Solid-State Formation of a Potential Melphalan Delivery Nanosystem Based on β-Cyclodextrin and Silver Nanoparticles

Abstract

Melphalan (Mel) is an antineoplastic widely used in cancer and other diseases. Its low solubility, rapid hydrolysis, and non-specificity limit its therapeutic performance. To overcome these disadvantages, Mel was included in β-cyclodextrin (βCD), which is a macromolecule that increases its aqueous solubility and stability, among other properties. Additionally, the βCD-Mel complex has been used as a substrate to deposit silver nanoparticles (AgNPs) through magnetron sputtering, forming the βCD-Mel-AgNPs crystalline system. Different techniques showed that the complex (stoichiometric ratio 1:1) has a loading capacity of 27%, an association constant of 625 M^-1, and a degree of solubilization of 0.034. Added to this, Mel is partially included, exposing the NH₂ and COOH groups that stabilize AgNPs in the solid state, with an average size of 15 ± 3 nm. Its dissolution results in a colloidal solution of AgNPs covered by multiple layers of the βCD-Mel complex, with a hydrodynamic diameter of 116 nm, a PDI of 0.4, and a surface charge of 19 mV. The in vitro permeability assays show that the effective permeability of Mel increased using βCD and AgNPs. This novel nanosystem based on βCD and AgNPs is a promising candidate as a Mel nanocarrier for cancer therapy.

Keywords: cyclodextrin; drug delivery; inclusion complex; melphalan; nanomaterial; silver nanoparticle; solid-state formation; sputtering.

Figure 1

Schematic representation of nanosystem formation: inclusion process of the drug in βCD (a,b), formation of the crystals (c), obtaining and stabilization of AgNPs by magnetron sputtering (d), formation of the βCD–Mel–AgNPs crystalline system, (e) and solubilization process forming the βCD–Mel–AgNPs colloidal nanosystem (f).

Figure 2

Powder diffractograms of (a) βCD, (b) Mel, (c) βCD–Mel, and (d) physical mixture of βCD and Mel.

Figure 3

¹H-NMR spectra of the (a) βCD, (b) Mel, and (c) βCD–Mel complex in DMSO-d₆.

Figure 4

ROESY spectra of the interaction between (a) H′-2′/6′ and H′-3′/5′ of Mel and H-3, H-6, and H-5 of βCD; (b) H′-3a of Mel and H-3, H-6, and H-5 of βCD in βCD–Mel complex in DMSO-d₆; (c) molecular schematic of the proposed inclusion geometry for the βCD–Mel system.

Figure 5

(a) Scheme of the release of atoms and formation of AgNPs on crystals of the βCD–Mel complex from the cathodic sputtering of a metal foil; (b) absorbance spectra of AgNPs deposited on βCD–Mel using magnetron sputtering.

Figure 6

(a,b) FE-SEM micrograph of βCD–Mel with AgNPs, the time of exposure in sputtering was 32 s. (c) EDX spectrum taken at the marked area in the SEM micrograph at its right side of AgNPs deposited on βCD–Mel by sputtering, with elemental analysis values in the inset.

Figure 7

(a) Schematic representation of the solubilization process of AgNPs onto ꞵCD–Mel crystalline complex forming the ꞵCD–Mel–AgNPs nanosystem in colloidal solution, (b) TEM micrograph of βCD–Mel–AgNPs colloidal nanosystem with its respective size distribution histogram (c).

Figure 8

(a) Effective permeabilities of free Mel, Mel included in βCD and Mel in βCD–AgNPs nanosystem. Thiopental and Evans Blue solutions were used as negative and positive controls, respectively. The assays were performed at 37 °C for 24 h, using PBS as solvent, (n = 3); (b) representation of a transwell plate used in PAMPA with a scheme of permeation of the drug through an artificial membrane.