Mechanisms of disease: Preclinical reports of antineoplastic synergistic action of bisphosphonates

A multifaceted role of bisphosphonates from palliative care to anti-cancer therapy in solid tumors

INTRODUCTION

Bisphosphonates (P-C-Ps) also called diphosphonates are the structural analogs of naturally occurring pyrophosphates. Bisphosphonates are traditionally used and shown to provide long-term success in the treatment and prevention of osteoporosis and other bone loss pathologies. Furthermore, bisphosphonates are gaining popularity in the present era of cancer therapeutics and prevention. The usage of bisphosphonates as adjuvant or neoadjuvant therapy, either as a single agent or combined with other chemotherapy, has been studied in different solid tumors. This review aims to present the various roles of bisphosphonates in solid tumors.

DATA SOURCES

Articles in MEDLINE/PubMed and the National Institutes of Health Clinical Trials Registry (http://www. Clinicaltrials.gov) between 1 January 2011 and 1 February 2022 were extracted using MeSH terms "bisphosphonates/diphosphosphonates and mechanism," "bisphosphonates and breast cancer," "bisphosphonates and prostate cancer," "bisphosphonates and lung cancer," "bisphosphonates and cancer risk," and "bisphosphonates and adverse events." Manual searches of some major oncology journals were also conducted.

DISCUSSION

This review article focuses on the antitumor activity of bisphosphonates, safety profile, and the role of bisphosphonates as preventive, neoadjuvant, and adjuvant chemotherapy. A significant improvement in overall survival and cancer-specific survival and recurrence-free survival with the usage of bisphosphonates is noted in breast cancer patients, particularly in post-menopausal women. Though great progress has been achieved in over 20 years, further research is needed to identify the subgroup of patients that are most likely to benefit from adjuvant bisphosphonate therapy and to determine regimens with greater efficacy and better safety profile.

Targeted Drug Delivery for the Treatment of Blood Cancers

Blood cancers are a type of liquid tumor which means cancer is present in the body fluid. Multiple myeloma, leukemia, and lymphoma are the three common types of blood cancers. Chemotherapy is the major therapy of blood cancers by systemic administration of anticancer agents into the blood. However, a high incidence of relapse often happens, due to the low efficiency of the anticancer agents that accumulate in the tumor site, and therefore lead to a low survival rate of patients. This indicates an urgent need for a targeted drug delivery system to improve the safety and efficacy of therapeutics for blood cancers. In this review, we describe the current targeting strategies for blood cancers and recently investigated and approved drug delivery system formulations for blood cancers. In addition, we also discuss current challenges in the application of drug delivery systems for treating blood cancers.

Biology, pathology, and therapeutic targeting of RAS

RAS was identified as a human oncogene in the early 1980s and subsequently found to be mutated in nearly 30% of all human cancers. More importantly, RAS plays a central role in driving tumor development and maintenance. Despite decades of effort, there remain no FDA approved drugs that directly inhibit RAS. The prevalence of RAS mutations in cancer and the lack of effective anti-RAS therapies stem from RAS' core role in growth factor signaling, unique structural features, and biochemistry. However, recent advances have brought promising new drugs to clinical trials and shone a ray of hope in the field. Here, we will exposit the details of RAS biology that illustrate its key role in cell signaling and shed light on the difficulties in therapeutically targeting RAS. Furthermore, past and current efforts to develop RAS inhibitors will be discussed in depth.

Molecular recognition of bisphosphonate-based drugs by di-zinc receptors in aqueous solution and on gold nanoparticles

Metal-based anion receptors have several important applications in sensing, separation and transport of negatively charged species. Amongst these receptors, di-zinc(ii) complexes are of particular interest for the recognition of oxoanions, in particular phosphate derivatives. Herein we report the synthesis of a di-zinc(ii) receptor and show that it has high affinity and selectivity for bisphosphonates such as alendronate and etidronate - which are used to treat a number of skeletal disorders as well as showing interesting anticancer properties. The binding mode of the di-zinc(ii) receptor with alendronate and etidronate has been unambiguously established by single crystal X-ray crystallography. In addition, by modifying the backbone of the receptor, we show that the drug-loaded receptor can be attached onto gold nanoparticles as potential drug-delivery vehicles.

Therapeutic targeting of RAS: New hope for drugging the "undruggable"

RAS is the most frequently mutated oncogene in cancer and a critical driver of oncogenesis. Therapeutic targeting of RAS has been a goal of cancer research for more than 30 years due to its essential role in tumor formation and maintenance. Yet the quest to inhibit this challenging foe has been elusive. Although once considered "undruggable", the struggle to directly inhibit RAS has seen recent success with the development of pharmacological agents that specifically target the KRAS(G12C) mutant protein, which include the first direct RAS inhibitor to gain entry to clinical trials. However, the limited applicability of these inhibitors to G12C-mutant tumors demands further efforts to identify more broadly efficacious RAS inhibitors. Understanding allosteric influences on RAS may open new avenues to inhibit RAS. Here, we provide a brief overview of RAS biology and biochemistry, discuss the allosteric regulation of RAS, and summarize the various approaches to develop RAS inhibitors.

