Susanne Ostrowitzki

Mechanism of Amyloid Removal in Patients With Alzheimer Disease Treated With Gantenerumab

BACKGROUND Gantenerumab is a fully human anti-Aβ monoclonal antibody in clinical development for the treatment of Alzheimer disease (AD). OBJECTIVES To investigate whether treatment with gantenerumab leads to a measurable reduction in the level of Aβ amyloid in the brain and to elucidate the mechanism of amyloid reduction. DESIGN A multicenter, randomized, double-blind, placebo-controlled, ascending-dose positron emission tomographic study. Additionally, ex vivo studies of human brain slices from an independent sample of patients who had AD were performed. SETTING Three university medical centers. PATIENTS Patients with mild-to-moderate AD. INTERVENTION Two consecutive cohorts of patients received 2 to 7 infusions of intravenous gantenerumab (60 or 200 mg) or placebo every 4 weeks. Brain slices from patients who had AD were coincubated with gantenerumab at increasing concentrations and with human microglial cells. MAIN OUTCOME MEASURES Percent change in the ratio of regional carbon 11-labeled Pittsburgh Compound B retention in vivo and semiquantitative assessment of gantenerumab-induced phagocytosis ex vivo. RESULTS Sixteen patients with end-of-treatment positron emission tomographic scans were included in the analysis. The mean (95% CI) percent change from baseline difference relative to placebo (n = 4) in cortical brain amyloid level was -15.6% (95% CI, -42.7 to 11.6) for the 60-mg group (n = 6) and -35.7% (95% CI, -63.5 to -7.9) for the 200-mg group (n = 6). Two patients in the 200-mg group showed transient and focal areas of inflammation or vasogenic edema on magnetic resonance imaging scans at sites with the highest level of amyloid reduction. Gantenerumab induced phagocytosis of human amyloid in a dose-dependent manner ex vivo. CONCLUSION Gantenerumab treatment resulted in a dose-dependent reduction in brain amyloid level, possibly through an effector cell-mediated mechanism of action.

Enrichment through biomarkers in clinical trials of Alzheimer's drugs in patients with mild cognitive impairment.

Clinical trials of disease modifying drugs for Alzheimers disease (AD) in patients with mild cognitive impairment (MCI) might benefit from enrichment with true AD cases. Four hundred five MCI patients (143 converters and 262 nonconverters to AD within 2 years) of the Alzheimers disease Neuroimaging Initiative (ADNI) were used. Markers for enrichment were hippocampal atrophy on magnetic resonance (MRI), temporoparietal hypometabolism on FDG PET, cerebrospinal fluid (CSF) biomarkers (Abeta42, tau, and phospho-tau), and cortical amyloid deposition (11C-PIB positron emission tomography (PET)). Two separate enrichment strategies were tested to A) maximize the proportion of MCI converters screened in, and B) minimize the proportion of MCI converters screened out. Based on strategy A, when compared with no enrichment and ADAS-Cog as an outcome measure (sample size of 834), enrichment with 18F-FDG PET and hippocampal volume lowered samples size to 260 and 277 cases per arm, but at the cost of screening out 1,597 and 434 cases per arm. When compared with no enrichment and clinical dementia rating (CDR-SOB) as an outcome measure (sample size of 674), enrichment with hippocampal volume and Abeta42 lowered sample sizes to 191 and 291 cases per arm, with 639 and 157 screened out cases. Strategy B reduced the number of screened out cases (740 for [11C]-PIB PET, 101 hippocampal volume, 82 ADAS-COG and 330 for [18F]-FDG PET) but at the expense of decreased power and a relative increase size (740 for [11C]-PIB PET, 676 for hippocampal volume, 744 for ADAS-Cog, and 517 for [18F]-FDG PET). Enrichment comes at the price of an often relevant proportion of screened out cases, and in clinical trial settings, the balance between enrichment of screened in and loss of screened out patients should be critically discussed.

