Developing a new treatment for patients suffering from Major Depressive Disorder


CLE-100 is a tablet being developed as an add-on treatment for patients who do not get enough relief from standard antidepressant therapy. It targets a more rapid antidepressant effect than most current medications.

CLE-100 is a new investigational drug that has not been approved for commercial distribution.

Unmet need in the treatment of depression

Major depression can be devastating for patients and their loved ones.  Episodes of major depression are characterized by depressed mood or loss of interest or pleasure in usual activities that lasts for at least 2 weeks and often much longer. These episodes are accompanied by an array of symptoms including changes in eating or sleeping patterns, fatigue, difficulty concentrating, indecision, thoughts of death or suicide, or feelings of despair. About 20% of the population will experience major depression at some time during their lifetime and major depressive disorder (MDD) is a major public health problem.

While many treatments are available, they are often not effective enough.  The National Institute of Mental Health-funded Sequenced Treatment Alternatives to Relieve Depression (STAR*D), the most comprehensive and largest clinical study of MDD, showed that remission of depressive symptoms is achieved in only one-third of patients after their first antidepressant treatment trial with an established antidepressant medication and 33% of patients did not reach remission even after treatment with 4 different medications (Rush et al. 2006). Since most antidepressant medications generally take 4- 6 weeks to relieve depression, patients who required multiple medication trials spent months waiting for relief to come.

Our program

Scientific aspects

CLE-100 targets blockade of the NMDA receptor, with high affinity to PCP site of the receptor.

Clinical aspects


CLE-100 was tested in a first Proof of Concept Phase 2 study (CLEO), in the US. This study assessed the efficacy and safety profile of CLE-100 in subjects with Major Depressive Disorder who have had inadequate response to standard antidepressant therapies. Subjects were randomized in a 1:1 ratio to receive CLE-100 or placebo once daily for 4 weeks, followed by 2 weeks post-treatment follow-up. The primary end point of this study is the reduction of symptoms of depression measured by the MADRS (Montgomery-Åsberg Depression Rating Scale) from baseline to week 4.

In this study, CLE-100 showed a good safety profile and, in the subgroup of subjects enrolled during the post-acute Covid period, promising efficacy. The CLEO study results were presented at the American Society of Clinical Psychopharmacology Annual Meeting (ASCP 2023) – for the full poster presentation please visit the Publications & Presentations section.


Clexio has initiated enrollment in the SOLEO study in the US.

SOLEO is a Phase 2 study assessing the safety and efficacy of  a higher dose of CLE-100 as an adjunctive treatment in subjects with Major Depressive Disorder, who have had inadequate response to standard antidepressant therapies. Subjects will be randomized to receive either placebo or CLE-100 once daily for 4 weeks. All subjects who adequately complete the 4-week double-blind treatment period and who meet the eligibility criteria, will be offered the option to roll-over to a 6-month Open-Label Extension (OLE) treatment period with CLE-100.

For more information on this study please visit:  


* Patient voices throughout this website are paraphrased examples of typical experiences of people suffering from this disease.
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