TNX-102 SL in Major Depressive Disorder: Targeting Slow-Wave Sleep

Gregory Sullivan, MD, discussed the rationale and design of the HORIZON trial, a phase 2 randomized, double-blind, placebo-controlled study evaluating TNX-102 SL (a sublingual formulation of cyclobenzaprine) as first-line monotherapy for major depressive disorder (MDD).

Sullivan described TNX-102 SL as a fundamentally distinct mechanistic approach from all currently marketed antidepressants in that it specifically targets sleep quality rather than monoamine reuptake or receptor modulation. The compound's active ingredient, cyclobenzaprine—long used as a muscle relaxant—exerts potent antagonist activity at 2 receptors Sullivan identified as central to sleep architecture: the 5-HT2A serotonin receptor and the alpha-1 adrenergic receptor. The sublingual formulation bypasses hepatic first-pass metabolism, limiting accumulation of the persistent active metabolite norcyclobenzaprine. TNX-102 SL received approval from the US Food and Drug Administration in August 2025 under the brand name Tonmya for the treatment of fibromyalgia in adults, where impaired slow-wave sleep is also a core pathophysiological feature.

The HORIZON trial, which enrolled its first patient in June 2026, targets 360 adult participants with MDD (Montgomery–Asberg Depression Rating Scale (MADRS) score ≥25) and evaluates TNX-102 SL 5.6 mg administered once nightly versus placebo, with change from baseline in MADRS total score at week 6 as the primary endpoint.¹

Sullivan also shared the mechanistic rationale for targeting slow-wave sleep in MDD, emphasizing that the brain performs critical homeostatic functions during deep non-rapid eye movement (NREM) sleep: glymphatic clearance of inflammatory metabolites and cytokines, synaptic downscaling of superfluous daytime memory traces, restoration of hypothalamic-pituitary-adrenal axis balance, and normalization of the default mode network (DMN).² He described MDD as characterized by DMN hyperactivation—manifesting clinically as ruminative, self-referential thinking—and prefrontal cortex hypoactivation, both of which deep sleep is theorized to help correct on a nightly basis. Sullivan framed TNX-102 SL as an attempt to re-engage this natural homeostatic reset mechanism in patients with MDD.

Dr Sullivan is chief medical officer at Tonix Pharmaceuticals.

References

1. Tonix Pharmaceuticals announces first patient enrolled in phase 2 HORIZON study of TNX-102 SL for the treatment of major depressive disorder. Press release. June 29, 2026. https://ir.tonixpharma.com/news-events/press-releases/detail/1634/tonix-pharmaceuticals-announces-first-patient-enrolled-in

2. Hauglund NL, Nedergaard M. Is glymphatic clearance the secret to restorative sleep? Brain. 2026;159:1819-1831.