Induction of cell death of human osteogenic sarcoma cells by zoledronic acid resembles anoikis

A Mathematical Model of In Vitro Cellular Uptake of Zoledronic Acid and Isopentenyl Pyrophosphate Accumulation

The mevalonate pathway is an attractive target for many areas of research, such as autoimmune disorders, atherosclerosis, Alzheimer’s disease and cancer. Indeed, manipulating this pathway results in the alteration of malignant cell growth with promising therapeutic potential. There are several pharmacological options to block the mevalonate pathway in cancer cells, one of which is zoledronic acid (ZA) (an N-bisphosphonate (N-BP)), which inhibits the farnesyl pyrophosphate (FPP) synthase enzyme, inducing cell cycle arrest, apoptosis, inhibition of protein prenylation, and cholesterol reduction, as well as leading to the accumulation of isopentenyl pyrophosphate (IPP). We extrapolated the data based on two independently published papers that provide numerical data on the uptake of zoledronic acid (ZA) and the accumulation of IPP (Ag) and its isomer over time by using in vitro human cell line models. Two different mathematical models for IPP kinetics are proposed. The first model (Model 1) is a simpler ordinary differential equation (ODE) compartmental system composed of 3 equations with 10 parameters; the second model (Model 2) is a differential algebraic equation (DAE) system with 4 differential equations, 1 algebraic equation and 13 parameters incorporating the formation of the ZA+enzyme+Ag complex. Each of the two models aims to describe two different experimental situations (continuous and pulse experiments) with the same ZA kinetics. Both models fit the collected data very well. With Model 1, we obtained a prevision accumulation of IPP after 24 h of 169.6 pmol/mgprot/h with an IPP decreasing rate per (pmol/mgprot) of ZA (kXGZ) equal to 13.24/h. With Model 2, we have comprehensive kinetics of IPP upon ZA treatment. We calculate that the IPP concentration was equal to 141.6 pmol/mgprot/h with a decreasing rate/percentage of 0.051 (kXGU). The present study is the first to quantify the influence of ZA on the pharmacodynamics of IPP. While still incorporating a small number of parameters, Model 2 better represents the complexity of the biological behaviour for calculating the IPP produced in different situations, such as studies on γδ T cell-based immunotherapy. In the future, additional clinical studies are warranted to further evaluate and fine-tune dosing approaches.

Synthesis and Evaluation of Structurally Diverse C-2-Substituted Thienopyrimidine-Based Inhibitors of the Human Geranylgeranyl Pyrophosphate Synthase

Novel analogues of C-2-substituted thienopyrimidine-based bisphosphonates (C2-ThP-BPs) are described that are potent inhibitors of the human geranylgeranyl pyrophosphate synthase (hGGPPS). Members of this class of compounds induce target-selective apoptosis of multiple myeloma (MM) cells and exhibit antimyeloma activity in vivo. A key structural element of these inhibitors is a linker moiety that connects their (((2-phenylthieno[2,3-d]pyrimidin-4-yl)amino)methylene)bisphosphonic acid core to various side chains. The structural diversity of this linker moiety, as well as the side chains attached to it, was investigated and found to significantly impact the toxicity of these compounds in MM cells. The most potent inhibitor identified was evaluated in mouse and rat for liver toxicity and systemic exposure, respectively, providing further optimism for the potential value of such compounds as human therapeutics.

Chondroblastic Osteosarcoma of the Mandible in a Patient on Risedronate: A Rare Case of Neoadjuvant Chemotherapy Failure

Osteosarcoma of the jaw only represents 0.5-1% of tumors of the facial mass. Due to its rarity, clinical diagnosis is thus difficult. The guidelines for this pathology remain unclear, and the need for neoadjuvant chemotherapy is still debated. This case report aims to describe a rare case of chondroblastic osteosarcoma in a 50-year-old woman on risedronate treated by neoadjuvant chemotherapy. The tumor extended from the mandibular left first premolar to the mandibular right canine. An excisional biopsy was performed, leading to a diagnosis of chondroblastic osteosarcoma. Neoadjuvant chemotherapy was ineffective, as it did not result in the shrinkage of the tumor. A pelvi-mandibulectomy with fibula free flap reconstruction of the mandible was subsequently successfully performed followed by radiotherapy.

Bisphosphonates in common pediatric and adult bone sarcomas

The therapeutic strategies proposed currently for bone sarcomas are based on neo-adjuvant chemotherapy, delayed en-bloc wide resection, and adjuvant chemotherapy. Unfortunately, bone sarcomas are characterized by high rates of poor drug response, with a high risk of drug resistance, local recurrence and/or a high propensity for induced metastases. The pathogenesis of bone sarcomas is strongly associated with dysregulation of local bone remodeling and increased osteolysis that plays a part in tumor development. In this context, bisphosphonates (BPs) have been proposed as a single agent or in combination with conventional drugs to block bone resorption and the vicious cycle established between bone and sarcoma cells. Pre-clinical in vitro studies revealed the potential "anti-tumor" activities of nitrogen-bisphosphonates (N-BPs). In pre-clinical models, N-BPs reduced significantly primary tumor growth in osteosarcoma and Ewing sarcoma, and the installation of lung metastases. In chondrosarcoma, N-BPs reduced the recurrence of local tumors after intralesional curettage, and increased overall survival. In pediatric and adult osteosarcoma patients, N-BPs have been assessed in combination with conventional chemotherapy and surgery in randomized phase 3 studies with no improvement in clinical outcome. The lack of benefit may potentially be explained by the biological impact of N-BPs on macrophage differentiation/recruitment which may alter CD8⁺-T lymphocyte infiltration. Thanks to their considerable affinity for the mineralized extracellular matrix, BPs are an excellent platform for drug delivery in malignant bone sites with reduced systemic toxicity, which opens up new opportunities for their future use.

New insights into molecular and cellular mechanisms of zoledronate in human osteosarcoma

Osteosarcoma is the most common primary malignant tumor of the skeleton in teenagers and young adults and continues to confer a generally poor prognosis in patients who do not respond to chemotherapy or who present with metastatic diseases at diagnosis. The nitrogen-containing zoledronate, the third generation bisphosphonate (BP), effectively inhibits osteoclastic bone resorption and is widely utilized in the treatment of metabolic and metastatic bone diseases nowadays. Owing to an acceptable safety profile and tolerability, zoledronate is the only BP currently approved for the prevention and treatment of skeletal relevant events in patients with metastatic bone lesions, especially bone metastases from advanced renal cell carcinoma and prostate cancer, and breast cancer, due to all solid malignancy. Moreover, zoledronate possesses diverse anti-osteosarcoma properties and may have potential to become an adjunctive treatment for high-grade osteosarcoma to enhance survival rates and to obliterate complications of the chemotherapy. Herein we highlighted the pharmacology of BPs and its underlying molecular mechanisms in osteoclasts and various cancer cells. We further provided the available literature on in vitro studies to illustrate the new insights into the intracellular molecular mechanisms of zoledronate in human osteosarcoma cell lines and in vivo animal models that led to the development and regulatory approval of zoledronate in patients with human osteosarcoma. This review also addresses clinical trials to focus on the efficacy of zoledronate on human osteosarcoma.

Minimally effective concentration of zoledronic acid to suppress osteoclasts in vitro

Zoledronic acid is regarded as the most potent bisphosphonate and is widely used in patients with osteoporosis; however, its side effects, including acute-phase reactions, gastrointestinal complaints, renal dysfunction and bisphosphonate-associated osteonecrosis impair the safety and quality of life of patients. The present study was designed to determine the minimal effective concentration of zoledronic acid through testing the dose-dependent effects of zoledronic acid on osteoclast suppression. A primary culture of bone marrow mononuclear cells obtained from C57 mice (age, 6 weeks) was established and induced to form osteoclasts. The number of multinuclear cells was determined by tartrate-resistant acid phosphatase staining and compared among cultured marrow cells treated with different concentrations of zoledronic acid. Furthermore, the cellular properties, including adhesion, migration and bone resorption, were compared at the minimal effective concentration. At a concentration of 1×10⁻⁶ mol/l, zoledronic acid significantly inhibited the formation of osteoclasts. This inhibitory effect was further enhanced at the concentration of 1×10⁻⁵ mol/l. However, the inhibitory effect of zoledronic acid tapered at the concentration of 1×10⁻⁴ mol/l and there was no further dose-dependent increase. In addition, the concentration of 1×10⁻⁶ mol/l was sufficient to alter cellular functions, including cell adhesion, migration and bone resorption. In conclusion, zoledronic acid was effective in reducing osteoclast formation and suppressing cellular functions. The minimal effective concentration of zoledronic acid in vitro was 1 µmol/l. Based on these results, a comparable dosage should be explored in clinical applications.

Zoledronic Acid Regulates Autophagy and Induces Apoptosis in Colon Cancer Cell Line CT26

Zoledronic acid (ZOL) is the third generation of bisphosphonates, which can inhibit many tumors growth, especially to inhibit the growth of colon cancer. However, the molecular mechanism is still very mysterious. In this study, we observed that ZOL could regulate CT26 colon cancer cells autophagy, promote CT26 cells apoptosis, and inhibit CT26 cells proliferation. Western blotting analysis showed that proapoptosis protein caspase-3 was basically unchanged, whereas the expression of the activated caspase-3 was significantly increased, after CT26 cells were treated with different doses of zoledronic acid. Western blot also showed that ZOL could significantly affect the expression of p-p53 and autophagy-related proteins beclin-1 and p62. In conclusion, the antitumor effect of ZOL on CT26 colon cancer cells in vitro is achieved by apoptosis induction and autophagy regulation, resulting in inhibition of cell proliferation.

Comparative review of human and canine osteosarcoma: morphology, epidemiology, prognosis, treatment and genetics

Osteosarcoma (OSA) is a rare cancer in people. However OSA incidence rates in dogs are 27 times higher than in people. Prognosis in both species is relatively poor, with 5 year OSA survival rates in people not having improved in decades. For dogs, 1 year survival rates are only around ~ 45%. Improved and novel treatment regimens are urgently required to improve survival in both humans and dogs with OSA. Utilising information from genetic studies could assist in this in both species, with the higher incidence rates in dogs contributing to the dog population being a good model of human disease. This review compares the clinical characteristics, gross morphology and histopathology, aetiology, epidemiology, and genetics of canine and human OSA. Finally, the current position of canine OSA genetic research is discussed and areas for additional work within the canine population are identified.

Role of zoledronic acid in oncolytic virotherapy: Promotion of antitumor effect and prevention of bone destruction

Osteosarcoma is an aggressive malignant bone tumor that causes bone destruction. Although tumor‐specific replicating oncolytic adenovirus OBP‐301 induces an antitumor effect in an osteosarcoma tumor, it cannot prevent bone destruction. Zoledronic acid (ZOL) is a clinically available agent that inhibits bone destruction. In this study, we investigated the potential of combination therapy with OBP‐301 and ZOL against osteosarcomas with bone destruction. The antitumor activity of OBP‐301 and ZOL in monotherapy or combination therapy was assessed using three human osteosarcoma cell lines (143B, MNNG/HOS, SaOS‐2). The cytotoxic effect of OBP‐301 and/or ZOL was measured by assay of cell apoptosis. The effect of OBP‐301 and ZOL on osteoclast activation was investigated. The potential of combination therapy against tumor growth and bone destruction was analyzed using an orthotopic 143B osteosarcoma xenograft tumor model. OBP‐301 and ZOL decreased the viability of human osteosarcoma cells. Combination therapy with OBP‐301 and ZOL displayed a synergistic antitumor effect, in which OBP‐301 promoted apoptosis through suppression of anti‐apoptotic myeloid cell leukemia 1 (MCL1). Combination therapy significantly inhibited tumor‐mediated osteoclast activation, tumor growth and bone destruction compared to monotherapy. These results suggest that combination therapy of OBP‐301 and ZOL suppresses osteosarcoma progression via suppression of MCL1 and osteoclast activation.

Clusterin inhibition using OGX-011 synergistically enhances zoledronic acid activity in osteosarcoma

Purpose

Despite recent improvements in therapeutic management of osteosarcoma, ongoing challenges in improving the response to chemotherapy warrants new strategies still needed to improve overall patient survival. Among new therapeutic approaches, zoledronic acid (ZOL) represents a promising adjuvant molecule to chemotherapy to limit the osteolytic component of bone tumors. However, ZOL triggers the elevation of heat shock proteins (Hsp), including Hsp27 and clusterin (CLU), which could enhance tumor cell survival and treatment resistance. We hypothesized that targeting CLU using siRNA or the antisense drug, OGX-011, will suppress treatment-induced CLU induction and enhance ZOL-induced cell death in osteosarcoma (OS) cells.

Methods

The combined effects of OGX-011 and ZOL were investigated in vitro on cell growth, viability, apoptosis and cell cycle repartition of ZOL-sensitive or -resistant human OS cell lines (SaOS2, U2OS, MG63 and MNNG/HOS).

Results

In OS cell lines, ZOL increased levels of HSPs, especially CLU, in a dose- and time-dependent manner by mechanism including increased HSF1 transcription activity. The OS resistant cells to ZOL exhibited higher CLU expression level than the sensitive cells. Moreover, CLU overexpression protects OS sensitive cells to ZOL-induced cell death by modulating the MDR1 and farnesyl diphosphate synthase expression. OGX-011 suppressed treatment-induced increases in CLU and synergistically enhanced the activity of ZOL on cell growth and apoptosis. These biologic events were accompanied by decreased expression of HSPs, MDR1 and HSF1 transcriptional activity. In vivo, OGX-011, administered 3 times a week (IP, 20mg/kg), potentiated the effect of ZOL (s.c; 50μg/kg), significantly inhibiting tumor growth by 50% and prolonging survival in MNNG/HOS xenograft model compared to ZOL alone.

Conclusion

These results indicate that ZOL-mediated induction of CLU can be attenuated by OGX-011, with synergistic effects on delaying progression of osteosarcoma.

