Comments on Initial experience with teriparatide in the United States

Teriparatide therapy for severe, refractory osteoradionecrosis of the jaw

Although osteoradionecrosis (ORN) is a serious complication of craniofacial radiotherapy, the current management methods remain suboptimal. Teriparatide (TPTD), a recombinant human parathyroid hormone (1-34), has shown beneficial effects on osseous regeneration in medication-related osteonecrosis of the jaw or periodontitis. However, TPTD therapy in irradiated bones has not been indicated yet because of the theoretical risk of osteosarcoma seen in rat models. Hence, we first report here two patients with tongue cancer with late-emerging ORN who were successfully treated with TPTD for 4-6 months with serum calcium and vitamin D supplementation. In contrast to the usual progress of ORN, the bone defect regenerated well and bone turnover markers including serum C-terminal telopeptide of type 1 collagen and osteocalcin were restored with TPTD therapy. Our experience might suggest that TPTD therapy with careful monitoring can provide an effective treatment option for patients with ORN in select refractory cases, with the benefits outweighing the potential risks.

Parathyroid hormone/parathyroid hormone-related peptide regulate osteosarcoma cell functions: Focus on the extracellular matrix (Review)

Osteosarcoma (OS) is a primary bone tumor of mesenchymal origin mostly affecting children and adolescents. The OS extracellular matrix (ECM) is extensively altered as compared to physiological bone tissue. Indeed, the main characteristic of the most common osteoblastic subtype of OS is non-mineralized osteoid production. Parathyroid hormone (PTH) is a polypeptide hormone secreted by the chief cells of the parathyroid glands. The PTH-related peptide (PTHrP) may be comprised of 139, 141 or 173 amino acids and exhibits considerate N-terminal amino acid sequence homology with PTH. The function of PTH/PTHrP is executed through the activation of the PTH receptor 1 (PTHR1) and respective downstream intracellular pathways which regulate skeletal development, bone turnover and mineral ion homeostasis. Both PTHR1 and its PTH/PTHrP ligands have been shown to be expressed in OS and to affect the functions of these tumor cells. This review aims to highlight the less well known aspects of PTH/PTHrP functions in the progression of OS by focusing on ECM-dependent signaling.

Management of severe osteoporosis

INTRODUCTION

Severe osteoporosis represents a disease of high mortality and morbidity. Recognition of what constitutes and causes severe osteoporosis and aggressive intervention with pharmacological agents with evidence to reduce fracture risk are outlined in this review.

AREAS COVERED

This review is a blend of evidence obtained from literature searches from PubMed and The National Library of Medicine (USA), clinical experience and the author's opinions. The review covers the recognition of what constitutes severe osteoporosis, and provides up-to-date references on this sub-set of high risk patients.

EXPERT OPINION

Severe osteoporosis can be classified by using measurements of bone densitometry, identification of prevalent fractures, and, knowledge of what additional risk factors contribute to high fracture risk. Once recognized, the potential consequences of severe osteoporosis can be mitigated by appropriate selection of pharmacological therapies and modalities to reduce the risk for falling.

Combination anabolic and antiresorptive therapy for osteoporosis

Osteoanabolic agents directly stimulate bone formation to improve bone mass and skeletal microarchitecture. At present, parathyroid hormone (PTH), in the form of the full-length molecule (PTH(1-84)) and its fully active, but truncated amino-terminal fragment, PTH(1-34) (teriparatide), are the only medications that belong to the osteoanabolic class. It is appealing to consider simultaneous combination therapy with antiresorptive and osteoanabolic drugs as potentially more beneficial than monotherapy with either class, given that their mechanisms of action differ. This review focuses on the research that has been conducted on combination therapy with PTH and an antiresorptive drug.

Combination antiresorptive and osteoanabolic therapy for osteoporosis: we are not there yet

Osteoanabolic therapy is theoretically and practically an appealing therapeutic option for men and postmenopausal women with osteoporosis because bone formation is directly stimulated, an action that is not shared by any antiresorptive agent. Parathyroid hormone (PTH), in the form of the full-length molecule (PTH[1-84]) and its fully active but truncated amino-terminal fragment teriparatide (PTH[1-34]), belong to this osteoanabolic class. Both formulations of PTH increase bone mineral density, increase biochemical markers of bone turnover, and reduce fracture incidence. They improve skeletal microstructure. While antiresorptive agents are considered by most to be first line for the treatment of osteoporosis, there are situations when anabolic therapy could be reasonably considered as first line. In most situations, however, treatment with PTH follows a course of antiresorptive therapy. Simultaneous combination therapy with PTH and an antiresorptive drug does not appear to provide any advantages over monotherapy. After the recommended 2-year period of PTH treatment, an antiresorptive should be used to maintain densitometric gains. The drugs are well tolerated. Early safety concerns about osteosarcoma in rats have not been borne out after almost 9 years experience with human subjects.

