A Study of the Efficacy and Safety of SP-624 in the Treatment of Adults With Major Depressive Disorder

Key Inclusion Criteria:

• Males and females, aged 18 to 65 years, inclusive.

• Meet DSM-5 criteria for moderate to severe MDD, as confirmed by the MiniInternational Neuropsychiatric Interview (MINI).

• In generally good physical health, in the opinion of the Investigator.

• Body mass index (BMI) must be ≥ 18 and ≤ 45 kg/m2.

Key Exclusion Criteria:

• Female who is pregnant, breastfeeding, or less than 6 months postpartum at screen.

• A history of or current DSM-5 diagnosis of MDD with psychotic features, anyschizophrenia spectrum and other psychotic disorders, bipolar disorder, orpersonality disorder.

• Presence or history of any known clinically significant cardiovascular disordersincluding, but not limited to: coronary artery disease, heart failure, valvularheart disease, cardiomyopathies, myocardial infarction, chamber enlargement orhypertrophy, or orthostatic hypotension.

• Presence of uncontrolled hypertension, defined as consistent sitting systolic bloodpressure (SBP) >160 mmHg or consistent sitting diastolic blood pressure (DBP) >95mmHg despite present therapy.

• Screening laboratory value(s) outside the laboratory reference range that areconsidered to be clinically significant by the Investigator (clinical chemistry,hematology, thyroid function, and urinalysis).