A Phase 2 Study to Evaluate Efficacy and Safety of KH607 Tablets in Adult Participents With Major Depressive Disorder

This is a two-part (open-label followed by double-blind) study evaluating the safety, tolerability, pharmacokinetics, and efficacy of KH607 in 120 participants diagnosed with moderate or severe Major Depressive Disorder.

Inclusion Criteria: 1. Age: 18 to 65 years old (inclusive), Male or female. 2. Participant with diagnosis of MDD as diagnosed by Structured Clinical Interview for Diagnostic and Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) , with symptoms that have been present for at least a 4-week period 3. Participant has a Hamilton Rating Scale for Depression (HAM-D) total score ≥24 at screening and Day 1 (prior to dosing). 4. Participants who is taking antidepressants must have stopped for 7 days or 5 half-lives of the antidepressant prior to Day 1. 5. Participant is willing to stop other antidepressant or antianxiety medications and any new pharmacotherapy regimens, including as-needed benzodiazepine anxiolytics and sleep aids, until after completion of the Day 42 visit. 6. Fully understand the procedures and sigh the informed consent. key exclusion criteria： 1. Participant is currently at significant risk of suicide, or has attempted suicide associated with the current episode of MDD. 2. Participant has a history of treatment-resistant depression, defined as persistent depressive symptoms despite treatment with adequate doses of antidepressants from two different classes for an adequate amount of time. 3. Participant has active psychosis. 4. Participant had used modified electroconvulsive therapy (MECT), transcranial magnetic stimulation (TMS), vagus nerve stimulation (VNS), deep brain stimulation (DBS), light therapy, etc. within 1 month prior to Day 1. 5. Subject has a history of sleep apnea. 6. Participant has a medical history of bipolar disorder, schizophrenia, and/or schizoaffective disorder (such as olanzapine, risperidone, quetiapine, aripiprazole, eptifamol, ziprasidone, caliparazine, sodium valproate, lithium carbonate, etc.) within the current major depressive episode. 7. Participant has a clinically significant abnormal 12-lead ECG at the screening or baseline visits. NOTE: mean QT interval calculated using the Fridericia method (QTcF) of \>450 msec in males or \>470 msec in females will be the basis for exclusion from the study.