Design of Engineered Cyclodextrin Derivatives for Spontaneous Coating of Highly Porous Metal-Organic Framework Nanoparticles in Aqueous Media

Abstract

Nanosized metal-organic frameworks (nanoMOFs) MIL-100(Fe) are highly porous and biodegradable materials that have emerged as promising drug nanocarriers. A challenging issue concerns their surface functionalization in order to evade the immune system and to provide molecular recognition ability, so that they can be used for specific targeting. A convenient method for their coating with tetraethylene glycol, polyethylene glycol, and mannose residues is reported herein. The method consists of the organic solvent-free self-assembly on the nanoMOFs of building blocks based on β-cyclodextrin facially derivatized with the referred functional moieties, and multiple phosphate groups to anchor to the nanoparticles' surface. The coating of nanoMOFs with cyclodextrin phosphate without further functional groups led to a significant decrease of macrophage uptake, slightly improved by polyethylene glycol or mannose-containing cyclodextrin phosphate coating. More notably, nanoMOFs modified with tetraethylene glycol-containing cyclodextrin phosphate displayed the most efficient "stealth" effect. Mannose-coated nanoMOFs displayed a remarkably enhanced binding affinity towards a specific mannose receptor, such as Concanavalin A, due to the multivalent display of the monosaccharide, as well as reduced macrophage internalization. Coating with tetraethylente glycol of nanoMOFs after loading with doxorubicin is also described. Therefore, phosphorylated cyclodextrins offer a versatile platform to coat nanoMOFs in an organic solvent-free, one step manner, providing them with new biorecognition and/or "stealth" properties.

Keywords: MIL-100(Fe); isothermal titration calorimetry; macrophage; mannose; metal-organic frameworks; molecular recognition; multivalent effect; β-cyclodextrin; “stealth” effect.

Scheme 1

Synthesis of per-functionalized β-cyclodextrin (β-CD) phosphate derivatives 8–10.

Scheme 2

Synthesis of per-functionalized β-CD phosphate derivative 16.

Figure 1

TEM images of nanosized metal-organic frameworks (nanoMOFs) before and after coating step: (a) Uncoated nanoMOFs; (b) nanoMOFs@CD-P; (c) nanoMOFs@8; (d) nanoMOFs@9; (e) nanoMOFs@10; (f) nanoMOFs@16. Scale bar: 200 nm.

Figure 2

Phosphate β-CD derivatives (PCDs) grafting (wt%) versus nanoMOFs:PCDs mass ratio assayed.

Figure 3

Zeta potential of nanoMOFs coated or not with PCDs in 10 mM PBS at pH 7.4.

Figure 4

Titration of concanavalin A (ConA) with conjugate 10 in 20 mM phosphate buffer (pH 7.2) at 25 °C. The top panel shows the raw calorimetric data denoting the amount of generated (negative exothermic peaks) heat following each injection of the conjugate. The area under each peak represents the amount of heat released upon binding of the conjugate to the lectin. Note that as the titration progresses, the area under the peaks gradually becomes smaller because of the increasing saturation of the sugar binding sites of the protein. This area was integrated and plotted against the molar ratio of the conjugate to ConA (as tetramer). The smooth solid line represents the best fit of the experimental data to the model of n equal and independent binding sites.

Figure 5

Thermodynamic profiles comprising free energy (−ΔG⁰), enthalpy (−ΔH), and entropy changes (TΔS⁰) for the interaction of conjugates 8, 10, nanoMOFs@8, and nanoMOFs@10 with ConA in 20 mM phosphate buffer (pH 7.2) at 25 °C for 8 and 10, and 10 mM TRIS buffer (pH 7.5) at 25 °C for nanoMOFs@8 and nanoMOFs@10.

Figure 6

In vitro interaction of uncoated and coated nanoMOFs with PCDs CD-P, 8–10, and 16 with a J774A.1 macrophage cell line. 50 µg/mL nanoMOFs were incubated with 3 × 10⁵ J774A.1 cells for 4 h, and then washed to remove the nonfirmly bound nanoMOFs. After cell lysis, the amount of internalized nanoMOFs was determined by ICP-MS and was expressed as a % of the initial amount put in contact with the cells.