A phase 3 trial of the efficacy and safety of oral recombinant calcitonin: The oral calcitonin in postmenopausal osteoporosis (ORACAL) trial

Authors


Abstract

The Oral Calcitonin in Postmenopausal Osteoporosis (ORACAL) study was a randomized, double-blind, double-dummy, active- and placebo-controlled, multiple-dose, phase 3 study to assess the efficacy and safety of oral recombinant calcitonin for treatment of postmenopausal osteoporosis. A total of 565 women age 46 to 86 (mean 66.5) years were randomized (4:3:2) to receive oral recombinant salmon calcitonin (rsCT) tablets (0.2 mg/d) plus placebo nasal spray, synthetic salmon calcitonin (ssCT) nasal spray (200 IU/d) plus placebo tablets, or placebo (placebo tablets plus placebo nasal spray), respectively for 48 weeks. All women received calcium (≥1000 mg/d) and vitamin D (800 IU/d). Women randomized to oral rsCT had a mean ± SD percent increase from baseline in lumbar spine bone mineral density (BMD) (1.5% ± 3.2%) that was greater than those randomized to ssCT nasal spray (0.78% ± 2.9%) or placebo (0.5% ± 3.2%). Lumbar spine BMD change in those receiving nasal calcitonin did not differ from placebo. Oral rsCT treatment also resulted in greater improvements in trochanteric and total proximal femur BMD than ssCT nasal spray. Reductions in bone resorption markers with oral rsCT were greater than those observed in ssCT nasal spray or placebo recipients. Approximately 80% of subjects in each treatment group experienced an adverse event, the majority of which were mild or moderate in intensity. Gastrointestinal system adverse events were reported by nearly one-half of women in all treatment groups and were the principal reason for premature withdrawals. Less than 10% of women experienced a serious adverse event and no deaths occurred. Overall, oral rsCT was superior to nasal ssCT and placebo for increasing BMD and reducing bone turnover. Oral rsCT was safe and as well tolerated as ssCT nasal spray or placebo. Oral calcitonin may provide an additional treatment alternative for women with postmenopausal osteoporosis. © 2012 American Society for Bone and Mineral Research.

Introduction

Calcitonin is a 32–amino acid naturally occurring peptide hormone that is a regulator of serum calcium; it is produced by the thyroid gland in mammals and the ultimobranchial glands in birds and fish.1 It has long been used as a therapeutic agent because of its antiresorptive properties, effected by binding to specific G protein-coupled receptors on osteoclasts.2 Pharmaceutical preparations of calcitonin generally use salmon calcitonin (sCT) because it is a more potent antiresorptive than human calcitonin.3 Synthetic salmon calcitonin (ssCT), administered parenterally, is used for treatment of Paget's disease, hypercalcemia, and osteoporosis.4–7 Recombinant salmon calcitonin (rsCT) and ssCT nasal sprays are approved for postmenopausal osteoporosis treatment and have similar safety, pharmacokinetic, and pharmacodynamic profiles, and effects on bone mineral density (BMD) and markers of bone resorption.4, 5, 8 Side effects of sCT are minimal, apart from nausea and vomiting, which may resolve with continued dosing.1

Although several classes of medications are approved to treat osteoporosis, all such agents have limitations, and most, including nasal sCT, are associated with poor compliance.9 Recent reports of a relationship between long-term use of bisphosphonates, the most commonly used class of agents, and the development of atypical femoral fractures may make some patients and prescribers reluctant to use such agents.10, 11 Some providers and patients may find an oral formulation of sCT preferable with respect to safety, convenience, and compliance. The Oral Calcitonin in Postmenopausal Osteoporosis (ORACAL) trial was a 48-week, randomized, double-blind, double-dummy, active- and placebo-controlled study to evaluate the efficacy, safety, and tolerability of oral rsCT in women with postmenopausal osteoporosis.

Methods

Participants

We screened 1167 postmenopausal women. Of these, 565 with documented osteoporosis (BMD T-score at the lumbar spine, femoral neck, or total proximal femur of ≤ −2.5 (or < −2.0 if there was a documented prior vertebral fragility fracture) provided informed consent and were enrolled. Other major inclusion criteria included age ≥ 45 years and a BMI ≤ 39 kg/m2. Major exclusion criteria were the presence of metabolic or other bone disease (eg, osteogenesis imperfecta, osteomalacia, Paget's disease), vitamin D deficiency (25[OH]D < 70 nmol/L [28 ng/mL]), or uncontrolled major intercurrent illness. Any prior use of denosumab, teriparatide, or strontium was exclusionary. Any prior intravenous bisphosphonate use was exclusionary as was prior oral bisphosphonate use (unless less than 6 months of treatment and off for 6 months, or 6–12 months of treatment and off for 2 years, or more than 12 months of treatment and off for 5 years).

