Ru(II) Complex-Mediated Phase Separation Amplifies Photocatalytic RNA Damage to Stimulate RIG‑I Immunotherapy

Phase separation is closely related to the transcription, processing, translation, and metabolism of RNA, and regulating RNA phase separation may serve as an effective antitumor strategy. However, small molecule-based RNA phase separation inducers have not yet been reported. Herein, based on our previous work, we designed a Ru-(II) complex (Ru1) that can form multivalent interactions with RNA and induce the phase separation of both double-stranded RNA (dsRNA) and single-stranded RNA (ssRNA) in vitro. Interestingly, the substituents on the ligands, including the positively charged triphenylphosphine and the hydroxyl groups, play decisive roles in its capability to induce RNA phase separation, which is also confirmed by molecular dynamics simulations. Moreover, Ru1-mediated phase separation preceding photoactivation establishes a novel RNA-centric immune activation mechanism, wherein subsequent photodamage to RNA triggers the retinoic-acid-inducible gene I (RIG-I) pathway. Finally, we demonstrate that Ru1 can significantly improve tumor immune microenvironments.