Tumor-targeted biopolymer capped mesoporous silica nanocarriers for intracellular acid-triggered drug release

摘要

Introduction: Chemotherapy remains the gold standard in the management of cancer. However it owns several limitations, such as its lack of specificity towards tumor cells and the poor bioavallability of some antitumor drugs. Much effort is being dedicated to develop new nanocarriers that load, protect, transport and selectively release antitumor drugs at the target site. Among them, mesoporous silica nanoparticles (MSNs) are receiving growing attention in the management of solid tumors. Herein we purpose a novel tumor-targeted pH-responsive MSNs as topotecan (Top) nanocarriers. Top is an antitumor drug whose direct systemic administration is frequently associated to low therapeutic efficacy. The natural biopolymer gelatin is used as sensitive capping agent to prevent premature cargo departure and allow its release upon pH decrease, i.e. in the acidic environment of endosomes/lysosomes. Folic acid (FA) is grafted to the outermost surface of the nanosystem to favor its selective internalization in cancer cells. Materials and Methods: MSNs were synthetized following the well-known modified Stober method. Then MSNs were loaded with Top by soaking in an aqueous drug solution. Capping with gelatin was accomplished following a slightly modified method reported elsewhere. Then, FA acid was grafted to the gelatin shell via an EDC/NHS crosslinking method (Fig. 1). The materials were characterized by TG, FTIR, ~(13)C solid state NMR, N_2 adsorption, SEM, HR-TEM, zeta-potential and DLS. The pH-responsive drug delivery behavior of the nanosystem was tested in vial. Finally, in vitro assays using healthy (MC3T3-E1) and prostate cancer (LnCAP) cell cultures were performed to investigate the internalization and killing capabilities of free Top and Top/MSN@GEL-FA. MSNs after each synthesis step. The amounts of Top, GEL and FA present in Top/MSN@GEL-FA were ca. 5%, 29% and 22% in weight, respectively, proving the suitability of the loading, capping and grafting methods here reported. The nanosystem drug release performance evaluated in vial showed that almost 3-fold higher release was obtained under acidic (pH 5.2) than under neutral (pH 7.4) conditions, demonstrating the pH-responsive drug delivery capability of the system. This finding proves the suitability of the nanosystem for smart Top delivery to release the drug in the acidic environment of the endosomes once it has been internalized by the cell (Fig 2.A). The in vitro tests indicated that the presence of FA as targeting ligand leads to higher nanosystem internalization degree in cells overexpressing folate receptors (FR), i.e. LnCAP, than in MC3T3-E1 cells, which exhibit lower FR overexpression. The enhanced killing capability of Top/MSN@GEL-FA compared to that of free Top was also demonstrated by cell viability assays (Fig. 2B) Conclusion: We have developed a novel tumor-targeted pH-responsive drug delivery nanosystem based in MSNs loaded with Top, capped with a GEL shell and decorated with FA. This nanosystem permits selectively killing tumor cells overexpressing FR. After 72 h of assay the nanosystem is capable of producing almost 90% of cell death, whereas no cell death is observed using the same doses of free Top. These findings open promising expectations for the further in vivo evaluation of the nanosystems.