Overview of Clinical Trial: Many age-associated neurodegenerative diseases, including Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), are associated with increased inflammatory signaling in the central nervous system. While there is growing evidence that activation of inflammatory signaling leads to neuronal death in cell-based models and leads to signs and symptoms of neurodegeneration in animal models, no disease modifying anti-inflammatory drugs for AD or ALS have been found to date. Recent observational studies of anti-inflammatory drugs used to treat rheumatoid arthritis suggest the potential of these drugs to prevent a diagnosis of AD.

This is an open-label, biomarker-driven basket trial of baricitinib in individuals with mild cognitive impairment (MCI), subjective cognitive decline (SCD), AD, ALS, or asymptomatic carriers of an ALS causative gene, such as a hexanucleotide expansion in the C9ORF72 gene. Baricitinib at 2 mg per day is approved by the FDA in the United States (US) for rheumatoid arthritis. Baricitinib at 4 mg per day is approved has emergency use authorization by the FDA for COVID-19 in the US. Each participant will be treated with open-label baricitinib for 24 weeks. No patient will receive a placebo. Participants will receive baricitinib 2 mg per day by mouth for the first 8 weeks and baricitinib 4 mg per day by mouth for the remaining 16 weeks. Participants will have a lumbar puncture (LP) at screening and cerebrospinal fluid (CSF) will be examined for study eligibility. Participants will be enrolled if their CSF level inflammatory biomarker meets threshold requirements and if they meet all other eligibility criteria. All enrolled participants must have received a first dose of recombinant zoster vaccine (RZV; also known as Shingrix) within 4 years prior to treatment initiation. Over the course of 32-week trial, there will be a total of 8 visits. Blood will be collected at 7 visits, urine and CSF will be collected at 4 visits. Clinical outcomes will be measured at 2 visits.

Rationale: Converging evidence reveals inflammatory signaling is robustly active within the central nervous system of subsets of patients with AD and ALS, both in autopsied brains and profiles of CSF of living patients. Moreover, investigators find biomarkers of inflammatory signaling in the CSF of a subset of patients with AD and ALS. Baricitinib, an FDA-approved drug for rheumatoid arthritis, rescued inflammatory biomarkers and neural cell death in a human neural cell culture model of inflammatory-mediated death in a dose-dependent manner. Independently, in computational biology studies of gene expression profiles of AD brains termed DRIAD (drug repurposing in AD), baricitinib was among the leading drugs that reversed the actions of AD. Investigators have characterized a signature of inflammatory signaling in the brains and CSF of AD and ALS patients that is specific for this inflammatory mechanism of neuronal death.

This work has laid the foundation for the design of a mechanistic, biomarker-driven trial. In this trial, investigators will evaluate the FDA-approved JAK inhibitor baricitinib using an escalating dose design. Baricitinib is an oral medication FDA-approved for rheumatoid arthritis at a 2-mg daily dosage and FDA emergency use authorized for COVID-19 at a 4 mg daily dosage. The trial will determine whether baricitinib at 2 mg per day 4 mg per day, or both enters the cerebrospinal fluid and attains therapeutic levels, as well as whether it reduces inflammatory biomarkers in the CSF of patients at risk for or with AD and at risk for or with ALS. If this Phase I/II trial demonstrates that baricitinib is safe in AD and ALS patients and achieves therapeutic levels in the CSF as determined by drug concentration and pharmacodynamic biomarkers, then a Phase III clinical trial powered to assess clinical outcomes in AD patients, ALS patients, or both would be warranted.