Phosphate-Surface-Modified Silica Nanoparticles for 5-Fluorouracil as a Prolonged Drug Delivery System

Background/Objectives: This paper describes the synthesis of silica nanoparticles (SiNPs) and their surface modification with amino and phosphate groups (SiNPs-NH₂-PO₃). The functionalized nanoparticles were subsequently loaded with the anticancer drug 5-fluorouracil (SiNPs-NH₂-PO₃-5-FLU) and further modified with PEG2000 (SiNPs-NH₂-PO₃-5-FLU-PEG2000). Methods: In this study, a one-step, two-phase, sol-gel method carried out at room temperature was used to synthesize the nanoparticles. The size and surface zeta potential of the created SiNPs were determined by DLS measurements. HPLC was used to determine the amount of drug loaded into silica nanoparticles and the drug release profile in two different pH environments (slightly acidic and physiological). Based on physicochemical characteristics, the SiNPs-NH₂-PO₃-5-FLU and SiNPs-NH₂-PO₃-5-FLU-PEG2000 formulations were chosen for comprehensive characterization. The cytotoxicity of the studied complexes was assessed in MCF7 breast cancer cells, while their ability to induce apoptosis in those cells was examined using specific immunofluorescence markers: active caspase-7, active poly(ADP-ribose) polymerase (PARP), and p53 protein. Results: Our findings demonstrate that SiNPs-NH₂-PO₃-5-FLU can induce a stronger apoptotic response than free 5-FLU at equivalent concentrations. We observed that drug release occurs not only under physiological conditions but is further enhanced in a mildly acidic environment (pH 5.0), characteristic of the tumor microenvironment. Conclusions: Most 5-fluorouracil formulations are administered as injectable solutions, resulting in systemic exposure and significant adverse effects. However, their encapsulation within nanoparticles could favor preferential drug release in the acidic tumor microenvironment, thus supporting targeted therapy and reducing toxicity to healthy tissues. Moreover, PEGylation of the nanoformulation allows prolonged and controlled release.