Bisphosphonates in cancer therapy

Function of gamma delta (γδ) T cell in cancer with special emphasis on cervical cancer

Cervical cancer is the second-most prevalent gynecologic cancer in India. It is typically detected in women between the ages of 35 and 44. Cervical cancer is mainly associated with the human papillomavirus (HPV). The report shows that 70 % of cervical cancer is caused by HPV 16 and 18. There are few therapeutic options and vaccines available for cervical cancer treatment and γδ T cell therapy is one of them. This therapy can kill various types of cancers, including cervical cancer. The major γδ T cell subset is the Vγ9Vδ2 T cell, mainly distributed in peripheral blood which recognize non-MHC peptide antigens and can eliminate MHC-downregulated cancer. Moreover, γδ T cells can express different types of receptors that bind to the molecules of stressed cells, often produced on cancerous cells but absent from healthy tissue. γδ T cells possess both direct and indirect cytotoxic capabilities against malignancies and show potential antitumoral responses. However, γδ T cells also encourage the progression of cancer. Cancer immunotherapy using γδ T cells will be a potential cancer treatment, as well as cervical cancer. This review focused on the γδ T cell and its function in cancer, with special emphasis on cervical cancer. It also focused on the ligand recognition site of γδ T cells, galectin-mediated therapy and pamidronate-treated therapy for cervical cancer. Instead of the great potential of γδ T cell for the eradication of cervical cancer, no comprehensive in-depth review is available to date, so there is a need to jot down the various roles and modes of action and different applications of γδ T cells for cancer research, which we believe will be a handy tool for the researchers and the readers.

Are macrophages in tumors good targets for novel therapeutic approaches?

The development of cancer has been an extensively researched topic over the past few decades. Although great strides have been made in cancer prevention, diagnosis, and treatment, there is still much to be learned about cancer's micro-environmental mechanisms that contribute to cancer formation and aggressiveness. Macrophages, lymphocytes which originate from monocytes, are involved in the inflammatory response and often dispersed to areas of infection to fight harmful antigens and mutated cells in tissues. Macrophages have a plethora of roles including tissue development and repair, immune system functions, and inflammation. We discuss various pathways by which macrophages get activated, various approaches that can regulate the function of macrophages, and how these approaches can be helpful in developing new cancer therapies.

Zoledronic acid at subtoxic dose extends osteoblastic stage span of primary human osteoblasts

OBJECTIVE

This study aimed to check the effect of zoledronic acid (ZA) at subtoxic dose on human osteoblasts (HOs) in terms of cell viability, apoptosis occurrence, and differentiation induction. ZA belongs to the family of bisphosphonates (BPs), largely used in the clinical practice for the treatment of bone diseases, often associated with jaw osteonecrosis onset. Their pharmacological action consists in the direct block of the osteoclast-mediated bone resorption along with indirect action on osteoblasts.

MATERIALS AND METHODS

HOs were treated choosing the highest limit concentration (10(-5) M) which does not induce toxic effects. Live/dead staining, flow cytometry, mitochondrial membrane potential assay, osteocalcin western blotting, gp38 RT-PCR, collagen type I, PGE2, and IL-6 ELISA assays were performed.

RESULTS

Similar viability level between control and ZA-treated samples is found along with no significant increase of apoptotic and necrotic cells in ZA-treated sample. To establish if an early apoptotic pathway was triggered, Bax expression and mitochondrial membrane potential were evaluated finding a higher protein expression in control sample and a good integrity of mitochondrial membrane in both experimental points. Type I collagen secretion and alkaline phosphatase (ALP) activity appear increased in ZA-treated sample, osteocalcin expression level is reduced in ZA-treated cells, whereas no modifications of gp38 mRNA level are evidenced. No statistical differences are identified in PGE2 secretion level whereas IL-6 secretion is lower in ZA-treated HOs with respect to control ones.

CONCLUSIONS

These results highlight that ZA, delaying the osteoblastic differentiation process versus the osteocytic lineage, strengthens its pharmacological activity enhancing bone density.

