CRISPR Therapeutics and Sirius Partner to Develop FXI-Targeting New Drug

The collaboration features joint development of a next-gen anticoagulant and includes options for future product licenses.

May 20, 2025

Strategic Alliance to Target Factor XI

CRISPR Therapeutics is teaming up with Sirius Therapeutics on a high-impact partnership to bring a new class of RNA-based drugs to market. The agreement, signed May 19, 2025, centers on the joint development of SRSD107, a long-acting siRNA therapeutic aimed at selectively inhibiting coagulation Factor XI—a key player in thrombosis.

This is a multi-layered collaboration. CRISPR is issuing $70 million in common shares and paying an additional $25 million in cash to Sirius as part of the upfront consideration. On top of that, CRISPR gains the option to license Sirius' siRNA technology for two additional drug targets from a pool of seven. If CRISPR moves forward with both, it will pay $10 million per option —in cash, shares, or a mix of the two.

Shared Development and Defined Governance

From here, the two companies will share responsibility for development and commercialization. Costs and profits? Split equally. CRISPR will take the lead in the U.S., Sirius will handle Greater China, and decisions for other regions will be made later. A joint steering committee will oversee progress, meeting quarterly to align on research and clinical milestones.

The financial structure is built for flexibility and long-term alignment:

For SRSD107: Sirius is eligible for up to $87.5 million in milestone payments.

For licensed products: Up to $300 million in development and sales milestones per product.

Royalties: Tiered, based on net sales, ranging from mid-single to low double digits.

CRISPR takes full ownership of the research, development, manufacturing, and global commercialization for any licensed products it chooses to pursue.

Flexibility and Risk Management

The agreement includes opt-out provisions that allow either party to step away from a product at defined points in development. If one party opts out, it moves from cost-sharing to receiving royalties and milestone payments tied to future product sales. Termination rights are also clearly outlined for breach or insolvency, with fallback mechanisms to maintain forward momentum if needed.

SRSD107: Promising Early Data

So, why all this focus on SRSD107? The therapy has already completed two Phase 1 trials, with encouraging results. Single-dose injections delivered:

Over 93% reduction in FXI levels and activity

More than a 2x increase in activated partial thromboplastin time

Sustained response lasting up to six months

By targeting FXI, SRSD107 aims to reduce clotting risk while preserving natural hemostasis—addressing a common shortfall in current anticoagulant therapies. The target patient population includes those with atrial fibrillation, cancer-associated thrombosis, and individuals undergoing major orthopedic procedures where bleeding is a top concern.

What’s Next: Phase 2 Underway

A Phase 2 trial is now in motion. It focuses on preventing venous thromboembolism in patients undergoing total knee arthroplasty. The trial will inform dose selection and help shape future pivotal studies.

With CRISPR expanding beyond gene editing and Sirius bringing its siRNA expertise to the table, this partnership is positioned to move with speed and clarity. The agreement sets both companies up to execute on a shared roadmap with clearly defined milestones, tight governance, and aligned incentives.