Influence of bone affinity on the skeletal distribution of fluorescently labeled bisphosphonates in vivo

Factors influencing therapeutic efficacy of denosumab against osteoporosis in systemic lupus erythematosus

OBJECTIVE

Osteoporosis is a common comorbidity in patients with SLE, and bone loss in patients with SLE has a multifactorial aetiology. This study aimed to evaluate the therapeutic efficacy of denosumab in patients with SLE with osteoporosis and to analyse the factors influencing therapeutic efficacy.

METHODS

A total of 166 patients with SLE with osteoporosis who initiated denosumab between January 2016 and December 2023 were included. Changes in the T-score and areal bone mineral density (BMD) at the lumbar spine, total hip and femur neck from denosumab initiation to 12 months were measured. Correlation analysis was performed between the degree of BMD improvement and covariates including SLE-specific factors such as SLE duration, SLE Disease Activity Index 2000 (SLEDAI-2K) score, glucocorticoid dose and hydroxychloroquine use. Multiple linear regression analysis was conducted to identify predictors of the therapeutic efficacy of denosumab.

RESULTS

Denosumab significantly increased BMD and decreased bone turnover markers at 12 months compared with baseline. The degree of BMD improvement revealed a significant negative correlation with SLEDAI-2K score, hydroxychloroquine use, prior osteoporosis treatment and baseline BMD values. In contrast, body mass index and c-telopeptide of collagen type 1 levels were positively correlated with the degree of BMD improvement. Higher baseline BMD values, SLEDAI-2K scores and hydroxychloroquine use were significant predictors of attenuated BMD improvement.

CONCLUSIONS

Our study suggests that denosumab is an effective treatment option for osteoporosis in patients with SLE. The therapeutic efficacy of denosumab can be predicted by baseline BMD values, SLEDAI-2K scores and hydroxychloroquine use.

Anti-osteoporotic drug efficacy for periprosthetic bone loss after total hip arthroplasty: A systematic review and network meta-analysis

BACKGROUND

Periprosthetic bone loss following total hip arthroplasty (THA) threatens prosthesis stability. This systematic review and network meta-analysis aimed to compare the efficacy of anti-osteoporotic drugs for measures of hip function according to functional outcomes, periprosthetic femoral bone mineral density loss in each Gruen zone, and revision surgery after THA.

METHODS

The systematic search of six literature databases was conducted in December 2021 in accordance with PRISMA guidelines. Adult participants who underwent primary THA were included. A random-effects network meta-analysis was performed within a frequentist framework, and the confidence in the evidence for each outcome was evaluated using the CINeMA tool, which assessed the credibility of results from the network meta-analysis. We included 22 randomized controlled trials (1243 participants) comparing the efficacy and safety of bisphosphonates (including etidronate, clodronate, alendronate, risedronate, pamidronate, and zoledronate), denosumab, selective estrogen receptor modulator, teriparatide, calcium + vitamin D, calcium, and vitamin D. We defined the period for revision surgery as the final follow-up period.

RESULTS

Raloxifene, bisphosphonate, calcium + vitamin D, and denosumab for prosthetic hip function might have minimal differences when compared with placebos. The magnitude of the anti-osteoporotic drug effect on periprosthetic femoral bone loss varied across different Gruen zones. Bisphosphonate, denosumab, teriparatide might be more effective than placebo in Gruen zone 1 at 12 months after THA. Additionally, bisphosphonate might be more effective than placebo in Gruen zones 2, 5, 6, and 7 at 12 months after THA. Denosumab was efficacious in preventing bone loss in Gruen zones 6 and 7 at 12 months after THA. Teriparatide was likely to be efficacious in preventing bone loss in Gruen zone 7 at 12 months after THA. Raloxifene was slightly efficacious in preventing bone loss in Gruen zones 2 and 3 at 12 months after THA. Calcium was slightly efficacious in preventing bone loss in Gruen zone 5 at 12 months after THA. None of the studies reported revision surgery.

CONCLUSIONS

Bisphosphonate and denosumab may be effective anti-osteoporotic drugs for preventing periprosthetic proximal femoral bone loss due to stress shielding after THA, particularly in cementless proximal fixation stems, which are the most commonly used prostheses worldwide.

Targeting TREM2 signaling shows limited impact on cerebrovascular calcification

Brain calcification, the ectopic mineral deposits of calcium phosphate, is a frequent radiological finding and a diagnostic criterion for primary familial brain calcification. We previously showed that microglia curtail the growth of small vessel calcification via the triggering receptor expressed in myeloid 2 (TREM2) in the Pdgfb ret/ret mouse model of primary familial brain calcification. Because boosting TREM2 function using activating antibodies has been shown to be beneficial in other disease conditions by aiding in microglial clearance of diverse pathologies, we investigated whether administration of a TREM2-activating antibody could mitigate vascular calcification in Pdgfb ret/ret mice. Single-nucleus RNA-sequencing analysis showed that calcification-associated microglia share transcriptional similarities to disease-associated microglia and exhibited activated TREM2 and TGFβ signaling. Administration of a TREM2-activating antibody increased TREM2-dependent microglial deposition of cathepsin K, a collagen-degrading protease, onto calcifications. However, this did not ameliorate the calcification load or alter the mineral composition and the microglial phenotype around calcification. We therefore conclude that targeting microglia with TREM2 agonistic antibodies is insufficient to demineralize and clear vascular calcifications.

Zoledronate interrupts pre-osteoclast-induced angiogenesis via SDF-1/CXCR4 pathway

Introduction

In this study, we tested the hypothesis that pre-osteoclast signaling is key in triggering post-traumatic angiogenesis in alveolar bone via the SDF-1/CXCR4 pathway. Interruption of osteoclast differentiation through zoledronate (Zol) disrupts the crosstalk between pre-osteoclasts and endothelial cells, hindering the initial angiogenic reaction following dental trauma. This disruption could therefore play a role in the pathogenesis of medication-related osteonecrosis of the jaw (MRONJ).

Methods

The effect of zoledronate on the expression of SDF1 was tested in pre-osteoclasts (POC) in vitro. Then, we tested the effect of pre-osteoclast conditioned medium on HUVEC cell differentiation, migration, tube-formation, and CXCR4 expression and activity in-vitro. Lastly, we quantified the effect of zoledronate treatment on post-traumatic vascular perfusion of alveolar bone, using microCT-angiography and immunohistochemistry.

Results

SDF-1 mRNA expression decreased in Zol-treated POCs (p = 0.02). Flow-Cytometry analysis showed a decrease in CXCL-12+ (SDF-1α) expressing POCs with Zol treatment (p = 0.0058). On the other hand, CXCR4 mRNA expression was significantly inhibited in Zol-treated HUVECs (p = 0.0063). CXCR4 protein expression and activity showed a corresponding dose-dependent downregulation HUVEC surface treated with conditioned media from POC treated with Zol (p = 0.008 and 0.03, respectively). Similar inhibition was observed of HUVEC migration (p = 0.0012), and tube formation (p < 0.0001), effects that were reversed with SDF-1. Finally, there was a significant reduction of CD31+ HUVECs in Alveolar bone of Zol-treated rats (p = 0.0071), confirmed by significantly lower percentage of blood vessel volume (p = 0.026), and marginally lower vessel number (p = 0.062) in the alveolar bone.

Conclusion

Pre-osteoclasts play a crucial role in the initial angiogenic response in alveolar bone following dental extraction. Disruption of this process may be a predisposing factor to osteonecrosis.

Superior bone regenerative properties of carbonate apatite with locational bone-active factors through an inorganic process

Rapid bone regeneration is crucial for restoring alveolar bone and oral functions following periodontal diseases. However, the development of effective biomedical materials for this purpose remains insufficient. While bone autografts can enhance bone regeneration, they are invasive to healthy areas. Specifically, for alveolar bone regeneration, the implanted material must possess adequate mechanical strength. Moreover, local administration is preferred for older adults, who are a primary target population, to maintain their quality of life. We developed a silica-substituted carbonate apatite (CO3Ap-silica) block as newly bone substitute with a bone growth factor, featuring the major inorganic component of mature bone to enhance bone regeneration. CO3Ap-silica block stimulated the bone remodeling process at the implantation site and demonstrated significantly better bone regeneration compared to currently used carbonate apatite substitutes. Therefore, this new material is expected to advance technologies for restoring occlusal function after periodontal disease.

Roles of osteoclasts in alveolar bone remodeling

Osteoclasts are large multinucleated cells from hematopoietic origin and are responsible for bone resorption. A balance between osteoclastic bone resorption and osteoblastic bone formation is critical to maintain bone homeostasis. The alveolar bone, also called the alveolar process, is the part of the jawbone that holds the teeth and supports oral functions. It differs from other skeletal bones in several aspects: its embryonic cellular origin, the form of ossification, and the presence of teeth and periodontal tissues; hence, understanding the unique characteristic of the alveolar bone remodeling is important to maintain oral homeostasis. Excessive osteoclastic bone resorption is one of the prominent features of bone diseases in the jaw such as periodontitis. Therefore, inhibiting osteoclast formation and bone resorptive process has been the target of therapeutic intervention. Understanding the mechanisms of osteoclastic bone resorption is critical for the effective treatment of bone diseases in the jaw. In this review, we discuss basic principles of alveolar bone remodeling with a specific focus on the osteoclastic bone resorptive process and its unique functions in the alveolar bone. Lastly, we provide perspectives on osteoclast-targeted therapies and regenerative approaches associated with bone diseases in the jaw.