Bisphosphonates-much more than only drugs for bone diseases

α,α-Bisphosphonates (BPs) are well established in the treatment of bone diseases such as osteoporosis and Paget's disease. Their successful application originates from their high affinity to hydroxyapatite. While the initially appreciated features of BPs are already beneficial to many patients, recent developments have further expanded their pleiotropic applications. This review describes the background of the interactions of BPs with bone cells that form the basis of the classical treatment. A better understanding of the mechanism behind their interactions allows for the parallel application of BPs against bone cancer and metastases followed by palliative pain relief. Targeted therapy with bone-seeking BPs coupled with a diagnostic agent in one particle resulted in theranostics which is also described here. For example, in such a system, BP moieties are bound to contrast agents used in magnetic resonance imaging or radionuclides used in positron emission tomography. In addition, another example of the pleiotropic function of BPs which involves targeting the imaging agents to bone tissues accompanied by pain reduction is presented in this work.

Prognostic Effect of Bisphosphonate Exposure for Patients With Diagnosed Solid Cancer: A Systematic Review With Meta-Analysis of Observational Studies

Background: Bisphosphonates are widely prescribed for the prevention and treatment of osteoporosis. Recent epidemiological studies indicate that people with bisphosphonate use may have lower cancer risk and have improved survival. The aim of this study is to determine the association between bisphosphonate use and survival outcomes in solid cancer patients using systematic review and meta-analysis.

Methods: A systematic literature search was performed using the PubMed, Embase, and Cochrane databases. Original articles published until April, 2018 were selected. The survival outcome measures assessed included overall survival (OS), cancer-specific survival (CSS) and recurrence-free survival (RFS). Pooled hazard ratio (HR) and their 95% confidence interval (95% CI) were derived using a random-effects model.

Results: Out of 9,742 retrieved citations, six cohort studies and two nested case-control studies satisfying the inclusion criteria were included for analyses. Bisphosphonate use was significantly associated with improved OS (HR 0.84, 95% CI 0.76–0.93), CSS (HR 0.73, 95% CI 0.58–0.90) and RFS (HR 0.72, 95% CI 0.53–0.96). The results of subgroup analyses stratified by major study characteristics were generally consistent with the main findings. For individual cancer type, we found that bisphosphonate use was significantly associated with longer OS for patients with gastroesophageal cancer (HR 0.62, 95% CI 0.40–0.98), as well as longer CSS for patients with breast cancer (HR 0.73, 95% CI 0.55–0.95).

Conclusions: Current evidence indicates that bisphosphonate use is significantly associated with improved survival for patients with solid cancer. However, the prognostic effects in specific solid tumors remains to be confirmed by further large prospective cohort studies.

Zoledronic acid enhances the efficacy of the MEK inhibitor trametinib in KRAS mutant cancers

KRAS mutation is the most common type of mutation in human cancers. However, the direct pharmacological inhibition of KRAS has not been clinically successful. Trametinib (GSK1120212, Tram), a newer MEK inhibitor, inhibits RAS signaling through mitogen-activated protein kinase (MAPK) cascade suppression. The effectiveness of Tram in clinical practice is limited in KRAS mutant tumors compared to that in BRAF mutant tumors. Here, we found that Tram treatment provoked feedback activation of upstream RAS, thus causing an induction of phosphorylated MEK (pMEK) and phosphorylated ERK (pERK) rebound in KRAS mutant tumors. This failure of persistent ERK inhibition led to drug resistance. Zoledronic acid (ZA), a nitrogen-containing bisphosphonate, disrupts the biological activity of RAS by inhibiting its isoprenylation. Surprisingly, ZA overcame Tram resistance, and augmented antitumor activity was observed in KRAS mutant tumors both in vitro and in vivo. Furthermore, ZA enhanced the effect of Tram partially through the mevalonate pathway. In summary, the combination of the two FDA-approved drugs Tram and ZA may represent a novel therapeutic strategy for the treatment of KRAS mutant cancers.

FPPS mediates TGF-β1-induced non-small cell lung cancer cell invasion and the EMT process via the RhoA/Rock1 pathway

Farnesyl pyrophosphate synthase (FPPS), a key enzyme in the mevalonate pathway, was recently shown to play a role in cancer progression. However, its role in non-small cell lung cancer (NSCLC) metastasis and the underlying mechanism remain unclear. In this study, FPPS expression was significantly correlated with TNM stage, and metastasis. Inhibition or knockdown of FPPS blocked TGF-β1-induced cell invasion and epithelial-to-mesenchymal transition (EMT) process. FPPS expression of FPPS was induced by TGF-β1 and FPPS promoted cell invasion and EMT via the RhoA/Rock1 pathway. In conclusion, FPPS mediates TGF-β1-induced lung cancer cell invasion and EMT via the RhoA/Rock1 pathway. These findings suggest new treatment strategies to reduce mortality associated with metastasis in patients with NSCLC.

Physiologic Activity of Bisphosphonates – Recent Advances

Background:

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

Objective:

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

Method:

Critical review of recent literature data.

Results:

Comprehensive review of activities revealed by bisphosphonates.

