In Vivo Bone Effects of a Novel Bisphosphonate-EP4a Conjugate Drug (C3) for Reversing Osteoporotic Bone Loss in an Ovariectomized Rat Model

Effect of Primary Stabilisation on Osseointegration of Implants With Local and Systemic Zoledronic Acid Application

ABSTRACT

Primary stabilization (PS) is defined as initial tight fit during the surgical placement of an implant. Tight implant placement is quite difficult in cases where bone quality and quantity are insufficient. Zoledronic acid (ZA) is a powerful bisphosphonate that prevents bone resorption. The aim of this study is to investigate the effect of local and systemic ZA application on osseointegration in titanium implants with and without PS. Male Sprague Dawley rats were divided into 2 main groups, with PS, PS + (n = 24), and without primary stabilisation, PS - (n = 24). These main groups were divided into control (n = 8), 2 mg/1 mL local ZA (n = 8) and 0.1 mg/kg systemic ZA (n = 8) groups. All of the subjects were sacrificed after a 4-week recovery period. Bone implant connection (BIC) and thread filling (TF) (%) of the samples was analyzed according to the non-decalcified histological analysis method. In terms of BIC percentages and TF, statistically significant differences were found between the groups with and without PS and between the ZA treatment groups (P < 0.05). The common effect of PS and ZA use on the percentage of BIC was found to be statistically significant (P < 0.05). The common effect of PS and acid type on TF was not statistically significant (P < 0.05). Within the limitations of this study, it may be concluded that systemic and local administration of ZA may increase implant osseointegration.

Design, Synthesis, Pharmacokinetics, and Biodistribution of a Series of Bone-Targeting EP4 Receptor Agonist Prodrugs for Treatment of Osteoporosis and Other Bone Conditions

A series of bone-targeting EP4 receptor agonist conjugate prodrugs were prepared wherein a potent EP4 receptor agonist was bound to a biologically inactive, bisphosphonate-based bone-targeting moiety. Singly and doubly radiolabeled conjugates were synthesized and were shown to be stable in blood, to be rapidly eliminated from the bloodstream, and to be effectively taken up into bone in vivo after intravenous dosing. From these preliminary studies a preferred conjugate 4 (also known as C3 and Mes-1007) was selected for follow up biodistribution and elimination studies. Doubly radiolabeled conjugate 4 was found to partition largely to the liver and bones, and both labels were eliminated from liver at the same rate indicating the conjugate was eliminated intact. Quantification of the labels in bones indicated that free EP4 agonist (EP4a)(2a) was released from bone-bound 4 with a half-time of about 7 days. When dosed orally, radiolabeled 4 was not absorbed and passed through the gastrointestinal tract essentially unchanged, and only traces of radiolabeled 4 were found in the liver, blood, or bones. 4 was found to bind rapidly and completely to powdered bone mineral or to various forms of calcium phosphate, forming a stable matrix suitable for implant and that could made into powders or solid forms and be sterilized without decomposition or release of 4. Basic hydrolysis released free EP4 agonist 2a quantitatively from the material.

Effects of treatment with a bone-targeted prostaglandin E2 receptor 4 agonist C3 (Mes-1007) in a mouse model of severe osteogenesis imperfecta

OBJECTIVE

Osteogenesis imperfecta (OI) is a heritable bone fragility disorder that is usually caused by mutations affecting collagen type I synthesis in osteoblasts. Bisphosphonates are widely used to decrease fracture rate but are only partially effective. Bone anabolic compounds, such as prostaglandin E2 receptor 4 (EP4) agonists may be an alternative treatment approach. Here we assessed the effect of Mes-1007, a novel bone-targeted EP4 agonist in Jrt mice, a model of severe OI.

STUDY DESIGN

Experimental study.

RESULTS

Male 8-week old wild type (WT) and OI mice were randomly assigned to 4 weeks of three intraperitoneal injections per week with Mes-1007 (25 mg per kg body mass), phosphate-buffered saline, zoledronate (5 μg per kg), or a combination treatment of zoledronate and Mes-1007. Treatment with Mes-1007 alone did not lead to higher trabecular bone volume per tissue volume (BV/TV) in the distal femur or lumbar vertebra 4 in either WT or OI mice. Treatment with zoledronate alone was associated with a significant increase in distal femur and vertebra BV/TV in both genotypes. In zoledronate-treated WT and OI mice, Mes-1007 increased bone formation rate in vertebral trabecular bone and had an additive effect on BV/TV. Vertebral BV/TV in OI mice that received zoledronate or Mes-1007/zoledronate combination treatment was similar to untreated WT mice (p = 0.25). At the femoral midshaft, Mes-1007/zoledronate combination treatment increased cortical thickness in both genotypes and led to higher periosteal diameter in OI mice. Three-point bending tests of femurs showed that Mes-1007/zoledronate combination treatment increased the stiffness, load at yield and maximal load in WT but not in OI mice.