Alendronate prolongs the reversal-resorption phase in human cortical bone remodeling

Despite their ability to reduce fracture-risk and increase Bone Mineral Density (BMD) in osteoporotic women, bisphosphonates are reported to reduce formation of new bone. Reduced bone formation has been suggested to lead to accumulation of microfractures and contribute to rare side effects in cortical bone such as atypical femur fractures. However, most studies are limited to trabecular bone. In this study, the cortical bone remodeling in human iliac bone specimens of 65 non-treated and 24 alendronate-treated osteoporotic women was investigated using a new histomorphometric classification of intracortical pores. The study showed that only 12.4 ± 11% of the cortical pore area reflected quiescent pores/osteons in alendronate-treated patients versus 8.5 ± 5% in placebo, highlighting that new cortical remodeling events remain to be activated. The percent and size of eroded pores (events in resorption-reversal phase) remained unchanged, but their contribution to total pore area was 1.4-fold higher in alendronate versus placebo treated patients (66 ± 22% vs 48 ± 22%, p < 0.001). On the other hand, the mixed eroded-formative pores (events with mixed resorption-reversal-formation phases) was 2-fold lower in alendronate versus placebo treated patients (19 ± 14% vs 39 ± 23% of total pore area, p < 0.001), and formative pores (event in formation phase) was 2.2-fold lower in alendronate versus placebo treated patients (2.1 ± 2.4% vs 4.6 ± 3.6%, p < 0.01), and their contribution to total pore area was 2.4-fold lower (1.3 ± 2.1% vs 3.1 ± 4.4%, p < 0.05). Importantly, these differences between alendronate and placebo treated patients were significant in patients after 3 years of treatment, not after 2 years of treatment. Collectively, the results support that cortical remodeling events activated during alendronate treatment has a prolonged reversal-resorption phase with a delayed transition to formation, becoming increasingly evident after 3-years of treatment. A potential contributor to atypical femur fractures associated with long-term bisphosphonate treatment.

Bisphosphonates: The role of chemistry in understanding their biological actions and structure-activity relationships, and new directions for their therapeutic use

The bisphosphonates ((HO)2P(O)CR1R2P(O)(OH)2, BPs) were first shown to inhibit bone resorption in the 1960s, but it was not until 30 years later that a detailed molecular understanding of the relationship between their varied chemical structures and biological activity was elucidated. In the 1990s and 2000s, several potent bisphosphonates containing nitrogen in their R2 side chains (N-BPs) were approved for clinical use including alendronate, risedronate, ibandronate, and zoledronate. These are now mostly generic drugs and remain the leading therapies for several major bone-related diseases, including osteoporosis and skeletal-related events associated with bone metastases. The early development of chemistry in this area was largely empirical and only a few common structural features related to strong binding to calcium phosphate were clear. Attempts to further develop structure-activity relationships to explain more dramatic pharmacological differences in vivo at first appeared inconclusive, and evidence for mechanisms underlying cellular effects on osteoclasts and macrophages only emerged after many years of research. The breakthrough came when the intracellular actions on the osteoclast were first shown for the simpler bisphosphonates, via the in vivo formation of P-C-P derivatives of ATP. The synthesis and biological evaluation of a large number of nitrogen-containing bisphosphonates in the 1980s and 1990s led to the key discovery that the antiresorptive effects of these more complex analogs on osteoclasts result mostly from their potency as inhibitors of the enzyme farnesyl diphosphate synthase (FDPS/FPPS). This key branch-point enzyme in the mevalonate pathway of cholesterol biosynthesis is important for the generation of isoprenoid lipids that are utilized for the post-translational modification of small GTP-binding proteins essential for osteoclast function. Since then, it has become even more clear that the overall pharmacological effects of individual bisphosphonates on bone depend upon two key properties: the affinity for bone mineral and inhibitory effects on biochemical targets within bone cells, in particular FDPS. Detailed enzyme-ligand crystal structure analysis began in the early 2000s and advances in our understanding of the structure-activity relationships, based on interactions with this target within the mevalonate pathway and related enzymes in osteoclasts and other cells have continued to be the focus of research efforts to this day. In addition, while many members of the bisphosphonate drug class share common properties, now it is more clear that chemical modifications to create variations in these properties may allow customization of BPs for different uses. Thus, as the appreciation for new potential opportunities with this drug class grows, new chemistry to allow ready access to an ever-widening variety of bisphosphonates continues to be developed. Potential new uses of the calcium phosphate binding mechanism of bisphosphonates for the targeting of other drugs to the skeleton, and effects discovered on other cellular targets, even at non-skeletal sites, continue to intrigue scientists in this research field.

Alveolar socket healing in 5-lipoxygenase knockout aged female mice treated or not with high dose of zoledronic acid

This study investigated the role 5-lypoxigenase (5-LO) on alveolar socket healing in aged female mice treated with zoledronic acid (ZL). Forty 129/Sv female mice (64–68 weeks old), 20 wild type (WT) and 20 5-LO knockout (5LOKO) were equally distributed according to ZL treatment: WT Control, WT ZL, 5LOKO Control, and 5LOKO ZL. ZL groups were treated with an intraperitoneal injection of 250 µg/Kg of ZL, while controls were treated with saline. Treatments were administered once a week, starting four weeks before surgery for tooth extraction and until 7 and 21 days post-surgery. Mice were euthanized for a comprehensive microscopic analysis (microCT, histomorphometry and immunohistochemistry). WT ZL mice presented intense inflammatory infiltrate (7 days), delayed bone formation (21 days), reduced collagenous matrix quality, and a deficiency in Runx-2 + , TRAP + , and macrophages as compared to controls. 5LOKO ZL animals presented decreased number of Runx-2 + cells in comparison to 5LOKO Control at 7 days, but no major changes in bone healing as compared to WT or 5LOKO mice at 21 days. The knockout of 5LO favored intramembranous bone healing in aged female mice, with a direct impact on inflammatory response and bone metabolism on the development of ONJ-like lesions.

Aromatic Bis[aminomethylidenebis(phosphonic)] Acids Prevent Ovariectomy-Induced Bone Loss and Suppress Osteoclastogenesis in Mice

Osteoporosis is a skeletal disease associated with excessive bone turnover. Among the compounds with antiresorptive activity, nitrogen-containing bisphosphonates play the most important role in antiosteoporotic treatment. In previous studies, we obtained two aminomethylidenebisphosphonates—benzene-1,4-bis[aminomethylidene(bisphosphonic)] (WG12399C) acid and naphthalene-1,5-bis[aminomethylidene(bisphosphonic)] (WG12592A) acid—which showed a significant antiproliferative activity toward J774E macrophages, a model of osteoclast precursors. The aim of these studies was to evaluate the antiresorptive activity of these aminobisphosphonates in ovariectomized (OVX) Balb/c mice. The influence of WG12399C and WG12592A administration on bone microstructure and bone strength was studied. Intravenous injections of WG12399C and WG12592A bisphosphonates remarkably prevented OVX-induced bone loss; for example, they sustained bone mineral density at control levels and restored other bone parameters such as trabecular separation. This was accompanied by a remarkable reduction in the number of TRAP-positive cells in bone tissue. However, a significant improvement in the quality of bone structure did not correlate with a parallel increase in bone strength. In ex vivo studies, WG12399C and WG12592A remarkably bisphosphonates reduced osteoclastogenesis and partially inhibited the resorptive activity of mature osteoclasts. Our results show interesting biological activity of two aminobisphosphonates, which may be of interest in the context of antiresorptive therapy.

Men who stare at bone: multimodal monitoring of bone healing

Knowledge of the physiological and pathological processes, taking place in bone during fracture healing or defect regeneration, is essential in order to develop strategies to enhance bone healing under normal and critical conditions. Preclinical testing allows a wide range of imaging modalities that may be applied both simultaneously and longitudinally, which will in turn lower the number of animals needed to allow a comprehensive assessment of the healing process. This work provides an up-to-date review on morphological, functional, optical, biochemical, and biophysical imaging techniques including their advantages, disadvantages and potential for combining them in a multimodal and multiscale manner. The focus lies on preclinical testing of biomaterials modified with artificial extracellular matrices in various animal models to enhance bone remodeling and regeneration.

