Enpatoran Gets FDA Breakthrough Therapy Designation for Lupus With Cutaneous Manifestations

The United States (US) Food and Drug Administration (FDA) has granted Breakthrough Therapy designation to enpatoran, an investigational oral toll-like receptor (TLR) 7/8 inhibitor, for the treatment of lupus with active cutaneous manifestations, Merck KGaA, Darmstadt, Germany, (EMD Serono in the US and Canada) announced July 8, 2026.¹ The designation, supported by Phase 2 data from the WILLOW study, is intended to expedite development and review of a drug that could become the first therapy specifically approved for cutaneous lupus erythematosus (CLE) — a population that currently has no approved targeted therapies.

Cutaneous manifestations affect an estimated 72%–85% of patients with lupus erythematosus and can occur in the context of CLE alone or alongside systemic lupus erythematosus (SLE). Beyond their physical presentation — inflammatory, photosensitive lesions on the face, scalp, and other areas that may be irreversible — skin manifestations carry substantial psychosocial burden. Despite representing the first clinical sign of disease in approximately 29% of patients, many do not achieve adequate disease control on existing regimens.¹

Mechanism of action

Enpatoran selectively inhibits TLR7 and TLR8, innate immune receptors that recognize single-stranded RNA and drive downstream type I interferon and inflammatory cytokine production centrally implicated in lupus pathogenesis. By blocking TLR7/8 activation at the source of the inflammatory cascade, the drug aims to reduce both cutaneous and systemic disease activity without the broad immunosuppression associated with current standard-of-care agents.¹

WILLOW Phase 2 data

The Breakthrough Therapy designation was supported by results from WILLOW (NCT05162586), a randomized, double-blind, placebo-controlled, Phase 2 dose-finding study using an adaptive basket design that enrolled patients across 2 cohorts: Cohort A (CLE or SLE with active lupus rash) and Cohort B (moderate-to-severe active SLE with or without cutaneous manifestations).

In Cohort A, published in Lancet Rheumatology in May 2026, enpatoran produced clinically meaningful reductions in Cutaneous Lupus Erythematosus Disease Area and Severity Index Activity (CLASI-A) scores at weeks 16 and 24.² More than 60% of enpatoran-treated patients achieved a CLASI-A improvement of 70% or greater at week 16, compared with approximately 11%–12% in the placebo arm.² In Cohort B, published in The Lancet in 2026, enpatoran did not meet the primary endpoint of a dose-response relationship in BICLA response rate at week 24 in the overall SLE population; however, improvements in cutaneous and systemic disease activity were observed in prespecified subpopulations with active cutaneous manifestations at baseline (CLASI-A ≥8).³ Enpatoran was overall well tolerated across both cohorts, with treatment-emergent adverse events distributed across dosing arms.

Investigators enrolled patients from 132 sites across 22 countries in Cohort B alone; 3 doses of enpatoran (25 mg, 50 mg, and 100 mg twice daily) were evaluated against placebo plus standard of care over 24 weeks.³

Phase 3 program

Merck KGaA has initiated the ELOWEN-1 (NCT07332481) and ELOWEN-2 (NCT07355218) global Phase 3 program, which will evaluate enpatoran twice daily versus placebo added to standard of care in patients with lupus and active cutaneous manifestations across 266 sites in 26 countries. Each study will enroll approximately 200 participants, with change in CLASI-A from baseline as the primary endpoint. Enpatoran is not approved for any indication in any jurisdiction.¹

“The ELOWEN program builds on Phase 2 findings, where enpatoran demonstrated clinically meaningful improvements in patients with active cutaneous manifestations, regardless of their underlying lupus diagnosis,” principal investigator Professor Eric Morand, MBBS, PhD, MOnash University, said in a previous statement.⁴ “These studies are designed to further explore how targeting shared inflammatory pathways may benefit patients across the lupus spectrum.”

References

1. Merck KGaA, Darmstadt, Germany. Merck KGaA announces FDA Breakthrough Therapy designation for enpatoran in lupus patients with active skin manifestations. Press release. July 8, 2026. https://www.emdgroup.com/en/news/fda-btd-enpatoran-07-08-2026.html

2. Morand EF, Werth VP, Wenzel J, et al. Efficacy and safety of enpatoran, a toll-like receptor 7/8 inhibitor, in patients with skin manifestations of cutaneous lupus erythematosus or systemic lupus erythematosus: findings from Cohort A of a multicentre, international, double-blind, placebo-controlled, dose-finding phase 2 trial. Lancet Rheumatol. Published online May 7, 2026. doi:10.1016/S2665-9913(25)00337-6

3. Morand EF, Dall'Era M, Sanchez-Guerrero J, et al. Enpatoran, a Toll-like receptor 7/8 inhibitor, in moderate-to-severe systemic lupus erythematosus: findings from Cohort B of a multicentre, international, double-blind, placebo-controlled dose-finding phase 2 trial. Lancet. 2026;407(10541):1809-1824. doi:10.1016/S0140-6736(26)00463-0