Acquired resistance to bisphosphonates in Paget's disease of bone

Diagnosis and treatment of Paget's disease of bone: position paper from the Italian Society of Osteoporosis, Mineral Metabolism and Skeletal Diseases (SIOMMMS)

INTRODUCTION

Paget's disease of bone is a focal skeletal disorder causing bone deformities and impairing bone quality. Despite the prevalence of asymptomatic cases is increasing, the progression of the disease can lead to invalidating complications that compromise the quality of life. Doubts on clinical and therapeutic management aspects exist, although beneficial effects of antiresorptive drugs, particularly bisphosphonates are known. However, limited information is available from randomized controlled trials on the prevention of disease complications so that somewhat contrasting positions about treatment indications between expert panels from the main scientific societies of metabolic bone diseases exist. This task force, composed by expert representatives appointed by the Italian Society of Osteoporosis, Mineral Metabolism and Skeletal Diseases and members of the Italian Association of Paget's disease of bone, felt the necessity for more specific and up to date indications for an early diagnosis and clinical management.

METHODS

Through selected key questions, we propose evidence-based recommendations for the diagnosis and treatment of the disease. In the lack of good evidence to support clear recommendations, available information from the literature together with expert opinion of the panel was used to provide suggestions for the clinical practice.

RESULTS AND CONCLUSION

Description of the evidence quality and support of the strength of the statements was provided on each of the selected key questions. The diagnosis of PDB should be mainly based on symptoms and the typical biochemical and radiological features. While treatment is mandatory to all the symptomatic cases at diagnosis, less evidence is available on treatment indications in asymptomatic as well as in previously treated patients in the presence of biochemical recurrence. However, given the safety and long-term efficacy of potent intravenous bisphosphonates such as zoledronate, a suggestion to treat most if not all cases at the time of diagnosis was released.

Safety and effectiveness of risedronate in Paget's disease of bone: postmarketing surveillance study in Japan

INTRODUCTION

We conducted an all-case postmarketing surveillance study between 2008 and 2017 to evaluate the safety and effectiveness of risedronate for Paget's disease of bone (PDB) in Japan.

MATERIAL AND METHODS

This study registered all patients who received once-daily risedronate 17.5 mg for the treatment of PDB and collected data over a 48-week follow-up period per treatment cycle for each patient.

RESULTS

The safety analysis set included 184 patients (mean age, 63.7 years), 81 (44.0%) of whom previously received a bisphosphonate. Of them, 41 (22.3%) experienced 72 adverse drug reactions (ADRs), and 8 (4.3%) experienced 14 serious ADRs. Common ADRs included gastrointestinal disorders (20 patients, 10.9%) and hypocalcemia (6 patients, 3.3%). The effectiveness analysis set included 182 patients, 124 of whom completed only one treatment cycle and 58 of whom completed multiple treatment cycles. The proportions of patients who normalized serum alkaline phosphatase (ALP) concentration were 71.1% (113/159 patients) and 67.3% (33/49 patients) for the first and second treatment cycles, respectively. The relapse rate according to ALP levels after the end of treatment for the first cycle was 5.0% (95% confidence interval [CI] = 2.1-11.5) at 24 weeks and 12.9% (95% CI = 7.5-21.7) at 40 weeks. Regarding pain relief, the achievement rates were 70.0% (49/70 patients) and 30.8% (4/13 patients) for the first and second treatment cycles, respectively.

CONCLUSION

To conclude, risedronate 17.5 mg/day is safe and effective for treating patients with PDB in daily practice.

Genetic Determinants of Paget's Disease of Bone

PURPOSE OF REVIEW

To provide an overview of the role of genes and loci that predispose to Paget's disease of bone and related disorders.

RECENT FINDINGS

Studies over the past ten years have seen major advances in knowledge on the role of genetic factors in Paget's disease of bone (PDB). Genome wide association studies have identified six loci that predispose to the disease whereas family based studies have identified a further eight genes that cause PDB. This brings the total number of genes and loci implicated in PDB to fourteen. Emerging evidence has shown that a number of these genes also predispose to multisystem proteinopathy syndromes where PDB is accompanied by neurodegeneration and myopathy due to the accumulation of abnormal protein aggregates, emphasising the importance of defects in autophagy in the pathogenesis of PDB. Genetic factors play a key role in the pathogenesis of PDB and the studies in this area have identified several genes previously not suspected to play a role in bone metabolism. Genetic testing coupled to targeted therapeutic intervention is being explored as a way of halting disease progression and improving outcome before irreversible skeletal damage has occurred.

