Zoledronic acid induces apoptosis and inhibits adhesion to mineralized matrix in prostate cancer cells via inhibition of protein prenylation

Design, Synthesis, Molecular Docking, Dynamics and in vitro Evaluation of Novel 2-substituted-1-hydroxyethane-1, 1-bis(phosphonic acid) Derivatives as Human Farnesyl Pyrophosphate Synthase Inhibitors with Expected Anticancer Activity

BACKGROUND

Nitrogenous bisphosphonates (NBPs) are the major class of drugs that are used to treat osteoporosis. Recently, bisphosphonates (BPs) were reported to have an anticancer effect. These agents feature a high affinity that enables them to bind strongly to the human farnesyl pyrophosphate synthase enzyme. The correlation between this affinity and their anticancer effect was confirmed.

OBJECTIVE

To date, the use of an oxygen atom as an isosteric replacement for the electronegative nitrogen atom in NBPs has not been reported, and its ability to retain the linker length and bisphosphonate pharmacophore remains unknown. The main aim of this work was to design some isosteric bisphosphonate analogs with oxygen atoms and evaluation of their binding affinity and anticancer activity.

METHODS

The binding mode and stability of the designed compounds were achieved using human farnesyl pyrophosphate synthase (HFPPS) by docking and dynamic simulations. The compounds were synthesized, characterized, and screened for their anticancer activity against the breast cancer MCF-7 cell line and lung cancer A-549 cell line. The inhibitory activity of the tested compounds against HFPPS was evaluated.

RESULTS

The compounds under investigation showed potential anticancer activity against the lung cell line with IC50 values of 41.7, 47.4, and 34.8 μg/ml in comparison to that of Risedronic acid (115 μg/ml). However, they do not exhibit potential activity against the breast cancer cell line.

CONCLUSION

Compounds VII and VIII showed in vitro inhibition of human farnesyl pyrophosphate synthase with IC50 values of 82.2 and 98.8 μg/ml, respectively. Further optimization may be required in the future.

Zoledronic acid-induced oxidative damage and endoplasmic reticulum stress-mediated apoptosis in human embryonic kidney (HEK-293) cells

Zoledronic acid, a nitrogen-containing bisphosphonate drug, is used for the treatment of osteoporosis, Paget's disease of bone, and tumor-induced osteolysis. Zoledronic acid has also gained a place in cancer treatment due to its cytotoxic and antiproliferative effects in many cancer cells. Although zoledronic acid is considered safe, kidney damage is still one of the concerns in therapeutic doses. In the study, the aim was to assess the nephrotoxic profiles of zoledronic acid in the human embryonic kidney (HEK-293) cells. Cytotoxicity evaluation was performed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) and neutral red uptake tests, while oxidative stress was performed by reactive oxygen species (ROS) production via flow cytometry, and the incomprehensible evaluation of ROS-related genes by RT-PCR and apoptosis was performed with Annexin-PI analysis in flow cytometry. The obtained result showed that zoledronic acid inhibited cell viability (IC₅₀ values were determined as 273.16  by MTT) and cell proliferation in a concentration-dependent manner, induced ROS production, caused glutathione depletion, and increased oxidative stress index and endoplasmic reticulum (ER) stress, indicating severe cellular stress. The expression levels of oxidative damage (L-fabp, α-GST, Nrf2, and HMOX1), ER stress (CASP4, IRE1-α, GADD153, and GRP78), and apoptosis (Bcl-2, Bax, Cyt-c, p53, CASP9, CASP3, NF-κB, TNF-α, and JNK) related genes were altered as well as IRE1-α protein levels. Herein, we were the first to show that increased oxidative stress and ER stress resulting in apoptosis are the key molecular pathways in zoledronic acid-induced nephrotoxicity equivalent to clinically administered concentrations.

A Review Into the Effects of Pamidronic Acid and Zoledronic Acid on the Oral Mucosa in Medication-Related Osteonecrosis of the Jaw

Medication-related osteonecrosis of the jaw (MRONJ) is a growing problem without an effective treatment, presenting as necrotic bone sections exposed via lesions in the overlying soft tissue. There is currently a lack of clarity on how the factors involved in MRONJ development and progression contribute to disease prognosis and outcomes. Bisphosphonates (BPs), the most common cause of MRONJ, affect bone remodeling, angiogenesis, infection, inflammation and soft tissue toxicity, all of which contribute to MRONJ development. This article reviews the cellular mechanisms through which BPs contribute to MRONJ pathology, with a focus on the effects on cells of the oral mucosa. BPs have been shown to reduce cell viability, reduce proliferation, and increase apoptosis in oral keratinocytes and fibroblasts. BPs have also been demonstrated to reduce epithelial thickness and prevent epithelial formation in three-dimensional tissue engineered models of the oral mucosa. This combination of factors demonstrates how BPs lead to the reduced wound healing seen in MRONJ and begins to uncover the mechanisms through which these effects occur. The evidence presented here supports identification of targets which can be used to develop novel treatment strategies to promote soft tissue wound healing and restore mucosal coverage of exposed bone in MRONJ.

Targeting SREBP-2-Regulated Mevalonate Metabolism for Cancer Therapy

Recently, targeting metabolic reprogramming has emerged as a potential therapeutic approach for fighting cancer. Sterol regulatory element binding protein-2 (SREBP-2), a basic helix-loop-helix leucine zipper transcription factor, mainly regulates genes involved in cholesterol biosynthesis and homeostasis. SREBP-2 binds to the sterol regulatory elements (SREs) in the promoters of its target genes and activates the transcription of mevalonate pathway genes, such as HMG-CoA reductase (HMGCR), mevalonate kinase and other key enzymes. In this review, we first summarized the structure of SREBP-2 and its activation and regulation by multiple signaling pathways. We then found that SREBP-2 and its regulated enzymes, including HMGCR, FPPS, SQS, and DHCR4 from the mevalonate pathway, participate in the progression of various cancers, including prostate, breast, lung, and hepatocellular cancer, as potential targets. Importantly, preclinical and clinical research demonstrated that fatostatin, statins, and N-BPs targeting SREBP-2, HMGCR, and FPPS, respectively, alone or in combination with other drugs, have been used for the treatment of different cancers. This review summarizes new insights into the critical role of the SREBP-2-regulated mevalonate pathway for cancer and its potential for targeted cancer therapy.

Endothelial progenitors increase vascularization and improve fibroblasts function that prevent medication-related osteonecrosis of the jaw

OBJECTIVES

In a previous rat model, MRONJ occurrence was 50%. Our aim was to investigate the potential of endothelial progenitor cells (EPCs) to improve fibroblasts function and prevent MRONJ.

METHODS

Human gingival fibroblasts were cultured with EPC-conditioned media (EPC-CM); endothelial growth media (EGM-2) or DMEM followed by incubation with 10 µM zoledronic (ZOL) and dexamethasone (DEX). Cell proliferation and migration were assessed by XTT and scratch wound healing assays. In vivo, ten Lewis rats were treated weekly with ZOL and DEX for 11 weeks. After a week, EPCs or EGM-2 were injected to the gingiva around the molars. At 3 weeks, bilateral molars were extracted. After 8 weeks, wound healing was assessed, and serum VEGF and blood vessels were quantified.

RESULTS

ZOL/DEX significantly reduced fibroblasts proliferation and wound healing. Treatment with EPC-CM before ZOL/DEX improved cell proliferation, and scratch healing (p = .007, p = .023). In vivo, local EPC injection before tooth extraction increased serum VEGF (p = .01) and soft tissue vascularization (p = .05). Normal healing was similar (80%) in EPCs and EGM-2 groups.

