Dual-payload small-molecule drug conjugates enable bystander anticancer activity with reduced nonspecific release.

Small-molecule drug conjugates (SMDCs) have emerged as a promising class of targeted therapeutics, yet their clinical translation has been hindered by suboptimal efficacy and safety, with conventional optimization largely restricted to variations in ligand design and linker chemistry. We propose a dual-payload strategy that enhances therapeutic efficacy while concurrently minimizing off-target diffusion that contributes to systemic toxicity. In this proof-of-concept study, a representative SMDC bearing two degrader payloads, termed Bi-LIVTAC (XZ1618), demonstrates improved targeted cytotoxicity and a robust bystander effect, accompanied by a significant reduction in receptor-independent uptake. Notably, XZ1618 achieves complete tumor regression in combination with sorafenib in a Huh-7 xenograft model, thereby markedly expanding the therapeutic window without inducing hematological toxicity or organ damage. Moreover, this dual-payload design is broadly applicable to SMDCs targeting other membrane receptors, such as folate receptor, and to diverse payload types, including conventional cytotoxins and fluorescent probes. These findings establish the dual-payload strategy as a versatile and translatable platform for developing next-generation SMDCs with improved therapeutic windows.