CRISPR's Secret siRNA Weapon: A Smart Bet or Too Late?

While CRISPR Therapeutics (CRSP) is known for its gene-editing therapy Casgevy, the company is expanding its horizons. In May 2025, CRISPR paid $95 million up front to acquire CTX611 from Sirius Therapeutics.

CTX611 is not a gene-editing drug. It is a long-acting small interfering RNA (siRNA) therapy designed to prevent dangerous blood clots. It works by silencing the mRNA for a key blood clotting enzyme called Factor XI in the liver.

The candidate is engineered for convenient, twice-yearly dosing via a simple injection under the skin. This could be a major advantage over daily pills or monthly infusions required by other anticoagulants.

Critically, CRISPR's financial commitment is tiny compared to rivals. For example, Novartis paid up to $3.1 billion for a similar antibody therapy. While CRISPR could pay over $800 million more in milestones, its initial bet is a fraction of the cost for a shot at the same multi-billion dollar market.

This move matters because it could transform CRISPR's revenue, which was a mere $1.4 million last quarter (excluding its share of Casgevy). Even a small slice of the anticoagulant market, led by drugs like Eliquis ($14.4 billion in 2025 revenue), would be game-changing for the stock.

However, the competitive landscape is fierce. Novartis has a similar therapy, and other big pharma companies are developing improved pills. More directly, a Chinese company, Suzhou Ribo Life Science, already has a competing siRNA drug in more advanced clinical trials.

This means CTX611 is almost certainly entering the market as a follower, not a leader. Its success will depend on beating rivals on cost, convenience, safety, and effectiveness in a crowded field.

For investors, the upcoming catalyst is a progress update from phase 2 trials expected in the second half of this year. Positive data could boost the stock, while setbacks would highlight the program's risks.