A promising approach for treatment of tumor-induced bone diseases: utilizing bisphosphonate derivatives of nucleoside antimetabolites

Novel Approaches to Monitor Pharmacokinetics and Metabolism of Gemcitabine-Ibandronate Conjugate in Mice and Dogs

BACKGROUND

The use of the bone-seeking properties of bisphosphonates (BPs) to target the delivery of therapeutic drugs is a promising approach for the treatment of bone metastases. Currently, the most advanced example of this approach is a gemcitabine-ibandronate conjugate (GEM-IB), where the bone-targeting BP ibandronate (IB) is covalently linked to the antineoplastic agent gemcitabine (GEM) via a spacer phosphate group. In the present study, we describe the development of a new analytical platform to evaluate the metabolism and pharmacokinetics of GEM-IB in mice and dogs and the results of proof-of-concept studies assessing the pharmacokinetics of GEM-IB in dogs and mice.

METHODS

We validated analytical platforms to analyze GEM-IB and five of its major metabolites IB, gemcitabine-5'-phosphate (GEMMP), gemcitabine (GEM), 2',2'-difluoro-2'-deoxyuridine-5'-phosphate (dFdUMP), and 2',2'-difluoro-2'-deoxyuridine (dFdU) and performed proof-of-concept pharmacokinetic studies in mice (5 mg/kg i.p.) and dogs (5 mg/kg i.v.).

RESULTS

Intra- and inter-run accuracy and imprecision (3 days) of the assays met the (FDA) acceptance criteria. The proof-of-concept plasma pharmacokinetic studies in mice showed AUCs of 1278, 10,652, 405, 38, 1063, 3389, and 38 h·ng/mL for GEM-IB, IB, GEMMP, dFdU-MP, GEM, and dFdU, respectively. In dog plasma, AUCs of 295, 5725, 83, 11, 1625, and 6569 h·ng/mL were observed for GEM-IB, IB, GEMMP, dFdUMP, GEM, and dFdU.

CONCLUSIONS

Pharmacokinetic studies in dogs and mice showed that GEM-IB is rapidly converted to IB and GEM; dFdU is formed (from GEM) with a delay. The rapid disappearance of GEM-IB from circulation could be explained by a combination of metabolism and rapid distribution to tissue/bone.

Engineering small-molecule and protein drugs for targeting bone tumors

Bone cancer is common and severe. Both primary (e.g., osteosarcoma, Ewing sarcoma) and secondary (e.g., metastatic) bone cancers lead to significant health problems and death. Currently, treatments such as chemotherapy, hormone therapy, and radiation therapy are used to treat bone cancer, but they often only shrink or slow tumor growth and do not eliminate cancer completely. The bone microenvironment contributes unique signals that influence cancer growth, immunogenicity, and metastasis. Traditional cancer therapies have limited effectiveness due to off-target effects and poor distribution on bones. As a result, therapies with improved specificity and efficacy for treating bone tumors are highly needed. One of the most promising strategies involves the targeted delivery of pharmaceutical agents to the site of bone cancer by introduction of bone-targeting moieties, such as bisphosphonates or oligopeptides. These moieties have high affinities to the bone hydroxyapatite matrix, a structure found exclusively in skeletal tissue, and can enhance the targeting ability and efficacy of anticancer drugs when combating bone tumors. This review focuses on the engineering of small molecules and proteins with bone-targeting moieties for the treatment of bone tumors.

Research progress of bone-targeted drug delivery system on metastatic bone tumors

Bone metastases are common in malignant tumors and the effect of conventional treatment is limited. How to effectively inhibit tumor bone metastasis and deliver the drug to the bone has become an urgent issue to be solved. While bone targeting drug delivery systems have obvious advantages in the treatment of bone tumors. The research on bone-targeted anti-tumor therapy has made significant progress in recent years. We introduced the related tumor pathways of bone metastases. The tumor microenvironment plays an important role in metastatic bone tumors. We introduce a drug-loading systems based on different environment-responsive nanocomposites for anti-tumor and anti-metastatic research. According to the process of bone metastases and the structure of bone tissue, we summarized the information on bone-targeting molecules. Bisphosphate has become the first choice of bone-targeted drug delivery carrier because of its affinity with hydroxyapatite in bone. Therefore, we sought to summarize the bone-targeting molecule of bisphosphate to identify the modification effect on bone-targeting. And this paper discusses the relationship between bisphosphate bone targeting molecular structure and drug delivery carriers, to provide some new ideas for the research and development of bone-targeting drug delivery carriers. Targeted therapy will make a more outstanding contribution to the treatment of tumors.

