Pharmacology: Pharmacodynamics: Mechanism of action: Denosumab is a human monoclonal antibody (IgG2) that targets and binds with high affinity and specificity to RANKL preventing RANKL from activating its only receptor, RANK, on the surface of osteoclasts and their precursors, independent of bone surface. Prevention of the RANKL/RANK interaction inhibits osteoclast formation, function, and survival. Denosumab therefore reduces bone resorption and increases bone mass and strength in both cortical and trabecular bone.
Pharmacodynamic effects: In clinical studies, treatment with 60 mg of denosumab resulted in rapid reduction in the bone resorption marker serum type 1 C-telopeptides (CTX) within 6 hours of subcutaneous administration (by approximately 70%) with reductions of approximately 85% occurring by 3 days. CTX reductions were maintained over the 6-months dosing interval. At the end of each dosing interval, CTX reductions were partially attenuated from maximal reduction of ≥ 87% to approximately ≥ 45% (range 45-80%), reflecting the reversibility of denosumab's effects on bone remodelling once serum levels diminish. These effects were sustained with continued treatment. Consistent with the physiological coupling of bone formation and resorption in skeletal remodelling, reductions in bone formation markers (e.g. bone specific alkaline phosphatase [BSAP] and serum N-terminal propeptide of type I collagen [P1NP]) were observed beginning 1 month after the first dose of denosumab.
Bone turnover markers (bone resorption and formation markers) generally reached pre-treatment levels within 9 months after the last 60 mg subcutaneous dose. Upon re-initiation, the degree of inhibition of CTX by denosumab was similar to that observed in patients initiating denosumab treatment.
In a clinical study of postmenopausal women with low bone mass (N = 504) who were previously treated with alendronate for a median duration of 3 years, those transitioning to receive denosumab experienced additional reductions in serum CTX, compared with women who remained on alendronate. In this study the changes in serum calcium were similar between the two groups.
Immunogenicity: Denosumab is a human monoclonal antibody; as with all therapeutic proteins, there is a theoretical potential for immunogenicity. More than 13,000 patients were screened for binding antibodies using a sensitive electrochemiluminescent bridging immunoassay. Less than 1% of patients treated with denosumab for up to 5 years tested positive (including pre-existing, transient and developing antibodies). The patients that tested positive for binding antibodies were further evaluated for neutralising antibodies using a chemiluminescent cell-based in vitro biological assay and none of them tested positive. No evidence of altered pharmacokinetic profile, toxicity profile, or clinical response was associated with binding antibody development.
Clinical Studies: OSTEOPOROSIS: Treatment of Postmenopausal Osteoporosis: FREEDOM, a 3-year, randomised, double-blind, placebo-controlled, multinational study that demonstrated that denosumab was effective compared to placebo in reducing new vertebral, non-vertebral and hip fractures in postmenopausal women with osteoporosis. 7,808 women aged 60-91 years were enrolled of which 23.6% had prevalent vertebral fractures.
Women received calcium (at least 1,000 mg) and vitamin D (at least 400 IU) supplementation daily.
Effect on vertebral fractures: Denosumab significantly reduced the risk of new vertebral fractures (primary endpoint) by 68% (risk ratio: 0.32; p <0.0001) over 3 years. The 3-year fracture rates for new vertebral fractures were 7.2% in the placebo group and 2.3% in the PROLIA group (unadjusted absolute risk reduction of 4.8%).
Effect on all clinical fractures: Denosumab significantly decreased the risk of non-vertebral fractures (secondary endpoint) by 20% (hazard ratio: 0.80; p = 0.0106) over 3 years. Three-year non-vertebral fracture rates were 8.0% in the placebo group to 6.5% in the denosumab group (unadjusted absolute risk reduction of 1.5%).
Effect on hip fractures: Denosumab significantly decreased the risk of hip fractures (secondary endpoint) by 40% (hazard ratio: 0.60; p = 0.0362) over 3 years. Three-year hip fracture rates were 1.2% in the placebo group and 0.7% in the denosumab group (unadjusted absolute risk reduction of 0.5%).
