http://informahealthcare.com/drd ISSN: 1071-7544 (print), 1521-0464 (electronic) Drug Deliv, Early Online: 1–9 ! 2014 Informa Healthcare USA, Inc. DOI: 10.3109/10717544.2013.870259

CRITICAL REVIEW

Bisphosphonates: therapeutics potential and recent advances in drug delivery Mohammad Fazil, Sanjula Baboota, Jasjeet K. Sahni, Ameeduzzafar, and Javed Ali

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Department of Pharmaceutics, Faculty of Pharmacy, Jamia Hamdard, Hamdard Nagar, New Delhi, India

Abstract

Keywords

Context: Bisphosphonates (BPs) are widely used for prevention and treatment of osteoporosis. BPs are known as gold standard for osteoporosis (OP) treatment due to their positive results in clinical studies. But some serious side effects are associated with BPs like gastrointestinal adverse effect i.e. esophagitis and ulcer of esophagus. Oral bioavailability (BA) of BPs ranges from 0.6 to 1% due to poor absorption through gastrointestinal tract (GIT). Objective: The main objective of this review is to explore the role of novel drug delivery systems (DDSs) for the delivering of BPs and minimizing the drawbacks associated with them. Methods: The current review is focusing on classification, mechanism of action, and limitations of BPs, and is also dwelling on the use of novel DDSs like nanoparticles, liposomes, topical, transdermal systems, implants, bisphosphonate osteotropic DDS (BP-ODDS), microspheres, and calcium phosphate cements (CPCs) for BPs. This review also gives a critically reviewed compilation of the various in vitro and in vivo studies conducted till date. Conclusion: On the basis of the exhaustive literature, it has been found that the novel DDS minimizes the side effects associated with BPs and enhances the BA. The advance drug delivery has a greater impact on reducing the undesirable effects and increasing the BA of BPs.

Bisphosphonates, gastric side effects, novel drug delivery, nanoparticles, osteoporosis

Introduction Osteoporosis (OP) is a disease of skeletal system and is associated with fragility fracture of the hip, spine and wrist. The demographic data of this disease have shown that hip fractures throughout globe will rise from 1.66 million in 1990 to 6.26 million by 2050 (Dhanwal et al., 2011). It is characterized by low bone mass and micro architectural deterioration of bone tissue, finally increasing the susceptibility of bone fracture with a low energy trauma (Feldstein et al., 2003). National Institute of Health consensus statement defines OP as ‘‘a skeletal disorder characterized by compromised bone strength predisposing a person to an increased risk of fracture’’ (NIH Consensus Development Panel on Osteoporosis Prevention, Diagnosis, and Therapy, 2001). It is known as a silent disease due to its progression without symptoms. It is more prevalent in women especially after menopause when estrogen level decreases. It reflects the disruption in bone remodeling process, where the rate of bone resorption is higher than the bone formation (Liu et al., 2011). Age is the main risk factor for its progression. There are several other risk factors for fractures, and among them reduced bone mineral density is the strongest one (Leichter et al., 1982). Various drugs are being used to treat OP as per Address for correspondence: Dr. Javed Ali, Department of Pharmaceutics, Faculty of Pharmacy, Jamia Hamdard, Hamdard Nagar, New Delhi-110062, India. Tel: +91 9811312247. Fax: +91 1126059633. Email: [email protected], [email protected]

History Received 4 October 2013 Revised 25 November 2013 Accepted 25 November 2013

the severity of disease. The treatment aim is to prevent further bone loss in order to reduce the risk of initial or subsequent fracture. Bisphosphonates (BPs), denusumab, estrogen, raloxifene, salmon calcitonin, and teriparatide are US FDA approved drugs for OP (Baylink et al., 1999, 2012). Besides the above-mentioned drugs, some other drugs are also being used in other countries although they are not approved by US FDA like strontium ranelate (Sr). BPs have a potential value for the treatment of OP among all the drugs available for OP. BPs are the most widely used antiresorptive agents for treatment of OP, and it have been used clinically since 1960s (Anna, 2012). Clinically, BPs have a profound effect on OP. Clinical data have shown that BPs yield a 47% reduction in vertebral fractures as well as wrist fractures, 50% in hip fractures, and a 19% overall drop in all non-vertebral fractures (Black & Cummings, 1996). The current review outlines the various BPs for the treatment of OP along with their drawbacks and what strategies are being used to overcome them for making them more patients compliant.

Classification of BPs BPs are classified on the basis of their chemical structure. They are derived chemically from pyrophosphates that inhibit precipitation of calcium carbonate. Initially these were used as ‘‘water softeners’’ due to their ability to inhibit calcium carbonate precipitation. In early days, they were also used as corrosion inhibitors, complexing agents in the textile, fertilizer, and oil industries (Blomen, 1995). On the basis of the

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Figure 1. Pictorial view of bisphosphonates drugs.

structure, BPs are categorized in mainly two categories, namely nitrogen-containing BPs and non-nitrogen-containing BPs. BPs are characterized by two carbon–phosphorus bonds, when located on the same carbon atom, they allow large variations in side-chains. The variations in side chain make them physiologically and biochemically specific (Akesson, 2003). BPs have a strong binding affinity to the bone which is a unique property of this class and are routinely used for treatment in bone resorption and other bone disorders like osteoporosis, Paget’s disease, or tumor induced osteolysis (Lalatone et al., 2010). Classification of the BPs are given in Figure 1.

