Single-dose, placebo-controlled, randomized study of AMG 785, a sclerostin monoclonal antibody

Authors


Abstract

Sclerostin, an osteocyte-secreted protein, negatively regulates osteoblasts and inhibits bone formation. In this first-in-human study, a sclerostin monoclonal antibody (AMG 785) was administered to healthy men and postmenopausal women. In this phase I, randomized, double-blind, placebo-controlled, ascending, single-dose study, 72 healthy subjects received AMG 785 or placebo (3:1) subcutaneously (0.1, 0.3, 1, 3, 5, or 10 mg/kg) or intravenously (1 or 5 mg/kg). Depending on dose, subjects were followed for up to 85 days. The effects of AMG 785 on safety and tolerability (primary objectives) and pharmacokinetics, bone turnover markers, and bone mineral density (secondary objectives) were evaluated. AMG 785 generally was well tolerated. One treatment-related serious adverse event of nonspecific hepatitis was reported and was resolved. No deaths or study discontinuations occurred. AMG 785 pharmacokinetics were nonlinear with dose. Dose-related increases in the bone-formation markers procollagen type 1 N-propeptide (P1NP), bone-specific alkaline phosphatase (BAP), and osteocalcin were observed, along with a dose-related decrease in the bone-resorption marker serum C-telopeptide (sCTx), resulting in a large anabolic window. In addition, statistically significant increases in bone mineral density of up to 5.3% at the lumbar spine and 2.8% at the total hip compared with placebo were observed on day 85. Six subjects in the higher-dose groups developed anti-AMG 785 antibodies, 2 of which were neutralizing, with no discernible effect on the pharmacokinetics or pharmacodynamics. In summary, single doses of AMG 785 generally were well tolerated, and the data support further clinical investigation of sclerostin inhibition as a potential therapeutic strategy for conditions that could benefit from increased bone formation. © 2011 American Society for Bone and Mineral Research.

Introduction

Sclerostin is secreted by osteocytes and negatively regulates osteoblast-mediated bone formation, most likely by binding to low-density lipoprotein (LDL) receptor–related proteins 5/6 (LRP5/6) and antagonizing Wnt signaling.1–7 Individuals who are homozygous for null mutations in SOST, the gene that encodes sclerostin, have sclerosteosis.8, 9 This syndrome is characterized by progressive bone thickening that results in significant increases in bone mass and bone mineral density (BMD) throughout the skeleton.10–12 The sclerosteosis phenotype is similar to that of another rare, recessively inherited high bone mass disorder known as Van Buchem disease.13–15 Individuals with Van Buchem disease are homozygous for a deletion downstream of the SOST gene that prevents postnatal expression of sclerostin.16–18

Similar to the human SOST mutation phenotype, SOST knockout mice have high bone mass and bone strength as a result of increased bone formation.19 Rats treated with a sclerostin antibody not only experience complete reversal of estrogen deficiency–induced bone loss at multiple skeletal sites but also have further increases in bone mass and bone strength to levels greater than nonovariectomized controls.20 Sclerostin inhibition in monkeys increased bone formation, bone mass, and bone strength at the lumbar vertebrae and increased areal BMD at the femoral neck and ultradistal radius.21 In a mouse model of colitis, treatment with a sclerostin antibody increased bone formation, thereby countering the accelerated bone loss caused by chronic inflammation.22 Additionally, in models of fracture healing in mice and rats, sclerostin antibody increased bridging and bone strength at sites of fracture, which resulted in improved bone healing compared with controls.23 No adverse effects of sclerostin inhibition have been observed in these preclinical studies.

To investigate the potential of sclerostin inhibition in humans, a study was conducted with AMG 785, a humanized sclerostin monoclonal antibody, in healthy men and postmenopausal women to evaluate its safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD).