The combined use of Camellia sinensis and metronomic zoledronate in 4T1 mouse carcinoma against tumor growth and metastasis

In previous studies, we demonstrated that the green tea Camellia sinensis (CS) water extract had potent antitumor and antimetastatic effects on 4T1 breast cancer. The metronomic regimen (0.0125 mg/kg twice a week for 4 weeks) of zoledronate (ZOL) was found to be effective in decreasing tumor burden and metastasis as compared with conventional regimen. The aim of the present study was to investigate the antitumor, antimetastatic and anti-osteolytic effects of the combined use of CS water extract and metronomic ZOL against 4T1 breast carcinoma in vitro and in vivo. The results demonstrated that the combination of CS+ZOL exerted a more potent effect on lung and liver by decreasing tumor burden and metastasis, when compared to CS or metronomic ZOL as monotherapies. The combination of CS+ZOL demonstrated optimal bone protection against breast cancer-induced osteolysis for the three groups of CS, ZOL and CS+ZOL. The in vitro results further demonstrated that ZOL enhanced CS-induced apoptosis in 4T1 cells as assessed by the Annexin V-FITC/PI staining and caspase-3 activity assays. In addition, the combined use of CS+ZOL significantly inhibited 4T1 cell migration. Mechanistic studies showed that the enzyme levels of matrix metalloproteinases (MMP)-2 and MMP-9 were suppressed significantly by CS+ZOL. In conclusion, to the best of our knowledge, this is the first study to investigate the novel combined application of herbal extract CS and chemotherapy ZOL in 4T1 breast cancer. The combination of CS plus metronomic ZOL demonstrated significant antitumor, antimetastatic and anti-osteolytic effects against breast cancer, and suggested potential clinical application for breast cancer patients.

The importance of being dead: cell death mechanisms assessment in anti-sarcoma therapy

Cell death can occur through different mechanisms, defined by their nature and physiological implications. Correct assessment of cell death is crucial for cancer therapy success. Sarcomas are a large and diverse group of neoplasias from mesenchymal origin. Among cell death types, apoptosis is by far the most studied in sarcomas. Albeit very promising in other fields, regulated necrosis and other cell death circumstances (as so-called "autophagic cell death" or "mitotic catastrophe") have not been yet properly addressed in sarcomas. Cell death is usually quantified in sarcomas by unspecific assays and in most cases the precise sequence of events remains poorly characterized. In this review, our main objective is to put into context the most recent sarcoma cell death findings in the more general landscape of different cell death modalities.

The combined use of Camellia sinensis and metronomic zoledronic acid in a breast cancer-induced osteolysis mouse model

PURPOSE

In previous studies, we demonstrated that green tea (Camellia sinensis, CS) water extract had potent anti-tumor and anti-metastasis effects in the 4T1 mouse breast cancer xenograft model, and the metronomic regimen (0.0125 mg/kg twice a week for 4 weeks) of zoledronic acid (ZOL) was also effective in decreasing tumor burden and metastasis when compared with the conventional regimen. This study aimed to investigate the combined use of CS water extract and metronomic ZOL against tumor metastasis and bone destruction in MDA-MB-231-TXSA human breast cancer.

METHODS

Female nude mice were injected with MDA-MB-231-TXSA cells into the marrow space of tibia and were treated with CS water extract and/or metronomic ZOL for 4 weeks. Tumor growth and metastasis to lungs and livers were assessed by in vivo bioluminescence imaging. Abilities of migration and invasion of MDA-MB-231-TXSA cells were also evaluated in vitro.

RESULTS

Our results demonstrated that combination of CS and ZOL had the most potent effects on tumor burden and metastasis to bone, lung and liver, while treatment with CS or ZOL alone significantly protected the bone from cancer-induced osteolysis. In vitro, the combined use of CS + ZOL significantly inhibited MDA-MB-231-TXSA cell migration and invasion. Mechanistic zymography studies showed that the enzyme activities of MMP-9 and MMP-2 were significantly suppressed by CS and CS + ZOL.

CONCLUSIONS

The combination of CS plus metronomic ZOL demonstrated potent anti-tumor, anti-metastasis and anti-osteolysis effects against breast cancer, suggesting the potential clinical application against breast cancer patients.

Pharmacological management of osteogenesis

Osteogenesis and bone remodeling are complex biological processes that are essential for the formation of new bone tissue and its correct functioning. When the balance between bone resorption and formation is disrupted, bone diseases and disorders such as Paget's disease, fibrous dysplasia, osteoporosis and fragility fractures may result. Recent advances in bone cell biology have revealed new specific targets for the treatment of bone loss that are based on the inhibition of bone resorption by osteoclasts or the stimulation of bone formation by osteoblasts. Bisphosphonates, antiresorptive agents that reduce bone resorption, are usually recommended as first-line therapy in women with postmenopausal osteoporosis. Numerous studies have shown that bisphosphonates are able to significantly reduce the risk of femoral and vertebral fractures. Other antiresorptive agents indicated for the treatment of osteoporosis include selective estrogen receptor modulators, such as raloxifene. Denosumab, a human monoclonal antibody, is another antiresorptive agent that has been approved in Europe and the USA. This agent blocks the RANK/RANKL/OPG system, which is responsible for osteoclastic activation, thus reducing bone resorption. Other approved agents include bone anabolic agents, such as teriparatide, a recombinant parathyroid hormone that improves bone microarchitecture and strength, and strontium ranelate, considered to be a dual-action drug that acts by both osteoclastic inhibition and osteoblastic stimulation. Currently, anti-catabolic drugs that act through the Wnt-β catenin signaling pathway, serving as Dickkopf-related protein 1 inhibitors and sclerostin antagonists, are also in development. This concise review provides an overview of the drugs most commonly used for the control of osteogenesis in bone diseases.

Recent advances in the management of osteosarcoma and forthcoming therapeutic strategies

Osteosarcoma is the most frequent primary bone tumor and occurs mainly in young patients (average age: 18 years). No evolution of the survival rates has been recorded for two decades in response to current treatment, associating often toxic and badly tolerated cures of chemotherapy (given a significant rate of bad responders) with preserving surgery. Among the proposed innovative strategies, immune-based therapy, antiangiogenesis agents, tumor-suppressor or suicide gene therapy, or anticancer drugs not commonly used in osteosarcoma are presented. A further strategy is to target the tumor microenvironment rather than the tumor itself.

Anti-tumor and anti-osteolysis effects of the metronomic use of zoledronic acid in primary and metastatic breast cancer mouse models

This study aims to determine the effect of metronomic (0.0125 mg/kg twice a week for 4 weeks) zoledronic acid (ZOL) on cancer propagation and osteolysis against both metastatic and primary breast cancer in mice model. From our results, metronomic ZOL resulted in a significant reduction of tumor burden and did not promote lung or liver metastasis. The metronomic ZOL appeared to be more effective than the conventional regimen (0.1 mg/kg once in 4 weeks) in reducing breast cancer tumor burden, and regulating its movement to lung and liver. This dosing schedule of ZOL showed great potential against metastatic breast cancer.

