Study to Assess the Safety, Pharmacokinetics, and Pharmacodynamics of DS-1040b in Subjects With Acute Ischemic Stroke

Inclusion Criteria

• Has a clinical diagnosis of acute ischemic stroke (including lacunar stroke/infarct) supported by computed topography or magnetic resonance imaging to rule out alternative cause for presenting symptoms
• Has onset of stroke symptoms within 4.5 to 12 hours before initiation of study drug administration - for subjects with a stroke upon waking, time of symptom onset is the last time the subject was known to be well
• Has a NIHSS score of ≥ 2 (for Cohorts 1-5) and ≥ 5 (for Cohort 6)
• Has Low dose heparin or low molecular weight heparin at a preventive dose are allowed from 24 hours after treatment start completion and after confirmation of no intracranial bleeding on the 24-hours repeat brain imaging.
• Is a Cohort 6 participant who is treated or anticipated to be treated with intra-arterial therapy (IAT) for ischemic stroke at the time of randomization (for enrollment in the IAT subgroup)
• Has given written informed consent to participate in the study prior to participating in any study-related procedures - depending on country-specific practice, written informed consent may be acceptable from legally authorized representative
• Has given a separate written informed consent for collecting a blood sample for genotyping

Exclusion Criteria

• Is a Cohort 1-5 participant who has been treated or is going to be treated with tissue plasminogen activator (tPA) and/or endovascular thrombectomy during current stroke
• Is a Cohort 6 participant treated or anticipated to be treated with tPA during current stroke
• Has evidence of intracranial hemorrhage on non-contrast computed tomography (CT/CAT) scan or magnetic resonance imaging (MRI)
• Has symptoms of subarachnoid hemorrhage, even with normal imaging
• Has an Alberta Stroke Program Early CT Score (ASPECTS) 185/110 mmHg, or requires aggressive medication to maintain blood pressure below this limit (routine medical treatment including IV drug treatment is allowed to lower the blood pressure below this limit)
• Has had intracranial surgery, clinically significant head trauma (in the opinion of Principal Investigator), Alteplase treatment, or a previous stroke within 1 month
• Has had major surgery within 14 days
• Has had gastrointestinal or genitourinary bleeding in the last 21 days
• Has had a lumbar puncture (or epidural steroid injection) within 14 days
• Has had a preexisting disability classified by modified Rankin Scale (mRS) > 2
• Has an estimated glomerular filtration rate < 60 mL/min/1.73 m^2
• Has baseline hemoglobin < 10.5 g/dL
• Has a positive pregnancy test
• Is currently participating in another investigational study or has participated in an investigational drug study within 30 days or 5 half-lives of that investigational drug prior to administration of the study drug
• Is an employee or an immediate family member of an employee of the Sponsor, the Contract Research Organization (CRO), or the Site
• Has any other condition the investigator determines would preclude participation in the study