The global health community faces an escalating challenge in Alzheimer’s disease, a neurodegenerative condition that progressively erodes memory, thinking, and behavior, ultimately devastating lives. Affecting millions worldwide, with projections indicating a significant increase in prevalence, the urgency for effective treatments and preventative measures has never been greater. Traditional pharmaceutical development, a notoriously protracted and costly endeavor spanning over a decade and billions of dollars with a high failure rate, often struggles to deliver breakthroughs at the pace required by this escalating crisis. However, an innovative and pragmatic approach, known as drug repurposing, is emerging as a beacon of hope, leveraging the extensive safety data and established manufacturing processes of existing medications to fast-track potential therapies.
In a significant development for Alzheimer’s research, a collaborative study funded by the Alzheimer’s Society and spearheaded by the University of Exeter has identified a trio of existing pharmaceutical compounds that demonstrate considerable promise in either preventing or treating this debilitating condition. Instead of embarking on the arduous journey of de novo drug discovery, scientists meticulously examined a broad spectrum of medicines already approved for other health issues, scrutinizing their potential to offer neuroprotection. The findings, published in the esteemed journal Alzheimer’s Research and Therapy, highlight a shingles vaccine (Zostavax), the erectile dysfunction medication sildenafil (commonly known as Viagra), and riluzole, a drug prescribed for motor neurone disease, as leading candidates warranting immediate further investigation.
Dementia, of which Alzheimer’s disease accounts for more than half of all diagnoses, represents the leading cause of mortality in the United Kingdom. Current statistics paint a stark picture: approximately one million individuals are currently living with dementia in the UK, and a staggering one in three people born today are projected to develop the condition during their lifetime. Despite this immense societal burden, a definitive cure remains elusive. The inherent advantages of drug repurposing—significantly reduced development timelines, lower financial investment, and established safety profiles—make it an attractive and potentially transformative strategy in the relentless pursuit of effective Alzheimer’s interventions. This critical research initiative also received robust backing from the National Institute for Health and Care Research (NIHR), the Exeter Biomedical Research Centre, and the NIHR HealthTech Research Centre in Brain Health, underscoring the collaborative effort behind this promising avenue.
The rigorous selection process for these priority candidates involved an international consortium of 21 preeminent dementia specialists. This diverse group comprised academics from leading universities, clinicians from hospitals, experts from the pharmaceutical industry, and crucially, individuals directly impacted by dementia, ensuring a comprehensive and patient-centric evaluation. The panel undertook an exhaustive review of 80 existing medications, with the explicit objective of identifying those demonstrating the most compelling evidence for either the therapeutic management or primary prevention of Alzheimer’s disease. Through multiple iterative rounds of assessment and deliberation, the experts converged on three principal compounds. Each selected agent satisfied stringent criteria: it must modulate biological pathways known to be implicated in Alzheimer’s pathology, exhibit encouraging results in preceding cellular and animal model investigations, and crucially, possess a well-established safety record for use in older adult populations, minimizing potential risks during future clinical applications.
Among the three identified frontrunners, the shingles vaccine, Zostavax, emerged with the most compelling preliminary signals. This vaccine, designed to protect against the varicella-zoster virus, has a longstanding record of safety and typically requires no more than two doses for efficacy. Prior epidemiological research, while observational and thus necessitating cautious interpretation, has indicated that individuals who received the shingles vaccination exhibited approximately a 16% reduced likelihood of developing dementia. The hypothesized link between viral infections, systemic inflammation, and neurodegeneration forms the basis for exploring Zostavax’s potential in Alzheimer’s prevention. A robust immune response elicited by the vaccine could, theoretically, mitigate inflammatory processes in the brain that are increasingly recognized as contributors to Alzheimer’s pathology. Researchers are now actively seeking to initiate a large-scale clinical trial in the UK to definitively ascertain whether this vaccine confers a tangible benefit to individuals either living with Alzheimer’s or at heightened risk of developing the condition. The PROTECT online registry, a vital resource where volunteers routinely complete annual questionnaires detailing their health and lifestyle and participate in various brain health studies, is envisioned as a key platform for recruiting participants and tracking outcomes in such a trial.