Mechanism of action of BPs BPs are preferentially incorporated into active sites for bone remodeling, which commonly occurs in conditions characterized by accelerated skeletal turnover. BPs inhibit calcification as well as hydroxyapatite (HA) breakdown, which effectively suppress the bone resorption (Drake et al., 2008). Although it has low intestinal absorption but show highly selective localization and retention in bone. BPs show their effects at cellular level, tissue level, and biochemical level (Russell, 2006). BPs are highly effective inhibitors of bone resorption which are osteoclasts (Roelofs et al., 2006). The benefit from BPs treatment depends on the weight of risk factors for osteoporotic fracture such as age, bone mineral density, race, family history, and fracture history, and on the presence of risk factors for atypical femur fractures and other potential complications (Hermann & Abrahamsen, 2013). BPs act on the osteoclast cells by two different mechanism, depending on the category whether it is nitrogen containing or not. Non-nitrogen-containing BPs are incorporated into newly formed adenosine triphosphate (ATP) molecules by the class II aminoacyl-transfer RNA synthetases after osteoclastmediated uptake from the bone mineral surface (Russell, 2006). Accumulation of these non-hydrolyzable ATP analogues into the cells are found to be cytotoxic to osteoclast cells due to their inhibitory action on ATP-dependent cellular processes, which leads to osteoclasts apoptosis. Nitrogencontaining BPs work in different ways and promote osteoclasts apoptosis which is distinct from the non–nitrogen

containing BPs. Nitrogen-containing BPs provide antiresorptive effects by binding to the calcium HA crystal at sites of bone resorption, where the bone matrix is exposed (Kavanagh et al., 2006). The BPs are associated with the newly formed bone, where they remain inert and have no skeletal effects. During the bone resorption, drug is released from the bone matrix and is ingested by osteoclast cells. BPs inhibit farnesyl diphosphate synthase (FDPS), a key enzyme and as a primary rate limiting step in the molecular action of nitrogen containing BPs in the cholesterol synthesis and involved in post-translational modification of important signalling molecules (Ras, Rac, Rho, and Rab). Inhibitory action of the FDPS disrupts several pathways that is involved in cytoskeletal organization, cell survival, and cell proliferation, which leads to osteoclast cells’ apoptosis (Rodan & Reszka 2002).

Side effects of BPs therapy Anti-osteoporotic drugs have vast number of side effects. All the drugs of BPs class have a gastrointestinal adverse effect like esophagitis and ulcer of esophagus during therapy. BPs can be given orally or parenterally. BPs are absorbed poorly from the gastrointestinal tract (GIT), which unease their oral administration and has prompted the development of new drug delivery and dosage regimens. Oral administration of alendronate (ALD) and risedronate (RIS) requires fasting before and immediately after the drug is taken. ALD, in particular, has been associated with severe gastric side-effects because it produces esophageal erosions (Akesson, 2003). In addition, BPs also cause abdominal pain and nausea. Patients with intolerance of BPs orally should be treated with parenteral BPs like ibandronate (IBR), or zoledronate (ZOL) administered 3-monthly and once a year. Bioavailability (BA) of BPs has been found to be less than 1% when administered orally, which is too less and adverse effects are too much. The dose needs to be administered with water only, after an overnight fast and for 30–60 min after taking the dose nothing else has to be given by mouth, and additionally patients must remain upright afterwards in order to prevent any gastroesophageal reflux (Anna, 2012). Osteonecrosis of jaw (ONJ) has been reported in some people taking BPs (ZOL-Reclast). The risks of incidence are

