A theranostic endoperoxide agent with targeted singlet oxygen release and concomitant fluorescence signals

To circumvent the lingering limitations of photodynamic therapy, we developed a novel naphthalene-derived endoperoxide through structural optimization of 1,4-dimethylnaphthalene. Strategic introduction of an amide group at the 2-position enabled precise modulation of steric and electronic properties, resulting in prolonged ¹O₂ release half-life (t_1/2 = 8.6 h) compared to simpler derivatives. This temporal control is likely to result in more ¹O₂ release in tumor tissues, significantly enhancing the therapeutic effect. Our studies reveal that thermal cycloreversion drives ¹O₂ generation from these compounds, achieving potent cytotoxicity in cancer cell cultures (IC₅₀ = 11.6 µM). In vivo evaluation using a murine 4T1 breast cancer model demonstrated marked tumor suppression following intraperitoneal administration, with no observable systemic toxicity at the therapeutic doses. To enable real-time evaluation of therapeutic efficacy, we designed a modular system combining a naphthalimide fluorescent group with an H₂O₂-responsive phenylboronic ester. This construct capitalizes on the pathological overproduction of H₂O₂, a well-established biomarker of tumor progression. When exposed to elevated H₂O₂ levels in cancer cells, the phenylboronic ester undergoes specific cleavage to generate hydroxyl groups. This structural transformation triggers a blue-to-green fluorescence emission change, providing direct visual confirmation of therapeutic activation within the tumor microenvironment.