BROTHERS<sup>TM</sup> Technology: A Non-Equilibrium Approach to the Efficacy-Safety Dilemma in Antisense Oligonucleotides

Clinical development of antisense oligonucleotides (ASOs) is frequently constrained by the efficacy-safety dilemma, in which increased target affinity is accompanied by enhanced off-target toxicity. We propose that this apparent trade-off arises from an equilibrium specificity limit inherent to conventional thermodynamically controlled ASO-RNA recognition. To address this limitation, we developed BROTHERSTM technology, a non-equilibrium-inspired molecular design framework that mitigates the efficacy-toxicity coupling by integrating two orthogonal principles. 1) Static shielding suppresses non-specific interactions of single-stranded ASOs, while 2) dynamic selection enables kinetically driven target RNA recognition via a toehold-mediated strand displacement (TMSD) reaction. In vivo studies demonstrate that BROTHERSTM-based ASOs (BROs) achieve potent and selective gene silencing while markedly reducing toxicities observed with conventional single-stranded ASOs. These results indicate that non-equilibrium control of molecular recognition can effectively alleviate the efficacy-safety dilemma, establishing BROTHERSTM technology as a robust platform for next-generation antisense therapeutics.