Investigating Partially Discordant Results in Phase 3 Studies of Aducanumab.

OBJECTIVES: Efficacy and safety results from the EMERGE (NCT02484547) and ENGAGE (NCT02477800) phase 3 studies of aducanumab in early Alzheimer's disease (AD) have been published. In EMERGE, but not in ENGAGE, high-dose aducanumab demonstrated significant treatment effects across primary and secondary endpoints. Low-dose aducanumab results were consistent across studies with non-significant differences versus placebo that were intermediate to the high-dose arm in EMERGE. The present investigation examined data from EMERGE and ENGAGE through post-hoc analyses to determine factors that contributed to discordant results between the high-dose arms of the two studies. DESIGN: EMERGE and ENGAGE were 2 phase 3, randomized, double-blind, placebo-controlled, parallel-group studies. SETTING: EMERGE and ENGAGE were 2 global multicenter studies involving 348 sites in 20 countries. PARTICIPANTS: Participants in EMERGE and ENGAGE were aged 50 to 85 years and had mild cognitive impairment or mild AD dementia with confirmed amyloid pathology. The randomized and dosed population (all randomized patients who received at least one dose of study treatment) included 1638 patients in EMERGE and 1647 in ENGAGE. INTERVENTION: In EMERGE and ENGAGE, participants were randomized to receive low- or high-dose aducanumab or placebo (1:1:1) once every 4 weeks. MEASUREMENTS: In this paper, 4 areas were investigated through post-hoc analyses to understand the discordance in the high-dose arms of the EMERGE and ENGAGE studies: baseline characteristics, amyloid-related imaging abnormalities, non-normality of the data, and dosing/exposure to aducanumab. RESULTS: Post-hoc analyses showed that outcomes in the ENGAGE high-dose group were affected by an imbalance in a small number of patients with extremely rapid progression and by lower exposure to the target dose of 10 mg/kg. These factors were confounded and present in early enrolled patients but were not present in later-enrolled patients who were randomized to the target dosing regimen of 10 mg/kg after titration. Neither baseline characteristics nor amyloid-related imaging abnormalities contributed to the difference in results between the high-dose arms. CONCLUSIONS: Results were consistent across studies in later enrolled patients in which the incidence of rapidly progressing patients was balanced across treatment arms.

Two Randomized Phase 3 Studies of Aducanumab in Early Alzheimer's Disease.

BACKGROUND: Alzheimer's disease is a progressive, irreversible, and fatal disease for which accumulation of amyloid beta is thought to play a key role in pathogenesis. Aducanumab is a human monoclonal antibody directed against aggregated soluble and insoluble forms of amyloid beta. OBJECTIVES: We evaluated the efficacy and safety of aducanumab in early Alzheimer's disease. DESIGN: EMERGE and ENGAGE were two randomized, double-blind, placebo-controlled, global, phase 3 studies of aducanumab in patients with early Alzheimer's disease. SETTING: These studies involved 348 sites in 20 countries. PARTICIPANTS: Participants included 1638 (EMERGE) and 1647 (ENGAGE) patients (aged 50-85 years, confirmed amyloid pathology) who met clinical criteria for mild cognitive impairment due to Alzheimer's disease or mild Alzheimer's disease dementia, of which 1812 (55.2%) completed the study. INTERVENTION: Participants were randomly assigned 1:1:1 to receive aducanumab low dose (3 or 6 mg/kg target dose), high dose (10 mg/kg target dose), or placebo via IV infusion once every 4 weeks over 76 weeks. MEASUREMENTS: The primary outcome measure was change from baseline to week 78 on the Clinical Dementia Rating Sum of Boxes (CDR-SB), an integrated scale that assesses both function and cognition. Other measures included safety assessments; secondary and tertiary clinical outcomes that assessed cognition, function, and behavior; and biomarker endpoints. RESULTS: EMERGE and ENGAGE were halted based on futility analysis of data pooled from the first approximately 50% of enrolled patients; subsequent efficacy analyses included data from a larger data set collected up to futility declaration and followed prespecified statistical analyses. The primary endpoint was met in EMERGE (difference of -0.39 for high-dose aducanumab vs placebo [95% CI, -0.69 to -0.09; P=.012; 22% decrease]) but not in ENGAGE (difference of 0.03, [95% CI, -0.26 to 0.33; P=.833; 2% increase]). Results of biomarker substudies confirmed target engagement and dose-dependent reduction in markers of Alzheimer's disease pathophysiology. The most common adverse event was amyloid-related imaging abnormalities-edema. CONCLUSIONS: Data from EMERGE demonstrated a statistically significant change across all four primary and secondary clinical endpoints. ENGAGE did not meet its primary or secondary endpoints. A dose- and time-dependent reduction in pathophysiological markers of Alzheimer's disease was observed in both trials.

Clinical Development of Aducanumab, an Anti-Aß Human Monoclonal Antibody Being Investigated for the Treatment of Early Alzheimer's Disease.

The amyloid hypothesis has been the dominant framework for Alzheimer's disease (AD) research, including the development of anti-AD therapies. However, none of the phase III clinical trials conducted to date that targeted amyloid ß (Aß) production, aggregation, or clearance demonstrated a statistically significant treatment effect in patients with AD. This includes the approach of using monoclonal antibodies that recognize various Aß epitopes and display different binding selectivity. While some monoclonal antibodies have failed in phase III trials, several are still in development. Aducanumab (BIIB037) is a human antibody that selectively targets aggregated forms of Aß, including soluble oligomers and insoluble fibrils. In PRIME (NCT01677572), an ongoing phase Ib trial (N=196 patients dosed), aducanumab was shown to reduce Aß plaques and slow decline in clinical measures in patients with prodromal or mild AD, with acceptable safety and tolerability. The main safety finding was amyloid-related imaging abnormalities (ARIA), a side effect associated with removal of Aß, which was dose-dependent and occurred more often in ApoE ε4 carriers than non-carriers. ENGAGE (NCT02477800) and EMERGE (NCT02484547), the ongoing phase III trials of aducanumab in early AD, have been designed based on the outcomes of PRIME and on lessons from past clinical trials in patients with AD. Those study design features include patient selection with confirmed Aß pathology, ensuring sufficient target engagement, and conducting clinical trials in patients at earlier symptomatic stages of AD.