In vitro and in vivo responses to high and low doses of nitrogen-containing bisphosphonates suggest engagement of different mechanisms for inhibition of osteoclastic bone resorption

The effects of nitrogen-containing bisphosphonates (N-BPs) on osteoclasts (Ocs) may differ with dose and regimen. N-BPs reduce Oc bone resorption by inhibiting the enzyme farnesyl diphosphate synthase (FPPS), an effect counteracted by geranylgeraniol (GGOH), which restores geranylgeranylation downstream of FPPS. We assessed GGOH effects on inhibition of bone resorption by the N-BPs alendronate (ALN), ibandronate (IBN), and zoledronate (ZOL) in an assay of rabbit Oc resorption of bovine cortical bone. GGOH blocked inhibition of resorption at low, but not high, N-BP concentrations, with a 14- to 20-fold increase in IC50 values for each N-BP. In vivo, growing male rats were administered doses calculated to mimic bioavailable exposures in daily (ALN, IBN), weekly (ALN), monthly (IBN), and yearly (ZOL) clinical regimens. Tibiae were harvested at 48 h, and metaphyses were analyzed. With lower ALN and IBN doses, Oc numbers rose by 26-48 %, morphology was normal, and there was no increase in apoptotic Ocs. In contrast, with higher IBN and ZOL doses, bone-associated Ocs were generally rounded in appearance and numbers of nuclei/Oc versus vehicle increased 42 and 31 %, respectively (P < 0.05). With ZOL, there was no rise in Oc number, but there was a 6.5-fold increase in apoptotic Ocs versus vehicle and a ≥13.5-fold increase versus lower-dose ALN or IBN (P < 0.05). With higher-dose IBN there was no rise in Oc number but 7- and 14-fold increases in Oc apoptosis versus low-dose ALN and IBN (P < 0.02). These results suggest that different mechanisms may come into play across the dosing spectrum of N-BPs.

Feasibility and dose discovery analysis of zoledronic acid with concurrent chemotherapy in the treatment of newly diagnosed metastatic osteosarcoma: a report from the Children's Oncology Group

AIM

Patients with metastatic osteosarcoma (OS) have a poor outcome with conventional therapies. Zoledronic acid (ZA) is a third-generation bisphosphonate that reduces skeletal-related events in many adult cancers, and pre-clinical data suggest a possible benefit in OS. This study assessed the maximum tolerated dose (MTD) and the feasibility of ZA when combined with chemotherapy in patients with metastatic OS.

PATIENTS AND METHODS

Patients with a histological diagnosis of OS were eligible if they were <40 years of age, had initially metastatic disease and met organ function requirements. Treatment combined surgery and a conventional chemotherapy regimen. ZA was given concurrent with chemotherapy for a total of eight doses over 36 weeks. Three dose levels of ZA were tested: 1.2 mg/m(2) [max 2 mg], 2.3 mg/m(2) [max 4 mg] and 3.5 mg/m(2) [max 6 mg]. The MTD was determined during induction. Six patients were to be treated at each dose level, with an additional six patients treated with the MTD to help assess post-induction feasibility.

RESULTS

Twenty-four patients (median age 13.5 years [range, 7-22]; 16 females) were treated. Five patients experienced dose-limiting toxicities (DLTs) during induction, including three patients treated with 3.5 mg/m(2). DLTs included hypophosphatemia, hypokalemia, hyponatremia, mucositis, limb pain and limb oedema. There were no reports of excessive renal toxicity or osteonecrosis of the jaw. The MTD was defined as 2.3 mg/m(2) (max 4 mg).

CONCLUSIONS

ZA can be safely combined with conventional chemotherapy with an MTD of 2.3 mg/m(2) (max 4 mg) for patients with metastatic osteosarcoma.

The Current and Future Therapies for Human Osteosarcoma

Osteosarcoma (OS) is the most common non-hematologic malignant tumor of bone in adults and children. As sarcomas are more common in adolescents and young adults than most other forms of cancer, there are a significant number of years of life lost secondary to these malignancies. OS is associated with a poor prognosis secondary to a high grade at presentation, resistance to chemotherapy and a propensity to metastasize to the lungs. Current OS management involves both chemotherapy and surgery. The incorporation of cytotoxic chemotherapy into therapeutic regimens escalated cure rates from <20% to current levels of 65-75%. Furthermore, limb-salvage surgery is now offered to the majority of OS patients. Despite advances in chemotherapy and surgical techniques over the past three decades, there has been stagnation in patient survival outcome improvement, especially in patients with metastatic OS. Thus, there is a critical need to identify novel and directed therapy for OS. Several Phase I trials for sarcoma therapies currently ongoing or recently completed have shown objective responses in OS. Novel drug delivery mechanisms are currently under phase II and III clinical trials. Furthermore, there is an abundance of preclinical research which holds great promise in the development of future OS-directed therapeutics. Our continuously improving knowledge of the molecular and cell-signaling pathways involved in OS will translate into more effective therapies for OS and ultimately improved patient survival. The present review will provide an overview of current therapies, ongoing clinical trials and therapeutic targets under investigation for OS.

Bone sarcomas: from biology to targeted therapies. Sarcoma. 2012;2012:301975. [PMID: 23226965 PMCID: PMC3514839 DOI: 10.1155/2012/301975]

Primary malignant bone tumours, osteosarcomas, and Ewing sarcomas are rare diseases which occur mainly in adolescents and young adults. With the current therapies, some patients remain very difficult to treat, such as tumour with poor histological response to preoperative CT (or large initial tumour volume for Ewing sarcomas not operated), patients with multiple metastases at or those who relapsed. In order to develop new therapies against these rare tumours, we need to unveil the key driving factors and molecular abnormalities behind the malignant characteristics and to broaden our understanding of the phenomena sustaining the metastatic phenotype and treatment resistance in these tumours. In this paper, starting with the biology of these tumours, we will discuss potential therapeutic targets aimed at increasing local tumour control, limiting metastatic spread, and finally improving patient survival.

The role of osteoclasts and tumour-associated macrophages in osteosarcoma metastasis

Osteosarcoma (OS) is the most common primary bone tumour in the paediatric age group. Treatment-refractory pulmonary metastasis continues to be the major complication of OS, reducing the 5-year survival rate for these patients to 10-20%. The mechanisms underlying the metastatic process in OS are still unclear, but undoubtedly, a greater understanding of the factors and interactions involved in its regulation will open new and much needed opportunities for therapeutic intervention. Recent published data have identified a new role for bone-specific macrophages (osteoclasts) and tumour-associated macrophages (TAMs), in OS metastasis. In this review we discuss the contribution of TAMs and osteoclasts in the establishment and maintenance of secondary metastatic lesions, and their novel role in the prevention of metastatic disease in a primary bone cancer such as osteosarcoma.

Microarray: an instrument for cancer surgeons of the future?

Microarray enables the study of thousands of genes simultaneously. While still in its infancy as a technique and with a number of barriers to be overcome, microarray is allowing scientists to thoroughly examine the molecular pathways of cancer pathogenesis. However, the adoption of microarray as a clinically applicable technique has been slow coming. Current literature suggests roles in the diagnosis of tumours of unknown origin, in the evaluation of prognostic markers, and in guiding treatment for recurrent and resistant malignancy. This review outlines the science of microarray and draws on clinical examples, including osteosarcoma, breast, prostate and pancreatic carcinomas, to highlight the potential of microarray as a technique of surgical importance.

