Systemic and Local Delivery of siRNA to the CNS and Periphery via Anti-IGF1R Antibody Conjugation

siRNA delivery platforms capable of accessing both central and peripheral tissues are critically needed to expand the therapeutic potential of oligonucleotides. To address this, we developed a novel siRNA-antibody conjugate by attaching an Hprt-targeting siRNA to an engineered antibody shuttle. This shuttle targets the insulin-like growth factor 1 receptor (IGF1R) using a fused antibody fragment (Clone F) and utilizes an antibody backbone with no tissue-relevant binding in this study. The resulting conjugate, designated Clone F-Hprt, demonstrated robust in vivo knockdown across multiple tissues. Clone F-Hprt demonstrated enhanced penetration into central nervous system (CNS) tissues compared to unconjugated siRNA following intracerebroventricular (ICV) and intravenous (IV) administration. In peripheral tissues, Clone F-Hprt achieved widespread knockdown in muscle, heart, and lung, consistent with IGF1R expression. The conjugate was well tolerated across all routes, including with repeated dosing. Although several receptor-mediated approaches for CNS delivery are progressing to the clinic (e.g., targeting the transferrin receptor), clinical validation remains to be demonstrated. Our findings highlight IGF1R as an alternative receptor capable of supporting delivery across both central and peripheral tissues, offering a complementary strategy for expanding the therapeutic landscape of oligonucleotide delivery.