A securities class action has been filed after MoonLake Immunotherapeutics announced disastrous Phase III trial results for its only product candidate, sonelokimab (SLK), its highly anticipated treatment for patients with the skin disease hidradenitis suppurativa (HS).
On this announcement, MoonLake investors saw the price of their shares crater $55.75, or about 90%, on September 29th 2025.
The development and severe market reaction prompted national shareholders' rights firm Hagens Berman to investigate claims that, before September 28th, 2025, MoonLake misled investors about SLK's trial design and efficacy data.
The litigation is focused on the propriety of MoonLake's statements about the trial design and data for SLK.
The clinical-stage biotechnology company is focused on skin inflammatory diseases driven by cytokines known as IL-17A and IL-17F.
Central to SLK's commercial prospects was its ability to demonstrate efficacy in HS comparable to or superior to a competitor's FDA-approved product (BIMZELX), which is used for the same HS indication and targets the same cytokines.
One difference between SLK and BIMZELX is that SLK's nanobody structure is significantly smaller than BIMZELX's monoclonal antibody format.
Throughout the Class Period, MoonLake repeatedly touted SLK's structural advantages as translating into superior efficacy.
The company has said that SLK could achieve benefits "a monoclonal antibody cannot do," that "the molecular advantages of our nanobody translate into higher clinical responses for patients" and that nanobodies "offer a more convenient and effective treatment."
MoonLake also assured investors that "we really have a drug here that can become the gold standard and obviously that will facilitate any winning that we do with sonelokimab in HS."
The complaint alleges that these statements by MoonLake, as well as others, were false and misleading and that the company withheld crucial information from investors.
More specifically, the lawsuit claims that the company misled investors about the distinction between nanobodies and monoclonal antibodies, including the following:
- SLK and BIMZELX share the same molecular targets (IL-17A and IL-17F)
- SLK's nanobody structure would not confer a superior clinical benefit over the traditional monoclonal structure of BIMZELX
- SLK's nanobody structure purported increased tissue penetration that would not translate to clinical efficacy.
Investors learned the truth on September 28th, 2025, after MoonLake revealed that only one of its two SLK Phase III trials achieved statistical significance — and even those results demonstrated substantially lower efficacy than BIMZELX.
On this news, the price of MoonLake shares cratered $55.75 (-90%) on September 29th, 2025, with one analyst reportedly writing in a note to investors that the results "arguably fall into the worst case outcome."
"We're focused on investors' losses and whether MoonLake may have intentionally misled investors about the SLK's purported advantages over BIMZELX while claiming that SLK could become a 'gold standard'," said Reed Kathrein, the Hagens Berman partner leading the investigation.