Gemcitabine-Ibandronate Conjugate Enables the Bone-Targeted Combination Therapy in Bone Cancer: Synthesis and Efficacy in Combination with Docetaxel

Patients with cancer-induced bone disease, including primary bone cancers such as osteosarcoma (OS) and metastases from other tissues of origin, present a high unmet medical need. We present a potential therapeutic approach built upon a proven bone-targeting bisphosphonate conjugate platform with the known synergies of gemcitabine (GEM) and docetaxel (DTX). The synthesis of rationally designed GEM-IB, the conjugate of GEM-5'-phosphate with ibandronate (IB), is presented. GEM-IB as a single agent or in combination with DTX demonstrated reduced tumor burden, preservation of the bone architecture, and improved the survival in a murine model of OS. This is the first demonstration of a bone-targeting conjugate in combination with a second drug to create effective drug ratios in the bone compartment.

Bisphosphonate-Based Conjugates and Derivatives as Potential Therapeutic Agents in Osteoporosis, Bone Cancer and Metastatic Bone Cancer

Metastatic bone cancer occurs in every type of cancer but is prevalent in lung, breast, and prostate cancers. These metastases can cause extensive morbidity, including a range of skeletal-related events, often painful and linked with substantial hospital resource usage. The treatment used is a combination of chemotherapy and surgery. However, anticancer drugs are still limited due to severe side effects, drug resistance, poor blood supply, and non-specific drug uptake, necessitating high toxic doses. Bisphosphonates are the main class of drugs utilized to inhibit metastatic bone cancer. It is also used for the treatment of osteoporosis and other bone diseases. However, bisphosphonate also suffers from serious side effects. Thus, there is a serious need to develop bisphosphonate conjugates with promising therapeutic outcomes for treating metastatic bone cancer and osteoporosis. This review article focuses on the biological outcomes of designed bisphosphonate-based conjugates for the treatment of metastatic bone cancer and osteoporosis.

"The use of bisphosphonates to treat skeletal complications in solid tumours"

The skeleton is the most common site of secondary disease in breast cancer and prostate cancer, with up to 80% of patients with advanced disease developing bone metastases (BM). The proportion is also substantial in advanced lung cancer (20%-40%). Because of the high prevalence of cancers of the breast, prostate and lung, these cancers account for more than 80% of cases of metastatic bone disease occurring in solid tumours. Metastatic bone disease is associated with greatly increased bone resorption by osteoclasts, leading to moderate to severe pain and other skeletal complications, with major impact on quality of life (QoL). Skeletal Related Events (SREs) have been defined as: pathological long bone or vertebral fractures; spinal cord compression; need for radiation for pain relief or to prevent fracture/spinal cord compression, need for surgery to bone and hypercalcaemia. More recently, Symptomatic Skeletal Events (SSEs) have been defined to monitor QoL. Although there are currently no curative treatments for metastatic bone disease, patients with breast or prostate cancer and BM are now surviving for several years and sometimes longer, and prevention of SREs is the key aim to optimization of QoL. Since their discovery 50 years ago and their introduction more than 30 years ago into the field of metastatic bone disease, a range of oral and intravenous bisphosphonate drugs have made a major contribution to prevention of SREs. Large trials have clearly demonstrated the clinical value of different bisphosphonate-based drugs (including the oral drugs ibandronate and clodronate and intravenous agents such as zoledronate and pamidronate), in treatment of hypercalcaemia of malignancy and the reduction of SREs and SSEs in a range of cancers. Despite the success of denosumab in reducing osteolysis, bisphosphonates also remain mainstay drugs for treatment of metastatic bone disease. Recognizing the 50th Anniversary of the discovery of bisphosphonates, this review focuses on their continuing value in BM treatment and their future potential, for example in providing a bone-targeting vehicle for cytotoxic drugs.