First‐in‐human assessment of PRX002, an anti–α‐synuclein monoclonal antibody, in healthy volunteers

Background: α‐Synuclein is a major component of pathologic inclusions that characterize Parkinsons disease. PRX002 is an antibody that targets α‐synuclein, and its murine parent antibody 9E4 has been shown in preclinical studies to reduce α‐synuclein pathology and to protect against cognitive and motor deteriorations and progressive neurodegeneration in human α‐synuclein transgenic mice. Methods: This first‐in‐human, randomized, double‐blind, placebo‐controlled, phase 1 study assessed the impact of PRX002 administered to 40 healthy participants in 5 ascending‐dose cohorts (n = 8/cohort) in which participants were randomly assigned to receive a single intravenous infusion of study drug (0.3, 1, 3, 10, or 30 mg/kg; n = 6/cohort) or placebo (n = 2/cohort). Results: PRX002 demonstrated favorable safety, tolerability, and pharmacokinetic profiles at all doses tested, with no immunogenicity. No serious adverse events, discontinuations as a result of adverse events, or dose‐limiting toxicities were reported. Serum PRX002 exposure was dose proportional; the average terminal half‐life across all doses was 18.2 days. A significant dose‐dependent reduction in free serum α‐synuclein (unbound to PRX002) was apparent within 1 hour after PRX002 administration, whereas total α‐synuclein (free plus bound) increased dose‐dependently, presumably because of the expected change in kinetics following antibody binding. Conclusions: This study demonstrates that serum α‐synuclein can be safely modulated in a dose‐dependent manner after single intravenous infusions of an anti–α‐synuclein antibody. These findings support continued development of PRX002, including further characterization of its safety, tolerability, pharmacokinetics, and pharmacodynamic effects in the central nervous system in patients with Parkinsons disease.

Tau: From research to clinical development

Alzheimers Association Research Roundtable Fall 2015—Tau: From research to clinical development. Tau pathology is recognized as the key driver of disease progression in Alzheimers and other neurodegenerative diseases. Although this makes tau an attractive target for the development of novel diagnostic and therapeutic strategies, the mechanisms underlying the onset and progression of tau‐related neurotoxicity remain elusive. Recent strides in the development of sophisticated preclinical models and the emergence of tau PET imaging and fluid biomarkers provide new opportunities to increase our understanding of tau biology, overcome translational challenges, and accelerate the advancement of tau therapeutics from bench to bedside. With this in mind, the Alzheimers Association convened a Research Roundtable in October 2015, bringing together experts from academia, industry, and regulatory agencies to discuss the latest understanding of tau pathogenic pathways and review the evolution of tau therapeutics and biomarkers currently in development. The meeting provided a forum to share experience and expertise with the common goal of advancing the discovery and development of new treatment strategies and expediting the design and implementation of efficient clinical trials.

Glycine Transporter Type 1 Occupancy by Bitopertin: a Positron Emission Tomography Study in Healthy Volunteers

Deficient N-methyl-D-aspartate (NMDA) receptor transmission is thought to underlie schizophrenia. An approach for normalizing glutamate neurotransmission by enhancing NMDA receptor transmission is to increase glycine availability by inhibiting the glycine transporter type 1 (GlyT1). This study investigated the relationship between the plasma concentration of the glycine reuptake inhibitor bitopertin (RG1678) and brain GlyT1 occupancy. Healthy male volunteers received up to 175 mg bitopertin once daily, for 10–12 days. Three positron emission tomography scans, preceded by a single intravenous infusion of ∼30 mCi [11C]RO5013853, were performed: at baseline, on the last day of bitopertin treatment, and 2 days after drug discontinuation. Eighteen subjects were enrolled. At baseline, regional volume of distribution (VT) values were highest in the pons, thalamus, and cerebellum (1.7–2.7 ml/cm3) and lowest in cortical areas (∼0.8 ml/cm3). VT values were reduced to a homogeneous level following administration of 175 mg bitopertin. Occupancy values derived by a two-tissue five-parameter (2T5P) model, a simplified reference tissue model (SRTM), and a pseudoreference tissue model (PRTM) were overall comparable. At steady state, the relationship between bitopertin plasma concentration and GlyT1 occupancy derived by the 2T5P model, SRTM, and PRTM exhibited an EC50 of ∼190, ∼200, and ∼130 ng/ml, respectively. Emax was ∼92% independently of the model used. Bitopertin plasma concentration was a reliable predictor of occupancy because the concentration–occupancy relationship was superimposable at steady state and 2 days after drug discontinuation. These data allow understanding of the concentration–occupancy–efficacy relationship of bitopertin and support dose selection of future molecules.