Conclusion:

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

Proteomic analysis of zoledronic-acid resistant prostate cancer cells unveils novel pathways characterizing an invasive phenotype

Proteomic analysis identified differentially expressed proteins between zoledronic acid-resistant and aggressive DU145R80 prostate cancer (PCa) cells and their parental DU145 cells. Ingenuity Pathway Analysis (IPA) showed a strong relationship between the identified proteins within a network associated with cancer and with homogeneous cellular functions prevalently related with regulation of cell organization, movement and consistent with the smaller and reduced cell-cell contact morphology of DU145R80 cells. The identified proteins correlated in publically available human PCa genomic data with increased tumor expression and aggressiveness. DU145R80 exhibit also a clear increase of alpha-v-(αv) integrin, and of urokinase receptor (uPAR), both included within the same network of the identified proteins. Interestingly, the actin-rich structures localized at the cell periphery of DU145R80 cells are rich of Filamin A, one of the identified proteins and uPAR which, in turn, co-localizes with αv-integrin, in podosomes and/or invadopodia. Notably, the invasive feature of DU145R80 may be prevented by blocking anti-αv antibody. Overall, we unveil a signaling network that physically links the interior of the nucleus via the cytoskeleton to the extracellular matrix and that could dictate PCa aggressiveness suggesting novel potential prognostic markers and therapeutic targets for PCa patients.

Bisphosphonates for cancer treatment: Mechanisms of action and lessons from clinical trials

A growing body of evidence points toward an important anti-cancer effect of bisphosphonates, a group of inexpensive, safe, potent, and long-term stable pharmacologicals that are widely used as osteoporosis drugs. To date, they are already used in the prevention of complications of bone metastases. Because the bisphosphonates can also reduce mortality in among other multiple myeloma, breast, and prostate cancer patients, they are now thoroughly studied in oncology. In particular, the more potent nitrogen-containing bisphosphonates have the potential to improve prognosis. The first part of this review will elaborate on the direct and indirect anti-tumoral effects of bisphosphonates, including induction of tumor cell apoptosis, inhibition of tumor cell adhesion and invasion, anti-angiogenesis, synergism with anti-neoplastic drugs, and enhancement of immune surveillance (e.g., through activation of γδ T cells and targeting macrophages). In the second part, we shed light on the current clinical position of bisphosphonates in the treatment of hematological and solid malignancies, as well as on ongoing and completed clinical trials investigating the therapeutic effect of bisphosphonates in cancer. Based on these recent data, the role of bisphosphonates is expected to further expand in the near future outside the field of osteoporosis and to open up new avenues in the treatment of malignancies.

Effects of bisphosphonate zoledronic acid in hepatocellular carcinoma, depending on mevalonate pathway

BACKGROUND AND AIM

Zoledronic acid (ZOL) is a nitrogen-containing bisphosphonate and is used to reduce cancer-induced osteolysis. We reported previously that ZOL delayed both the growth and pain progression of bone metastases from hepatocellular carcinoma. The present study was designed to evaluate the effects of ZOL on hepatoma cell lines and the molecular mechanisms of such effects.

METHODS

Cell viability assay, scratch assay, immunohistochemistry, Western blotting, and flow cytometry analysis were performed using Huh7 and HepG2 cells treated with and without ZOL.

RESULTS

ZOL reduced cell growth in a dose-dependent manner and prevented cell migration when used at a concentration exceeding 10 μM. Immunohistochemistry showed that the inhibitory effects of ZOL on hepatoma cell progression was not due to the suppression of Ras and RhoA expression but due to inhibition of their translocation from the cytosol to the cell membrane, which terminates mevalonate pathway. Immunoblotting and flow cytometry showed that ZOL inhibited the mitogen-activated protein kinase pathway (MAPK) and induced apoptosis of hepatoma cells.

CONCLUSIONS

Our results indicated that ZOL prevented cell growth and metastasis based on direct antitumor effects in hepatoma cells. The use of ZOL could not only suppress the progression to bone metastatic lesions but also prevented growth of primary hepatocellular carcinoma.

[Management of bone metastases]

The skeleton is the most common site to be affected by advanced breast, prostatic, lung, kidney, thyroid and other solid tumors (in addition to myeloma multiplex). Bone metastases cause significant morbidity with nearly always fatal outcome. Over 600 000 new patients diagnosed in the developed countries yearly. On average every 4-6 months patients suffer from series of severe skeletal complications such as pathologic fractures, spinal cord compression, hypercalcemic events, etc., besides the permanent pain. Local external beam radiotherapy, systemic radioisotope-, endocrine-, and chemotherapy, oral and i.v. bisphosphonates and recently s.c. denosumab are the mainstays of treatment, in addition to pain-killers and other usual "classical" interventions. The modern treatments singificantly reduce the probability of skeletal complications and improve the patients' quality of life and, sometimes, they extend the survival as well. The authors briefly summarize the available treatment options.

Adjuvant zoledronic acid therapy for patients with early stage breast cancer: an updated systematic review and meta-analysis

BACKGROUND

Zoledronic acid is a potent inhibitor of osteoclast-mediated bone resorption and has been widely used in bone metastasis malignancies and postmenopausal osteoporosis as a preventive therapy against skeletal-related events. The purpose of this study was to evaluate the clinical outcome of zoledronic acid as an adjuvant therapy for patients with early stage breast cancer.