Study design

We randomly assigned volunteers to one of three groups: oral rsCT tablets (plus placebo nasal spray), ssCT nasal spray (plus placebo tablets), or placebo (placebo tablets plus placebo nasal spray) using a predetermined block size of nine. Within each block participants were randomized in a 4:3:2 ratio (oral rsCT tablet: ssCT nasal spray: placebo). All participants were also provided with supplemental calcium carbonate or calcium citrate (at least 1000 mg/d) and vitamin D (800 IU/d).

Study medication and supplements were self-administered daily for 48 weeks. Subjects returned to the research clinic every 3 months during the study to replenish their drug supply, for adverse event (AE) assessment and to report use of concomitant medications. Compliance was encouraged by monthly telephone calls (in the months with no clinic visit) from research site staff and was calculated based upon the number of tablets returned and the volume of liquid remaining in the spray bottles.

All patients provided written informed consent to participate in the study; appropriate ethics committees and regulatory authorities approved the protocol. A Data Safety Monitoring Board (DSMB) met on three prespecified occasions during the study to review partially blinded safety data. On each occasion the DSMB recommended the study continue unchanged.

Treatments

Identical-appearing tablets contained either 0.2 mg (200 µg/1200 IU) of rsCT or placebo. The oral calcitonin and placebo tablets are coated with an acid-resistant enteric coat (Eudragit L 30 D-55) that prevents dissolution in the stomach. The tablet core contains citric acid, which is present to inhibit intestinal proteases and improve paracellular transport. Nasal spray contained 33 µg/200 IU ssCT (Miacalcin [US], Miacalcic [EU and RSA], Novartis Pharmaceuticals, East Hanover, NJ, USA) or placebo identical in appearance to Miacalcin and similar in appearance to Miacalcic. These synthetic calcitonin nasal spray products were commercially obtained and the labels were masked. All treatments and placebos were supplied by the sponsor, except for vitamin D and calcium supplements, which were obtained commercially by each clinic site.

All participants self-administered one tablet daily with a glass of water approximately 1 hour before sleeping, and concurrently administered one puff of nasal spray.

Bone density measurement

We measured BMD at the lumbar spine (L1–L4) and proximal femur (neck, trochanter, and total hip) using replicate dual-energy X-ray absorptiometry (DXA) scans at screening, week 24, and week 48. BMD results were averaged if the two scans were within 5% of each other. If the results fell outside of this range, a third scan was obtained and the two scans closest to one another were averaged. Each participant was scanned on only one instrument throughout the study. All DXA scans were reviewed independently in blinded fashion by two expert technicians at a central imaging facility (BioClinica, Inc.) for technical adequacy of acquisition and then analyzed in accordance with prespecified standard guidelines.

Bone biomarkers

We obtained fasting blood samples prior to 11 a.m. for assessment of biomarkers of bone resorption (cross-linked C-telopeptide 1 [CTx-1], cross-linked N-telopeptide of type I collagen 1 [NTx-1]) and formation (total amino-terminal propeptide of type I procollagen [P1NP]) at baseline, week 24, and week 48. Serum CTx-1, NTx-1, and total P1NP were measured using a commercial assay (Elecsys; Roche Diagnostics). All bone biomarker assays were performed by Pacific Biomarkers, Inc., Seattle, WA, USA.

Fracture risk assessment

We performed fracture risk calculations for each participant with available data and they were interpreted by a central, blinded, qualified individual (John Kanis, MD, University of Sheffield) based upon baseline demographic and BMD data and using the World Health Organization FRAX risk assessment tool web version 3.1. Individual participant data were imported into the central database prior to unblinding.