Characterization of [11C]RO5013853, a novel PET tracer for the glycine transporter type 1 (GlyT1) in humans.

We characterize a novel radioligand for the glycine transporter type 1 (GlyT1), [(11)C]RO5013853, in humans. Ten healthy male volunteers, 23-60 years of age, were enrolled in this PET study; seven subjects participated in the evaluation of test-retest reliability and three subjects in whole body dosimetry. Subjects were administered intravenous bolus injections of approximately 1100 MBq (30 mCi) [(11)C]RO5013853 with a high specific activity of about 481 GBq (13 Ci)/μmol. Standard compartmental model analysis with arterial plasma input function, and an alternative noninvasive analysis method which was evaluated and validated by occupancy studies in both baboons and humans, were performed. Mean parameter estimates of the volumes of distribution (VT) obtained by a 2-tissue 5-parameter model were higher in the cerebellum, pons, and thalamus (1.99 to 2.59 mL/mL), and lower in the putamen, caudate, and cortical areas (0.86 to 1.13 mL/mL), with estimates showing less than 10% difference between test and retest scans. Tracer retention was effectively blocked by the specific glycine reuptake inhibitor (GRI), bitopertin (RG1678). [(11)C]RO5013853 was safe and well tolerated. Human dosimetry studies showed that the effective dose was approximately 0.0033 mSv/MBq, with the liver receiving the highest absorbed dose. In conclusion, quantitative dynamic PET of the human brain after intravenous injection of [(11)C]RO5013853 attains reliable measurements of GlyT1 binding in accordance with the expected transporter distribution in the human brain. [(11)C]RO5013853 is a radioligand suitable for further clinical PET studies. Full characterization of a novel radiotracer for GlyT1 in humans is provided. The tracer has subsequently been used to assess receptor occupancy in healthy volunteers and to estimate occupancy at doses associated with best efficacy in a clinical trial with schizophrenic patients with predominantly negative symptoms.

Functional improvement in mouse models of familial amyotrophic lateral sclerosis by PEGylated insulin-like growth factor I treatment depends on disease severity

Abstract Insulin-like growth factor I (IGF-I) has been successfully tested in the SOD1-G93A mouse model of familial amyotrophic lateral sclerosis (ALS) and proposed for clinical treatment. However, beneficial effects required gene therapy or intrathecal application. Circumventing the dosing issues we recently found that polyethylene glycol (PEG) modified IGF-I (PEG-IGF-I) modulated neuromuscular function after systemic application, and protected against disease progression in a motor neuron disease model. Here we investigated its effects in two SOD1-G93A mouse lines, the G1L with a milder and the G1H with a more severe phenotype. Results showed that in G1L mice, PEG-IGF-I treatment significantly improved muscle force, motor coordination and animal survival. In contrast, treatment of G1H mice with PEG-IGF-I or IGF-I even at high doses did not beneficially affect survival or functional outcomes despite increased signalling in brain and spinal cord by both agents. In conclusion, the data point towards further investigation of the therapeutic potential of PEG-IGF-I in ALS patients with less severe clinical phenotypes.