Bisphosphonates in dentistry: Historical perspectives, adverse effects, and novel applications

Studies of the potential role of bisphosphonates in dentistry date back to physical chemical research in the 1960s, and the genesis of the discovery of bisphosphonate pharmacology in part can be linked to some of this work. Since that time, parallel research on the effects of bisphosphonates on bone metabolism continued, while efforts in the dental field included studies of bisphosphonate effects on dental calculus, caries, and alveolar bone loss. While some utility of this drug class in the dental field was identified, leading to their experimental use in various dentrifice formulations and in some dental applications clinically, adverse effects of bisphosphonates in the jaws have also received attention. Most recently, certain bisphosphonates, particularly those with strong bone targeting properties, but limited biochemical effects (low potency bisphosphonates), are being studied as a local remedy for the concerns of adverse effects associated with other more potent members of this drug class. Additionally, low potency bisphosphonate analogs are under study as vectors to target active drugs to the mineral surfaces of the jawbones. These latter efforts have been devised for the prevention and treatment of oral problems, such as infections associated with oral surgery and implants. Advances in the utility and mechanistic understanding of the bisphosphonate class may enable additional oral therapeutic options for the management of multiple aspects of dental health.

Design and Synthesis of Cathepsin-K-Activated Osteoadsorptive Fluorogenic Sentinel (OFS) Probes for Detecting Early Osteoclastic Bone Resorption in a Multiple Myeloma Mouse Model

We describe the design and synthesis of OFS-1, an Osteoadsorptive Fluorogenic Sentinel imaging probe that is adsorbed by hydroxyapatite (HAp) and bone mineral surfaces, where it generates an external fluorescent signal in response to osteoclast-secreted cathepsin K (Ctsk). The probe consists of a bone-anchoring bisphosphonate moiety connected to a Förster resonance energy transfer (FRET) internally quenched fluorescent (IQF) dye pair, linked by a Ctsk peptide substrate, GHPGGPQG. Key structural features contributing to the effectiveness of OFS-1 were defined by structure-activity relationship (SAR) and modeling studies comparing OFS-1 with two cognates, OFS-2 and OFS-3. In solution or when preadsorbed on HAp, OFS-1 exhibited strong fluorescence when exposed to Ctsk (2.5-20 nM). Time-lapse photomicrographs obtained after seeding human osteoclasts onto HAp-coated well plates containing preadsorbed OFS-1 revealed bright fluorescence at the periphery of resorbing cells. OFS-1 administered systemically detected early osteolysis colocalized with orthotopic engraftment of RPMI-8226-Luc human multiple myeloma cells at a metastatic skeletal site in a humanized mouse model. OFS-1 is thus a promising new imaging tool for detecting abnormal bone resorption.

Analysis of the subsequent treatment of osteoporosis by transitioning from bisphosphonates to denosumab, using quantitative computed tomography: A prospective cohort study

Purpose

Denosumab reduces bone resorption and improves bone mineral density (BMD). Studies have analyzed subsequent treatment transitioning from bisphosphonates to denosumab based on dual-energy X-ray absorptiometry scanning (DXA). Quantitative computed tomography (QCT) can help assess cortical and trabecular bones separately in three dimensions without the interference of the surrounding osteophytes. In the present study, we analyzed the subsequent treatment transition from bisphosphonates to denosumab using QCT.

Methods

Thirty-two patients with postmenopausal osteoporosis to be treated with denosumab were recruited. The patients were divided into two groups (15 prior bisphosphonate and 17 naïve) based on their previous treatment. BMD of the lumbar spine and hip were evaluated by DXA and QCT at baseline and 12 months following denosumab treatment.

Results

The percentage change in volumetric BMD assessed by QCT at 12 months significantly improved in the naïve group compared with that in the prior bisphosphonate group. The region-specific assessment of femur at 12 months revealed that denosumab treatment was effective in both cortical and trabecular bones except the trabecular region of the prior bisphosphonate group.

Conclusion

Our study suggests that although denosumab treatment was useful in both treatment groups, BMD increase was significantly higher in the naïve group than in the prior-bisphosphonate group. Interestingly, in the prior-bisphosphonate group, denosumab treatment was more effective in the cortical region than the trabecular region. Our study offers insights into the subsequent treatment and permits greater confidence when switching to denosumab from bisphosphonates.

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We analyzed the treatment transition from bisphosphonates to denosumab using QCT.

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Percentage change in volumetric BMD at 12 months significantly improved in the naïve group.

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Denosumab treatment was more effective on the cortical region than the trabecular region.

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Our study offers insights into the subsequent treatment when switching to denosumab.

A Bisphosphonate With a Low Hydroxyapatite Binding Affinity Prevents Bone Loss in Mice After Ovariectomy and Reverses Rapidly With Treatment Cessation

Bisphosphonates (BPs) are a mainstay of osteoporosis treatment; however, concerns about bone health based on oversuppression of remodeling remain. Long‐term bone remodeling suppression adversely affects bone material properties with microdamage accumulation and reduced fracture toughness in animals and increases in matrix mineralization and atypical femur fractures in patients. Although a “drug holiday” from BPs to restore remodeling and improve bone quality seems reasonable, clinical BPs have long functional half‐lives because of their high hydroxyapatite (HAP) binding affinities. This places a practical limit on the reversibility and effectiveness of a drug holiday. BPs with low HAP affinity and strong osteoclast inhibition potentially offer an alternative approach; their antiresorptive effect should reverse rapidly when dosing is discontinued. This study tested this concept using NE‐58025, a BP with low HAP affinity and moderate osteoclast inhibition potential. Young adult female C57Bl/6 mice were ovariectomized (OVX) and treated with NE‐58025, risedronate, or PBS vehicle for 3 months to test effectiveness in preventing long‐term bone loss. Bone microarchitecture, histomorphometry, and whole‐bone mechanical properties were assessed. To test reversibility, OVX mice were similarly treated for 3 months, treatment was stopped, and bone was assessed up to 3 months post‐treatment. NE‐58025 and RIS inhibited long‐term OVX‐induced bone loss, but NE‐58025 antiresorptive effects were more pronounced. Withdrawing NE‐58025 treatment led to the rapid onset of trabecular resorption with a 200% increase in osteoclast surface and bone loss within 1 month. Cessation of risedronate treatment did not lead to increases in resorption indices or bone loss. These results show that NE‐58025 prevents OVX‐induced bone loss, and its effects reverse quickly following cessation treatment in vivo. Low‐HAP affinity BPs may have use as reversible, antiresorptive agents with a rapid on/off profile, which may be useful for maintaining bone health with long‐term BP treatment. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Molecular mechanisms of action of bisphosphonates and new insights into their effects outside the skeleton

Bisphosphonates (BP) are a class of calcium-binding drug used to prevent bone resorption in skeletal disorders such as osteoporosis and metastatic bone disease. They act by selectively targeting bone-resorbing osteoclasts and can be grouped into two classes depending on their intracellular mechanisms of action. Simple BPs cause osteoclast apoptosis after cytoplasmic conversion into toxic ATP analogues. In contrast, nitrogen-containing BPs potently inhibit FPP synthase, an enzyme of the mevalonate (cholesterol biosynthesis) pathway. This results in production of a toxic metabolite (ApppI) and the loss of long-chain isoprenoid lipids required for protein prenylation, a process necessary for the function of small GTPase proteins essential for the survival and activity of osteoclasts. In this review we provide a state-of-the-art overview of these mechanisms of action and a historical perspective of how they were discovered. Finally, we challenge the long-held dogma that BPs act only in the skeleton and highlight recent studies that reveal insights into hitherto unknown effects on tumour-associated and tissue-resident macrophages.

On the pharmacological evaluation of bisphosphonates in humans

One of the key parameters for a successful treatment with any drug is the use of an optimal dose regimen. Bisphosphonates (BPs) have been in clinical use for over five decades and during this period clinical pharmacokinetic (PK) and pharmacodynamic (PD) evaluations have been instrumental for the identification of optimal dose regimens in patients. Ideal clinical PK and PD studies help drug developers explain variability in responses and enable the identification of a dose regimen with an optimal effect. PK and PD studies of the unique and rather complex pharmacological properties of BPs also help determine to a significant extent ideal dosing for these drugs. Clinical PK and PD evaluations of BPs preferably use study designs and assays that enable the assessment of both short- (days) and long-term (years) presence and effect of these drugs in patients. BPs are mainly used for metabolic bone diseases because they inhibit osteoclast-mediated bone resorption and the best way to quantify their effects in humans is therefore by measuring biochemical markers of bone resorption in serum and urine. In these very same samples BP concentrations can also be measured. Short-term serum and urine data after both intravenous (IV) and oral administration enable the assessment of oral bioavailability as well as the amount of BP delivered to the skeleton. Longer-term data provide information on the anti-resorptive effect as well as the elimination of the BP from the skeleton. Using PK-PD models to mathematically link the anti-resorptive action of the BPs to the amount of BP at the skeleton provides a mechanism-based explanation of the pattern of bone resorption during treatment. These models have been used successfully during the clinical development of BPs. Newer versions of such models, which include systems pharmacology and disease progression models, are more comprehensive and include additional PD parameters such as BMD and fracture risk. Clinical PK and PD studies of BPs have been useful for the identification of optimal dose regimens for metabolic bone diseases. These analyses will also continue to be important for newer research directions, such as BP use in the delivery of other drugs to the bone to better treat bone metastases and bone infections, as well as the potential benefit of BPs at non-skeletal targets for the prevention and treatments of soft tissue cancers, various fibroses, and other cardiovascular and neurodegenerative diseases, and reduction in mortality and extension of lifespan.

