This is a Randomized, Double-Blind, Placebo-Controlled, Multiple-Dose Escalation in depressed human subjects study.

Inclusion Criteria:

1. Patient has the ability to understand the purpose and risks of the study and to provide signed and dated informed consent, authorizing to use of protected health information in accordance with national and local patient privacy regulations.

2. Males and females 18 to 60 years of age, inclusive, at the time of informed consent.

3. Diagnosis of major depressive disorder, recurrent, as per DSM-IV-TR criteria and confirmed by SCID-CT. Their major depressive episode must be confirmed via SCID mood module interview administered by remote, independent raters.

   Note: Both patients who are being treated with antidepressants and patients who are not on antidepressants but had a history of taking antidepressants are permitted in the study.

4. Montgomery-Asberg Depression Scale (MADRS) score of 15 to 30, inclusive, at Screening and baseline.

5. The following applies to female patients:Non-pregnant, non-lactating females of childbearing potential who agree to use medically acceptable forms of birth control (hormonal contraception, abstinence, diaphragm with spermicide, condom with spermicide, or intrauterine device) from Screening until the end-of-study.

6. The following applies to male subjects: