Argo Biopharmaceutical Co., Ltd. (Argo Biopharma) provided updated Phase II data for BW-20805, an investigational small interfering RNA (siRNA) therapy targeting prekallikrein (PKK) for hereditary angioedema (HAE) prophylaxis. The data show monthly attack rate reductions of 83%–96% across three dosing regimens in a small open-label study. Argo, which operates out of Shanghai and New York, is presenting the findings in an oral session at the Bradykinin Symposium 2026 in Berlin held this week.
BW-20805 silences hepatic PKK messenger RNA through RNA interference, reducing prekallikrein synthesis and suppressing downstream bradykinin generation — the mediator of swelling in HAE. The drug holds FDA Fast Track Designation and FDA Orphan Drug Designation for HAE.
The Phase II open-label, global, multicenter study enrolled 25 adults with HAE type 1 or 2 across three arms: 600 mg every 24 weeks (Q24W), 300 mg Q24W, and 300 mg every 12 weeks (Q12W). Using a June 2026 data cut-off, the primary endpoint — time-normalized monthly attack rate change from baseline over Days 29 to 169 — showed reductions of 83%, 96%, and 93% in each respective arm (n=24 primary analysis population). Attack-free rates over the same period were 50% (4/8), 75% (6/8), and 62.5% (5/8). In the PKK-evaluable population (n=19), mean plasma PKK reductions at Day 169 were 86%, 85%, and 94% across the three arms. The company reported no treatment-emergent adverse event led to discontinuation or death, and no participant met protocol-defined hepatic laboratory criteria. Transient injection-site reactions were the most common adverse event.
The study is small and open-label, without a placebo comparator, which limits interpretation of the magnitude of effect. Argo Biopharma has stated it plans a global Phase III study following Phase II primary completion, expected in the second half of 2026.
The dosing intervals being evaluated — every 12 and 24 weeks — are the program's principal commercial proposition. The HAE prophylaxis market now includes six FDA-approved prophylactic agents. Among injectable biologics, Takeda's Takhzyro (lanadelumab) requires subcutaneous dosing every two to four weeks, while CSL Behring's Andembry (garadacimab), approved in June 2025, achieves once-monthly dosing. Ionis Pharmaceuticals' Dawnzera (donidalorsen), an antisense oligonucleotide (ASO) that also reduces PKK at the mRNA level, was approved in August 2025 with a four- or eight-week dosing interval. BW-20805, if Phase III data support the Q24W regimen, would offer a substantially longer interval than any currently approved injectable prophylactic.