Cerliponase alfa (Brineura®) – Ceroid lipofuscinosis 2 (CLN2 disease)

NINDS and other NIH institutes contributed to the development of cerliponase alfa, from the identification of the genetic cause of CLN2 disease, to production of the deficient enzyme, and initial tests of treatment efficacy in animal models.

Identifying a missing enzyme and its gene

Descriptions of the NCLs appear in the medical literature as early as the 1820s, but their causes remained elusive over a century later. The development of the electron microscope allowed researchers to more accurately classify different forms of the disease according to distinct pathological findings. This classification, together with the occurrence of NCLs in well-defined populations, made these diseases an ideal focus for new methods in genetics research. By the late 1990s, the genes responsible for several NCLs had been identified. To find the causal gene in CLN2, researchers first conducted linkage analysis studies in families with multiple affected members and localized the gene to a region on human chromosome 11. This study¹ made use of a cell bank at the Indiana University School of Medicine, which was supported by NINDS through a targeted funding opportunity for NCL research. Around the same time, NINDS and NIDDK-supported researchers Peter Lobel and David Sleat at Rutgers University had devised a clever biochemical approach for isolating lysosomal enzymes. Suspecting a lysosomal defect in CLN2 disease, they purified lysosomal enzymes² from normal and CLN2 patient cells and revealed the missing enzyme³ in CLN2. The genetic sequence for the enzyme mapped to the previously identified chromosomal location for the CLN2 gene, and the enzyme was later confirmed^4,5 to be tripeptidyl peptidase-1 (TPP1).

With a known cause for CLN2 disease, researchers began to look for ways to compensate for TPP1 deficiency. One promising strategy pioneered by NINDS intramural investigator Roscoe Brady⁶ was enzyme replacement therapy (ERT). The FDA had approved the first ERT for the lysosomal storage disorder Gaucher disease in 1991, and ERTs for five additional disorders followed over the next two decades⁷. However, while these therapies represented significant advances in the clinical management of some aspects of lysosomal storage disorders, they do not reach all tissues in the body. In particular, ERTs delivered intravenously do not address neurological symptoms because the enzymes cannot cross the blood-brain barrier—an intricate cell network that controls which substances can access the brain and central nervous system. This limitation is especially relevant for enzyme deficiencies like the NCLs that primarily affect neurological function. Therefore, to develop an effective ERT for CLN2, researchers needed to determine not only how to produce the missing enzyme in sufficient quantities but also how to ensure the enzyme would reach the brain and enter neuronal lysosomes.

Preclinical development of enzyme replacement therapy

In 2001, again with NINDS support, Lobel reported a method to produce recombinant TPP1 from genetically engineered cells and showed that this form of the enzyme effectively entered lysosomes and reduced protein accumulation in cells from CLN2 patients⁸. Subsequently, Lobel and Sleat and their associates also developed mouse models of CLN2 disease⁹ for further studies of disease mechanisms and early tests of ERT and other potential treatments. In one study supported by NINDS and NICHD, this team generated mouse models with different levels of TPP1 activity and showed that restoring just 3% of normal TPP1 activity in the brain was sufficient to delay disease and that 6% of normal TPP1 activity dramatically attenuated motor impairment and allowed mice to reach near-normal lifespans¹⁰. These results helped set target levels for further development of ERT and other therapies for CLN2 disease.

To circumvent the blood-brain barrier, Lobel and Sleat tested the delivery of TPP1 directly to the cerebrospinal fluid (CSF) that surrounds the brain and spinal cord. In an NINDS-supported study, they collaborated with Beverly Davidson at the University of Iowa to deliver TPP1 to CLN2 mice through a thin tube into the brain’s ventricles, interconnected spaces in the brain where CSF is produced¹¹. They reported broad distribution of TPP1 in several brain regions in treated mice. Moreover, treated mice had less neuropathology and decreased tremor, a marker of less neurological impairment. These results provided important proof-of-concept evidence for the feasibility and therapeutic value of intraventricular enzyme delivery for CLN2. (Intraventricular delivery was already in use for cancer drugs and other treatments requiring access to the brain and employs a device called an Ommaya reservoir, invented at NINDS in 1963, by neurosurgeon Ayub K. Ommaya.^12,13)

By this time, the biotechnology company BioMarin had obtained an exclusive license to further develop TPP1 ERT and began collaborating with Lobel and Sleat to optimize a formulation and delivery method for TPP1 that would be safe and effective for use in humans. The broad distribution of enzyme seen in small mouse brains was promising but could not guarantee similar success in bigger and more complex human brains. Therefore, BioMarin conducted studies for safety and effectiveness in larger animals¹⁴, including a naturally occurring canine model of the disease^15,16,17 which had been characterized in part with NIH support¹⁸.

Demonstrating clinical benefit

Based on positive preclinical results, BioMarin began clinical trials of intraventricular TPP1 replacement in 2013, in children with CLN2 ages three years and older^19,20,21. Typically, clinical trials for new therapies compare treated patients with a concurrently tested group of untreated patients (the control group). However, the rarity of lysosomal storage disorders like CLN2 makes recruiting sufficient numbers of patients for such trials difficult. Fortunately, a major research collaboration – the DEM-CHILD project, supported by the European Union and other partners – had built a large international disease registry for CLN2²². Data on disease progression in untreated patients from this project, including data from NIH-supported investigators, was ultimately used in place of a concurrent control group in a pivotal trial to assess the benefit of BioMarin’s intraventricular TPP1 replacement. The results showed that treatment slowed declines in walking ability in children with CLN2 disease²³. In April 2017, the FDA approved BioMarin’s formulation of TPP1 replacement (cerliponase alfa, brand name Brineura®) for children with CLN2 disease three years of age and older²⁴.

As with treatments for other neurodevelopmental disorders, cerliponase alfa is most likely to be successful if given early in the course of disease. Moving forward, the FDA has requested studies to assess the safety and effectiveness of cerliponase alfa in children with CLN2 below the age of two years. The research that led to cerliponase alfa also has set the stage for more advances to improve CLN2 treatment. For example, researchers supported by NIH and others are working to develop therapies for retinal degeneration and other aspects of CLN2 that are not addressed by ERT, as well as different treatment approaches, including small molecule drugs, stem cell-based treatments, and gene therapies, some of which have proceeded to early stage clinical trials²⁵.