Pamidronate: A model compound of the pharmacology of nitrogen-containing bisphosphonates; A Leiden historical perspective

Pamidronate [3-amino-1-hydroxypropylidene-1,1-bisphosphonate (APD)] was the first nitrogen-containing bisphosphonate (N-BP) investigated in clinical studies. In contrast to other clinically used bisphosphonates, pamidronate was discovered and its properties were initially studied in an Academic Institution. On the occasion of the 50th Anniversary of the first publications on the biological effects of bisphosphonates, I review in this article the contribution of Leiden investigators to the development of pamidronate that led to the recognition of the significance of the Nitrogen atom in the side chain of bisphosphonates for their action on bone resorption and to the formulation of principles for the use of N-BPs in the management of patients with different skeletal disorders.

Paget's Disease of Bone

Paget's disease of bone (PDB) is a chronic and focal bone disorder, characterized by increased osteoclast-mediated bone resorption and a subsequent compensatory increase in bone formation, resulting in a disorganized mosaic of woven and lamellar bone at one or more affected skeletal sites. As a result, bone pain, noticeable deformities, arthritis at adjacent joints, and fractures can occur. In a small proportion of cases neoplastic degeneration in osteosarcoma, or, less frequently, giant cell tumor has been also described at PDB sites. While recent epidemiological evidences clearly indicate a decrease in the prevalence and the severity of PDB, over the past 2 decades there have been consistent advances on the genetic mechanisms of disease. It is now clear that PDB is a genetically heterogeneous disorder, with mutations in at least two different genes (SQSTM1, ZNF687) and more common predisposing variants. As a counterpart to the genetic hypothesis, the focal nature of lesions, the decline in prevalence rates, and the incomplete penetrance of the disease among family members suggest that one or more environmental triggers may play a role in the pathophysiology of PDB. The exact nature of these triggers and how they might interact with the genetic factors are less understood, but recent experimental data from mice models suggest the implication of paramixoviral infections. The clinical management of PDB has also evolved considerably, with the development of potent aminobisphosphonates such as zoledronic acid which, given as a single intravenous infusion, now allows a long-term disease remission in the majority of patients.

Acquired resistance to pamidronate treated effectively with zoledronate in juvenile Paget's disease

Juvenile Paget's disease (JPD) is a rare autosomal recessive osteopathy. There is still a question about the most effective treatment modality in long-term prognosis. A 9-month-old boy who suffered from bone pain and deformities with a very high alkaline phosphatase level was diagnosed as JPD by radiographic findings. Genetic analysis showed a homozygous large deletion in TNFRSF11B gene encoding osteoprotegerin. Clinical improvement was observed with intravenous pamidronate therapy. However, the effect of drug reduced in time so the annual dose per kilogram body weight was increased after 2 years. Despite this increment, bone fractures developed and bone pain recurred with high-ALP levels, which suggested resistance to pamidronate. Switching to zoledronate resulted a significant improvement in bone findings radiographically and ALP level. Severe hypocalcemia requiring intravenous calcium treatment complicated the first dose of zoledronate, but not recurred thereafter. Intravenous pamidronate therapy is effective in reducing bone pain, improving bone deformities and motor development in infantile onset JPD. However, this effect can be transient. Switching to another bisphosphonate like zoledronate may provide long-term clinical and biochemical improvement as an alternative treatment in case of resistance to pamidronate therapy.

New insights into human farnesyl pyrophosphate synthase inhibition by second-generation bisphosphonate drugs

Pamidronate, alendronate, APHBP and neridronate are a group of drugs, known as second-generation bisphosphonates (2G-BPs), commonly used in the treatment of bone-resorption disorders, and recently their use has been related to some collateral side effects. The therapeutic activity of 2G-BPs is related to the inhibition of the human Farnesyl Pyrophosphate Synthase (hFPPS). Available inhibitory activity values show that 2G-BPs act time-dependently, showing big differences in their initial inhibitory activities but similar final IC₅₀ values. However, there is a lack of information explaining this similar final inhibitory potency. Although different residues have been identified in the stabilization of the R₂ side chain of 2G-BPs into the active site, similar free binding energies were obtained that highlighted a similar stability of the ternary complexes, which in turns justified the similar IC₅₀ values reported. Free binding energy calculations also demonstrated that the union of 2G-BPs to the active site were 38 to 54 kcal mol^-1 energetically more favourable than the union of the natural substrate, which is the basis of the inhibition potency of the hFPPS activity.