Differing Effects of Zoledronic Acid on Bone Microarchitecture and Bone Mineral Density in Men Receiving Androgen Deprivation Therapy: A Randomized Controlled Trial

Androgen deprivation therapy (ADT) given to men with prostate cancer causes rapid and severe sex steroid deficiency, leading to increased bone remodeling and accelerated bone loss. To examine the effects of a single dose of zoledronic acid on bone microarchitecture, we conducted a 2-year randomized placebo controlled trial in 76 men, mean age (interquartile range [IQR]) 67.8 years (63.8 to 73.9) with non-metastatic prostate cancer commencing adjuvant ADT; 39 were randomized to zoledronic acid and 37 to matching placebo. Bone microarchitecture was measured using high-resolution peripheral quantitative computed tomography (HR-pQCT). Using a mixed model, mean adjusted differences (MAD; 95% confidence interval [95% CI]) between the groups are reported as the treatment effect at several time points. Over 24 months, zoledronic acid showed no appreciable treatment effect on the primary outcomes for total volumetric bone mineral density (vBMD); radius (6.7 mg HA/cm³ [-2.0 to 15.4], p = 0.21) and tibia (1.9 mg HA/cm³ [-3.3 to 7.0], p = 0.87). Similarly, there were no between-group differences in other measures of microarchitecture, with the exception of a modest effect of zoledronic acid over placebo in total cortical vBMD at the radius over 12 months (17.3 mgHA/cm³ [5.1 to 29.5]). In contrast, zoledronic acid showed a treatment effect over 24 months on areal bone mineral density (aBMD) by dual-energy X-ray absorptiometry (DXA) at all sites, including lumbar spine (0.10 g/cm² [0.07 to 0.13]), p < 0.001), and total hip (0.04 g/cm² [0.03 to 0.05], p < 0.001). Bone remodeling markers were initially suppressed in the treatment group then increased but remained lower relative to placebo (MADs at 24 months CTX -176 ng/L [-275 to -76], p < 0.001; P1NP -18 mg/L [-32 to -5], p < 0.001). These findings suggest that a single dose of zoledronic acid over 2 years is ineffective in preventing the unbalanced bone remodeling and severe microstructural deterioration associated with ADT therapy. © 2020 American Society for Bone and Mineral Research.

Targeting anti-cancer agents to bone using bisphosphonates

The skeleton is affected by numerous primary and metastatic solid and hematopoietic malignant tumors, which can cause localized sites of osteolysis or osteosclerosis that can weaken bones and increase the risk of fractures in affected patients. Chemotherapeutic drugs can eliminate some tumors in bones or reduce their volume and skeletal-related events, but adverse effects on non-target organs can significantly limit the amount of drug that can be administered to patients. In these circumstances, it may be impossible to deliver therapeutic drug concentrations to tumor sites in bones. One attractive mechanism to approach this challenge is to conjugate drugs to bisphosphonates, which can target them to bone where they can be released at diseased sites. Multiple attempts have been made to do this since the 1990s with limited degrees of success. Here, we review the results of pre-clinical and clinical studies made to target FDA-approved drugs and other antineoplastic small molecules to bone to treat diseases affecting the skeleton, including osteoporosis, metastatic bone disease, multiple myeloma and osteosarcoma. Results to date are encouraging and indicate that drug efficacy can be increased and side effects reduced using these approaches. Despite these successes, challenges remain: no drugs have gone beyond small phase 2 clinical trials, and major pharmaceutical companies have shown little interest in the approach to repurpose any of their drugs or to embrace the technology. Nevertheless, interest shown by smaller biotechnology companies in the technology suggests that bone-targeting of drugs with bisphosphonates has a viable future.

Imaging with radiolabelled bisphosphonates

Radiolabeled bisphosphonates were developed in the 1970s for scintigraphic functional imaging of the skeleton in benign and malignant disease. Tracers such as 99mTc-methylene diphosphonate, that map focal or global changes in mineralization in the skeleton qualitatively and quantitatively, have been the backbone of nuclear medicine imaging for decades. While competing technologies are evolving, new indications and improvements in scanner hardware, in particular hybrid imaging (e.g. single photon emission computed tomography combined with computed tomography), have allowed improved diagnostic accuracy and a continued role for radiolabeled bisphosphonate imaging in current practice.

Short-term high-dose zoledronic acid enhances crystallinity in mandibular alveolar bone in rats

Owing to its antiresorptive properties, zoledronic acid (ZOL) is commonly used in the management of benign as well as malignant bone diseases. This molecule targets sites where bone is actively remodeling, and high concentrations have been reported in the jaw. The purpose of this study was to investigate whether treatment of male rats with ZOL, at a dosage equivalent to that used for antitumor treatment, impacts the short-term qualitative properties of mandibular bone independent of bone remodeling. Thirty rats were randomly assigned to treatment either with ZOL or with serum-vehicle (control) (weekly injections: 100 μg kg^-1 for 6 wk, n = 15 per group). Using the tetracycline double-labeling technique, remodeled bone areas, corresponding to the preferential site of bisphosphonate binding, were found in the alveolar bone along the alveolar bone proper. The composition of bone in these areas was characterized using Raman microspectroscopy and compared with adjacent, non-remodeled, older bone. The ZOL-treated group exhibited higher crystallinity in the remodeled bone areas (+2%), reflecting an early maturation of the apatite mineral after ZOL injection. Our findings highlight a direct and rapid effect of clinically relevant anti-tumoral ZOL doses on the qualitative properties of mandibular bone, especially on mineral crystallinity in the vicinity of the teeth, namely, the alveolar bone proper.

Sequential Treatment of Estrogen Deficient, Osteopenic Rats with Alendronate, Parathyroid Hormone (1-34), or Raloxifene Alters Cortical Bone Mineral and Matrix Composition

Anti-resorptive and anabolic treatments can be used sequentially to treat osteoporosis, but their effects on bone composition are incompletely understood. Osteocytes may influence bone tissue composition with sequential therapies because bisphosphonates diffuse into the canalicular network and anabolic treatments increase osteocyte lacunar size. Cortical bone composition of osteopenic, ovariectomized (OVX) rats was compared to that of Sham-operated rats and OVX rats given monotherapy or sequential regimens of single approved anti-osteoporosis medications. Adult female Sprague-Dawley rats were OVX (N = 37) or Sham-OVXd (N = 6). After 2 months, seven groups of OVX rats were given three consecutive 3-month periods of treatment with vehicle (V), h-PTH (1-34) (P), alendronate (A), or raloxifene (R), using the following orders: VVV, PVV, RRR, RPR, AAA, AVA, and APA. Compositional properties around osteocyte lacunae of the left tibial cortex were assessed from Raman spectra in perilacunar and non-perilacunar bone matrix regions. Sequential treatments involving parathyroid hormone (PTH) caused lower mean collagen maturity relative to monotherapies. Mean mineral:matrix ratio was 2.2% greater, mean collagen maturity was 1.4% greater, and mean carbonate:phosphate ratio was 2.2% lower in the perilacunar than in the non-perilacunar bone matrix region (all P < 0.05). These data demonstrate cortical bone tissue composition differences around osteocytes caused by sequential treatment with anti-osteoporosis medications. We speculate that the region-specific differences demonstrate the ability of osteocytes to alter bone tissue composition adjacent to lacunae.

Bone Mineral Density After Transitioning From Denosumab to Alendronate

CONTEXT

There are few studies on patients transitioning from denosumab to bisphosphonates.

OBJECTIVE

To investigate patient characteristics and changes in bone mineral density (BMD) after transitioning from denosumab to alendronate.

DESIGN

Randomized, open-label, 2-year crossover Denosumab Adherence Preference Satisfaction (DAPS) study (NCT00518531).

SETTING

25 study centers in the US and Canada.

PATIENTS

Treatment-naïve postmenopausal women with BMD T-scores from -2.0 to -4.0.

INTERVENTIONS

This post hoc analysis evaluated women randomized to subcutaneous denosumab 60 mg every 6 months in year 1 followed by once-weekly oral alendronate 70 mg in year 2.

MAIN OUTCOME MEASURE

A 3% BMD threshold identified participants who lost, maintained, or gained BMD in year 2 on alendronate.

RESULTS

Of 126 participants randomized to denosumab, 115 (91%) transitioned to alendronate in year 2. BMD increased by 3% to 6% with denosumab in year 1 and by 0% to 1% with alendronate in year 2. After transitioning to alendronate, most participants maintained or increased BMD; 15.9%, 7.6%, and 21.7% lost BMD at the lumbar spine, total hip, and femoral neck, respectively. Few participants fell below their pretreatment baseline BMD value; this occurred most often in those who lost BMD in year 2. Women who lost BMD with alendronate in year 2 also showed a greater percent change in BMD with denosumab in year 1. The BMD change in year 2 was similar regardless of baseline characteristics or adherence to oral alendronate.

