Translating preclinical models of neuronal ceroid lipofuscinosis: progress and prospects

Neuronal Ceroid Lipofuscinosis: Potential for Targeted Therapy

Neuronal ceroid lipofuscinosis (NCLs) is a group of inherited neurodegenerative lysosomal storage diseases that together represent the most common cause of dementia in children. Phenotypically, patients have visual impairment, cognitive and motor decline, epilepsy, and premature death. A primary challenge is to halt and/or reverse these diseases, towards which developments in potential effective therapies are encouraging. Many treatments, including enzyme replacement therapy (for CLN1 and CLN2 diseases), stem-cell therapy (for CLN1, CLN2, and CLN8 diseases), gene therapy vector (for CLN1, CLN2, CLN3, CLN5, CLN6, CLN7, CLN10, and CLN11 diseases), and pharmacological drugs (for CLN1, CLN2, CLN3, and CLN6 diseases) have been evaluated for safety and efficacy in pre-clinical and clinical studies. Currently, cerliponase alpha for CLN2 disease is the only approved therapy for NCL. Lacking is any study of potential treatments for CLN4, CLN9, CLN12, CLN13 or CLN14 diseases. This review provides an overview of genetics for each CLN disease, and we discuss the current understanding from pre-clinical and clinical study of potential therapeutics. Various therapeutic interventions have been studied in many experimental animal models. Combination of treatments may be useful to slow or even halt disease progression; however, few therapies are unlikely to even partially reverse the disease and a complete reversal is currently improbable. Early diagnosis to allow initiation of therapy, when indicated, during asymptomatic stages is more important than ever.

Comparative proteomic profiling reveals mechanisms for early spinal cord vulnerability in CLN1 disease

CLN1 disease is a fatal inherited neurodegenerative lysosomal storage disease of early childhood, caused by mutations in the CLN1 gene, which encodes the enzyme Palmitoyl protein thioesterase-1 (PPT-1). We recently found significant spinal pathology in Ppt1-deficient (Ppt1^−/−) mice and human CLN1 disease that contributes to clinical outcome and precedes the onset of brain pathology. Here, we quantified this spinal pathology at 3 and 7 months of age revealing significant and progressive glial activation and vulnerability of spinal interneurons. Tandem mass tagged proteomic analysis of the spinal cord of Ppt1^−/−and control mice at these timepoints revealed a significant neuroimmune response and changes in mitochondrial function, cell-signalling pathways and developmental processes. Comparing proteomic changes in the spinal cord and cortex at 3 months revealed many similarly affected processes, except the inflammatory response. These proteomic and pathological data from this largely unexplored region of the CNS may help explain the limited success of previous brain-directed therapies. These data also fundamentally change our understanding of the progressive, site-specific nature of CLN1 disease pathogenesis, and highlight the importance of the neuroimmune response. This should greatly impact our approach to the timing and targeting of future therapeutic trials for this and similar disorders.

Advances in the Treatment of Neuronal Ceroid Lipofuscinosis

Neuronal ceroid lipofuscinoses (NCL) represent a class of neurodegenerative disorders involving defective lysosomal processing enzymes or receptors, leading to lysosomal storage disorders, typically characterized by observation of cognitive and visual impairments, epileptic seizures, ataxia, and deterioration of motor skills. Recent success of a biologic (Brineura®) for the treatment of neurologic manifestations of the central nervous system (CNS) has led to renewed interest in therapeutics for NCL, with the goal of ablating or reversing the impact of these devastating disorders. Despite complex challenges associated with CNS therapy, many treatment modalities have been evaluated, including enzyme replacement therapy, gene therapy, stem cell therapy, and small molecule pharmacotherapy. Because the clinical endpoints for the evaluation of candidate therapies are complex and often reliant on subjective clinical scales, the development of quantitative biomarkers for NCLs has become an apparent necessity for the validation of potential treatments. We will discuss the latest findings in the search for relevant biomarkers for assessing disease progression. For this review, we will focus primarily on recent pre-clinical and clinical developments for treatments to halt or cure these NCL diseases. Continued development of current therapies and discovery of newer modalities will be essential for successful therapeutics for NCL.

AREAS COVERED

The reader will be introduced to the NCL subtypes, natural histories, experimental animal models, and biomarkers for NCL progression; challenges and different therapeutic approaches, and the latest pre-clinical and clinical research for therapeutic development for the various NCLs. This review corresponds to the literatures covering the years from 1968 to mid-2019, but primarily addresses pre-clinical and clinical developments for the treatment of NCL disease in the last decade and as a follow-up to our 2013 review of the same topic in this journal.

EXPERT OPINION

Much progress has been made in the treatment of neurologic diseases, such as the NCLs, including better animal models and improved therapeutics with better survival outcomes. Encouraging results are being reported at symposiums and in the literature, with multiple therapeutics reaching the clinical trial stage for the NCLs. The potential for a cure could be at hand after many years of trial and error in the preclinical studies. The clinical development of enzyme replacement therapy (Brineura® for CLN2), immunosuppression (CellCept® for CLN3), and gene therapy vectors (for CLN1, CLN2, CLN3, and CLN6) are providing encouragement to families that have a child afflicted with NCL. We believe that successful therapies in the future may involve the combination of two or more therapeutic modalities to provide therapeutic benefit especially as the patients grow older.

Progress in gene and cell therapies for the neuronal ceroid lipofuscinoses

INTRODUCTION

The neuronal ceroid lipofuscinoses (NCLs) are a subset of lysosomal storage diseases (LSDs) that cause myoclonic epilepsy, loss of cognitive and motor function, degeneration of the retina leading to blindness, and early death. Most are caused by loss-of-function mutations in either lysosomal proteins or transmembrane proteins. Current therapies are supportive in nature. NCLs involving lysosomal enzymes are amenable to therapies that provide an exogenous source of protein, as has been used for other LSDs. Those that involve transmembrane proteins, however, require new approaches.

AREAS COVERED

This review will discuss potential gene and cell therapy approaches that have been, are, or may be in development for these disorders and those that have entered clinical trials.

EXPERT OPINION

In animal models, gene therapy approaches have produced remarkable improvements in neurological function and lifespan. However, a complete cure has not been reached for any NCL, and a better understanding of the limits of the current crop of vectors is needed to more fully address these diseases. The prospects for gene therapy, particularly those that can be delivered systemically and treat both the brain and peripheral tissue, are high. The future is beginning to look bright for NCL patients and their families.