PATIENTS AND METHODS

Entries in the PubMed and EMBASE databases up to 12 July 2013 were systematically reviewed. Online abstracts from the proceedings of the Annual Meetings of the American Society of Clinical Oncology (ASCO) (1992-2013) and the San Antonio Breast Cancer Symposium (SABCS) (2004-2013) were also reviewed. Primary endpoints included overall survival (OS) and disease-free survival (DFS), while secondary endpoints included bone metastasis-free survival (BMFS), distant metastasis-free survival (DMFS), and fracture-free rate (FFR).

RESULTS

A total of eight studies including 3,866 subjects and 3,864 controls met our search criteria and were evaluated. The use of zoledronic acid was found to improve OS (relative risk (RR), 0.88; 95% confidence interval (CI), 0.77-1.01; p-value = 0.06) and DMFS (RR, 0.77; 95% CI, 0.60-1.00; p-value = 0.05). Furthermore, statistically significant benefits were associated with BMFS (RR, 0.81; 95% CI, 0.66-0.99; p-value = 0.04) and FFRs (RR, 0.75; 95% CI, 0.61-0.92; p-value = 0.007). In contrast, there was no significant difference in DFS with the application of zoledronic acid (RR, 0.88; 95% CI, 0.72-1.09; p-value = 0.24). Sensitivity analysis further identified the improvement of 5-year OS for the adjuvant zoledronic acid therapy in early stage breast cancer patients (RR, 0.86; 95% CI, 0.75-0.99; p-value = 0.03), while a borderline statistically significant benefit was observed for 5-year DFS (RR, 0.90; 95% CI, 0.81-1.00; p-value = 0.06).

CONCLUSION

Zoledronic acid as an adjuvant therapy appears to improve the 5-year OS rate for early stage breast cancer patients, and was associated with a protective effect for the bone metastases and fractures evaluated in more than 7,000 patients. However, further research is needed to confirm our findings, and sub-group analyses according to menopause status or hormone status may provide further insight.

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

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

Hyaluronan synthesis inhibitor supplements the inhibitory effects of zoledronic acid on bone metastasis of lung cancer

Hyaluronan is known to have pivotal roles in the growth, migration and invasion of malignant tumors. Bone metastases are critical lesions greatly impairing the quality of patients with malignancies. We investigated whether hyaluronan synthesis inhibitor supplements the inhibitory effects of zoledronic acid, which is a conventional therapeutic agent for bone metastasis. We examined the effects of methylumbelliferone, an inhibitor of hyaluronan synthesis and/or ZA on the tumorigenicity of one murine lung carcinoma and two human (A549, SK-MES-1) lung cancer cell lines in vitro. The interaction between methylumbelliferone and zoledronic acid was analyzed using Calcucyn software. With a murine bone metastasis model of lung cancer in vivo, we investigated the inhibitory effects and interaction of the two drugs on the progression of metastatic bone lesions. Methylumbelliferone or zoledronic acid treatment individually suppressed proliferation, migration and invasion of 3 cell lines, and combination treatment showed synergistic effects. Although methylumbelliferone as a single agent did not enhance apoptotic activity, it showed additive effects on apoptotic activity to those of zoledronic acid. Co-localization of CD44 and ezrin, which might be a pathway of hyaluronan signaling, was abrogated by methylumbelliferone treatment. Combination therapy showed additive inhibitory effects on metastatic bone lesions in vivo, which paralleled the inhibition of hyaluronan accumulation by methylumbelliferone, and inhibition of osteoclastogenesis. Although the detailed mechanisms underlying the synergistic or additive inhibitory effects of these two drugs should be further analyzed, inhibition of hyaluronan synthesis by methylumbelliferone is a promising novel therapeutic candidate for bone metastasis of lung cancer in addition to zoledronic acid.

Geranylgeranyl diphosphate synthase: an emerging therapeutic target

Proteins modified post-translationally by geranylgeranylation have been implicated in numerous cellular processes related to human disease. In recent years, the study of protein geranylgeranylation has advanced tremendously in both cellular and animal models. The advances in our understanding of the biological roles of geranylgeranylated proteins have been paralleled by advances in the medicinal chemistry of geranylgeranylation inhibitors such as those that target geranylgeranyl transferases I and II and geranylgeranyl diphosphate synthase (GGDPS). Although these findings provide the rationale for further development of geranylgeranylation as a therapeutic target, more advanced studies on the efficacy of this approach in various disease models will be required to support translation to clinical studies. This article attempts to describe the advances in (and the challenges of) validation of GGDPS as a novel therapeutic target and assesses the advantages of targeting GGDPS relative to other enzymes involved in geranylgeranylation.

