Fine-tuning the electronic structure of heavy-atom-freeBODIPYphotosensitizers for fluorescence imaging and mitochondria-targeted photodynamic therapy

Abstract

Theranostics that combines both diagnosis and therapy into a single platform has recently emerged as a promising biomedical approach for cancer treatment; however, the development of efficient theranostic agents with excellent optical properties remains a challenge. Here, we report novel mitochondria-targetingBODIPYphotosensitizers (R-BODs) that possess considerable singlet oxygen generation capabilities and good fluorescence properties for imaging-guided photodynamic therapy (PDT). The incorporation of sulfur atoms into the pi-conjugated skeleton ofBODIPYalong with the introduction of different functional groups at themeso-position of theBODIPYcore is essential for tuning the photophysical and photosensitizing properties. Notably, the MeOPh-substituted thiophene-fusedBODIPY(MeO-BOD, R =p-methoxyphenyl) displayed the highest singlet oxygen generation capability (phi(Delta)approximate to 0.85 in air-saturated acetonitrile) and a moderate fluorescence quantum yield (phi(f)= 17.11). Furthermore,MeO-BODshowed good biocompatibility, low dark toxicity and superior fluorescence imaging properties in living cells. More importantly, the PDT efficacy of mitochondria-specific anchoring ofMeO-BODwas remarkably amplified with an extremely low half-maximal inhibitory concentration (IC50) value of 95 nM. We believe that the incorporation of an electron-donating group at themeso-position of the thiophene-fusedBODIPYplatform may be an effective approach for developing theranostic agents for precision cancer therapy.