Ricolinostat in Patients With Painful Diabetic Peripheral Neuropathy

Inclusion Criteria: * Type 1 or Type 2 diabetes of at least 6 months with optimized and stable glycemic control during the 3 months prior to Screening * Painful distal symmetric sensorimotor polyneuropathy due to diabetes * Douleur Neuropathique 4 (DN4) score of ≥4 * Satisfactory diary data during the 14-day Pain Observation period determined by an algorithm that includes diary compliance, overall level of pain and day-to-day variability in pain Exclusion Criteria: * Pregnant or lactating * Body Mass Index (BMI) \>40 kg/m2 * Presence of any neuropathy other than DPN and/or significant risk factors for neuropathy other than diabetes * Other pain conditions that could confound the results of this study, or other chronic pain condition(s) that could affect compliance with pain medication restrictions or confound pain assessments * Painful DPN patients who have undergone lower limb amputations, are non-ambulatory, or whose walking is so impaired as to require a walker or other assistance for ambulation * Have met Diagnostic and Statistical Manual of Mental Disorders V (DSM V) criteria for opioid use disorder or alcohol use disorder * Opioid use at a dose of ≥ 30 morphine milligram equivalents on 3 or more days a week during the month prior to Screening * Suicidal ideation/behavior as measured by the Columbia-Suicide Severity Rating Scale (C-SSRS) * The use of marijuana or cannabidiol (CBD) during the 30 days prior to starting study drug * Chronic use of over-the-counter capsai…