Models for anti-tumor activity of bisphosphonates using refined topochemical descriptors

An in silico approach comprising of decision tree (DT), random forest (RF) and moving average analysis (MAA) was successfully employed for development of models for prediction of anti-tumor activity of bisphosphonates. A dataset consisting of 65 analogues of both nitrogen-containing and non-nitrogen-containing bisphosphonates was selected for the present study. Four refinements of eccentric distance sum topochemical index termed as augmented eccentric distance sum topochemical indices 1-4 [formula: see text] have been proposed so as to significantly augment discriminating power. Proposed topological indices (TIs) along with the exiting TIs (>1,400) were subsequently utilized for development of models for prediction of anti-tumor activity of bisphosphonates. A total of 43 descriptors of diverse nature, from a large pool of molecular descriptors, calculated through E-Dragon software (version 1.0) and an in-house computer program were selected for development of suitable models by employing DT, RF and MAA. DT identified two TIs as most important and classified the analogues of the dataset with an accuracy of 97% in training set and 90.7% in tenfold cross-validated set. Random forest correctly classified the analogues with an accuracy of 89.2%. Four independent models developed through MAA predicted the activity of analogues of the dataset with an accuracy of 87.6% to 89%. The statistical significance of proposed models was assessed through intercorrelation analysis, specificity, sensitivity and Matthew's correlation coefficient. The proposed models offer a vast potential for providing lead structures for development of potent anti-tumor agents for treatment of cancer that has spread to the bone.

Peritoneal carcinomatosis from ovarian cancer: chemosensitivity test and tissue markers as predictors of response to chemotherapy

Background

Platinum-based regimens are the treatments of choice in ovarian cancer, which remains the leading cause of death from gynecological malignancies in the Western world. The aim of the present study was to compare the advantages and limits of a conventional chemosensitivity test with those of new biomolecular markers in predicting response to platinum regimens in a series of patients with peritoneal carcinomatosis from ovarian cancer.

Methods

Fresh surgical biopsy specimens were obtained from 30 patients with primary or recurrent peritoneal carcinomatosis from ovarian cancer. ERCC1, GSTP1, MGMT, XPD, and BRCA1 gene expression levels were determined by Real-Time RT-PCR. An in vitro chemosensitivity test was used to define a sensitivity or resistance profile to the drugs used to treat each patient.

Results

MGMT and XPD expression was directly and significantly related to resistance to platinum-containing treatment (p = 0.036 and p = 0.043, respectively). Significant predictivity in terms of sensitivity and resistance was observed for MGMT expression (75.0% and 72.5%, respectively; p = 0.03), while high predictivity of resistance (90.9%) but very low predictivity of sensitivity (37.5%) (p = 0.06) were observed for XPD. The best overall and significant predictivity was observed for chemosensitivity test results (85.7% sensitivity and 91.3% resistance; p = 0.0003).

Conclusions

The in vitro assay showed a consistency with results observed in vivo in 27 out of the 30 patients analyzed. Sensitivity and resistance profiles of different drugs used in vivo would therefore seem to be better defined by the in vitro chemosensitivity test than by expression levels of markers.

Anti-tumour activity of bisphosphonates in preclinical models of breast cancer

There is increasing evidence of anti-tumour effects of bisphosphonates from pre-clinical studies, supporting a role for these drugs beyond their traditional use in treatment of cancer-induced bone disease. A range of model systems have been used to investigate the effects of different bisphosphonates on tumour growth, both in bone and at peripheral sites. Most of these studies conclude that bisphosphonates cause a reduction in tumour burden, but that early intervention and the use of high and/or repeated dosing is required. Successful eradication of cancer may only be achievable by targeting the tumour cells directly whilst also modifying the tumour microenvironment. In line with this, bisphosphonates are demonstrated to be particularly effective at reducing breast tumour growth when used in combination with agents that directly target cancer cells. Recent studies have shown that the effects of bisphosphonates on breast tumours are not limited to bone, and that prolonged anti-tumour effects may be achieved following their inclusion in combination therapy. This has opened the field to a new strand of bisphosphonate research, focussed on elucidating their effects on cells and components of the local, regional and distal tumour microenvironment. This review highlights the recent developments in relation to proposed anti-tumour effects of bisphosphonates reported from in vitro and in vivo models, and summarises the data from key breast cancer studies. Evidence for effects on different processes and cell types involved in cancer development and progression is discussed, and the main outstanding issues identified.

[Molecular basis of bone metastasis formation and its targeted therapy]

Formation of bone metastasis is a hallmark of the progression of several solid cancers, providing example for the organ specificity of the process. Bone metastasis may result in both venous and arterial dissemination. Though the molecular basis of the lytic and plastic bone metastasis formation is different, in reality these organ metastases represent a mixture of the two processes. The basis of bone metastasis formation is the activation of osteoclasts and the resulting bone resorption, initiating a vicious circle by activating the initiator cancer cell. The discovery of osteoclast-bone matrix interaction inhibitor bisphosphonates revolutionized the therapy of bone metastasis. Clarifying the molecular pathways involved in bone metastasis formation identified osteoclast differentiation as another feasible target. This process is under control of the TNF receptor family member RANK and its ligand RANKL. The feasibility of using this system to control bone resorption or cancer-induced skeletal events was proven clinically in trials using an anti-RANKL antibody. The clinical success of anti-RANKL antibody therapy provide further evidence that only precise identification of molecular pathways operational in cancers can lead to discovery of more effective (targeted) therapies.

