Neurofilament light as a translational biomarker from preclinical drug discovery to clinical application

In this interview, industry expert Phillip Mitchell discusses the role of NfL biomarkers in CNS drug discovery, neurodegenerative disease research, treatment monitoring, neurotoxicity detection, and AI-driven biomarker selection.

Can you tell us about your background and current role?

My name is Phillip Mitchell, I am currently Science Director at Charles River Laboratories. I have a background in Biochemistry and a Ph.D. in Molecular Biology. My career spans over 30 years in drug discovery, encompassing roles in academia, biotech, pharmaceutical environments, and more recently, the contract research organization sector.

What are some of the key challenges and recent advancements in biomarkers for central nervous system (CNS) drug discovery?

CNS diseases represent a growing global health burden partly attributed to an aging population. However, even with an improved understanding of disease mechanisms, a high failure rate persists in neuroscience drug discovery, often due to efficacy challenges. Additionally, many clinical trials rely on subjective clinician-rated measures as primary endpoints, which can be time-consuming and prone to variability.

In recent years neuroimaging biomarkers, such as positron emission tomography (PET) ligands, have significantly contributed to the clinical stages of CNS drug development by assisting in dose determination for investigational drugs targeting novel mechanisms. Also the discovery of less invasive, fluid-based biomarkers, particularly in cerebrospinal fluid (CSF) and blood, has been instrumental in advancing CNS biomarker research, although notable challenges remain.

One prominent example is neurofilament light (NfL), a structural protein exclusively found in neurons. NfL plays a crucial role in the stability of neuronal structures, particularly in large, myelinated axons, which rely on NfL for radial growth. Low levels of NfL are released continuously under normal conditions, but a significant increase can occur in response to axonal damage from inflammatory, neurodegenerative, traumatic, or vascular events. Given its stability and abundance, NfL is a valuable biomarker for assessing CNS health.

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How is NfL measurement applied across in vitro, preclinical, and clinical stages of drug discovery and development?

NfL has extensive applications as a biomarker across various stages of CNS research, from in vitro and preclinical studies to clinical trials. In vitro studies have utilized NfL to measure inflammatory toxicity mediated by microglia in response to antisense oligonucleotides, for example. Similarly, preclinical models have shown that plasma and CSF NfL levels can indicate axonal health and disease progression in models of neurodegenerative and neuroinflammatory diseases.

NfL levels are a surrogate biomarker in clinical settings used to monitor CNS health, track neurodegenerative disease susceptibility, and evaluate treatment efficacy. NfL’s consistent sensitivity across these stages makes it invaluable for monitoring axonal degeneration and assessing neurotoxicity risks, underscoring its critical role in therapeutic development and patient safety.

How does NfL function as a biomarker for neurodegeneration and CNS injury?

High NfL levels in CSF indicate leakage from injured or degenerating neurons and research has demonstrated that elevated CSF NfL correlates strongly with CNS injury. For instance, a 2006 study on amateur boxers found significant increases in CSF NfL following bouts, with levels declining after rest. Additionally, higher baseline NFL levels have been associated withincreased severity of injuries and faster disease progression in conditions like amyotrophic lateral sclerosis (ALS).

Numerous studies have shown a strong correlation between plasma and CSF NfL levels, suggesting that plasma measurements can effectively reflect ongoing CNS damage. However, because NfL levels in plasma are typically lower than in CSF, ultra-sensitive assays are essential for accurate quantification.

In the context of neurodegenerative diseases such as Huntington’s and Alzheimer’s disease (AD), elevated NfL levels in patient plasma and CSF serve as valuable diagnostic and prognostic indicators, correlating with disease progression and helping to distinguish between different levels of injury.

How is NfL used in AD research, and what insights does it provide for dementia risk?

Elevated NfL levels are typically observed in AD patients, when compared to those with mild cognitive impairment or healthy controls. However, plasma NfL levels increase with age even in healthy populations, so these measurements must carefully consider age. When used alongside other biomarkers, such as amyloid-beta 42, NfL shows promise in identifying individuals at higher risk of developing dementia.

This combined biomarker approach can improve patient selection in Alzheimer’s clinical trials. Recent studies have established reference levels of plasma NfL across various ages, contributing to integration of NfL measurements into diagnostic and disease-monitoring routines for neuropsychiatric and neurodegenerative conditions.

How can NfL levels indicate treatment responses in neurodegenerative diseases like spinal muscular atrophy?

NfL levels have proven valuable in monitoring treatment responses in spinal muscular atrophy, which causes motor neuron degeneration. For instance, in infants and children treated with the antisense oligonucleotide nusinersen, NfL levels in CSF were normalized following treatment, coinciding with notable motor function improvements. This rapid decrease in NfL levels suggests that NfL could serve as an early response marker, assisting physicians in assessing treatment efficacy and guiding therapeutic decisions.

Similarly, a recent study on ALS patients treated with Tofersen demonstrated significant reductions in plasma NfL levels, even though the treatment’s primary clinical endpoints were unmet. The FDA granted approval based on these biomarker changes, underscoring NfL’s role as a response marker for neurodegenerative disease treatments.

What is the significance of NfL as a safety biomarker for detecting drug-induced neurotoxicity?

NfL levels offer a non-invasive, sensitive approach to detecting neurotoxicity, which is crucial for evaluating the safety of certain treatments, such as chemotherapy, known for causing peripheral neuropathy. Research has shown that changes in serum NfL levels can predict subsequent onset and severity of peripheral neuropathy, allowing clinicians to balance treatment efficacy with patient safety.

NfL’s role as a neurotoxicity marker has also translated into preclinical settings. For example, in a Phase 2B trial for Huntington’s disease involving the drug Branaplam, some patients developed peripheral neuropathy. Follow-up studies showed elevated NfL levels in animals treated with Branaplam despite the absence of neurological symptoms, reinforcing NfL’s utility as a preclinical safety biomarker.

How is artificial intelligence (AI) currently impacting biomarker selection strategies?

AI greatly enhances biomarker discovery by rapidly analyzing large databases, including proteomics, metabolomics, and transcriptomics. AI streamlines data mining and helps identify new biomarkers and therapeutic targets by analyzing disease risk factors.

At Charles River Laboratories, we recently partnered with Aitia, a company specializing in AI-guided biomarker prediction. This collaboration uses cancer patient-derived xenograft models to create “digital twins” that simulate patient responses, offering a precise, efficient approach to biomarker selection in drug discovery.

About Phillip Mitchell

Phil Mitchell holds a PhD in Molecular Cell Biology (Cancer) from the Institute of Cancer Research, and a BSc Hons in Biochemistry from the University of Liverpool. He is currently the Science Director of Integrated Biology at Charles River Laboratories, where he has led preclinical drug discovery efforts for over eight years, specializing in assay development and in vitro pharmacology.

About Charles River Laboratories

At Charles River, we are passionate about our role in improving the quality of people’s lives. Our dedicated team of preclinical neuroscience CRO scientists want the same thing as you do: to find a cure for the devastating diseases of the central nervous system. From basic research to regulatory approval, we have the leading science, range of services, and collaborative approach you need to discover and develop novel therapies. 

We understand the challenges and complexities in the search of potential therapies for neurological disorders. The combination of our comprehensive neuroscience drug discovery services and expertise supports the creation of customizable, innovative and efficient solutions for your research. Our team of neuroscientists continues to establish the most relevant in vitro and in vivo models and assays of acute and chronic neurological diseases to help our partners identify and test new compounds in this challenging field.