Multivalent antiviral conjugates enhance activity against Influenza via cross-linking viruses

Long-acting drug-Fc conjugate (CD388) has emerged as a new class of antivirals against influenza A and B, yet the mechanisms governing how Fc conjugation reshapes small-molecule function remain undefined. Here we establish a programmable multivalent antiviral conjugates (AVCs) platform by click chemistry that enables flexible combination of valencies and conjugated drugs, allowing systematic interrogation of valency-dependent antiviral mechanisms. Using zanamivir as a model, mono-, di-, and trivalent zanamivir are conjugated with Fc, with trivalent zanamivir-Fc conjugates (AVC-Z3) exhibiting higher activity than lower-valent AVCs. AVC-Z3 induces inter-virion aggregation, thereby coupling blockade of viral entry with restriction of viral release. This cross-linking-mediated dual-stage inhibition represents a mechanistic shift from neuraminidase suppression to physical viral immobilization. Furthermore, trivalent peramivir-Fc conjugate (AVC-P3) is synthesised and exhibits stronger antiviral activity than AVC-Z3 in vitro, with much longer half-life in vivo than AVC-Z3, and CD388 with YTE mutation. The in vivo antivirus efficacy of AVC-P3 surpasses other AVCs, baloxavir, and CD388 in H1N1-, H3N2-, H5N1-, and influenza B-infection mice models. Together, our findings define ligand valency as a determinant of antiviral mechanism.