CONCLUSION

Alendronate can effectively maintain the BMD gains accrued after 1 year of denosumab in most patients, regardless of baseline characteristics.

Targeting Bortezomib to Bone Increases Its Bone Anabolic Activity and Reduces Systemic Adverse Effects in Mice

Bortezomib (Btz) is a proteasome inhibitor approved by the FDA to treat multiple myeloma. It also increases bone volume by promoting osteoblast differentiation and inhibiting osteoclastogenesis in mice. However, Btz has severe systemic adverse effects, which would limit its use as a bone anabolic agent. Here, we designed and synthesized a bone-targeted form of Btz by conjugating it to a bisphosphonate (BP) with no antiresorptive activity. We report that BP-Btz inhibited osteoclast formation and bone resorption and stimulated osteoblast differentiation in vitro similar to Btz. In vivo, BP-Btz increased bone volume more effectively than Btz in three mouse models: untreated wild-type mice, mice with ovariectomy, and aged mice with tibial factures. Importantly, BP-Btz had significantly less systemic side effects than Btz, including less thymic cell death, sympathetic nerve damage, and thrombocytopenia, and it improved survival rates in aged mice. Thus, BP-Btz represents a novel anabolic agent to treat conditions, such as postmenopausal and age-related bone loss. Bone targeting is an attractive approach to repurpose approved drugs to treat skeletal diseases. © 2019 American Society for Bone and Mineral Research. © 2019 American Society for Bone and Mineral Research.

Role of osteoclasts in oral homeostasis and jawbone diseases

The jawbone is a unique structure as it serves multiple functions in mastication. Given the fact that the jawbone is remodeled faster than other skeletal bones, bone cells in the jawbone may respond differently to local and systemic cues to regulate bone remodeling and adaptation. Osteoclasts are bone cells responsible for removing old bone, playing an essential role in bone remodeling. Although bone resorption by osteoclasts is required for dental tissue development, homeostasis and repair, excessive osteoclast activity is associated with oral skeletal diseases such as periodontitis. In addition, antiresorptive medications used to prevent bone homeostasis of tumors can cause osteonecrosis of the jaws that is a major concern to the dentist. Therefore, understanding of the role of osteoclasts in oral homeostasis under physiological and pathological conditions leads to better targeted therapeutic options for skeletal diseases to maintain patients' oral health. Here, we highlight the unique features of the jawbone compared to the long bone and the involvement of osteoclasts in the jawbone-specific diseases.

Bisphosphonates and Cancer: A Relationship Beyond the Antiresorptive Effects

Bisphosphonates (BPs) are stable analogues of the Inorganic Pyrophosphate (PPi), an endogenous regulator of bone mineralization, which can resist the hydrolysis in the gastrointestinal tract. Their conformation allows targeting the bone as a result of their three-dimensional structure, which makes them primary agents against osteoclast-mediated bone loss. They are used in many bone pathological conditions, like bone metastasis, because of its ability to modulate bone metabolism into a less favorable place to cancer cell growth, through the inhibition of osteoclastogenesis and bone resorption. This review is focused on the mechanisms of action through which BPs affect the cellular activity and survival, mainly on their antitumoral effects. In conclusion, BPs are considered the primary therapy for skeletal disorders due to its high affinity for bone, but now they are also considered as potential antitumor agents due to its ability to induce tumor cell apoptosis, inhibition of cell adhesion, invasion and proliferation, modulation of the immune system to target and eliminate cancer cells as well as affect the angiogenic mechanisms. Like any other drug, they also have some adverse effects, but the most common, the acute phase reaction, can be minimized with the intake of calcium and vitamin D.

WY 1048, a 17-methyl 19-nor D-ring analog of vitamin D3, in combination with risedronate restores bone mass in a mouse model of postmenopausal osteoporosis

Bisphosphonates like risedronate inhibit osteoclast-mediated bone resorption and are therefore used in the prevention and treatment of osteoporosis. Also vitamin D₃ and calcium supplementation is commonly used in the prevention or treatment of osteoporosis. Combined therapy of risedronate with 1,25(OH)₂D₃, the active metabolite of vitamin D₃, may be advantageous over the use of either monotherapy, but bears a risk of causing hypercalcemia thereby decreasing the therapeutic window for osteoporosis treatment. In this study, we evaluated the effect on bone mass of the combination of risedronate with the 17-methyl 19-nor five-membered D-ring vitamin D₃ analog WY 1048 in a mouse ovariectomy model for postmenopausal osteoporosis. Ovariectomy-induced bone loss was restored by administration of risedronate or a combination of risedronate with 1,25(OH)₂D_3. However, the combination of WY 1048 with risedronate induced an even higher increase on total body and spine bone mineral density and on trabecular and cortical bone mass. Our data indicate that combination therapy of risedronate with WY 1048 was superior in restoring and improving bone mass over a combination of risedronate with 1,25(OH)₂D₃ with minimal calcemic side effects.

Pharmacology of bisphosphonates

The biological effects of the bisphosphonates (BPs) as inhibitors of calcification and bone resorption were first described in the late 1960s. In the 50 years that have elapsed since then, the BPs have become the leading drugs for the treatment of skeletal disorders characterized by increased bone resorption, including Paget's disease of bone, bone metastases, multiple myeloma, osteoporosis and several childhood inherited disorders. The discovery and development of the BPs as a major class of drugs for the treatment of bone diseases is a paradigm for the successful journey from "bench to bedside and back again". Several of the leading BPs achieved "blockbuster" status as branded drugs. However, these BPs have now come to the end of their patent life, making them highly affordable. The opportunity for new clinical applications for BPs also exists in other areas of medicine such as ageing, cardiovascular disease and radiation protection. Their use as inexpensive generic medicines is therefore likely to continue for many years to come. Fifty years of research into the pharmacology of bisphosphonates have led to a fairly good understanding about how these drugs work and how they can be used safely in patients with metabolic bone diseases. However, while we seemingly know much about these drugs, a number of key aspects related to BP distribution and action remain incompletely understood. This review summarizes the existing knowledge of the (pre)clinical and translational pharmacology of BPs, and highlights areas in which understanding is lacking.

A power law function describes the time- and dose-dependency of Vγ9Vδ2 T cell activation by phosphoantigens

Phosphoantigens stimulate Vγ9Vδ2 T cells after binding to BTN3A1 in target cells and cell-cell contact. We evaluated phosphoantigens including diphosphates, bisphosphonates, and prodrugs for ability to induce leukemia cells to stimulate Vγ9Vδ2 T cell interferon-γ secretion. Most compounds displayed time-dependent activity at exposure times between 15 and 240 min. Potency (EC₅₀ values) ranged between 8.4 nM and >100 µM. The diphosphate C-HMBPP displayed a shallow dose-response slope (Hill slope = 0.71), while the bisphosphonate slopes were steep (Hill slopes > 2), and the prodrugs intermediate. The bis-acyloxyalkyl POM₂-C-HMBP showed low nanomolar potency even at an exposure time of 1 min. Mixed aryl-POM prodrugs also retained excellent potency at 15 min, while aryl-amidates were time dependent below 240 min. The sum of the dose and time logarithms is often constant, while a power law function fits most compounds. Collectively, these findings illustrate the exquisite activity of prodrugs relative to diphosphates and bisphosphonates.

Skeletal accumulation of fluorescently tagged zoledronate is higher in animals with early stage chronic kidney disease

This work examines the skeletal accumulation of fluorescently tagged zoledronate in an animal model of chronic kidney disease. The results show higher accumulation in 24-h post-dose animals with lower kidney function due to greater amounts of binding at individual surfaces.

INTRODUCTION

Chronic kidney disease (CKD) patients suffer from increased rates of skeletal-related mortality from changes driven by biochemical abnormalities. Bisphosphonates are commonly used in reducing fracture risk in a variety of diseases, yet their use is not recommended in advanced stages of CKD. This study aimed to characterize the accumulation of a single dose of fluorescently tagged zoledronate (FAM-ZOL) in the setting of reduced kidney function.

METHODS

At 25 weeks of age, FAM-ZOL was administered to normal and CKD rats. Twenty-four hours later, multiple bones were collected and assessed using bulk fluorescence imaging, two-photon imaging, and dynamic histomorphometry.

RESULTS

CKD animals had significantly higher levels of FAM-ZOL accumulation in the proximal tibia, radius, and ulna, but not in lumbar vertebral body or mandible, based on multiple measurement modalities. Although a majority of trabecular bone surfaces were covered with FAM-ZOL in both normal and CKD animals, the latter had significantly higher levels of fluorescence per unit bone surface in the proximal tibia.

CONCLUSIONS

These results provide new data regarding how reduced kidney function affects drug accumulation in rat bone.