Clinical efficacy of oral risedronate therapy in Japanese patients with Paget's disease of bone

Paget's disease of bone (PDB) is a chronic disorder characterized by localized bone regions with excessive bone turnover. Although oral risedronate (17.5 mg daily for 8 weeks) was recently approved in Japan, its efficacy is not well understood. We retrospectively examined the efficacy of oral risedronate in PDB patients in a clinical setting. Eleven patients whose serum alkaline phosphatase (ALP) level exceeded the upper limit of the normal range were treated. Patients whose ALP levels normalized and remained so for 12 months after therapy initiation were defined as responders. Treatment was repeated if bone pain recurred or if serum ALP levels increased at least 25% above the nadir. Six patients (55%) were responsive to the therapy. A higher prevalence of skull lesions, higher serum calcium levels at treatment initiation and antecedent treatments of bisphosphonates were predictors of resistance against the therapy. Fresh frozen serum samples obtained from some treatment sessions were evaluated for metabolic bone markers such as bone-specific ALP (BAP), type I procollagen N-terminal pro-peptide (PINP), N-treminal crosslinking telopeptide of type I collagen and C-treminal crosslinking telopeptide of type I collagen (CTX). A significant reduction of P1NP preceded that of serum ALP levels in the responders, which was followed by a similar occurrence for BAP and osteocalcin (BGP) levels. A temporary decrease in CTX levels was noted. No significant changes in markers (including ALP level) were observed in non-responder and repeat-treatment groups. P1NP levels may be more useful than ALP levels in assessing treatment efficacy. Repeat treatment effectiveness for the repeat-treatment group was limited.

ZOLEDRONIC ACID THERAPY OF PATIENTS WITH PAGET DISEASE OF BONE RESISTANT TO OR WITH UNSUSTAINED REMISSION FOLLOWING PRIOR BISPHOSPHONATE THERAPY

OBJECTIVE

To evaluate the effect of zoledronic acid (ZA) in patients with Paget disease (PD) who had not had a biochemical remission with prior bisphosphonate therapy or had a remission ≤12 months.

METHODS

The effects of ZA therapy were studied in 14 patients aged 54 to 90. Serum alkaline phosphatase (ALP) levels were elevated to at least 40% above the normal reference range, and glomerular filtration rates (GFRs) were ≥40 mL/minute. ZA (5 mg) was infused over 15 minutes. ALP and urine N-telopeptide/creatinine (NTx/Cr) were obtained before therapy and at 3, 6, 9, and 12 months, and thereafter at 4-month intervals.

RESULTS

At baseline, ALP ranged from 141 to 1,009 U/L. In 13 patients, ALP fell to normal following ZA administration. Remissions occurred in 9 patients who had not previously had a remission. Remissions varied from 12 to 60 months and were more prolonged in 4 patients with prior remissions ≤12 months. ZA failed to induce a remission in 1 patient. Ten to 12 days after therapy in 3 asymptomatic patients, serum calcium levels fell to 7.9, 8, and 8.3 mg/dL. Other than flu-like symptoms in 3 patients after ZA infusion, there were no other adverse effects.

CONCLUSION

Therapy with ZA induced remissions in 13/14 patients and induced more prolonged remissions in patients who previously had remissions ≤12 months. The lack of remission in 1 patient despite 2 courses of therapy is evidence of a continuing therapeutic challenge for some patients with a more resistant form of PD.

