Controlled Dual Activation of Rhenium(I) Photosensitizers and Profluorophores/Prodrugs via a Dissociative Bioorthogonal Tetrazine–Isonitrile Reaction

Strategies for prodrug activation have been developed to enhance treatment efficacy, with bioorthogonal dissociation reactions emerging as a promising approach due to their remarkable specificity. In this work, we designed three rhenium(I) polypyridine complexes featuring a tetrazylmethyl (TzMe) group capable of bioorthogonal activation by 3-isocyanopropyl (ICPr) or 3-isocyanopropyl-1-carbamoyl (ICPrc) derivatives. This design serves as a dual-release platform, which liberates rhenium(I) 3-hydroxypyridine complexes and functional payloads from rhenium(I) TzMe complexes and ICPr/ICPrc-caged compounds, respectively. Upon incubation with an ICPrc derivative, the TzMe complexes exhibited strong emission in acidic buffers, attributed to the predominant existence of the resulting rhenium(I) 3-hydroxypyridine complexes in their protonated form. Confocal imaging of live cells incubated with a TzMe complex and ICPr-caged fluorescein unveiled intense intracellular emission in distinct channels. Importantly, the therapeutic potential of this approach was underscored by the treatment of cells with a TzMe complex and ICPrc-caged doxorubicin. The anticancer effect was amplified through the synergy between singlet oxygen (¹O₂) photosensitization and prodrug activation, effectively combining photodynamic therapy with chemotherapy. The more pronounced ¹O₂ generation of the 3-hydroxypyridine complexes in acidic media and their specific accumulation within the acidic lysosomes of cancer cells highlight the potential of bioorthogonal prodrug activation for effective cancer-targeted therapy.