis, and osteoblast proliferation, alkaline phosphatase (ALP) activity, and apoptosis were investigated in vitro. With a surface density of loaded alendronate 0.046 mg/cm(2) or higher, fibroblast proliferation was suppressed due to increased apoptosis, while osteoblast proliferation and ALP activity increased with minimal apoptosis. In a coculture of fibroblasts and osteoblasts in a 1:1 ratio, ~60% of the cells on these alendronate-loaded substrates were osteoblasts 1 day after cell seeding. The percentage of osteoblasts increased to about 75% 4 days after cell seeding. These results suggest that fibroblasts and osteoblasts respond differently toward the alendronate-modified substrates, and this phenomenon can potentially be capitalized to reduce fibrous encapsulation.

Atorvastatin requires geranylgeranyl transferase-I and Rac1 activation to exert neuronal protection and induce plasticity

Statins are widely used cholesterol-lowering drugs that may reduce the incidence of stroke and the progression of Alzheimer's disease (AD). However, how statins exert these beneficial effects remains poorly understood. Thus, this study evaluated the roles of Rac1 geranylgeranylation and the relationship between Rac1 and αN-catenin in the protective activity of atorvastatin (ATV) in a cortical neuronal culture model of glutamate (GLU) excitotoxicity. We found that ATV-induced neuroprotection and plasticity were blocked by isoprenoids, such as farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP), inhibition of farnesylation (FTI-277) and geranylgeranylation (GGTI-286), down-regulation of GGTase-Iβ and Rac activity and promotion of active RhoA. Additionally, ATV rescued the distribution of dendritic αN-catenin and increased the number and length of dendritic branches; these effects were reversed by GGTI-286, GGTase-Iβ shRNA, Rac1 shRNA and a dominant-negative version of Rac1 (T17N). In summary, our findings suggest that ATV requires GGTase-Iβ, prenylation and active Rac1 to induce protection and plasticity. In this regard, αN-catenin is a marker for stable interactions between adhesion proteins and the actin cytoskeleton and is necessary for the neuroprotective action of ATV.

Biomedical applications of bisphosphonates

Since their discovery over 100 years ago, bisphosphonates have been used industrially as corrosion inhibitors and complexing agents. With the discovery of their pharmacological activity in the late 1960s, implicating their high affinity for hydroxyapatite, bisphosphonates have been employed in the treatment of bone diseases and as targeting agents for colloids and drugs. They have notably been investigated for the treatment of Paget's disease, osteoporosis, bone metastases, malignancy-associated hypercalcemia, and pediatric bone diseases. Currently, they are first-line medications for several of these diseases and are taken by millions of patients worldwide, mostly postmenopausal women. A major problem associated with their use is their low oral bioavailability. Several delivery systems have been proposed to improve their absorption and to direct them to sites other than bone tissues. Beyond their important pharmacological role, the medical applications of bisphosphonates are numerous. In addition, their metal-chelating properties have been exploited to coat and stabilize implants, nanoparticulates, and contrast agents. In this contribution, we review the pharmacological and clinical uses of bisphosphonates and highlight their novel applications in the pharmaceutical and biomedical fields.

YM-175 induces apoptosis of human native monocyte-lineage cells via inhibition of prenylation

Nitrogen-containing bisphosphonates (NCBPs) have been widely used as standard supportive therapy to reduce skeletal-related events (SREs) in myeloma patients through suppression of osteoclast activity. In various prospective randomized trials that were performed following preliminary reports concerning efficacy, NCBPs have shown a significant beneficial effect on myeloma bone disease through both suppression of bone resorption and direct antimyeloma activity. Thus, NCBPs have an influence on many types of human cells. In this study, we examined the effect of an NCBP (YM-175) on an apoptosis of a monocytic cell line and of human native monocytes/macrophages and dendritic cells (DCs). We confirmed that monocytes, monocyte-derived macrophages, DCs, and a monoblastic cell line (THP-1) showed dose-dependent and time-dependent apoptosis related to the activation of caspases after exposure to YM-175 at concentrations below that at which the apoptosis of myeloma cell lines was induced. Such apoptosis of monocytic cells was suppressed by the addition of farnesol or geranylgeraniol. These findings suggest that the inhibition of monocyte-lineage cells or DCs by NCBPs might interfere with phagocytic activity or pathogen-presenting activity.