CONCLUSION

EPC rescued fibroblasts from the cytotoxic effect of ZOL/DEX and elevated serum VEGF and vessel density that might reduce MRONJ occurrence to 20% compared to 50% in a similar model.

Cholesterol and beyond - The role of the mevalonate pathway in cancer biology

Cancer is a multifaceted global disease. Transformation of a normal to a malignant cell takes several steps, including somatic mutations, epigenetic alterations, metabolic reprogramming and loss of cell growth control. Recently, the mevalonate pathway has emerged as a crucial regulator of tumor biology and a potential therapeutic target. This pathway controls cholesterol production and posttranslational modifications of Rho-GTPases, both of which are linked to several key steps of tumor progression. Inhibitors of the mevalonate pathway induce pleiotropic antitumor-effects in several human malignancies, identifying the pathway as an attractive candidate for novel therapies. In this review, we will provide an overview about the role and regulation of the mevalonate pathway in certain aspects of cancer initiation and progression and its potential for therapeutic intervention in oncology.

Bone-Bound Bisphosphonates Inhibit Proliferation of Breast Cancer Cells

Bisphosphonates are used in treating patients with breast cancer. In vitro studies have shown that bisphosphonates act directly on tumour cells, inhibiting cell proliferation and inducing apoptosis. In most such studies, drugs were added to culture media exposing cells to high bisphosphonate concentrations in solution. However, since bisphosphonates bind to bone hydroxyapatite with high affinity and remain bound for very long periods of time, these experimental systems are not an optimal model for the action of the drugs in vivo. The aim of this study was to determine whether bone-bound zoledronate has direct effects on adjacent breast cancer cells. Bone slices were pre-incubated with bisphosphonate solutions, washed, and seeded with cells of the breast cancer cell lines, MCF7 or MDA-MB-231. Proliferation was assessed by cell counts and thymidine incorporation for up to 72 h. Inhibition of the mevalonate pathway was tested by measuring the levels of unprenylated Rap1A, and apoptosis was examined by the presence of cleaved caspase-8 on western blots. The proliferation rate of breast cancer cells on zoledronate-treated bone was significantly lower compared to cells on control bone. Other bisphosphonates showed a similar inhibitory effect, with an order of potency similar to their clinical potencies. Unprenylated Rap1A accumulated in MCF7 cells on zoledronate-treated bone, suggesting zoledronate acted through the inhibition of the mevalonate pathway. Accumulation of cleaved caspase-8 in MDA-MB-231 cells on bisphosphonate-treated bone indicated increased apoptosis in the cells. In conclusion, bone-bound zoledronate inhibits breast cancer cell proliferation, an activity that may contribute to its clinical anti-tumour effects.

Antiproliferative and antimigratory activities of bisphosphonates in human breast cancer cell line MCF-7

Bisphosphonates (BPs) are antiresorptive drugs that act as effective inhibitors of cancer cell proliferation. However, not all bisphosphonates are equally effective against breast cancer cells in vitro. The present study investigated the extent to which three BPs decrease the viability of MCF-7 human breast cancer cells, stimulate cell apoptosis and inhibit cell migration by modulating proteins in the mevalonate pathway. The three BPs exerted direct anticancer effects against MCF-7 cells in a dose- and time-dependent manner, with pamidronate demonstrating the highest efficacy. In addition, the BPs inhibited colony formation ability. The activity of BPs against MCF-7 cells was inhibited by the mevalonate product geranylgeranyl pyrophosphate, which was potentiated by doxorubicin. It was also identified that BPs modulated Ras-related C3 botulinum toxin substrate 1, Ras homolog gene family member A and cell division control protein 42 homolog gene expression. Consistent with the observed growth inhibitory effects, BPs also inhibited the cell cycle by promoting G1 phase arrest and the downregulation of cyclin D1 and upregulation of p21. Additionally, BPs were revealed to induce reactive oxygen species expression, caspase-3 activity and increase the mitochondrial transmembrane potential, which was associated with apoptosis. BP-induced cancer cell apoptosis was detected by acridine orange/ethidium bromide staining and flow cytometry analysis, and was identified to be associated with the induction of caspase-3 and cytochrome c protein expression. Furthermore, BPs significantly decreased cancer cell migration in a dose-dependent manner and reduced matrix metallopeptidase-9 protein expression. In summary, the current study demonstrated that BPs exhibited a direct anticancer effect and an antimigratory effect on MCF-7 cells. These findings suggest that BPs may be developed as a therapeutic option for breast cancer and may serve as sensitizing chemotherapeutic agents.

Bisphosphonates and Cancer: A Relationship Beyond the Antiresorptive Effects

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

Zoledronic acid induces cytogenetic toxicity in male germline cells of Swiss albino mice

This study mainly focuses on the cytogenetic toxicity induction by zoledronic acid (ZA), a nitrogen containing bisphosphonate (N-BPs) in the male germline cells of Swiss albino mice. A single intraperitoneal exposure with three different doses of ZA (2, 4, and 8 mg/kg body weight), toxicity was assessed by analyzing spermatogonial metaphase chromosome aberrations at 24 h, aberrant primary spermatocytes at week 4, and abnormal spermatozoa at week 8 posttreatment. Cyclophosphamide (40 mg/kg) and 0.9% NaCl were used as positive and vehicle controls respectively in the study. The results showed that there was a significant induction in the number of chromosomal aberrations especially at two doses of ZA (4 and 8 mg/kg) after 24 h in the spermatogonial cells (p < 0.001) compared to vehicle control. The transmission genetic damages were noticed as aberrant spermatocytes with atypical bivalents (X-Y/autosomal asynapsis) at 4 mg/kg of ZA (p < 0.01) and at 8 mg/kg of ZA (p < 0.001) at week 4 posttreatment. A statistically significant higher number of abnormal spermatozoa (sperm) were also noticed at week 8 posttreatment of both at 4 and 8 mg/kg of ZA (p < 0.001). Hence, from these genotoxicity studies, it can be concluded that ZA is genotoxic in male germline cells and has the potential of transmitting the genotoxic effects from spermatogonial cells to sperm in male Swiss mice.

Zoledronate suppresses VEGF‑induced capillary tube formation and inhibits expression of interferon‑induced transmembrane protein‑1 in human umbilical vein endothelial cells

Interferon‑induced transmembrane protein 1 (IFITM1) is a member of the interferon‑induced transmembrane protein family and has recently been identified as a novel protein participant in angiogenesis. Zoledronate (ZON), a nitrogen‑containing bisphosphonate, is widely used in the treatment of osteoporosis and to prevent bone metastases of certain cancer types. However, the association between ZON and IFITM1 has remained elusive. The present study investigated the effect of ZON on the expression of IFITM1 during vascular endothelial growth factor (VEGF)‑induced capillary tube formation in human umbilical vein endothelial cells. It was observed that cell proliferation and VEGF‑induced tube formation were significantly inhibited by treatment with 10 µM ZON. The expression of IFITM1 increased during VEGF‑induced tube formation. However, the VEGF‑induced increase in IFITM1 expression exhibited a dose‑ and time‑dependent decrease with ZON treatment at the mRNA and protein level. Furthermore, matrix metalloproteinase‑9 activation was markedly decreased by ZON treatment. These results suggest that induction of IFITM1 expression may be involved in the anti‑angiogenic activity of ZON.

