Nanobody–chlorin e6 conjugate for Nectin‐4‐mediated tumor targeting and enhanced photodynamic therapy

Abstract Photodynamic therapy (PDT) holds promise for tumor ablation, but the clinical translation of photosensitizers, such as chlorin e6 (Ce6), is limited by poor aqueous solubility, low bioavailability, and insufficient tumor selectivity. To address these limitations, we constructed a nanobody–photosensitizer conjugate (NPC) by covalently linking Ce6 to a variable heavy‐chain domain targeting Nectin‐4, a clinically relevant tumor biomarker. Cell‐based assays demonstrated that NPC exhibited markedly enhanced aqueous solubility, efficient cellular uptake, and strong Nectin‐4‐dependent binding compared with free Ce6. Upon light activation, NPC generated abundant reactive oxygen species (ROS), triggered lysosomal disruption, and induced apoptosis and immunogenic cell death. In xenograft mouse models, NPC displayed prolonged circulation, rapid and selective tumor‐specific accumulation, and potent PDT to inhibit tumor growth, whereas free Ce6 displayed weak tumor retention and limited therapeutic benefit. Importantly, NPC treatment caused no measurable systemic toxicity or body weight loss during repeated administration. Collectively, these findings demonstrate that nanobody conjugation can overcome key pharmacological limitations of conventional photosensitizers by improving solubility, tumor targeting, and therapeutic index. NPC, thus, represents a promising next‐generation PDT agent with potential for tumor‐selective and clinically translatable phototherapy.