MoonLake's Sonelokimab Hits All Endpoints in Phase 3 IZAR-1 Psoriatic Arthritis Trial

MoonLake Immunotherapeutics (NASDAQ: MLTX) announced positive topline results from the Phase 3 IZAR-1 trial of sonelokimab in biologic-naïve adults with active psoriatic arthritis. The trial met all clinical endpoints at Week 16, marking the second major Phase 3 win for the IL-17A/F Nanobody after the hidradenitis suppurativa VELA program. MLTX closed at $18.26 on Friday.

Sonelokimab 60 mg with induction achieved a 42.1% ACR50 response on the primary endpoint at Week 16. Across key secondary endpoints, 66.5% of patients reached ACR20, 41.2% achieved Minimal Disease Activity, and 61% of patients with skin involvement hit PASI90. Patient-reported outcomes showed clinically meaningful improvement: mean HAQ-DI change was -0.427 and SF-36 Physical Component Summary score was 6.54.

The trial remains blinded; no placebo comparison data were disclosed, consistent with FDA-agreed unblinding protocol. The blinded safety analysis showed a profile consistent with prior sonelokimab studies, with no new safety signals and low dropout through Week 16.

IZAR-1 is the first of two registrational trials in the IZAR program. IZAR-2 enrolls TNF-inhibitor-refractory patients and includes a risankizumab (AbbVie’s Skyrizi) active comparator arm. Enrollment is expected to complete in Q3 2026, with topline data expected in H1 2027.

The readout matters because it validates sonelokimab outside of HS, where MoonLake already plans a BLA submission in the second half of 2026. The IL-17A/F dual inhibition mechanism, which blocks IL-17A/A, IL-17A/F, and IL-17F/F dimers, differentiates sonelokimab from Novartis’ Cosentyx (IL-17A only) and AbbVie’s Skyrizi (IL-23). The IZAR-1 data position the drug to compete in a psoriatic arthritis market worth upward of $10 billion annually.

MoonLake reported $537 million in cash as of June 30 and expects runway to mid-2028, with up to $400 million in additional non-dilutive debt available from Hercules Capital. The IZAR-1 results land ahead of a catalyst-heavy second half: HS BLA submission, IZAR-2 enrollment completion, and the Phase 2 P-OLARIS imaging trial in PsA and axial spondyloarthritis.

The PsA indication opens a second major market for MoonLake, with approximately 30% of psoriasis patients developing psoriatic arthritis. The absolute ACR50 response (42.1%) is consistent with what other IL-17 programs have shown in bio-naïve populations, though cross-trial comparisons are limited without placebo-adjusted data. The multi-domain efficacy across joint, skin, function, and patient-reported outcomes supports the broad mechanism thesis MoonLake has advanced since its Phase 2 ARGO trial.

Read the full press release on MoonLake’s investor site.