Safety assessments

We performed a physical examination, including nasal exam, and we collected specimens for safety laboratory analyses (clinical chemistry, hematology, and urinalysis) at screening, week 12, and week 48. Adverse events were assessed at weeks 0, 12, 24, 36, and 48 at the research clinic and by interim phone calls at weeks 4, 8, 16, 20, 28, 32, 40, 44, and 52. Fasting serum samples for assessment of antibodies directed against salmon calcitonin (anti-sCT) were collected at baseline, week 12, and week 48. Antibody assays included total anti-sCT titer, isotyping (immunoglobulin G [IgG] or IgA) and neutralizing activity were measured using validated assays. Neutralizing antibody activity was determined using a cell-based assay. CHO cells containing the authentic calcitonin receptor were incubated in the absence of patient's serum with increasing concentrations of sCT and the second messenger cyclic adenosine monophosphate (cAMP) measured as an indicator of rsCT biologic activity. Serum from patients with a confirmed positive anti-rsCT response was subsequently added to the CHO cell cAMP assay to determine if the antibodies were capable of decreasing the magnitude of the cAMP response to rsCT. Those patients whose serum decreased the cAMP response to sCT were considered to have a neutralizing antibody response. Cross reactivity against human calcitonin and human calcitonin gene-related peptide were also assessed. All immunogenicity testing was performed at Unigene Laboratories, Fairfield, NJ, USA.

Statistical analysis

The sample size was based on the method proposed by Pigeot.12 It was assumed that the placebo-adjusted effect for both treatment groups was 1.56% and that the placebo-adjusted effect for the oral rsCT tablets must be at least 0.5 times the placebo-adjusted effect for the ssCT nasal spray for the study to demonstrate the non-inferiority of the oral rsCT tablets to the ssCT nasal spray. Thus we wished to have 95% confidence that the oral tablets were not less than one-half as effective as nasal spray. Assuming an SD of 2.5%, power of 80%, and a two-sided 5% level of significance, it was determined that approximately 133 patients were required for each of the active treatment groups and 84 patients were needed for the placebo treatment group. To allow for some departure in the assumptions, patient withdrawal, and safety considerations, a total of 550 patients was planned.

All analyses of safety were based upon the safety population: those patients who were randomized, received study drug, and contributed any postrandomization safety data (vital signs, laboratory results, or an AE). The primary efficacy analysis was based upon the modified intent-to-treat (mITT) population: those patients who were randomized, received treatment, and had at least one postbaseline BMD value (obtained ≥154 days after randomization). The last-observation-carried-forward method of data imputation was used for BMD in this population. The per-protocol population was a subset of the mITT population and included patients who met all entrance criteria, had baseline and week 48 DXA scans (≥45 weeks after randomization), had ≥80% compliance with study drug tablets, received the correct treatment as dictated by the randomization, and did not take a concomitant medication which was a bisphosphonate, parathyroid hormone, or calcitonin. No BMD data imputation was used in this population.

The primary comparison of interest was the percent change in lumbar spine BMD in the mITT population. Specifically, the null hypothesis tested was:

equation image

The alternative hypothesis was that the above expression was > 0, which implied that the oral tablet group was non-inferior to the ssCT nasal spray group.

Secondary endpoints included percent change in BMD from baseline to week 48 at the total hip, femoral neck, and trochanter, and percent change in BMD from baseline to week 24 at all sites (ie, including the lumbar spine) in the mITT and per protocol populations. The data were analyzed using an analysis of covariance. The model included the factors of covariate (baseline value for the variable being analyzed, treatment group, and center). An additional sensitivity analysis included a mixed model repeated measures assessment of BMD changes at the lumbar spine. Changes in biomarkers of bone resorption, CTx-1, NTx-1, and P1NP, were also assessed as secondary endpoints. For each treatment group, the significance of the mean percent change from baseline was determined using a paired t test.

Treatment group comparisons with respect to demographic and other baseline characteristics were based on a one-way analysis of variance for continuous variables and Fisher's exact test for categorical variables. Statistical significance was declared if the two-sided p value was ≤0.05.

Results

Participant characteristics

The study was conducted at 18 study sites in six countries: Bulgaria, Hungary, Poland, the Republic of South Africa, the United Kingdom, and the United States. Study volunteers were predominantly white (98.0%), normal to overweight, postmenopausal women (Table 1). Demographic characteristics, T-scores, FRAX scores (10-year probability of fractures calculated using baseline femoral neck BMD), and 25-hydroxyvitamin D [25(OH)D] levels did not differ among the three treatment groups at baseline. T-scores were lowest at the lumbar spine followed by the femoral neck. There were no statistically significant differences among groups for any baseline characteristic.

Table 1. Baseline Patient Characteristics
Baseline characteristicsSafety population
Oral tablet (n = 263)Nasal spray (n = 182)Placebo (n = 104)
  • Values are expressed as mean ± SD.

  • BMI = body mass index; FRAX-1 = 10-year probability of major osteoporotic fracture; FRAX-2 = 10-year probability of hip fracture.

  • a

    Both FRAX-1 and FRAX-2 were calculated using femoral neck T-scores.

