Ingenious pH-sensitive etoposide loaded folic acid decorated mesoporous silica-carbon dot with carboxymethyl-βcyclodextrin gatekeeper for targeted drug delivery and imaging

Abstract

A new strategy is reported for the synthesis of label-free fluorescent mesoporous silica (MS) by the introduction of fluorescent carbon dots in the MSs (MSCDs) in this work. Etoposide (ETO) loaded MSCDs have been used as a drug model. Carboxymethyl β-cyclodextrin (CβCD) used as a gatekeeper agent was attached to amine-functionalized MSCDs to retain ETO molecules inside the nanocarrier. In order to target the nanocarrier to the site of action, folic acid (FA) was grafted onto the MSCDs surface (FA-CβCD-MSCDs). The in vitro release of an entrapped ETO from the formulation in phosphate buffered saline (PBS) (pH 7.4) and citrate buffer (pH 5.4) was investigated. At neutral pH in PBS, the pores are blocked by CβCD which prevent premature ETO release. However, under the weakly acidic intercellular environment of the tumor, the amide bond can be partially hydrolyzed and consequently lead to the ETO release from the nanocarrier. The targeted and ETO-loaded FA-CβCD-MSCDs showed a higher growth inhibition towards FA-positive HeLa cells compared with FA-negative HepG2 cells, as demonstrated by comparison of in vitro cytotoxicity experiments. In addition, the CDs emission was used for the fluorescent microscopic imaging. Moreover, molecular docking and molecular dynamics simulations (MDS) were applied to examine the interactions of ETO molecules with the topoisomerase II (Top II). ETO molecules bind Top II with overall binding constants of 3.08 × 1010 M−1, according to docking results. Based on MDS results, ETO-Top II complex is formed through hydrophobic interactions.