Epidermal growth factor enhances the malignant phenotype in canine mammary carcinoma cell lines

Canine mammary gland tumours (CMTs) are the most common malignancies in female dogs. The receptor tyrosine kinase EGFR (erbb1), a receptor for epidermal growth factor (EGF) and related factors, mediates multiple oncogenic functions in human epithelial neoplasms. While previous studies have demonstrated EGFR expression in canine tumours, its function has not been studied in canine cancer. The purpose of this study was to determine the in vitro effects of EGF and vandetanib (ZD6474), a small molecule inhibitor of VEGFR-2, EGFR and RET tyrosine kinases, on proliferation, invasion, survival and chemosensitivity in CMT cells. In low serum, EGF enhanced proliferation and chemotaxis, attenuated apoptosis, and stimulated vascular endothelial growth factor (VEGF) production. Vandetanib dose-dependently inhibited EGFR phosphorylation as well as PI3K/Akt activation, and inhibited all EGF-induced phenotypic effects. In conclusion, EGF stimulates multiple features promoting the malignant phenotype in CMT. Thus, CMT may be an important translational model for the investigation of novel EGFR-directed therapies.

Addition of pamidronate to chemotherapy for the treatment of osteosarcoma

BACKGROUND

This study evaluated the safety and feasibility of the addition of pamidronate to chemotherapy for treatment of osteosarcoma.

METHODS

The authors treated 40 patients with osteosarcoma with cisplatin, doxorubicin, and methotrexate with the addition of pamidronate 2 mg/kg/dose (max dose 90 mg) monthly for 12 doses. Survival, event-free survival (EFS), and durability of orthopedic reconstruction were evaluated.

RESULTS

For patients with localized disease, event-free survival (EFS) at 5 years was 72% and overall survival 93%. For patients with metastatic disease, EFS at 5 years was 45% and overall survival 64%. Toxicity was similar to patients treated with chemotherapy alone. Thirteen of 14 uncemented implants demonstrated successful osteointegration. Among allograft reconstructions, there were 2 graft failures, 4 delayed unions, and 6 successful grafts. Overall, 5 of 33 reconstructions failed. There were no stress fractures or growth disturbances.

CONCLUSIONS

Pamidronate can be safely incorporated with chemotherapy for the treatment of osteosarcoma. It does not impair the efficacy of chemotherapy. Pamidronate may improve the durability of limb reconstruction.

Loss of osteoclasts contributes to development of osteosarcoma pulmonary metastases

We conducted a transcriptomic screen of osteosarcoma (OS) biopsies and found that expression of osteoclast-specific tartrate-resistant acid phosphatase 5 (ACP5/TRAP) is significantly downregulated in OS compared with nonmalignant bone (P < 0.0001). Moreover, lesions from OS patients with pulmonary metastases had 2-fold less ACP5/TRAP expression (P < 0.018) than lesions from patients without metastases. In addition, we found a direct correlation (P = 0.0166) between ACP5/TRAP expression and time to metastasis. Therefore, we examined whether metastasis-competent (MC) OS cells could induce loss of ACP5(+) osteoclasts and contribute to metastasis. We found that MC OS cell lines can inhibit osteoclastogenesis in vitro and in vivo. In addition, osteoclasts can inhibit the migration of MC OS cells in vitro. Finally, ablation of osteoclasts with zoledronic acid increases the number of metastatic lung lesions in an orthotopic OS model, whereas fulvestrant treatment increases osteoclast numbers and reduces metastatic lesions. These data indicate that the metastatic potential of OS is determined early in tumor development and that loss of osteoclasts in the primary lesion enhances OS metastasis.

Zoledronic acid protects against osteosarcoma-induced bone destruction but lacks efficacy against pulmonary metastases in a syngeneic rat model

Osteosarcoma (OS) is the most common primary malignant tumor of bone in children and adolescents. In spite of successful control of the primary tumor, death from lung metastasis occurs in more than a third of patients. To investigate the efficacy of zoledronic acid (ZOL) on the development, progression and metastatic spread of OS, we used a rat model of OS, with features of the disease similar to human patients, including spontaneous metastasis to lungs. Rat OS cells were inoculated into the tibial marrow cavity of syngeneic rats. OS development was associated with osteolysis mixed with new bone formation, adjacent to the periosteum and extended into the surrounding soft tissue. Metastatic foci in the lungs formed 3-4 weeks postcancer cell transplantation. Treatment with a clinically relevant dose of ZOL was initiated 1 week after tumors were established and continued once weekly or as a single dose. ZOL preserved the integrity of both trabecular and cortical bone and reduced tumor-induced bone formation. However, the overall tumor burden at the primary site was not reduced because of the persistent growth of cancer cells in the extramedullary space, which was not affected by ZOL treatment. ZOL treatment failed to prevent the metastatic spread of OS to the lungs. These findings suggest that ZOL as a single agent protects against OS-induced bone destruction but lacks efficacy against pulmonary metastases in this rat model. ZOL may have potential value as an adjuvant therapy in patients with established OS.

The administration of demethyl fruticulin A from Salvia corrugata to mammalian cells lines induces "anoikis", a special form of apoptosis

Recently demethyl fruticulin A was identified as the major diterpenoid component of the exudates produced by the trichomes of Salvia corrugata leafs. Given the documented apoptotic effects of some of the other known components of the exudates from Salvia species, we assessed if demethyl fruticulin A, once administered to mammalian cells, was involved in the onset of apoptosis and if its biological effects were exerted through the participation of a scavenger membrane receptor, CD36. Three model cell lines were chosen, one of which lacking CD36 expression. Functional availability of the receptor, or its transcriptional rate, were blocked/reduced with a specific antibody or by the administration of vitamin E. Immunodetection of cell cytoskeletal components and tunel analysis revealed that demethyl fruticulin A triggers the onset of anoikis, a special form of apoptosis induced by cell detachment from the substrate. Impairment of CD36 availability/transcription confirmed the receptor partial involvement in the intake of the substance and in anoikis, as also sustained by FACS analysis and by the downregulation of p95, a marker of anoikis, upon blockade of CD36 transcription. However, experiments with CD36-deficient cells suggested that alternate pathways, still to be determined, may take part in the biological effects exerted by demethyl fruticulin A.