Sildenafil, widely recognized by its brand name Viagra, primarily functions as a phosphodiesterase-5 (PDE5) inhibitor, leading to vasodilation and increased blood flow in specific tissues. The rationale for its potential role in Alzheimer’s stems from its capacity to improve cerebral blood flow, which is often compromised in individuals with cognitive decline. Beyond its vascular effects, preclinical studies have suggested that sildenafil may possess neuroprotective properties, potentially enhancing neurogenesis (the formation of new neurons), reducing the accumulation of amyloid-beta plaques (a hallmark of Alzheimer’s), and improving synaptic plasticity, which is crucial for learning and memory. These multifaceted effects offer a compelling hypothesis for its therapeutic application in neurodegenerative contexts.
Riluzole, the third priority candidate, is an approved treatment for amyotrophic lateral sclerosis (ALS), also known as motor neurone disease. Its primary mechanism of action involves modulating glutamate, a neurotransmitter that, while essential for brain function, can become neurotoxic in excessive concentrations—a phenomenon known as excitotoxicity. Glutamate dysregulation is a recognized factor in the pathogenesis of Alzheimer’s disease, contributing to neuronal damage and death. By regulating glutamate levels, riluzole could potentially protect neurons from this excitotoxic damage, thereby slowing the progression of neurodegeneration. Preclinical investigations have provided evidence of its neuroprotective capabilities across various neurodegenerative models, further bolstering its candidacy.
In addition to these three priority compounds, the expert panel also identified five other medications for shortlisting, although they did not meet the stringent criteria for immediate prioritization. These included fingolimod, used in the treatment of multiple sclerosis; vortioxetine, an antidepressant for major depressive disorder; microlithium, employed for mood stabilization; dasatinib, an anti-cancer drug for leukemia; and cytisine, which has applications in anesthetics. Their consideration underscores the breadth of the initial search and the rigorous, evidence-based filtering process employed by the specialists.
Experts in the field are united in emphasizing the critical next step: robust, large-scale clinical trials are indispensable to conclusively determine the efficacy and true value of these repurposed medications in human populations. Dr. Anne Corbett, Professor of Dementia Research at the University of Exeter, articulated the comprehensive approach necessary for conquering dementia, stating, "Tackling dementia will require every research pathway—from harnessing existing knowledge to discovering novel compounds for treatment and prevention." She underscored the pivotal role of drug repurposing within this multifaceted strategy, observing, "It’s crucial to acknowledge that these agents necessitate further rigorous investigation before we can definitively ascertain their utility in managing or preventing Alzheimer’s. We now urgently need to implement robust clinical trials to understand their true therapeutic potential and confirm their effectiveness against Alzheimer’s."
Professor Fiona Carragher, Chief Policy and Research Officer at the Alzheimer’s Society, echoed this sentiment, highlighting the transformative potential of this research. "Dementia profoundly impacts countless lives, but we hold a firm belief that research will ultimately overcome it," she affirmed. Drawing a parallel to historical medical breakthroughs, she noted, "Years ago, aspirin transitioned from being a common painkiller to a crucial agent in reducing the risk of heart attacks and strokes. This is precisely the kind of paradigm shift we aspire to achieve in the realm of dementia, and it is why we consider drug repurposing to be one of the most exciting frontiers in contemporary dementia research."
The journey from identifying promising candidates to delivering approved treatments is complex, but the strategic application of drug repurposing offers a streamlined and pragmatic pathway. By leveraging the vast repository of already-approved medications, this research not only accelerates the search for Alzheimer’s therapies but also provides a renewed sense of hope for millions affected by this devastating disease. The scientific community now eagerly awaits the outcomes of the forthcoming clinical trials, which hold the key to unlocking the full potential of these repurposed drugs in the fight against cognitive decline.
About the Author