Ibandronate increases the expression of the pro-apoptotic gene FAS by epigenetic mechanisms in tumor cells

There is growing evidence that aminobisphosphonates like ibandronate show anticancer activity by an unknown mechanism. Biochemically, they prevent posttranslational isoprenylation of small GTPases, thus inhibiting their activity. In tumor cells, activated RAS-GTPase, the founding member of the gene family, down-regulates the expression of the pro-apoptotic gene FAS via epigenetic DNA-methylation by DNMT1. We compared ibandronate treatment in neoplastic human U-2 osteosarcoma and in mouse CCL-51 breast cancer cells as well as in the immortalized non-neoplastic MC3T3-E1 osteoblastic cells. Ibandronate attenuated cell proliferation in all cell lines tested. In the neoplastic cells we found up-regulation of caspases suggesting apoptosis. Further we found stimulation of FAS-expression as a result of epigenetic DNA demethylation that was due to down-regulation of DNMT1, which was rescued by re-isoprenylation by both geranylgeranyl-pyrophosphate and farnesylpyrophosphate. In contrast, ibandronate did not affect FAS and DNMT1 expression in MC3T3-E1 non-neoplastic cells. Data suggest that bisphosphonates via modulation of the activity of small-GTPases induce apoptosis in neoplastic cells by DNA-CpG-demethylation and stimulation of FAS-expression. In conclusion the shown epigenetic mechanism underlying the anti-neoplastic activity of farnesyl-transferase-inhibition, also explains the clinical success of other drugs, which target this pathway.

A population-based 2-year follow-up study on the relationship between bisphosphonates and the risk of stroke

This study aimed to explore the effect of bisphosphonate treatment on stroke using a large population cohort study. We found that the patients who received bisphosphonate therapy were less likely to suffer a stroke than comparison patients (hazard ratio (HR) = 0.79; 95% confidence interval (CI) = 0.66-0.99; p = 0.005) during a 2-year follow-up period.

INTRODUCTION

Animal models have suggested that bisphosphonates have a beneficial effect on the cardiovascular system. However, data on this topic in human subjects are still lacking. This study aimed to explore the protective effect of bisphosphonate treatment on stroke using a large population cohort study.

METHODS

We identified 2,148 patients who received bisphosphonate therapy for osteoporotic fractures. We randomly extracted 6,444 subjects with vertebral or hip fractures as a comparison group matched with the study group on age, sex, and year of index date. Each patient was individually tracked for 2 years to identify those who suffered a stroke. Stratified Cox proportional hazards regressions were performed to assess the effect of bisphosphonate treatment on the risk of stroke.

RESULTS

We found that 184 (8.6%) patients who received bisphosphonate therapy and 696 (10.8%) comparison patients suffered a stroke during the follow-up period. After adjusting for demographic variables and medical co-morbidities, stratified Cox proportional hazards regressions stratified by propensity score revealed that patients who received bisphosphonate therapy were less likely to suffer a stroke than comparison patients (HR = 0.79; 95% CI = 0.66-0.99). The adjusted HR for subarachnoid/intra-cerebral hemorrhage for patients who received bisphosphonate therapy was only 0.53 times (95% CI = 0.33-0.92) that of comparison patients, and the hazard of having an ischemic stroke during the 2-year follow-up period was 0.81 times that of comparison patients (95% CI = 0.65-0.96).

CONCLUSION

Patients who received bisphosphonate therapy were associated with a lower risk of stroke during a 2-year follow-up period.

