Targeted Delivery to Dying Cells Through P-Selectin–PSGL-1 Axis: A Promising Strategy for Enhanced Drug Efficacy in Liver Injury Models

To minimize off-target adverse effects and improve drug efficacy, various tissue-specific drug delivery systems have been developed. However, even in diseased organs, both normal and stressed, dying cells coexist, and a targeted delivery system specifically for dying cells has yet to be explored to mitigate off-target effects within the same organ. This study aimed to establish such a system. By examining the surfaces of dying cells in vitro, we identified P-selectin glycoprotein ligand-1 (PSGL-1) as a universal marker for dying cells, positioning it as a potential target for selective drug delivery. We demonstrated that liposomes conjugated with the PSGL-1 binding protein P-selectin had significantly greater binding efficiency to dying cells compared to control proteins such as E-selectin, L-selectin, galectin-1, and C-type lectin-like receptor 2. Using thioacetamide (TAA) to induce hepatitis and hepatocyte damage in mice, we assessed the effectiveness of our P-selectin-based delivery system. In vivo, P-selectin-conjugated liposomes effectively delivered fluorescent dye and the apoptosis inhibitor z-DEVD to TAA-damaged livers in wild-type mice, but not in PSGL-1 knockout mice. In TAA-treated wild-type mice, unconjugated liposomes required a 100-fold higher z-DEVD dose compared to P-selectin-conjugated liposomes to achieve a comparable, albeit less effective, therapeutic outcome in lowering plasma alanine transaminase levels and alleviating thrombocytopenia. This emphasizes that P-selectin conjugation enhances drug delivery efficiency by approximately 100-fold in mice. These results suggest that P-selectin-based liposomes could be a promising strategy for targeted drug delivery, enabling both diagnosis and treatment by specifically delivering cell-labeling agents and rescue agents to dying cells via the P-selectin-PSGL-1 axis at the individual cell level.