The purpose of this study is to evaluate the safety and tolerability of ascending doses (Part A) and selected doses (Part B) of BB-031 in acute ischemic stroke patients presenting within 24 hours of stroke onset.

Participants will be randomized to receive one dose of either the investigational drug or placebo and will be followed for 90 days. A total of 228 patients are planned in this study.

This is a two-part, randomized, placebo-controlled, double-blinded study in acute ischemic stroke patients. In Part A, up to 48 participants will be randomized in a 3:1 ratio (investigational drug: placebo) into 1 of 3 planned ascending dose groups to determine the dose levels to be studied in Part B. Two dose levels will be chosen based upon a review of all available data including safety, PK, PD and preliminary efficacy. In Part B, approximately 180 participants will be randomized to receive a single dose of two sequential dose levels of study drug or placebo.

All participants will be screened for participation after confirmed diagnosis of an anterior circulation ischemic stroke by neurovascular imaging. Enrolled participants will be followed for 90 days. Radiological outcomes will be assessed by a central blinded reviewer. A Data Safety Monitoring Committee will review safety and preliminary efficacy data throughout the study as outlined in the protocol.

Inclusion Criteria:

• Clinical diagnosis of acute ischemic stroke
• 18 years or older
• Anterior circulation intra-cranial occlusion
• NIHSS score >3
• Onset of stroke symptoms within 24 hours of enrollment

Exclusion Criteria:

• Large volume ischemic stroke
• Intracranial hemorrhage on baseline imaging or previous intracranial hemorrhage
• Chronic intracranial occlusion
• Weight >125kg
• Administration of thrombolytic drug or glycoprotein IIb/IIIa inhibitors
• Ongoing clinically significant coagulopathy, history of bleeding disorder or other conditions for high-risk bleeding or active uncontrolled bleeding
• Prior stroke within 90 days
• Unable to undergo a contrast brain perfusion scan with either MRI or CT