Effect on bone mineral density (BMD): Denosumab significantly increased BMD at all clinical sites measured, relative to treatment with placebo at 1, 2 and 3 years. Denosumab increased BMD by 9.2% at the lumbar spine, 6.0% at the total hip, 4.8% at the femoral neck, 7.9% at the hip trochanter, 3.5% at the distal 1/3 radius and 4.1% at the total body over 3 years. Increases in BMD at lumbar spine, total hip and hip trochanter were observed as early as 1 month after the initial dose. Denosumab increased lumbar spine BMD from baseline in 96% of postmenopausal women at 3 years. Consistent effects on BMD were observed at the lumbar spine regardless of baseline age, race, weight/BMI, BMD and bone turnover level.
Open-label extension study in the treatment of postmenopausal osteoporosis: 4,550 patients who completed the study (N = 7,808) enrolled in a 7-year, open-label, single-arm extension study to evaluate the long-term safety and efficacy of denosumab. All patients in the extension study received denosumab every 6 months as a single 60 mg SC dose, as well as daily calcium (at least 1 g) and vitamin D (at least 400 IU).
Denosumab treatment maintained a low incidence of new vertebral and non-vertebral fractures through to year 7 (7% of patients had at least one new vertebral fracture, 9.3% of patients had at least one non-vertebral fracture).
Denosumab treatment increase BMD at the lumbar spine (10.8%), total hip (3.4%), femoral neck (3.8%) and trochanter (5.1%) from the extension baseline through 7 years. Percent increase in BMD from the original FREEDOM study baseline (i.e, after 10 years of treatment) in the long-term group was 21.7% at the lumbar spine, 9.2% at the total hip, 9.0% at the femoral neck and 13% at the trochanter.
Comparative clinical data vs alendronate in the treatment of postmenopausal women with low bone mass: In two randomised, double-blind, active-controlled studies, one in treatment-naïve women and another in women previously treated with alendronate, denosumab showed significantly greater increases in BMD and reductions in bone turnover markers (e.g. serum CTX), compared to alendronate.
Consistently greater increases in BMD were seen at the lumbar spine, total hip, femoral neck, hip trochanter, and distal 1/3 radius in women treated with denosumab, compared to those who continued to receive alendronate therapy (all p < 0.05).
Bone histology: Histology assessments showed bone of normal architecture and quality, as well as the expected decrease in bone turnover relative to placebo treatment. There was no evidence of mineralisation defects, woven bone or marrow fibrosis.
Treatment of osteoporosis in men: The efficacy and safety of PROLIA in the treatment of men with osteoporosis was demonstrated in a 1-year, randomised, double-blind, placebo-controlled, multinational study of men with low bone mass, who had a baseline BMD T-score between -2.0 and -3.5 at the lumbar spine or femoral neck. Men with a BMD T-score between -1.0 and -3.5 at the lumbar spine or femoral neck and with history of prior fragility fracture were also enrolled. Men with other diseases (such as rheumatoid arthritis, osteogenesis imperfecta, and Paget's disease) or on therapies that may affect bone were excluded from this study.
The 242 men enrolled in the study ranged in age from 31 to 84 years and were randomised to receive SC injections of either placebo (n = 121) or PROLIA 60 mg (n = 121) once every 6 months. Patients also received at least 1,000 mg calcium and at least 800 IU vitamin D supplementation daily. The primary efficacy variable was percent change in lumbar spine BMD at 1 year. Secondary efficacy variables included percent change in total hip, hip trochanter, femoral neck, and distal 1/3 radius BMD at 1 year, and change in CTX at day 15.
Treatment with PROLIA significantly increased BMD from baseline at the lumbar spine and all measured skeletal sites (proximal femur, distal radius) at 1 year. PROLIA increased lumbar spine BMD by 4.8%, total hip BMD by 2.0%, hip trochanter by 2.3%, femoral neck BMD by 2.2%, distal 1/3 radius BMD by 0.9%, relative to placebo.