Methods

Study design

This was a first-in-human, randomized, double-blind, placebo-controlled, ascending-single-dose study in healthy men and postmenopausal women conducted between December 2006 and July 2007 at a single center in Miami, Florida (USA). Subjects received AMG 785 or placebo (3:1) subcutaneously (s.c.; 0.1, 0.3, 1, 3, 5, or 10 mg/kg) or intravenously (i.v.; 1 or 10 mg/kg). The s.c. cohorts were dosed sequentially. The decision to proceed to the next dose cohort was made by the investigator and sponsor after all subjects in a given cohort received investigational product and had been monitored for safety for 6 days or more after dosing. Enrollment into the next cohort could begin as early as 14 days after dosing of the last subject in the preceding cohort. For the i.v. cohorts, enrollment could begin in the 1 mg/kg i.v. cohort once the 3 mg/kg s.c. cohort was completed and determined to be safe. Similarly, enrollment could begin in the 10 mg/kg i.v. cohort when the 10 mg/kg s.c. cohort was completed and determined to be safe. After review of data from the 10 mg/kg s.c. cohort, the dose for all subjects in the 10 mg/kg i.v. cohort was reduced to 5 mg/kg in part owing to one adverse event of severe nonspecific hepatitis. Based on predicted exposure, subjects receiving 0.1 or 0.3 mg/kg were followed for 29 days, those receiving 1 or 3 mg/kg were followed for 57 days, and those receiving 5 or 10 mg/kg were followed for 85 days. The objectives were to evaluate the effects of AMG 785 on safety, tolerability, PK, and PD.

This study was approved by the local institutional review board and was conducted in accordance with Food and Drug Administration and International Conference on Harmonisation (ICH) good clinical practice guidelines. All subjects provided written informed consent prior to study initiation. Amgen Inc. designed the study and conducted the statistical analysis of the data. All authors had access to the data, made contributions to the article, and vouch for its accuracy and completeness.

Study subjects

Eligible subjects were healthy men or postmenopausal women between 45 and 59 years of age with no history or evidence of a condition that would jeopardize subject safety or interpretation of study results. Postmenopausal was defined as having 12 continuous months of spontaneous amenorrhea confirmed by a serum follicle-stimulating hormone (FSH) concentration greater than 40 mIU/mL or having a bilateral oophorectomy (with or without hysterectomy) within the prior 6 weeks, as documented in the medical history (verified with an operative note, if available). Key exclusion criteria included any condition that would affect bone metabolism; prior receipt of hormone-replacement therapy, calcitonin, parathyroid hormone, doses of vitamin D greater than 1000 IU/day, glucocorticosteroids, anabolic steroids, or calcitriol (including analogues) within the previous 6 months; prior receipt of bisphosphonates or fluoride for osteoporosis within the previous 12 months; a bone fracture within the previous 6 months; or a lumbar spine L1–L4 or femoral neck T-score of less than −2.5.

Study procedures

The following procedures were performed prestudy and periodically during the study: physical examination, vital signs, electrocardiogram, hematology, chemistry, urinalysis, anti-AMG 785 antibody screen, blood sample draws (for PK, PD, and serum calcium measurements), and dual-energy X-ray absorptiometry (DXA) scans (except for the 0.1 and 0.3 mg/kg s.c. cohorts). DXA scans were conducted predose and on days 29 and 57 (approximately). For the 5 and 10 mg/kg cohorts, additional scans were conducted on day 85 (approximately). Serum concentrations of AMG 785 were measured at Amgen Inc. by a validated ELISA. Screening for anti-AMG 785 antibodies was conducted at Amgen Inc. using a validated Meso Scale Discovery (MSD) electrochemiluminescence (ECL) immunoassay. Samples found to be positive for binding antibodies were further tested using a validated bioassay to determine if the antibodies were able to neutralize the activity of AMG 785. N-terminal propeptide of type 1 procollagen (P1NP) and serum C-telopeptide (sCTx) were analyzed at the University of Liège (Liège, Belgium) using an ELISA and RIA, respectively. Serum concentrations of osteocalcin, bone-specific alkaline phosphatase (BAP), total and ionized calcium, and intact parathyroid hormone (iPTH) were measured using standard laboratory procedures. Adverse events and concomitant medications were recorded at all study visits.

