Bone-targeting Properties Research Articles

Nonviral genetic manipulation system with microenvironmental cascade sensitivity for the treatment of TNBC-associated metastatic bone tumor

Gene therapy is an efficacious therapeutic modality for triple negative breast cancer (TNBC). However, the practicable applicability is strictly confined in TNBC-associated metastatic bone tumor due to the low blood flow and poor accumulation in bone tissue, as well as the vicious cycle of mutual promotion between tumor growth and bone erosion. To address those problems, a versatile nonviral genetic manipulation system PSMCA/miR-34a, with caveolae-activated endocytosis and microenvironmental cascade-responsive release profile was exploited. In vitro and in vivo experiments confirmed that PSMCA/miR-34a not only possessed bone-targeting properties to accumulate at bone tumor tissue, also could respond to the bone tumor microacidic environment to release alendronate to inhibit the bone erosion. After internalized into cells mainly through caveolae-mediated endocytosis, it was spurred to disassemble for controlling release the miR-34a by high intracellular GSH environment, generating an effective anti-tumor effect. Moreover, due to the synergistic effect, PSMCA/miR-34a could breakdown the vicious cycle between bone destruction and tumor growth in the tumor microenvironment, showing high potential in the clinical gene therapy for TNBC-associated metastatic bone tumor.

Micellar solution of [223Ra]RaCl2: Reaching renal excretion, potent efficacy in osteoblastic osteosarcoma in PDX model, biochemistry alterations and pharmacokinetics

Despite the successful use of the radiopharmaceutical radium-223 dichloride ([223Ra]RaCl2) for targeted alpha therapy of castration-resistant prostate cancer patients with bone metastases, some short-term side effects, such as diarrhea and vomiting, have been documented, causing patient discomfort. Hence, we prepared a nanosized micellar solution of [223Ra]RaCl2 and evaluated its biodistribution, pharmacokinetics, and induced biochemical changes in healthy mice up to 96 h after intraperitoneal administration as an alternative to overcome the previous limitations. In addition, we evaluated the bone specificity of micellar [223Ra]RaCl2 in patient-derived xenografts in the osteosarcoma model. The biodistribution studies revealed the high bone-targeting properties of the micellar [223Ra]RaCl2. Interestingly, the liver uptake remained significantly low (%ID/g = 0.1–0.02) from 24 to 96 h after administration. In addition, the micellar [223Ra]RaCl2 exhibited a significantly higher uptake in left (%ID/g = 0.85–0.23) and right (%ID/g = 0.76–0.24) kidneys than in small (%ID/g = 0.43–0.06) and large intestines (%ID/g = 0.24–0.09) over time, suggesting its excretion pathway is primarily through the kidneys into the urine, in contrast to the non-micellar [223Ra]RaCl2. The micellar [223Ra]RaCl2 also had low distribution volume (0.055 ± 0.003 L) and longer elimination half-life (28 ± 12 days). This nanosystem was unable to change the enzymatic activities of alanine aminotransferase, aspartate aminotransferase, gamma GT, glucose, and liquiform lipase in the treated mice. Finally, microscopic examination of the animals' osteosarcoma tumors treated with micellar [223Ra]RaCl2 indicated regression of the tumor, with large areas of necrosis. In contrast, in the control group, we observed tumor cellularity and cell anaplasia, mitotic figures and formation of neoplastic extracellular bone matrix, which are typical features of osteosarcoma. Therefore, our findings demonstrated the efficiency and safety of nanosized micellar formulations to minimize the gastrointestinal excretion pathway of the clinical radiopharmaceutical [223Ra]RaCl2, in addition to promoting regression of the osteosarcoma. Further studies must be performed to assess dose–response outcomes and organ/tissue dosimetry for clinical translation.

Establishment of bone-targeted nano-platform and the study of its combination with 2-deoxy-d-glucose enhanced photodynamic therapy to inhibit bone metastasis

At present, simple anti-tumor drugs are ineffective at targeting bone tissue and are not purposed to treat patients with bone metastasis. In this study, zoledronic acid (ZOL) demonstrated excellent bone-targeting properties as a bone-targeting ligand. The metal-organic framework (MOF) known as ZIF-90 was modified with ZOL to construct a bone-targeting-based drug delivery system. Chlorin e6 (Ce6) was loaded in the bone-targeted drug delivery system and combined with 2-deoxy-D-glucose (2-DG), which successfully treated bone tumors when enhanced photodynamic therapy was applied. The Ce6@ZIF-PEG-ZOL (Ce6@ZPZ) nanoparticles were observed to have uniform morphology, a particle size of approximately 210 nm, and a potential of approximately −30.4 mV. The results of the bone-targeting experiments showed that Ce6@ZPZ exhibited a superior bone-targeted effect when compared to Ce6@ZIF-90-PEG. The Ce6@ZPZ solution was subjected to 660 nm irradiation and the resulting production of reactive oxygen species increased over time, which could be further increased when Ce6@ZPZ was used in combination with 2-DG. Their combination had a stronger inhibitory capacity against tumor cells than either 2-DG or Ce6@ZPZ alone, increasing the rate of tumor cell apoptosis. The apoptosis rate caused by HGC-27 was 61.56% when 2-DG was combined with Ce6@ZPZ. In vivo results also showed that Ce6@ZPZ combined with 2-DG maximally inhibited tumor growth and prolonged mice survival compared to the other experimental groups. Therefore, the combination of PDT and glycolytic inhibitors serves as a potential option for the treatment of cancer.

Capturing Magnesium Ions via Microfluidic Hydrogel Microspheres for Promoting Cancellous Bone Regeneration.

Metal ions are important trace elements in the human body, which directly affect the human metabolism and the regeneration of damaged tissues. For instance, the advanced combination of magnesium ions (Mg2+) and bone repair materials make the composite materials have the function of promoting vascular repair and enhancing the adhesion of osteoblasts. Herein, inspired by magnets to attract metals, we utilized the coordination reaction of metal ion ligand to construct a bisphosphonate-functionalized injectable hydrogel microsphere (GelMA-BP-Mg) which could promote cancellous bone reconstruction of osteoporotic bone defect via capturing Mg2+. By grafting bisphosphonate (BP) on GelMA microspheres, GelMA-BP microspheres could produce powerful Mg2+ capture ability and sustained release performance through coordination reaction, while sustained release BP has bone-targeting properties. In the injectable GelMA-BP-Mg microsphere system, the atomic percentage of captured Mg2+ was 0.6%, and the captured Mg2+ could be effectively released for 18 days. These proved that the composite microspheres could effectively capture Mg2+ and provided the basis for the composite microspheres to activate osteoblasts and endothelial cells and inhibit osteoclasts. Both in vivo and in vitro experimental results revealed that the magnet-inspired Mg2+-capturing composite microspheres are beneficial to osteogenesis and angiogenesis by stimulating osteoblasts and endothelial cells while restraining osteoclasts, and ultimately effectively promote cancellous bone regeneration. This study could provide some meaningful conceptions for the treatment of osteoporotic bone defects on the basis of metal ions.

Bisphosphonates in dentistry: Historical perspectives, adverse effects, and novel applications.

Studies of the potential role of bisphosphonates in dentistry date back to physical chemical research in the 1960s, and the genesis of the discovery of bisphosphonate pharmacology in part can be linked to some of this work. Since that time, parallel research on the effects of bisphosphonates on bone metabolism continued, while efforts in the dental field included studies of bisphosphonate effects on dental calculus, caries, and alveolar bone loss. While some utility of this drug class in the dental field was identified, leading to their experimental use in various dentrifice formulations and in some dental applications clinically, adverse effects of bisphosphonates in the jaws have also received attention. Most recently, certain bisphosphonates, particularly those with strong bone targeting properties, but limited biochemical effects (low potency bisphosphonates), are being studied as a local remedy for the concerns of adverse effects associated with other more potent members of this drug class. Additionally, low potency bisphosphonate analogs are under study as vectors to target active drugs to the mineral surfaces of the jawbones. These latter efforts have been devised for the prevention and treatment of oral problems, such as infections associated with oral surgery and implants. Advances in the utility and mechanistic understanding of the bisphosphonate class may enable additional oral therapeutic options for the management of multiple aspects of dental health.

Calcium-bisphosphonate Nanoparticle Platform as a Prolonged Nanodrug and Bone-Targeted Delivery System for Bone Diseases and Cancers.

Bone and bone-related diseases are the major cause of mobility hindrance and mortality in humans and there is no effective and safe treatment for most of them, especially, for bone and bone metastatic cancers. Bisphosphonates (BPs) are a group of small-molecule drugs for treating osteoporosis and bone cancers but have a very short half-life in circulation, requiring high doses and long-term repeat use that can cause severe side effects. Previous attempts of using nanoparticles to deliver BPs have issues of drug loading capacity and endosome escape/drug release. The present study reports the direct synthesis of BP nanoparticles by precipitating bone-favorable calcium ions and a third-generation BP, risedronate (Ca-RISNPs), to achieve high drug loading, endosomal release, and strong bone-targeting properties. The Ca-RISNPs are monodispersed with high stability at physiological pH but readily dissociate at endosomal pH conditions. They demonstrate strong penetration ability and uniform distribution in human bone and cartilage tissues and the superior drug and DNA (plasmid and oligo double strand DNA) delivery capacity in bone cells. These NPs also exhibit high specificity in killing tumor-associated macrophages (TAMs) and inhibit TAM-induced tumor cell migration. Collectively, our data indicate that this BP nanodrug platform has a great potential in managing bone-related diseases and cancers as a prolonged BP nanodrug and simultaneously as the bone-targeted drug delivery system.

Enhancement of osteoblast differentiation using poly(ethylene sodium phosphate)

Biodegradable polyphosphoesters (PPEs) are of increasing interest due to their promising biomedical applications. Polyphosphodiesters (PPDEs), formed by polyphosphotriester (PPTE) dealkylation, have bone-targeting properties in vivo and therefore are promising polymer drug candidates for bone disease treatment. However, their effects on osteoblasts are still unclear. This study prepared two polymer structures, poly(methyl ethylene phosphate) (PMP) and poly(ethylene sodium phosphate) (PEP•Na), as PPTE and PPDE models, respectively, and investigated their effects on mouse osteoblastic cell (MC3T3-E1) differentiation. Results showed that PMP is inert toward osteoblast differentiation. In contrast, PEP•Na enhanced alkaline phosphatase (ALP) synthesis, matrix mineralization, and osteoblast-related gene expression. PEP•Na also enhanced Wnt signaling pathway–dependent Alp expression, in addition to its own internalization into the cytosol during 3 days of differentiation culture. These results showed that dealkylated PPEs are a polymer drug candidate for osteoporosis treatment, not only because of their bone-targeting properties but also because of the controllable effects of bone anabolism via osteoblast differentiation enhancement.

Poly(Aspartic Acid) Functionalized Poly(ϵ-Caprolactone) Microspheres with Enhanced Hydroxyapatite Affinity as Bone Targeting Antibiotic Carriers.

Bone infection is a feared complication for patients with surgically fixed bone fractures and local antibiotic delivery is important in prophylaxis and treatment of these infections. Recent studies indicated that Staphylococcus aureus can penetrate bone tissue through micron-sized canaliculi and evade systemic and currently available local antibiotic treatments. Targeting bacteria within the bone requires highly efficient delivery of antimicrobials to the infected bone tissue. In this work, a biodegradable microsphere carrier loaded with antibiotics and with specific affinity to bone mineral was developed. Two widely used antibiotics, i.e., Gentamicin-dioctyl sulfosuccinate (GM-AOT) and Ciprofloxacin (CF) were embedded in poly(ϵ-caprolactone) (PCL) microspheres fabricated by oil-in-water emulsion techniques with carboxylated poly(vinyl alcohol) (cPVA) as surfactant. The carboxylic acid groups present at the Poly(ϵ-caprolactone)/cPVA (PCL-cPVA) microsphere surface were functionalized with aspartic acid oligomers (ASP) granting bone targeting properties. We report on cPVA synthesis, microsphere formulation, and antibiotic loading of PCL/cPVA-ASP microspheres. Antibiotic loaded PCL/cPVA-ASP microspheres show sustained release of its antibiotic load and can inhibit bacterial growth in vitro for up to 6 days. PCL/cPVA-ASP microspheres show enhanced affinity to mineralized substrates compared to non-functionalized PCL/cPVA microspheres. These findings support further development of these bone targeting antibiotic carriers for potential treatment of persistent bone infections.