Dynamic Analyses of the Short-Term Effects of Different Bisphosphonates Using Intravital Two-Photon Microscopy

Bisphosphonates are commonly used for the treatment of bone disorders such as osteoporosis; however, the mechanism by which they affect the dynamics of living mature osteoclasts in vivo remains unknown. Here, we describe the short-term effects of different bisphosphonates on controlling the bone resorptive activity of mature osteoclasts in living bone tissues of mice using intravital two-photon microscopy with a pH-sensing chemical fluorescent probe. Three types of nitrogen-containing bisphosphonates, risedronate, alendronate, and minodronate, inhibited osteoclastic acidification during osteoporotic conditions just 12 hours after i.v. injection. Among the three types of drugs, risedronate was the most effective at increasing osteoclast motility and changing the localization of proton pumps, which led to an inhibition of bone resorption. Together, these results demonstrate that the intravital imaging system is a useful tool for evaluating the similarities and differences in currently used antibone resorptive drugs. © 2018 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Fluorescence Detection of Bone Microcracks Using Monophosphonated Carbon Dots

Phosphonated compounds, in particular, bisanalogs are widely applied in clinical settings for the treatment of severe bone turnovers and recently as imaging probes when conjugated with organic fluorophores. Herein, we introduce a bone seeking luminescent probe that shows a high binding affinity toward bone minerals based on monophosphonated carbon dots (CDs). Spheroidal CDs tethered with PEG monophosphates are synthesized in a one-pot hydrothermal method and are physicochemically characterized, where the retention of phosphonates is confirmed by ¹³P NMR and X-ray photoelectron spectroscopy. Interestingly, the high abundance of multiple monodentate phosphonates exhibited strong binding to hydroxyapatite, the main bone mineral constituent. The remarkable optophysical properties of monophosphonated CDs were confirmed in an ex vivo model of the bovine cortical bone where the imaging feasibility of microcracks, which are calcium-rich regions, was demonstrated. The in vivo studies specified the potential application of monophosphonated CDs for imaging when injected intramuscularly. The biodigestible nature and cytocompatibility of the probe presented here obviate the demand for a secondary fluorophore, while offering a nanoscale strategy for bone targeting and can eventually be employed for potential bone therapy in the future.

Removal of matrix-bound zoledronate prevents post-extraction osteonecrosis of the jaw by rescuing osteoclast function

Unlike other antiresorptive medications, bisphosphonate molecules accumulate in the bone matrix. Previous studies of side-effects of anti-resorptive treatment focused mainly on systemic effects. We hypothesize that matrix-bound bisphosphonate molecules contribute to the pathogenesis of bisphosphonate-related osteonecrosis of the jaw (BRONJ). In this study, we examined the effect of matrix-bound bisphosphonates on osteoclast differentiation in vitro using TRAP staining and resorption assay, with and without pretreatment with EDTA. We also tested the effect of zoledronate chelation on the healing of post-extraction defect in rats. Our results confirmed that bisphosphonates bind to, and can be chelated from, mineralized matrix in vitro in a dose-dependent manner. Matrix-bound bisphosphonates impaired the differentiation of osteoclasts, evidenced by TRAP activity and resorption assay. Zoledronate-treated rats that underwent bilateral dental extraction with unilateral EDTA treatment showed significant improvement in mucosal healing and micro-CT analysis on the chelated sides. The results suggest that matrix-bound bisphosphonates are accessible to osteoclasts and chelating agents and contribute to the pathogenesis of BRONJ. The use of topical chelating agents is a promising strategy for the prevention of BRONJ following dental procedures in bisphosphonate-treated patients.

Selective inhibition of matrix metalloproteinase-2 in the multiple myeloma-bone microenvironment

Multiple myeloma is a plasma cell malignancy that homes aberrantly to bone causing extensive skeletal destruction. Despite the development of novel therapeutic agents that have significantly improved overall survival, multiple myeloma remains an incurable disease. Matrix metalloproteinase-2 (MMP-2) is associated with cancer and is significantly overexpressed in the bone marrow of myeloma patients. These data provide rationale for selectively inhibiting MMP-2 activity as a multiple myeloma treatment strategy. Given that MMP-2 is systemically expressed, we used novel “bone-seeking” bisphosphonate based MMP-2 specific inhibitors (BMMPIs) to target the skeletal tissue thereby circumventing potential off-target effects of MMP-2 inhibition outside the bone marrow-tumor microenvironment. Using in vivo models of multiple myeloma (5TGM1, U266), we examined the impact of MMP-2 inhibition on disease progression using BMMPIs. Our data demonstrate that BMMPIs can decrease multiple myeloma burden and protect against cancer-induced osteolysis. Additionally, we have shown that MMP-2 can be specifically inhibited in the multiple myeloma-bone microenvironment, underscoring the feasibility of developing targeted and tissue selective MMP inhibitors. Given the well-tolerated nature of bisphosphonates in humans, we anticipate that BMMPIs could be rapidly translated to the clinical setting for the treatment of multiple myeloma.

Bisphosphonate-Linked TrkB Agonist: Cochlea-Targeted Delivery of a Neurotrophic Agent as a Strategy for the Treatment of Hearing Loss

Hearing loss affects more than two-thirds of the elderly population, and more than 17% of all adults in the U.S. Sensorineural hearing loss related to noise exposure or aging is associated with loss of inner ear sensory hair cells (HCs), cochlear spiral ganglion neurons (SGNs), and ribbon synapses between HCs and SGNs, stimulating intense interest in therapies to regenerate synaptic function. 7,8-Dihydroxyflavone (DHF) is a selective and potent agonist of tropomyosin receptor kinase B (TrkB) and protects the neuron from apoptosis. Despite evidence that TrkB agonists can promote survival of SGNs, local delivery of drugs such as DHF to the inner ear remains a challenge. We previously demonstrated in an animal model that a fluorescently labeled bisphosphonate, 6-FAM-Zol, administered to the round window membrane penetrated the membrane and diffused throughout the cochlea. Given their affinity for bone mineral, including cochlear bone, bisphosphonates offer an intriguing modality for targeted delivery of neurotrophic agents to the SGNs to promote survival, neurite outgrowth, and, potentially, regeneration of synapses between HCs and SGNs. The design and synthesis of a bisphosphonate conjugate of DHF (Ris-DHF) is presented, with a preliminary evaluation of its neurotrophic activity. Ris-DHF increases neurite outgrowth in vitro, maintains this ability after binding to hydroxyapatite, and regenerates synapses in kainic acid-damaged cochlear organ of Corti explants dissected in vitro with attached SGNs. The results suggest that bisphosphonate-TrkB agonist conjugates have promise as a novel approach to targeted delivery of drugs to treat sensorineural hearing loss.

Fluorous-tag assisted synthesis of bile acid-bisphosphonate conjugates via orthogonal click reactions: an access to potential anti-resorption bone drugs

The synthesis of a small collection of novel bile acid-bisphosphonate (BA-BP) conjugates as potential drug candidates is reported. The disclosed methodology relied on the installation of azide and thiol functionalities at the head and tail positions, respectively, of the BA scaffold and its subsequent decoration by orthogonal click reactions (copper-catalyzed azide-alkyne cycloaddition, thiol-ene or thiol-yne coupling) to introduce BP units and a fluorophore. Because of the troublesome isolation of the target conjugates by standard procedures, the methodology culminated with the functionalization of the BA scaffold with a light fluorous tag to rapidly and efficiently purify intermediates and final products by fluorous solid-phase extraction.

Protective effect of low-dose risedronate against osteocyte apoptosis and bone loss in ovariectomized rats

Osteocyte apoptosis is the first reaction to estrogen depletion, thereby stimulating osteoclastic bone resorption resulting in bone loss. We investigated the effects of two different risedronate (RIS) doses (high and low) on osteocyte apoptosis, osteoclast activity and bone loss in ovariectomized rats. Forty rats with ovariectomy (OVX) and sham ovariectomy (SHAM) were divided into 4 groups: 1) SHAM rats treated with saline (SHAM); 2) OVX rats treated with saline (OVX); 3) OVX rats treated with low-dose RIS (OVX-LR, 0.08 μg/kg/day); 4) OVX rats treated with high-dose RIS (OVX-HR, 0.8 μg/kg/day). All animals were sacrificed 90 days after surgery for the examinations of osteocyte apoptosis by caspase-3 staining, osteoclast activity by TRAP staining and bone volume by micro-CT scanning in lumbar vertebral cancellous bone. Both low and high dose RIS significantly reduced caspase-3 positive osteocytes, empty lacunae and TRAP positive osteoclasts in OVX rats. Although the difference in caspase-3 positive osteocytes was not significant between the OVX-LR and OVX-HR groups, numerically these cells were significantly more prevalent in OVX-HR (not OVX-LR) group than in SHAM group. TRAP positive osteoclasts were significantly higher in OVX-LR group than in SHAM or OVX-HR group. There was no significant difference in bone volume among the OVX-LR, OVX-HR and SHAM groups, but lower in OVX group alone. However, significant increase in trabecular thickness only occurred in OVX-LR group. We conclude that both low and high dose RIS significantly inhibit osteocyte apoptosis and osteoclast activity in OVX rats, but the low-dose RIS has weaker effect on osteoclast activity. However, low-dose RIS preserves cancellous bone mass and microarchitecture as well as high-dose RIS after estrogen depletion.

