Triple-Targeted Peptide–Photosensitizer–Drug Conjugate Enables NIR-II Imaging-Guided Multimodal Therapy Against Osteosarcoma

Conventional antibody- or peptide-drug conjugates (ADCs/PDCs) improve tumor selectivity, yet the unimolecular integration of imaging guidance and multimodal therapy remains limited. Here, we introduce a peptide-photosensitizer-drug conjugate (P²DC) strategy that enables unified NIR-II imaging and synergistic multimodal therapy. As a proof of concept, a hypoxia-activated prodrug, IT-azo-RGD, is constructed by integrating a computationally optimized photosensitizer core, a hypoxia-cleavable azo linker bridging a drug payload, and bis-cRGDfK for multivalent integrin targeting. Theoretical calculations reveal that the active photosensitizer core (IT-m-NH₂) exhibits bright NIR-II fluorescence, efficient photothermal conversion, and type-I photodynamic reactivity, while also elucidating the mechanisms underlying IT-azo-RGD self-assembles into nanospheres that undergo hypoxia-triggered disassembly upon drug release. IT-azo-RGD displays triple tumor targeting through integrin affinity, EPR-mediated accumulation, and hypoxia activation. Upon azo cleavage, •OH generation increases by approximately 6-fold, and the photothermal efficiency reaches 59.7%. These features support NIR-II imaging-guided chemo-photothermal-photodynamic synergy. In the orthotopic osteosarcoma mouse model, IT-azo-RGD achieves 97.7% tumor inhibition, suppresses lung metastasis, and shows no systemic toxicity. This P²DC concept provides a generalizable design framework for a unimolecular theranostic prodrug.