Immunoengineering of a Photocaged 5´‐triphosphate Oligoribonucleotide Ligand for Spatiotemporal Control of RIG‐I Activation in Cancer

Abstract Photochemical control of oligonucleotides bears great potential for the spatio‐temporal control of therapeutic targets, such as immune sensing receptors. Retinoic acid‐inducible gene I (RIG‐I) is a cytoplasmic receptor of the innate immune system that triggers antiviral responses upon detection of viral RNA. RIG‐I can be specifically activated by short double‐stranded (ds) RNA with a blunt 5′ end bearing a triphosphate, mimicking nascent viral transcripts. Tumor cells are specifically sensitive to RIG‐I‐induced cell death. Here we developed a potent oligonucleotide ligand for spatiotemporally controlled activation of RIG‐I by light exposure. Through structural considerations and functional studies we identified a combination of two nucleoside positions in a RIG‐I oligonucleotide ligand for which the substitution of both respective 2′‐hydroxy groups of the ribose by photolabile protecting groups (2′‐photocages) resulted in a complete loss of RIG‐I ligand activity, whereas photocaging the individual positions was not sufficient to turn off RIG‐I. Light exposure fully restored RIG‐I activation by the photocaged RIG‐I ligand, enabling light‐controlled RIG‐I‐mediated cell death of human cancer cells which had internalized the photocaged RIG‐I ligand prior to light exposure. This novel photoactivatable RIG‐I oligonucleotide ligand may be applicable for precise light‐controlled induction of tumor cell death in superficial cancer such as melanoma.