CONCLUSION

Dosing Mes-1007 in combination with zoledronate improved the bone properties in a manner that is consistent with a mechanism of action of EP4 agonists on bone and additive to effects of anti-resorptives typified by zoledronate.

Targeting anti-cancer agents to bone using bisphosphonates

The skeleton is affected by numerous primary and metastatic solid and hematopoietic malignant tumors, which can cause localized sites of osteolysis or osteosclerosis that can weaken bones and increase the risk of fractures in affected patients. Chemotherapeutic drugs can eliminate some tumors in bones or reduce their volume and skeletal-related events, but adverse effects on non-target organs can significantly limit the amount of drug that can be administered to patients. In these circumstances, it may be impossible to deliver therapeutic drug concentrations to tumor sites in bones. One attractive mechanism to approach this challenge is to conjugate drugs to bisphosphonates, which can target them to bone where they can be released at diseased sites. Multiple attempts have been made to do this since the 1990s with limited degrees of success. Here, we review the results of pre-clinical and clinical studies made to target FDA-approved drugs and other antineoplastic small molecules to bone to treat diseases affecting the skeleton, including osteoporosis, metastatic bone disease, multiple myeloma and osteosarcoma. Results to date are encouraging and indicate that drug efficacy can be increased and side effects reduced using these approaches. Despite these successes, challenges remain: no drugs have gone beyond small phase 2 clinical trials, and major pharmaceutical companies have shown little interest in the approach to repurpose any of their drugs or to embrace the technology. Nevertheless, interest shown by smaller biotechnology companies in the technology suggests that bone-targeting of drugs with bisphosphonates has a viable future.

Improved bone regeneration using bone anabolic drug conjugates (C3 and C6) with deproteinized bovine bone mineral as a carrier in rat mandibular defects

BACKGROUND

Deproteinized bovine bone mineral (DBBM) has been extensively studied and used for bone regeneration in oral and maxillofacial surgery. However, it lacks an osteoinductive ability. We developed two novel bone anabolic conjugated drugs, known as C3 and C6, of an inactive bisphosphonate and a bone activating synthetic prostaglandin agonist. The aim was to investigate whether these drugs prebound to DBBM granules have the potential to achieve rapid and enhanced bone regeneration.

METHODS

Bilateral defects (4.3 mm diameter circular through and through) were created in mandibular angles of 24 Sprague-Dawley rats were filled with DBBM Control, DBBM with C3 or DBBM with C6 (n = 8 defects per group/ each timepoint). After 2 and 4 weeks, postmortem samples were analyzed by microcomputed tomography followed by backscattering electron microscopy and histology.

RESULTS

DBBM grafts containing the C3 and C6 conjugated drugs showed significantly more bone formation than DBBM control at 2 and 4 weeks. The C6 containing DBBM demonstrated the highest percentage of new bone formation at 4 weeks. There was no significant difference in the percentage of the remaining graft between the different groups at 2 or 4 weeks.

CONCLUSIONS

DBBM granules containing conjugated drugs C3 and C6 induced greater new bone volume generated and increased the bone formation rate more than the DBBM controls. This is expected to allow the development of clinical treatments that provide more predictable and improved bone regeneration for bone defect repair in oral and maxillofacial surgery.

Achieving enhanced bone regeneration using monetite granules with bone anabolic drug conjugates (C3 and C6) in rat mandibular defects

Bone grafting procedures are commonly used to manage bone defects in the craniofacial region. Monetite is an excellent biomaterial option for bone grafting, however, it is limited by lack of osteoinduction. Several molecules can be incorporated within the monetite matrix to promote bone regeneration. The aim was to investigate whether incorporating bone forming drug conjugates (C3 and C6) within monetite can improve their ability to regenerate bone in bone defects. Bilateral bone defects were created in the mandible of 24 Sprague-Dawley rats and were then packed with monetite control, monetite+C3 or monetite+C6. After 2 and 4 weeks, post-mortem samples were analyzed using microcomputed tomography, histology and back-scattered electron microscopy to calculate the percentages of bone formation and remaining graft material. At 2 and 4 weeks, monetite with C3 and C6 demonstrated higher bone formation than monetite control, while monetite+C6 had the highest bone formation percentage at 4 weeks. There were no significant differences in the remaining graft material between the groups at 2 or 4 weeks. Incorporating these anabolic drug conjugates within the degradable matrix of monetite present a promising bone graft alternative for bone regeneration and repair in orthopedic as well as oral and maxillofacial applications.