A Novel Bone-Targeting Enoxacin Delivery System to Eradicate Staphylococcus Aureus-Related Implantation Infections

Post-operative infections in orthopaedic implants are severe complications that require urgent solutions. Owing to the presence of implants and the formation of bacterial biofilms, the efficacy of antibiotics is limited. Furthermore, osteoclasts can become extremely active, accompanied by bone loss in the infected microenvironment. Therefore, implants often need to be removed. To improve the concentrations of antibiotics in bony tissues and enhance their effectiveness in preventing bacterial biofilm formation, the infection rate must be controlled to preserve the implants. Enoxacin exerts combined antibacterial and osteoclast inhibitory effects. It also plays a role in limiting infections and preventing bone loss. Aspartic acid octapeptide (ASP8) can also recognize and combine with hydroxyapatite crystals in bones and can be targeted to increase antibiotic concentrations in bones. Our previous research showed that preparing mesoporous nanomaterials resulted in optimal drug loading, releasing, and bone-targeting properties. Based on earlier research, a new bone-targeted antibiotic release system was developed. Enoxacin and ASP8 were loaded on mesoporous silica nanoparticles (MSNs) to increase antibiotic concentrations, prevent bacterial biofilm formation, inhibit aberrant osteoclast activities, and reduce bone loss. Enoxacin-loaded MSNs (Gen@MSN-D) were assessed using a variety of experimental methods, including rat models. We studied the in vitro antibacterial properties of the new drug delivery system. We found that these materials had antibacterial properties in vivo, inhibitory effects on osteoclasts, and can be used to prevent and treat post-implantation infections and bone loss. Therefore, we believe these materials will provide a new method for preventing and treating post-operative, orthopaedic implant-associated infections.

Bortezomib-catechol conjugated prodrug micelles: combining bone targeting and aryl boronate-based pH-responsive drug release for cancer bone-metastasis therapy.

The treatment of metastatic tumors is highly desirable in clinics, which has also increased the interest in the design of nanoscale drug delivery systems. Bone metastasis is one of the most common pathways in the metastasis of breast cancer, and it is also an important cause for tumor recurrence and death. The aryl boronate group, as an acid-labile linker, has been introduced into nano-assemblies in recent years. Especially, as a proteasome inhibitor anticancer drug with a boric acid group, bortezomib can facilitate the formation of pH-sensitive aryl boric acid ester linkage with the catecholic group. In this study, bortezomib-loaded micelles with bone targeting properties were constructed for the treatment of breast cancer bone metastasis. The mixed micelles employed alendronate (ALN) as the bone-targeting ligand and encapsulated bortezomib-catechol conjugates as the cargo. In vitro and in vivo studies showed that compared with free drugs or control micelles, these prodrug micelles (ALN-NP) exhibited many favorable properties such as reduced systemic toxicity and improved therapeutic effects. Therefore, ALN-NP is promising as a nanovehicle for bone-targeting delivery of chemotherapeutic drugs. Furthermore, this study offers a novel strategy combining bone targeting and aryl boronate-based pH-responsive drug release for anti-metastasis therapy.

Alpha particle radium-223 dichloride (223RaCl2 ) in high risk osteosarcoma.

11029Background: Radium-223 dichloride (223RaCl2 ) is an alpha-emitting radiopharmaceutical and calcimimetic that has intrinsic bone-targeting properties. It is now approved for bone metastases fro...

Bisphosphonic acids as effective inhibitors of Mycobacterium tuberculosis glutamine synthetase

Inhibition of glutamine synthetase (GS) is one of the most promising strategies for the discovery of novel drugs against tuberculosis. Forty-three bisphosphonic and bis-H-phosphinic acids of various scaffolds, bearing aromatic substituents, were screened against recombinant GS from Mycobacterium tuberculosis. Most of the studied compounds exhibited activities in micromolar range, with N-(3,5-dichlorophenyl)-2-aminoethylidenebisphoshonic acid, N-(3,5-difluorophenyl)-2-aminoethylidene-bisphoshonic acid and N-(3,4-dichlorophenyl)-1-hydroxy-1,1-ethanebisphosphonic acid showing the highest potency with kinetic parameters similar to the reference compound – L-methionine-S-sulfoximine. Moreover, these inhibitors were found to be much more effective against pathogen enzyme than against the human ortholog. Thus, with the bone-targeting properties of the bisphosphonate compounds in mind, this activity/selectivity profile makes these compounds attractive agents for the treatment of bone tuberculosis.

