Alzheimer Combination Therapies: Overview and Scenarios.

Progress in understanding the complexity of Alzheimer's disease informs the search for combination therapies that can successfully prevent or substantially slow the progression of the disease. Anti-amyloid monoclonal antibodies are the first approved disease targeted therapies; they slow disease progression by approximately 30 %. Building on these agents in add-on therapies is one avenue to designing combination treatments. Development of combination drugs consisting of two or more novel interventions is an alternate pathway for combination treatment development. Combination therapies can involve small molecule drugs, biological agents, devices, stem cells, gene therapies, lifestyle interventions, or cognitive training. Nonclinical assessment of drug combinations may involve animal models or new approach methodologies such as induced pluripotent stem cells or organoids. Phase 1 trials are required to characterize each member of a novel combination. Phase 2 trials may use a 2-by-2 factorial design comparing each drug to placebo and the drug combination. In Phase 3, comparison of the novel combination to standard of care may be sufficient or more complex designs may be required. Targets for combination therapies beyond amyloid-related processes include tau abnormalities, inflammation, neurodegeneration, and co-pathologies such as alpha-synuclein and TDP-43. The choice of combination therapies will depend on the strength of the information regarding the target, biomarkers to guide clinical trials, and a candidate agent with the appropriate mechanism of action. Computational strategies based on network analysis of disease and drugs, validation in non-clinical models, and use of real-world data may facilitate prioritization of candidates for combination treatments.