CLINICAL RELEVANCE

The knowledge of ZA effects on osteoblasts at subtoxic dose allows to improve therapeutic protocols in order to strengthen drug pharmacological activity through a combined action on both osteoclastic and osteoblastic cells.

Zoledronic acid and geranylgeraniol regulate cellular behaviour and angiogenic gene expression in human gingival fibroblasts

The mevalonate pathway (MVP) and the anti-angiogenic effect of bisphosphonates have been shown to play a role in the pathogenesis of bisphosphonate-related osteonecrosis of the jaw (BRONJ). This study determined the effect of the bisphosphonate, zoledronic acid and the replenishment of the MVP by geranylgeraniol on human gingival fibroblasts. Cell viability, apoptosis, morphological analysis using transmission electron microscopy, and gene expression for vascular endothelial growth factor A, bone morphogenic protein 2, ras homologue gene family member B, epiregulin and interferon-alpha were conducted. Results showed cellular viability was decreased in the presence of zoledronic acid and the co-addition of zoledronic acid with geranylgeraniol restored cell viability to control levels. Caspase 3/7 was detected in zoledronic-acid-treated cells indicating apoptosis. Transmission electron microscopy revealed dilation of the rough endoplasmic reticulum with zoledronic acid and the appearance of multiple lipid-like vesicles following the addition of geranylgeraniol. Zoledronic acid significantly (P < 0.05, FR > ± 2) up-regulated vascular endothelial growth factor A, bone morphogenic protein 2, ras homologue gene family member B and epiregulin at one or more time points but not interferon-alpha. Addition of geranylgeraniol resulted in a reduction in the expression of all five genes compared with zoledronic-acid-treated human gingival fibroblasts. The study concluded geranylgeraniol partially reversed the effects of zoledronic acid in human gingival fibroblasts both at the cellular and genetic levels, suggesting the regulation of these genes is mediated via the mevalonate pathway.

Oral bisphosphonates and the risk of Barrett's esophagus: case-control analysis of US veterans

OBJECTIVES

This study examined Barrett's esophagus (BE) risk factors in veterans to determine the association between risk of BE and use of oral bisphosphonates.

METHODS

We conducted a case-control study among eligible patients scheduled for an elective esophagogastroduodenoscopy (EGD) and a sample of patients eligible for screening colonoscopy recruited from primary care clinics from a single VA Medical Center. Cases with definitive BE were compared with controls; all underwent study EGD. Use of oral bisphosphonates was ascertained by reviewing filled prescriptions in electronic pharmacy records. We calculated odds ratios (ORs) and 95% confidence intervals (95% CIs), using multivariate logistic regression modeling while adjusting for sex, age, race, proton-pump inhibitor use, hiatal hernia, waist-to-hip ratio, Helicobacter pylori infection, and gastroesophageal reflux disorder (GERD) symptoms.

RESULTS

There were 285 BE cases, 1,122 endoscopy controls, and 496 primary care controls. Alendronate and risedronate were the only oral bisphosphonates prescribed. The proportion of BE cases with filled prescription of oral bisphosphonates (4.6%) was greater than in endoscopy controls (1.6%) or primary care controls (2.9%). In the adjusted analysis, oral bisphosphonate use was significantly associated with BE risk (OR=2.33; 95% CI: 1.11-4.88) compared with the combined control groups. This association remained significant when BE cases were compared with endoscopy controls only (OR=2.74; 95% CI: 1.28-5.87) but was attenuated when compared with primary care controls only (OR=2.60; 95% CI: 0.99-6.84). The association was observed in patients with GERD symptoms (OR=3.29; 95% CI: 1.36-7.97) but not in those without GERD symptoms.

CONCLUSION

Oral bisphosphonate use may increase the risk for BE, especially among patients with GERD.