Reversible and Species-Specific Depigmentation Effects of AZD3293, a BACE Inhibitor for the Treatment of Alzheimer's Disease, Are Related to BACE2 Inhibition and Confined to Epidermis and Hair.

BACKGROUND: AZD3293 (also known as LY3314814) is a novel, potent, non-selective BACE1/BACE2 inhibitor currently in Phase 3 clinical development for the treatment of Alzheimer's disease. OBJECTIVES: The purpose of these studies was to characterize the effects, putative mechanism, and reversibility of hypopigmentation following treatment with AZD3293 in pigmented Long-Evans rats, Beagle dogs, human cell cultures, and humans. DESIGN: Nonclinical studies were conducted in Long-Evans pigmented rats, and both young and older Beagle dogs using a variety of oral dose levels of AZD3293 or AZD3839 (BACE inhibition reference compound; used in older dogs only) for dosing durations of 13 to 26 weeks. In vitro studies of normal human epidermal melanocytes and reconstituted human epidermis were also conducted. Skin biopsy data from a multiple-dose Phase 1 clinical study of AZD3293 (NCT01795339) are also reported. SETTING: Nonclinical in vivo and in vitro studies were conducted in laboratory settings in the US, Canada, and France; the multiple dose clinical study was conducted in a specialized inpatient setting in the US. PARTICIPANTS: Beagle dogs: 13-week study N=36 young (8-10 mo) animals; 39-week study N=64 young animals; and a second 13-week study N=32 older (30-32 mo) animals. Long-Evans rats: N=68 animals. Multiple-dose clinical study: only data for subjects enrolled in Part 2 of this study are included in this report (N=16). INTERVENTIONS: AZD3293 was the primary intervention used in these studies. AZD3839, a relatively BACE1-selective reference inhibitor compound was used in one group in the 13 week study in older Beagle dogs and one in vitro assessment. Finally, AZ1340, another relatively BACE1-selective reference inhibitor compound was used only in one in vitro assessment. MEASUREMENTS: Measurements for the nonclinical studies in dogs and rats included macroscopic observation and assessment of skin biopsies via histopathology, immunochemistry, and electron microscopy. Measurements for the in vitro studies included melanocyte premelanosome protein (PMEL) processing, cytotoxicity, melanin synthesis, Pmel17 labeling, and melanocyte dendricity. Measurements in the clinical study included scoring of melanin content in skin biopsies taken before and after dosing with AZD3293 over 14 days at dose levels up to 150 mg. RESULTS: Depigmentation in rats and dogs was limited to skin, hair, and mucosa with no effects on other pigmented tissues. At a cellular level depigmentation was observed within a week of treatment, whereas the appearance of depigmentation in skin and hair did not become apparent until, at earliest, 4 weeks of treatment. The depigmentation effects were reversible, not associated with degenerative or inflammatory changes, and were dose- and species-dependent in severity. Full recovery of melanization was observed at the microscopic (cellular) level and at least partial recovery was seen in the macroscopic appearance of animals by the end of the 12-week recovery period in both rats and dogs. Interestingly, no changes in melanin production or melanocyte morphology were seen in human primary melanocytes or reconstituted human epidermis in vitro. Finally, there were no changes in melanization level in skin biopsies following 12 days of daily AZD3293 treatment at doses of AZD3293 up to 150 mg/day in human subjects. CONCLUSIONS: AZD3293, a novel, potent, non-selective BACE1/BACE2 inhibitor is in development as a potentially disease-modifying treatment for Alzheimer's disease. Chronic nonclinical studies in Beagle dogs and pigmented rats showed macroscopic and microscopic hypopigmentation effects of AZD3293 that were limited to skin, hair, and mucosa. These effects were shown to be reversible in both species. Analysis of data from nonclinical and in vitro studies suggests that hypopigmentation is caused by BACE2 inhibition resulting in accumulation of a premelanosome protein fragment, which interrupts the normal production of melanin. No macroscopic or microscopic reports of hypopigmentation were observed in a Phase 1 clinical study following 13 doses of AZD3293 over 14 days at dose levels up to 150 mg/day. These data suggest that hypopigmentation is species-specific and humans appear to be least sensitive to the depigmentation effect caused by BACE2 inhibition.

Promising Targets for the Treatment of Neurodegenerative Diseases.

Genetics and pathology have proven to be an effective combination to identify an evolving and deepening landscape of pathways and potential therapeutic targets in neurodegenerative diseases. Initially this landscape appeared to be populated with distinct therapeutic targets but with potentially overlapping mechanisms in each neurodegenerative disease. Our understanding has expanded to recognize that multiple pathologies are common in neurodegenerative disease, and that there is considerable overlap in pathways and targets driving neurodegenerative diseases. This potentially opens the way for future treatments to be indicated by tissue pathology and genetic basis rather than clinical phenotype. The potential to treat neurodegenerative disease by addressing underlying pathophysiology is still in the early days and challenges remain, especially the likely need to address pathologies early in disease. This will require redefinition of diagnosis and the tools to enable earlier diagnosis.