Lysosomal-mitochondrial axis in zoledronic acid-induced apoptosis in human follicular lymphoma cells

Bisphosphonates (BPs) are potent inhibitors of osteoclast function, widely used to treat excessive bone resorption associated with bone metastases, that also have anti-tumor activity. Zoledronic acid (ZOL) represents a potential chemotherapeutic agent for the treatment of cancer. ZOL is the most potent nitrogen-containing BPs, and it inhibits cell growth and induces apoptosis in a variety of cancer cells. Recently we demonstrated that accumulation of isopentenyl pyrophosphate and the consequent formation of a new type of ATP analog (ApppI) after mevalonate pathway inhibition by nitrogen-containing BPs strongly correlates with ZOL-induced cell death in cancer cells in vitro. In this study we show that ZOL-induced apoptosis in HF28RA human follicular lymphoma cells occurs exclusively via the mitochondrial pathway, involves lysosomes, and is dependent on mevalonate pathway inhibition. To define the exact signaling pathway connecting them, we used modified HF28RA cell lines overexpressing either BclXL or dominant-negative caspase-9. In both mutant cells, mitochondrial and lysosomal membrane permeabilization (MMP and LMP) were totally prevented, indicating signaling between lysosomes and mitochondria and, additionally, an amplification loop for MMP and/or LMP regulated by caspase-9 in association with farnesyl pyrophosphate synthetase inhibition. Additionally, the lysosomal pathway in ZOL-induced apoptosis plays an additional/amplification role of the intrinsic pathway independently of caspase-3 activation. Moreover, we show a potential regulation by Bcl-XL and caspase-9 on cell cycle regulators of S-phase. Our findings provide a molecular basis for new strategies concomitantly targeting cell death pathways from multiple sites.

The level of ATP analog and isopentenyl pyrophosphate correlates with zoledronic acid-induced apoptosis in cancer cells in vitro

Bisphosphonates are potent inhibitors of osteoclast function widely used to treat excessive bone resorption associated, e.g., with bone metastases. They have also antitumor activity. However, it is unclear whether this reflects an indirect effect via inhibition of bone resorption or a direct antitumor effect. Nitrogen-containing bisphosphonates (N-BPs), including zoledronic acid (ZOL), act by inhibiting farnesyl pyrophosphate synthase (FPPS). The mevalonate pathway is blocked and the accumulation of isopentenyl pyrophosphate (IPP) consequently occurs. IPP is conjugated to AMP to form a novel ATP analog (ApppI). The present study was undertaken to clarify whether IPP and/or ApppI has a direct involvement in apoptosis caused by ZOL in different cancer cell lines. There are marked differences in ZOL-induced ApppI formation between different cancer cell lines. On this basis, we selected three cancer cell lines that differ significantly from each other in their ZOL-induced IPP and ApppI accumulation: human estrogen-dependent (MCF7) and estrogen-independent (MDA-MB 436) breast cancer cell lines and a human myeloma cell line (RPMI 8226). The amount of IPP/ApppI correlated with the capacity of cells to undergo apoptosis. Geranylgeraniol (GGOH), an intermediate of mevalonate metabolism, blocks both IPP and ApppI formation and to some degree ZOL-induced apoptosis in a cell line-dependent manner. In addition, lovastatin (LOV), an inhibitor of the enzyme HMGCoA reductase, completely blocks IPP/ApppI formation as determined by mass spectrometry analysis, but enhances apoptosis. In conclusion, the current data suggest that ZOL-induced IPP/ApppI formation can contribute to ZOL-induced apoptosis. This mechanism and the inhibition of protein prenylation, both outcomes of FPPS inhibition in mevalonate pathway, seem to act in concert in ZOL-induced apoptosis in cancer cells.

Risedronate inhibits human osteosarcoma cell invasion

BACKGROUND

Osteosarcoma is a highly malignant bone tumor and is the most commonly encountered malignant bone tumor in children and adolescents. Furthermore, significant numbers of patients eventually develop pulmonary metastases and succumb to the disease even after conventional multi-agent chemotherapy and surgical excision. Several solid tumors display enhanced expression of matrix metalloproteinases (MMPs), and recently clinical trials have been initiated on MMP-inhibitors. On the other hand, bisphosphonates (BPs), which have a profound effect on bone resorption, are widely used to treat osteoclast-mediated bone diseases. BPs are also known to inhibit tumor growths and metastases in some tumors such as breast cancer, renal cell carcinoma, and prostate cancer.

METHODS

Two osteosarcoma cell lines (SaOS-2 and U2OS) were treated with risedronate (0, 0.1, 1, 10 microM) for 48 hours. Cell viabilities were determined using MTT assay, the mRNA levels of MMP-2 and MMP-9 were analyzed by reverse-transcription polymerase chain reaction, the amount of MMP-2 and MMP-9 protein were analyzed by Westernblot, the activities of MMP-2 and MMP-9 were observed by Gelatin zymography, and Matrigel invasion assays were used to investigate the invasive potential of osteosarcoma cell lines before and after risedronate treatment.

RESULTS

The invasiveness of osteosarcoma cell lines (SaOS-2, U2OS) were reduced in a dose dependent manner follow 48 hour treatment of up to 10 microM of the risedronate at which concentration no cytotoxicity occurred. Furthermore, the gelatinolytic activities and protein and mRNA levels of MMP-2 and MMP-9 were also suppressed by increasing risedronate concentrations.

CONCLUSION

Given that MMP-2 and MMP-9 are instrumental in tumor cell invasion, our results suggest the risedronate could reduce osteosarcoma cell invasion.

Zoledronic acid inhibits both the osteolytic and osteoblastic components of osteosarcoma lesions in a mouse model

PURPOSE

To evaluate the efficacy of zoledronic acid (ZOL) against osteosarcoma (OS) growth, progression, and metastatic spread using an animal model of human OS that closely resembles the human disease.

EXPERIMENTAL DESIGN

Human K-HOS or KRIB OS cells, tagged or untagged with a luciferase reporter construct, were transplanted directly into the tibial cavity of nude mice. ZOL was given as weekly, or a single dose of 100 microg/kg body weight, equivalent to the 4 mg i.v. dose used clinically. Tumor growth at the primary site and as pulmonary metastases was monitored by bioluminescence imaging and histology, and OS-induced bone destruction was measured using high-resolution micro-computed tomography.

RESULTS

Mice transplanted with OS cells exhibited aberrant bone remodeling in the area of cancer cell transplantation, with areas of osteolysis mixed with extensive new bone formation extending from the cortex. ZOL administration prevented osteolysis and significantly reduced the amount of OS-induced bone formation. However, ZOL had no effect on tumor burden at the primary site. Importantly, ZOL failed to reduce lung metastasis and in some cases was associated with larger and more numerous metastatic lesions.

CONCLUSIONS

Our data show that clinically relevant doses of ZOL, while protecting the bone from OS-induced bone destruction, do not inhibit primary tumor growth. Moreover, lung metastases were not reduced and may even have been promoted by this treatment, indicating that caution is required when the clinical application of the bisphosphonate class of antiresorptives is considered in OS.

Zoledronate inhibits the proliferation, adhesion and migration of vascular smooth muscle cells

Bisphosphonates, which are extensively used in bone-related disorders, have been reported to inhibit atherosclerosis and neointimal hyperplasia. In the present study, we investigated the effects of a bisphosphonate, zoledronate, on the proliferation, adhesion, migration and microstructure of vascular smooth muscle cells (VSMCs) from Sprague-Dawley rats. It was shown that zoledronate suppressed VSMCs proliferation after 48 h cultivation in a dose depend manner, most obviously at concentrations above 10 microM. Cell cycle analysis indicated that zoledronate inhibited the proliferation of VSMCs via cell cycle arrest at S/G2/M phase. This inhibition was not associated with cell death. In a modified Boyden chamber model, it was shown that zoledronate dose-dependently inhibited VSMCs adhesion to collagen and migration stimulated by platelet-derived growth factor-BB. Western blot analysis suggested that zoledronate significantly inhibited the phosphorylation of focal adhesion kinase. Furthermore, we observed that more and more VSMCs changed from a bipolar appearance to a globular shape under inverted light microscope as zoledronate concentration increased from 0.1 to 100 microM. Images under transmission electron microscope confirmed this morphological change, and many electron density bodies were observed in zoledronate-treated VSMCs. These findings indicated that bisphosphonates' effects of suppressing atherosclerosis and neointimal hyperplasia might be due to inhibition of VSMCs, at least for zoledronate.

