Korro Bio doses first cohort in ANCHOR Phase 1/2 UCD trial
Korro Bio has dosed the first cohort of healthy volunteers in ANCHOR, its Phase 1/2 clinical trial programme for KRRO-121, a GalNAc-conjugated RNA-editing oligonucleotide in development for hyperammonemia driven by urea cycle disorders (UCDs) and hepatic encephalopathy (HE). The Cambridge, Massachusetts company said a single dose of 2 mg/kg was administered, with enrolment currently under way in Australia.
KRRO-121 is designed to generate a stabilised, de novo glutamine synthetase protein that augments the liver's capacity to clear ammonia. Korro is using its proprietary OPERA platform, which employs adenosine deaminase acting on RNA (ADAR) proteins to introduce precise, transient single-base edits at the mRNA level, avoiding permanent changes to the genome. The company says the subcutaneous GalNAc-conjugate delivery route should enable infrequent dosing, which would represent a meaningful step up from the multiple-daily-dose regimens that many UCD patients currently depend on.
Trial design and timeline
ANCHOR is structured in two parts. Part 1 is a Phase 1 single ascending dose study followed by a multiple ascending dose study enrolling up to 50 healthy volunteers across seven cohorts; both arms are placebo-controlled. Part 2 is a Phase 2 multiple-dose study in up to 15 UCD patients, covering all UCD genotypes. Korro expects to begin dosing UCD patients in the first half of 2027, with an interim clinical readout anticipated in the second half of that year.
Ram Aiyar, chief executive and president of Korro, said the company hoped to show that KRRO-121 could help patients "irrespective of their mutational background," noting that preclinical studies across different mutations had demonstrated the candidate's ability to "blunt ammonia excursions." The pan-genotypic positioning is commercially significant: UCDs encompass at least eight enzyme deficiencies, and a mutation-agnostic approach would substantially broaden the eligible patient population.
Market context and competitive landscape
UCDs are individually rare but collectively affect an estimated one in 35,000 live births. The current standard of care relies on dietary protein restriction, nitrogen scavenger drugs such as sodium phenylbutyrate and glycerol phenylbutyrate, and, in severe cases, liver transplantation. No disease-modifying therapy is approved for the full UCD spectrum.
The RNA-editing field is attracting growing interest as an alternative to DNA-editing approaches, on the basis that transient, reversible edits may offer a more manageable long-term safety profile. Several academic groups and early-stage companies are exploring ADAR-mediated editing, though the space remains lightly populated by clinical-stage programmes. Korro's use of GalNAc conjugation for liver-targeted delivery aligns it with a delivery modality that has a well-established regulatory and manufacturing track record in approved oligonucleotide medicines, which may ease the path through regulatory review compared with newer delivery technologies.
The HE indication, if pursued alongside UCD, would expand the addressable population considerably: HE affects a substantial proportion of patients with liver cirrhosis, a condition with a global prevalence in the tens of millions. Whether Korro pursues both indications in parallel or sequences them will be a key strategic question for investors watching the ANCHOR readout in late 2027.
The interim data expected in the second half of 2027 will be the first clinical signal on KRRO-121's safety and pharmacokinetics in healthy subjects, and the first hint of activity in UCD patients. Analysts will focus on whether the preclinical ammonia-blunting effect translates into human pharmacodynamic data, and on the tolerability profile of a novel RNA-editing modality administered subcutaneously.