Clinical trials

Abnormal prion protein, infectivity and neurofilament light-chain in blood of macaques with experimental variant Creutzfeldt-Jakob disease

Transmissible spongiform encephalopathies (TSEs) are fatal neurodegenerative infections. Variant Creutzfeldt-Jakob disease (vCJD) and sporadic CJD (sCJD) are human TSEs that, in rare cases, have been transmitted by human-derived therapeutic products. There is a need for a blood test to detect infected donors, identify infected individuals in families with TSEs and monitor progression of disease in patients, especially during clinical trials. We prepared panels of blood from cynomolgus and rhesus macaques experimentally infected with vCJD, as a surrogate for human blood, to support assay development. We detected abnormal prion protein (PrP^TSE) in those blood samples using the protein misfolding cyclic amplification (PMCA) assay. PrP^TSE first appeared in the blood of pre-symptomatic cynomolgus macaques as early as 2 months post-inoculation (mpi). In contrast, PMCA detected PrP^TSE much later in the blood of two pre-symptomatic rhesus macaques, starting at 19 and 20 mpi, and in one rhesus macaque only when symptomatic, at 38 mpi. Once blood of either species of macaque became PMCA-positive, PrP^TSE persisted through terminal illness at relatively constant concentrations. Infectivity in buffy coat samples from terminally ill cynomolgus macaques as well as a sample collected 9 months before clinical onset of disease in one of the macaques was assayed in vCJD-susceptible transgenic mice. The infectivity titres varied from 2.7 to 4.3 infectious doses ml^-1. We also screened macaque blood using a four-member panel of biomarkers for neurodegenerative diseases to identify potential non-PrP^TSE pre-symptomatic diagnostic markers. Neurofilament light-chain protein (NfL) increased in blood before the onset of clinical vCJD. Cumulatively, these data confirmed that, while PrP^TSE is the first marker to appear in blood of vCJD-infected cynomolgus and rhesus macaques, NfL might offer a useful, though less specific, marker for forthcoming neurodegeneration. These studies support the use of macaque blood panels to investigate PrP^TSE and other biomarkers to predict onset of CJD in humans.

Viral and Prion Infections Associated with Central Nervous System Syndromes in Brazil

Virus-induced infections of the central nervous system (CNS) are among the most serious problems in public health and can be associated with high rates of morbidity and mortality, mainly in low- and middle-income countries, where these manifestations have been neglected. Typically, herpes simplex virus 1 and 2, varicella-zoster, and enterovirus are responsible for a high number of cases in immunocompetent hosts, whereas other herpesviruses (for example, cytomegalovirus) are the most common in immunocompromised individuals. Arboviruses have also been associated with outbreaks with a high burden of neurological disorders, such as the Zika virus epidemic in Brazil. There is a current lack of understanding in Brazil about the most common viruses involved in CNS infections. In this review, we briefly summarize the most recent studies and findings associated with the CNS, in addition to epidemiological data that provide extensive information on the circulation and diversity of the most common neuro-invasive viruses in Brazil. We also highlight important aspects of the prion-associated diseases. This review provides readers with better knowledge of virus-associated CNS infections. A deeper understanding of these infections will support the improvement of the current surveillance strategies to allow the timely monitoring of the emergence/re-emergence of neurotropic viruses.

Repurposing approved drugs on the pathway to novel therapies

The time and cost of developing new drugs have led many groups to limit their search for therapeutics to compounds that have previously been approved for human use. Many "repurposed" drugs, such as derivatives of thalidomide, antibiotics, and antivirals have had clinical success in treatment areas well beyond their original approved use. These include applications in treating antibiotic-resistant organisms, viruses, cancers and to prevent burn scarring. The major theoretical justification for reusing approved drugs is that they have known modes of action and controllable side effects. Coadministering antibiotics with inhibitors of bacterial toxins or enzymes that mediate multidrug resistance can greatly enhance their activity. Drugs that control host cell pathways, including inflammation, tumor necrosis factor, interferons, and autophagy, can reduce the "cytokine storm" response to injury, control infection, and aid in cancer therapy. An active compound, even if previously approved for human use, will be a poor clinical candidate if it lacks specificity for the new target, has poor solubility or can cause serious side effects. Synergistic combinations can reduce the dosages of the individual components to lower reactivity. Preclinical analysis should take into account that severely ill patients with comorbidities will be more sensitive to side effects than healthy trial subjects. Once an active, approved drug has been identified, collaboration with medicinal chemists can aid in finding derivatives with better physicochemical properties, specificity, and efficacy, to provide novel therapies for cancers, emerging and rare diseases.