Therapeutics

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higher in those individuals who have received BPs intravenously (Woo et al., 2006). Various clinical studies have stated that ALD is generally well tolerated but irritation of the esophagus, inflammation of the esophagus (esophagitis), and ulcers of the esophagus have been reported sporadically with ALD use. The main side effect of nitrogen-containing BPs given intravenously is an acute phase reaction (fever, myalgia, lymphopenia, etc.) due to the release of pro-inflammatory cytokines. An increased risk of atrial fibrillation (AF) has been reported with ZOL once yearly. A number of cases of esophageal cancer in BPs users have been recently reported (Anna, 2012). The most common side effects of ZOL include low grade fever, pain, and stiffness in the muscles, bones or joints, and headache usually found in last few days. IV administration of ZOL, and to a lesser extent, pamidronate causes tubular necrosis leading to renal failure. (Tanvetyanon & Stiff, 2006). But majority of cases have been reversible (Gertz et al., 1995; Osteoporosis, 2013). Novel drug delivery system (DDS) approaches can be undertaken to overcome the shortcoming of BPs, thus making them more patient compliant (De Groen et al., 1996; Giger et al., 2013). These approaches can be the use of absorption enhancers along with BPs or increasing solubility by calcium complex/salts or developing prodrug of BPs. Approximately 50% intravenous bisphosphonates are available for incorporation into the bone matrix compared to an average of 1% of oral bisphosphonates absorbed by the gastrointestinal tract (Ezra & Golomb, 2000). Targeted drug delivery has an immense role to avoid the side effects and toxicity to the body, however, targeting should be highly specific to the organs, tissues, and cells. In order to develop targeted DDSs of BPs, it should be targeted to bones which are more prone to the osteoporotic fracture i.e. hip, spine, and wrist. It is mandatory to study about bone chemical, morphological, and histopathological features and their nature of affinity to the BPs. Prominent side effects and advances in novel DDSs of BPs are given in Figure 2. Local delivery systems also need cautions especially when applied to sensitive skin. Treatment of OP regimen requires longer therapy, which can provoke inflammatory interleukins present locally leading to the erythrema. Local delivery is unsuitable for drugs that irritate or sensitize skin. Some potent drugs

Figure 2. Disadvantages of BPs and their advances as novel drug delivery systems.

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cannot permeate completely leading to insufficient dose delivery to systemic pool. Skin irritation of contact dermatitis may occur due to the drug and/or excipients. Some enzymes present in epidermis may denature the drugs. Drugs with high molecular weight cannot easily permeate through skin. Sometimes adhesives may not adhere well to all types of skin and maybe uncomfortable to apply (Nishiyama et al., 1996; Hsu et al., 2006).

Novel drug delivery for delivering BPs A vast number of delivery systems have been investigated to overcome the problem of poor BA of BPs, more efficient delivery to the target sites and minimize their side effects, and alter their biodistribution. These novel DDSs include nanoparticles, liposomes, topical, transdermal systems, implants, Bisphosphonate Osteotropic DDS (BP-ODDS), microspheres, and calcium phosphate cements (CPCs). Polymeric nanoparticles NPs having great advantages over others novel DDS due to property of easy modifications according to our needs. These systems are attractive because the methods of preparation are generally simple and easy to scale-up. NPs penetrate even into small capillaries and are taken up within cells, allowing an efficient drug accumulation at the targeted sites in the body due to their small size. Nanoparticulate DDSs hold great potential to overcome the obstacles to efficiently target a number of diverse cell types. The small size, customized surface, improved solubility, and multi-functionality of NPs continue to open many doors and create new biomedical applications (Singh & Lillard 2009). The size of the NPs should be less the 100 nm in diameter for delivering the drugs to the bone (Wang et al., 2005). The smaller size NPs can be developed easily with polymers using simple and economical methods. Their small size also favors a high surface-to-volume ratio, makes more compatible with cell structures, and enables their inclusion with target cells, which is desired for developing the targeted and controlled delivery of BPs. PNPs are found more stable in the GIT than other colloidal carriers, such as liposomes, and can protect encapsulated drugs from gastrointestinal environment (Galindo-Rodriguez et al., 2005). Therefore, PNPs may provide a possible solution to overcome many challenges associated with BPs for treating OP. Cenni and associates developed NPs conjugate of poly (D,L-lactide-co-glycolide) with ALD (PLGA-ALD NPs) using emulsion/solvent evaporation technique. The aim of the research was to evaluate the haemocompatibility and the cytotoxicity for endothelial cells and osteoblasts of a carrier system designed to selectively target drugs to the bone tissue. Bone-targeted NPs were prepared through conjugation of a biodegradable polymer PLGA with ALD. All the experiments of haemocompatibility were performed using human venous blood from healthy volunteer donors, which was supplied by a blood bank and various biochemical studies were performed. They concluded that PLGA-ALD NPs showed no effect, did not affect platelets, leukocytes, did not induce hemolysis, and did not have any cytotoxic effect on endothelial cells and osteoblasts. The conjugation with ALD did not affect the biocompatibility of PLGA. So these results confirmed that