Overexpression of geranylgeranyl diphosphate synthase contributes to tumour metastasis and correlates with poor prognosis of lung adenocarcinoma

This study aimed to evaluate the biological role of geranylgeranyl diphosphate synthase (GGPPS) in the progression of lung adenocarcinoma. GGPPS expression was detected in lung adenocarcinoma tissues by qRT‐PCR, tissue microarray (TMA) and western blotting. The relationships between GGPPS expression and the clinicopathological characteristics and prognosis of lung adenocarcinoma patients were assessed. GGPPS was down‐regulated in SPCA‐1, PC9 and A549 cells using siRNA and up‐regulated in A549 cells using an adenoviral vector. The biological roles of GGPPS in cell proliferation, apoptosis, migration and invasion were determined by MTT and colony formation assays, flow cytometry, and transwell and wound‐healing assays, respectively. In addition, the regulatory roles of GGPPS on the expression of several epithelial‐mesenchymal transition (EMT) markers were determined. Furthermore, the Rac1/Cdc42 prenylation was detected after knockdown of GGPPS in SPCA‐1 and PC9 cells. GGPPS expression was significantly increased in lung adenocarcinoma tissues compared to that in adjacent normal tissues. Overexpression of GGPPS was correlated with large tumours, high TNM stage, lymph node metastasis and poor prognosis in patients. Knockdown of GGPPS inhibited the migration and invasion of lung adenocarcinoma cells, but did not affect cell proliferation and apoptosis. Meanwhile, GGPPS inhibition significantly increased the expression of E‐cadherin and reduced the expression of N‐cadherin and vimentin in lung adenocarcinoma cells. In addition, the Rac1/Cdc42 geranylgeranylation was reduced by GGPPS knockdown. Overexpression of GGPPS correlates with poor prognosis of lung adenocarcinoma and contributes to metastasis through regulating EMT.

Could drugs inhibiting the mevalonate pathway also target cancer stem cells?

Understanding the connection between metabolic pathways and cancer is very important for the development of new therapeutic approaches based on regulatory enzymes in pathways associated with tumorigenesis. The mevalonate cascade and its rate-liming enzyme HMG CoA-reductase has recently drawn the attention of cancer researchers because strong evidences arising mostly from epidemiologic studies, show that it could promote transformation. Hence, these studies pinpoint HMG CoA-reductase as a candidate proto-oncogene. Several recent epidemiological studies, in different populations, have proven that statins are beneficial for the treatment-outcome of various cancers, and may improve common cancer therapy strategies involving alkylating agents, and antimetabolites. Cancer stem cells/cancer initiating cells (CSC) are key to cancer progression and metastasis. Therefore, in the current review we address the different effects of statins on cancer stem cells. The mevalonate cascade is among the most pleiotropic, and highly interconnected signaling pathways. Through G-protein-coupled receptors (GRCP), it integrates extra-, and intracellular signals. The mevalonate pathway is implicated in cell stemness, cell proliferation, and organ size regulation through the Hippo pathway (e.g. Yap/Taz signaling axis). This pathway is a prime preventive target through the administration of statins for the prophylaxis of obesity-related cardiovascular diseases. Its prominent role in regulation of cell growth and stemness also invokes its role in cancer development and progression. The mevalonate pathway affects cancer metastasis in several ways by: (i) affecting epithelial-to-mesenchymal transition (EMT), (ii) affecting remodeling of the cytoskeleton as well as cell motility, (iii) affecting cell polarity (non-canonical Wnt/planar pathway), and (iv) modulation of mesenchymal-to-epithelial transition (MET). Herein we provide an overview of the mevalonate signaling network. We then briefly highlight diverse functions of various elements of this mevalonate pathway. We further discuss in detail the role of elements of the mevalonate cascade in stemness, carcinogenesis, cancer progression, metastasis and maintenance of cancer stem cells.

Zoledronic acid induces apoptosis via stimulating the expressions of ERN1, TLR2, and IRF5 genes in glioma cells

Glioblastoma multiforme (GBM) is the most common and aggressive brain tumor that affects older people. Although the current therapeutic approaches for GBM include surgical resection, radiotherapy, and chemotherapeutic agent temozolomide, the median survival of patients is 14.6 months because of its aggressiveness. Zoledronic acid (ZA) is a nitrogen-containing bisphosphonate that exhibited anticancer activity in different cancers. The purpose of this study was to assess the potential effect of ZA in distinct signal transduction pathways in U87-MG cells. In this study, experiments performed on U87-MG cell line (Human glioblastoma-astrocytoma, epithelial-like cell line) which is an in vitro model of human glioblastoma cells to examine the cytotoxic and apoptotic effects of ZA. IC50 dose of ZA, 25 μM, applied on U87-MG cells during 72 h. ApoDIRECT In Situ DNA Fragmentation Assay was used to investigate apoptosis of U87MG cells. The quantitative reverse transcription polymerase chain reaction (qRT-PCR) (LightCycler480 System) was carried out for 48 gene expression like NF-κB, Toll-like receptors, cytokines, and inteferons. Our results indicated that ZA (IC50 dose) increased apoptosis 1.27-fold in U87MG cells according to control cells. According to qRT-PCR data, expression levels of the endoplasmic reticulum-nuclei-1 (ERN1), Toll-like receptor 2 (TLR2), and human IFN regulatory factor 5 (IRF5) tumor suppressor genes elevated 2.05-, 2.08-, and 2.3-fold by ZA, respectively, in U87MG cells. Our recent results indicated that ZA have a key role in GBM progression and might be considered as a potential agent in glioma treatment.

Cytochrome P450 17A1 inhibitor abiraterone attenuates cellular growth of prostate cancer cells independently from androgen receptor signaling by modulation of oncogenic and apoptotic pathways

Abiraterone provides significant survival advantages in prostate cancer (PC), however, the current understanding of the molecular mechanisms of abiraterone is still limited. Therefore, the abiraterone impact on androgen receptor (AR)-positive LNCaP and AR-negative PC-3 cells was assessed by cellular and molecular analyses. The present study demonstrated, that abiraterone treatment significantly decreased cell growth, AR expression, and AR activity of AR-positive LNCaP cells. Notably, AR-negative PC-3 cells exhibited comparable reductions in cellular proliferation, associated with DNA fragmentation and pro-apoptotic modulation of p21, caspase-3, survivin, and transforming growth factor β (TGFβ). Our observations suggest that the attenuation of AR signaling is not the only rationale to explain the abiraterone anticancer activity. Abiraterone efficacy may play a more global role in PC progression control than originally hypothesized. In this regard, abiraterone is not only a promising drug for treatment of AR-negative PC stages, even more, abiraterone may represent an alternative for treatment of other malignancies besides prostate cancer.

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.

The influence of geranylgeraniol on human oral keratinocytes after bisphosphonate treatment: An in vitro study

This in vitro study analyzed the influence of geranylgeraniol (GGOH) on human oral keratinocytes (HOK) after exposure to bisphosphonates. HOK were incubated with four different bisphosphonates (clodronate, ibandronate, pamidronate, zoledronate) in two experimental set-ups: with and without GGOH. MTT and PrestoBlue assays were used to analyze HOK cell viability. HOK migration ability was examined with Boyden and Scratch assays, and Tunel and ToxiLight assays were used to detect the HOK apoptosis rate. No significant differences between the experimental set-ups, with and without GGOH, could be found for clodronate (p each >0.3). For the nitrogen-containing bisphosphonates, negative effects could be shown in the experimental set-ups without GGOH in all assays. In the GGOH experimental set-ups, the levels of HOK cell viability were significantly increased (MTT: p each ≤0.001; PrestoBlue: p each ≤0.012). The HOK migration ability was also greater (Boyden: p each <0.001; Scratch: p each ≤0.015). Regarding the apoptosis rate, reduced numbers of apoptotic HOK in the Tunel assay (p each <0.001) and decreased adenylate kinase release in the ToxiLight assay (p each ≤0.002) were observed. GGOH reversed the negative effects of bisphosphonates on HOK. These findings provide evidence that GGOH could be a promising treatment option for BP-ONJ.