Bisphosphonates for delivering drugs to bone

Advances in the design of potential bone-selective drugs for the treatment of various bone-related diseases are creating exciting new directions for multiple unmet medical needs. For bone-related cancers, off-target/non-bone toxicities with current drugs represent a significant barrier to the quality of life of affected patients. For bone infections and osteomyelitis, bacterial biofilms on infected bones limit the efficacy of antibiotics because it is hard to access the bacteria with current approaches. Promising new experimental approaches to therapy, based on bone-targeting of drugs, have been used in animal models of these conditions and demonstrate improved efficacy and safety. The success of these drug-design strategies bodes well for the development of therapies with improved efficacy for the treatment of diseases affecting the skeleton. LINKED ARTICLES: This article is part of a themed issue on The molecular pharmacology of bone and cancer-related bone diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.9/issuetoc.

Drug delivery nanocarriers and recent advances ventured to improve therapeutic efficacy against osteosarcoma: an overview

BACKGROUND

Osteosarcoma (OS) is one of the key cancers affecting the bone tissues, primarily occurred in children and adolescence. Recently, chemotherapy followed by surgery and then post-operative adjuvant chemotherapy is widely used for the treatment of OS. However, the lack of selectivity and sensitivity to tumor cells, the development of multi-drug resistance (MDR), and dangerous side effects have restricted the use of chemotherapeutics.

MAIN BODY

There is an unmet need for novel drug delivery strategies for effective treatment and management of OS. Advances in nanotechnology have led to momentous progress in the design of tumor-targeted drug delivery nanocarriers (NCs) as well as functionalized smart NCs to achieve targeting and to treat OS effectively. The present review summarizes the drug delivery challenges in OS, and how organic nanoparticulate approaches are useful in overcoming barriers will be explained. The present review describes the various organic nanoparticulate approaches such as conventional nanocarriers, stimuli-responsive NCs, and ligand-based active targeting strategies tested against OS. The drug conjugates prepared with copolymer and ligand having bone affinity, and advanced promising approaches such as gene therapy, gene-directed enzyme prodrug therapy, and T cell therapy tested against OS along with their reported limitations are also briefed in this review.

CONCLUSION

The nanoparticulate drugs, drug conjugates, and advanced therapies such as gene therapy, and T cell therapy have promising and potential application in the effective treatment of OS. However, many of the above approaches are still at the preclinical stage, and there is a long transitional period before their clinical application.

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.

First-in-Human Phase I Study of MBC-11, a Novel Bone-Targeted Cytarabine-Etidronate Conjugate in Patients with Cancer-Induced Bone Disease

Lessons Learned.

Results are consistent with MBC‐11 targeting and treating cancer‐induced bone lesions by concentrating cytarabine and etidronate at the site of disease.

MBC‐11 was well tolerated, with an maximum tolerated dose of 5 mg/kg per day and myelosuppression as the principal toxicity.

Treatment significantly reduced cancer cell activity in over half of bone lesions detected at baseline.

MBC‐11 pharmacokinetic and pharmacodynamic parameters are consistent with the novel drug design goals, and encouraging results warrant further clinical development.

Background.

MBC‐11 is a first‐in‐class conjugate of the bone‐targeting bisphosphonate etidronate covalently linked to the antimetabolite cytarabine (araC). This first‐in‐human phase I dose escalation study assessed safety, tolerability, maximum tolerated dose (MTD), plasma pharmacokinetics, bone turnover, tumor biomarkers, and bone lesion activity by fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F‐FDG‐PET/CT) imaging.

Methods.