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PLGA-ALD NPs are suitable for the intravenous administration, and the drug-loading could make them a promising tool for delivering the BPs for treating OP (Cenni et al., 2008; Pignatello et al., 2009). Thus the developed nanoparticulate drug delivery did not show any bleeding from esophagus and no hemolysis was recorded. It can be concluded that the nanoparticulate DDS can be a novel treatment for OP using BPs in near future. PLGA NPs were also prepared by Choi and associates using estrogen as the active constituent but prepared NPs were modified with both ALD and polyethylene glycol (PEG) to evaluate the potency of the bone-targeted drug delivery. Surface modified with BPs showed strong affinity to the bone surface. The sizes of resulting NPs were under 80 nm as measured by dynamic light scattering (DLS). The estrogen was loaded as a therapeutic agent onto ALD-modified NPs and their release studies showed that ALD serves mainly as a targeting moiety to guide the NPs. The study of Choi and associates confirmed that ALD-modified NPs had a strong and specific adsorption to HA. It was concluded that the modified NPs with ALD enhanced the targeting of PLGA NPs and reduced the undesirable distribution of drug to the non-target sites and reduced the side effects of the drug-treating OP (Choi & Kim, 2007). PEG makes PLGA NPs long circulatory, make the core materials more available to the desired sites and BPs increase their affinity towards the bone tissues. Another study on PLGA was performed by Chaudhari and associates using ZOL. The results revealed that ZOLconjugated PLGA NPs showed more cellular uptake than pegylated PLGA NPs with change in cellular uptake route. In vitro cell lines studies on MCF-7 and BO2 cell line revealed that ZOL anchored PLGA-PEG NPs showed enhanced cell cytotoxicity, increase in cell cycle arrest and more apoptotic activity. In vivo animal studies using technetium-99 m radiolabeling showed prolonged blood circulation half-life, and significantly higher retention of ZOL-tagged NPs at the bone site with enhanced tumor retention. These showed that the targeting ability of ZOL was enhanced and it showed a by strong affinity towards the bone. It was concluded that ZOL-anchored PLGA NPs can be a novel drug delivery tool for delivering BPs for bone targeting their by minimizing the adverse side effects in case of OP treatment therapy (Ramanlal et al., 2012). Thamake and associates also found similar results when ALD was conjugated with PLGA NPs. In vivo non-invasive bioimaging study showed that the higher localization of ALD coated NPs was achieved to the bone as compared to control groups, which was further confirmed by histological analysis. NPs coated with ALD-protected bone resorption and decreased the rate of tumor growth as compared to control groups in an intraosseous model of bone metastasis. They concluded that BPs modified NPs would be a very promising DDS for OP treatment (Thamake et al., 2012). Salzano and associates developed ZOL-containing selfassembly PEGylated NPs. ZOL complexes with calcium phosphate NPs (CaPZ NPs) and cationic liposomes. PEGylation was achieved by two different strategies. CaPZ NPs were covered with PEGylated liposomes (pre-PLCaPZ NPs); alternatively, CaPZ NPs were previously mixed with cationic liposomes and then PEGylated by post-insertion

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method (post-PLCaPZ NPs). NPs had a mean diameter of about 309 nm with a broad size distribution with PDI of 0.36. Results revealed that NPs with BPs had strong effect on bone-related disease as compared to BPs alone (Salzano et al., 2011). Sahana and associates developed and investigated the potential of using novel RIS-HA NPs-based formulation in an animal model of established OP. RIS-HA-loaded NPs of various sizes (80–130 nm) were developed for bone-targeted drug delivery. Three months after ovariectomy, 36 ovariectomized (OVX) rats were divided into six equal groups and treated with various doses of RIS-HA-loaded NPs (500, 350, and 250 mg/kg intravenous single dose) and RIS (500 mg/kg, intravenous single dose). Untreated OVX and sham OVX served as controls. One month after drug administration, the left tibia and femur were tested for bone mechanical properties and histology, respectively. In the right femur, bone density was measured by method based on Archimedes principle and bone porosity analyses were performed using X-ray imaging. RIS-HA-loaded NPs (250 mg/kg) showed a significant increase in bone density and reduced bone porosity when compared with OVX control. Moreover, RIS-HA-loaded NPs (250 mg/kg) significantly increased bone mechanical properties and bone quality when compared with OVX control. The results strongly advocate that the RIS-HA-loaded NPs, which is a novel nanoparticle-based formulation, has a therapeutic advantage over RIS monotherapy for the treatment of OP in a rat model of postmenopausal OP. It may be useful in future for the treatment of OP in human being (Sahana et al., 2013). Liposomes Liposomes are the most widely investigated delivery system for targeted therapies due to their properties like low immunogenicity, biocompatibility, cell specificity, and drug protection. But it has some shortcomings like poor scale-up, cost, short shelf life, and in some cases toxicity and off target effects. To make it long circulatory, shielding with PEG is required, and concept of stealth liposomes has risen out (Kelly et al., 2011). Hosny and associates prepared and evaluated sodium ALD-loaded nanoliposomes (NLS) with a mean size ranging from 70 to 150 nm and spherical in shape. The challenges with sodium ALD were included, very poor oral BA (0.6%), esophageal ulcers, and complicated instructions for its use. So with the use of nanotechnology, they developed sodium ALD into enteric-coated NLS to overcome the previously mentioned drawbacks. NLS were prepared with lipid components of phosphatidylcholine (PC), cholesterol (CH), and lecithin (Lec) in ratios 4:1:1, 4:2:1, 4:3:1, and 4:4:1, respectively. Spherical NLS were successfully developed with a mean size ranging from 70 to 150 nm. Eudragit-coated NLS (EuC-NLS) with PC:CH:Lec:dicetyl phosphate (4:3:1:1) successfully resisted the release of sodium ALD in acidic environment and enhanced the BA in rabbits 12-fold compared with the marketed tablets. It was revealed that EuC-NLS was a promising novel formula for sodium ALD with higher BA and a lower dose, avoiding the side effects of esophageal ulceration during the OP treatments (Hosny et al., 2013).