Statistical analyses

For all analyses, subjects were analyzed according to the dose and treatment they received. Both men and women were enrolled in the placebo, 1 mg/kg, and 5 mg/kg groups. Data for the men and women within each of these groups were not reported separately but were combined and reported together. Data from subjects who received placebo from all s.c. cohorts or all i.v. cohorts, respectively, were combined into one s.c. placebo group and one i.v. placebo group, respectively. The PK analyses included all treated subjects for whom the PK parameters could be estimated. Serum AMG 785 concentration-time data were analyzed by noncompartmental methods using WinNonlin Enterprise Version 5.1.1 (Pharsight Corporation, Mountain View, CA, USA). The PD analyses included all subjects who received investigational product and had both predose and postdose measurements. Data are summarized for each dose level for each route of administration. Change and percent change from baseline for selected PD parameters between placebo and each AMG 785 group were tested in a mixed-effects model using linear contrasts. For safety analyses, all subjects who received AMG 785 or placebo were included, and placebo-treated subjects from all cohorts were combined to form a composite placebo group.

Results

Study population

A total of 72 subjects received investigational product (18 placebo, 54 AMG 785). Of these, 56 subjects (14 placebo, 42 AMG 785) received s.c. investigational product and 16 subjects (4 placebo, 12 AMG 785) received i.v. investigational product. All subjects who received investigational product completed the study. The demographics and baseline characteristics of the study population are summarized in Table 1. Most of the subjects were women (78%) and were Hispanic (90%). The mean age of each cohort ranged from 49 to 55 years. The mean T-score of each cohort ranged from −1.09 to −0.17 (lumbar spine) and −0.57 to 0.27 (total hip).

Table 1. Demographics and Baseline Characteristics
 Placebo (s.c.) (n = 14)AMG 785 (s.c.)Placebo (i.v.) (n = 4)AMG 785 (i.v.)
0.1 mg/kg (n = 6)0.3 mg/kg (n = 6)1 mg/kg (n = 9)3 mg/kg (n = 6)5 mg/kg (n = 9)10 mg/kg (n = 6)All AMG (n = 42)1 mg/kg (n = 6)5 mg/kg (n = 6)All AMG (n = 12)
Sex, n (%)
 Women12 (86)6 (100)6 (100)6 (67)6 (100)6 (67)6 (100)36 (86)2 (50)3 (50)3 (50)6 (50)
 Men2 (14)0 (0)0 (0)3 (33)0 (0)3 (33)0 (0)6 (14)2 (50)3 (50)3 (50)6 (50)
Ethnicity, n (%)            
 White2 (14)0 (0)0 (0)0 (0)0 (0)0 (0)1 (17)1 (2)2 (50)1 (17)0 (0)1 (8)
 Black or African American0 (0)0 (0)0 (0)0 (0)0 (0)0 (0)0 (0)0 (0)0 (0)1 (17)0 (0)1 (8)
 Hispanic or Latino12 (86)6 (100)6 (100)9 (100)6 (100)9 (100)5 (83)41 (98)2 (50)4 (67)6 (100)10 (83)
Age, years, mean (SD)52.8 (4.2)53.0 (4.0)53.3 (3.2)52.0 (4.6)55.0 (4.1)51.9 (2.3)52.5 (4.3)52.8 (3.7)52.5 (4.4)49.3 (4.6)51.0 (3.4)50.2 (4.0)
Lumbar spine BMD, g/cm2, mean (min, max)1.12 (0.94, 1.29)1.07 (1.00, 1.14)1.05 (0.96, 1.28)1.14 (0.97, 1.27)1.08 (0.96, 1.22)1.09 (0.96, 1.28)1.18 (1.09, 1.34)1.18 (0.98, 1.37)1.16 (1.07, 1.24)1.17 (0.98, 1.37)
Total hip BMD, g/cm2, mean (min, max)0.96 (0.87, 1.06)0.96 (0.85, 1.04)1.03 (0.88, 1.24)1.02 (0.96, 1.09)0.98 (0.84, 1.14)0.99 (0.84, 1.24)1.01 (0.97, 1.06)1.08 (0.91, 1.23)1.02 (0.86, 1.18)1.05 (0.86, 1.23)
Lumbar spine T-score, mean (SE)−0.55 (0.32)−1.09 (0.11)−1.07 (0.39)−0.43 (0.27)−0.83 (0.35)−0.84 (0.14)−0.20 (0.44)−0.17 (0.53)−0.38 (0.28)−0.28 (0.29)
Total hip T-score, mean (SE)−0.44 (0.20)−0.57 (0.20)0.25 (0.42)−0.11 (0.09)−0.17 (0.40)−0.19 (0.14)−0.28 (0.09)0.27 (0.43)−0.18 (0.45)0.04 (0.31)

