Balancing stability and activation: A pseudoparabolic activity spectrum guides fatty acid chain length optimization in prodrug-albumin nanoparticles.

Despite advances in prodrug-albumin nanoparticles (ANPs), critical mechanistic gaps persist-including quantitatively undefined prodrug-HSA affinity relationships, unresolved tumor-specific activation mechanisms, and suboptimal therapeutic outcomes (e.g., Limited drug loading capacity and insufficient stability). To bridge these gaps, we engineered a cathepsin B (CTSB)-cleavable doxorubicin (DOX) prodrug (D8·P, D12·P, D14·P, D16·P, and D18·P) with fatty acid (FAs) modification modules (C8-C18), yielding prodrug ANPs (DNS8, DNS12, DNS14, DNS16, and DNS18) with >25 % drug loading. Interestingly, we discovered a unified "pseudoparabolic" structure-activity relationship and meticulously delineated the complete structure-activity spectrum encompassing "insufficient chain length-optimal window-excessive chain length", underpinned by the interplay of intermolecular interactions versus steric hindrance/enzyme accessibility. With 50.4× higher AUC and 77 % lower cardiac accumulation than DOX and enhanced early tumor targeting over Doxil®, palmitic acid (C16) was identified as the "sweet-spot" chain length for designing prodrug-HSA-based nanoparticles. These findings provide crucial rational design principles and a highly promising candidate strategy for developing promising albumin nanomedicines with the potential for enhanced efficacy and reduced toxicity.