Tumour macrophages as potential targets of bisphosphonates

Tumour cells communicate with the cells of their microenvironment via a series of molecular and cellular interactions to aid their progression to a malignant state and ultimately their metastatic spread. Of the cells in the microenvironment with a key role in cancer development, tumour associated macrophages (TAMs) are among the most notable. Tumour cells release a range of chemokines, cytokines and growth factors to attract macrophages, and these in turn release numerous factors (e.g. VEGF, MMP-9 and EGF) that are implicated in invasion-promoting processes such as tumour cell growth, flicking of the angiogenic switch and immunosuppression. TAM density has been shown to correlate with poor prognosis in breast cancer, suggesting that these cells may represent a potential therapeutic target. However, there are currently no agents that specifically target TAM's available for clinical use.

Bisphosphonates (BPs), such as zoledronic acid, are anti-resorptive agents approved for treatment of skeletal complication associated with metastatic breast cancer and prostate cancer. These agents act on osteoclasts, key cells in the bone microenvironment, to inhibit bone resorption. Over the past 30 years this has led to a great reduction in skeletal-related events (SRE's) in patients with advanced cancer and improved the morbidity associated with cancer-induced bone disease. However, there is now a growing body of evidence, both from in vitro and in vivo models, showing that zoledronic acid can also target tumour cells to increase apoptotic cell death and decrease proliferation, migration and invasion, and that this effect is significantly enhanced in combination with chemotherapy agents. Whether macrophages in the peripheral tumour microenvironment are exposed to sufficient levels of bisphosphonate to be affected is currently unknown. Macrophages belong to the same cell lineage as osteoclasts, the major target of BPs, and are highly phagocytic cells shown to be sensitive to bisphosphonates in model studies; In vitro, zoledronic acid causes increased apoptotic cell death; in vivo the drug has been shown to inhibit the production of pro-angiogenic factor MMP-9, as well as most recent evidence showing it can trigger the reversal of the TAMs phenotype from pro-tumoral M2 to tumoricidal M1. There is thus accumulating evidence supporting the hypothesis that effects on TAMs may contribute to the anti-tumour effect of bisphosphonates. This review will focus in detail on the role of tumour associated macrophages in breast cancer progression, the actions of bisphosphonates on macrophages in vitro and in tumour models in vivo and summarise the evidence supporting the potential for the targeting of tumour macrophages with bisphosphonates.

Cytotoxic effect of clodronate and zoledronate on the chondrosarcoma cell lines HTB-94 and CAL-78

The wide surgical tumour resection is the only effective treatment in chondrosarcoma. However, a major problem remains the high rate of local recurrences and metastases due to the lack of adjuvant therapies. In this study the cytotoxic effect of the bisphosphonate clodronate (0.1-1000 μM) and zoledronate (0.1-1000 μM) in different concentrations on two chondrosarcoma cell lines (HTB-94 and CAL-78) has been investigated. After an incubation period of 48, 72 and 96 hours the chondrosarcoma cell viability was measured as the MTT-proliferation rate. In concentrations of >1 μm zoledronate the cell activity was reduced by up to 95% for the CAL-78 cells. Further, zoledronate has been more effective in lower concentrations than clodronate in the reduction of cell viability for both cell lines. However, clodronate showed significant cytotoxic effects in high concentrations and after longer incubation periods. Further research is necessary, but in the light of these results bisphosphonates may also play a role in the treatment of chondrosarcomas.

The rabbit biodistribution of a therapeutic dose of zoledronic acid labeled with Tc-99m

The aim of the present study was to label a therapeutic dose of zoledronic acid (ZOL) with Tc-99m, evaluate its in vitro stability and compare its biodistribution to (99m)Tc-methylene biphosphonate ((99m)Tc-MDP) in normal rabbits. Preparation of 0.50 mg of (99m)Tc-ZOL was carried out by the reduction of (99m)Tc-pertechnetate in the presence of stannous chloride. The radiolabeling efficiency was found to be greater than 99%. The labeled complex was stable at least up to 6 h at room temperature determined by paper chromatography. (99m)Tc-ZOL and (99m)Tc-MDP were administered intravenously to the rabbits for scintigraphic studies. Between (99m)Tc-ZOL and (99m)Tc-MDP, there were no significant differences in the ratios of femur/BG and lumbar vertebrae/BG, whereas epiphysis/BG and the kidney/BG ratios of (99m)Tc-MDP were higher than (99m)Tc-ZOL at the static studies.