Pharmacokinetics

As shown in Fig. 1, after s.c. and i.v. dosing, a greater-than-dose-proportional increase in AMG 785 serum concentrations was observed, with clearance or apparent clearance decreasing as dose increased. Similar to other monoclonal antibody therapeutics, nonlinear PK were observed and were most pronounced between the 1 and 3 mg/kg s.c. dose groups.24 Peak AMG 785 serum concentrations occurred within the first week following s.c. administration. In the highest s.c. and i.v. dose groups, the serum concentrations of AMG 785 declined in a biphasic manner with discernible beta (11 to 18 days) and gamma (6 to 7 days) half-lives. Exposures (AUC0-inf) in the 1 and 5 mg/kg s.c. dose groups were approximately 50% and 70%, respectively, of the corresponding i.v. doses.

Figure 1.

Serum concentration-time profiles of AMG 785. Profiles shown are following a single subcutaneous (s.c.) dose (A) or intravenous (i.v.) dose (B) of AMG 785. Data are mean and SD.

Bone turnover markers

After a single s.c. or i.v. dose of AMG 785, there was a dose-dependent increase in the concentrations of the bone-formation markers P1NP, BAP, and osteocalcin, calculated as mean percent change from baseline (Fig. 2A–C, E–G). The maximum percent changes from baseline for P1NP, BAP, and osteocalcin were 184%, 126%, and 176% for the 10 mg/kg s.c. dose and 167%, 125%, and 143% for the 5 mg/kg i.v. dose, respectively (p < .01 compared with placebo). Concentrations of the bone-resorption marker sCTx, calculated as mean percent change from baseline, decreased in an approximately dose-dependent fashion after a single s.c. or i.v. dose of AMG 785 (Fig. 2D, H). The maximum significant percent changes from baseline for sCTx were −54% for the 10 mg/kg s.c. dose and −49% for the 5 mg/kg i.v. dose, respectively (p < .01 compared with placebo).

Figure 2.

The effect of AMG 785 on bone metabolism. Mean percent change from baseline on markers of bone metabolism following a single subcutaneous (s.c.) dose (A–D) or intravenous (i.v.) dose (E–H) of placebo or AMG 785. P1NP = N-terminal propeptide of type 1 procollagen; BAP = bone-specific alkaline phosphatase; sCTx = serum C-telopeptide.

Bone mineral density (BMD)

Compared with placebo, a single s.c. dose of AMG 785 increased BMD at the lumbar spine and total hip in all cohorts that were measured on days 29, 57, and 85, with the exception of total hip BMD for the 5 mg/kg cohort on day 29 (Fig. 3A, B). These BMD increases appeared to be dose-dependent. The largest significant increase in lumbar spine (5.3%) and total hip (2.8%) BMD was observed on day 85 with a s.c. dose of 10 mg/kg (p < .01 compared with placebo). In the i.v. cohorts, the largest increase in lumbar spine (5.2%) and total hip (1.1%) BMD also was observed on day 85 with a dose of 5 mg/kg (p < .01 for the lumbar spine; p > .05 for total hip; Fig. 3C, D).

Figure 3.

The effect of AMG 785 on BMD. Mean percent change from baseline in lumbar spine (A, C) or total hip (B, D) BMD following a single subcutaneous (s.c.) dose (A, B) or intravenous (i.v.) dose (C, D) of placebo or AMG 785. Per protocol, BMD measurements for the 1 and 3 mg/kg cohorts were not obtained on day 85. Data are mean and SE. ap < .05; bp < .01.

Safety

AMG 785 generally was well tolerated at all administered doses. At least one adverse event was reported by 64% or 60% of the subjects who received s.c. placebo or AMG 785, respectively, and 50% or 25% of the subjects who received i.v. placebo or AMG 785, respectively (Table 2). Most adverse events were considered mild by the investigator. None of the subjects discontinued the study or died because of an adverse event. Of the 56 subjects who received either placebo or AMG 785 s.c. injections, the most frequently reported adverse events included injection-site erythema, back pain, headache, constipation, injection site hemorrhage, arthralgia, and dizziness. All these events were considered mild and not serious. One subject who received 10 mg/kg s.c. AMG 785 reported a serious adverse event of severe nonspecific hepatitis, evidenced as elevated liver function test, beginning 1 day after dosing, with nausea and vomiting starting the night of dosing. Three days after dosing, no gastrointestinal symptoms were observed; alanine aminotransferase and aspartate aminotransferase concentrations peaked at about 13 and 6 times the upper normal limit, respectively, and bilirubin concentrations were normal. Hepatitis panels and abdominal ultrasound tests were conducted 6 to 8 days after dosing and were normal. Resolution of the event occurred on day 26. Of the 16 subjects who received placebo or AMG 785 i.v. injections, none reported more than 1 mild adverse event, which included constipation, headache, cough, and hot flush. Except for injection-site erythema and hemorrhage, no relationship was apparent between the subject incidence of adverse events and either the dose or the route of administration of AMG 785.