Age (years)66.5 ± 7.666.4 ± 7.066.5 ± 8.0
Height (cm)158.91 ± 6.54158.67 ± 5.90158.62 ± 6.26
Weight (kg)64.62 ± 11.2564.96 ± 10.7264.52 ± 9.83
BMI (kg/m2)25.63 ± 4.4425.80 ± 4.0625.67 ± 3.79
FRAX-1 (%)a12.05 ± 5.6611.76 ± 5.6312.33 ± 5.53
FRAX-2 (%)a3.31 ± 3.363.07 ± 2.923.34 ± 3.19
25-hydroxyvitamin D (nmol/L)72.9 ± 19.172.5 ± 18.974.1 ± 28.0
Lumbar spine (L1–L4) T-score−2.80 ± 0.68−2.88 ± 0.72−2.92 ± 0.67
Femoral neck T-score−2.04 ± 0.73−1.99 ± 0.66−2.09 ± 0.62
Total hip T-score−1.53 ± 0.73−1.45 ± 0.71−1.59 ± 0.72
Trochanter T-score−1.48 ± 0.72−1.47 ± 0.68−1.52 ± 0.74

Participant disposition is presented in Fig. 1. Most randomized women met the prespecified criteria for the safety population, approximately three-quarters met the criteria for the mITT population, and approximately 60% met the criteria for the per-protocol population, regardless of treatment assignment. Approximately one-third of women in each treatment group withdrew prematurely from the study. The most common reasons for withdrawal (>5% of participants) in the oral rsCT, ssCT nasal spray, and placebo groups were adverse events (19.6% versus 19.5% versus 14.7%, respectively) and withdrawal of consent (7.7% versus 7.0% versus 4.6%, respectively).

Figure 1.

Patient disposition and study populations.

Mean daily compliance with oral tablet dosing was calculated to be between 92% and 94% for each group. Mean compliance with nasal spray exceeded 100% for each group, possibly reflecting unnecessary spray pump priming by participants.

Lumbar spine BMD

Mean percentage changes (ie, least squares mean) in lumbar spine BMD for the mITT population are provided in Table 2 and displayed over time in Fig. 2. At week 24, lumbar spine BMD was significantly improved from baseline for the all groups in the mITT population. At that time point the oral rsCT recipients' change in BMD was superior to placebo recipients' (p = 0.006), but not to nasal spray recipients' change. Lumbar spine BMD significantly increased from baseline to end of study in the oral rsCT and ssCT nasal spray groups; no change was observed in the placebo group. At the end of the study oral rsCT was both non-inferior (p = 0.002) and superior (p = 0.027) to ssCT nasal spray. The difference between the oral rsCT group and the placebo group was also significant (p = 0.010). Lumbar spine BMD change did not differ between the ssCT nasal spray group and the placebo group, despite the fact that the ssCT nasal spray group had a statistically significant improvement in BMD from baseline.

Table 2. Change in Lumbar Spine BMD
Change in lumbar spine BMDOral tabletNasal sprayPlacebo
  • BMD = bone mineral density; NS = not significant.

  • a

    p value for percent change of mean from screening within each treatment group based on a paired t test.

  • b

    End of study = week 48. If week 48 assessment was missing, week 24 or later assessment, if available, was carried forward.

Percent change from baseline to week 24
 n18613881
 Least squares mean (%)1.761.290.71
 SD (%)2.902.702.80
 pa<0.001<0.0010.03
Percent change from baseline to end of studyb
 n18914082
 Least squares mean (%)1.530.760.47
 SD (%)3.172.913.21
 pa<0.0010.014NS
Figure 2.

Change from baseline to week 24 and end-of-study in lumbar spine bone mineral density in mITT patients receiving 0.2 mg/d oral calcitonin, 200 IU/d intranasal calcitonin, or placebo. mITT = modified intent-to-treat.

In the per-protocol population (n = 344), lumbar spine BMD was significantly improved from baseline to week 48 only in the oral rsCT group (1.85%, p < 0.001). As with the mITT population, oral rsCT was superior to both ssCT nasal spray (0.80%, p = 0.005) and placebo (0.85%, p = 0.027) in effecting change in BMD at the lumbar spine. As with the mITT population, calcitonin nasal spray recipients did not differ from placebo recipients in change in lumbar spine BMD.

A sensitivity analysis was performed using a mixed model, repeated measures analysis. This analysis led to essentially identical conclusions as that for the primary efficacy analysis: oral rsCT was superior to ssCT nasal spray (1.65% versus 0.73%, p = 0.007) and placebo (0.59%, p = 0.010) at the end of study.