Pre-clinical characterization of [11C]R05013853 as a novel radiotracer for imaging of the glycine transporter type 1 by positron emission tomography

A specific positron emission tomography (PET) radiotracer for the glycine transporter type 1 (GlyT1) would constitute an imaging biomarker to investigate the distribution of GlyT1 in normal individuals and those with neuropsychiatric disorders. In addition it could demonstrate the ability of a novel drug to reach its target in the brain and enable receptor occupancy studies, thus facilitating drug development. In this article we describe the evaluation in non-human primates of two candidate PET radiotracers ([(11)C]RO5013852 and [(11)C]RO5013853) previously characterized in the rat. Both radiotracers showed acceptable uptake in the baboon brain and heterogeneous distribution consistent with that reported for GlyT1. In vivo blockade studies with two specific glycine reuptake inhibitors (GRIs), RO5013853 and bitopertin (RG1678, reduced uptake of both tracers to homogenous levels across brain regions and demonstrated specificity of the signal. [(11)C]RO5013853 showed a larger specific signal and slightly higher brain uptake and was therefore selected for further characterization. Quantitative compartmental analysis of PET data showed that the 2-tissue compartment model with 5 parameters was the most appropriate to describe the kinetics of [(11)C]RO5013853. Two additional methods were used: a) the Logan graphical analysis using plasma input and, b) a linear parametric imaging approach with the 2-tissue compartmental model. These produced VT estimates of comparable magnitude, namely, pons, thalamus and cerebellum>caudate, putamen and cortical regions. High resolution autoradiography with tritiated RO5013853 was used to confirm the binding pattern observed by PET. In vivo metabolism studies in the baboon demonstrated the formation of a single, radiolabeled metabolite more polar than the parent compound. Finally, [(11)C]RO5013853 was used to quantify the degree of cerebral GlyT1 occupancy observed in the baboon following oral administration of bitopertin, a selective GRI presently in Phase III clinical trial. Plasma concentrations of approximately 150-300 ng/mL were estimated to produce 50% GlyT1 occupancy in the thalamus, the cerebellum and the pons. [(11)C]RO5013853 is a promising radiotracer for in vivo imaging of the GlyT1. It can be easily radiolabeled, exhibits moderate metabolism, displays a good specific signal, and is suitable for receptor occupancy studies of therapeutic compounds that target the GlyT1. The successful characterization of [(11)C]RO5013853 in healthy volunteers is presented in this NeuroImage issue (Wong et al., 2013).

Single- and multiple-dose pharmacokinetics of levovirin valinate hydrochloride (R1518) in healthy volunteers

R1518 is a valine ester prodrug of levovirin as an investigational new drug for the treatment of hepatitis C virus. Two phase 1, single‐ and multiple‐dose studies were conducted to investigate the pharmacokinetics of R1518 in healthy volunteers. After oral dosing, R1518 was rapidly and exclusively converted to levovirin. Levovirin plasma concentrations peaked at 2 hours, with T1/2 ranging from 6 to 8 hours. The T1/2 of R1518 was less than 1 hour, with relative exposures (R1518/levovirin) less than 6%. A high‐fat meal did not affect the pharmacokinetics. The female groups in both studies had higher plasma levels than males did due to age and renal function difference. An accumulation ratio of 1.3 to 1.5 was observed with the twice‐daily regimen. About 75% to 90% of the levovirin equivalent dose was recovered in urine. Increase in exposure was slightly disproportionate to increase in dose. Significantly improved oral absorption of levovirin was achieved following administration of R1518.

Challenges, solutions, and recommendations for Alzheimer's disease combination therapy

Given the complex neuropathology Alzheimers disease (AD), combination therapy may be necessary for effective treatment. However, scientific, pragmatic, regulatory, and business challenges need to be addressed before combination therapy for AD can become a reality. Leaders from academia and industry, along with a former member of the Food and Drug Administration and the Alzheimers Association, have explored these challenges and here propose a strategy to facilitate proof‐of‐concept combination therapy trials in the near future. First, a more integrated understanding of the complex pathophysiology and progression of AD is needed to identify the appropriate pathways and the disease stage to target. Once drug candidates are identified, novel clinical trial designs and selection of appropriate outcome assessments will be needed to enable definition and evaluation of the appropriate dose and dosing regimen and determination of efficacy. Success in addressing this urgent problem will only be achieved through collaboration among multiple stakeholders.