Fifteen patients with advanced solid cancers and cancer‐induced bone disease (CIBD) were treated with 0.5–10 mg/kg per day of MBC‐11 administered daily for 5 days of every 4 weeks for up to four cycles.

Results.

Grade 1–2 myelosuppression, involving all lineages, was the principal toxicity. Two of three patients treated with 10 mg/kg experienced dose‐limiting grade 4 neutropenia and thrombocytopenia (adverse event [AE] duration ≤5 days); the MTD was 5 mg/kg. Four of five patients with pretreatment elevations of the bone resorption marker TRAP5b (tartrate resistant acid phosphatase‐5b) had persistent decrements. Six of 13 patients who reported baseline pain noted a reduction after MBC‐11. ¹⁸F‐FDG‐PET/CT imaging demonstrated partial metabolic responses in three patients and stable metabolic responses in three other patients. SUV_max (standard unit of emission normalized to total uptake) was reduced by at least 25% in 110 (52%) of 211 bone lesions. Significant activity was noted across all doses, and myelosuppression increased with dose.

Conclusion.

At MBC‐11 doses that were well tolerated, substantial reductions in metabolic activity of bone‐associated cancer cells provide a foundation for further disease‐directed efficacy studies.

Bisphosphonate conjugation for bone specific drug targeting

Bones provide essential functions and are sites of unique biochemistry and specialized cells, but can also be sites of disease. The treatment of bone disorders and neoplasia has presented difficulties in the past, and improved delivery of drugs to bone remains an important goal for achieving effective treatments. Drug targeting strategies have improved drug localization to bone by taking advantage of the high mineral concentration unique to the bone hydroxyapatite matrix, as well as tissue-specific cell types. The bisphosphonate molecule class binds specifically to hydroxyapatite and inhibits osteoclast resorption of bone, providing direct treatment for degenerative bone disorders, and as emerging evidence suggests, cancer. These bone-binding molecules also provide the opportunity to deliver other drugs specifically to bone by bisphosphonate conjugation. Bisphosphonate bone-targeted therapies have been successful in treatment of osteoporosis, primary and metastatic neoplasms of the bone, and other bone disorders, as well as refining bone imaging. In this review, we focus upon the use of bisphosphonate conjugates with antineoplastic agents, and overview bisphosphonate based imaging agents, nanoparticles, and other drugs. We also discuss linker design potential and the current state of bisphosphonate conjugate research progress. Ongoing investigations continue to expand the possibilities for bone-targeted therapeutics and for extending their reach into clinical practice.

Pharmacologically Inactive Bisphosphonates as an Alternative Strategy for Targeting Osteoclasts: In Vivo Assessment of 5-Fluorodeoxyuridine-Alendronate in a Preclinical Model of Breast Cancer Bone Metastases

Bisphosphonates have effects that are antiresorptive, antitumor, and antiapoptotic to osteoblasts and osteocytes, but an effective means of eliciting these multiple activities in the treatment of bone metastases has not been identified. Antimetabolite-bisphosphonate conjugates have potential for improved performance as a class of bone-specific antineoplastic drugs. The primary objective of the study was to determine whether an antimetabolite-bisphosphonate conjugate will preserve bone formation concomitant with antiresorptive and antitumor activity. 5-FdU-ale, a highly stable conjugate between the antimetabolite 5-fluoro-2'-deoxyuridine and the bisphosphonate alendronate, was tested for its therapeutic efficacy in a mouse model of MDA-MB231 breast cancer bone metastases. In vitro testing revealed osteoclasts to be highly sensitive to 5-FdU-ale. In contrast, osteoblasts had significantly reduced sensitivity. Tumor cells were resistant in vitro but in vivo tumor burden was nevertheless significantly reduced compared with untreated mice. Sensitivity to 5-FdU-ale was not mediated through inhibition of farnesyl diphosphate synthase activity, but cell cycle arrest was observed. Although serum tartrate-resistant acid phosphatase (TRAP) levels were greatly reduced by both drugs, there was no significant decrease in the serum bone formation marker osteocalcin with 5-FdU-ale treatment. In contrast, there was more than a fivefold decrease in serum osteocalcin levels with alendronate treatment (p < 0.001). This finding is supported by time-lapse micro-computed tomography analyses, which revealed bone formation volume to be on average 1.6-fold higher with 5-FdU-ale treatment compared with alendronate (p < 0.001). We conclude that 5-FdU-ale, which is a poor prenylation inhibitor but maintains potent antiresorptive activity, does not reduce bone formation and has cytostatic antitumor efficacy. These results document that conjugation of an antimetabolite with bisphosphonates offers flexibility in creating potent bone-targeting drugs with cytostatic, bone protection properties that show limited nephrotoxicity. This unique class of drugs may offer distinct advantages in the setting of targeted adjuvant therapy and chemoprevention of bone diseases. © 2016 American Society for Bone and Mineral Research.

