Safety and efficacy of long-term gantenerumab treatment in dominantly inherited Alzheimer's disease: an open-label extension of the phase 2/3 multicentre, randomised, double-blind, placebo-controlled platform DIAN-TU trial

Background: Amyloid plaque removal by monoclonal antibody therapies slows clinical progression in symptomatic Alzheimer's disease; however, the potential for delaying the onset of clinical symptoms in asymptomatic people is unknown. The Dominantly Inherited Alzheimer Network Trials Unit (DIAN-TU) is an ongoing platform trial assessing the safety and efficacy of multiple investigational products in participants with dominantly inherited Alzheimer's disease (DIAD). Based on findings of amyloid removal and downstream biological effects from the gantenerumab group of the platform trial, we continued a 3-year open-label extension (OLE) study to assess the safety and efficacy of long-term treatment with high doses of gantenerumab. Methods: The randomised, placebo-controlled, double-blind, phase 2/3 multi-arm trial (DIAN-TU-001) assessed solanezumab or gantenerumab versus placebo in participants who were between 15 years before and 10 years after their estimated years to symptom onset and who had a Clinical Dementia Rating (CDR) global score of 0 (cognitively normal) to 1 (mild dementia). This study was followed by an OLE study of gantenerumab treatment, conducted at 18 study sites in Australia, Canada, France, Ireland, Puerto Rico, Spain, the UK, and the USA. For inclusion in the OLE, participants at risk for DIAD had participated in the double-blind period of DIAN-TU-001 and were required to know their mutation status. We investigated increasing doses of subcutaneous gantenerumab up to 1500 mg every 2 weeks. Due to the lack of a regulatory path for gantenerumab, the study was stopped early after a prespecified interim analysis (when most participants had completed 2 years of treatment) of the clinical measure CDR-Sum of Boxes (CDR-SB). The primary outcome for the final analysis was the amyloid plaque measure ¹¹C-Pittsburgh compound-B positron emission tomography (PiB-PET) standardised uptake value ratio (SUVR [PiB-PET SUVR]) at 3 years, assessed in the modified intention-to-treat group (mITT; defined as participants who received any gantenerumab treatment post-OLE baseline, had at least one PiB-PET SUVR assessment before gantenerumab treatment, and a post-baseline assessment). All participants who received at least one dose of study drug in the OLE were included in the safety analysis. DIAN-TU-001 (NCT01760005) and the OLE (NCT06424236) are registered with ClinicalTrials.gov. Findings: Of 74 participants who were recruited into the OLE study between June 3, 2020, and April 22, 2021, 73 were enrolled and received gantenerumab treatment. 47 (64%) stopped dosing due to early termination of the study by the sponsor, and 13 (18%) prematurely discontinued the study for other reasons; 13 people completed 3 years of treatment. The mITT group for the primary analysis comprised 55 participants. At the interim analysis, the hazard ratio for clinical decline of CDR-SB in asymptomatic mutation carriers was 0·79 (n=53 [95% CI 0·47 to 1·32]) for participants who were treated with gantenerumab in either the double-blind or OLE period (Any Gant), and 0·53 (n=22 [0·27 to 1·03]) for participants who were treated with gantenerumab the longest (Longest Gant). At the final analysis, the adjusted mean change from OLE baseline to year 3 in PiB-PET SUVR was –0·71 SUVR (95% CI –0·88 to –0·53, p<0·0001). Amyloid-related imaging abnormalities occurred in 53% (39 of 73) of participants: 47% (34 of 73) with microhaemorrhages, 30% (22 of 73) with oedema, and 6% (five of 73) were associated with superficial siderosis. No treatment-associated macrohaemorrhages or deaths occurred. Interpretation: Partial or short-term amyloid removal did not show significant clinical effects. However, long-term full amyloid removal potentially delayed symptom onset and dementia progression. Our conclusions are limited due to the OLE design and use of external controls and need to be confirmed in long-term trials. Funding: National Institute on Aging, Alzheimer's Association, GHR Foundation, and F Hoffmann-La Roche/Genentech.