Figure 3 shows the cumulative distribution of participants' changes from baseline to the end-of-study in lumbar spine BMD. Throughout the entire distribution, women in the oral rsCT tablet group had higher BMD than those in the placebo group by approximately 1%.

Figure 3.

The graph is a cumulative distribution function which shows, on the horizontal axis, the change in lumbar spine BMD between baseline and week 48 and, on the vertical axis, the percent of (mITT) subjects with that BMD change or lower. Oral calcitonin group = solid line; 200 IU/d intranasal calcitonin group = dotted line; placebo group = dashed line. BMD = bone mineral density; mITT = modified intent-to-treat.

BMD at total hip, femoral neck, and trochanter

The oral rsCT group had a trend toward improvement from baseline BMD at the femoral neck of 0.33% ± 3.44% (p = 0.057) and demonstrated improved BMD at the trochanter of 0.64% ± 3.09% (p < 0.001). The total hip BMD was not significantly changed (−0.23% ± 2.18%) in the mITT population at week 48. The ssCT nasal spray group had nonsignificant changes from baseline in BMD at the femoral neck of 0.22% ± 3.11% and trochanter (−0.43% ± 3.39%), and a significant decrease from baseline in BMD at the total hip of −0.79% ± 2.31% (p = 0.01). The placebo group had nonsignificant changes from baseline in BMD at the femoral neck of −0.20% ± 2.75%, trochanter of −0.19% ± 4.09%, and trended to a decrease in BMD of the total hip of −0.74% ± 2.69% (p = 0.08). The difference between the oral rsCT tablet group and the ssCT nasal spray group was significant for BMD at the trochanter (p = 0.005) and total hip (p = 0.033). However, oral rsCT tablets and ssCT nasal spray were not significantly different from placebo for BMD at any of the three sites.

The trial was not designed or powered to constitute a fracture prevention efficacy trial. However, as would be expected in this population, some women did experience fractures, which were recorded as AEs. As such, they were not subject to independent radiologic verification. Excluding fractures not generally considered osteoporosis-related (ie, fractures of the small bones of the hands or feet, or nasal fracture), 5 (1.9%) women in the oral tablet group, 3 (1.6%) women in the active nasal spray group, and 1 (0.9%) woman in the placebo group reported fractures.

Serum markers of bone turnover

Table 3 summarizes the changes in biochemical indices of bone remodeling at week 24 and at the exit visit in the mITT population. At week 24 the oral and nasal CT groups had significant decreases from baseline in morning fasting CTx-1, NTx-1, and PINP but at the end of study only the oral CT group had all three biomarkers significantly suppressed compared to baseline. At week 24 the difference between the oral rsCT tablet group and the ssCT nasal spray group was significant for CTx-1 (p < 0.001) and NTx-1 (p = 0.037) but not for P1NP; the difference between the oral tablet group and the placebo group was significant for all three biomarkers (≤0.001). Calcitonin nasal spray was significantly different from placebo only for P1NP at week 24 (p = 0.017).

Table 3. Change in Bone Biomarkers to Week 24 and End of Study
 Oral tabletNasal sprayPlacebo
  • CTx-1 = cross-linked C-telopeptide 1; NS = not significant; NTx-1 = cross-linked N-telopeptide of type I collagen 1; P1NP = N-terminal propeptide of type I collagen.

  • a

    p value for percent change from screening within each treatment group based on a paired t test.

  • b

    End of study = week 48. If week 48 assessment was missing, week 24 or later assessment, if available, was carried forward.

Percent change from baseline to week 24
 CTx-1   
  n18413578
  Least squares mean (%)−42.93−24.64−21.09
  SD (%)41.9941.6162.46
  pa<0.001<0.001NS
 NTx-1   
  n18413378
  Least squares mean (%)−16.39−8.54−1.12
  SD (%)27.3543.5431.39
  pa<0.0010.012NS
 P1NP   
  n18914078
  Least squares mean (%)−25.31−22.93−13.55
  SD (%)27.5331.0426.48
  pa<0.001<0.0010.001
Percent change from baseline to end of studyb
 CTx-1   
  n18814081
  Least squares mean (%)−29.92−11.41−11.83
  SD (%)47.5340.2435.58
  pa<0.0010.0040.024
 NTx-1   
  n18813980
  Least squares mean (%)−8.090.026.36
  SD (%)35.0554.7136.12
  pa<0.001NSNS
 P1NP   
  n18813981
  Least squares mean (%)−24.17−12.44−10.81
  SD (%)26.1338.5731.74
  pa<0.001<0.001<0.001

At the end of study the difference between the oral rsCT tablet group and the ssCT nasal spray group was significant for CTx-1 (p < 0.001) and P1NP (p = 0.033), and approached significance for Ntx-1 (p = 0.077). The difference between the oral tablet group and the placebo group was significant for CTx-1 (p = 0.001), NTx-1 (p = 0.009), and P1NP (p = 0.001). Calcitonin nasal spray was not significantly different from placebo for any of the three biomarkers at the end of study.