Effects of zoledronic acid and docetaxel on small GTP-binding proteins in prostate cancer

Increasingly, in castration-resistant prostate cancer, patients are often treated with docetaxel and the bisphosphonate zoledronic acid concurrently, yet there is still a paucity in the literature regarding the molecular basis of how this drug combination works. The study was performed on the hormone-resistant cell line PC-3. Cells were treated with clinically relevant concentrations of docetaxel and zoledronic acid either as single agents or in sequence and combination. Cell viability and apoptosis were assessed along with the prenylation status of the GTPases Ras and RhoA. Following 1-mM zoledronic acid treatment, inhibition of the prenylation of H-Ras and Rho A was observed along with an increase in the unprenylated form in the cytoplasm. Docetaxel 1 nM and zoledronic acid 1 mM also showed an increase in the unprenylated form of both small GTP-binding proteins in the cytoplasm and a reduction of protein in the membrane fraction. Overall, zoledronic acid followed by docetaxel was the best regimen producing the greatest reduction in cell viability and increase in apoptosis. At the highest concentrations of zoledronic acid and docetaxel, zoledronic acid followed by docetaxel was also the most effective at reducing the prenylation of both H-Ras and RhoA at the membrane. We have demonstrated that clinically achievable concentrations of zoledronic acid and docetaxel cause a reduction in the prenylation of both H-Ras and Rho A and a reduction of protein movement into the membrane. The most effective regimen overall was high-dose zoledronic acid followed by docetaxel, suggesting that this regimen may be of benefit in clinical practice.

Manumycin induces apoptosis in prostate cancer cells

Background

Manumycin exhibits an antitumor effect in a variety of cancer cell lines, including prostate cancer cell lines (DU145 and PC-3). Our previous studies demonstrated that manumycin induced the apoptosis of anaplastic thyroid cancer cells and leukemia cells via the intrinsic apoptosis pathway. In the current study, we further evaluated the effect of manumycin in two prostate cancer cell lines (LNCaP and 22Rv1), and here we elucidate some of the underlying mechanisms.

Materials and methods

The cell viability of prostate cancer cells was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay after treatment with manumycin for 48 hours. Apoptosis was detected by flow cytometry using annexin V and propidium iodide. The expressions of B-cell lymphoma (Bcl)-2 family members and the activations of caspase-9 and caspase-3 were detected by Western blotting.

Results

Manumycin treatment resulted in significant decreases in the viabilities of the two prostate cancer cell lines in a dose-dependent manner through apoptosis, and this apoptosis involved caspase-9 activation. A specific inhibitor of caspase-9 protected cells from caspase-3 activation, apoptosis, and cytotoxicity induced by manumycin. We also found that manumycin downregulated Bcl-2 expression and upregulated Bax expression.

Conclusion

Our data suggest that manumycin induces apoptosis in prostate cancer cells through regulation of the Bcl-2 family involving caspase-9 activation. These results suggest that manumycin may be beneficial for the treatment of prostate cancer.

Zoledronic acid but not somatostatin analogs exerts anti-tumor effects in a model of murine prostatic neuroendocrine carcinoma of the development of castration-resistant prostate cancer

BACKGROUND

Since neuroendocrine (NE) cells play an important role in the development of castration-resistant prostate cancer (CRPC), target therapy to NE cells should be considered for treating CRPC. We investigated the effects zoledronic acid (ZOL) and two somatostatin analogs (octreotide: SMS, and pasireotide: SOM) on an NE allograft (NE-10) and its cell line (NE-CS), which were established from the prostate of the LPB-Tag 12T-10 transgenic mouse.

METHODS

We examined the in vivo effects of ZOL, SMS and SOM as single agents and their combinations on subcutaneously inoculated NE-10 allografts and the in vitro effects on NE-CS cells. Apoptosis and cell cycle activity were assessed by immunohistochemistry using TdT-mediated dUTP-biotin nick-end labeling (TUNEL) and a Ki-67 antibody, respectively.

RESULTS

In vivo growth of NE-10 tumors treated with ZOL, ZOL plus SMS, or ZOL plus SOM was significantly inhibited compared to the control as a consequence of induction of apoptosis and cell cycle arrest. ZOL induced time- and dose-dependent inhibition of in vitro proliferation of NE-CS cells, but the somatostatin analogs (SMS and SOM) did not. ZOL also inhibited migration of NE-CS cells. These effects were caused by inhibition of Erk1/2 phosphorylation via impairment of prenylation of Ras.

CONCLUSIONS

ZOL, but not SMS or SOM, induced apoptosis and inhibition of proliferation and migration through impaired prenylation of Ras in NE carcinoma models. Our findings support the possibility that ZOL could be used in the early phase for controlling NE cells, which may trigger progression to CRPC.

Analysis of molecular mechanisms and anti-tumoural effects of zoledronic acid in breast cancer cells

Zoledronic acid (ZOL) is the most potent nitrogen-containing bisphosphonate (N-BPs) that strongly binds to bone mineral and acts as a powerful inhibitor of bone resorption, already clinically available for the treatment of patients with osteolytic metastases. Recent data also suggest that ZOL, used in breast cancer, may provide more than just supportive care modifying the course of the disease, though the possible molecular mechanism of action is still unclear.As breast cancer is one of the primary tumours with high propensity to metastasize to the bone, we investigated, for the first time, differential gene expression profile on Michigan Cancer Foundation-7 (MCF-7) breast cancer cells treated with low doses of ZOL (10 μM). Microarrays analysis was used to identify, describe and summarize evidence regarding the molecular basis of actions of ZOL and of their possible direct anti-tumour effects. We validated gene expression results of specific transcripts involved in major cellular process by Real Time and Western Blot analysis and we observed inhibition of proliferation and migration through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Matrigel assay. We then focused on changes in the cytoskeletal components as fibronectin 1 (FN1), actin, and anti angiogenic compounds as transforming growth factor-β1 (TGF-β1) and thrombospondin 1 (THBS1). The up-regulation of these products may have an important role in inhibiting proliferation, invasion and angiogenesis mediated by ZOL.

Evaluation of the in vitro and in vivo antiangiogenic effects of denosumab and zoledronic acid

Denosumab (Dmab) and zoledronic acid (ZOL) are antiresorptive agents, with different mechanisms of action, that are indicated for delaying the onset of skeletal-related events in patients with bone metastases from solid tumors. Clinical and preclinical data suggest that ZOL may have also anti-angiogenic activity; however, the effects of Dmab (a fully humanized antibody against the receptor activator of nuclear factor kappa B ligand) on angiogenesis are largely unknown. The objective of this study was to compare the potential anti-angiogenic activity of Dmab with that of ZOL in preclinical models. Dmab (0.31 to 160 μM) had no effect on the viability of human MDA-MB-436 and CG5 breast cancer cells or human umbilical vein endothelial cells (HUVECs) and no effect on tubule formation or invasion of HUVECs. In contrast, ZOL (0.31 to 160 μM) decreased the viability of breast cancer and HUVECs in a time- and concentration-dependent manner and also inhibited HUVEC tubule formation and invasion. In vivo, ZOL (20 μg/mouse for three times a week for three consecutive weeks) inhibited angiogenesis in Matrigel plugs and inhibited the growth and neo-angiogenesis of CG5 xenografts in athymic nude mice. In contrast, Dmab (10 mg/Kg twice a week for 4 consecutive weeks) had no effect on Matrigel vascularization or xenograft growth in this model. These findings support the potential antiangiogenic and anticancer activity of ZOL in vitro and in vivo and further suggest that Dmab does not have antiangiogenic activity. Additional studies are needed to elucidate the potential anticancer activity of Dmab.

