CRISPR Therapeutics (CRSP) and Sirius Therapeutics have entered a collaboration to develop small interfering RNA-based treatments, starting with SRSD107, a Factor XI-targeting therapy for thromboembolic conditions, the companies said late Monday.

Under the agreement, CRISPR will provide $25 million in cash and $70 million in equity to Sirius upfront. The companies will jointly develop SRSD107 under a 50-50 cost and profit-sharing model, with CRISPR leading US commercialization and Sirius overseeing Greater China.

CRISPR also holds exclusive rights to license up to two additional siRNA programs, according to a joint statement.

SRSD107 is a long-acting siRNA that selectively inhibits Factor XI, a driver of pathological clot formation, with limited effect on normal clotting. Phase 1 trials showed the therapy was safe, well-tolerated, and delivered sustained reductions in FXI levels for up to six months after a single dose, suggesting potential as a twice-yearly treatment.