Safety and tolerability

An overview of AEs is presented in Table 4. Approximately 80% of subjects in each treatment group experienced at least one AE during the study, the majority of which were mild or moderate in intensity. More than one-third of women in each group experienced an AE that was considered by the blinded investigator to be drug-related. Gastrointestinal system AEs were reported by nearly one-half of all women in each treatment group. The most common AEs (≥10% of participants) in the oral rsCT, ssCT nasal spray, and placebo groups were abdominal pain (27.8% versus 23.6% versus 26.9%, respectively) and nausea (12.2% versus 8.2% versus 6.7%, respectively). Serious AEs (SAEs) in the oral rsCT group were reported more frequently (7.6%) than those in the ssCT nasal spray group (4.9%), but were similar to those in the placebo group (8.7%). SAEs were generally those that would be expected in this population. No SAE was reported by more than 2 volunteers and no deaths occurred during the study. AEs resolved with no change in study treatment in the large majority of such subjects. AEs (primarily gastrointestinal) accounted for approximately one-half of all withdrawals. The rate of withdrawal due to AEs was similar across all three treatment groups, and tended to occur early in the study.

Table 4. Summary of AEs
CategorySafety population
Oral tablet (n = 263)Nasal spray (n = 182)Placebo (n = 104)
  • Values are n (%).

  • AE = adverse event; SAE = serious adverse event.

  • a

    A subject with >1 AE is counted only once within a dose group, using the maximum severity.

Subjects with ≥1 AE221 (84.0%)146 (80.2%)83 (79.8%)
Subjects with ≥1 SAEs20 (7.6%)9 (4.9%)9 (8.7%)
Subjects with AEs leading to premature withdrawal64 (24.3%)39 (21.4%)18 (17.3%)
Subjects with drug-related AEs109 (41.4%)61 (33.5%)35 (33.7%)
Subjects with AEs by severitya
 Mild75 (28.5%)64 (35.2%)27 (26.0%)
 Moderate117 (44.5%)61 (33.5%)45 (43.3%)
 Severe29 (11.0%)21 (11.5%)11 (10.6%)

Eosinophil values above the upper limit of normal were reported at least once during the study for some participants the oral rsCT (5.7%, 15/263), ssCT nasal spray (5.5%, 10/182), and placebo (4.8%, 5/104) groups. Most occurrences of eosinophilia resolved, either with no change in study drug administration or following temporary discontinuation of treatment. The occurrence of eosinophilia was not country- or continent-specific. No women with eosinophilia experienced any associated clinical symptoms or hypersensitivity reactions. The clinical significance of these elevated eosinophil counts is not known.

No other clinically relevant changes in vital signs, laboratory values (hematology, biochemistry, or urinalysis), or 25(OH) D were observed in any treatment group over the course of the study.

Immunogenicity

Sera of calcitonin recipients was tested for antibodies directed against sCT at baseline, week 12, and at the study's conclusion, week 48 (placebo subjects' sera was not tested). Anti-sCT antibodies were detected at any time postbaseline in significantly fewer women in the oral rsCT group than in the ssCT nasal spray group (6.5% versus 32.5%, p < 0.001). Correspondingly, neutralizing activity was demonstrated in fewer antibody-positive specimens from oral rsCT subjects than nasal ssCT participants (9/13 versus 33/48), although in those specimens that were antibody-positive, the percentage with neutralizing antibodies was similar between groups (69.2% versus 68.8%). One participant in the oral rsCT group was positive for IgA isotype anti-rsCT versus 12 women in the nasal spray group. At the exit visit the sera of 2 of 13 (15.4%) and 17 of 48 (35.4%) antibody-positive oral rsCT and nasal spray CT recipients, respectively, demonstrated cross-reactivity against human CT. Only 1 patient's sera (oral) demonstrated cross-reactivity against human calcitonin gene-related protein (hCGRP).

