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

Inclusion Criteria:

• Willing and able to provide written informed consent to participate in the study

• Males and females, aged 18 to 65 years

• In generally good physical health

• Body mass index (BMI) must be between 18 and 40 kg/m2

• Females of reproductive potential and males with partners of reproductive potentialmust agree to remain abstinent or use adequate and reliable contraception throughoutthe study and for at least 30 days after the last dose of study drug

• Subjects must meet criteria for moderate to severe Major Depressive Disorder, asconfirmed by the Mini International Neuropsychiatric Interview (MINI)

• Willing and able to comply with the study design schedule and other requirements

Exclusion Criteria:

• Female who is pregnant, breastfeeding, or less than six months postpartum atScreening

• History or presence of any clinically significant medical condition, disease, orsurgical history that could jeopardize the safety of the subject or validity of thestudy data, or interfere with the absorption, distribution, metabolism, or excretionof the study drug

• Failure to discontinue all psychoactive medications or psychoactive supplementsincluding antidepressants and mood stabilizers, within a time period prior toBaseline corresponding to at least five half-lives of the medication in question

• Presence of a clinically significant abnormality on physical examination orelectrocardiogram (ECG), including a corrected QT interval using Fridericia'sformula (QTcF) >450 msec for males and >470 msec for females

• Presence of uncontrolled hypertension, defined as consistent systolic blood pressure (SBP) >160 mmHg or consistent diastolic blood pressure (DBP) >95 mmHg despitepresent therapy

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

• Screening liver function tests (ALT, AST, Alkaline phosphatase) > 2x the upper limitof normal

• Subjects who, in the opinion of the Investigator, are not suitable candidates forthe study