Poly(γ-benzyl-l-glutamate)-PEG-alendronate multivalent nanoparticles for bone targeting

Hydroxyapatite (HAP), a highly specific component of bone tissue, is the main target in order to impart osteotropicity. Bone targeted nanoparticles can increase the strength of the interaction with HAP through multivalency and thus constitute a valuable strategy in the therapeutics of skeletal diseases. PBLG10k-b-PEG6k-alendronate nanoparticles (~ 75 nm) were prepared by a simple nanoprecipitation method. The calcium affinity (KCa(+2)=1.8 × 10(4)M(-1)) of these nanoparticles was evaluated using isothermal titration calorimetry. The multivalent interaction with HAP surfaces (KHAP) was studied by fluorescence and was estimated to be 1.1 × 10(10)M(-1), which is more than 4000 times stronger than the reported monovalent interaction between alendronate and HAP surfaces. Molecular modeling suggests that the number of binding sites available at the HAP surface is in large excess than what is required for the whole surface coverage by alendronate decorated nanoparticles. The lower calcium affinity of these nanoparticles than for HAP allows calcium bound nanoparticles to interact with HAP, which yields a deeper understanding of bone targeted carriers and could potentially improve their bone targeting properties.

Designing calcium phosphate-based bifunctional nanocapsules with bone-targeting properties

Using sodium dodecyl sulphate micelles as template, hollow-cored calcium phosphate nanocapsules were produced. The surfaces of the nanocapsule were subsequently silanised by a polyethylene glycol (PEG)-based silane with an N-hydroxysuccinimide ester end groups which permits for further attachment with bisphosphonates (BP). Characterisations of these nanocapsules were investigated using Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy, Fourier Transform Infra-Red Spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Dynamic Light Scattering. To further validate the bone-targeting potential, dentine discs were incubated with these functionalised nanocapsules. FESEM analysis showed that these surface-modified nanocapsules would bind strongly to dentine surfaces compared to non-functionalised nanocapsules. We envisage that respective components would give this construct a bifunctional attribute, whereby (1) the shell of the calcium phosphate nanocapsule would serve as biocompatible coating aiding in gradual osteoconduction, while (2) surface BP moieties, acting as targeting ligands, would provide the bone-targeting potential of these calcium phosphate nanocapsules.

Evaluation of the relative efficacy of an alloplast used alone and in conjunction with an osteoclast inhibitor in the treatment of human periodontal infrabony defects: A clinical and radiological study

Mucoperiosteal flap surgery stimulates varying amounts of alveolar bone loss due to accelerated osteoclastic activity [Regional Accelerated Phenomenon (RAP)]. Alendronate sodium inhibits osteoclastic activity and is thought to result in a net increase in osteoblastic activity. We undertook a preliminary study evaluating the effect of adjunctive use of topically delivered bisphosphonate alendronate (ALN) along with regenerative bone graft material in the treatment of periodontal infrabony defects. Fifteen patients with two-walled or three-walled infrabony defects were selected. In each patient, the infrabony defect of one side of arch was designated as group A (control site) and received hydroxyapatite (HA) bone graft material, while the infrabony defect on the contralateral side of same arch was designated as group B (test site) and received HA+200 μg drug solution of ALN. Both the groups exhibited a highly significant reduction in probing depth and gain in clinical attachment level and linear bone fill at the end of 24 weeks. Comparative evaluation between the study groups revealed a statistically nonsignificant reduction in probing depth (P=0.128NS) and mean gain in attachment level (P=0.218NS). However, there was a statistically significant gain in linear bone fill (P=0.040*) in group B as compared to group A. The results suggest that use of ALN along with graft material led to enhanced linear bone fill at the surgical site. This research provides a clue that bone-targeting properties of bisphosphonates can be harnessed along with regenerative materials to potentiate osseous regeneration.