The presence of antibodies, including neutralizing antibodies, did not appear to have a deleterious effect on efficacy or the frequency, severity, or nature of AEs, although there were too few antibody-positive subjects to draw definitive conclusions.

Discussion

We report here the results of a phase 3 efficacy trial of oral calcitonin, using novel delivery technology. The oral delivery of peptide-based therapeutics must overcome a number of obstacles to successfully achieve therapeutic blood levels. Pepsin in the acidic environment of the stomach will readily cleave peptides including calcitonin; to avoid this enzymatic degradation oral calcitonin tablets were coated with an acid-stable enteric coat to prevent dissolution in the stomach. Once the tablet leaves the stomach and reaches the upper intestine the elevation in pH results in dissolution of the enteric coat and release of the tablet contents. Intestinal and pancreatic enzymes are also capable of rapidly degrading peptides. The optimal pH for these gastrointestinal (GI) enzymes is neutral to basic; inclusion of citric acid in the tablet results in a local, transient decrease in pH resulting in inhibition of the resident peptidases. Citric acid also has been shown to improve paracellular transport and further increase bioavailability.

In this population of postmenopausal women with documented osteoporosis, we observed that treatment with orally administered sCT resulted in improvement in lumbar spine BMD which was superior to that obtained with commercial nasal sCT spray or placebo after 48 weeks of treatment, with significant improvement observed after 6 months of treatment. Changes in biomarkers of bone resorption and formation were consistent with the known pharmacology of sCT; the relative changes in these biomarkers between groups were consistent with changes in lumbar spine BMD. The changes in proximal femur BMD in oral rsCT recipients were not significantly different from placebo at the end of study, but oral rsCT recipients did experience improved BMD at the trochanter compared to baseline. Consistent with these results, oral rsCT recipients experienced greater suppression of bone turnover markers than did subjects receiving nasal spray calcitonin or placebo. The per protocol analysis and a sensitivity analysis using imputed data mirrored these primary analysis results.

Oral calcitonin was well tolerated. The safety findings did not materially differ by treatment assignment, and few women in any group experienced serious adverse events. However, it is noteworthy that patients in all treatment groups experienced GI side effects as the most common adverse events, and this also constituted the most common reason for withdrawal. Whether this is due to the population under study or the formulation of study drug (as opposed to the active pharmaceutical ingredient, calcitonin) is unclear. However, oral rsCT recipients did experience more nausea and dyspepsia than nasal spray recipients, potentially reflecting greater exposure to calcitonin. Few serious adverse events occurred, however.

In contrast to the results observed with oral calcitonin, lumbar spine BMD of nasal calcitonin recipients did not differ after 48 weeks from those assigned to placebo. The reason for this finding is unclear, as there were no apparent differences in demographics, tolerability, or compliance between groups. The ongoing antibody acquisition in nasal sCT recipients during the study between weeks 12 and 48 is consistent with prior data, and suggests ongoing exposure to nasal calcitonin.13

The lumbar spine BMD improvement with oral rsCT recipients, 1.5%, is modest compared to other antiresorptive agents. However, although BMD is a measure of the composition of bone which is readily quantified, it does not capture other important skeletal properties such as size, stiffness, flexibility, and strength.14 As such, BMD change underestimates fracture risk reduction efficacy for antiresorptive drugs (including calcitonin). Fracture reduction efficacy for antiresorptives may be greatest early in the course of treatment. A meta-analysis of all trials available as of 2001 revealed that 1% to 4% BMD improvements are associated with 65% to 68% decreases in risk of vertebral fracture early in therapy.15 The immediate improvement in risk is likely due to improvement in bone strength by decreasing the number and depth of resorption pits, and suppressing the birth of new remodeling units. It has also been reported that protection is conferred on compliant women losing BMD on an antiresorptive drug (alendronate).16 Thus suppressing bone turnover is important in reducing fracture risk. This is concordant with the observation that elderly women with high bone turnover have an increased risk of hip fracture independent of hip BMD.17 Therefore, the modest BMD increase and concomitant reduction in bone turnover observed with oral calcitonin may translate to reduced fracture risk; this study was not powered to evaluate this possibility.

The significantly lower immune response in subjects receiving oral calcitonin compared to nasal calcitonin is interesting. Although the antibody response did not appear to affect efficacy or safety, it is likely that various mucosal surfaces differ in their innate ability to mount immune responses to foreign antigens.18 For example, oral vaccines may require strong adjuvants to mount an effective immune response. As such, it is plausible that GI mucosa is less efficient than the nasopharyngeal mucosa at mounting an immune response to this potential antigen.

