Autobahn’s CNS thyroid hormone receptor agonist earns FDA Fast Track designation for bipolar depression

Edited by Robert McTiernan··2 min read

Autobahn Therapeutics, a San Diego-based biotechnology company, announced receipt of US FDA Fast Track Designation for elunetirom (ABX-002), an oral, once-daily, brain-penetrant CNS thyroid hormone receptor (CNS-TR) agonist, for the adjunctive treatment of depressive episodes associated with bipolar I or bipolar II disorder in adults. Elunetirom is the company’s lead asset and has no prior expedited designations on record.

Fast Track Designation allows Autobahn more frequent interactions with the US FDA during development and makes elunetirom eligible for Rolling Review of a future marketing application, as well as potential Priority Review and Accelerated Approval if relevant criteria are met at submission.

Elunetirom is a small molecule prodrug designed to selectively engage CNS-TRs while limiting peripheral thyroid hormone receptor activity — the principal liability associated with systemic synthetic thyroid hormone administration, such as triiodothyronine (T3). T3 has demonstrated efficacy across multiple placebo-controlled studies in major depressive disorder (MDD) and bipolar depression, providing a validated biological rationale for the CNS-TR target. Elunetirom’s CNS-selective design is intended to capture that activity while avoiding cardiac, bone, and metabolic effects linked to peripheral thyroid hormone exposure.

The company’s Phase II AMPLIFY-BD trial (NCT06869187), evaluating elunetirom as an adjunctive bipolar depression treatment, is ongoing, with topline data expected in Q2 2026. A parallel Phase II AMPLIFY trial (NCT06633016) in adjunctive MDD is also active, with topline data expected in Q3 2026.

The AllSci BriefSystematic R&D and deal news. Daily.

The most recent public clinical data for elunetirom come from a first-in-human Phase I single- and multiple-ascending dose study in healthy volunteers, results from which were presented at the American Society of Clinical Psychopharmacology (ASCP) Annual Meeting in May 2025. The Phase I data showed no serious adverse events across all dose cohorts, dose-proportional pharmacokinetics supporting once-daily dosing, and evidence of CNS-TR target engagement in brain regions associated with depression.

Research context

Bipolar depression affects approximately 7 million adults in the US. Approved adjunctive options include quetiapine, lurasidone, cariprazine, and the olanzapine-fluoxetine combination, each carrying liabilities that include weight gain, metabolic effects, movement disorders, and sexual dysfunction. More than half of patients do not achieve adequate relief on available therapies, and the standard of care has not materially changed in decades.

Elunetirom’s CNS-TR agonist mechanism is without an approved comparator in psychiatry. Unlike atypical antipsychotics, which act primarily through dopamine and serotonin receptor modulation, elunetirom targets mitochondrial function, cellular energy production, and neuroplasticity through CNS-TR agonism — a distinct biological pathway. No other CNS-selective thyroid hormone receptor agonist is currently approved or, based on available public data, in late-stage development for bipolar depression.

This article was generated with AI assistance and reviewed and edited by the AllSci editorial team Explore more at AllSci News: https://allsci.com/news/