The bisphosphonate zoledronic acid decreases tumor growth in bone in mice with defective osteoclasts

Bisphosphonates (BPs), bone targeted drugs that disrupt osteoclast function, are routinely used to treat complications of bone metastasis. Studies in preclinical models of cancer have shown that BPs reduce skeletal tumor burden and increase survival. Similarly, we observed in the present study that administration of the Nitrogen-containing BP (N-BP), zoledronic acid (ZA) to osteolytic tumor-bearing Tax+ mice beginning at 6 months of age led to resolution of radiographic skeletal lesions. N-BPs inhibit farnesyl diphosphate (FPP) synthase, thereby inhibiting protein prenylation and causing cellular toxicity. We found that ZA decreased Tax+ tumor and B16 melanoma viability and caused the accumulation of unprenylated Rap1a proteins in vitro. However, it is presently unclear whether N-BPs exert anti-tumor effects in bone independent of inhibition of osteoclast (OC) function in vivo. Therefore, we evaluated the impact of treatment with ZA on B16 melanoma bone tumor burden in irradiated mice transplanted with splenic cells from src(-/-) mice, which have non-functioning OCs. OC-defective mice treated with ZA demonstrated a significant 88% decrease in tumor growth in bone compared to vehicle-treated OC-defective mice. These data support an osteoclast-independent role for N-BP therapy in bone metastasis.

[Bisphosphonates for malignant bone tumors]

Bisphosphonates (BPs) are able to prevent, reduce, or delay skeletal complications caused by tumors. Since the introduction of BPs, there has been a marked reduction of skeletal events. Today we can choose from a variety of BPs with different potency, efficacy, dosing, and administration regimens, as well as BPs for different indications. For patients with tumors who have a risk of developing osteoporosis induced by the tumor or antitumor treatment, we should think of prevention. In general, BPs are well tolerated. But there are also side effects: flulike syndrome, arthralgias, or, when administered orally, gastrointestinal symptoms. In a number of cases, the dosing regime must be adjusted according to renal function and baseline creatinine clearance. This paper reviews the current evidence-based use of BPs in solid tumors and the recommendations for treatment.

Effect of zoledronic acid and an antibody against bone sialoprotein II on MDA-MB-231(GFP) breast cancer cells in vitro and on osteolytic lesions induced in vivo by this cell line in nude rats

The aim of this study was to investigate the combined effect of zoledronic acid and an antibody against bone sialoprotein II (BSPII) on proliferation and osteolytic activity of MDA-MB-231(GFP) breast cancer cells. For this purpose, the cells were exposed to zoledronic acid (10-20 microg/ml [25-50 microgM]) and an anti-BSPII IgY (10-100 microg/ml) for up to 5 days alone or in combination. The combined treatment showed synergistic antiproliferative effects at the higher dose of zoledronic acid. Following inoculation of 1 x 10(5) MDA-MB-231 (GFP) breast cancer cells into a branch of the femoral artery of nude rats, lytic lesions developed in the tibia, femur or fibula of the injected hind leg after approximately 30 days. The appearance and development of these lesions were monitored radiographically. Rats with lytic lesions were treated with zoledronic acid (60 microg/kg/week sc x 8; n = 10), zoledronic acid and an anti-BSPII IgY antibody (60 microg/kg/week sc x 8 + 10 mg/kg/week sc x 8; n = 10), or left untreated (n = 20). In addition, rats were treated for 4 weeks (n = 10) with both regimens starting right after tumor cell inoculation. Finally, ten rats were treated with zoledronic acid for 2 weeks before tumor cell inoculation (60 microg/kg/week sc x 2). The antiosteolytic effect of zoledronic acid was high as shown by inhibition of osteolytic growth. Addition of the anti-BSPII IgY further decreased the incidence of femoral osteolytic lesions (40% reduction), indicating remineralization, and reduced periosteal defects of cortical bone (20% reduction). These observations favor using the IgY-antibody in addition to zoledronic acid in order to stimulate osteoblast-induced remineralization.