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Han and associates developed and characterized chitosan-coated liposomes of ALD. Liposomes were prepared with 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)/1,2distearoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (DSPG) by using thin layer film hydration method and then the surface of anionic liposomes was coated by chitosan. Lipid vesicles of 200  13 nm size were obtained with narrow size distribution (PI50.1) and subsequently coated with chitosan which was stable for 24 h. It was also found that developed liposomes had strong mucoadhesive properties. When compared to the untreated drug (non-liposome), the chitosan-coated liposomes indicated significantly (p50.05) increased cellular uptake of ALD in Caco-2 cells and also 2.6-fold enhancement in oral BA of alendronate in rats. Thus liposomal delivery system provides an additional advantage with patient compliance. The drug leakage out of liposomes was minimal in GI fluids, the majority of ALD stayed inside of liposomal vesicles and thus drug itself did not have a chance to contact esophagus. Thus the developed liposomal delivery system of ALD could be a novel DDS for BA enhancement as well as potentially reduced esophageal side effect to the patient for treating OP (Han et al., 2012). Epstein and associates prepared ALD-loaded liposomes by modified thin lipid film hydration technique followed by extrusion. Their studies concluded that the formulation of ALD-loaded liposomes showed in vitro stability (42.5 years) and bioactivity, formulation was found to be effective in the reduction of restenosis. ALD-loaded liposomes can be very useful for delivery of ALD that are long circulating (Epstein et al., 2008). In another study, Hengst and associates prepared BP-loaded liposomes of cholesteryl-trisoxyethylene bisphosphonic acid (CHOL-TOE-BP), a new tailor-made BP derivative, used as bone targeting moiety. The results showed that the prepared liposomes of CHOL-TOEBP-ligand on the surface of the liposomes are an important factor influencing the binding capacity. In vitro data suggested that CHOL-TOE-BP-targeted liposomes would be a potential drug delivery for bone (Hengst et al., 2007). Anada and associates formulated liposomes with calcium phosphatebinding property for a bone-targeting DDS. They synthesized a novel amphipathic molecule having BP head group to recognize and bind to HA. Their results showed liposomes having BP moieties and showed high affinity for HA. It was revealed that liposomes would be excellent carrier for bonetreating therapeutic agent, and BPs have a special role for delivering the molecules (Anada et al., 2009). Shmeeda and associates prepared ZOL-loaded liposomes and concluded that it was more toxic to the experimental rodents. The results indicated that liposomal delivery of ZOL causes a major change in tissue drug distribution and an increase in tumor ZOL levels. But in vivo toxicity of liposomal ZOL seriously limits its dose and its utility in tumor cells. It would be a novel strategy for delivering BPs with minimization of dose and dose-related toxicity to the bone (Shmeeda et al., 2013). Marra and associates developed the ZOL-encapsulated liposomes and concluded that the prepared liposomes increased the BA of ZOL. Their results revealed that it could be useful for the treatment of bone-related disease and delivering the BPs with increased BA and reduced dose (Marra et al., 2011).

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Nasr and associates developed and tested the RIS-loaded liposome for systemic delivery using pulmonary nebulization. Reversed phase evaporation technique was employed for the preparation of liposomes (REVs). RIS accumulation in rat bones following intra-tracheal administration of the selected formulation was assessed using a radiolabeling-based technique, and histological examination of rat lung tissue was performed to assess its safety. The EE% of RIS REVs ranged from 8.8 to 58.96% depending on cholesterol molar ratio, phospholipid type, and presence of stearylamine. The amount of radiolabeled RIS deposited in rat bones after pulmonary administration was 20%, while being considerably safe on lung tissues (Nasr et al., 2013). Topical BP The advantages of topical delivery are to bypass first pass effects, avoidance of the risks and inconveniences of intravenous therapy and of the varied conditions of absorption, like pH changes, presence of enzymes, gastric emptying time. Due to the gastric erosion, it is better to deliver the BPs using topical route. Nam and associates investigated the therapeutic effect of topical RIS on a mouse model of estrogen-deficient OP. The prepared samples containing RIS 10% (w/w), PEG (MW 400), were applied on the mice’s mid-backs every three days for five weeks in four groups having 14-week-old female mice, and ovariectomized the groups were SHAM-operated (SHAM), OVX mice treated with vehicle (OVX-V), OVX mice treated with 0.2% RIS (OVX-0.2% RIS), and OVX-mice treated with 0.02% RIS (OVX-0.02% RIS). The results revealed that topically administered RIS had anti-OP effects and even supported new bone formation. Topical RIS application also reduced the many side effects of orally administered RIS. It is concluded that topical delivery could be an alternate drug delivery for others BPs which can give better compliance to people suffering from OP (Nam et al., 2012). Torger and associates developed polyelectrolyte complex (PEC) nanoparticulate films of ZOL. Colloidally stable dispersions of PEC particles loaded by osteotherapeutic ZOL in the size range 11–141 nm was prepared by mixing pure (PEI) or maltose-modified poly (ethyleneimine) (PEI-M) with cellulose sulfate in the presence of ZOL. A significant retardation of drug releases of ZOL from various PEC films compared to the pure drug film was observed. Generally, after one day, the ZOL release process was finished for all measured ZOL/PEC samples. For systemic administration, large amounts of drug are being used, but ZOL/PEC films contain ZOL in the range of micrograms. The developed film uses 4.6 mg ZOL per film sample, which would be easily upscaled to be large enough for local therapy and preventing systemic side effects (Torger et al., 2013). Transdermal delivery (TD) Delivery of BPs for OP treatment is very problematic using oral route due to its severe gastric side effects. BPs have common side effects as esophageal irritation, abdominal pain, and nausea. To reduce this effect, an alternate route is developed and known as TD. Nam and associates tested the in vitro permeation effects of RIS. They prepared solutions of

