A designed 5-fluorouracil-based bridged silsesquioxane as an autonomous acid-triggered drug-delivery system

Two new prodrugs, bearing two and three 5-fluorouracil (5-FU) units, respectively, have been synthesized and were shown to efficiently treat human breast cancer cells. In addition to 5-FU, they were intended to form complexes through H-bonds to an organo-bridged silane prior to hydrolysis-condensation through sol-gel processes to construct acid-responsive bridged silsesquioxanes (BS). Whereas 5-FU itself and the prodrug bearing two 5-FU units completely leached out from the corresponding materials, the prodrug bearing three 5-FU units was successfully maintained in the resulting BS. Solid-state NMR ((29) Si and (13) C) spectroscopy show that the organic fragments of the organo-bridged silane are retained in the hybrid through covalent bonding and the (1) H NMR spectroscopic analysis provides evidence for the hydrogen-bonding interactions between the prodrug bearing three 5-FU units and the triazine-based hybrid matrix. The complex in the BS is not affected under neutral medium and operates under acidic conditions even under pH as high as 5 to deliver the drug as demonstrated by HPLC analysis and confirmed by FTIR and (13) C NMR spectroscopic studies. Such functional BS are promising materials as carriers to avoid the side effects of the anticancer drug 5-FU thanks to a controlled and targeted drug delivery.