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(RTTNews) - Korro Bio, Inc. (KRRO), a clinical-stage biopharmaceutical company pioneering RNA editing therapies, today announced its third quarter 2025 financial results and provided a comprehensive update on its advancing pipeline.

Shares of Korro plunged more than 77% to $6.89 in premarket trading, following mixed clinical data and strategic restructuring.

Korro's pipeline is anchored by its proprietary OPERA platform (Oligonucleotide Promoted Editing of RNA), which enables precise single-base RNA edits to treat both rare and prevalent diseases. The company is currently advancing two key programs targeting liver-based indications, KRRO-110 and KRRO-121.

KRRO-110: REWRITE Trial and Strategic Pivot:

KRRO-110, Korro's lead candidate, is being evaluated in the Phase 1/2 a REWRITE trial for Alpha-1 Antitrypsin Deficiency (AATD), a genetic disorder caused by a missense mutation in the SERPINA1 gene.

The trial is a two-part, single- and multiple-dose escalating study assessing the safety and tolerability of KRRO-110 in AATD patients with the PiZZ genotype.

Initial data from the single-administration cohorts confirmed that KRRO-110 successfully produced functional M-AAT protein in AATD patients, confirming RNA editing activity in humans. However, peak protein levels (~2 µM) fell short of the 11 µM protective threshold. Due to pharmacokinetic differences between healthy volunteers and patients, Korro is shifting to a GalNAc-conjugated version, with a new development candidate expected in the first half of 2026.

KRRO-110 showed a favorable safety profile with no serious adverse events and only mild infusion-related reactions that resolved quickly. Its safety was consistent with known effects of lipid nanoparticle delivery.

On the regulatory front, KRRO-110 became the first RNA editing therapy to receive IND clearance from the FDA and was granted Fast Track and Orphan Drug Designations by both the FDA and EMA, highlighting its therapeutic potential.

These designations remain active, as the company continues to evaluate next steps within the REWRITE trial.

KRRO-121 and a GalNAc-conjugated Pipeline Expansion:

Korro nominated KRRO-121 as its next development candidate, targeting patients with hyperammonaemia, including those with urea cycle disorders (UCD) and hepatic encephalopathy (HE).

KRRO-121 is designed to create a de novo protein variant to activate a biological pathway to reduce ammonia levels. It is intended to treat all UCD patients regardless of mutational background and to prevent or reduce hyperammonemia crises in HE patients.

KRRO-121 will be administered subcutaneously using a GalNAc-conjugated oligonucleotide, with a regulatory filing for first-in-human trials anticipated in the second half of 2026.

In parallel, Korro is advancing a GalNAc-conjugated version of KRRO-110 for AATD, with a development candidate nomination expected in the first half of 2026.

The company is also progressing additional GalNAc-conjugated programs targeting liver-based cardiometabolic indications, leveraging subcutaneous delivery for improved patient accessibility and therapeutic durability.

To support these pipeline priorities, Korro is implementing a strategic restructuring, including a 34% workforce reduction, to extend its cash runway into the second half of 2027.

The company ended Q3 2025 with $102.5 million in cash, cash equivalents, and marketable securities.

On the financial front, Korro reported a net loss of $18.1 million for the third quarter of 2025, compared to $21.0 million in the same period last year.

R&D expenses declined to $13.8 million, reflecting reduced spending on KRRO-110 and other early-stage programs. G&A expenses also decreased to $6.5 million, driven by lower professional service costs.

Collaboration revenue for the quarter was $1.1 million, attributed to the company's ongoing partnership with Novo Nordisk.

Despite the validation of its RNA editing platform and strategic pipeline realignment, Korro's stock fell sharply in premarket trading. The decline reflects investor concerns over the lower-than-expected protein expression in KRRO-110's initial data and the delay in advancing a next-gen candidate.

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