Exposure to oral bisphosphonates and risk of cancer

Recently, oral bisphosphonate use has increased markedly in the United States and elsewhere. Little is known about cancer risks associated with these drugs. A few studies have observed associations between bisphosphonates and the risk of breast, colorectal and esophageal cancer. However, the risk of all cancer and the risk of other cancers have not been investigated. In our study, we examined the risk of all cancer and site specific cancers in individuals taking bisphosphonates. Data were extracted from the UK General Practice Research Database to compare site-specific cancer incidence in a cohort of oral bisphosphonate users and a control cohort. Hazard ratios (HRs) were calculated using Cox regression modeling. The bisphosphonate and control cohort contained 41,826 participants (mean age 70, 81% female). Overall, the bisphosphonate cohort compared with the control cohort had a reduced risk of all cancer after any bisphosphonate usage [HR=0.87, 95% confidence interval (CI) 0.82, 0.92]. In the bisphosphonate cohort, compared with the control cohort, there was no evidence of a difference in the risk of lung (HR=1.03, 95% CI 0.88, 1.20) or prostate cancer (HR=0.86, 95% CI 0.67, 1.09) but breast (HR=0.71, 95% CI 0.62, 0.81) and colorectal cancer (HR=0.74, 95% CI, 0.60-0.91) were both reduced. Our findings indicate that bisphosphonates do not appear to increase cancer risk. Although reductions in breast and colorectal cancer incidence were observed in bisphosphonate users it is unclear, particularly for breast cancer, to what extent confounding by low bone density may explain the association.

Oral alendronate use and risk of cancer in postmenopausal women with osteoporosis: A nationwide study

The association between use of oral bisphosphonates and cancer development in elderly women is still uncertain, and previous studies have shown controversial results. We used a nationwide, population-based database to explore the relationship between the use of alendronate, an oral bisphosphonate agent used for the treatment of osteoporosis, and the risk of all malignancies in women with osteoporosis and age over 55 years. In the study group, we included 6906 women with osteoporosis (age, mean ± SD, 73.4 ± 8.4 years) taking oral alendronate, who were selected from a 1,000,000 sample cohort dataset collected between January 1998 and December 2009. Another 20,697 age- and comorbidity-matched women (73.5 ± 8.4 years) without bisphosphonates treatment were included in the control group. No subjects had any history of being diagnosed with cancer before inclusion. We used a log-rank test to analyze the differences in accumulated cancer-free survival rates between these two groups. A Cox proportional-hazard model, adjusted for confounding factors, was used to evaluate the association between alendronate use and the development of all cancer events in postmenopausal women with osteoporosis. During the mean follow-up period of 4.8 years, 821 patients from the study group and 2646 patients from the control group had new cancers. There was no significant difference in cancer incidence between alendronate users and controls (11.9% versus 12.8%, p = 0.054). The person-year incidence of newly-developed cancer in alendronate users and controls was 28.0 and 29.4 per 1000 person-years, respectively. Alendronate use was not associated with increased risk of cancer development in women with osteoporosis (adjusted hazard ratio, 1.05; 95% confidence interval [CI], 0.97-1.13; p = 0.237). However, due to the limited study size and underpowered results, further larger prospective studies or meta-analysis are suggested to further confirm our findings.

Adjuvant bisphosphonate treatment for breast cancer: Where are we heading and can the pre-clinical literature help us get there?

Bisphosphonates have demonstrated anti-tumour activity in preclinical studies of bone metastatic disease, thus it was natural to transition these agents into the adjuvant cancer therapy setting. Surprisingly, the results of adjuvant breast cancer trials have shown either modest to no benefit or even harm. We sought to explore whether the preclinical results supporting bisphosphonate use provided clues to help explain the current clinical data. Interestingly, the majority of preclinical data suggested that bisphosphonate treatment was more efficacious when administered after the establishment of osseous metastases. This is similar to the findings of one clinical study whereby patients with biopsy evidence of osseous micrometastases derive greater survival benefit from bisphosphonate treatment. Another clinical study found bisphosphonates were associated with increased incidence of visceral metastases, similar to what has been previously published in preclinical models using “preventative” dosing strategies. While the current clinical data suggest bisphosphonates may be more efficacious in post-menopausal or oestrogen depleted patients, or those with hormone receptor positive tumours, to date no appropriately designed preclinical studies have evaluated these effects. Furthermore, putative mechanisms that regulate response to bisphosphonates in other tumour types remain to be evaluated in breast cancer. Despite the initial optimism regarding adjuvant bisphosphonate therapy, the conflicting clinical results from large trials suggest that we should return to the bench to further investigate factors that may influence response to bisphosphonate treatment or identify appropriate characteristics that would indicate the sub-groups of patients most likely to benefit from bisphosphonate treatment.

[Bone metastasis in prostate cancer]

Bone metastasis and skeletal complications have a devastating impact on the quality of life and are a major cause of morbidity in prostate cancer patients. In addition to established bone-targeted therapies, new drugs such as endothelin A receptor antagonists, MET and VEGFR-2 antagonists or radiopharmaceuticals are in the focus of development. The standard care in prostate cancer patients with bone metastases to prevent skeletal-related events (SRE) are bisphosphonates. Denosumab, a human monoclonal antibody against RANKL, appeared to be superior to zoledronic acid for prevention of SRE and has been shown to prolong bone metastases-free survival. In contrast to zoledronic acid, denosumab clearance is not dependent on kidney function and can be administered subcutaneously. Similar rates of toxicity were observed for both substances; however, long-term data for denosumab are limited.

Recent developments in treatments targeting castration-resistant prostate cancer bone metastases

BACKGROUND

Prostate cancer is the most common male cancer and one of the top causes of male cancer-related death. Most patients with prostate cancer respond to initial androgen deprivation therapy before progressing to castration-resistant prostate cancer (CRPC) and eventually developing bone metastases. Growth of prostate cancer metastases in the bone microenvironment produces numerous factors that disrupt the dynamic equilibrium of osteogenesis and osteolysis existing in healthy bone, leading to progressive morbidity, poor quality of life, and increased treatment costs.

MATERIALS AND METHODS

Relevant studies of CRPC and targeted therapies were identified from literature and clinical trial databases, websites, and conference abstracts.

RESULTS

Available data on agents potentially targeting bone metastatic CRPC or the bone microenvironment in patients with CRPC are discussed, including inhibitors of tumor growth/survival and bone turnover (SRC family kinase inhibitors, endothelin-1 inhibitors, MET inhibitors, and thalidomide and its derivatives), inhibitors of bone turnover (bisphosphonates and receptor activator of nuclear factor-kB ligand inhibitors), antiangiogenic agents (vascular endothelial growth factor receptor and platelet-derived growth factor blockers), prostate cancer vaccines, and bone-directed radiopharmaceuticals.

CONCLUSIONS

With increasing data availability demonstrating tumor-bone microenvironment interactions and routine incorporation of bone-related end points into CRPC trials, bone microenvironment-targeted agents are likely to become an increasingly important component of CRPC treatment.

