A phase 2 study of MK-5442, a calcium-sensing receptor antagonist, in postmenopausal women with osteoporosis after long-term use of oral bisphosphonates

In women with osteoporosis treated with alendronate for >12 months and oral bisphosphonates for >3 of the last 4 years, switching to MK-5442, a calcium receptor antagonist, stimulated endogenous parathyroid hormone (PTH) secretion and increased bone turnover marker levels, but produced a decline in bone mineral density (BMD) at all sites.

INTRODUCTION

This study assessed the effects of switching from long-term oral bisphosphonate therapy to the calcium-sensing receptor antagonist MK-5442 on BMD and bone turnover markers (BTMs) in post-menopausal women with osteoporosis.

METHODS

This randomized, active and placebo-controlled, dose-ranging study enrolled 526 postmenopausal women, who had taken alendronate (ALN) for ≥12 months preceding the trial and any oral bisphosphonate for ≥3 of the preceding 4 years and had spine or hip BMD T-scores ≤-2.5 or ≤-1.5 with ≥1 prior fragility fracture. Women were randomized to continue ALN 70 mg weekly or switch to MK-5442 (5, 7.5, 10, or 15 mg daily) or placebo.

RESULTS

Switching from ALN to MK-5442 produced a dose-dependent parathyroid hormone (PTH) pulse of threefold to sixfold above baseline at 1 h, with PTH levels that remained twofold to threefold above baseline at 4 h and returned to baseline by 24 h. Switching to MK-5442 or placebo increased BTM levels compared to baseline within 3 months and MK-5442 10 mg increased BTM levels compared to placebo by 6 months. With all MK-5442 doses and placebo, spine and hip BMD declined from baseline, and at 12 months, BMD levels were below those who continued ALN (all groups P < 0.05 vs ALN). There was also a dose-dependent increase in the incidence of hypercalcemia with MK-5442.

CONCLUSION

Switching from ALN to MK-5442 resulted in a pulsatile increase in PTH and increases in BTMs, but a decline in BMD compared with continued ALN. MK-5442 is not a viable option for the treatment of osteoporosis.

Adherence to treatment of osteoporosis: a need for study

Adherence to anti-osteoporosis medications is currently low and is associated with poor anti-fracture efficacy. This manuscript reviews the potential design of clinical studies that aim to demonstrate improved adherence, with new chemical entities to be used in the management of osteoporosis.

INTRODUCTION

Several medications have been unequivocally shown to decrease fracture rates in clinical trials. However, in real life settings, long-term persistence and compliance to anti-osteoporosis medication is poor, hence decreasing the clinical benefits for patients.

METHODS

An extensive search of Medline from 1985 to 2006 retrieved all trials including the keywords osteoporosis, compliance, persistence or adherence followed by a critical appraisal of the data obtained through a consensus expert meeting.

RESULTS

The impact of non-adherence on the clinical development of interventions is reviewed, so that clinicians, regulatory agencies and reimbursement agencies might be better informed of the problem, in order to stimulate the necessary research to document adherence.

CONCLUSION

Adherence to therapy is a major problem in the treatment of osteoporosis. Both patients and medication factors are involved. Adherence studies are an important aspect of outcomes studies, but study methodologies are not well developed at the moment and should be improved. Performing adherence studies will be stimulated when registration authorities accept the result of these studies and include the relevant information in Sect. 5.1 of the summary of product characteristics. Reimbursement authorities might also consider such studies as important information for decisions on reimbursement.

Trabecular bone microarchitecture after alendronate treatment of osteoporotic women

OBJECTIVE

To compare the microarchitecture of iliac crest trabecular bone from women treated for two to three years with alendronate versus that of women treated with placebo.

RESEARCH DESIGN AND METHODS

Three-dimensional micro-computed tomography (micro-CT; resolution 20 microm) and two-dimensional histomorphometry (resolution 5-7 microm) were used to examine trabecular bone from single transilial biopsies obtained at the completion of clinical trials.

MAIN OUTCOME MEASURES

Microarchitectural variables, including bone volume, trabecular number, trabecular thickness, and trabecular spacing in specimens from alendronate- and placebo-treated women were examined. Three-dimensional images of trabecular bone from both groups were constructed from CT images. Correlations among variables and between techniques were also calculated.

RESULTS

Eighty-eight specimens were suitable for evaluation by both techniques. As measured by two-dimensional histomorphometry, bone volume fraction (as a proportion of total volume) and trabecular thickness were significantly greater in alendronate specimens, 17.1 +/- 5.5% vs. 13.4 +/- 5.5% (p = 0.0043) and 127 +/- 29 microm vs. 109 +/- 28 microm (p = 0.0090), respectively, and trabecular spacing was significantly smaller, 729 +/- 227 microm vs. 862 +/- 338 microm (p = 0.005). Micro-CT yielded similar findings: bone volume and trabecular number were significantly greater in alendronate specimens: 19.4 +/- 6.2% vs. 16.2 +/- 6.3% (p = 0.0412) and 1.46(+/-) 0.32 vs. 1.31(+/-) 0.33 per mm (p = 0.0346). Two-dimensional and micro-CT measured characteristics correlated strongly with one another, with Pearson product moment correlation coefficients ranging from 0.60 (for trabecular thickness) to 0.83 (for bone volume).