Current perspectives on bisphosphonate treatment in Paget's disease of bone

Paget's disease of bone is a chronic metabolic bone disease with focal increase in bone turnover. The exact etiology of the disease is uncertain, although genetic and environmental factors are believed to be important. Bisphosphonate is the main class of medication being used to control disease activity via its antiresorptive effect. This review discusses the controversies concerning the use of bisphosphonates in the treatment of Paget's disease of bone, the efficacy of different bisphosphonates in controlling disease activity, and the possible rare side effects of bisphosphonates. Symptoms are the main indication for treatment in Paget's disease of bone. As treatment benefits in asymptomatic individuals remain controversial and nonevidence based, the decision to treat these patients should be individualized to their risk and benefit profiles. There are several trials conducted to evaluate and compare the efficacy of different regimes of bisphosphonates for treating Paget's disease of bone. Most trials used biochemical markers rather than clinical symptoms or outcomes as parameters for comparison. Zoledronate is an attractive option as it can achieve high rates of biochemical remission and sustain long duration of suppression by a single dose. Atypical femoral fracture and osteonecrosis of the jaw are two rare and severe side effects reported, possibly related to the use of bisphosphonates in patients with osteoporosis and malignancy-induced hypercalcemia. As the regimes of bisphosphonates used for treating Paget's disease of bone are different from those two diseases, the risks of developing these two possible side effects are expected to be very low, although this remains unknown. Vitamin D and calcium supplement should be given to patients at risk of vitamin D insufficiency when given zoledronate, as symptomatic hypocalcemia may develop. For those intolerant of bisphosphonates, subcutaneous calcitonin can be used for a limited period due to its associated risk of malignancy.

Long-term treatment of osteoporotic women with bisphosphonates does not impair the response to subsequently administered intravenous pamidronate

We addressed the question whether the response of osteoporotic patients to bisphosphonate treatment is reduced with time. Bisphosphonate-treated women with postmenopausal or glucocorticoid-induced osteoporosis showed adequate and consistent changes of bone markers to subsequently administered intravenous pamidronate. Response of osteoporotic patients to bisphosphonates is not impaired during their long-term administration.

INTRODUCTION

Inadequate response to bisphosphonate treatment has been described in patients with Paget's disease of bone but has not been addressed in osteoporosis although treatment failure is a clinically relevant problem.

METHODS

Twenty one women with postmenopausal osteoporosis (PMO) aged 68 ± 8.2 years and 14 women with glucocorticoid-induced osteoporosis (GIOP) aged 65 ± 10 years were treated with tri-monthly intravenous infusions of 45 mg of pamidronate for 1 year. All patients had been previously treated with bisphosphonates (alendronate, risedronate, pamidronate) for a mean period of 6.2 years (range, 1.3-14 years). Blood samples were taken for measurement of the bone resorption marker C-terminal crosslinking telopeptide of type I collagen (CTX-I) on days 1 and 4 and of the bone formation marker procollagen type I N propeptide, (P1NP) on day 1 of every tri-monthly treatment course.

RESULTS

With each treatment course there was a significant decrease in serum CTX-I on day 4 and an increase to baseline values 3 months after each infusion in both PMO (mean values, day 1: 291.33 ± 160.78 pg/ml vs. day 4: 131 ± 91.7 pg/ml, p < 0.001) and GIOP (day 1: 219.3 ± 114.8 pg/ml vs. day 4: 98.8 ± 51.6 pg/ml, p < 0.001). Serum P1NP remained stable during the whole year of treatment.

CONCLUSIONS

Long-term bisphosphonate treatment of women with either PMO or GIOP does not impair the response to subsequently administered intravenous pamidronate suggesting that inadequate response to long-term bisphosphonate treatment is not responsible for treatment failure.

Paget's Disease of Bone: A Review of Epidemiology, Pathophysiology and Management

Paget's disease of bone is a common disorder which may affect one or many bones. Although many patients are asymptomatic, a variety of symptoms and complications may occur. Fortunately, effective pharmacologic therapy, primarily with potent bisphosphonates, is now available to treat patients with complications or symptoms. This review of Paget's disease of bone will include epidemiology and pathophysiology, complications and clinical findings, indications for treatment, and the drugs currently available to treat this condition.

Emerging strategies and therapies for treatment of Paget's disease of bone

Paget's disease of bone (PDB) is a progressive monostotic or polyostotic metabolic bone disease characterized by focal abnormal bone remodeling, with increased bone resorption and excessive, disorganized, new bone formation. PDB rarely occurs before middle age, and it is the second most frequent metabolic bone disorder after osteoporosis, affecting up to 3% of adults over 55 years of age. One of the most striking and intriguing clinical features is the focal nature of the disorder, in that once the disease is established within a bone, there is only local spread within that bone and no systemic dissemination. Despite many years of intense research, the etiology of PDB has still to be conclusively determined. Based on a detailed review of genetic and viral factors incriminated in PDB, we propose a unifying hypothesis from which we can suggest emerging strategies and therapies. PDB results in weakened bone strength and abnormal bone architecture, leading to pain, deformity or, depending on the bone involved, fracture in the affected bone. The diagnostic assessment includes serum total alkaline phosphatase, total body bone scintigraphy, skull and enlarged view pelvis x-rays, and if needed, additional x-rays. The ideal therapeutic option would eliminate bone pain, normalize serum total alkaline phosphatase with prolonged remission, heal radiographic osteolytic lesions, restore normal lamellar bone, and prevent recurrence and complications. With the development of increasingly potent bisphosphonates, culminating in the introduction of a single intravenous infusion of zoledronic acid 5 mg, these goals of treatment are close to being achieved, together with long-term remission in almost all patients. Based on the recent pathophysiological findings, emerging strategies and therapies are reviewed: ie, pulse treatment with zoledronic acid; denosumab, a fully human monoclonal antibody directed against RANK ligand; tocilizumab, an interleukin-6 receptor inhibitor; odanacatib, a cathepsin K inhibitor; and proteasome and Dickkopf-1 inhibitors.