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RIS with L-arginine (ARG), L-lysine (LYS), and diethylenetriamine (DETA) and performed on the skin of hairless mice. The results indicated that ion-paired RIS could penetrate mice skin about 36 times more effectively than RIS alone. The cumulative amount of ion paired RIS after 24 h resulted in 475.18  94.19 mg/cm2 and 511.21  106.52 mg/cm2 at a molar ratio of 1:2 and 1:1. The cumulative amount of RIS alone was as low as 14.13  5.49 mg/cm2 in 24 h. This study showed that RIS could be delivered transdermally, and the ion-paired system in an aqueous solution showed an enhanced flux through the skin barrier (Nam et al., 2011). Kusamori and associates developed a novel hydrophilic transdermal patch of ALD. The developed patch showed permeation fluxes of ALD through rat and human skin after application 1.9 and 0.3 mg/cm2/h, respectively. BA of ALD in rats was approximately 8.3% after the application of ALD patch and approximately 1.7% after oral administration. It is indicated that the transdermal permeation of ALD using this patch system was sufficient for the treatment of bone diseases. The plasma calcium level was effectively reduced after application of the ALD patch in 1a-hydroxyvitamin D3-induced hypercalcemia model rats (Kusamori et al., 2010). These results indicated that the developed transdermal delivery system of ALD is a promising approach that would improve therapeutic effects and better compliance and QOL (quality of life) in patients undergoing treatment for OP. Implants Stadelmann and associates studied bone density around orthopedic implants after delivering ZOL. Study was based on a model ‘‘bone remodeling and drug diffusion equations’’. The hypothesis based on the equation predicted that a dose of 0.3 mg of ZOL on the implant would induce a maximal bone density. After finding of this dose, they implanted 0.3 mg of ZOL in rat femurs for 3, 6, and 9 weeks. The peri-implant bone density was found to be 4% greater with the calculated dose compared to the dose empirically by the model described as best (Stadelmann et al., 2011). Stadelmann and associates also assessed the combined effects of ZOL and mechanical loading on bone adaptation using an in vivo axial compression model of the mouse tibia and subcutaneous injection (80 ml) of ZOL. Structures of bone were studied using mCT (microcomputed tomography) before and after the stimulation and the mechanical properties of the tibias were evaluated with three point-bending tests after sacrifice. They found that the axial loading induced a localized increase of cortical thickness and bone area (Stadelmann et al., 2011). Bobyn and associates assessed the effectiveness of ZOL in adult mongrel dogs using HA-coated porous tantalum implant conjugated with ZOL. They concluded that enhancement of local bone formation resulting from direct elution of ZOL from porous implants persists for one year after surgery (Bobyn et al., 2009). Tanzer associates and Roberts associates also studied the elution profile of ZOL and described as a biphasic ZOL elution profile, an initial burst release within a few hours followed by a much slower, protracted, and progressive release over many weeks (Tanzer et al., 2005; Roberts et al., 2008). These studies suggested that the implant of BPs have controlled release profile and reduces the unnecessary

