The linker governs the organelle targeting of TPP⁺-modified zinc phthalocyanine photosensitizers.

Mitochondria are key targets in anticancer drug design owing to their central roles in cancer cell apoptosis and energy metabolism. In this study, we design and synthesize two triphenylphosphonium (TPP⁺)-modified zinc phthalocyanine (ZnPc) photosensitizers: ZnPc-O3-P(ph)3 linked by a polyethylene glycol (PEG) chain and ZnPc-C5-P(ph)3 linked by an alkyl chain. Subcellular localization studies show that ZnPc-O3-P(ph)3 precisely targets mitochondria, whereas ZnPc-C5-P(ph)3 unexpectedly accumulates in lysosomes. This finding overturns the conventional assumption that TPP⁺ confers universal mitochondrial targeting and reveals that linker structure critically governs TPP⁺-mediated subcellular localization. ZnPc-O3-P(ph)3 has a phototoxic index (PI, defined as the ratio of IC₅₀ in the dark to IC₅₀ under illumination) of 7.51 × 103, 544-fold higher than that of ZnPc-C5-P(ph)3 (PI = 13.8) and 10.4-fold higher than the clinical phthalocyanine photosensitizer photosens (PI = 725). In an orthotopic bladder cancer mouse model, ZnPc-O3-P(ph)3 exhibits therapeutic efficacy comparable to that of the first-line drug mitomycin C (MMC). This study demonstrates that linker design can dominate the subcellular fate of TPP⁺-conjugated agents, providing a new paradigm for targeted therapeutic development.