Comparison of intravenous and intramuscular neridronate regimens for the treatment of Paget disease of bone

Aminobisphosphonates actually represent the most common treatment for Paget disease of bone (PDB). In a previous study we demonstrated that either zoledronic acid (4 mg) or neridronate (200 mg) given as a single intravenous infusion showed a similar short-term efficacy in achieving biochemical remission in up to 90% of patient nonresponders to pamidronate. In this study we compared the long-term (36 months) effects of a same neridronate dose (200 mg) given as an intravenous (100-mg infusion for 2 consecutive days) or intramuscular (25-mg injection weekly for 2 months) regimen in 56 patients with active PDB. All patients were advised to receive calcium plus vitamin D supplementation throughout the study period. At 6 months, 92.6% and 96.5% of patients receiving intravenous and intramuscular neridronate, respectively, achieved a therapeutic response [defined as normalization of alkaline phosphatase (ALP) levels or a reduction of at least 75% in total ALP excess]. The response to treatment was significantly correlated with baseline ALP and 25-hydroxyvitamin D [25(OH)D] levels at 6 months. The decrease in ALP levels was highest in patients with higher baseline total or bone-specific ALP levels and with higher 25(OH)D levels at 6 months. Response rates were maintained at 12 months but decreased progressively at 24 and 36 months without significant differences between the two neridronate regimens. Both regimens were well tolerated. The only relevant side effect was an acute-phase response occurring in 14% of the patients. In conclusion, these results indicate that a 200-mg intramuscular neridronate course has a similar efficacy as an intravenous infusion of the same dose for the treatment of PDB and might be of particular value for patients intolerant to oral bisphosphonates and unwilling or unable to undergo intravenous infusions.

Paget's disease of bone

Paget's disease of bone is a focal bone disorder that is common among older people of Western European descent. It is an unusual disorder, for although we now have safe and highly effective treatment, there are many aspects of its pathogenesis and natural history that we do not yet understand. Recent years have seen significant advances in the understanding of its epidemiology, genetics and molecular biology, but an integrated view that incorporates all these aspects remains elusive. In this review we examine some of the outstanding problems, the solutions to which seem likely to change our understanding of bone cell biology.

Identification of secondary targets of N-containing bisphosphonates in mammalian cells via parallel competition analysis of the barcoded yeast deletion collection

Growth competition assays using barcoded yeast deletion-mutants reveal the molecular targets of nitrogen containing bisphosphonates used for the treatment of bone cancers and osteoporosis.

Background

Nitrogen-containing bisphosphonates are the elected drugs for the treatment of diseases in which excessive bone resorption occurs, for example, osteoporosis and cancer-induced bone diseases. The only known target of nitrogen-containing bisphosphonates is farnesyl pyrophosphate synthase, which ensures prenylation of prosurvival proteins, such as Ras. However, it is likely that the action of nitrogen-containing bisphosphonates involves additional unknown mechanisms. To identify novel targets of nitrogen-containing bisphosphonates, we used a genome-wide high-throughput screening in which 5,936 Saccharomyces cerevisiae heterozygote barcoded mutants were grown competitively in the presence of sub-lethal doses of three nitrogen-containing bisphosphonates (risedronate, alendronate and ibandronate). Strains carrying deletions in genes encoding potential drug targets show a variation of the intensity of their corresponding barcodes on the hybridization array over the time.

Results

With this approach, we identified novel targets of nitrogen-containing bisphosphonates, such as tubulin cofactor B and ASK/DBF4 (Activator of S-phase kinase). The up-regulation of tubulin cofactor B may explain some previously unknown effects of nitrogen-containing bisphosphonates on microtubule dynamics and organization. As nitrogen-containing bisphosphonates induce extensive DNA damage, we also document the role of DBF4 as a key player in nitrogen-containing bisphosphonate-induced cytotoxicity, thus explaining the effects on the cell-cycle.