NF-κB as a Therapeutic Target in Inflammatory-Associated Bone Diseases

Inflammation is a defensive mechanism for pathogen clearance and maintaining tissue homeostasis. In the skeletal system, inflammation is closely associated with many bone disorders including fractures, nonunions, periprosthetic osteolysis (bone loss around orthopedic implants), and osteoporosis. Acute inflammation is a critical step for proper bone-healing and bone-remodeling processes. On the other hand, chronic inflammation with excessive proinflammatory cytokines disrupts the balance of skeletal homeostasis involving osteoblastic (bone formation) and osteoclastic (bone resorption) activities. NF-κB is a transcriptional factor that regulates the inflammatory response and bone-remodeling processes in both bone-forming and bone-resorption cells. In vitro and in vivo evidences suggest that NF-κB is an important potential therapeutic target for inflammation-associated bone disorders by modulating inflammation and bone-remodeling process simultaneously. The challenges of NF-κB-targeting therapy in bone disorders include: (1) the complexity of canonical and noncanonical NF-κB pathways; (2) the fundamental roles of NF-κB-mediated signaling for bone regeneration at earlier phases of tissue damage and acute inflammation; and (3) the potential toxic effects on nontargeted cells such as lymphocytes. Recent developments of novel inhibitors with differential approaches to modulate NF-κB activity, and the controlled release (local) or bone-targeting drug delivery (systemic) strategies, have largely increased the translational application of NF-κB therapy in bone disorders. Taken together, temporal modulation of NF-κB pathways with the combination of recent advanced bone-targeting drug delivery techniques is a highly translational strategy to reestablish homeostasis in the skeletal system.

Methyl donor deficiency impairs bone development via peroxisome proliferator-activated receptor-γ coactivator-1α-dependent vitamin D receptor pathway

Deficiency in methyl donor (folate and vitamin B12) and in vitamin D is independently associated with altered bone development. Previously, methyl donor deficiency (MDD) was shown to weaken the activity of nuclear receptor coactivator, peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α), for nuclear signaling in rat pups, including estrogen receptor-α and estrogen-related receptor-α; its effect on vitamin D receptor (VDR) signaling, however, is unknown. We studied bone development under MDD in rat pups and used human MG-63 preosteoblast cells to better understand the associated molecular mechanism. In young rats, MDD decreased total body bone mineral density, reduced tibia length, and impaired growth plate maturation, and in preosteoblasts, MDD slowed cellular proliferation. Mechanistic studies revealed decreased expression of VDR, estrogen receptor-α, PGC1α, arginine methyltransferase 1, and sirtuin 1 in both rat proximal diaphysis of femur and in MG-63, as well as decreased nuclear VDR-PGC1α interaction in MG-63 cells. The weaker VDR-PGC1α interaction could be attributed to the reduced protein expression, imbalanced PGC1α methylation/acetylation, and nuclear VDR sequestration by heat shock protein 90 (HSP90). These together compromised bone development, which is reflected by lowered bone alkaline phosphatase and increased proadipogenic peroxisome proliferator-activated receptor-γ, adiponectin, and estrogen-related receptor-α expression. Of interest, under MDD, the bone development effects of 1,25-dihydroxyvitamin D3 were ineffectual and these could be rescued by the addition of S-adenosylmethionine, which restored expression of arginine methyltransferase 1, PGC1α, adiponectin, and HSP90. In conclusion, MDD inactivates vitamin D signaling via both disruption of VDR-PGC1α interaction and sequestration of nuclear VDR attributable to HSP90 overexpression. These data suggest that vitamin D treatment may be ineffective under MDD.-Feigerlova, E., Demarquet, L., Melhem, H., Ghemrawi, R., Battaglia-Hsu, S.-F., Ewu, E., Alberto, J.-M., Helle, D., Weryha, G., Guéant, J.-L. Methyl donor deficiency impairs bone development via peroxisome proliferator-activated receptor-γ coactivator-1α-dependent vitamin D receptor pathway.

