Study to Evaluate the Efficacy, Safety, and Pharmacokinetics of SUN13837 Injection in Adult Subjects With Acute Spinal Cord Injury (ASCI)

Inclusion Criteria: 1. Acute traumatic injury to the cervical neurological spinal cord as follows: 1. American Spinal Injury Association Impairment Scale A (AIS A) with a level of injury at either cervical level C4, C5, C6, C7 (for C4, the participant must have at least 1 point of motor activity within the zone of partial preservation (ZPP) inclusive of C5 to thoracic level 1 \[T1\]). In addition, the AIS A participant may be included if ALL of the following are present 1) the most caudal intact sensory segment (both pinprick and light touch) is C3, 2) at least one side (right or left) has both intact pinprick and light touch sensation in the C4 dermatome, AND 3) at least 1 point of motor activity within the ZPP inclusive of C5 to T1 2. American Spinal Injury Association Impairment Scale B or C (AIS B or C) with a neurological level of injury at either C3, C4, C5, C6, C7, or C8 AND a total LEMS of 5 or fewer motor points 2. Closed single traumatic spinal cord injury occurring within 12 hours of first dosing 3. Male or female cervical AIS A participants ≥ 16 to ≤ 80 years and male or female cervical AIS B or C participants ≥16 to ≤70 years 4. Females of childbearing potential and males must agree to maintain adequate contraception for the first 35 days of the study Exclusion Criteria: 1. Unable to obtain informed consent (either from the participant or from the participant's legally authorized representative \[LAR\]) 2. Women who are breastfeeding (if unwilling to stop for the first 35 days of the study) or who are pregnant 3. Coma or significant impairment in the level of consciousness that interferes with the performance or interpretation of protocol specified assessments 4. Any disease, concomitant injury, or condition that interferes with the performance or interpretation of the protocol specified assessments 5. Unable, as determined by the investigator, or unwilling to discontinue use of potent P-glycoprotein (P-gp) inhibitors for the first 35 days of the study 6. Unable, as determined by the investigator, or unwilling to discontinue use of potent cytochrome P450 (CYP) 3A4/5 inducers for the first 35 days of the study 7. Renal compromise (serum creatinine greater than 1.5 times the age- and sex-appropriate upper limit of normal \[ULN\]) at screening before the first dose of study drug 8. Severe Hepatic dysfunction (serum alanine transaminase \[ALT\], aspartate transaminase \[AST\], and/or gamma-glutamyltransferase \[GGT\] ALL greater than 2.5 times the age- and sex-appropriate ULN) or hepatic impairment (detectable ascites, serum bilirubin greater than 2 mg/dL, serum albumin less than 3.5 g/dL, and prothrombin time prolonged by more than 6 seconds above the ULN for the local laboratory in the absence of anticoagulant therapy) at screening before the first dose of study drug 9. Concomitant spinal cord injury or abnormality as determined by routine imaging: 1. Conclusive radiological evidence of complete spinal cord transection 2. Multiple injuries to the neurological spinal cord at different levels 10. History of symptomatic cervical spinal stenosis with myelopathy as a factor confounding participant assessment 11. Unlikely to be available for follow-up as specified in the protocol 12. Participated in a previous clinical study and received an investigational product within 30 days of screening 13. Previous exposure to SUN13837 14. Allergy to SUN13837 or any of its excipients 15. Any other issue which, in the opinion of the investigator, made the participant unsuitable for study participation.