Effect of Sequential Treatment with Bisphosphonates After Teriparatide in Ovariectomized Rats: A Direct Comparison Between Risedronate and Alendronate

Teriparatide (TPTD), a recombinant human parathyroid hormone N-terminal fragment (1-34), is a widely used bone anabolic drug for osteoporosis. Sequential treatment with antiresorptives such as bisphosphonates after TPTD discontinuation is generally recommended. However, relative effects of bisphosphonates have not been determined. In the present study, we directly compared effects of risedronate (RIS) and alendronate (ALN) on bone mineral density (BMD), bone turnover, structural property and strength in ovariectomized (OVX) rats, when administered after TPTD. Female Sprague Dawley rats were divided into one sham-operated and eight ovariectomized groups. TPTD, RIS, and ALN were given subcutaneously twice per week for 4 or 8 weeks after 4 week treatment with TPTD. TPTD significantly increased BMD (+9.6%) in OVX rats after 4 weeks of treatment. 8 weeks after TPTD withdrawal, vehicle-treated group showed a blunted BMD increase of +8.4% from the baseline. In contrast, 8 weeks of treatment with RIS and ALN significantly increased BMD to 17.4 and 21.8%, respectively. While ALN caused a consistently larger increase in BMD, sequential treatment with RIS resulted in lower Tb.Sp compared to ALN in the fourth lumbar vertebra as well as in greater stiffness in compression test. In conclusion, the present study demonstrated that sequential therapy with ALN and RIS after TPTD both improved bone mass and structure. Our results further suggest that RIS may have a greater effect on improving bone quality and stiffness than ALN despite less prominent effect on BMD. Further studies are necessary to determine clinical relevance of these findings to fracture rate.

Intermittent Ibandronate Maintains Bone Mass, Bone Structure, and Biomechanical Strength of Trabecular and Cortical Bone After Discontinuation of Parathyroid Hormone Treatment in Ovariectomized Rats

Although parathyroid hormone (PTH) expresses an anabolic effect on bone mass, the increased bone mass disappears once PTH treatment is withdrawn. Therefore, sequential treatment with anti-bone-resorptive agents is required to maintain bone mass after PTH treatment. We examined the effect of sequential treatment with ibandronate (IBN), a nitrogen-containing bisphosphonate, following PTH in ovariectomized (OVX) rats. Wistar-Imamichi rats (27 weeks old) were ovariectomized and treated with PTH (10 µg/kg, s.c.; 5 times/week; PTH group) for 8 weeks from 8 weeks after OVX. Thereafter, PTH was withdrawn and rats were administered IBN (10 µg/kg, s.c.; every 4 weeks; PTH-IBN group) or vehicle (PTH-Veh group) for another 8 weeks. PTH increased bone mineral density (BMD) measured by dual-energy X-ray absorptiometry and biomechanical strength in the lumbar spine and femur as compared to the disease control rats. BMD and biomechanical strength in the PTH-Veh group were lower than in the PTH group, whereas in the PTH-IBN group they were maintained at the level of the PTH group. Microstructure of the trabecular and cortical bone in the PTH-IBN group was not significantly different from that in the PTH group. In histomorphometric analysis of the lumbar vertebra, eroded surface and osteoclast surface in the PTH-Veh group were no different from those in the PTH group, whereas they were lower in the PTH-IBN group. Osteoid surface, osteoblast surface, and mineralize surface decreased in both PTH-IBN and PTH-Veh groups compared to the PTH group, and these parameters in the PTH-IBN group were lower than in the PTH-Veh group. These results indicated that intermittent IBN after PTH treatment suppressed bone turnover and maintained BMD, biomechanical strength, and microstructure in the lumbar spine and femur of OVX rats.

Pain prediction by serum biomarkers of bone turnover in people with knee osteoarthritis: an observational study of TRAcP5b and cathepsin K in OA

OBJECTIVES

To investigate serum biomarkers, tartrate resistant acid phosphatase 5b (TRAcP5b) and cathepsin K (cath-K), indicative of osteoclastic bone resorption, and their relationship to pain and pain change in knee osteoarthritis (OA).

METHODS

Sera and clinical data were collected from 129 people (97 with 3-year follow-up) with knee OA from the Prediction of Osteoarthritis Progression (POP) cohort. Knee OA-related outcomes in POP included: WOMAC pain, National Health and Nutrition Examination Survey (NHANES) I (pain, aching and stiffness), subchondral sclerosis, and radiographically determined tibiofemoral and patellofemoral OA. Two putative osteoclast biomarkers were measured in sera: TRAcP5b and cath-K. Medial tibia plateaux were donated at knee arthroplasty for symptomatic OA (n = 84) or from 16 post mortem (PM) controls from the Arthritis Research UK (ARUK) Pain Centre joint tissue repository. Osteoclasts were stained for tartrate resistant acid phosphatase (TRAcP) within the subchondral bone of the medial tibia plateaux.

RESULTS

Serum TRAcP5b activity, but not cath-K-immunoreactivity, was associated with density of TRAcP-positive osteoclasts in the subchondral bone of medial tibia plateaux. TRAcP-positive osteoclasts were more abundant in people with symptomatic OA compared to controls. Serum TRAcP5b activity was associated with baseline pain and pain change.

CONCLUSIONS

Our observations support a role for subchondral osteoclast activity in the generation of OA pain. Serum TRAcP5b might be a clinically relevant biomarker of disease activity in OA.

Reverse Microemulsion-Based Synthesis of (Bis)phosphonate-Metal Materials with Controllable Physical Properties: An Example Using Zoledronic Acid-Calcium Complexes

The development of phosphonate-metal materials is tightly related to the advancement in their synthesis methods. Herein, using zoledronic acid (Zol), a bisphosphonate (bioacitve phosphonate with a "P-C-P" structure), and calcium as model molecules, we applied the reverse microemulsion (RM) method to synthesize a series of Zol-Ca complexes. We comprehensively (i) studied the relationship between RM conditions, including the component ratio of RM, cosurfactants, reaction time, reactant concentration, reaction temperature, and the presence of a phospholipid, 1, 2-dioleoyl-sn-glycero-3-phosphate acid (DOPA), and the physical properties of the complexes synthesized (i.e., shape, size, uniformity, monodispersity, and hydrophilicity/hydrophobicity) and (ii) explored the underlying mechanisms. To evaluate the biomedical application potential of the Zol-Ca complexes synthesized, one type of hydrophobic, DOPA-coated spherical Zol-Ca complexes (denoted as Zol-Ca@DOPA) was formulated into a PEGylated lipid-based nanoparticle formulation (i.e., Zol-Ca@bilipid NPs, ∼24 nm in diameter). In a mouse model with orthotopic mammary tumors, the Zol-Ca@bilipid NPs significantly enhanced the distribution of Zol in tumors, as compared to free Zol. It is expected that the RM-based synthesis of (bis)phosphonate-metal materials with controllable physical properties will help expand their applications.

In vivo distribution of zoledronic acid in a bisphosphonate-metal complex-based nanoparticle formulation synthesized by a reverse microemulsion method

Bisphosphonates are used to treat bone diseases such as osteoporosis and cancer-induced bone pain and fractures. It is thought that modifying the pharmacokinetics and biodistribution profiles of bisphosphonates (i.e. rapid renal clearance and extensive bone absorption) will not only reduce their side effects, but also expand their clinical applications to extraskeletal tissues. In the present work, using zoledronic acid (Zol) and calcium as model bisphosphonate and metal molecules, respectively, we prepared DOPA (an anionic lipid)-coated spherical Zol-Ca nanocomposites (Zol-Ca@DOPA) and developed Zol-nanoparticle formulations (i.e. Zol-Ca@bi-lipid NPs) based on the nanocomposites. The influence of the inputted weight ratio of Zol-Ca@DOPA to DSPE-PEG_2k on the properties (e.g. size, size distribution, loading efficiency, encapsulation efficiency, zeta potential, and polydispersity) of Zol-Ca@bi-lipid NPs was investigated, and a type of Zol-Ca@bi-lipid NPs with size around 25nm was selected for further studies. In a mouse model, the Zol-Ca@bi-lipid NPs significantly reduced the bone distribution of Zol, increased the blood circulating time of Zol, and altered the distribution of Zol in major organs, as compared to free Zol. It is expected that similar nanoparticles prepared with bisphosphonate-metal complexes can be explored to expand the applications to bisphosphonates in extraskeletal tissues.