Targeted delivery to bone and mineral deposits using bisphosphonate ligands

The high concentration of mineral present in bone and pathological calcifications is unique compared with all other tissues and thus provides opportunity for targeted delivery of pharmaceutical drugs, including radiosensitizers and imaging probes. Targeted delivery enables accumulation of a high local dose of a therapeutic or imaging contrast agent to diseased bone or pathological calcifications. Bisphosphonates (BPs) are the most widely utilized bone-targeting ligand due to exhibiting high binding affinity to hydroxyapatite mineral. BPs can be conjugated to an agent that would otherwise have little or no affinity for the sites of interest. This article summarizes the current state of knowledge and practice for the use of BPs as ligands for targeted delivery to bone and mineral deposits. The clinical history of BPs is briefly summarized to emphasize the success of these molecules as therapeutics for metabolic bone diseases. Mechanisms of binding and the relative binding affinity of various BPs to bone mineral are introduced, including common methods for measuring binding affinity in vitro and in vivo. Current research is highlighted for the use of BP ligands for targeted delivery of BP conjugates in various applications, including (1) therapeutic drug delivery for metabolic bone diseases, bone cancer, other bone diseases, and engineered drug delivery platforms; (2) imaging probes for scintigraphy, fluorescence, positron emission tomography, magnetic resonance imaging, and computed tomography; and (3) radiotherapy. Last, and perhaps most importantly, key structure-function relationships are considered for the design of drugs with BP ligands, including the tether length between the BP and drug, the size of the drug, the number of BP ligands per drug, cleavable tethers between the BP and drug, and conjugation schemes.

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.

In vitro and in vivo toxicity of 5-FdU-alendronate, a novel cytotoxic bone-seeking duplex drug against bone metastasis

BACKGROUND

Bone remains one of the most common anatomic sites for cancer metastases, and the limited therapeutic options aggravate cancer-related morbidity and mortality in multiple malignancies. The covalent conjugation of the amino-bisphosphonate alendronate (ale) with the antimetabolite 5-fluoro-2'-desoxyuridine (5-FdU) results in N(4)-(butyl-(4-hydroxy-4-phosphono)phosphate)-5-fluoro-2'-desoxyuridine (5-FdU-alendronat, 5-FdU-ale), an effective, novel bone-targeting duplex drug directed against skeletal cancer manifestations.

METHODS

In vitro cytotoxicity of ale, 5-FdU or 5-FdU-ale was measured with Alamar Blue and MUH cell viability assays in 14 malignant melanoma, multiple myeloma, bone marrow-derived stromal cell and osteoblast-like cell lines. In vivo toxicity was evaluated using the chicken embryo assay and evaluation of nephrotoxicity and the systemic toxicity in Balb/c nude mice. The effect of 5-FdU-ale on osteoclast was evaluated with Balb/c nude mice in a metastatic breast cancer mouse model.

RESULTS

A cell line-specific, dose-related cytotoxicity was observed for 5-FdU-ale in all cancer cell lines tested, which was significantly less toxic than 5-FdU alone when compared to the benign osteoblasts or stromal cells. The embryotoxicity of 5-FdU-ale was significantly less than that of the parental drugs alendronate or 5-FdU. 5-FdU-ale showed no signs of unwanted side effects, weight loss or nephrotoxicity in mice. In a bone metastasis mouse model, 5-FdU-ale reduced the number of tumor-associated osteoclasts.