Osteoclasts derived from patients with neurofibromatosis 1 (NF1) display insensitivity to bisphosphonates in vitro

A total of 20 patients with neurofibromatosis 1 (NF1) were screened for NF1-related osteoporosis, and blood samples were collected for isolation of peripheral blood osteoclast progenitors. Patients with NF1 had higher levels of serum bone turnover markers (CTX and PINP) compared to controls. In addition, persons with high bone resorption in vitro on average had high levels of serum CTX. Of the 20 patients with NF1, 15 had low bone mineral density (osteopenia/osteoporosis), but these 15 patients did not have marked risk factors for low bone mineral density. Thus, we recommend screening for osteoporosis to all adult patients with NF1. Our aim was also to characterize the effects of bisphosphonates on NF1 osteoclasts in vitro. NF1 osteoclasts and osteoclasts from healthy controls in vitro were treated with zoledronic acid, alendronate and clodronate. These bisphosphonates caused a marked reduction in the number of normal control osteoclasts in vitro, while only a slight change was observed in the number of NF1 osteoclasts. Ras-inhibitor FTS counteracted this NF1-related insensitivity to zoledronic acid, suggesting that Ras may play a role in this phenomenon.

Targeting and localized signalling by small GTPases

Polarized cellular responses, for example, cell migration, require the co-ordinated assembly of signalling complexes at a particular subcellular location, such as the leading edge of cells. Small GTPases of the Ras superfamily play central roles in many (polarized) responses to growth factors, chemokines or integrin ligands. These small GTPases are functionally distinct, yet remarkably homologous in their primary sequence and especially in their effector domains. Therefore it has long been unclear how GTPase signalling specificity is regulated. Small GTPases carry a lipid anchor, in the context of a hypervariable region, which mediates membrane association. However, whereas the lipid has long been proposed to be the critical regulator of subcellular GTPase targeting, there is now increasing evidence that specific protein-protein interactions are important as well. This review discusses recent findings on GTPase targeting and proposes a revised model for GTPase signalling. In this model, the hypervariable domain acts in conjunction with the lipid tail to target the GTPase to specific membrane-associated protein complexes. Here, local GTPase activation occurs, leading to subsequent exposure of the effector domain, binding to effector proteins and the initiation of downstream signalling.

Defect in mevalonate pathway induces pyroptosis in Raw 264.7 murine monocytes

The inhibition of mevalonate pathway by the aminobisphosphonate alendronate (ALD) has been previously associated with an augmented lipopolysaccharide-induced interleukin-1beta (IL-1β) secretion in monocytes, as demonstrated in an auto-inflammatory disease known as mevalonate kinase deficiency (MKD). In this study we investigated the effect of ALD + LPS on monocyte cell line (Raw 264.7) death. ALD strongly augmented LPS-induced programmed cell death (PCD) as well as IL-1β secretion in Raw murine monocytes, whereas necrosis was rather unaffected. ALD + LPS induced caspase-3 activation. Inhibition of IL-1β stimulation partially restored cell viability. These findings suggest that the inhibition of mevalonate pathway, together with a bacterial stimulus, induce a PCD partly sustained by the caspase-3-related apoptosis and partly by caspase-1-associated pyroptosis. The involvement of pyroptosis is a novel hit in our cell model and opens discussions about its role in inflammatory cells with chemical or genetic inhibition of mevalonate pathway.

Pharmacological actions of statins: a critical appraisal in the management of cancer

Statins, among the most commonly prescribed drugs worldwide, are cholesterol-lowering agents used to manage and prevent cardiovascular and coronary heart diseases. Recently, a multifaceted action in different physiological and pathological conditions has been also proposed for statins, beyond anti-inflammation and neuroprotection. Statins have been shown to act through cholesterol-dependent and -independent mechanisms and are able to affect several tissue functions and modulate specific signal transduction pathways that could account for statin pleiotropic effects. Typically, statins are prescribed in middle-aged or elderly patients in a therapeutic regimen covering a long life span during which metabolic processes, aging, and concomitant novel diseases, including cancer, could occur. In this context, safety, toxicity, interaction with other drugs, and the state of health have to be taken into account in subjects treated with statins. Some evidence has shown a dichotomous effect of statins with either cancer-inhibiting or -promoting effects. To date, clinical trials failed to demonstrate a reduced cancer occurrence in statin users and no sufficient data are available to define the long-term effects of statin use over a period of 10 years. Moreover, results from clinical trials performed to evaluate the therapeutic efficacy of statins in cancer did not suggest statin use as chemotherapeutic or adjuvant agents. Here, we reviewed the pharmacology of the statins, providing a comprehensive update of the current knowledge of their effects on tissues, biological processes, and pathological conditions, and we dissected the disappointing evidence on the possible future use of statin-based drugs in cancer therapy.