The role of bisphosphonates in the management of prostate cancer

Current therapies have extended the survival of patients with prostate cancer. However, these patients often develop skeletal morbidity from disease- and treatment-related effects that undermine skeletal integrity throughout the course of the disease. Low bone mineral density (BMD) is prevalent in patients with early-stage prostate cancer, and androgen-deprivation therapy by either pharmaceutical agent (including hormonal) or surgical castration causes significant decreases in BMD. Fractures can result in a loss of independence and have been associated with shorter survival in patients with prostate cancer. Zoledronic acid is the only bisphosphonate that has demonstrated objective and long-term benefits in reducing skeletal morbidity in patients with bone metastases due to prostate cancer, and it has produced long-term reductions in pain levels compared with placebo in this setting. Therefore, bisphosphonates, particularly zoledronic acid, may provide important benefits for preserving bone health during the course of prostate cancer progression.

Myeloma bone disease: pathogenetic mechanisms and clinical assessment

Bone disease in multiple myeloma (MM) leads to progressive devastation of the skeleton and is the most severe cause of morbidity. Its pathogenetic mechanisms are not fully defined, though the current evidence points to hyperactivation of osteoclasts (OC) in presence of a major defect of bone repairing in erosion sites due to osteoblast (OB) impairment. Bone resorption, however, is promoted by early OB, namely stromal cells that respond to chronic stimulation by myeloma cells by enhancing marrow levels of RANKL and other osteoclastogenic factors and thus accelerating the maturation of OC progenitors. In myeloma bone disease (MBD), OBs are systematically defeated by a number of inhibiting effects induced by the malignant clone within the marrow microenvironment. Thus, MBD primarily affects the OB lineage, particularly in overt MM, where serum markers of osteoblastogenesis, such as osteocalcin and osteoprotegerin, are extremely low in contrast with their slight increase in inactive MM. These markers, in association with others of bone turnover (RANKL, MIP-1alpha, type I collagen telopeptides such as NTX and CTX) may be used in the clinical assessment of MBD as well as to monitor the efficacy of bisphosphonate in delaying the progressive skeletal destruction.

The Bisphosphonate YM529 Inhibits Osteolytic and Osteoblastic Changes and CXCR-4–Induced Invasion in Prostate Cancer

Bisphosphonates are useful for the treatment of prostate cancer bone metastasis. However, the role of bisphosphonate on the development of the osteoblastic component of prostate cancer bone metastases is not defined. In the present study, the third-generation bisphosphonate, YM529 (minodoronate), was tested for its effects on the osteolytic PC-3 and novel osteoblastic LNCaP-SF cell lines. YM529 inhibited both osteolytic and osteoblastic changes in an intratibial tumor injection murine model. In vitro, YM529 inhibited both the proliferation and the invasion of both prostate cancer cell lines. The stromal cell-derived factor-1 (or CXCL12)/CXCR-4 pathway is believed to play an important role in the development of prostate cancer bone metastases. Thus, we determined if YM529 affected this pathway. YM529 suppressed CXCR-4 expression in PC-3 and LNCaP-SF in vitro and in vivo and this was associated with decreased in vitro invasion. These results suggest that YM529 may inhibit cancer cell invasion into the bone matrix by repressing the expression of CXCR-4 in bone metastasis lesions.

Clodronate treatment influences MMP-2 associated outcome in node positive breast cancer

PURPOSE

Serum postoperative matrix metalloproteinase 2 (MMP-2) level is a predictor of outcome in node positive breast cancer and can be used to stratify patients into low and high risk groups. Our aim was to determine how clodronate treatment influences MMP-2 associated clinical outcome.