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higher concentration in plasma which is the main factor for side effects. Thus implant has an immense potential to minimize the toxicity associated with BPs. Peter and associates prepared the HA coated titanium implants and ZOL was grafted over it. The implants were inserted in rat condyles with various ZOL concentrations. A positive concentration-dependent effect was observed on the peri-implant bone density. The outcome of these studies suggested that the mechanical fixation was increased by the presence of ZOL. Qualitative study showed the positive effect of ZOL HA-coated implants on the peri-implant bone density (Peter et al., 2006). Thus it could be helpful in implant stability in the body, local, and precise delivery of BPs and other anti-osteoporotic drugs which would reduce the side effects and increase the availability of drug to the target site. Gao and coworkers prepared and investigated implant (HA-coated titanium implant) of basic fibroblast growth factor (bFGF) that stimulates osteoblast-mediated bone formation and ZOL, which could enhance fixation of implants under osteoporotic conditions. Ovariectomized (OVX) rats were taken and bilateral tibiae implantation was done. After three months of implantation, animals were sacrificed and the tibiae were harvested for histology, micro-CT examinations, and biomechanical testing. The increased percentage osteointegration effects were found by ZOL treatment significantly. The study concluded that local application of ZOL or bFGF may improve implant fixation, and the combined treatment has more beneficial effects on osteointegration, peri-implant bone formation, and maximum force than either intervention alone (Gao et al., 2009). Harmankaya and associates prepared raloxifene and ALD containing thin mesoporous titanium oxide films and evaluated in vivo in rat tibia. The drug release kinetics were monitored in vitro by quartz crystal microbalance with dissipation and showed sustained release of both drugs. The osteogenic effect was evaluated by quantitative polymerase chain reaction (qPCR), removal torque, histomorphometry, and ultrastructural interface analysis. The drug-loaded implants showed significantly improved bone fixation and stronger bone-remodeling activity when compared with controls and ALD-loaded implants (Harmankaya et al., 2013). BP-ODDS The novel BP-ODDS was developed and evaluated by Institut Nord Sud de Cooperation Biopharmaceutique (INSCB/CNRS Montpellier, France) to improve BPs oral BA and GIT tolerability. This system has been patented by INSCB in 2011. Breul and associates prepared BP-ODDS and studied about the BA of BP RIS (ActonelÕ ). The BP-ODDS is developed with a combination of two excipients, one intestinal penetration enhancer (sodium dodecyl sulfate) and one calcium chelator (Myo-Inositol), a classical physical mixture of excipients system and drug substance. When film-coated oral tablet of BP-ODDS was compared with marketed ActonelÕ , it is found that BP-ODDS was supra-bioavailable with 300% higher AUC and almost 500% higher Cmax. This study was conducted on healthy volunteers in fasting conditions. Results of this study revealed that the novel BP-ODDS could be a more bioavailable oral formulation of BPs for treating OP (Pilot Bioavailability).

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Fujisaki and associates synthesized and studied the pharmacological effects of bisphosphonic prodrug of 17b-estradiol (E2-BP) on bone. Estradiol (E2) has been shown to depress bone resorption, increase bone density, and help to decrease the risk of fracture in women with established OP. Fujisaki and coworkers recently proposed an osteotropic DDS based on a bisphosphonic prodrug concept as a novel method for site specific and controlled delivery of other drugs to the bone. This approach is based on the chemical adsorption of the prodrug to the mineral component, HA, in the bone through the bisphosphonic promoiety (Fujisaki et al., 1996).

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Microspheres Another approach to reduce the oral limitations of BPs is local, sustained delivery system of BPs as bioabsorbable calcium phosphate (CaP) microspheres where BPs will be encapsulated and direct contact of drug to mucosa minimized and GIT erosion will be reduced or abolished. Kim and associates developed and investigated the CaP microspheres loaded with ALD. This delivery systems have played an important role as controlled release of therapeutic agents due to its well-defined shape and size (Huang et al., 2009). Developed ALD-loaded CaP microspheres were found to be in size range of 163–195 mm and spherical in shape. In vitro release study showed a sustained release over 40 d, and the release showed linear kinetics with a burst release during the initial 24 h. Biological evaluation of ALD-loaded CaP microspheres showed that it directly blocked osteoclast formation by releasing ALD to monocytic precursor cells and effectively inhibited their differentiation into osteoclasts (Kim et al., 2010). This study revealed that CaP microspheres loaded with ALD showed local sustained delivery systems and CaP microspheres could serve as a good alternative to current oral formulations, increased the BA, and decreased patient discomfort due to their frequent administration and undesirable gastrointestinal effects. Lee and associates developed micro-structured HA microspheres for local delivery of ALD and BMP-2. HA microspheres that have microstructures were prepared in this study by enzymatic decomposition followed by water-in-oil emulsification and sintering. Results showed the promising potential of HA microspheres as a drug carrier for local delivery of both chemical and biological therapeutic drugs (Lee et al., 2013). CPCs CPCs were developed as a local delivery system for various drugs for OP. BPs are the drugs which are widely used in early days but currently drawbacks have restricted their oral delivery. Calcium phosphate (CaP) is a family of bioceramics. Its main component is mineral of natural bones which impart excellent biocompatibility to it. CPCs are hydraulic cements, which are formed by a combination of one or more calcium orthophosphate powders. CPCs have been categorized as nonswellable monolithic systems. Some CPCs are resorbable. It has been found that the drug release is mainly controlled by the process of diffusion through the cement matrix. CPCs have been successfully used as synthetic bone grafts over decades due to their excellent biocompatibility, bioactivity,