CONCLUSIONS

Trabecular microarchitecture of the ilium, whether studied by two- or three-dimensional methods, is better (greater bone volume, greater trabecular thickness, decreased trabecular spacing) after alendronate treatment than after two to three years of treatment with placebo. Bone volume in a trabecular region is strongly correlated to its microarchitecture, suggesting that bone quantity predicts values for these microarchitectural endpoints.

Weekly administration of alendronate: rationale and plan for clinical assessment

OBJECTIVE

This paper describes the rationale and supporting data for once-weekly dosing of alendronate.

BACKGROUND

Alendronate sodium, a bisphosphonate that potently inhibits bone resorption, has been shown to increase bone mass and substantially reduce the incidence of osteoporotic fractures, including fractures of the hip. The standard regimen of daily administration has generally been well tolerated. However, weekly administration may provide greater convenience to patients without compromising efficacy or tolerability. The pharmacokinetics of alendronate and bone remodeling theory predict similar efficacy for weekly and daily administration if the cumulative dose is the same. Bone resorption in individual remodeling units normally proceeds for approximately 2 weeks; alendronate inhibits the rate and extent of resorption. Because the half-life of residence on bone surfaces is several weeks, weekly administration of alendronate should inhibit bone resorption to an overall extent similar to that of daily dosing, thereby producing similar effects on bone mass and strength. Animal studies demonstrate that both weekly and daily parenteral administration of alendronate effectively increase bone mass and strength, but confirmation of efficacy is needed for weekly oral dosing in humans. Although daily bisphosphonates (alendronate and risedronate) elicited esophageal irritation in a canine model of gastroesophageal reflux, weekly dosing with alendronate at a higher unit dose did not. Thus, the lower frequency of weekly dosing with a higher unit dose may actually reduce the risk of upper gastrointestinal irritation compared with daily administration of a lower dose.

CONCLUSIONS

Current safety and efficacy data justify further investigation of once-weekly dosing of alendronate. Two positive-control, double-blind, randomized trials of osteoporosis treatment and prevention are currently being performed to assess the comparability of weekly, biweekly, and daily dosing of alendronate with regard to effects on bone density, safety, and tolerability.

Functional epithelial cell line cloned from rat parathyroid glands

Primary cultures of rat parathyroid cells were developed in medium containing 5% calf serum, 1% Nutridoma-SP (a serum-free medium supplement from Boehringer Mannheim), and 0.7 mM calcium. The PT-r strain was purified by successive colony isolations and maintained differentiated characteristics (secretion of bioactive and radioimmunoactive parathyroid hormone into the culture medium, sensitivity to calcium regulation, and modulation by secretin) for 7 months in continuous culture. These cultured cells are epithelioid, display diploid chromosome numbers, and do not show a transformed phenotype. There has been no decrease in the rate of cell division or decline in parathyroid hormone secretion since the cell line was established. This clonal cell line provides an important system for further studies on the biology of the parathyroid cell.

Selective resistance to parathyroid hormone in cultured skin fibroblasts from patients with pseudohypoparathyroidism type Ib

We measured cAMP production in response to agonists in cultured skin fibroblasts from subjects with pseudohypoparathyroidism type Ib (PHP Ib; normal phenotype, resistance to PTH only, normal guanine nucleotide stimulatory coupling protein activity) and skin fibroblasts from normal subjects. There were no significant differences in basal or prostaglandin E1- and forskolin-stimulated cAMP production in PHP Ib vs. normal fibroblasts. Fibroblasts from 7 of 10 subjects with PHP Ib had significantly reduced peak cAMP responses to PTH [3.95 +/- 0.88 vs. 15.9 +/- 4.2 pmol/100 micrograms protein (mean +/- SD); n = 7 for both groups; P less than 0.001]. PTH-stimulated cAMP production was significantly reduced in the 7 subjects with PHP Ib at all concentrations of PTH tested [3-1000 ng/ml human PTH-(1-34)]. In the other 3 subjects with PHP Ib, the cAMP response to PTH was either normal (2 subjects) or above the normal range (1 subject). Thus, skin fibroblasts from many, but not all, subjects with PHP Ib have selective resistance to PTH in terms of cAMP response. Since the defect is hormone specific and persists in culture, we suggest that an intrinsic defect in the PTH receptor may cause PTH resistance in certain subjects with PHP Ib. The cause of PTH resistance in the subjects with a normal cAMP response to PTH is not known, but the data suggest heterogeneity even within the PHP Ib subgroup.