Bone-modifying agents in the treatment of bone metastases in patients with advanced genitourinary malignancies: a focus on zoledronic acid

Many patients with advanced genitourinary malignancies develop bone metastases, which can lead to potentially debilitating skeletal complications. Moreover, age-related bone loss and cancer treatments such as hormonal therapy for prostate cancer can weaken bone, placing patients at risk for osteoporotic fractures in addition to skeletal-related events (SREs) from bone metastases. Zoledronic acid, a bisphosphonate, is approved worldwide to reduce the risk of SREs in patients with bone metastases from solid tumors or bone lesions from multiple myeloma. Zoledronic acid, although underutilized in genitourinary malignancies, has long been the mainstay of treatment in patients with bone metastases, and can also help preserve bone during anticancer therapy. Recently, denosumab, a monoclonal antibody directed against the receptor activator of nuclear factor kappa-B ligand, was approved in the United States and the European Union for reducing the risk of SREs in patients with bone metastases from solid tumors. Denosumab (at a lower dose) is also approved in the European Union and the United States to treat androgen deprivation-induced bone loss in men with prostate cancer. In addition, preclinical rationale and emerging clinical data suggest that bone-modifying agents may be able to delay disease progression in genitourinary cancers, just as newly developed anticancer treatments have produced reductions in SREs, possibly by indirect effects on the disease course. This review article summarizes current data and ongoing studies to preserve bone health in patients with advanced genitourinary cancers.

Bisphosphonates: prevention of bone metastases in prostate cancer

Bone metastases and their associated morbidities are common in patients with advanced prostate cancer and other genitourinary (GU) malignancies. Zoledronic acid> (a bisphosphonate) has long been the mainstay of treatment for reducing the risk of skeletal-related events in patients with bone metastases from GU cancers, and denosumab (a monoclonal antibody directed against the receptor activator of nuclear factor kappa B ligand [RANKL]) has recently received approval for this indication in the United States. Preclinical data indicate that modifying the bone microenvironment may render it less conducive to metastasis, and emerging clinical findings suggest that the potential benefits from bone-directed therapies are not limited to reducing skeletal morbidity-these agents might help to improve survival and delay bone disease progression or even development of bone metastases (if used earlier in the disease course). This chapter reviews the rationale and recent clinical data supporting an antimetastatic role for bone-directed therapies in patients with GU malignancies.

Zoledronic acid in the treatment of early-stage breast cancer: is there a final verdict?

Breast cancer, which preferentially metastasizes to bone, is the most common malignancy among women worldwide and is a leading cause of death. Clinical data from large, phase 3 trials (ie, ABCSG-12, ZO-FAST, and AZURE) demonstrate significantly improved disease-free survival with zoledronic acid in some patient populations with early breast cancer. Although the interim results from the AZURE trial did not show a disease-free survival benefit with zoledronic acid in the overall patient population, subset analyses showed that zoledronic acid significantly improved disease-free survival in women with established postmenopausal status at baseline. Similarly, subset analyses of the ABCSG-12 trial showed greater benefits from zoledronic acid in patients over 40 years of age who theoretically would have achieved more complete ovarian suppression. Together, these data support a potential role for zoledronic acid beyond bone health in breast cancer and suggest that the endocrine environment may influence the anticancer potential of zoledronic acid.

Altered expression of farnesyl pyrophosphate synthase in prostate cancer: evidence for a role of the mevalonate pathway in disease progression?

BACKGROUND

Preclinical studies demonstrated effects of drugs inhibiting the mevalonate pathway including nitrogen-containing bisphosphonates (N-BPs) and statins on tumor growth and progression. The exact role of this pathway in prostate cancer (PC) has not been identified yet. Herein, we evaluate the expression of farnesyl pyrophosphate synthase (FPPS), the key enzyme of the mevalonate pathway, in PC.

PATIENTS AND METHODS

Prostate cancer (PC) and benign prostate tissue of 114 men who underwent radical prostatectomy were constructed to a tissue microarray. Immunohistochemical staining of FPPS was quantified by the Remmele/Stegner immunoreactivity-score. Patients' clinical follow-up was assessed. IRS was correlated to pathological and clinical data. The impact of FPPS expression on clinical course was assessed univariate and multivariate.

RESULTS

Mean IRS in PC and benign tissue was 5.7 (95% CI 5.0-6.5) and 2.6 (2.1-3.0, p < 0.0001). Mean IRS in PC tissue of patients with organ-confined and locally advanced disease (pT ≥ 3) was 5.09 (4.22-5.96) and 6.87 (5.57-8.17, p = 0.035). IRS of PC tissue significantly correlated with Gleason score (p = 0.03). Patients with PC tissue IRS >3 showed shorter recurrence-free survival compared to the remaining (p = 0.01). Increased FPPS expression is an independent risk factor for early biochemical recurrence (p = 0.032).

CONCLUSIONS

This is the first study on FPPS in PC specimens. The association of FPPS with established histopathological risk parameters and biochemical recurrence implicates a contribution of the mevalonate pathway to PC progression. Further functional analysis is required to explore the role of this pathway in PC and to investigate whether FPPS expression affects the response of PC cells to N-BPs.

Significance of combination therapy of zoledronic acid and gemcitabine on pancreatic cancer

In the present study, we examined the cytotoxic effects of combination therapy with zoledronic acid (ZOL) and gemcitabine (GEM) on pancreatic cancer cells in vitro and in vivo. Four human pancreatic cancer cell lines were treated with ZOL, GEM or a combination of both, and the effects of the respective drug regimens on cell proliferation, invasion and matrix metalloproteinase (MMP) expression were examined. A pancreatic cancer cell line was also intrasplenically or orthotopically implanted into athymic mice and the effects of these drugs on tumor metastasis and growth in vivo were evaluated by histological and immunohistochemical analyses. Combination treatment with low doses of ZOL and GEM efficiently inhibited the proliferation (P < 0.001) and invasion (P < 0.001) of pancreatic cancer cells in vitro. Western blotting assay revealed that MMP-2 and MMP-9 expression levels were decreased after ZOL treatment. In vivo, combined treatment significantly inhibited tumor growth (P < 0.05) and the development of liver metastasis (P < 0.05). These data revealed that ZOL and GEM, when used in combination, have significant antitumor, anti-metastatic and anti-angiogenic effects on pancreatic cancer cells. The present study is the first to report the significance of the combination treatment of ZOL and GEM in pancreatic cancer using an in vivo model. These data are promising for the future application of this drug regimen in patients with pancreatic cancer.

New role for an established drug? Bisphosphonates as potential anticancer agents

As a result of their ability to effectively reduce the risk of skeletal-related events, bisphosphonates (BPs) were incorporated into clinical practice over a decade ago, leading to a new treatment paradigm for patients with skeletal involvement from advanced cancer. BPs are now a well-established treatment option in this setting. Our review of the literature found that in addition to maintaining bone health in patients with malignant bone lesions and patients at risk for cancer therapy-induced bone loss, emerging preclinical and clinical data suggest that BPs may also have anticancer activity. Later generation, nitrogen-containing BPs (N-BPs), such as zoledronic acid (ZOL), inhibit the mevalonate pathway, subsequently inhibiting a number of cellular functions in bone-resorbing osteoclasts. In addition, N-BPs inhibit cancer cell proliferation, viability, motility, invasion and angiogenesis; induce cancer cell apoptosis; and act in synergy with antineoplastic agents. N-BPs, especially ZOL, may be useful as anticancer agents. As evidence continues to emerge, another shift in cancer treatment paradigms, in which N-BPs are considered for their anticancer activity as well as palliative effects, may be approaching.

