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 makers) 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: Treatment of Postmenopausal Osteoporosis: The efficacy and safety of denosumab in the treatment of postmenopausal osteoporosis was demonstrated in 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 post-menopausal women with osteoporosis.
7,808 women aged 60-91 years were enrolled of which 23.6% had prevalent vertebral fractures.
Women were randomised to receive subcutaneous injections of either placebo (n=3,906) or denosumab 60 mg (n=3,902) once every 6 months. Women received calcium (at least 1,000 mg) and vitamin D (at least 400 IU) supplementation daily. The primary efficacy variable was the incidence of new vertebral fractures. Secondary efficacy variables included the incidence of non-vertebral fractures and hip fractures, assessed at 3 years.
Denosumab significantly reduced the risk of new vertebral, nonvertebral, and hip fractures compared with placebo. All 3 efficacy fracture endpoints achieved the statistical significance level based on the pre-specified sequential testing scheme.
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 Denosumab (Prolia) group (unadjusted absolute risk reduction of 4.8%). Reductions were also observed over 1 year (61% relative risk reduction; 1.4% unadjusted absolute risk reduction) and 2 years (71% relative risk reduction; 3.5% unadjusted absolute risk reduction) (all p<0.0001).
Denosumab also reduced the risk of other prespecified categories of fractures, including new and worsening vertebral fractures (67% relative risk, reduction, 4.8% unadjusted absolute risk reduction), multiple new vertebral fractures (61% relative risk reduction, 1.0% unadjusted absolute risk reduction), clinical vertebral fractures (69% relative risk reduction, 1.8% unadjusted absolute risk reduction) over 3 years.
The reductions in the risk of new vertebral fractures by denosumab over 3 years were consistent and significant regardless of 10-year major osteoporotic baseline fracture risk as assessed by FRAX (WHO's Fracture Risk Assessment Tool algorithm) and whether or not women had a prevalent vertebral fracture or history of a non-vertebral fracture, and regardless of baseline age, BMD, bone turnover level and prior use of a medicinal product for osteoporosis.
In postmenopausal women with osteoporosis over the age of 75, Denosumab reduced the incidence of new vertebral (64%), and non-vertebral (16%) fractures.
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%).
Denosumab also reduced the risk of clinical (30% relative risk reduction, 2.9% unadjusted absolute risk reduction), major non-vertebral (20% relative risk reduction, 1.2% unadjusted absolute risk reduction), and major osteoporotic fractures (35% relative risk reduction, 2.7% unadjusted absolute risk reduction) over 3 years.
In women with baseline femoral neck BMD T-score ≤-2.5, denosumab reduced the incidence of non-vertebral fractures (35% relative risk reduction, 4.1% unadjusted absolute risk reduction, p<0.001) over 3 years. Reductions in non-vertebral fractures were observed regardless of baseline 10-year probability of a major osteoporotic fracture as assessed by FRAX.
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%). The reductions in the risk of hip fractures over 3 years were consistent and significant regardless of baseline 10-year probability of a hip fracture as assessed by FRAX.
In women with high fracture risk as defined above by baseline age, BMD and prevalent vertebral fracture, a 48% relative risk reduction was observed with denosumab (1.1% unadjusted absolute risk reduction).
In a post-hoc analysis in postmenopausal women with osteoporosis over the age of 75 denosumab reduced the incidence of hip fractures (62%).
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.
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.
Open-Label Extension Study in the Treatment of Postmenopausal Osteoporosis: A total of 4550 patients who completed the FREEDOM study (N=7808) enrolled in a 7-year, multinational, multicenter, open label, single-arm extension study to evaluate the long-term safety and efficacy of Denosumab (Prolia). 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).
Based on data from the first 2 years of the extension study for patients who received Denosumab in the FREEDOM study and continued on therapy (years 4 and 5 of Denosumab treatment), the overall subject incidence rates of adverse events and serious adverse events reported were similar to that observed in the initial 3 years of the FREEDOM study.
For patients who crossed over to Denosumab from placebo in the FREEDOM study, the overall subject incidence rates of adverse events and serious adverse events reported also similar to the first 3 years of the FREEDOM study. Two cases of ONJ were observed; both resolved.
Denosumab treatment maintained a low incidence of new vertebral and non-vertebral fractures in years 4 and 5 (2.8% of patients had at least one new vertebral fracture by month 24, 2.5% of patients had a nonvertebral fracture).
Denosumab treatment continued to increase BMD at the lumbar spine (3.3%), total hip (1.3%), femoral neck (1.2%) and trochanter (1.8%) in years 4 and 5. Percent increase in BMD from the original FREEDOM study baseline (ie, after 5 years of treatment) in the long-term group was 13.8% at the lumbar spine, 7.0% at the total hip, 6.2% at the femoral neck and 9.7% 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-naive 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).
Clinical Efficacy in the Treatment of Bone Loss Associated with Hormone Ablation: Treatment of Bone Loss Associated with Androgen Deprivation: 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. Subjects either received subcutaneous injections of either denosumab 60 mg (n=734) or placebo (n=734) once every 6 months. Men received calcium (at least 1,000 mg) and vitamin D (at least 400 IU) supplementation daily.
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. Reductions were also observed over 1 year (85% relative risk reduction; 1.6% absolute risk reduction), and 2 years (69% relative risk reduction; 2.2% absolute risk reduction) (all p<0.01). 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 were randomised to receive subcutaneous injections of either denosumab 60 mg (n=127) or placebo (n=125) once every 6 months. Women received calcium (at least 1,000 mg) and vitamin D (at least 400 IU) supplementation daily. The primary efficacy variable was percent change in lumbar spine BMD.
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.
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.
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 metabolized by cytochrome P450 3A4 (CYP3A4). This indicates that denosumab should not alter the PK of drugs metabolized by CYP3A4.
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): No pharmacokinetic data are available in paediatric patients.
Race: The pharmacokinetics of Denosumab were not affected by race in post-menopausal 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: Pre-Clinical 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 mineralization defects, accumulation of osteoid or woven bone.
Transition from 6-months treatment with alendronate to 25 mg/kg Denosumab in ovariectomized monkeys did not cause any meaningful decreases of serum calcium. Bone strength and reduction in bone resorption at all skeletal sites were maintained or improved.
Abnormal growth plates were observed in adolescent monkeys dosed with Denosumab at 10 and 50 mg/kg SC (27 and 150 times the AUC exposure in adult humans dosed with Denosumab at 60 mg SC every 6 months), 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; there were no adverse effects on tooth eruption; and minimal to moderate mineralisation in multiple tissues was seen in one recovery animal. Maternal mammary gland development was normal. Additional information on the pharmacodynamic properties of Denosumab has been obtained from knockout mice lacking RANK or RANKL, and by the use of inhibitors of the RANKL pathway in rodents such as OPG-Fc. Knockout mice: (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.
Tissue distribution studies indicated that denosumab does not bind to tissues known for expression of other members of TNF superfamily, including TNF-related apoptosis-inducing ligand (TRAIL).