Safety, tolerability, and efficacy of PBT2 in Huntington's disease: a phase 2, randomised, double-blind, placebo-controlled trial

Summary Background PBT2 is a metal protein-attenuating compound that might reduce metal-induced aggregation of mutant huntingtin and has prolonged survival in a mouse model of Huntington's disease. We aimed to assess the safety, tolerability, and efficacy of PBT2 in patients with Huntington's disease. Methods In this 26-week, randomised, double-blind, placebo-controlled trial, adults (≥25 years old) with early-stage to mid-stage Huntington's disease were randomly assigned (1:1:1) by a centralised interactive response system to once daily PBT2 250 mg, PBT2 100 mg, or placebo. Randomisation was stratified by site with a block size of three. Participants, carers, the steering committee, site investigators, study staff, and the study sponsor were masked to treatment assignment. Primary endpoints were safety and tolerability. The safety population consisted of all participants who were randomly assigned and had at least one dose of study drug. The principal secondary endpoint was cognition, measured by the change from baseline to week 26 in the main composite Z score of five cognitive tests (Category Fluency Test, Trail Making Test Part B, Map Search, Symbol Digit Modalities Test, and Stroop Word Reading Test) and scores on eight individual cognitive tests (the five aforementioned plus the Trail Making Test Part A, Montreal Cognitive Assessment, and the Speeded Tapping Test). The intention-to-treat population comprised participants who were randomly assigned and had at least one efficacy assessment after administration of study drug. This trial is registered with ClinicalTrials.gov , NCT01590888. Findings Between April 18, 2012, and Dec 14, 2012, 109 participants were randomly assigned to PBT2 250 mg (n=36), PBT2 100 mg (n=38), or placebo (n=35) at 19 research centres in Australia and the USA. 32 (89%) individuals on PBT2 250 mg, 38 (100%) on PBT2 100 mg, and 34 (97%) on placebo completed the study. Six serious adverse events (acute coronary syndrome, major depression, pneumonia, suicide attempt, viral infection, and worsening of Huntington's disease) occurred in five participants in the PBT2 250 mg group, three (fall with subdural haematoma, suicide attempt, and hospital admission for stabilisation of Huntington's disease) occurred in two participants in the PBT2 100 mg group, and one (increasing aggression) occurred in a participant in the placebo group. The site investigators deemed all, except the worsening of Huntington's disease, as unrelated to study dru