The inhibitory guanine nucleotide regulatory protein modulates agonist-stimulated cAMP production in rat osteosarcoma cells

We identified the subunits of the stimulatory and inhibitory guanine nucleotide binding proteins (Gs and Gi, respectively) associated with adenylate cyclase in rat osteosarcoma (ROS) cells. Pertussis toxin catalyzed ADP-ribosylation of Gi alpha in ROS cells increased agonist (PTH and isoproterenol)-stimulated, but not basal, cAMP production. The effect of pertussis toxin was dose and time dependent, and slowly reversible (T 1/2 approximately 30 h) during continued culture without toxin. Pertussis toxin treatment of ROS cell lines (17/2.8 and 24/l) with markedly different agonist responsiveness increased agonist-stimulated cAMP production in proportion to the response without toxin treatment. Pertussis toxin treatment further increased cAMP response to PTH in dexamethasone treated cells. We conclude that ROS cells contain functional Gi which modulates agonist-stimulated cAMP formation. Alterations in ROS cAMP responsiveness caused by steroids, and the reduced responsiveness of the 24/1 cell line, however, are unlikely to be due to changes in Gi.

Morphologic and functional studies of a rat hypercalcemia-associated testicular tumor maintained in cell culture

The Rice H500 tumor is a transplantable nonmetastasizing testicular tumor of Fischer rats associated with hypercalcemia and increased urine cyclic adenosine monophosphate (AMP) excretion, features similar to those of the clinical syndrome of humoral hypercalcemia of malignancy. Tumor cells can be maintained in tissue culture; one million cells grown in culture reinoculated in Fischer rats reproduce the syndrome of tumor growth and lethal hypercalcemia. Infusion of concentrated, serum-free cell culture supernatant into parathyroidectomized rats produced an increase in urine cyclic AMP similar to that produced by an infusion of bovine parathyroid hormone. Light and electron microscopic appearance of the H500 tumor in vivo and in vitro is similar to previous descriptions of a hypercalcemia-associated rat testicular tumor believed to be of Leydig cell origin. Ultrastructural characteristics of microvilli, intracellular glandlike lumina, and cell-cell attachments, however, suggest an epithelial origin. Absence of smooth endoplasmic reticulum typical of steroid-secreting Leydig cells suggest these cells are not actively involved in steroid synthesis and secretion. The ultrastructure of this tumor is sufficiently different from that of normal Leydig cells that the cell of origin is unclear. Nonetheless, this tumor provides a useful model of hormonally mediated tumor-associated hypercalcemia.

A factor produced by cultured rat Leydig tumor (Rice 500) cells associated with humoral hypercalcemia stimulates adenosine 3',5'-monophosphate production via the parathyroid hormone receptor in human skin fibroblasts

The Rice-500 Leydig cell tumor of Fischer rats is associated with humoral hypercalcemia in vivo and produces a factor that stimulates cAMP formation in cultured rat osteosarcoma cells. We found that cultured human skin fibroblasts respond to both human PTH-(1-34) and the factor produced by cultured rat Leydig tumor cells with a dose-dependent rise in cAMP formation. The time courses for stimulation of the two agents were similar, and stimulation by both was blocked by the competitive PTH antagonist [8,18-norleucine,34-tyrosine]bovine PTH-(3-34) amide. These data suggest that PTH-like factors secreted by a murine tumor are capable of interacting with the human PTH receptor.

Projecting physician requirements in a two-county region in Ohio

A methodology for projecting physician requirements in a geographical region is presented. The procedure incorporates variables defining physician workloads, rates of retirement and estimated population changes to determine the future needs for health care practitioners. A case study using data from a two-county region of northeastern Ohio is included to illustrate the applicability of the projection methodology.

Skeletal response in rats following the implantation of hypercalcemia-producing Leydig cell tumors

The effect of Rice H-500 Leydig cell tumor tissue on bone in rats was assessed by morphometric analysis and tetracycline labeling of the lower femoral metaphyses. The rats in which tumor was implanted showed hypercalcemia, increased osteoclastic bone resorption, inhibition of bone formation with reduction in the bone apposition rate, and a loss in trabecular volume compared with the control rats. There was no evidence of tumor metastasis to bone. The results are consistent with the hypothesis that the Leydig cell tumor secretes a humoral factor capable of causing systemic bone resorption.

Persistent hyperparathyroidism caused by incomplete parathyroid resection and a hyperfunctioning parathyroid autograft

A case of familial primary hyperparathyroidism occurred in which persistent hypercalcemia was caused by hyperplastic parathyroid tissue left in the neck and mediastinum after initial surgery and by a hyperfunctioning parathyroid autograft in the forearm. Successful therapy required parathyroid localization and resection of tissue from the neck, mediastinum, and forearm. Parathyroid tissue should be autotransplanted at the time of initial surgery only when total parathyroidectomy is judged likely to have been achieved.