The effects of adding zoledronic acid to neoadjuvant chemotherapy on tumour response: exploratory evidence for direct anti-tumour activity in breast cancer

Background:

Pre-clinical studies have demonstrated synergistic anti-tumour effects of chemotherapy (CT) and zoledronic acid (ZOL). Within the AZURE trial, designed to determine whether the addition of ZOL to neoadjuvant therapy improves disease outcomes, a subgroup received neoadjuvant CT. We report a retrospective evaluation comparing pathological response in the primary tumour between treatment groups.

Methods:

In total, 205 patients received neoadjuvant CT±ZOL (CT+ZOL, n=102; CT, n=103). The primary end point was pathologically assessed residual invasive tumour size (RITS) at surgery. Secondary end points were pathological complete response (pCR) rate and axillary nodal involvement. Following review of surgical pathology reports (n=195), outcome differences between groups were assessed adjusting for potential response modifiers.

Results:

Baseline characteristics and CT treatments were similar. In multivariate analysis, allowing for biological and clinical factors known to influence tumour response, the adjusted mean RITS in CT and CT+ZOL groups were 27.4 and 15.5 mm, respectively, giving a difference in means of 12 mm (95% confidence interval: 3.5–20.4 mm; P=0.006). The pCR rate was 6.9% in the CT group and 11.7% in the CT+ZOL group (P=0.146). There was no difference in axillary nodal involvement (P=0.6315).

Conclusion:

These data suggest a possible direct anti-tumour effect of ZOL in combination with CT, warranting formal evaluation in prospective studies.

Preserving functional independence in elderly patients with cancer-associated bone disease: the role of zoledronic acid

Increases in life expectancy in the developed world will inevitably lead to larger numbers of elderly patients with cancer-associated (malignant) bone disease. Most elderly patients with metastatic cancer also suffer from numerous comorbidities. The management of bone health in this setting requires special consideration. This article centers on malignant bone disease in the elderly and the role of bisphosphonates in geriatric oncology. The challenges involved in the treatment of older patients with bone metastases are described, and the potential utility of bisphosphonates, such as zoledronic acid, is discussed. Moreover, recent data from several large clinical trials suggest that zoledronic acid provides additional benefits, including antitumor effects that may extend beyond the preservation of bone health and prevention of skeletal-related events.

Higher incidence of Osteonecrosis of the Jaw (ONJ) in patients with metastatic castration resistant prostate cancer treated with anti-angiogenic agents

ONJ is an important toxicity in cancer patients receiving bisphosphonate therapy. Here we report a higher than usual incidence of ONJ, 11 of 60 (18.3%, 95% Confidence Interval, CI: 9%-28%) patients enrolled in a phase II clinical trial combining bevacizumab, docetaxel, thalidomide, and prednisone (ATTP) in chemotherapy-naive men with metastatic castration resistant prostate cancer (mCRPC). The use of bisphosphonates was allowed at study entry. Our study suggests that anti-angiogenic and chemotherapy agents can predispose to the development of ONJ in men with mCRPC on zoledronic acid. Imaging modalities, such as bone scans, may be useful in following the clinical course of patients who develop ONJ.

Exploring the anti-tumour activity of bisphosphonates in early breast cancer

Bisphosphonates are potent inhibitors of osteoclast-mediated bone resorption and are firmly established in the management of breast cancer patients with metastatic skeletal disease. There are extensive data that bisphosphonates, particularly nitrogen-containing bisphosphonates such as zoledronic acid, exhibit anti-tumour activity potentially via both indirect and direct mechanisms in vitro. In vivo studies using animal models of breast cancer induced bone disease have shown that bisphosphonates exert anti-tumour effects via inhibiting osteolysis and reducing skeletal tumour burden. Furthermore, pre-clinical studies have demonstrated synergistic anti-tumour effects between chemotherapy agents commonly used in breast cancer treatment and nitrogen-containing bisphosphonates. This, coupled with emerging evidence from pre-clinical in vivo studies suggesting that bisphosphonates may have additional anti-tumour activity outside of the bone microenvironment, could be of significant importance in the clinical management of breast cancer. The evidence in favour of an anti-tumour effect of bisphosphonates in the clinical setting is inconclusive however, with conflicting evidence from several trials. This review focuses on the anti-tumour activity of bisphosphonates in breast cancer, with particular focus on zoledronic acid. The pre-clinical evidence for anti-tumour activity will be reviewed, followed by the synergistic effects with anti-cancer agents. Finally, the clinical relevance and strategies for the evaluation of anti-tumour activity in breast cancer will be discussed. We are currently exploring the potential synergistic anti-tumour effects of the sequential treatment of neoadjuvant chemotherapy followed by zoledronic acid in a randomised phase II study evaluating biological endpoints including apoptosis, proliferation and angiogenesis in patients with breast cancer.

Antitumor effects of doxorubicin followed by zoledronic acid in a mouse model of breast cancer

BACKGROUND

The potent antiresorptive drug zoledronic acid (Zol) enhances the antitumor effects of chemotherapy agents in vitro. We investigated the effects of clinically achievable doses of doxorubicin (Dox) and Zol, given alone, in sequence, and in combination, on the growth of established breast tumors in vivo.