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.

Zoledronic acid inhibits osteosarcoma growth in an orthotopic model

Zoledronic acid (ZOL) has been shown to reduce osteolysis in bone metastasis. Its efficacy in osteosarcoma has not been convincingly proved in a clinically relevant model for the disease. In vitro, ZOL decreased osteosarcoma cell proliferation, mainly due to an increase in apoptosis in a dose-dependent fashion. There was a decrease in cell migration at >or=10 micromol/L concentrations, but invasion was inhibited at a much lower dose of 0.1 micromol/L. Reverse transcription-PCR showed that ZOL overall caused an increased expression of osteocalcin and decreased expression of alkaline phosphatase, osteopontin, osteonectin, and vascular endothelial growth factor, with no change in expression of osteoprotegerin. ZOL administration s.c. twice weekly at 0.12 mg/kg to SaOS-2 tumor-bearing mice resulted in primary tumor growth inhibition, reduction in lung metastases, and dramatic decrease in osteolysis. Furthermore, in the ZOL cohort, there was a clear reduction in the number of osteoclasts in bone exposed to tumor and a lower tumor vessel density. These data point to the adjuvant potential of ZOL in the management of osteosarcoma not only for its antiosteolytic properties but also for its ability to directly halt tumor cell growth and metastasis via its effects on viability, invasion, differentiation, and angiogenesis.

Zoledronate has an antitumor effect and induces actin rearrangement in dexamethasone-resistant myeloma cells

New strategies are needed to overcome the resistance of multiple myeloma (MM) to dexamethasone (Dex). Several recent in vitro studies demonstrated the antitumor effect of nitrogen-containing amino-bisphosphonates (N-BPs) in various tumor cell lines. Inhibition of the prenylation of small G proteins is assumed to be one of the principal mechanisms by which N-BPs exert their effects. There have been few reports on N-BP treatment of MM cells that are resistant to Dex. Additionally, it is not known how small G proteins are altered in N-BP-treated MM cells. In this study, we evaluated the effect of the most potent N-BP, zoledronate (ZOL), on a Dex-resistant human MM cell subline (Dex-R) that we established from the well-documented RPMI8226 cell line. ZOL reduced the viability and induced apoptosis of Dex-R cells. Some of the ZOL-treated RPMI8226 cells and ZOL-treated Dex-R cells were elongated; however, elongated cells were not seen among the Dex-treated RPMI8226 cells. Furthermore, we found that portions of the small G proteins, Rho and Rap1A, were unprenylated in the ZOL-treated MM cells. Geranylgeraniol reduced the above-mentioned ZOL-induced effects. These findings suggest that ZOL may be beneficial for the treatment of Dex-resistant MM by suppressing the processing of RhoA and Rap1A.

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.

Bisphosphonate action: Revelations and deceptions from in vitro studies

Bisphosphonates (BPs) are a class of drugs used in the treatment of osteoporosis and diseases of high bone turnover, as well as for control of skeletal related events secondary to malignant disease. The key to BP specificity is their capacity to bind rapidly and with high affinity to bone surfaces. The cellular targets of BPs at the bone surface have been a source of controversy. In addition to osteoclasts, it has been frequently proposed that BPs may affect a variety of cell types including osteoclast precursors, osteoblasts and bone-lining cells, immunogenic cells, and tumour cells. However, there is an emerging body of literature from in vitro studies indicating that BPs are only released and taken up from bone surfaces by resorbing osteoclasts. In this scenario, the only significant exposure of non-resorbing cells to BP would occur during the initial period after dosing, prior to drug clearance from the soft tissues. Auspiciously, several groups have reported on revised culture systems that better reflect the pharmacology of BP dosing.

Mevalonate pathway: a review of clinical and therapeutical implications

Mevalonate pathway is an important metabolic pathway which plays a key role in multiple cellular processes by synthesizing sterol isoprenoids, such as cholesterol, and non-sterol isoprenoids, such as dolichol, heme-A, isopentenyl tRNA and ubiquinone. While extensively studied in regard with cholesterol synthesis and its implications in cardiovascular diseases, in recent years the mevalonate pathway has become a challenging and, in the meantime, fascinating topic, when a large number of experimental and clinical studies suggested that inhibition of non-sterol isoprenoids might have valuable interest in human pathology. These molecules that are essential for cell growth and differentiation appear to be potential interesting therapeutic targets for many areas of ongoing research: oncology, autoimmune disorders, atherosclerosis, and Alzheimer disease. Also, considerable progress has been made in the past decade in understanding the pathophysiology of two auto-inflammatory disorders resulting from an inherited deficiency of mevalonate kinase, the first committed enzyme of the mevalonate pathway. Here we present a brief description of the biochemistry of the mevalonate pathway, together with a review of the current knowledge of the clinical and therapeutical implications of this fascinating and complex metabolic pathway.

Combined effects of a third-generation bisphosphonate, zoledronic acid with other anticancer agents against murine osteosarcoma

Bisphosphonates (BPs) are widely used to treat bone diseases and also appear to possess direct antitumour activity. We have previously reported that third-generation BPs such as zoledronic acid (ZOL) and minodronic acid (YM529) synergistically augment the effects of anticancer agents in various cancer cells. Recently, we have also reported the antitumour effects of YM529 on murine osteosarcoma cells. As YM529 has not been clinically available, we herein focused on the anti-osteosarcoma effects of ZOL which is clinically available. In addition to ZOL alone, we evaluated the concurrent or sequential combined effects of ZOL with other anticancer agents against murine osteosarcoma cell lines. ZOL showed almost same anti-osteosarcoma activity compared with YM529 and more sensitive growth inhibitory effects against osteosarcoma cells than normal cells. Moreover, ZOL acted synergistically in vitro when administered concurrently with paclitaxel (PAC) or gemcitabine (GEM), not only in wild-type osteosarcoma cells but also in P-glycoprotein (P-gp)-overexpressing osteosarcoma cells, which were much less sensitive against each anticancer agent. Furthermore, 24 h of ZOL pretreatment significantly augmented the sensitivity of doxorubicin (DOX), PAC or GEM against osteosarcoma cells. These findings suggest that combined administration of ZOL with other anticancer agents may improve the osteosarcoma treatment.