The kinetochore protein Cenp-F is a potential novel target for zoledronic acid in breast cancer cells

The anti-resorptive agent zoledronic acid inhibits key enzymes in the mevalonate pathway, disrupting post-translational modification and thereby correct protein localization and function. Inhibition of prenylation may also be responsible for the reported anti-tumour effects of zoledronic acid, but the specific molecular targets have not been identified. Cenp-F/mitosin, a kinetochore-associated protein involved in the correct separation of chromosomes during mitosis, has been shown to undergo post-translational prenylation and may therefore be a novel target contributing to the anti-tumour effects of zoledronic acid. We investigated whether zoledronic acid causes loss of Cenp-F from the kinetochore in breast cancer cells, to determine if the reported anti-tumour effects may be mediated by impairing correct chromosome separation. MDA-MB-436, MDA-MB-231 and MCF-7 breast cancer cells and MCF-10A non-malignant breast epithelial cells were treated with zoledronic acid in vitro, and the effect on Cenp-F localization was analysed by immunoflourescence microscopy. Zoledronic acid caused loss of Cenp-F from the kinetochore, accompanied by an increase in the number of cells in pro-, /prometa- and metaphase in all of the cancer cell lines. There was also a significant increase in the number of lagging chromosomes in mitotic cells. The effects of zoledronic acid could be reversed by inclusion of an intermediary of the mevalonate pathway, showing that the loss of Cenp-F from the kinetochore was caused by the inhibition of farnesylation. In contrast, no effect was seen on Cenp-F in non-malignant MCF-10A cells. This is the first report showing a specific effect of zoledronic acid on a protein involved in the regulation of chromosome segregation, identifying Cenp-F as a potential new molecular target for NBPs in tumour cells.

Bisphosphonate enhances TRAIL sensitivity to human osteosarcoma cells via death receptor 5 upregulation

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), a member of the TNF superfamily of cytokines, is one of the most promising candidates for cancer therapeutics. However, many osteosarcomas are resistant to TRAIL. Bisphosphonates are very effective in the treatment of bone problems associated with malignancies; the antitumor effects are due to the inhibition of protein prenylation that is essential for cell function and survival. The purpose of this study was to determine the effects of bisphosphonates on TRAIL-resistant MG 63 human osteosarcoma cells. The cells showed no response to TRAIL alone; however, pre-treatment with bisphosphonates significantly increased TRAIL-mediated apoptosis and cellular activation of caspase-3. Bisphosphonates significantly induced mRNA and protein expression of the TRAIL receptor, DR5. Bisphosphonates induced protein unprenylation in MG 63 cells; in addition, co-treatment with TRAIL also significantly increased protein unprenylation. Blocking of protein unprenylation using geranylgeraniol attenuated the cellular responses, including cell apoptosis and protein unprenylation induced by bisphosphonates and TRAIL. This is the first study to demonstrate that bisphosphonates markedly enhanced TRAIL-induced apoptosis in human osteosarcoma cells. These findings suggest that bisphosphonates may be a new and effective anticancer treatment with TRAIL proteins for TRAIL-resistant cancer cells.

Could targeting bone delay cancer progression? Potential mechanisms of action of bisphosphonates

Although dissemination may occur early in the course of many cancers, the development of overt metastases depends upon a variety of factors inherent to the cancer cells and the tissue(s) they colonize. The time lag between initial dissemination and established metastases could be several years, during which period the bone marrow may provide an unwitting sanctuary for disseminated tumor cells (DTCs). Survival in a dormant state within the bone marrow may help DTCs weather the effects of anticancer therapies and seed posttreatment relapses. The importance of the bone marrow for facilitating DTC survival may vary depending on the type of cancer and mechanisms of tumor cell dissemination. By altering the bone microenvironment, bisphosphonates may reduce DTC viability. Moreover, some bisphosphonates have demonstrated multiple anticancer activities. These multiple mechanisms may help explain the improvement in disease outcomes with the use of zoledronic acid in malignancies like breast cancer and multiple myeloma.

Synergistic Effect of Geranylgeranyltransferase Inhibitor, GGTI, and Docetaxel on the Growth of Prostate Cancer Cells

Most advanced prostate cancers progress to castration resistant prostate cancer (CRPC) after a few years of androgen deprivation therapy and the prognosis of patients with CRPC is poor. Although docetaxel and cabazitaxel can prolong the survival of patients with CRPC, inevitable progression appears following those treatments. It is urgently required to identify better or alternative therapeutic strategies. The purpose of this study was to confirm the anti-cancer activity of zoledronic acid (Zol) and determine whether inhibition of geranylgeranylation in the mevalonate pathway could be a molecular target of prostate cancer treatment. We examined the growth inhibitory effect of Zol in prostate cancer cells (LNCaP, PC3, DU145) and investigated a role of geranylgeranylation in the anticancer activity of Zol. We, then, evaluated the growth inhibitory effect of geranylgeranyltransferase inhibitor (GGTI), and analyzed the synergy of GGTI and docetaxel by combination index and isobolographic analysis. Zol inhibited the growth of all prostate cancer cell lines tested in a dose-dependent manner through inhibition of geranylgeranylation. GGTI also inhibited the prostate cancer cell growth and the growth inhibitory effect was augmented by a combination with docetaxel. Synergism between GGTI and docetaxel was observed across a broad range of concentrations. In conclusion, our results demonstrated that GGTI can inhibit the growth of prostate cancer cells and has synergistic effect with docetaxel, suggesting its potential role in prostate cancer treatment.

The use of zoledronic acid in pediatric cancer patients

BACKGROUND

The third generation bisphosphonate zoledronic acid has demonstrated efficacy in reducing skeletal-related events in adult patients with multiple cancer types that have skeletal disease. The use of zoledronic acid in pediatric oncology patients with bone metastases for the purpose of reducing pain, improving bone strength and altering the progression of metastatic disease has not been thoroughly evaluated.

PROCEDURE

From October 2005 to December 2008, 19 patients at the Aflac Cancer Center received one or more doses of zoledronic acid as part of their therapy. A retrospective review of these patients was performed and information was collected including indication for treatment, toxicities, and outcomes.

RESULTS

Most patients (n = 15) received zoledronic acid following relapse of their malignancy with metastatic disease present in one or more bony sites. Hypocalcemia and hypophosphatemia were frequent, but did not result in clinical symptoms. More significant toxicities associated with zoledronic acid, including clinically apparent renal insufficiency and osteonecrosis of the jaw, were not seen. Overall, zoledronic acid was well tolerated in this population.

CONCLUSIONS

The benefits of zoledronic acid seen in randomized trials of adults with bone metastases have sparked interest in its use for children with metastatic cancer. The administration of zoledronic acid in pediatric oncology appears safe, and may result in improved bone strength and pain control. Further evaluation is warranted to prospectively evaluate its efficacy and long-term safety in pediatric patients with cancer and skeletal metastases.

CCN1, a candidate target for zoledronic acid treatment in breast cancer

CCN1, also known as CYR61, is a survival and proangiogenic factor overexpressed in about 30% of invasive breast carcinomas, and particularly in triple-negative breast carcinomas (TNBC). CCN1 expression in breast cancer promotes tumorigenicity, metastasis, antihormone, and chemoresistance. TNBCs often develop bone metastasis, thus the vast majority of patients receive bisphosphonate treatment as a companion to chemotherapy. Zoledronic acid (ZOL), a bisphosphonate currently in use, inhibits bone resorption, prevents development of new osteolytic lesions induced by tumor metastasis, and has a direct antitumor activity in breast cancer cells and tumors. We have shown that ZOL inhibits anchorage independent growth as well as branching and morphogenesis in CCN1 overexpressing cells. However, the mechanism is not yet well understood. In this study, we investigate the effect of ZOL in breast cancer cells with high and undetectable CCN1 expression levels. We show that CCN1-expressing cells are more sensitive to ZOL, that ZOL induces downregulation of the CCN1 promoter activity and CCN1 protein expression in a dose-dependent manner, and that ZOL is associated with a decrease in phosphorylated Akt and translocation of FOXO3a, a negative regulator of CCN1 expression, to the nucleus. Deletion of the FOXO3a binding site in the CCN1 promoter prevents ZOL inhibition of the CCN1 promoter activity showing that FOXO3a transcriptional activation is necessary for ZOL to induce CCN1 inhibition. This study provides evidence that ZOL targets the proangiogenic factor (CCN1) through FOXO3a and reveals a new mechanism of ZOL action in breast cancer cells.

