A Phase 2a Study to Evaluate the Safety and Tolerability of GM-2505 in Patients With MDD

Key Inclusion Criteria:

1. Patients are male or female, of any ethnic origin.

2. Patients are aged between 18 to 65 years, inclusive.

3. Patients meet the Diagnostic and Statistical Manual of Mental Disorders, FifthEdition (DSM-5) diagnostic criteria for recurrent MDD without psychotic features, asassessed with the Mini-International Neuropsychiatric Interview (MINI) at Screening.

4. Current moderate to severe MDD diagnosis confirmed with a MADRS-SIGMA

5. Concomitant depression therapy:

6. (Part A) Patients need to be stable and must not have taken any SSRI or SNRIfor at least 6 weeks prior to Screening and must be willing to avoid starting anew pharmacological treatment for MDD until the end of the study procedures andassessments. Discontinuing current treatment is not allowed if done for thepurposes of achieving eligibility for this study.

7. (Part B) Patients need to be on stable treatment with any SSRI or SNRI for atleast 6 weeks prior to screening and must be willing to remain on the SSRI orSNRI for the duration of the trial

8. Patients receiving any form of psychotherapy or counselling must have beenreceiving therapy at Screening and must be willing to remain in therapy untilthe end of the study procedures and assessments.

Key Exclusion Criteria:

1. Patient has current or past primary DSM-5 diagnosis of a psychotic disorder or MDDwith psychotic features, bipolar, or related disorders. A current diagnosis of PTSD,complex PTSD and borderline personality disorder are exclusionary. Other psychiatricdisorders besides MDD should not be the primary disorder.

2. In first degree relatives, a history of schizophrenia, psychosis, bipolar disorder,delusional disorder, paranoid personality disorder or schizoaffective disorder.

3. Current or prior (six weeks before Screening) use of any SSRI/SNRI medication (PartA only).

4. Current or prior (five weeks before Screening) use of any monoamine oxidaseinhibitor ([MAO-I]; including phenelzine, tranylcypromine, isocarboxazid,iproniazid, selegiline, rasagiline, the reversible MAO-I moclobemide and theantibiotic linezolid).or any tricyclic antidepressant