Increases in BMD at lumbar spine, total hip, and hip trochanter were observed as early as 6 months. PROLIA increased lumbar spine BMD from baseline in 94.7% of men at 1 year.
Consistent effects on BMD were observed at the lumbar spine regardless of baseline age, race, weight/body mass index (BMI), BMD, and level of bone turnover.
Bone histology and histomorphometry: A total of 29 transiliac crest bone biopsy specimens were obtained from men with osteoporosis at 12 months (17 specimens in PROLIA group, 12 specimens in placebo group). Qualitative histology assessments showed normal architecture and quality with no evidence of mineralisation defects, woven bone, or marrow fibrosis in patients treated with PROLIA.
TREATMENT OF BONE LOSS ASSOCIATED WITH HORMONE ABLATION: Treatment of bone loss associated with androgen deprivation therapy for prostate cancer: The efficacy and safety of denosumab in the treatment of bone loss associated with androgen deprivation was assessed in a 3-year randomised, double-blind, placebo-controlled, multinational study of 1,468 men with non-metastatic prostate cancer aged 48-97 years. Men less than 70 years of age also had either a BMD T-score at the lumbar spine, total hip, or femoral neck < -1.0 or a history of an osteoporotic fracture. Significant increases in BMD were observed at the lumbar spine, total hip, femoral neck and the hip trochanter as early as 1 month after the initial dose. Denosumab increased lumbar spine BMD by 7.9%, total hip BMD by 5.7%, femoral neck BMD by 4.9%, hip trochanter BMD by 6.9%, distal 1/3 radius BMD by 6.9%, and total body BMD by 4.7% over 3 years, relative to placebo (p < 0.0001). Consistent effects on BMD were observed at the lumbar spine regardless of age, race, geographical region, weight/BMI, BMD, bone turnover level; duration of androgen deprivation and presence of vertebral fracture at baseline.
Denosumab significantly decreased the risk of new vertebral fractures by 62% (hazard ratio: 0.38; p < 0.0063) over 3 years. Denosumab also reduced the subject incidence of more than one osteoporotic fracture at any site by 72% relative to placebo over 3 years (placebo 2.5% vs. denosumab 0.7%, p=0.0063).
Treatment of bone loss in women undergoing aromatase inhibitor therapy for breast cancer: The efficacy and safety of denosumab in the treatment of bone loss associated with adjuvant aromatase inhibitor therapy was assessed in a 2-year, randomised, double-blind, placebo-controlled multinational study of 252 women with non-metastatic breast cancer aged 35-84 years. Women had baseline BMD T-scores between -1.0 to -2.5 at the lumbar spine, total hip or femoral neck. Women received calcium (at least 1,000 mg) and vitamin D (at least 400 IU) supplementation daily.
Denosumab significantly increased BMD at all clinical sites measured, relative to treatment with placebo at 2 years: 7.6% at the lumbar spine, 4.7% at the total hip, 3.6% at the femoral neck, 5.9% at the hip trochanter, 6.1% at the distal 1/3 radius and 4.2% at the total body. Significant increases in BMD were observed at the lumbar spine as early as 1 month after the initial dose. Consistent effects on BMD were observed at the lumbar spine regardless of baseline age, duration of aromatase inhibitor therapy, weight/BMI, prior chemotherapy, prior selective estrogen receptor modulator (SERM) use, and time since menopause.
Treatment of Glucocorticoid-induced Osteoporosis: The efficacy and safety of PROLIA in the treatment of glucocorticoid-induced osteoporosis were demonstrated in a 1-year, randomized, multicenter, double-blind, double-dummy, parallel-group, active-controlled study of 795 patients (70% women and 30% men) aged 20 to 94 years (mean age of 63.1 years) treated with ≥ 7.5 mg daily oral prednisone (or equivalent).
Two subpopulations were studied: glucocorticoid-continuing (≥ 7.5 mg daily prednisone or its equivalent for ≥ 3 months prior to study enrollment and planning to continue treatment for a total of at least 6 months; n = 505) and glucocorticoid-initiating (≥ 7.5 mg daily prednisone or its equivalent for < 3 months prior to study enrollment and planning to continue treatment for a total of at least 6 months; n = 290). Within each subpopulation, randomization was stratified by gender and patients were randomized (1:1) to receive either PROLIA 60 mg subcutaneously once every 6 months (n = 398) or oral risedronate 5 mg once daily (active-control) (n = 397). All patients were to receive at least 1,000 mg calcium and 800 IU vitamin D supplementation daily.
Enrolled patients < 50 years of age were required to have a history of osteoporotic fracture. Enrolled patients ≥ 50 years of age who were in the glucocorticoid-continuing subpopulation were required to have a baseline BMD T-score of ≤ -2.0 at the lumbar spine, total hip, or femoral neck; or a BMD T-score ≤ -1.0 at the lumbar spine, total hip, or femoral neck and a history of osteoporotic fracture.
Effect on Bone Mineral Density (BMD): In the glucocorticoid-continuing subpopulation, PROLIA demonstrated a significantly greater increase in lumbar spine BMD compared to risedronate at 1 year (PROLIA 4.4%, risedronate 2.3%) with a treatment difference of 2.2% (p < 0.001). In the glucocorticoid-initiating subpopulation, PROLIA demonstrated a significantly greater increase in lumbar spine BMD compared to risedronate at 1 year (PROLIA 3.8%, risedronate 0.8%) with a treatment difference of 2.9% (p < 0.001).
Consistent effects on lumbar spine BMD were observed regardless of gender; race; geographic region; menopausal status; and baseline age, lumbar spine BMD T-score, and glucocorticoid dose within each subpopulation.
In addition, significant differences between treatment groups in the mean percent increase in BMD from baseline at 1 year were also observed at the total hip, femoral neck, and hip trochanter (both subpopulations), and distal 1/3 radius (glucocorticoid-continuing subpopulation only).
Bone Histology: Bone biopsy specimens were obtained from 17 patients (6 in the PROLIA treatment group and 11 in the risedronate treatment group). Qualitative histology assessments showed normal architecture and quality with no evidence of mineralization defects, woven bone, or marrow fibrosis in patients treated with PROLIA.
Pharmacokinetics: Following subcutaneous administration, denosumab displayed non-linear pharmacokinetics with dose over a wide dose range, and dose-proportional increases in exposure for doses of 60 mg (or 1 mg/kg) and higher.
Absorption: Following a 60 mg subcutaneous dose of denosumab, bioavailability was 61% and maximum serum denosumab concentrations (Cmax) of 6 μg/mL (range 1-17 μg/mL) occurred in 10 days (range 2-28 days). After Cmax, serum levels declined with a half-life of 26 days (range 6-52 days) over a period of 3 months (range 1.5-4.5 months). Fifty-three percent of patients had no measurable amounts of denosumab detected at 6 months post-dose.
Distribution: No accumulation or change in denosumab pharmacokinetics with time was observed upon multiple-dosing of 60 mg subcutaneously once every 6 months.
Denosumab pharmacokinetics were not affected by the formation of binding antibodies and were similar in men and women.
Metabolism: Denosumab is composed solely of amino acids and carbohydrates as native immunoglobulin. Based on nonclinical data, denosumab metabolism is expected to follow the immunoglobulin clearance pathways, resulting in degradation to small peptides and individual amino acids.
Elimination: Denosumab is composed solely of amino acids and carbohydrates as native immunoglobulin and is not expected to be eliminated via hepatic metabolic mechanisms (e.g. cytochrome P450 (CYP) enzymes). Based on nonclinical data, its elimination is expected to follow the immunoglobulin clearance pathways, resulting in degradation to small peptides and individual amino acids.
Drug interactions: In a study of 17 postmenopausal women with osteoporosis, midazolam (2 mg oral) was administered two weeks after a single dose of denosumab (60 mg subcutaneously), which corresponds to time of maximal pharmacodynamic effects of denosumab. Denosumab did not affect the pharmacokinetics of midazolam, which is metabolised by cytochrome P450 3A4 (CYP3A4). This indicates that denosumab should not alter the PK of drugs metabolised by CYP3A4.