Alendronate induces anti-migratory effects and inhibition of neutral phosphatases in UMR106 osteosarcoma cells

Bisphosphonates are nonhydrolysable pyrophosphate analogues that prevent bone loss in several types of cancer. However, the mechanisms of anticancer action of bisphosphonates are not completely known. We have previously shown that nitrogen-containing bisphosphonates directly inhibit alkaline phosphatase of UMR106 rat osteosarcoma cells. In this study, we evaluated the effects of alendronate on the migration of UMR106 osteosarcoma using a model of multicellular cell spheroids, as well as the alendronate effect on neutral phosphatases. Alendronate significantly inhibited the migration of osteoblasts in a dose-dependent manner (10(-6)-10(-4) M). This effect was also dependent on calcium availability. The spheroid morphology and distribution of actin fibers were also affected by alendronate treatment. Alendronate dose-dependently inhibited neutral phosphatase activity in cell-free osteoblastic extracts as well as in osteoblasts in culture. Our results show that alendronate inhibits cell migration through mechanisms dependent on calcium, and that seem to involve inhibition of phosphotyrosine-neutral-phosphatases and disassembly of actin stress fibers.

Growth inhibition and sensitization to cisplatin by zoledronic acid in osteosarcoma cells

Since osteosarcoma is a drug-resistant disease, the aim of the present study was to explore the possible interest of therapeutic approaches including nitrogen-containing biphosphonate zoledronic acid using osteosarcoma cell lines with different genetic backgrounds. Parental p53+/pRb+ U2-OS, p53-mutant U2-OS (U2-OS/175) and p53-/pRb- SAOS were sensitive to zoledronic acid with no significant differences in IC50 values. Analysis of cell cycle distribution revealed a time-dependent shifting of U2-OS cells towards G2 phase with cell cycle arrest in G2 phase at 96 h of exposure to the compound. Conversely, U2-OS/175 and SAOS cells responded to treatment with transient cell accumulation in S phase up to 48-72 h, respectively. Cell lines were exposed to increasing concentrations of cisplatin alone or combined with sub-toxic doses of zoledronic acid. A growth inhibitory effect was seen after combined treatment in U2-OS, otherwise resistant to cisplatin up to 100 ng/ml. Zoledronic acid did not efficiently sensitized U2-OS/175 and SAOS to cisplatin, thereby suggesting that different behavior may depend on p53 mutation. This data was confirmed in U2-OS cells where p53 expression was downregulated by RNA interference. Present findings indicate occurrence of sensitization to cisplatin by zoledronic acid in wild-type p53 osteosarcoma cells but not in p53-null cells nor in cells expressing a dominant-negative form of p53, supporting that wild-type p53 is required for synergistic interaction of cisplatin and zoledronic acid.

Activity of nitrogen-containing and non-nitrogen-containing bisphosphonates on tumor cell lines

We synthesized and tested three series of bisphosphonates for their activity in inhibiting the growth of three human tumor cell lines: MCF-7 (breast), NCI-H460 (lung), and SF-268 (CNS). The first series of compounds consisted of 49 nitrogen-containing bisphosphonates, the most active species being a tetrakispivaloyloxymethyl (POM) ester, having an (average) IC(50) of 6.8 microM. The second series of compounds consisted of nine terphenylbisphosphonates, the most active species also being a POM ester, having an IC(50) of 2.2 microM. The third series of compounds consisted of seven halogen or cyanophenylbisphosphonates, the most active species again being a POM ester, having an IC(50) of 500 nM. Taken together, these results are of interest because they show that bisphosphonate esters can have potent activity against a variety of tumor cell lines, with the most active terphenyl- and halophenyl-containing species having IC(50) values approximately 10-40x lower than the most potent commercially available bisphosphonates.

Zoledronic acid activates the DNA S-phase checkpoint and induces osteosarcoma cell death characterized by apoptosis-inducing factor and endonuclease-G translocation independently of p53 and retinoblastoma status

The molecular mechanisms responsible for the cellular effects of the nitrogen-containing bisphosphonate zoledronic acid (Zol) were assessed on several osteosarcoma cell lines differing in their p53 and retinoblastoma (Rb) status. Zol inhibited cell proliferation and increased atypical apoptosis. The Zol effects on proliferation were due to cell cycle arrest in S and G2/M phases subsequent to the activation of the intra-S DNA damage checkpoint with an increase in P-ATR, P-chk1, Wee1, and P-cdc2 levels and a decrease in cdc25c, regardless of the p53 and Rb status. In addition, the atypic apoptosis induced by Zol was independent of caspase activation, and it was characterized by nuclear alterations, increased Bax expression, and reduced Bcl-2 level. Furthermore, mitochondrial permeability was up-regulated by Zol independently of p53 in association with the translocation of apoptosis-inducing factor (AIF) and endonuclease-G (EndoG). Zol also disturbed cytoskeletal organization and cell junctions and inhibited cell migration and phosphorylation of focal adhesion kinases. The main difficulty encountered in treating cancer relates to mutations in key genes such as p53, Rb, or proteins affecting caspase signaling carried by many tumor cells. We have demonstrated for the first time that zoledronic acid activated the DNA damage S-phase checkpoint and the mitochondrial pathway via AIF and EndoG translocation, and it inhibited cell proliferation and induced cell death, bypassing these potentials mutations. Therefore, zoledronic acid may be considered as an effective therapeutic agent in clinical trials of osteosarcoma in which mutation for p53 and Rb very often occur, and where current treatment with traditional chemotherapeutic agents is ineffective.

The third-generation bisphosphonates inhibit proliferation of murine osteosarcoma cells with induction of apoptosis

Third generation bisphosphonates (BPs), including YM175 and YM529, are known to inhibit bone resorption. The aim of this study was to evaluate the anti-tumor effects of these drugs on murine osteosarcoma cell lines, in terms of proliferation and apoptosis. We found that both YM175 and YM529 strongly inhibited the in vitro proliferation and induced apoptosis of murine osteosarcoma cells. YM529 was more effective than YM175 in inhibiting cell proliferation. These observations suggest that third-generation BPs directly affect on the proliferation and survival of osteosarcoma cells, which supports the possibility that they could be beneficial in the treatment of osteosarcoma patients.

PI3-K/Akt-mediated anoikis resistance of human osteosarcoma cells requires Src activation

Considerable advances in understanding the mechanisms associated with anoikis resistance of normal and malignant epithelial cells have been made. However, little is still known about the pathways involved in anoikis resistance of non-epithelial cells such as fibroblasts and sarcomas. Our results show that Src activity contributes to anoikis resistance of human osteosarcoma SAOS-2 cells. Src was found to be upregulated in anoikis resistant SAOS cells, and pharmacological inhibition of its activity resulted in the restoration of anoikis sensitivity. A normal pattern of dephosphorylation of FAK was observed upon cell detachment of both anoikis sensitive and resistant SAOS-2 cells, suggesting that FAK activity during anoikis resistance is not essential. The activity of Akt was found to be upregulated in anoikis resistant SAOSar cells and the pharmacological inhibition of PI3-K activity restored sensitivity to anoikis resistant cells, reconfirming the critical role of PI3-K/Akt pathway in cell survival. Furthermore, pharmacological inhibition of Src resulted in a decrease of Akt phosphorylation at Ser473. Altogether, these studies indicated a survival pathway mediated by the Src-dependent activation of the PI3-K/Akt pathway in a manner independent of FAK activity.