METHODS

Female MF1 nude mice were inoculated subcutaneously with 5 x 10(5) human breast cancer MDA-MB-436 cells that stably expressed green fluorescent protein (ie, MDA-G8 cells). Beginning on day 7 after tumor cell injection, the mice were injected weekly for 6 weeks with saline, Dox (2 mg/kg body weight via intravenous injection), Zol (100 microg/kg body weight via intraperitoneal injection), Dox plus Zol, Zol followed 24 hours later by Dox, or Dox followed 24 hours later by Zol (n = 8-9 mice per group). The effects of treatment on tumor growth were determined by measuring tumor volume; on tumor cell apoptosis and proliferation by immunohistochemistry using antibodies for caspase-3 and Ki-67, respectively; and on bone by microcomputed tomography and bone histomorphometry. All P values are two-sided.

RESULTS

Treatment with Dox or Zol alone or Zol followed 24 hours later by Dox did not statistically significantly decrease final tumor volume compared with saline. Mice treated with Dox plus Zol had statistically significantly smaller final tumor volumes than those treated with Dox alone (mean = 122 mm(3) vs 328 mm(3), difference = 206 mm(3), 95% confidence interval [CI] = 78 to 335 mm(3), P < .001), with Zol alone (122 mm(3) vs 447 mm(3), difference = 325 mm(3), 95% CI = 197 to 454 mm(3), P < .001), or with Zol followed 24 hours later by Dox (122 mm(3) vs 418 mm(3), difference = 296 mm(3), 95% CI = 168 to 426 mm(3), P < .001). Treatment with Dox followed 24 hours later by Zol almost completely abolished tumor growth. Tumors from mice that were treated with Dox followed by Zol had more caspase-3-positive cells than tumors from mice treated with saline (mean number of caspase-3-positive cells per square millimeter: 605.0 vs 82.19, difference = 522.8, 95% CI = 488.2 to 557.4, P < .001), with Zol alone (605.0 vs 98.44, difference = 506.6, 95% CI = 472.0 to 541.2, P < .001), or with Zol followed by Dox (605.0 vs 103.1, difference = 501.9, 95% CI = 467.3 to 536.5, P < .001). The treatment-induced increase in the number of caspase-3-positive cells was mirrored by a decrease in the number of tumor cells positive for the proliferation marker Ki-67. No evidence of bone disease was detected in any of the treatment groups following microcomputed tomography and histological analysis of bone.

CONCLUSION

Sequential treatment with Dox followed by Zol elicited substantial antitumor effects in subcutaneous breast tumors in vivo, in the absence of bone disease.

Inhibition of geranylgeranyl diphosphate synthase induces apoptosis through multiple mechanisms and displays synergy with inhibition of other isoprenoid biosynthetic enzymes

Inhibitors of isoprenoid synthesis are widely used for treatment of human diseases, including hypercholesterolemia and osteoporosis, and they have the potential to be useful for treatment of cancer. Statin drugs inhibit the enzyme HMG-CoA reductase, whereas nitrogenous bisphosphonates have more recently been shown to inhibit farnesyl disphosphate synthase. In addition, our laboratory has recently developed several potent and specific bisphosphonate inhibitors of geranylgeranyl diphosphate synthase, including digeranyl bisphosphonate. Because all three enzymes fall in the same biosynthetic pathway and many of the biological effects are due to depletion of downstream products, we hypothesized that simultaneous inhibition of these enzymes would result in synergistic growth inhibition. In this study, we show that inhibition of geranylgeranyl diphosphate synthase induces apoptosis in K562 leukemia cells. This induction of apoptosis is in part dependent upon both geranylgeranyl diphosphate depletion and accumulation of farnesyl diphosphate. Combinations of either lovastatin or zoledronate with digeranyl bisphosphonate synergistically inhibited growth and induced apoptosis. These combinations also potently inhibited cellular geranylgeranylation. These results support the potential for combinations of multiple inhibitors of isoprene biosynthesis to inhibit cancer cell growth or metastasis at clinically achievable concentrations.

188Re-labelled gemcitabine/bisphosphonate (Gem/BP): a multi-functional, bone-specific agent as a potential treatment for bone metastases

PURPOSE

This study investigated the bone-binding affinity and biodistribution of a (188)Re-labelled gemcitabine/bisphosphonate (Gem/BP) conjugate, a multi-functional drug designed to deliver tumour-specific combined radiotherapy and chemotherapy to the bone using the high bone-binding affinity of the bisphosphonate group.

METHODS

The Gem/BP conjugate was labelled at high radiochemical purity with (188)Re. The bone-binding affinity of the (188)Re-Gem/BP was studied in vitro in purified hydroxyapatite emulsion and powdered bovine bone. In vivo biodistribution studies were carried out in normal BALB/c mice.