PATIENTS AND METHODS

Women with primary node-positive breast cancer were randomized to control group or to receive oral clodronate for 3 years. Adjuvant chemo- or endocrine therapy was given to all patients. The follow-up time for all patients was 5 years. MMP-2 and MMP-9 levels were quantitatively measured from the serum of 252 patients before and after 1 year clodronate treatment using enzyme-linked immunoassays.

RESULTS

In clodronate-treated patients, postoperative MMP-2 levels did not predict 5-year disease-free survival or overall survival (DFS, in low MMP-2 group (<5.32 ng/ml, median) 53% versus in high MMP-2 group (>median) 63%, p=NS; OS, 68% versus 63%, p=NS). When the patients were grouped according to serum MMP-2 levels, survival rates among patients with low MMP-levels were better in control than clodronate treated patients (DFS, 82% versus 53%, p = 0.003; OS, 91% versus 68%, p=0.014). Among patients with high serum MMP-2 levels, no significant difference in DFS or OS was found between control and clodronate groups. In multivariate analysis of low risk patients, independent predictors for DFS were treatment, age, nodal and PgR status, and those for OS treatment together with nodal and ER status. During 12 months follow-up, MMP-2 levels increased significantly more in clodonate receiving patients than in controls (p = 0.002). In comparison, when the patients were grouped according to MMP-9 levels, clodronate also impaired DFS among patients with low MMP-9 levels (82% versus 53%, p = 0.02), but no influence on OS was observed (83% versus 70%, p = 0.09).

CONCLUSIONS

Clodronate interferes with the prognostic value of serum MMP-2. Clodronate has a negative impact on outcome among patients with low serum MMP-2 and MMP-9 levels, while no such influence is observed among patients with high MMP-2 and MMP-9 levels.

Osteolytic bone diseases: physiological analogues of bone resorption effectors as alternative therapeutic tools

The recent identification of key molecular protagonists involved in osteoclast biology has led to the development of new therapeutic approaches of osteolytic diseases using biological molecules which could compete with bisphosphonate therapy.

Bisphosphonates: preclinical review

Bisphosphonates effectively inhibit osteoclast-mediated bone resorption and are integral in the treatment of benign and malignant bone diseases. The evolution of bisphosphonates over the past 30 years has led to the development of nitrogen-containing bisphosphonates (N-BPs), which have a mechanism of action different from that of the nonnitrogen-containing bisphosphonates. Studies conducted over the past decade have elucidated the mechanism of action and pharmacologic properties of the N-BPs. N-BPs exert their effects on osteoclasts and tumor cells by inhibiting a key enzyme in the mevalonate pathway, farnesyl diphosphate synthase, thus preventing protein prenylation and activation of intracellular signaling proteins such as Ras. Recent evidence suggests that N-BPs also induce production of a unique adenosine triphosphate analogue (Apppi) that can directly induce apoptosis. Our increased understanding of the pharmacologic effects of bisphosphonates is shedding light on the mechanisms by which they exert antitumor effects. As a result of their biochemical effects on protein prenylation, N-BPs induce caspase-dependent apoptosis, inhibit matrix metalloproteinase activity, and downregulate alpha(v)beta(3) and alpha(v)beta(5) integrins. In addition, zoledronic acid (Zometa; Novartis Pharmaceuticals Corp.; East Hanover, NJ and Basel, Switzerland) exerts synergistic antitumor activity when combined with other anticancer agents. Zoledronic acid also inhibits tumor cell adhesion to the extracellular matrix and invasion through Matrigel trade mark and has antiangiogenic activity. A growing body of evidence from animal models demonstrates that zoledronic acid and other bisphosphonates can reduce skeletal tumor burden and prevent metastasis to bone. Further studies are needed to fully elucidate these biochemical mechanisms and to determine if the antitumor potential of bisphosphonates translates to the clinical setting.

