ABX-002 Phase 1 Clears Safety Bar, But TRβ-MDD Efficacy Case Remains Entirely Unbuilt

Autobahn's ABX-002 Shows Positive Phase 1 Results for MDD

Autobahn Therapeutics announced positive topline results from its first-in-human Phase 1 clinical study of ABX-002, an orally administered, potent and selective thyroid hormone beta receptor (TRβ) agonist. The randomized, double-blind, placebo-controlled study enrolled 48 healthy volunteers, evaluating safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) across escalating single and multiple doses. ABX-002 was safe and well-tolerated with no serious adverse events. Crucially, clinical evidence of CNS target engagement, including "mood alteration," was observed at the top multiple ascending dose (0.0056 mg), supporting its progression to Phase 2 for adjunctive treatment of major depressive disorder (MDD) in 2024.

• Favorable Safety and Tolerability Profile: The Phase 1 study in 48 healthy volunteers demonstrated that ABX-002 was safe and well-tolerated across all tested doses (0.0075 to 0.15 mg SAD; 0.0028 to 0.0056 mg MAD). No serious adverse events or premature discontinuations related to safety were observed, with all subjects completing the study, indicating a robust safety profile suitable for further clinical investigation.
• Evidence of CNS Target Engagement and PK/PD: ABX-002 showed acceptable, dose-proportional pharmacokinetics (PK) in both single and multiple ascending dose cohorts. Significantly, clinical evidence of brain target engagement, manifested as "mood alteration," was observed in two subjects at the top multiple ascending dose (0.0056 mg) after 7 days of dosing, confirming its central nervous system activity and informing optimal dose selection for future studies.
• Advancement to Phase 2 for MDD: Based on these positive Phase 1 results, Autobahn Therapeutics plans to submit an Investigational New Drug (IND) application to the U.S. FDA and initiate a Phase 2 clinical study in the first half of 2024. ABX-002 is being developed as a potential adjunctive treatment for major depressive disorder, addressing the significant unmet need for patients who inadequately respond to existing antidepressant therapies.

Addressing Unmet Needs in MDD with ABX-002's Novel MoA

Despite decades of pharmacological development, treatment of Major Depressive Disorder remains constrained by fundamental limitations that affect a substantial proportion of patients. Approximately 30% of patients treated for MDD develop treatment-resistant depression (TRD), and remission rates decline progressively with each antidepressant failure — 37%, 31%, 14%, and 13%, respectively, across sequential treatment steps in the STAR*D study.

• Trial-and-error treatment selection: For most patients, response to available antidepressants — including SSRIs such as citalopram, fluoxetine, and sertraline — is expected to be similar, and treatment selection remains largely guided by trial-and-error rather than objective biomarkers. Machine learning-based data-driven antidepressant selection yields only a small improvement over current clinical practice, underscoring the limited ability to personalize SSRI selection at the individual level.

• Delayed onset of action and treatment resistance: Monoaminergic antidepressants have limitations in that they have delayed onset of action and many patients remain treatment-resistant. Failure to respond to two adequate trials of treatment meets the criteria for TRD, a condition associated with huge costs on individual and societal levels whose underlying disease processes are multifactorial and not well understood.

• Tolerability and discontinuation burden: Common treatment-emergent adverse events (TEAEs) contribute meaningfully to discontinuation rates. Withdrawal rates due to TEAEs with active comparators such as venlafaxine XR (225 mg/day) reached 14.2% and duloxetine (60 mg/day) reached 8.8% in randomized controlled studies. Sexual dysfunction, weight gain, and discontinuation-emergent symptoms represent class-level tolerability concerns that affect long-term adherence across multiple antidepressant classes.

• Absence of validated predictive biomarkers: Objective biomarkers capable of predicting and monitoring therapeutic response are urgently needed to enable personalized interventions and reduce patient exposure to ineffective treatments. While mass spectrometry-based multi-omics approaches show promise in characterizing molecular changes associated with treatment response, clinically informative biomarkers for precision psychiatry in MDD have not yet been established.

• Limited options for acute and refractory presentations: Acutely depressed and suicidal patients often require prolonged inpatient stabilization under current treatment paradigms. Although intranasal esketamine received FDA approval in 2019 for TRD and has demonstrated rapid reduction in suicidal ideation with a favorable side-effect profile, ketamine's therapeutic effects may subside within weeks, and repeated administrations given multiple times per week are often required to sustain decreases in suicidality and depressive symptoms.

Mood Alteration Signal Points to Novel MDD Adjunctive Therapy

The recent positive Phase 1 data for ABX-002, an orally administered, selective thyroid hormone beta receptor (TRβ) agonist, signals a potentially transformative shift in how we approach major depressive disorder (MDD). While the TRβ agonist class has already seen success with liver-targeted agents like resmetirom for metabolic dysfunction-associated steatohepatitis (MASH), ABX-002's focus on CNS penetration and its observed 'mood alteration' in healthy volunteers suggest a novel application for this mechanism.

This early signal of CNS target engagement is particularly compelling given the existing literature supporting thyroid hormone augmentation in mood disorders. Studies indicate that adjunctive thyroid hormone can shorten the time to antidepressant response and improve outcomes in both MDD and bipolar depression, without increasing the risk of manic episodes. ABX-002 aims to harness this pathway with a selective approach, potentially offering a more targeted and tolerable option than supraphysiologic doses of generic thyroid hormones.

However, the path forward is not without its considerations. While the 'mood alteration' is an encouraging early indicator, its precise clinical translation into a robust therapeutic effect for MDD patients requires rigorous validation in Phase 2 trials. Furthermore, ABX-002 will need to clearly differentiate itself from the established, albeit off-label, use of generic thyroid hormones as adjunctive therapy. The favorable safety profile observed with other TRβ agonists provides a strong foundation, but the specific long-term safety and tolerability in a chronically depressed patient population will be critical to monitor. If successful, ABX-002 could offer a much-needed adjunctive treatment, addressing the significant unmet need for faster and more complete remission in MDD.