The role of prion strain diversity in the development of successful therapeutic treatments

Prions are a self-propagating misfolded conformation of a cellular protein. Prions are found in several eukaryotic organisms with mammalian prion diseases encompassing a wide range of disorders. The first recognized prion disease, the transmissible spongiform encephalopathies (TSEs), affect several species including humans. Alzheimer's disease, synucleinopathies, and tauopathies share a similar mechanism of self-propagation of the prion form of the disease-specific protein reminiscent of the infection process of TSEs. Strain diversity in prion disease is characterized by differences in the phenotype of disease that is hypothesized to be encoded by strain-specific conformations of the prion form of the disease-specific protein. Prion therapeutics that target the prion form of the disease-specific protein can lead to the emergence of drug-resistant strains of prions, consistent with the hypothesis that prion strains exist as a dynamic mixture of a dominant strain in combination with minor substrains. To overcome this obstacle, therapies that reduce or eliminate the template of conversion are efficacious, may reverse neuropathology, and do not result in the emergence of drug resistance. Recent advancements in preclinical diagnosis of prion infection may allow for a combinational approach that treats the prion form and the precursor protein to effectively treat prion diseases.

Association of Blood and Cerebrospinal Fluid Tau Level and Other Biomarkers With Survival Time in Sporadic Creutzfeldt-Jakob Disease

IMPORTANCE

Fluid biomarkers that can predict survival time in sporadic Creutzfeldt-Jakob disease (sCJD) will be critical for clinical care and for treatment trials.

OBJECTIVE

To assess whether plasma and cerebrospinal fluid (CSF) biomarkers are associated with survival time in patients with sCJD.

DESIGN, SETTING, AND PARTICIPANTS

In this longitudinal cohort study, data from 193 patients with probable or definite sCJD who had codon 129 genotyping referred to a tertiary national referral service in the United States were collected from March 2004 to January 2018. Participants were evaluated until death or censored at the time of statistical analysis (range, 0.03-38.3 months). We fitted Cox proportional hazard models with time to event as the outcome. Fluid biomarkers were log-transformed, and models were run with and without nonfluid biomarkers of survival. Five patients were excluded because life-extending measures were performed.

MAIN OUTCOMES AND MEASURES

Biomarkers of survival included sex, age, codon 129 genotype, Barthel Index, Medical Research Council Prion Disease Rating Scale, 8 CSF biomarkers (total tau [t-tau] level, phosphorylated tau [p-tau] level, t-tau:p-tau ratio, neurofilament light [NfL] level, β-amyloid 42 level, neuron-specific enolase level, 14-3-3 test result, and real-time quaking-induced conversion test), and 3 plasma biomarkers (t-tau level, NfL level, and glial fibrillary acidic protein level).

RESULTS

Of the 188 included participants, 103 (54.8%) were male, and the mean (SD) age was 63.8 (9.2) years. Plasma t-tau levels (hazard ratio, 5.8; 95% CI, 2.3-14.8; P < .001) and CSF t-tau levels (hazard ratio, 1.6; 95% CI, 1.2-2.1; P < .001) were significantly associated with survival after controlling for codon 129 genotype and Barthel Index, which are also associated with survival time. Plasma and CSF t-tau levels were correlated (r = 0.74; 95% CI, 0.50-0.90; P < .001). Other fluid biomarkers associated with survival included plasma NfL levels, CSF NfL levels, t-tau:p-tau ratio, 14-3-3 test result, and neuron-specific enolase levels. In a restricted subset of 23 patients with data for all significant biomarkers, the hazard ratio for plasma t-tau level was more than 40% larger than any other biomarkers (hazard ratio, 3.4; 95% CI, 1.8-6.4).

CONCLUSIONS AND RELEVANCE

Cerebrospinal fluid and plasma tau levels, along with several other fluid biomarkers, were significantly associated with survival time in patients with sCJD. The correlation between CSF and plasma t-tau levels and the association of plasma t-tau level with survival time suggest that plasma t-tau level may be a minimally invasive fluid biomarker in sCJD that could improve clinical trial stratification and guide clinical care.

Review: Fluid biomarkers in the human prion diseases

The human prion diseases are a diverse set of often rapidly progressive neurodegenerative conditions associated with abnormal forms of the prion protein. We review work to establish diagnostic biomarkers and assays that might fill other important roles, particularly those that could assist the planning and interpretation of clinical trials. The field now benefits from highly sensitive and specific diagnostic biomarkers using cerebrospinal fluid: detecting by-products of rapid neurodegeneration or specific functional properties of abnormal prion protein, with the second generation real time quaking induced conversion (RT-QuIC) assay being particularly promising. Blood has been a more challenging analyte, but has now also yielded valuable biomarkers. Blood-based assays have been developed with the potential to screen for variant Creutzfeldt-Jakob disease, although it remains uncertain whether these will ever be used in practice. The very rapid neurodegeneration of prion disease results in strong signals from surrogate protein markers in the blood that reflect neuronal, axonal, synaptic or glial pathology in the brain: notably the tau and neurofilament light chain proteins. We discuss early evidence that such tests, applied alongside robust diagnostic biomarkers, may have potential to add value as clinical trial outcome measures, predictors of future disease course (including for asymptomatic individuals at high risk of prion disease), and as rapidly accessible and sensitive markers to aid early diagnosis.