Capsules containing 500 mg of inosine (active drug) or ~500 mg of lactose (placebo) will be taken orally up to two capsules three times per day (i.e., up to 3 g/day) for 24 months. In the inosine-treated group the number of capsules taken per day will be titrated to serum urate levels - measured at trough at study visits no more than three months apart - in order to achieve concentrations of 7.1-8.0 mg/dL. Initial dosing will be tailored to individualized factors including gender and pretreatment serum urate, and then advanced gradually toward the projected target dose. Adjustments in dosing of placebo capsules in the control arm will be algorithm-based to match dosing of inosine capsules in the active drug arm.
Following study drug discontinuation all subjects will be followed during a 3-month wash-out period by telephone calls and a final study visit. All study visits after screening will include measurement of the primary outcome variable (MDS-UPDRS) and most will include secondary outcome variables: adverse events, dose adjustments, disability warranting initiation of dopaminergic therapy, Quality of Life in Neurological Disorders (Neuro-QOL), 39-item Parkinson's Disease Questionnaire (PDQ-39), Schwab & England Activities of Daily Living (S&E ADL) scale, Montreal Cognitive Assessment (MoCA), and orthostatic vital signs.
Convergent laboratory, epidemiological and clinical observations have identified urate – the end product of purine metabolism in humans – as a neuroprotectant and the first molecular predictor of both reduced risk and slower progression of typical Parkinson’s disease (PD). Urate is also a potent antioxidant and confers protection in cellular and animal models of PD. Epidemiological studies of prospectively followed healthy populations have repeatedly demonstrated serum urate to be an inverse risk factor for PD. These findings led to the discovery that among people with early PD serum and CSF urate levels are predictors of slower progression, assessed clinically or by neuroimaging of dopamine transporter (DAT) loss over years. This led to the phase 2 SURE-PD trial, which demonstrated safety, tolerability and effectiveness of inosine as a CSF urate-elevating strategy in PD, supporting further clinical development.
SURE-PD3 (Study of URate Elevation in Parkinson’s Disease, phase 3) was a randomized, double-blind, placebo-controlled trial of urate-elevating inosine treatment to slow clinical decline in early PD. The primary aim of this study was to determine whether oral inosine dosed to moderately elevate serum urate (from ≤5.7 mg/dL to 7.1-8.0 mg/dL) over 2 years slows clinical decline in early PD, assessed as change in the primary outcome variable of the Movement Disorders Society-Unified Parkinson’s Disease Rating Scale (MDS-UPDRS). Secondary aims include assessing long-term safety and effects on a) the development of disability warranting dopaminergic medication, b) short-term changes in parkinsonian symptoms, c) changes in functional disability and quality of life, d) non-motor measures of cognition, mood and autonomic function, and e) loss of striatal dopamine transporter signal.
The SURE-PD3 study terminated following preplanned futility analysis after 2/3 of subjects’ data were collected, and did not meet the threshold for non-futility.