Table 2. Adverse Events
 Placebo (s.c.) (n = 14)AMG 785 (s.c.)Placebo (i.v.) (n = 4)AMG 785 (i.v.)
0.1 mg/kg (n = 6)0.3 mg/kg (n = 6)1 mg/kg (n = 9)3 mg/kg (n = 6)5 mg/kg (n = 9)10 mg/kg (n = 6)All AMG (n = 42)1 mg/kg (n = 6)5 mg/kg (n = 6)All AMG (n = 12)
  1. Note: All data are n (%). Adverse events listed occurred in 5% or more of all subjects who received either s.c. or i.v. AMG 785.

Any adverse event9 (64)4 (67)4 (67)1 (11)5 (83)6 (67)5 (83)25 (60)2 (50)1 (17)2 (33)3 (25)
 Injection-site erythema001 (17)02 (33)2 (22)4 (67)9 (21)0000
 Back pain1 (7)1 (17)0001 (11)2 (33)4 (10)0000
 Headache3 (21)1 (17)0001 (11)2 (33)4 (10)01 (17)01 (8)
 Constipation1 (7)00002 (22)1 (17)3 (7)1 (25)01 (17)1 (8)
 Injection-site hemorrhage000002 (22)1 (17)3 (7)0000
 Arthralgia1 (7)1 (17)0001 (11)1 (17)3 (7)0000
 Dizziness1 (7)1 (17)0001 (11)1 (17)3 (7)0000
 Diarrhea02 (33)000002 (5)0000
 Urinary tract infection000001 (11)1 (17)2 (5)1 (25)000
 Muscle spasms000002 (22)02 (5)0000
 Cough0000000001 (17)01 (8)
 Hot flush00000000001 (17)1 (8)
Serious adverse event0000001 (17)1 (2)0000
Death000000000000
Withdrawal due to adverse event000000000000

Mild, transient decreases in mean serum ionized calcium concentrations of about 4% from baseline occurred after a single s.c. or i.v. dose of AMG 785 and returned to baseline during the course of the study or over the follow-up period (data not shown). Likely owing to these decreases in calcium, mean percent change in iPTH concentrations from baseline increased with dose and returned to baseline concentrations by study end (data not shown). These findings were not associated with any reported adverse events. In some subjects who received higher doses of AMG 785, variable increases in alkaline phosphatase were observed, likely owing to changes in BAP. No clinically significant changes in other laboratory parameters were detected.

Of the 54 subjects who received AMG 785, 6 subjects (11%) tested positive for binding anti–AMG 785 antibodies in the highest-dose groups. Of these 6 subjects, 1 subject (10 mg/kg s.c.) tested positive for AMG 785 neutralizing antibodies at study end and up to day 283, and 1 subject (5 mg/kg i.v.) tested positive for neutralizing antibodies during follow-up on day 132 and up to day 252. The effects of neutralizing antibody formation on the PK and PD of AMG 785 could not be determined definitively in this study owing to the timing of antibody formation relative to when serum concentrations of AMG 785 and bone turnover markers began to return to baseline. However, the adverse events, laboratory results, vital signs, and electrocardiogram profiles for these subjects did not suggest any safety concerns associated with the neutralizing antibodies.

Discussion

In this first-in-human clinical study, single doses of a humanized sclerostin monoclonal antibody (AMG 785) were evaluated in healthy men and postmenopausal women. AMG 785 generally was well tolerated. One treatment-related serious adverse event of nonspecific hepatitis was reported. No deaths or study discontinuations occurred. Of the 54 subjects receiving AMG 785, 2 in the highest-dose groups developed neutralizing antibodies, with no discernible effect on the PK or PD. Compared with placebo, AMG 785 increased the bone-formation markers P1NP, BAP, and osteocalcin and decreased the bone-resorption marker sCTx, resulting in a large anabolic window. These effects with a single dose were associated with potentially clinically relevant increases in lumbar spine and total hip BMD.