Biochemical and molecular mechanisms of action of bisphosphonates

This review describes the key discoveries over the last 15 years that have led to a clearer understanding of the molecular mechanisms by which bisphosphonate drugs inhibit bone resorption. Once released from bone mineral surfaces during bone resorption, these agents accumulate intracellularly in osteoclasts. Simple bisphosphonates such as clodronate are incorporated into non-hydrolysable analogues of adenosine triphosphate, which induce osteoclast apoptosis. The considerably more potent nitrogen-containing bisphosphonates are not metabolised but potently inhibit farnesyl pyrophosphate (FPP) synthase, a key enzyme of the mevalonate pathway. This prevents the synthesis of isoprenoid lipids necessary for the post-translational prenylation of small GTPases, thereby disrupting the subcellular localisation and normal function of these essential signalling proteins. Inhibition of FPP synthase also results in the accumulation of the upstream metabolite isopentenyl diphosphate, which is incorporated into the toxic nucleotide metabolite ApppI. Together, these properties explain the ability of bisphosphonate drugs to inhibit bone resorption by disrupting osteoclast function and survival. These discoveries are also giving insights into some of the adverse effects of bisphosphonates, such as the acute phase reaction that is triggered by inhibition of FPP synthase in peripheral blood monocytes.

Physiology of the aging bone and mechanisms of action of bisphosphonates

Fragility fractures, a major public health concern, are expected to further increase due to aging of the world populations because age remains a cardinal, independent determinant of fracture risk. With aging the balance between bone formation and resorption during the remodeling process becomes negative, with increased resorption and reduced formation. Bisphosphonates (BPs) are widely prescribed anti-resorptive agents that inhibit osteoclasts attachment to bone matrix and enhance osteoclast apoptosis. BPs can be divided into nitrogen-containing (N-BPs) and non-nitrogen-containing BPs (non-N-BPs). Both classes induce apoptosis but they evoke it differently. Several studies have examined the molecular mechanisms underlying BPs' effects on osteoclasts and bone remodeling. N-BPs (alendronate, risedronate, zoledronate) inhibit the intracellular mevalonate pathway and protein isoprenylation, via the enzyme farnesyl pyrophosphate synthase. N-BPs act by competition, binding to the natural substrate-binding site of the enzyme. The less potent non-N-BPs (etidronate, clodronate), do not inhibit the mevalonate pathway and protein isoprenylation, but are metabolized intracellularly to metabolites, which are cytotoxic analogs of ATP. N-BPs represent the first choice treatment for diseases associated with excessive bone resorption, such as fragility fractures (due to postmenopausal-, male, glucocorticoid- and transplant-induced osteoporosis), Paget's disease of bone, and bone metastasis. Better understanding of BPs' effects on osteoblasts/osteocytes (e.g., preventing apoptosis) and differential distribution may further help explain anti-fracture benefit and bone quality effects. Lower affinity BPs (e.g., risedronate) may allow better access to osteocyte network. Effects of BPs on bone senescence, cancer cells apoptosis and prevention of cardiovascular calcifications may open new avenues for biogerontological research.

Bisphosphonates inhibit phosphorylation of signal transducer and activator of transcription 3 and expression of suppressor of cytokine signaling 3: implications for their effects on innate immune function and osteoclastogenesis

OBJECTIVE

This study tested the effects of bisphosphonates (BPs) on the suppressor of cytokine signaling 3 (SOCS3) protein in macrophages. SOCS3 has been shown to regulate cell differentiation and survival; however, its potential role in mediating the effects of BPs has not been explored.

STUDY DESIGN

The cell viability of murine RAW 267.4 macrophages was assessed after culturing with control medium or media containing increasing concentrations of 2 BPs (ibandronate or clodronate) for 24, 48, and 72 hours. The phosphorylation status of signal transducer and activator of transcription 3 (STAT3) and the expression of SOCS3 protein levels were determined by Western blot analysis.

RESULTS

In control cultures, STAT3 phosphorylation and STAT3 and SOCS3 protein levels increased within 5 minutes after the addition of fresh medium. This increase was inhibited in cultures treated with both BPs. Macrophage cell viability also decreased after BP treatment.

