Photodynamic therapy (
PDT) is an anticancer therapeutic modality with remarkable advantages over more conventional approaches. However,
PDT is greatly limited by its dependence on external light sources. Given this,
PDT would benefit from new systems capable of a light-free and intracellular photodynamic effect. Herein, we evaluated the heavy-atom effect as a strategy to provide anticancer activity to derivatives of
coelenterazine, a chemiluminescent single-molecule widespread in marine organisms. Our results indicate that the use of the heavy-atom effect allows these molecules to generate readily available triplet states in a chemiluminescent reaction triggered by a
cancer marker. Cytotoxicity assays in different
cancer cell lines showed a heavy-atom-dependent anticancer activity, which increased in the substituent order of
hydroxyl <
chlorine <
bromine. Furthermore, it was found that the magnitude of this anticancer activity is also dependent on the
tumor type, being more relevant toward breast and
prostate cancer. The compounds also showed moderate activity toward
neuroblastoma, while showing limited activity toward
colon cancer. In conclusion, the present results indicate that the application of the heavy-atom effect to marine
coelenterazine could be a promising approach for the future development of new and optimized self-activating and
tumor-selective sensitizers for light-free
PDT.