Conclusions

The dataset obtained from the yeast screen was validated in a mammalian system, allowing the discovery of new biological processes involved in the cellular response to nitrogen-containing bisphosphonates and opening up opportunities for development of new anticancer drugs.

Current options for the treatment of Paget's disease of the bone

Paget’s disease of bone (PDB) is a chronic bone remodelling disorder characterized by increased osteoclast-mediated bone resorption, with subsequent compensatory increases in new bone formation, resulting in a disorganized mosaic of woven and lamellar bone at affected skeletal sites. This disease is most often asymptomatic but can be associated with bone pain or deformity, fractures, secondary arthritis, neurological complications, deafness, contributing to substantial morbidity and reduced quality of life. Neoplastic degeneration of pagetic bone is a relatively rare event, occurring with an incidence of less than 1%, but has a grave prognosis. Specific therapy for PDB is aimed at decreasing the abnormal bone turnover and bisphosphonates are currently considered the treatment of choice. These treatments are associated with a reduction in plasma alkaline phosphatase (ALP) activity and an improvement in radiological and scintigraphic appearance and with a reduction in bone pain and bone deformity, Recently, the availability of newer, more potent nitrogen-containing bisphosphonates has improved treatment outcomes, allowing a more effective and convenient management of this debilitating disorder.

Vitamin D receptor gene polymorphisms predict acquired resistance to clodronate treatment in patients with Paget's disease of bone

Bisphosphonates are first-choice drugs for treatment of Paget's disease of bone (PDB); nevertheless, acquired resistance to bisphosphonate therapy has been described in PDB patients. The 1,25(OH)(2)D(3)/vitamin D receptor (VDR) system influences the effectiveness of antiresorptive treatments in metabolic bone disorders. This study evaluated the relationship between acquired resistance to clodronate treatment and BsmI, TaqI, and FokI VDR polymorphisms in Caucasian patients with polyostotic PDB (n = 84). We also evaluated the influence of mutations in exons 7 and 8 of the sequestosome 1 (SQSTM1) gene on the occurrence of this phenomenon. All patients were treated from diagnosis for several cycles with intravenous clodronate infusion (1500 mg/cycle). Acquired resistance to clodronate treatment was defined as the failure of total alkaline phosphatase serum levels to be suppressed to at least 50% of the patient's previous highest levels during a subsequent treatment course with the same compound, which produced a >50% response after the first exposure. During an observation period of 10.6 +/- 2.7 years, 31 PDB patients (36.9%) showed acquired resistance to clodronate. It was observed that the bb and TT VDR genotypes as well as a lower persistence of the biochemical response to the first treatment course were significantly and independently associated with the risk of developing resistance to clodronate treatment. SQSTM1 gene mutations, considered altogether, did not influence the occurrence of this phenomenon. Our results indicate that 3'VDR allelic variants and duration of biochemical response to the first treatment course are independent predictors of acquired resistance to clodronate treatment in patients with polyostotic PDB.

Farnesyl diphosphate synthase is involved in the resistance to zoledronic acid of osteosarcoma cells

We recently demonstrated original anti-tumor effects of zoledronic acid (Zol) on osteosarcoma cell lines independently of their p53 and Rb status. The present study investigated the potential Zol-resistance acquired by osteosarcoma cells after prolonged treatment. After 12 weeks of culture in the presence of 1 μm Zol, the effects of high doses of Zol (10–100 μm) were compared between the untreated rat (OSRGA, ROS) and human (MG63, SAOS2) osteosarcoma cells and Zol-pretreated cells in terms of cell proliferation, cell cycle analysis, migration assay and cytoskeleton organization. Long-term treatment with 1 μm Zol reduced the sensitivity of osteosarcoma cells to high concentrations of Zol. Furthermore, the Zol-resistant cells were sensitive to conventional anti-cancer agents demonstrating that this resistance process is independent of the multidrug resistance phenotype. However, as similar experiments performed in the presence of clodronate and pamidronate evidenced that this drug resistance was restricted to the nitrogen-containing bisphosphonates, we then hypothesized that this resistance could be associated with a differential expression of farnesyl diphos-phate synthase (FPPS) also observed in human osteosarcoma samples. The transfection of Zol-resistant cells with FPPS siRNA strongly increased their sensitivity to Zol. This study demonstrates for the first time the induction of metabolic resistance after prolonged Zol treatment of osteosarcoma cells confirming the therapeutic potential of Zol for the treatment of bone malignant pathologies, but points out the importance of the treatment regimen may be important in terms of duration and dose to avoid the development of drug metabolic resistance.