Improved and Scalable Synthetic Route to the Synthon 17-β-(2-Carboxyethyl)-1,3,5(10)-estratriene: An Important Intermediate in the Synthesis of Bone-Targeting Estrogens

An improved, highly scalable methodology for the multigram-scale preparation of an important synthon, 17-β-(2-carboxyethyl)-1,3,5(10)-estratriene, is described. Previous approaches have failed to provide useful quantities of the analytically pure product because of facile retro-Michael breakdown of the β-alkoxy carbonyl precursors during workup and isolation operations. The synthetic approach described herein has been designed specifically to sidestep this problematic breakdown process. This new scalable method of preparation overcomes a major hurdle in the exploration of structure–activity relationships centered around novel estradiol derivatives with bone-targeting properties and also provides a scalable process for subsequent developmental work.

SAR of Carbon‐Linked, 2‐Substituted Purines: Synthesis and Characterization of AP23451 as a novel Bone‐Targeted Inhibitor of Src Tyrosine Kinase With In Vivo Anti‐Resorptive Activity

Targeted disruption of the pp60(src) (Src) gene has implicated this tyrosine kinase in osteoclast-mediated bone resorption and as a therapeutic target for the treatment of osteoporosis and other bone-related diseases. Here, we describe structure activity relationships of a novel series of carbon-linked, 2-substituted purines that led to the identification of AP23451 as a potent inhibitor of Src tyrosine kinase with antiresorptive activity in vivo. AP23451 features the use of an arylphosphinylmethylphosphinic acid moiety which confers bone-targeting properties to the molecule, thereby increasing local concentrations of the inhibitor to actively resorbing osteoclasts at the bone interface. AP23451 exhibited an IC50 = 68 nm against Src kinase; an X-ray crystal structure of the molecule complexed with Src detailed the molecular interactions responsible for its Src inhibition. In vivo, AP23451 demonstrated a dose-dependent decrease in PTH-induced hypercalcemia. Moreover, AP23517, a structurally and biochemically similar molecule with comparable activity (IC50 = 73 nm) except devoid of the bone-targeting element, demonstrated significantly reduced in vivo efficacy, suggesting that Src activity was necessary but not sufficient for in vivo activity in this series of compounds.

Radium-223 in the treatment of metastatic hormone refractory prostate cancer (HRPC): Results from a randomized, placebo-controlled, phase II study

5071 Background: The alpha emitter radium-223 is a bone-seeking radionuclide studied as a novel treatment for patients with HRPC and bone metastases. Ra-223 showed minimal toxicity in a phase 1 study (Nilsson S, et al., Clin Cancer Res 2005;11 (12): 4451–59). Here we present outcome data from a randomised phase II study. Methods: Patients with HRPC and bone pain requiring external beam radiotherapy were randomized to treatment with 4 injections of either Ra-223 (50 kBq/kg b.w.) or saline (placebo) every 4 weeks. The primary endpoints were change in bone-alkaline phosphatase (ALP) levels from baseline to 4 weeks after last injection (previously reported (Bruland ØS, et al. Clin Cancer Res 2006;12:6250s-57s), and time to occurrence of Skeletal Related Events (SREs). Secondary endpoints included toxicity, PSA progression and overall survival. Results: 33 patients were randomised to Ra-223 and 31 to placebo. The two groups were well balanced with respect to standard prognostic factors. Mild, transient haematological toxicity was seen after Ra-223. Long term toxicity was not observed. SAEs were observed in 8 patients in the Ra-223 group versus 14 in the placebo group. Based on intention to treat analysis, the median time to PSA progression was 26 versus 8 weeks (p=0.047) for Ra-223 versus placebo, respectively. The median time to first SRE was 28 versus 26 weeks (p= 0.164). The median overall survival was 65.3 weeks versus 46.4 weeks (p = 0.066). The hazard ratio for overall survival, adjusted for baseline PSA, albumin, LDH and performance status was 2.11 (95 % CI: 1.08 - 4.13, p=0.029). At 18 months, 15 (45%) versus 8 (26%) patients patients were still alive. Conclusions: Alpharadin was extremely well tolerated, with minimal myelotoxicity, and with encouraging evidence of efficacy. Larger clinical trials are warranted to study the impact of Alpharadin on the prevention of SREs and on overall survival in HRPC. The bone targeting properties of Alpharadin, may also be applicable to the treatment of skeletal metastasis from other primary cancers. [Table: see text]