Docetaxel and zoledronic acid in patients with metastatic hormone-refractory prostate cancer

OBJECTIVE

To evaluate the safety and efficacy of combined docetaxel-zoledronic acid treatment in patients with metastatic hormone-refractory prostate cancer (HRPC), as bisphosphonates are reported have a synergistic antitumoral effect when combined with taxanes.

PATIENTS AND METHODS

Between January 2001 and June 2003, 14 patients with HRPC were treated; their mean (range) age was 71 (57-86) years and mean prostate-specific antigen (PSA) level 202 (6-489) ng/mL. Five patients had had previous chemotherapy (cyclophosphamide in two, mitoxantrone-prednisolone in three). The response criteria were the Karnofsky performance status, a positive response in mean daily analgesic consumption (defined as a decrease by more than half), decreased serum PSA (by more than half) at 8 weeks, blood transfusion, bone scan at 6 months, skeletal-related events and survival.

RESULTS

Patients received a mean (range) of 7.3 (6-10) cycles of therapy; there was no reported drug-related toxicity and all patients stayed at home for their treatment. Only three patients required a blood transfusion and no bone fractures were reported. At 2 months, six patients requiring analgesic drugs decreased their consumption by more than half (anti-inflammatory, paracetamol, narcotics) and eight had a reduction in PSA by more than half; of these eight with a PSA response at 2 months, six had biochemical progression with a mean delay of 6.2 (3-11) months. At 6 months, five patients had disease progression on bone scan. Nine patients had chemo-naïve hormone-refractory prostate cancer; three had biochemical progression at 2 months and two of these had progression on their bone scan. Two patients died at 7 and 15 months of follow-up; the mean follow-up was 10.2 (6-15) months. Using Kaplan-Meier plots, biochemical progression-free survivals were five of 14 at 6 months and two of 14 at 12 months; overall survival was 12 of 14 at 6 and 12 months.

CONCLUSION

Docetaxel-zoledronic acid therapy is safe and decreased the serum PSA by more than half at 2 months in more than half the patients. Prospective randomized trials are needed to assess this new approach.

Bisphosphonates: new therapeutic agents for the treatment of bone tumors

Bisphosphonates (BPs) have been used successfully for many years to reduce the skeletal complications associated with the benign and malignant bone diseases that are characterized by enhanced osteoclastic bone resorption. Until recently, it was thought that the clinical efficacy of BPs in the treatment of cancer patients with bone metastases was purely a result of the inhibition of osteoclast-mediated bone resorption. However, recent studies have demonstrated that BPs inhibit the growth, attachment and invasion of cancer cells in culture and promote their apoptosis. These results suggest that BPs are also anti-cancer agents, raising the possibility that BPs could inhibit cancer-cell colonization in visceral organs. However, results from clinical trials are conflicting, and whether BPs possess anti-cancer effects or not remains controversial.

The anti-tumor potential of zoledronic acid

Bone is a favorable microenvironment for tumor cell colonization because of abundant growth factors released during active bone resorption. Bisphosphonates can dramatically affect the ability of tumor cells to grow in bone by inhibiting osteoclast-mediated bone resorption and by depriving tumors of growth-promoting signals. Moreover, bisphosphonates have direct anti-tumor effects in vitro via induction of apoptosis. Zoledronic acid is a nitrogen-containing bisphosphonate that has demonstrated potent anti-tumor activity in vitro and in vivo. In vitro studies have provided important clues as to the molecular mechanisms by which zoledronic acid induces apoptosis of human breast cancer cell lines. Studies in multiple myeloma and breast cancer models have shed further light on the possible mechanisms underlying the in vivo anti-tumor effects of zoledronic acid. These studies have led to the development of novel strategies to target specific molecular pathways involved in osteoclast maturation and activity, tumor cell metastasis, and tumor growth and survival. The clinical application of these strategies may ultimately prevent bone metastasis.