Of mice and men: divergent risks of teriparatide-induced osteosarcoma

SUMMARY

Since approval by the U.S. Food and Drug Administration (FDA) in December 2002, teriparatide (recombinant 1-34 PTH; Forteo) has been safely used by more than 430,000 patients. Prior to FDA approval, however, there was concern that teriparatide might increase the risk for patients to develop osteosarcoma, as almost 45% of the rats treated with this drug at the highest-tested dose level developed this aggressive form of bone cancer. Balancing the proven benefits of teriparatide shown by clinical trials with the theoretical risk for teriparatide-induced human osteosarcoma, the FDA mandated both a 'black-box' warning of this potential side-effect and a company-sponsored postmarketing surveillance program. As a participating institute of that surveillance program, we report upon the second person with potential teriparatide-induced osteosarcoma, in this case, complicated by a history of pelvic radiation.

INTRODUCTION

Given the theoretic risk of the drug teriparatide and the known risk of radiation in inducing osteosarcoma, we raise the issue of whether teriparatide magnified the risk of radiation-induced osteosarcoma in our patient and try to determine which factor played the predominant role in the development of his disease.

METHODS

We analyzed preclinical rat data, human clinical experience with teriparatide, and our patient's clinical history to assess the human risk of teriparatide and radiation exposure.

RESULTS

After the first case of suspected osteosarcoma was reported in December 2005, we encountered a second possible teriparatide-induced osteosarcoma less than a year later. Review of the preclinical animal data would suggest that teriparatide is safe for human use when used as recommended by the manufacturer. Given the location of the sarcoma within the field of radiation and the limited exposure to teriparatide before diagnosis, it is unlikely that teriparatide played the predominant role in the emergence of this patient's osteosarcoma. We cannot, however, exclude the possibility that teriparatide magnified the carcinogenic effect of radiation therapy to induce the osteosarcoma.

CONCLUSION

Of more than 430,000 persons who have received teriparatide for treatment of severe osteoporosis, we report the second patient to develop osteosarcoma. Although teriparatide reduces osteoporosis-related fractures in select patient populations, important contraindications, such as prior radiation exposure, should be considered before use.

Teriparatide: a review of its use in osteoporosis

Recombinant teriparatide (Forteo; Forsteo) is an anabolic (bone forming) agent. Studies have shown that subcutaneous teriparatide 20 microg/day is effective in women with postmenopausal osteoporosis, men with idiopathic or hypogonadal osteoporosis and patients with glucocorticoid-induced osteoporosis. Teriparatide improves bone mineral density (BMD) and alters the levels of bone formation and resorption markers; histomorphometric studies showed teriparatide-induced effects on bone structure, strength and quality. Subcutaneous teriparatide 20 microg/day administered over a treatment period of 11-21 months was effective in reducing the risk of fractures in and in improving BMD in men with idiopathic or hypogonadal osteoporosis, women with postmenopausal osteoporosis and patients with glucocorticoid-induced osteoporosis. Furthermore, the beneficial effects of teriparatide on vertebral fracture prevention and BMD appear to persist following treatment cessation. Teriparatide is generally well tolerated and treatment compliance rates are favourable. However, current limitations on the length of treatment and the high acquisition cost mean that teriparatide is best reserved for the treatment of patients with osteoporosis at high risk of fracture, or for patients with osteoporosis who have unsatisfactory responses to or intolerance of other osteoporosis therapies.

Combination anabolic and antiresorptive therapy for osteoporosis: opening the anabolic window

Antiresorptive agents for osteoporosis are a cornerstone of therapy, but anabolic drugs have recently increased our options. By stimulating bone formation, anabolic agents reduce fracture incidence by improving bone qualities in addition to increasing bone mass. The only anabolic agent currently approved for osteoporosis by the US Food and Drug Administration, teriparatide (recombinant human parathyroid hormone ), has emerged as a major approach to selected patients with osteoporosis. Recombinant human parathyroid hormone (1-84) is also available in Europe. Teriparatide increases bone density and bone turnover, improves microarchitecture, and changes bone size. The incidence of vertebral and nonvertebral fractures is reduced. A current concept in the mechanism of teriparatide action is related to its effect to stimulate processes associated with bone formation before it stimulates processes associated with bone resorption. This sequence of events has led to the concept of the anabolic window, the period of time when teriparatide is maximally anabolic. Newer approaches to the use of teriparatide alone and in combination with antiresorptive agents have led to ways in which the anabolic window can be expanded.

Osteoporosis in men: its pathophysiology and the role of teriparatide in its treatment

As the population ages, the burden of osteoporosis in men is expected to rise. Implementation of preventive measures such as falls prevention strategies, exercise and adequate calcium and vitamin D intake is recommended. However, when the diagnosis of osteoporosis is made, effective treatments need to be initiated to prevent fractures. As opposed to postmenopausal women, reduced bone formation is the predominant mechanism of age-related bone loss in men, making anabolic agents a logical treatment option for men with osteoporosis. Teriparatide is the only anabolic agent currently approved for treatment of osteoporosis in men. This paper summarizes the mechanism of action of teriparatide, as well as its tolerability and safety. Furthermore, the evidence supporting the efficacy of teriparatide treatment in men with osteoporosis is reviewed and its current role in the management of osteoporosis in men is discussed.