Effect of zoledronic acid and amputation on bone invasion and lung metastasis of canine osteosarcoma in nude mice

Osteosarcoma (OSA) is an aggressive, highly metastatic and lytic primary bone neoplasm commonly affecting the appendicular skeleton of dogs and children. Current treatment options include amputation of the afflicted limb, limb-sparing procedures, or palliative radiation with or without adjunct chemotherapy. Therapies that inhibit bone resorption, such as the bisphosphonates, may be an effective palliative therapy by limiting the local progression of OSA in those patients that are not viable candidates for amputation. We have developed a mouse model of canine skeletal OSA following intratibial inoculation of OSCA40 cells that spontaneously metastasized to the lungs. We demonstrated that therapy with a nitrogen-containing bisphosphonate, zoledronic acid (Zol), reduced OSA-induced bone lysis; however, Zol monotherapy or in combination with amputation was not effective at inhibiting pulmonary metastasis. While not reaching statistical significance, amputation of the tumor-bearing limb reduced the average incidence of lung metastases; however, this effect was nullified when Zol was added to the treatment protocol. In untreated mice, the magnitude of proximal tibial lysis was significantly correlated with the incidence of metastasis. The data support amputation alone for the management of appendicular OSA rather than combining amputation with Zol. However, in patients that are not viable candidates for amputation, Zol may be a useful palliative therapy for OSA by reducing the magnitude of lysis and therefore bone pain, despite the risk of increased pulmonary metastasis.

Zoledronic acid use in cancer patients: more than just supportive care?

Bone is the most common site for metastasis from solid tumors, and the majority of patients will develop bone metastases during the natural course of their disease. Bisphosphonates are an effective treatment for preventing skeletal-related events in patients with bone metastases and may preserve functional independence and quality of life. Although several bisphosphonates have been investigated in patients with solid tumors, only zoledronic acid (ZOL) is approved by the US Food and Drug Administration and the European Medicines Agency for preventing skeletal-related events in patients across a broad range of solid tumors. In addition, bisphosphonates, notably ZOL, prevent cancer treatment-induced bone loss in breast and prostate cancer patients who are receiving endocrine therapy. It also has been demonstrated that ZOL directly and indirectly inhibits cancer cell growth in vitro and growth and tumorigenesis in animal model systems. These properties may produce clinically meaningful benefits. In recent clinical studies in patients with cancer, ZOL improved overall and prolonged disease-free survival. Ongoing clinical trials in patients with solid tumors will provide further insight into the potential of ZOL to prevent distant metastases and improve survival.

Zoledronic acid induces autophagic cell death in human prostate cancer cells

PURPOSE

Bisphosphonates are potent inhibitors of bone resorption. In vitro studies show that zolendronic acid inhibits prostate cancer cell growth by activating apoptosis. We investigated whether zolendronic acid also inhibits prostate cancer cell growth by autophagy (type II programmed cell death).

MATERIALS AND METHODS

We investigated the induction of autophagy in the PC-3, DU-145, LNCaP and CRW22Rv1 cell lines upon zolendronic acid treatment. LC3-II protein formation was detected by Western blot. LC3-II incorporation into autophagosomes was detected by immunofluorescence staining. Acidic organelle formation was detected by acridine orange staining. Rescue experiments using an apoptosis inhibitor and/or an autophagy inhibitor were performed by MTT assay.

RESULTS

Autophagy induction was detected by formation of the LC3-II protein after exposure to 100 μM zolendronic acid. LC3-II and caspase-3 processing was detected 6 days after treatment. Acidic organelles were detectable by acridine orange staining and immunofluorescence showed round-up and condensed staining of LC3-II, suggesting autophagosome formation in the cytoplasm during autophagic cell death. Cell growth was rescued only by administering an apoptosis and autophagy inhibitor during zolendronic acid treatment, indicating that zolendronic acid induces prostate cancer death by apoptotic and autophagic cell death.

CONCLUSIONS

To our knowledge we report the first study showing that zolendronic acid markedly inhibits human prostate cancer cell growth through autophagic cell death. Zolendronic acid shows its anticancer activity via apoptosis and autophagy. These findings can potentially contribute to the beneficial use of zolendronic acid for prostate cancer treatment.

Improving progression-free and overall survival in patients with cancer: a potential role for bisphosphonates

INTRODUCTION

Bisphosphonates are a well-established therapy for patients with multiple myeloma or bone metastases from advanced cancers and are used routinely to delay the onset and reduce the risk of skeletal-related events. Emerging evidence indicates that they also may provide additional anticancer benefits. These developments warrant reappraisal of their role in patients with cancer and reevaluation of optimal therapeutic regimens.

AREAS COVERED

This article reviews the evidence of the anticancer activity of bisphosphonates in patients with solid tumors or multiple myeloma. The underlying mechanisms of the anticancer activity of bisphosphonates are elucidated from preclinical and translational data that show that bisphosphonates suppress tumor growth and survival, inhibit tumor-mediated angiogenesis, or stimulate host anticancer immune response. These data also provide insights into the potential for therapeutic combinations. Preclinical and clinical data relating to the anticancer effects of bisphosphonates are reviewed by cancer type.

EXPERT OPINION

Future trials of bisphosphonates in cancer patients will explore the underlying mechanism of the anticancer benefit in greater detail and attempt to examine critically the potential clinical benefit in individual cancer types in early/advanced disease.

Zoledronic acid directly suppresses cell proliferation and induces apoptosis in highly tumorigenic prostate and breast cancers

Background:

Bisphosphonates (BPs) were designed for the prevention of skeletal-related events secondary to bone metastases. The purpose of this study was to show that zoledronic acid (ZA) directly eradicates highly tumorigenic and potentially metastatic cancer cells.

Materials and Methods:

Human prostate and breast highly tumorigenic (PC3, MCF 7) and low- or non-tumorigenic (LNCaP, MCF 10a) cell lines, respectively, were exposed to different concentrations of ZA (0-10 μM). Reverse transcriptase double quantitative polymerase chain reaction was used for quantitative gene expression analysis. Apoptosis and cell proliferation were determined using microscopic observation and MTS assays. Western blot was used to confirm the translational effects of apoptotic genes on protein expression.

Results:

Human prostate and breast highly tumorigenic (PC3, MCF 7) and low- or non-tumorigenic (LNCaP, MCF 10a) cell lines, respectively, showed multiple genes demonstrating differential expressions, including TRAF, TRADD, BCL2, CASPASES and IAP families. Increasing ZA concentrations showed a greater concentration-time response on cell proliferation and apoptosis in the highly tumorigenic cells. These results were confirmed by both reversing and enhancing the effect of ZA on cell proliferation with caspase 3, 7 or survivin siRNA, respectively. Pro-apoptotic proteins bax and caspase 2, 3, 7 and 9 were up-regulated, while the anti-apoptotic proteins bcl2, birc3 and survivin were down-regulated only in the highly tumorigenic cells.

Conclusions:

This explains the ability of ZA to inhibit bony metastasis in highly tumorigenic cells compared with the low- or non-tumorigenic cells through a significant decrease in cell proliferation and increase in apoptosis through gene-regulated and translational-mediated down-regulation of survivin coupled with the inhibition of caspase 3 or 7. This has significant implications toward understanding the pharmacophysiology of BPs in metastasis and supports the clinically observed effect of BPs when administered adjunctively with anticancer drugs such as cyclophosphamide/methotrexate/5-fluorouracil, epirubicin in combination with cyclophosphamide or docetaxel, and doxorubicin.