Zoledronate sensitizes endothelial cells to tumor necrosis factor-induced programmed cell death: evidence for the suppression of sustained activation of focal adhesion kinase and protein kinase B/Akt

Bisphosphonates are potent inhibitors of osteoclast function widely used to treat conditions of excessive bone resorption, including tumor bone metastases. Recent evidence indicates that bisphosphonates have direct cytotoxic activity on tumor cells and suppress angiogenesis, but the associated molecular events have not been fully characterized. In this study we investigated the effects of zoledronate, a nitrogen-containing bisphosphonate, and clodronate, a non-nitrogen-containing bisphosphonate, on human umbilical vein endothelial cell (HUVEC) adhesion, migration, and survival, three events essential for angiogenesis. Zoledronate inhibited HUVEC adhesion mediated by integrin alphaVbeta3, but not alpha5beta1, blocked migration and disrupted established focal adhesions and actin stress fibers without modifying cell surface integrin expression level or affinity. Zoledronate treatment slightly decreased HUVEC viability and strongly enhanced tumor necrosis factor (TNF)-induced cell death. HUVEC treated with zoledronate and TNF died without evidence of enhanced annexin-V binding, chromatin condensation, or nuclear fragmentation and caspase dependence. Zoledronate inhibited sustained phosphorylation of focal adhesion kinase (FAK) and in combination with TNF, with and without interferon (IFN) gamma, of protein kinase B (PKB/Akt). Constitutive active PKB/Akt protected HUVEC from death induced by zoledronate and TNF/IFNgamma. Phosphorylation of c-Src and activation of NF-kappaB were not affected by zoledronate. Clodronate had no effect on HUVEC adhesion, migration, and survival nor did it enhanced TNF cytotoxicity. Taken together these data demonstrate that zoledronate sensitizes endothelial cells to TNF-induced, caspase-independent programmed cell death and point to the FAK-PKB/Akt pathway as a novel zoledronate target. These results have potential implications to the clinical use of zoledronate as an anti-angiogenic or anti-cancer agent.

Rationale for the use of bisphosphonates in osteoblastic and osteolytic bone lesions

Various primary malignancies develop bone metastases, and the resultant skeletal complications cause significant morbidity/mortality in advanced cancer patients. Bone lesions associated with metastases are traditionally classified radiologically as either osteolytic or osteoblastic, and both types of lesions are associated with elevated levels of specific bone resorption markers. Some common aspects in the pathophysiology of bone lesions have prompted speculation that treatments for osteolytic metastases might also be effective for predominantly osteoblastic metastases, such as in prostate cancer. Potent osteoclast activity inhibitors, bisphosphonates have been successful in the treatment of osteolytic tumor bone disease. Zoledronic acid is the first bisphosphonate shown to have a direct clinical benefit in the treatment of osteoblastic bone metastases, reducing the number and rate of skeletal events in prostate cancer patients with metastatic bone disease. Moreover, the shorter, more convenient infusion time and similar safety profile of 4 mg zoledronic acid compared with 90 mg pamidronate presently make zoledronic acid the preferred therapy for treatment of bone metastases in patients with all types of advanced malignancy.

Future directions in the treatment and prevention of bone metastases

Preclinical studies are providing a growing body of evidence that bisphosphonates, particularly nitrogen-containing bisphosphonates, have antitumor activity. Bisphosphonates induce tumor cell apoptosis and reduce skeletal tumor burden in tumor xenograft models. Clinical studies with daily oral clodronate suggest that bisphosphonates can prevent bone metastases when used in the adjuvant setting, but the effect on overall survival is less certain. The more potent nitrogen-containing bisphosphonates, i.e., pamidronate and zoledronic acid, have demonstrated antitumor activity at approximately 10- to 100-fold lower concentrations than clodronate in vitro. A number of important unanswered questions must be addressed regarding the optimal use of bisphosphonates for prevention of bone metastases. For example, when should treatment begin, how long must treatment be continued, and what are the optimal dose and schedule to achieve clinically meaningful antitumor effects? Adjuvant studies of zoledronic acid in patients with breast and prostate cancer are under development, and the results are eagerly anticipated.