The most common treatments for osteoporosis are oral bisphosphonates, which reduce fracture risk primarily by inhibiting bone resorption, thereby preventing further bone loss.25, 26 However, with these antiresorptive agents, bone remodeling remains coupled, and decreases in bone formation are observed. In contrast, anabolic agents act primarily by stimulating osteoblast activity, leading to new bone growth. Currently, the only approved anabolic agent for the treatment of osteoporosis in the United States is teriparatide [parathyroid hormone (PTH) 1–34]. Teriparatide has been shown to significantly improve BMD and reduce vertebral and nonvertebral fracture risk, making it an attractive alternative for osteoporosis patients at high risk for fracture or with severe osteoporosis.27 However, teriparatide use is currently limited, in part, because of an inconvenient dosing regimen (administered s.c. on a daily basis).28

In this study, the magnitude of effect on bone-formation markers within the month following a single dose of AMG 785 was comparable with that observed after 6 months of daily treatment with teriparatide. Additionally, the increase in BMD at the lumbar spine (5.3%) and total hip (2.8%) 3 months after a single s.c. dose of 10 mg/kg of AMG 785 was similar to or greater than what has been observed following 6 months of daily treatment with teriparatide.29 Of note, if subjects enrolled in the AMG 785 first-in-human study were supplemented with calcium and vitamin D, this may have resulted in even greater BMD increases.

It is also noteworthy that AMG 785 not only increased bone formation (P1NP, BAP, and osteocalcin) but also decreased bone resorption (sCTx), resulting in a large anabolic window. Since this has not been demonstrated with other bone therapeutics, this appears to be novel to AMG 785. This uncoupling of osteoblast and osteoclast activity also has been observed in preclinical studies. In SOST knockout mice, osteocalcin was increased, whereas TRACP5b, an osteoclast marker, was unchanged.19 In a study in ovariectomized rats treated with a sclerostin antibody, osteoclast surface was decreased, whereas bone formation was increased significantly.20 In primates treated with a sclerostin antibody, significant increases in anabolic activity were observed with no change in bone resorption. These data collectively support the finding of uncoupled bone formation and bone resorption observed in humans treated with AMG 785. In addition, limited histomorphometric data reported from a single sclerosteosis patient demonstrated that the bone-formation rate was more than 9 SDs above the normal range and that the number of osteoclasts per area of bone tissue was within the low to normal range, suggestive of an uncoupling between osteoblasts and osteoclasts.30 For sclerostin inhibition (genetic and pharmacologic), it is unclear whether this uncoupling is from a direct effect on osteoclasts or secondary to the a marked increase in bone-forming surface. This mode of anabolism may differ from that found in PTH treatment studies, in which bone-resorption markers in humans31 and primates32 were increased 1 month after administration.

In summary, this study demonstrated that AMG 785 is a generally well tolerated and effective bone anabolic agent. The results from this first-in-human study further support clinical investigation of AMG 785 in human conditions that could benefit from an increase in bone formation such as osteoporosis.

Disclosures

The sclerostin antibody is being developed in collaboration with UCB, Inc., for bone-related conditions. This study was funded by Amgen Inc. and UCB, Inc. DP, GJ, BS, and EP are Amgen Inc. employees and shareholders. LF is a former Amgen Inc. employee and shareholder.

DP made substantial contributions to the conception and design of the study, the interpretation of the data, and the drafting and critical review of the manuscript. GJ made substantial contributions to the analysis and interpretation of the data and critical review of the manuscript. BS made substantial contributions to the analysis and interpretation of the data and critical review of the manuscript. LF made substantial contributions to the analysis and interpretation of the data and critical review of the manuscript. EP made substantial contributions to the conception and design of the study, interpretation of the data, and critical review of the manuscript. All authors reviewed and approved the final version of the manuscript.

Acknowledgements

We thank Michelle N Bradley, PhD, of Amgen Inc. for assistance in the preparation of this article.

Ancillary