ARROWHEAD PHARMACEUTICALS, INC. 8-K

What Happened
Arrowhead Pharmaceuticals announced interim results from two Phase 1/2a trials of its RNAi investigational drugs for obesity, ARO‑INHBE and ARO‑ALK7, and made a press release and presentation public on January 6, 2026. The company hosted a conference call and webcast the same day to discuss the data. Results are interim and based on small early cohorts (generally n=3–5 per group).

Key Details

• ARO‑INHBE (single 400 mg dose): mean maximum serum Activin E reduction of -85%; maximum observed -94% (n=4 per dose level).
• ARO‑INHBE (monotherapy): week 16 mean visceral fat -9.9%; mean liver fat relative reduction -38%; total lean tissue +3.6%. Two doses at week 24: visceral fat -15.6% (placebo‑adjusted).
• ARO‑INHBE + tirzepatide (400 mg ARO‑INHBE, n=4): week 16 weight change -9.4% vs -4.8% for tirzepatide + placebo; visceral fat -23.2% vs -7.4%; total fat -15.4% vs -5.3%; liver fat -76.7% vs -20% (MRI, week 12).
• ARO‑ALK7: first RNAi therapeutic to show adipocyte target silencing clinically — mean ALK7 mRNA reduction -88% at 200 mg (week 8), max -94% (n=4). Single dose produced a placebo‑adjusted visceral fat reduction of -14.1% at week 8.
• Safety: both agents generally well tolerated in these cohorts; most treatment‑emergent AEs were mild. One SAE (limb abscess) was reported and assessed as unrelated. No TEAEs caused study/drug discontinuation; no clinically significant lab trends reported.

Why It Matters
These interim data show early biological activity (target knockdown) and preliminary signals of fat and weight reductions for two RNAi candidates addressing obesity, including enhanced effects when ARO‑INHBE was combined with tirzepatide. For investors, the results indicate potential clinical proof‑of‑concept but are based on very small, early cohorts and are interim — outcomes may change as more patients are enrolled and data mature. The company highlighted safety was generally favorable so far, but further study is required to confirm efficacy and longer‑term safety.