CONCLUSIONS

These data demonstrate that, in addition to their effects on macrophage viability, BPs can decrease STAT3 and SOCS3 expression, which are important modulators of immune responses and bone homeostasis.

Bone metastasis: histological changes and pathophysiological mechanisms in osteolytic or osteosclerotic localizations. A review

The development of a bone metastasis involves interactions between the tumor cells, the bone marrow microenvironment and the bone cells themselves. A better understanding of the pathophysiological changes occurring in bone metastasis can be obtained from histopathological examination of invaded specimens. This review focuses on the main molecular mechanisms implied in the localization and growth of malignant cells in the bone marrow. The corresponding histologic developmental stages are illustrated both in osteolytic (or mixed metastasis) or in the osteosclerotic forms by histological analysis, immunohistochemistry and microcomputed tomographic analysis of bone samples. In both cases, the malignant cells find a "fertile soil" in the bone marrow microenvironment. They use the growth factors released by bone cells for the coupling between osteoclasts/osteoblasts to promote their own development. In turn, they elaborate a variety of cytokines that can promote osteoclastogenesis (PTHrP, IL-1, IL-6…) or on the contrary, other growth factors that can boost the osteoblastic activity (ET1, IGFs). A "vicious circle" occurs between the malignant cells and the bone cells leading to the radiological expression of the metastasis.

Bisphosphonates in the treatment of metabolic bone diseases

Osteoporosis is a disease characterized by low bone mass associated with the deterioration of microarchitecture, due to an imbalance either in high bone resorption or low bone formation or in both, leading to a high risk of fractures. Bisphosphonates are medications which reduce the ability of osteoclasts to induce bone resorption and consequently improve the balance between resorption and formation. There are bisphosphonates approved for the prevention and treatment of osteoporosis. Administration can be oral (daily, weekly or monthly) or intravenous (quarterly or yearly). These medications are well tolerated and with the correct instructions of administration have a good safety profile. Serious side effects, such as, osteonecrosis of jaw is very rare. Bisphosphonates are the most prescribed medication for the treatment of osteoporosis.

Shotgun proteomics analysis reveals new unsuspected molecular effectors of nitrogen-containing bisphosphonates in osteocytes

Nitrogen-containing bisphosphonates (N-BPs) are therapeutic agents used to treat osteoporosis and promote osteoblast and osteocyte survival. The molecular mechanisms underlying this effect have been extensively studied, but the global changes induced by N-BPs at the protein level are not known. In this context, we investigated the effect of 10(-7)M Risedronate for 1h and 48h on MLO-Y4 osteocytic cells, through a quantitative, label free shotgun proteomic analysis. We described herein a preliminary proteome map of untreated MLO-Y4 cells, composed of 353 protein species. Moreover, we identified 10 and 15 differentially expressed proteins after 1h and 48h of Risedronate treatment, respectively. Among these, PARK7/DJ-1 protein levels were induced up to 3 times and this event was associated with the activation of the pro-survival Akt pathway that we propose as a novel player in the effect of N-BPs on osteocytes. Risedronate was also able to induce the expression and the secretion of the growth factor pro-granulin. In addition, protein prenylation inhibition appeared to be involved in the modulation of MLO-Y4 proteome by RIS in a protein-specific manner. In conclusion, these findings unveil novel functions targeted by N-BPs in osteocytes and could be useful to design novel pharmaceutical compounds.

Pamidronate, farnesyl transferase, and geranylgeranyl transferase-I inhibitors affects cell proliferation, apoptosis, and OPG/RANKL mRNA expression in stromal cells of giant cell tumor of bone

