Cerebrospinal fluid and plasma biomarkers in individuals at risk for genetic prion disease

Abstract

<jats:p>BACKGROUND: Fluid biomarkers are important in the development of therapeutics to delay or prevent prion disease, but have not been systematically evaluated in pre-symptomatic individuals at risk for genetic prion disease. METHODS: We recruited pre-symptomatic individuals with pathogenic mutations in the prion protein gene (PRNP; N=27) and matched controls (N=16), to donate cerebrospinal fluid (CSF) and blood at multiple timepoints to a cohort study at Massachusetts General Hospital. We quantified total prion protein (PrP) and real-time quaking-induced conversion (RT-QuIC) prion seeding activity in CSF, and the neuronal damage markers total tau (T-tau) and neurofilament light chain (NfL) in both CSF and plasma. We compared these markers cross-sectionally between mutation carriers and controls, evaluated short-term test-retest reliability over 2-4 months, and conducted a pilot longitudinal study over 10-20 months for a subset of participants. FINDINGS: CSF PrP levels were stable on test-retest with a mean coefficient of variation of 7% both over 2-4 months in N=29 participants and over 10-20 months in N=10 participants. RT-QuIC was negative in 22/23 mutation carriers. The sole individual with positive RT-QuIC seeding activity at two study visits had steady CSF PrP levels and slightly increased tau and NfL concentrations compared with others, though still within the normal range, and remained asymptomatic one year later. Overall, tau and NfL showed no significant differences between mutation carriers and controls in either CSF or plasma. INTERPRETATION: CSF PrP will be interpretable as a pharmacodynamic readout of the effects of a PrP-lowering therapeutic in pre-symptomatic individuals, and may serve as a surrogate biomarker in a "primary prevention" trial paradigm. In contrast, current markers of prion seeding activity and of neuronal damage do not reliably cross-sectionally distinguish mutation carriers from controls, arguing against the feasibility of a "secondary prevention" paradigm in which trials specifically recruit pre-symptomatic participants with prodromal evidence of pathology.</jats:p>

Prion protein lowering is a disease-modifying therapy across prion disease stages, strains, and endpoints

“…Our findings provide basis for optimism that PrP lowering may be a promising therapeutic strategy, both for prophylaxis against prion disease onset in at-risk individuals with no evidence of disease process underway 43,44 , and for treatment of active prion disease, during either prodromal or manifest disease. The effectiveness of a given PrP-lowering dosing regimen may vary depending on the stage of the disease, suggesting that dose regimens and trial endpoints may need to be adjusted depending on the clinical profile of the trial population.…”

“…This supports the universality of PrP lowering as a therapeutic strategy across strains and subtypes of prion disease. The above observations are also important because quantification of CSF PrP concentration 44,64,65 is being developed as a pharmacodynamic biomarker for PrP-lowering drugs. The validation of ASOs' mechanism of action in vivo, the tight relationship between degree of PrP lowering and disease delay, and the efficacy across prion strains, observed here all support the disease relevance of this biomarker 2 .…”

“…Clinically, most prion disease patients die within half a year of first symptoms 36 , and this rapid decline is mirrored by high levels of biofluid neuronal injury and prion seeding biomarkers in the symptomatic phase of disease [37][38][39][40][41][42] . Meanwhile, individuals at risk for genetic prion disease, caused by protein-altering variants in the prion protein gene (PRNP), can be identified through predictive genetic testing when disease onset is on expectation years or decades away 43 , ahead of molecular markers of pathology 44 . This spectrum motivates investigation of a range of treatment timepoints relative to prion inoculation, development of molecular pathology, and presentation of frank symptoms to explore the potential of PrP-lowering treatment.…”

Characterization of the Prion Protein Binding Properties of Antisense Oligonucleotides

“…Measurement of PrP concentration in CSF has been proposed as a pharmacodynamic biomarker for clinical trials of PrP-lowering ASOs [14,16], meaning, it will be important to be able to accurately measure CSF PrP in the presence of ASO. We sought to determine whether the addition of ASOs would confound measurement of PrP in CSF.…”

“…These findings establish RNA-mediated PrP lowering as the mechanism of action of ASOs against prion disease in vivo. Importantly, this mechanism lends itself to measurement of cerebrospinal fluid (CSF) PrP concentration as a pharmacodynamic biomarker for ASO activity [14][15][16]. But the question remains as to why the apparently potent interactions between ASOs and PrP appear not to contribute to in vivo efficacy.…”