Farabursen (formerly RGLS8429/CYX082) is an anti-miR-17 therapy that literally halted kidney growth in Phase 1b — possibly the most impressive result in PKD drug development in decades. Novartis acquired the drug for $1.7 billion.
Background
Farabursen represents a fundamentally different approach to PKD: rather than targeting downstream symptoms, it addresses the root cause by restoring production of polycystin-1 and polycystin-2 — the proteins whose loss causes the disease. MicroRNA-17 (miR-17) suppresses polycystin production; by inhibiting miR-17, farabursen allows polycystin levels to recover. The Phase 1b results were extraordinary: kidney growth was effectively halted (0.05% growth vs. 2.58% in placebo). Novartis recognized the potential and acquired Regulus Therapeutics for $1.7 billion in a deal that closed June 2025.
How It Works
MiR-17 is a microRNA that binds to the 3' UTR of PKD1 and PKD2 mRNA transcripts, preventing their translation into polycystin-1 and polycystin-2 proteins. In ADPKD, where patients have one functional copy of PKD1/PKD2, miR-17 further reduces the already-limited polycystin production. Farabursen is a chemically modified antisense oligonucleotide that binds and inhibits miR-17, derepressing PKD1/PKD2 translation. This increases polycystin levels toward normal, reducing cyst cell proliferation and fluid secretion. The 300mg subcutaneous dose every 2 weeks was selected based on Phase 1b biomarker data showing restored PC1/PC2 protein markers.
Clinical Trial Details
Phase 1b (NCT05521191) showed htTKV growth of 0.05% in the treatment group vs. 2.58% in placebo over the study period — effectively halting kidney enlargement. Biomarker data confirmed increased polycystin-1 and polycystin-2 at the 300mg dose. Results presented at ASN Kidney Week 2025 and WCN 2026 (Yokohama). Novartis is planning a Phase 3 registrational trial; no NCT ID has been registered yet for Phase 3.
Why It's Promising
Farabursen may be the most promising drug in the PKD pipeline. The Phase 1b data is extraordinary — no other drug has halted kidney growth this completely. Novartis's $1.7B acquisition signals extreme confidence. The mechanism directly addresses the root genetic cause rather than downstream effects. If Phase 3 confirms these results, this could be the first disease-modifying therapy for ADPKD since tolvaptan — and potentially far more effective.
Limitations & Concerns
Subcutaneous injections every 2 weeks are a significant treatment burden. Long-term safety of miR-17 inhibition is unknown — miR-17 has roles in other tissues. Phase 1b was small and short; Phase 3 must confirm durability over years. Cost will likely be very high given the $1.7B acquisition price. Phase 3 has not yet been registered.