Bone-targeted radium-223 in symptomatic, hormone-refractory prostate cancer: a randomised, multicentre, placebo-controlled phase II study

The alpha-emitter radium-223 ((223)Ra) is a bone-seeking radionuclide studied as a new treatment for patients with bone metastases from hormone-refractory prostate cancer. We aimed to study mature outcomes from a randomised, multicentre, phase II study of (223)Ra. Patients with hormone-refractory prostate cancer and bone pain needing external-beam radiotherapy were assigned to four intravenous injections of (223)Ra (50 kBq/kg, 33 patients) or placebo (31 patients), given every 4 weeks. Primary endpoints were change in bone-alkaline phosphatase (ALP) concentration and time to skeletal-related events (SREs). Secondary endpoints included toxic effects, time to prostate-specific-antigen (PSA) progression, and overall survival. All tests were done at a 5% significance level, based on intention to treat. Median relative change in bone-ALP during treatment was -65.6% (95% CI -69.5 to -57.7) and 9.3% (3.8-60.9) in the (223)Ra group and placebo groups, respectively (p<0.0001, Wilcoxon ranked-sums test). Hazard ratio for time to first SRE, adjusted for baseline covariates, was 1.75 (0.96-3.19, p=0.065, Cox regression). Haematological toxic effects did not differ significantly between two groups. No patient discontinued (223)Ra because of treatment toxicity. Median time to PSA progression was 26 weeks (16-39) versus 8 weeks (4-12; p=0.048) for (223)Ra versus placebo, respectively. Median overall survival was 65.3 weeks (48.7-infinity) for (223)Ra and 46.4 weeks (32.1-77.4) for placebo (p=0.066, log rank). The hazard ratio for overall survival, adjusted for baseline covariates was 2.12 (1.13-3.98, p=0.020, Cox regression). (223)Ra was well tolerated with minimum myelotoxicity, and had a significant effect on bone-ALP concentrations. Larger clinical trials are warranted to study (223)Ra on the prevention of SREs and on overall survival in patients with hormone-refractory prostate cancer. Bone-targeting properties of (223)Ra could also potentially be used for treating skeletal metastasis from other primary cancers.

Structure-based design of an osteoclast-selective, nonpeptide src homology 2 inhibitor with in vivo antiresorptive activity.

Targeted disruption of the pp60(src) (Src) gene has implicated this tyrosine kinase in osteoclast-mediated bone resorption and as a therapeutic target for the treatment of osteoporosis and other bone-related diseases. Herein we describe the discovery of a nonpeptide inhibitor (AP22408) of Src that demonstrates in vivo antiresorptive activity. Based on a cocrystal structure of the noncatalytic Src homology 2 (SH2) domain of Src complexed with citrate [in the phosphotyrosine (pTyr) binding pocket], we designed 3',4'-diphosphonophenylalanine (Dpp) as a pTyr mimic. In addition to its design to bind Src SH2, the Dpp moiety exhibits bone-targeting properties that confer osteoclast selectivity, hence minimizing possible undesired effects on other cells that have Src-dependent activities. The chemical structure AP22408 also illustrates a bicyclic template to replace the post-pTyr sequence of cognate Src SH2 phosphopeptides such as Ac-pTyr-Glu-Glu-Ile (1). An x-ray structure of AP22408 complexed with Lck (S164C) SH2 confirmed molecular interactions of both the Dpp and bicyclic template of AP22408 as predicted from molecular modeling. Relative to the cognate phosphopeptide, AP22408 exhibits significantly increased Src SH2 binding affinity (IC(50) = 0.30 microM for AP22408 and 5.5 microM for 1). Furthermore, AP22408 inhibits rabbit osteoclast-mediated resorption of dentine in a cellular assay, exhibits bone-targeting properties based on a hydroxyapatite adsorption assay, and demonstrates in vivo antiresorptive activity in a parathyroid hormone-induced rat model.