In vitro evaluation of folic acid-conjugated redox-responsive mesoporous silica nanoparticles for the delivery of cisplatin

Abstract

The use of cisplatin(IV) prodrugs for the delivery of cisplatin have gained significant attention, because of their low toxicity and reactivity. Recent studies have shown that targeted cisplatin(IV)-prodrug nanoparticle-based delivery systems can improve the internalization of the cisplatin(IV) prodrug. We hypothesized that folic acid-conjugated mesoporous silica nanoparticles (MSNs) containing cisplatin(IV) prodrug could target cancer cells that overexpress the folate receptor and deliver the active cisplatin drug upon intracellular reduction. To prove this hypothesis, internalization and localization studies in HeLa cancer cells were performed using flow cytometry and confocal microscopy. The ability of MSNs to escape from the endolysosomal compartments, the formation of DNA adducts, and the cytotoxic effects of the MSNs were also evaluated. Our results confirmed that this MSN-based delivery platform was capable of delivering cisplatin into the cytosol of HeLa cells, inducing DNA adducts and subsequent cell death.

Keywords:

• cancer treatment
• cisplatin prodrug
• intracellular delivery
• folic acid
• mesoporous silica

Supplementary materials

Figure S1 Schematic representation of the synthesis of FA-PEG-NH₂.

Notes: To convert the alcohol group in the PEG_2K chain to amine group, the polymer was reacted with MsCl in anhydrous THF to afford a good leaving group. The PEG mesylate derivative was reacted with NaN₃, a strong nucleophile, to afford the azido-PEG product. To convert the diazido-PEG_2K derivative to the corresponding diamino-PEG_2K, a mild reduction was carried out by following Staudinger reaction conditions. The diazido-PEG_2K chain was reacted with PPh₃ in anhydrous THF to generate the corresponding iminophosphorane. An aqueous workup led to the desired diamino-PEG_2K derivative and the very stable phosphine oxide as by-product. The diamino-PEG polymer was further reacted with FA to afford the FA-PEG-NH₂ targeting ligand. Firstly, the carboxylic acid group in the FA molecule was activated by using a coupling reaction in the presence of EDC and NHS. The succinimide ester derivative enhanced the reactivity of the FA toward nucleophilic substitution by amines.

Abbreviations: FA, folic acid; PEG, polyethylene glycol; THF, tetrahydrofuran; EDC, N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride; NHS, N-hydroxysuccinimide; DIPEA, diisopropylethylamine; DMAP, dimethylaminopyridine; DMSO, dimethyl sulfoxide.

Figure S2 Internalization results by flow cytometry.

Notes: HeLa cancer cells were incubated with media containing 100 mg/L or 500 mg/L of free FA for 24 hours and exposed to 50 μg/mL of FA-FITC-MSNs or MeO-FITC-MSNs for 4 hours. Then, normalized mean fluorescence was obtained. Error bars represent the standard deviation of three independent experiments.

Abbreviations: FA, folic acid; FITC, fluorescein isothiocyanate; MSNs, mesoporous silica nanoparticles; MeO, methoxy.

Acknowledgments

We thank the following funding sources for their support: UNC Charlotte (start-up funding), the Nanoscale Science Program at UNC Charlotte, NIH AREA grant 1R15CA192160-01, and NSF instrument grant 1337873. We also acknowledge Mr Jimmy Pan for helping with the synthesis and characterization of the PEG ligands and the AAS measurements. The authors are grateful to Dr Richard Jew for critical reading of the manuscript and helpful suggestions.

Author contributions

MPAB performed the synthesis and characterization of the MSN materials and the in vitro experiments. MPAB and JLVE conceived and designed the experiments and wrote the paper. All authors contributed toward data analysis, drafting and revising the paper and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.