7

and osteoconductivity (Ginebra, 2008). Bioactivity, together with the perfect adaptability of the cement paste during implantation, leads to speeding up bone healing process. CPCs can be resorbed by two different mechanisms namely active resorption regulated by living cells like macrophages or osteoclasts, and/or passive resorption via chemical dissolution or hydrolysis in the body fluids (Mestres et al., 2012). Panzavolta and associates investigated the effect of ALD and Pamidronate (BPs) on the setting properties and in vitro bioactivity of a CPC. The results of in vitro experiment demonstrated that both BPs were positively involved in osteoblast proliferation. It was found that ALP activity was significantly higher when compared with control cement (CC). Based on the results obtained, it was proposed that the system optimized could be applied for the treatment of OP as local delivery to avoid oral drawbacks (Panzavolta et al., 2009). Verron and associates developed an injectable BP-combined CaP matrix. In vitro studies showed that CaP was effective for loading and releasing BPs at doses that can inhibit excessive bone resorption without affecting osteoblasts, an increase relative bone content improvement was found after implantation. It was revealed that the ZOLcombined calcium-deficient apatite (CDA-ZOL) forms a new bone to the osteoporotic site. It was concluded that an injectable bioactive carrier made of CDA would be more adapted for clinical applications in osteoporotic treatment to avoid oral side effects (Verron et al., 2010). Another study on CPCs was also carried out by Schnitzler and associates. They prepared apatitic CPC and loaded ALD. The study concluded that ALD could be combined with an apatitic CPC. ALD was chemisorbed on calcium-deficient apatite, one of the components of the cement. Local delivery of the BP using these biomaterials not only offered a promising tool to minimize the GI adverse effects of BP for the treatment of OP but also increased the BPs BA (Schnitzler et al., 2011). Shi and associates also developed an apatite cement loaded with BP and assessed in vitro BP-loaded HA/PLGA microsphere composites. In vitro release study showed an initial 20–40% of BPs was released from the matrix in the first four days and 70–90% release was found sustained after 30 d of incubation (Shi et al., 2011). Their study suggested that released ALD stimulated osteoblast proliferation and activity and reduced the viability and proliferation of macrophages in human fetus osteoblast cultures in in vitro tests. Thus it was revealed that CPCs would be an alternative local delivery system for delivering the BPs for the treatment of OP after clinical investigation. Jindong and associates developed CPC with different concentrations of ALD which is widely used to treat diseases related to bone loss. CPC containing ALD as a drug delivery system showed satisfactory results in vitro. A sustained release of ALD was observed over 21 days. The cytotoxicity test demonstrated that the novel drug delivery system had good biocompatibility. The results suggested that the composite may be a useful drug carrier for application in the local treatment of osteoporosis (Jindong et al., 2010).

Conclusion The management of OP is among one of the greatest challenges being faced by modern medicine. Since bone is

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M. Fazil et al.

Drug Deliv, Early Online: 1–9

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Table 1. US FDA approved bisphosphonates: their routes of administration, adverse effects and mechanism of action. S. no.

Drug

Routes of administration

1. 2.

Risedronate Zolendronate

Oral IV

3.

Ibandronate

Oral IV

4.

Alendronate

Oral

Adverse effects

Mechanism of action of BPs

Dyspepsia, back pain, abdominal pain, arthralgia Bisphosphonates bind to the surfaces of the bones and slow down the bone resorbing action of the osteoclast Arthralgia, osteonecrosis of jaw, flu like syndrome, cells. It alters the balance between the osteoclast renal failure, atrial fibrillation, fever, pain and cells and the osteoblast cells such that bone loss is stiffness in the muscles, bones or joints, and usually stopped and bone strength is improved headache Dyspepsia, dysphagia, esophagitis, ulcers, diarrhea, pain in extremities, flu like reaction, headache, pain in bone, muscle, or joint Abdominal pain, dyspepsia, bone, skeleton pain, nausea, constipation, diarrhea, esophagitis, esophageal erosions, osteonecrosis of jaw

composed of a mineralized matrix, a logical solution to the problem of bone targeting is the development of delivery systems that possess HA affinity via osteotropic molecules, such as BPs. BPs are the most widely used anticatabolic agents for the OP treatment, which act predominantly by inducing apoptosis of mature osteoclasts. The therapeutic potentials of BPs are not fully utilized owing to the low BA and severe side effects associated with BPs. BPs are the choice of drug class for OP but their limitations restrict from their use because of risk–benefit ratio. According to the patients age, gender, vitality of their organs, the drug is to be chosen from this class and there is a need to titrate the dose as well as dose regimen. The limitations of this class provoked various researchers for the development of novel and targeted delivery systems but it is up to the preclinical stages. Bisphosphonates, their administration routes, mechanism of action, and serious adverse effects associated with it are given in Table 1. The researchers have to study these delivery systems to the clinical phases. New researchers have to study the etiology and mechanism of BPs action more precisely before the development of drug delivery. The developed nanoparticles, liposomes, topical, transdermal systems, implants, BP-ODDS, microspheres, and CPCs would come in the clinical use in coming years to come.

Declaration of interest Authors are grateful to Indian Council of Medical Research (ICMR), New Delhi, for providing financial assistance to carry out the research work under Project (Ref. no. 35/18/ 2011-BMS).

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