Giant cell tumor (GCT) is the most common nonmalignant primary bone tumor reported in Hong Kong. It usually affects young adults between the ages of 20 and 40. This tumor is well known for its potential to recur following treatment. To date no effective adjuvant therapy exists for GCT. Our project aimed to study the effects of pamidronate (PAM), farnesyl transferase inhibitor (FTI-277), geranylgeranyl transferase inhibitor (GGTI-298), and their combinations on GCT stromal cells (SC). Individual treatment with PAM, FTI-277, and GGTI-298, inhibited the cell viability and proliferation of GCT SC in a dose-dependent way. Combination of FTI-277 with GGTI-298 caused synergistic effects in reducing cell viability, and its combination index was 0.49, indicating a strong synergism. Moreover, the combination of FTI-277 with GGTI-298 synergistically enhanced cell apoptosis and activated caspase-3/7, -8, and -9 activities. PAM induced cell-cycle arrest at the S-phase. The combination of PAM with GGTI-298 significantly increased OPG/RANKL mRNA ratio and activated caspase-3/7 activity. Our findings support that the combination of bisphosphonates with GGTIs or FTIs with GGTIs may be used as potential adjuvants in the treatment of GCT of bone.

The small GTPase RhoA localizes to the nucleus and is activated by Net1 and DNA damage signals

Background

Rho GTPases control many cellular processes, including cell survival, gene expression and migration. Rho proteins reside mainly in the cytosol and are targeted to the plasma membrane (PM) upon specific activation by guanine nucleotide exchange factors (GEFs). Accordingly, most GEFs are also cytosolic or associated with the PM. However, Net1, a RhoA-specific GEF predominantly localizes to the cell nucleus at steady-state. Nuclear localization for Net1 has been seen as a mechanism for sequestering the GEF away from RhoA, effectively rendering the protein inactive. However, considering the prominence of nuclear Net1 and the fact that a biological stimulus that promotes Net1 translocation out the nucleus to the cytosol has yet to be discovered, we hypothesized that Net1 might have a previously unidentified function in the nucleus of cells.

Principal Findings

Using an affinity precipitation method to pulldown the active form of Rho GEFs from different cellular fractions, we show here that nuclear Net1 does in fact exist in an active form, contrary to previous expectations. We further demonstrate that a fraction of RhoA resides in the nucleus, and can also be found in a GTP-bound active form and that Net1 plays a role in the activation of nuclear RhoA. In addition, we show that ionizing radiation (IR) specifically promotes the activation of the nuclear pool of RhoA in a Net1-dependent manner, while the cytoplasmic activity remains unchanged. Surprisingly, irradiating isolated nuclei alone also increases nuclear RhoA activity via Net1, suggesting that all the signals required for IR-induced nuclear RhoA signaling are contained within the nucleus.

Conclusions/Significance

These results demonstrate the existence of a functional Net1/RhoA signaling pathway within the nucleus of the cell and implicate them in the DNA damage response.

Zoledronic acid delays disease progression of bone metastases from hepatocellular carcinoma

AIM

  We conducted a retrospective cohort study to investigate the efficacy of combination therapy with radiotherapy (RT) and zoledronic acid for bone metastases from hepatocellular carcinoma (HCC). Additionally, we investigated the efficacy of zoledronic acid for non-irradiated bone metastases.

METHODS

  This study consisted of 31 patients who had received RT for bone metastases. Twelve of these patients with 23 sites of bone metastases were also treated with zoledronic acid (Z group). In the Z group, 14 sites received RT and nine sites did not. Nineteen patients with 38 sites of bone metastases were not treated with zoledronic acid (non-Z group). In the non-Z group, 22 sites received RT and 16 did not. We compared survival, pain response, time to pain progression, radiographic response, time to radiographic progression, and safety between groups.

RESULTS

  While pain response rates were similar between the two groups, time to pain progression rates of irradiated and non-irradiated bone metastases was significantly lower in the Z (0% and 20% at 6 months, respectively) than in the non-Z group (34% and 66% at 6 months, respectively) (P = 0.045 and P = 0.005). Further, while radiographic response rates were similar between the two groups, time to radiographic progression rate of non-irradiated bone metastases was significantly lower in the Z (29% at 3 months) than in the non-Z group (91% at 3 months) (P = 0.009). No significant side-effects were documented.

CONCLUSION

  Zoledronic acid delayed the pain progression of both irradiated and non-irradiated bone metastases and the radiographic progression of non-irradiated bone metastases from HCC.