The pharmacokinetics and pharmacodynamics of denosumab were similar in patients receiving hormone ablation for prostate or breast cancer.
The pharmacokinetics and pharmacodynamics of denosumab were similar in patients with glucocorticoid-induced osteoporosis.
Special patient populations: Elderly (greater than or equal to 65 years of age): Age was not found to be a significant factor on denosumab pharmacokinetics in a population pharmacokinetic analysis of patients ranging in age from 28 to 87 years of age.
Children and adolescents (up to 18 years of age): No pharmacokinetic data are available in paediatric patients.
Race: The pharmacokinetics of denosumab were not affected by race in postmenopausal women or in breast cancer patients undergoing hormone ablation.
Renal impairment: In a study of 55 patients with varying degrees of renal function, including patients on dialysis, the degree of renal impairment had no effect on the pharmacokinetics and pharmacodynamics of denosumab; therefore dose adjustment for renal impairment is not necessary.
Hepatic impairment: No clinical studies have been conducted to evaluate the effect of hepatic impairment on the pharmacokinetics of denosumab.
Toxicology: Preclinical safety data: Carcinogenicity: The carcinogenic potential of denosumab has not been evaluated in long-term animal studies.
Mutagenicity: The genotoxic potential of denosumab has not been evaluated.
Reproductive toxicology: Fertility: Denosumab had no effect on female fertility or male reproductive organs in monkeys at AUC exposures that were 100- to 150-fold higher than the human exposure at 60 mg administered subcutaneously once every 6 months.
Animal pharmacology: Long-term treatment (16 months) of aged ovariectomized monkeys with denosumab at doses of 25 or 50 mg/kg SC once monthly was associated with significant gains in the mass, density (BMD), and strength of cancellous and cortical bone. Bone tissue was normal with no evidence of mineralisation defects, accumulation of osteoid or woven bone.
Denosumab is a potent inhibitor of bone resorption via inhibition of RANK ligand.
Tissue distribution studies indicated that denosumab does not bind to tissues known for expression of other member of the TNF superfamily, including TNF-related apoptosis-inducing ligand (TRAIL).
Transition from 6-months treatment with alendronate to denosumab did not cause any meaningful decreases of serum calcium or have detrimental effects on bone quality and strength. Bone strength parameters at these sites were maintained or improved with transition relative to continuous treatment with alendronate. Bone strength and reduction in bone resorption at all skeletal sites were maintained or improved in monkeys switched from alendronate to denosumab.
Adolescent primates dosed with denosumab at 150 times (50 mg/kg dose) and 27 times (10 mg/kg dose) the area under the curve (AUC) exposure in adult humans dosed at 60 mg subcutaneously every 6 months had abnormal growth plates, considered to be consistent with the pharmacological activity of denosumab.
In neonatal cynomolgus monkeys exposed in utero to denosumab at 50 mg/kg, there was increased postnatal mortality; abnormal bone growth resulting in reduced bone strength, reduced haematopoiesis, and tooth malalignment; absence of peripheral lymph nodes; and decreased neonatal growth. Following a recovery period from birth to 6 months of age, the effects on bone returned to normal. Minimal to moderate mineralisation in multiple tissues was seen in one recovery animal. Maternal mammary gland development was normal.
Since the biological activity of denosumab in animals is specific to nonhuman primates evaluation of genetically engineered (knockout) mice or use of other inhibitors of the RANK/RANKL pathway, namely OPG-Fc provided additional information on the pharmacodynamic properties of denosumab. Knockout mice lacking RANK or RANKL: (1) had an absence of lactation due to inhibition of mammary gland maturation (lobulo-alveolar gland development during pregnancy); (2) exhibited impairment of lymph node formation; and (3) exhibited reduced bone growth and lack of tooth eruption. Similar phenotypic changes were seen in a corroborative study in 2-week old rats given OPG-Fc. These changes were partially reversible in this model when dosing with the RANKL inhibitors was discontinued.