The magnitude of increase in BMD in nasal calcitonin recipients, although significantly improved from baseline, was less than observed with some historical studies of calcitonin.19 However, other prior reports find a similar failure of nasal calcitonin to significantly improve lumbar spine BMD.20 The reason for the apparent lack of efficacy of nasal calcitonin is unclear, because compliance did not differ in any study arm for spray versus tablet administration nor between study arms. Moreover, ongoing exposure to nasal calcitonin is suggested by immunogenicity consistent with prior studies13 and increased in nasal spray subjects from week 12 to study end, suggesting ongoing exposure to nasal calcitonin. It is possible that the superior BMD response observed with oral calcitonin simply reflects greater calcitonin exposure. Consistent with this, a prior phase 1 study using oral calcitonin compared to recombinant nasal spray calcitonin (200 IU) suggested that 200-µg tablets of oral calcitonin may provide more consistent and greater exposure to calcitonin than nasal calcitonin.21

Additional study limitations include the fact that this study was conducted primarily in white, postmenopausal women. As such, it is unknown if these results are generalizable to other races or to men. Additionally, it is unknown whether oral calcitonin might be effective in preventing bone loss in individuals with low bone mass who have not progressed to frank osteoporosis. Calcitonin has been noted to have analgesic properties. Our study did not assess pain or pain relief.

Antiresorptive therapy with bisphosphonates has been associated with atypical fractures of the femur and other adverse events that might be due to oversuppression of bone resorption, such as osteonecrosis of the jaw.10 Despite decades of clinical use, we are not aware of any such reports following the use of calcitonin; our study was underpowered to detect such events. However, it is hypothetically possible that the lower suppression of bone resorption afforded by calcitonin (compared to bisphosphonates) may be less likely to foster an environment conducive to such events.

In conclusion, oral rsCT was superior to nasal ssCT and placebo for increasing BMD and reducing bone turnover. Oral rsCT was safe and as well tolerated as ssCT nasal spray or placebo. Oral calcitonin may provide an additional treatment alternative for women with postmenopausal osteoporosis.

Disclosures

DSK, JPG, and CEB are full-time employees of Tarsa Therapeutics, Inc., a company engaged in the development of oral calcitonin, and hold stock in Tarsa Therapeutics, Inc. NB, MB, ASB, and TV received research funding from Tarsa Therapeutics, Inc.

Acknowledgements

Funding for this study was provided by Tarsa Therapeutics, Inc. We thank John A Kanis, MD (University of Sheffield Medical School) for performing the FRAX analysis, and Robert Lindsay, MD (Helen Hayes Hospital) for chairing the DSMB.

In addition to the authors, the following investigators participated in the Oral Calcitonin in Postmenopausal Osteoporosis (ORACAL) trial: Bulgaria – D Yaneva, Synexus Bulgaria Clinical Research Center, Sofia; Hungary – R Cseuz, Synexus Hungary Clinical Research Center, Budapest; United Kingdom – N Bagul, Synexus Lancashire Clinical Research Center, Chorley; S Govindraj, Synexus Manchester Clinical Research Center, Manchester; E Abdulhakim, Synexus Merseyside Clinical Research Center, Liverpool; R Sarmiento, Synexus Midlands Clinical Research Center, Birmingham; R Ellahbadi, Synexus Scotland Clinical Research Center, Glasgow; H Shaw, Synexus Thames Valley Clinical Research Center, Berkshire; H Thomas, Synexus Wales Clinical Research Center, Cardiff; United States – M Greenwald, Desert Medical Advances, Palm Desert, CA; A Kivitz, Altoona Center for Clinical Research, Duncansville, PA; M Lewiecki, New Mexico Clinical Research and Osteoporosis Center, Albuquerque, NM; J Aloia, Winthrop-University Hospital Bone and Mineral Research Center, Mineola, NY; J Gallagher, Creighton University Medical Center, Omaha, NE; E Schwartz, Northern California Institute for Bone Health, Oakland, CA; W Shergy, Rheumatology Associates of Northern Alabama, Huntsville, AL.

Authors' roles: Study design: JPG, CM, RT. Study conduct: NB, MB, ASB, TV, CEB, CM. Data collection: CEB, CM. Data analysis: NB, RT, DSK. Data interpretation: NB, DSK, JPG. Drafting manuscript: DSK. Revising manuscript content: NB, DSK, JPG. Approving final version of manuscript: NB and DSK take responsibility for the integrity of the data analysis.

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