MICA: HD-CSF: Studying cerebrospinal fluid to understand key CNS pathobiological targets in Huntington's disease

Huntington's disease (HD) is a fatal, incurable inherited disease that causes brain degeneration and dementia. It is one of the commonest inherited causes of neurodegeneration and causes complex disability lasting around twenty years from onset to death. HD is always caused by a mutation that causes cells to produce a harmful protein called mutant huntingtin (mHTT).

The most promising experimental treatments being developed are drugs to reduce production of the mHTT protein that causes HD. This is called 'gene silencing' or 'huntingtin lowering'. Another promising approach is to develop drugs to restore the balance of protective and toxic chemicals produced by the brain's immune cells. These are known as kynurenine pathway or 'KP' metabolites and we know from animal models and post-mortem human brains that their balance is altered in HD in a way that seems to make the disease worse.

Cerebrospinal fluid (CSF) is a clear fluid, produced by the brain, which surrounds the brain and spinal cord, contains chemicals derived from the brain, and can be collected from living patients by a relatively straightforward procedure called lumbar puncture.

Developing huntingtin-lowering drugs would happen faster if we could measure how much mHTT is in the nervous system - then we would know if we have successfully lowered it. The same is true for KP metabolites and drugs to alter them. But nobody has ever measured CSF huntingtin levels, because the concentration is too low; and KP metabolites have never been accurately measured in HD patients.

We have developed an ultra-sensitive test to measure mutant huntingtin levels, using laser-activated counting of single huntingtin molecules labelled with newly-developed antibodies. Our pilot data show that this test can measure mHTT for the first time, in CSF from two different populations. What's more, the level of mHTT seems to increase as the disease progresses, meaning that it potentially serve as a 'biomarker' to predict progression or decide on the best time to treat patients with drugs in the future. We are working to develop tests that will mention the different chopped-up lengths of mHTT, to help figure out which are the most harmful ones.

We have also developed sensitive and reliable tests for KP metabolites, and we need good quality CSF to measure them in.

The 'HD-CSF' study will collect CSF and clinical data from 80 HD gene carriers and controls, twice each, two years apart, using methods designed to ensure the CSF is as pure and useful as possible. Poor quality CSF, and inconsistencies in handling and processing it, has been a problem with previous studies trying to use CSF to study HD.

Importantly, as well as CSF collection, HD-CSF participants will undergo detailed clinical and cognitive assessment, and MRI scanning to measure the rate of brain shrinkage. These assessments have been developed and proven to be of clinical relevance through our ground-breaking TRACK-HD study. The CSF and clinical and MRI data will be used to help us understand how mHTT levels and LP metabolites change as the disease progresses; and which chemical changes in CSF predict disease progression.

Measuring these chemicals in CSF using our ultra-sensitive tests will help understand how HD damages the brain, and provide new ways to measure its progression and, in future, whether a drug is having the desired effect, ultimately accelerating the development of treatments.

Huntington's disease (HD) is a fatal, autosomal dominantly inherited neurodegenerative disease causing motor and psychiatric symptoms and dementia. No disease-slowing treatment exists. HD is caused by an expanded CAG triplet repeat in HTT, resulting in mutant huntingtin protein (mHTT). Promising therapeutic candidates nearing human trials include nucleotide-based huntingtin-lowering drugs and kynurenine mono-oxygenase inhibitors.

Huntingtin has never been quantified in the living CNS, limiting our understanding of the role of wild-type and mutant HTT and their cleaved species in patients, and how these roles change over time; and preventing demonstration of target engagement by HTT-lowering drugs.

We have developed a novel, ultra-sensitive immunoassay which can quantify mHTT for the first time in patient CSF, completely distinguishing controls, premanifest mutation-carriers and patients. mHTT level correlates with neurofilament light chain, indicating likely neuronal origin.

Depending on the activity of KMO, the kynurenine pathway (KP) produces either neurotoxic or neuroprotective metabolites. It is deleteriously deranged in HD but has never been studied using accurate methods in patient CSF.

HD-CSF is the first comprehensive longitudinal study of CSF to elucidate key CNS pathobiological targets in HD. CSF, blood and robust phenotypic data including volumetric MRI will be collected from an 80-subject cohort at two timepoints. Samples will be analysed using our novel assays to quantify mHTT and KP metabolites and examine associations with disease progression. These core findings will be enriched through the targeted study of CNS-specific proteins in CSF.

Comprehensive longitudinal study of KP metabolites and huntingtin species in patient CSF, linked to robust clinical and MRI atrophy data, will enhance our understanding of HD neuropathobiology in the living patient CNS, and provide pharmacodynamic biomarkers to accelerate therapeutic development.

Through presentation of the results of this work in peer-reviewed articles and conference presentations, the academic beneficiaries will gain an increased understanding of the pathobiology of HD in the living patient CNS. This will benefit not only the global HD research community but also the broader neurodegenerative disease field, since HD can serve as a model for the earliest events in neurodegeneration.

HD-CSF will generate meaningful CSF biomarkers and an understanding of how those biomarkers predict progression. This will enable the efficient conduct of clinical trials through pharmacodynamic biomarkers of CNS huntingtin-lowering and KMO inhibition. More broadly, CSF HTT and kynurenine pathway metabolites may prove useful for stratification to determine which patients should enter clinical trials and when. The immediate beneficiaries of this will be industry-academic collaborations essential to the conduct of large-scale trials of disease-modifying therapies for HD. Patients and those at risk of HD will ultimately benefit through the accelerated development of disease-slowing therapeutics. Again, the applicability of these techniques beyond HD (especially given the involvement of the kynurenine pathway in many brain diseases) will benefit academia, industry and patients across neurodegeneration. Bringing pharma-funded clinical trials to the UK and to UCL will be financially advantageous to the UK economy and the UK academic sector's international reputation.

The biobank of CSF, collected longitudinally and rich phenotypic data including MRI that HD-CSF will generate will provide many opportunities for further research, primarily into HD but also to explore differences and similarities between HD and other brain diseases. The beneficiaries of this will be the researchers (including myself and future team members) whose work will be stimulated by this collection; UCL and the UK research community through attracting collaborations and funding; and the patient communities affected, through the discoveries that will emerge from this valuable resource.

HD-CSF may generate intellectual property through the identification of novel CSF pharmacodynamic and clinical biomarkers for Huntington's disease. This will enable clinical trials by identifying drug efficacy and consequently will be a valuable commercial tool of high interest to pharma companies. IP may come not only from the assays themselves, developed and tested in these samples, but their application to Huntington's disease and to detect a meaningful biological response to treatment with KMO inhibitors or HTT-lowering drugs. They will likely be of value in other neurodegenerative diseases such as Alzheimer's and Parkinson's. UCL Business PLC (UCLB) is the technology transfer company of UCL responsible for the management of UCL's intellectual property. Any IP that develops under the funded work at UCL will be appraised by UCLB for IP protection and, if appropriate, a patent application will be filed. UCLB will pay for the filing and the prosecution of the patent and will work with the MRC, GSK, CHDI Foundation and IRBM Promidis to identify appropriate routes to market.

The main motivation behind HD-CSF is to benefit the global community of HD patients and family members through accelerating the development of therapies for HD. Given the decades-long burden of complex physical, cognitive and behavioural disability that HD causes in every sufferer, and the psychological trauma to those at risk, the potential for benefits to the health of the nation are significant.