Bone-Seeking Matrix Metalloproteinase-2 Inhibitors Prevent Bone Metastatic Breast Cancer Growth

Bone metastasis is common during breast cancer progression. Matrix metalloproteinase-2 (MMP-2) is significantly associated with aggressive breast cancer and poorer overall survival. In bone, tumor- or host-derived MMP-2 contributes to breast cancer growth and does so by processing substrates, including type I collagen and TGFβ latency proteins. These data provide strong rationale for the application of MMP-2 inhibitors to treat the disease. However, in vivo, MMP-2 is systemically expressed. Therefore, to overcome potential toxicities noted with previous broad-spectrum MMP inhibitors (MMPIs), we used highly selective bisphosphonic-based MMP-2 inhibitors (BMMPIs) that allowed for specific bone targeting. In vitro, BMMPIs affected the viability of breast cancer cell lines and osteoclast precursors, but not osteoblasts. In vivo, we demonstrated using two bone metastatic models (PyMT-R221A and 4T1) that BMMPI treatment significantly reduced tumor growth and tumor-associated bone destruction. In addition, BMMPIs are superior in promoting tumor apoptosis compared with the standard-of-care bisphosphonate, zoledronate. We demonstrated MMP-2-selective inhibition in the bone microenvironment using specific and broad-spectrum MMP probes. Furthermore, compared with zoledronate, BMMPI-treated mice had significantly lower levels of TGFβ signaling and MMP-generated type I collagen carboxy-terminal fragments. Taken together, our data show the feasibility of selective inhibition of MMPs in the bone metastatic breast cancer microenvironment. We posit that BMMPIs could be easily translated to the clinical setting for the treatment of bone metastases given the well-tolerated nature of bisphosphonates. Mol Cancer Ther; 16(3); 494-505. ©2017 AACR.

Bone modeling and remodeling: potential as therapeutic targets for the treatment of osteoporosis

The adult skeleton is renewed by remodeling throughout life. Bone remodeling is a process where osteoclasts and osteoblasts work sequentially in the same bone remodeling unit. After the attainment of peak bone mass, bone remodeling is balanced and bone mass is stable for one or two decades until age-related bone loss begins. Age-related bone loss is caused by increases in resorptive activity and reduced bone formation. The relative importance of cortical remodeling increases with age as cancellous bone is lost and remodeling activity in both compartments increases. Bone modeling describes the process whereby bones are shaped or reshaped by the independent action of osteoblast and osteoclasts. The activities of osteoblasts and osteoclasts are not necessarily coupled anatomically or temporally. Bone modeling defines skeletal development and growth but continues throughout life. Modeling-based bone formation contributes to the periosteal expansion, just as remodeling-based resorption is responsible for the medullary expansion seen at the long bones with aging. Existing and upcoming treatments affect remodeling as well as modeling. Teriparatide stimulates bone formation, 70% of which is remodeling based and 20-30% is modeling based. The vast majority of modeling represents overflow from remodeling units rather than de novo modeling. Denosumab inhibits bone remodeling but is permissive for modeling at cortex. Odanacatib inhibits bone resorption by inhibiting cathepsin K activity, whereas modeling-based bone formation is stimulated at periosteal surfaces. Inhibition of sclerostin stimulates bone formation and histomorphometric analysis demonstrated that bone formation is predominantly modeling based. The bone-mass response to some osteoporosis treatments in humans certainly suggests that nonremodeling mechanisms contribute to this response and bone modeling may be such a mechanism. To date, this has only been demonstrated for teriparatide, however, it is clear that rediscovering a phenomenon that was first observed more half a century ago will have an important impact on our understanding of how new antifracture treatments work.

Doses effects of zoledronic acid on mineral apatite and collagen quality of newly-formed bone in the rat's calvaria defect

Due to their inhibitory effects on resorption, bisphosphonates are widely used in the treatment of diseases associated to an extensive bone loss. Yet, little is known about bisphosphonates effects on newly-formed bone quality. In the present study, adult male Sprague-Dawley rats (n=80) with a bone defect calvaria area were used and short-term effects of zoledronic acid (ZA) were studied on the healing bone area. Three ZA treatments were tested by using either: 1°) a low single dose (120μgZA/kg, n=10; equivalent to human osteoporosis treatment), 2°) a low fractionated doses (20μgZA/kg daily for 6days either a total of 120μg/kg, n=15), and 3°) a high fractionated doses, (100μgZA/kg weekly for 6weeks, n=15; equivalent to 6months of human bone metastasis treatment). For each treatment, a control "vehicle" treatment was performed (with an identical number of rats). After ZA administration, the intrinsic bone material properties were evaluated by quantitative backscattered electron imaging (qBEI) and Raman microspectroscopy. Neither single nor fractionated low ZA doses modify the intrinsic bone material properties of the newly-formed bone compared to their respective control animals. On the opposite, the high ZA treatment resulted in a significant decrease of the crystallinity (-25%, P< 0.05) and of the hydroxyproline-to-proline ratio (-30%, P<0.05) in newly-formed bones. Moreover, with the high ZA treatment, the crystallinity was positively correlated with the hydroxyproline-to-proline ratio (ρ=0.78, P<0.0001). The present data highlight new properties for ZA on bone formation in a craniofacial defect model. As such, ZA at high doses disrupted the apatite crystal organization. In addition, we report here for the first time that high ZA doses decreased the hydroxyproline-to-proline ratio suggesting that ZA may affect the early collagen organization during the bone healing.

Difference in Bone Mineral Density Change at the Lateral Femoral Cortices according to Administration of Different Bisphosphonate Agents

BACKGROUND

To retrospectively assess whether the response of subtrochanteric lateral cortex (STLC) is different according to the bisphosphonate agents in terms of bone mineral density (BMD) change.

METHODS

A total of 149 subjects, who had 2- to 4-year interval follow-up of BMD using dual energy X-ray absorptiometry (DXA), were included in this retrospective study divided into following 3 groups: control group (no consumption of any anti-osteoporotic drugs, n=38), alendronate group (naïve alendronate users, n=48), risedronate group (naïve risedronate users, n=63). BMD was measured at the STLC and subtrochanteric medial cortex (STMC) in each patient by drawing rectangular ROIs at the bone cortices. The percent change of BMD at the STLC were compared between the aforementioned 3 groups by using analysis of covariance model to control five independent variables of age, body mass index, percent change of STMC, hip axis length, time interval between DXA examinations.

RESULTS

The least square mean values±standard deviation of the percent change of BMD in the control, alendronate, and risedronate groups were 1.46±1.50, 2.23±1.26, and 6.96±1.11, respectively. The risedronate group showed significantly higher change of BMD percentage compared with the control (adjusted P=0.012) or alendronate (adjusted P=0.016) groups.

CONCLUSIONS

The percent change of BMD at the STLC in the risedronate user group was greater than the alendronate and control groups. The implication of these changes needs to be further verified.

Physiologic Activity of Bisphosphonates – Recent Advances

Background:

Bisphosphonates are drugs commonly used for the medication and prevention of diseases caused by decreased mineral density. Despite such important medicinal use, they display a variety of physiologic activities, which make them promising anti-cancer, anti-protozoal, antibacterial and antiviral agents.

Objective:

To review physiological activity of bisphosphonates with special emphasis on their ongoing and potential applications in medicine and agriculture.

Method:

Critical review of recent literature data.

Results:

Comprehensive review of activities revealed by bisphosphonates.

Conclusion:

although bisphosphonates are mostly recognized by their profound effects on bone physiology their medicinal potential has not been fully evaluated yet. Literature data considering enzyme inhibition suggest possibilities of far more wide application of these compounds. These applications are, however, limited by their low bioavailability and therefore intensive search for new chemical entities overcoming this shortage are carried out.

Targeted delivery to bone and mineral deposits using bisphosphonate ligands

The high concentration of mineral present in bone and pathological calcifications is unique compared with all other tissues and thus provides opportunity for targeted delivery of pharmaceutical drugs, including radiosensitizers and imaging probes. Targeted delivery enables accumulation of a high local dose of a therapeutic or imaging contrast agent to diseased bone or pathological calcifications. Bisphosphonates (BPs) are the most widely utilized bone-targeting ligand due to exhibiting high binding affinity to hydroxyapatite mineral. BPs can be conjugated to an agent that would otherwise have little or no affinity for the sites of interest. This article summarizes the current state of knowledge and practice for the use of BPs as ligands for targeted delivery to bone and mineral deposits. The clinical history of BPs is briefly summarized to emphasize the success of these molecules as therapeutics for metabolic bone diseases. Mechanisms of binding and the relative binding affinity of various BPs to bone mineral are introduced, including common methods for measuring binding affinity in vitro and in vivo. Current research is highlighted for the use of BP ligands for targeted delivery of BP conjugates in various applications, including (1) therapeutic drug delivery for metabolic bone diseases, bone cancer, other bone diseases, and engineered drug delivery platforms; (2) imaging probes for scintigraphy, fluorescence, positron emission tomography, magnetic resonance imaging, and computed tomography; and (3) radiotherapy. Last, and perhaps most importantly, key structure-function relationships are considered for the design of drugs with BP ligands, including the tether length between the BP and drug, the size of the drug, the number of BP ligands per drug, cleavable tethers between the BP and drug, and conjugation schemes.