Scintigraphic, biochemical, and clinical response to zoledronic acid treatment in patients with Paget's disease of bone

Bisphosphonates have long been used with success in the treatment of Paget's disease of bone (PDB). The aim of this study was to evaluate the early (up to 3 months) and late (at 12 months) scintigraphic, biochemical, and clinical response to a single intravenous infusion of zoledronic acid (ZOL) in patients with PDB serially assessed for 1 year. Nine patients with 30 bone lesions caused by PDB were prospectively evaluated. Total serum alkaline phosphatase (SAP) was serially measured. Scintigraphy was performed before and at 3 and 12 months after ZOL administration, and bone lesions were assessed quantitatively. After treatment, pain was alleviated in five of six patients starting from the first month. At 3 months, a significant decrease of SAP levels compared to baseline values was found (322 +/- 211 IU/l before vs. 101 +/- 36 IU/l 3 months after; P < 0.05), with normal values attained in all except one patient. The scintigraphic index of involvement (SII), a marker for the per-patient activity of the disease, was reduced from 14.4 +/- 7.6 to 7.2 +/- 1.8 (P = 0.01). The scintigraphic ratio (SR), a marker for the per-lesion activity of the disease, was reduced from 12.8 +/- 7.7 to 7.0 +/- 2.9 (P < 0.001). The values of markers of disease activity remained unchanged up to 12 months. A single intravenous administration of ZOL leads to a favorable clinical, biochemical, and scintigraphic response in patients with PDB starting as early as 3 months after treatment and lasting no less than 12 months (i.e., considerably longer than the other existing therapies).

Comparison of different intravenous bisphosphonate regimens for Paget's disease of bone

This randomized study compared different intravenous bisphosphonates in PDB. Zoledronate was superior with respect to pamidronate in achieving biochemical remission, with therapeutic response maintained in most patients at 15 mo. Single neridronate and zoledronate infusion showed a similar efficacy in up to 90% of patients nonresponders to pamidronate.

INTRODUCTION

Intravenous bisphosphonates represent a common therapy for Paget's disease of bone (PDB). However, there have been few head to head randomized trials comparing intravenous bisphosphonates.

MATERIALS AND METHODS

We performed a 15-mo, randomized study comparing different intravenous bisphosphonates in 90 subjects with active PDB. At baseline, patients were randomly assigned to receive pamidronate (30 mg, i.v., for 2 consecutive days every 3 mo; n = 60) or zoledronate (4 mg, i.v.; n = 30). After 6 mo, nonresponders to pamidronate were crossed over to zoledronate or neridronate (100 mg, i.v., for 2 consecutive days). The primary efficacy endpoint was therapeutic response at 6 mo, defined as normalization of alkaline phosphatase (ALP) or a reduction of at least 75% in total ALP excess.

RESULTS

At 6 mo, 97% of patients receiving zoledronate had a therapeutic response compared with 45% of patients receiving pamidronate. Normalization of ALP was achieved in 93% of patients in the zoledronate group and in 35% of patients in the pamidronate group. ALP normalization was maintained in 79% and 65% of zoledronate-treated patients after 12 and 15 mo, respectively; loss of therapeutic response was observed in 2 of 30 (6%) at 12 and 15 mo. At 6 mo, 27 patients showing therapeutic response to pamidronate continued the treatment, whereas nonresponders were crossed-over to neridronate (n = 15) or zoledronate (n = 18). Among these subjects, 14 of 15 (93%) in the neridronate group and 17 of 18 (94%) in the zoledronate group achieved a therapeutic response. Similar normalization rates were observed between neridronate- (80%) and zoledronate- (83%) treated subjects. Normalization and therapeutic response were maintained at 9 mo from treatment (corresponding to 15 mo from the baseline visit) in either neridronate or zoledronate groups.

CONCLUSIONS

Single neridronate and zoledronate infusion showed a similar efficacy in achieving biochemical remission in up to 90% of patients nonresponders to pamidronate. Therapeutic response to zoledronate seems to be maintained in most patients at 15 mo.