Development of a novel transdermal patch of alendronate, a nitrogen-containing bisphosphonate, for the treatment of osteoporosis

Bisphosphonates are widely used for the treatment and prevention of bone diseases, including Paget disease, hypercalcemia of malignancy, and postmenopausal osteoporosis. In this study, we developed a novel transdermal patch of alendronate, a nitrogen-containing bisphosphonate, for the treatment of bone diseases. The maximum permeation fluxes of alendronate through rat and human skin after application of this patch were 1.9 and 0.3 µg/cm(2) per hour, respectively. The bioavailability (BA) of alendronate in rats was approximately 8.3% after the application of alendronate patch and approximately 1.7% after oral administration. These results indicated that the transdermal permeation of alendronate using this patch system was sufficient for the treatment of bone diseases. The plasma calcium level was effectively reduced after application of the alendronate patch in 1α-hydroxyvitamin D(3) -induced hypercalcemia model rats. The alendronate patch also effectively suppressed the decrease in bone mass in model rats with osteoporosis. Modest alendronate-induced erythema of rat skin was observed after application of the alendronate patch. Incorporation of butylhydroxytoluene in the alendronate patch almost completely suppressed this alendronate-induced skin damage while maintaining the transdermal permeation and pharmacologic effects of alendronate. These findings indicate that our novel transdermal delivery system for alendronate is a promising approach to improve compliance and quality of life of patients in the treatment of bone diseases.

Inhibition of GGTase-I and FTase disrupts cytoskeletal organization of human PC-3 prostate cancer cells

The mevalonate synthesis pathway produces intermediates for isoprenylation of small GTPases, which are involved in the regulation of actin cytoskeleton and cell motility. Here, we investigated the role of the prenylation transferases in the regulation of the cytoskeletal organization and motility of PC-3 prostate cancer cells. This was done by using FTI-277, GGTI-298 or NE-10790, the specific inhibitors of FTase (farnesyltransferase), GGTase (geranylgeranyltransferase)-I and -II, respectively. Treatment of PC-3 cells with GGTI-298 and FTI-277 inhibited migration and invasion in a time- and dose-dependent manner. This was associated with disruption of F-actin organization and decreased recovery of GFP-actin. Immunoblot analysis of various cytoskeleton-associated proteins showed that the most striking change in GGTI-298- and FTI-277-treated cells was a markedly decreased level of total and phosphorylated cofilin, whereas the level of cofilin mRNA was not decreased. The treatment of PC-3 cells with GGTI-298 also affected the dynamics of GFP-paxillin and decreased the levels of total and phosphorylated paxillin. The levels of phosphorylated FAK (focal adhesion kinase) and PAK (p-21-associated kinase)-2 were also lowered by GGTI-298, but levels of paxillin or FAK mRNAs were not affected. In addition, GGTI-298 had a minor effect on the activity of MMP-9. RNAi knockdown of GGTase-Ibeta inhibited invasion, disrupted F-actin organization and decreased the level of cofilin in PC-3 cells. NE-10790 did not have any effect on PC-3 prostate cancer cell motility or on the organization of the cytoskeleton. In conclusion, our results demonstrate the involvement of GGTase-I- and FTase-catalysed prenylation reactions in the regulation of cytoskeletal integrity and motility of prostate cancer cells and suggest them as interesting drug targets for development of inhibitors of prostate cancer metastasis.

RHO GTPase signaling for axon extension: is prenylation important?

Many lines of evidence indicate the importance of the Rho family guanine nucleotide triphosphatases (GTPases) in directing axon extension and guidance. The signaling networks that involve these proteins regulate actin cytoskeletal dynamics in navigating neuronal growth cones. However, the intricate patterns that regulate Rho GTPase activation and signaling are not yet fully defined. Activity and subcellular localization of the Rho GTPases are regulated by post-translational modification. The addition of a geranylgeranyl group to the carboxy (C-) terminus targets Rho GTPases to the plasma membrane and promotes their activation by facilitating interaction with guanine nucleotide exchange factors and allowing sequestering by association with guanine dissociation inhibitors. However, it is unclear how these modifications affect neurite extension or how subcellular localization alters signaling from the classical Rho GTPases (RhoA, Rac1, and Cdc42). Here, we review recent data addressing this issue and propose that Rho GTPase geranylgeranylation regulates outgrowth.