RESULTS

(188)Re-Gem/BP demonstrated strong and stable binding in both in vitro systems. In vivo (188)Re-Gem/BP showed bone uptake, rapid blood clearance and rapid elimination of unbound activity. The bone tissue demonstrated the highest concentration of bound radioactivity exempting the kidneys. Approximately 67% of retained whole-body activity was bound to the bone at 8 h after (188)Re-Gem/BP administration.

CONCLUSIONS

(188)Re-Gem/BP demonstrated high, selective and persistent bone binding and can be considered as a model compound for multi-functional bone-specific therapy for bone metastases.

Repeated intermittent low-dose therapy with zoledronic acid induces an early, sustained, and long-lasting decrease of peripheral vascular endothelial growth factor levels in cancer patients

PURPOSE

On the basis of stimulating data on animals reporting that weekly regimens of zoledronic acid (ZA) were effective in reducing skeletal tumor burden, we designed a study on humans to investigate the potential antiangiogenic role of a weekly low-dose therapy with ZA in patients with malignancies.

EXPERIMENTAL DESIGN

Twenty-six consecutive patients with advanced solid cancer and bone metastases received 1 mg of ZA every week for four times (days 1, 7, 14, and 21) followed by 4 mg of ZA with a standard 28-day schedule repeated thrice (days 28, 56, and 84). Patients were prospectively evaluated for circulating levels of vascular endothelial growth factor (VEGF) just before the beginning of drug infusion (0) and again at 7, 14, 21, 28, 56, and 84 days after the first ZA infusion.

RESULTS

The median VEGF basal value showed an early statistically significant (P = 0.038) decrease 7 days after the first 1-mg infusion of ZA. This effect on VEGF-circulating levels persisted also after the following 1-mg infusions at 14 (P = 0.002), 21 (P = 0.001), and 28 days (P = 0.008). Interestingly, the decrease of VEGF-circulating levels persisted also at each programmed time point during the second phase of the study (ZA 4 mg every 4 weeks). No significant differences were recorded in platelet levels, WBC count, or hemoglobin concentration before and after each ZA infusion.

CONCLUSIONS

In the present study, we report that a repeated low-dose therapy with ZA is able to induce an early significant and long-lasting decrease of VEGF levels in cancer patients.

Efficacy and safety of intravenous bisphosphonates in patients with bone metastases caused by metastatic breast cancer

Solid tumors frequently metastasize to bone. This results in debilitating skeletal complications such as intractable bone pain, pathologic fractures, spinal cord compression, and hypercalcemia. Patients frequently require palliative radiation therapy or orthopedic surgery. Bisphosphonates have been shown to delay the incidence and decrease the frequency of skeletal-related events. Zoledronic acid is the only bisphosphonate that has provided benefits for patients with bone metastases secondary to a broad range of solid tumors. Among patients with metastatic breast or prostate cancer, zoledronic acid has demonstrated significant reductions in pain and skeletal morbidity compared with placebo. Zoledronic acid has also shown significant reductions in skeletal morbidity in patients with lung cancer or other solid tumors compared with placebo. Zoledronic acid is generally well tolerated. Flu-like symptoms which are manageable with standard treatment can occur. Renal monitoring is recommended, with dose reductions for patients with renal dysfunction. Osteonecrosis has been reported in patients receiving bisphosphonates and might be avoidable with appropriate dental care.

Post-translational modifications and regulation of the RAS superfamily of GTPases as anticancer targets

The involvement of the RAS superfamily of monomeric GTPases in carcinogenesis is increasingly being appreciated. A complex array of post-translational modifications and a highly sophisticated protein network regulate the spatio-temporal activation of these GTPases. Previous attempts to pharmacologically target this family have focused on the development of farnesyltransferase inhibitors, but the performance of such agents in cancer clinical trials has not been as good as hoped. Here, we review emerging druggable targets and novel therapeutic approaches targeting prenylation and post-prenylation modifications and the functional regulation of GDP/GTP exchange as exciting alternatives for anticancer therapy.

A third-generation bisphosphonate, minodronic acid (YM529), successfully prevented the growth of bladder cancer in vitro and in vivo

Minodronic acid (YM529) is a third-generation bisphosphonate (BP) that has been shown to directly and indirectly prevent proliferation, induce apoptosis, and inhibit metastasis of various types of cancer cells. In this study, we have investigated the therapeutic efficacy of YM529 against bladder cancer, both in vitro and in vivo. YM529 inhibited geranylgeranylation as well as farnesylation and reduced the growth of all seven bladder cancer cell lines in a dose- and time-dependent manner in vitro. YM529 demonstrated a good synergistic or additive antiproliferative effect when administered in combination with cisplatin or paclitaxel. Immunohistochemical study revealed YM529 inhibited the prenylation of Rap1A in vivo. YM529 administered systemically did not markedly inhibit the growth of visceral metastases but it showed a significant anticancer effect on bone metastases monitored by an in vivo imaging system. Moreover, intravesical YM529 demonstrated significant growth inhibition in a bladder cancer orthotopic model. No adverse effects were associated with the systemic as well as the intravesical treatment regimens. In conclusion, our study suggests that YM529 may be a potent anticancer agent for bladder cancer. The efficacy and safety of this BP as an agent for combination chemotherapies against bladder cancer should be verified by early-phase clinical trials.