Affiliations: [a] Laboratory of Clinical Pharmacology and Therapeutics, Faculty of Medicine, University of Lisbon, Lisbon, Portugal
| [b] Clinical Pharmacology Unit, Instituto de Medicina Molecular, Lisbon, Portugal
| [c] Huntington’s Disease Centre, Institute of Neurology, University College London, United Kingdom
| [d] Parkinson’s disease and Movement Disorders Center, Division of Neurology, Department of Medicine, The Ottawa Hospital Research Institute, University of Ottawa, Ottawa, Canada
| [e] CNS – Campus Neurológico Sénior, Torres Vedras, Portugal
Correspondence to: Joaquim J. Ferreira, MD, PhD, Laboratório de Farmacologia Clínica e Terapêutica, Faculdade de Medicina de Lisboa, Av. Prof. Egas Moniz, 1649-028 Lisboa, Portugal. Tel.: +351 21 7802120; E-mail: firstname.lastname@example.org.
Abstract: Background: Drug development in Huntington’s disease (HD) is particularly challenging, and only two compounds are approved by the FDA. It is therefore essential to appraise drug development programs in order to understand the reasons for their failure during the early stages of development. Objectives: To describe the landscape of HD therapeutic development and critically explore the causes of compound attrition in the different stages of drug development, from phase 1 to phase 4. Methods: All HD clinical trials registered in the WHO International Clinical Trials Search Portal, from inception to May 2017, were analyzed. Two independent authors selected and extracted data. Success rate in a trial phase was calculated as the number of compounds that progressed to the next trial phase divided by the number of compounds in that phase. The overall success rate was calculated as the ratio between the number of compounds that receive regulatory approval and the total number of compounds. Results: Ninety-nine trials assessing 41 compounds and eleven non-pharmacological interventions (devices and cell therapies) were identified. Twenty-four (24.2%) were phase 1 trials, 46 (46.5%) phase 2, 20 (20.2%) phase 3, and two (2.0%) phase 4. Sixty trials (60.6%) received industry sponsorship. The most frequently studied compounds were creatine, latrepirdine and pridopidine. The mean number of participants enrolled was 92.0 and the length of treatment was 262.9 days, and both increased from phase 1 to phase 3 trials. The success rate was 25.0% from phase 1 to phase 2, 19.4% from phase 2 to phase 3, and 14.3% from phase 3 to approval. The overall success rate was 3.5%. Conclusions: Although HD is a rare condition, 99 HD trials were identified in a comprehensive clinical trial registry. We found a low success rate at earlier phases of drug-development and a very low trial success rate at later phases. There is a significant gap between drug discovery and development success rates that warrants careful appraisal and improvement.