Zenas BioPharma’s stock climbed 33% following a positive mid-phase trial readout for its lead candidate, obexelimab, in relapsing multiple sclerosis (RMS).
During the Phase II MoonStone study (NCT06564311), the bifunctional monoclonal antibody (mAb) met its primary endpoint, significantly reducing the cumulative number of new gadolinium-enhancing (GdE) T1 hyperintense lesions.
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After eight weeks of treatment, subcutaneous (SC) obexelimab triggered a 95% relative reduction in the cumulative number of new lesions – an effect that was sustained through to week 12.
GdE T1 hyperintense lesions are a sign of active inflammation, a key mechanism involved in the disease pathology of MS.
Treatment with obexelimab also reduced the adjusted mean number of GdE T1 hyperintense lesions observed in patients per scan, producing a value of 0.01, as opposed to 0.23 in the placebo cohort.
In addition, the drug reduced the cumulative number of new or enlarging lesions compared with placebo, which can highlight the disease burden experienced by a patient with RMS.
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By GlobalDataIn the MoonStone study, obexelimab’s safety profile was consistent with previous studies conducted on the drug, most commonly triggering mild injection site reactions, as well as infections and hypersensitivity.
Investors seem pleased with the data readout, as Zenas’ stock soared 33% to $31.80 at market close on October 27, up from $23.90 at market close on October 24.
Following the positive top line results, Zenas’ CMO and head of R&D Lisa von Moltke noted that the company will continue the MoonStone study, with a 24-week data readout expected in Q1 2026.
She stated: “The 24-week data will include additional secondary and exploratory endpoints that may inform obexelimab’s potential impact on disability progression and help us determine next steps for future development of obexelimab in RMS.”
Obexelimab’s wide-spanning potential
While relapsing MS is a key focus area for obexelimab, Zenas believes that the dual-functioning nature of the mAb – binding to both CD19 and Fc fragment of IgG receptor IIb (FcγRIIb) – could highlight the drug’s potential in other chronic autoimmune diseases.
This has led to the company initiating trials exploring obexelimab’s potential in systemic lupus erythematosus (SLE) and immunoglobulin G4-related disease (IgG4-RD), which the company is currently evaluating in Phase II and III clinical trials, respectively.
The Phase III INDIGO trial in IgG4-RD will read out around the end of 2025 while the Phase II SunStone trial in SLE will have a top line readout in mid-2026.
MS market competition hots up
Despite the promising results of the MoonStone study in RMS, Zenas will still have to go head-to-head with drugs already on the market that GlobalData forecasts will grow to $25.9bn by 2034.
This includes Roche’s best-selling asset of 2024, Ocrevus (ocrelizumab), which brought in SFr6.7bn ($8.5bn) for the company. The drug, similar to obexelimab, is approved as a subcutaneous medication.
If obexelimab were to reach the market, it would also face competition from prospective drugs coming through the pipeline. This includes two Bruton’s tyrosine kinase (BTK) inhibitors, namely Sanofi’s tolebrutinib and Novartis’ Rhapsido (remibrutinib), which are stirring up significant interest in the MS indication.
However, tolebrutinib has had a bit of a bumpy road to approval thus far, as the drug is still awaiting an approval decision from the US Food and Drug Administration (FDA) following multiple application delays. The new target action date is 28 December 2025.
Meanwhile, Rhapsido is also garnering enthusiasm. Clinical Trials Arena previously evaluated the drug with key opinion leaders (KOLs) in the MS space.