CONCLUSION

The coupling of an amino-bisphosphonate with an antimetabolite via an N-alkyl-bonding offers a new strategy for the preparation of amino-bisphosphonates conjugates with a cancer cell-specific, efficacious cytotoxic bone-targeting potential along with a reduced systemic toxicity. The innovative duplex drug 5-FdU-ale therefore warrants further clinical investigation.

Biomedical applications of bisphosphonates

Since their discovery over 100 years ago, bisphosphonates have been used industrially as corrosion inhibitors and complexing agents. With the discovery of their pharmacological activity in the late 1960s, implicating their high affinity for hydroxyapatite, bisphosphonates have been employed in the treatment of bone diseases and as targeting agents for colloids and drugs. They have notably been investigated for the treatment of Paget's disease, osteoporosis, bone metastases, malignancy-associated hypercalcemia, and pediatric bone diseases. Currently, they are first-line medications for several of these diseases and are taken by millions of patients worldwide, mostly postmenopausal women. A major problem associated with their use is their low oral bioavailability. Several delivery systems have been proposed to improve their absorption and to direct them to sites other than bone tissues. Beyond their important pharmacological role, the medical applications of bisphosphonates are numerous. In addition, their metal-chelating properties have been exploited to coat and stabilize implants, nanoparticulates, and contrast agents. In this contribution, we review the pharmacological and clinical uses of bisphosphonates and highlight their novel applications in the pharmaceutical and biomedical fields.

Theoretical study of bone cancer therapy by plasmonic nanoparticles

BACKGROUND

Progress made by the scientific community in the understanding of cell receptors and metabolic pathways has led to discovery of chemical and protein agents which act as delivery vectors to specific tissues. Conjugating these agents to noble-metal nanoparticles allows for subsequent accumulation on or within targeted cells. Utilizing the unique light absorption properties of these nanoparticles then allows for photothermal heating of the particles and surrounding tissue.

DISCUSSION

The heat equations are solved for the case of gold nanoparticles in biological hard tissues, such as bone, for applications to two future cancer therapies: nanophotothermolysis and nanophotohyperthermia.

CONCLUSIONS

A survey of recent research in bone-targeting bioconjugates and simulations of nanoparticle thermal fields shows promise for these therapies in the near future.

N⁴-[Alkyl-(hydroxyphosphono)phosphonate]-cytidine-new drugs covalently linking antimetabolites (5-FdU, araU or AZT) with bone-targeting bisphosphonates (alendronate or pamidronate)

Amino-bisphosphonates (alendronate, pamidronate) were covalently linked in a three step synthesis, with protected and triazolylated derivatives of therapeutically used nucleoside analogs (5-FdU, araC, AZT) by substitution of their triazolyl residue. From the deprotected and chromatographically purified reaction mixtures N⁴-[alkyl-(hydroxyphosphono) phosphonate]-cytidine combining two differently cytotoxic functions were obtained. This new family of bisphosphonates (BPs) contains as novelty an alkyl side chain with a cytotoxic nucleoside. The BPs moiety allows for a high binding to hydroxyapatite which is a prerequisite for bone targeting of the drugs. In vitro binding of 5-FdU-alendronate (5-FdU-ale) to hydroxyapatite showed a sixfold increased binding of these BPs as compared to 5-FdU. Exploratory cytotoxic properties of 5-FdU-ale were tested on a panel of human tumor cell lines resulting in growth inhibition ranging between 5% and 38%. The determination of IC₅₀-concentrations of the conjugate in Lewis lung carcinoma and murine macrophages showed an incubation time dependent growth inhibition with higher sensitivity towards the tumor cells. We assume that the antimetabolite-BPs can be cleaved into different active metabolites that may exert cytotoxic and other therapeutic effects. However, the underlying mechanisms of these promising new antimetabolite-BPs conjugates remain to be evaluated in future experiments.