Diving on the Surface of a Functional Metal Oxide through a Multiscale Exploration of Drug-Nanocrystal Interactions

Abstract

While recent advances in nanotechnology offer significant possibilities for improving the development of targeted drug delivery systems (DDSs), the design of efficient nanocarriers remains challenging due to the complex interactions among nanoparticles, their surfaces, and therapeutic agents in biological environments. To shed light on such difficulties and provide an instrumental tool for the refinement of DDSs, this study presents a comprehensive computational and experimental approach for the development of zinc oxide nanocrystals (ZnO NCs), exploited as carriers for a hydrophobic drug used in the treatment of multiple myeloma (MM), namely, carfilzomib (CFZ). Oleic acid was adopted here as a stabilizing agent during the synthesis of iron-doped ZnO NCs, while aminopropyl groups were used as functionalizing moieties to improve drug adsorption. Advanced characterization techniques were employed to investigate the nanostructure and drug-loading properties. Furthermore, molecular modeling was exploited for elucidating the adsorption mechanism and the thermodynamics of the interactions between the drug and the NCs, offering a detailed understanding at the molecular level. These simulations provided predictive insights into possible molecular inactivation mechanisms and strategies to optimize the nanocarrier design, thus enabling tailored adjustments throughout the development process. While biological tests showed that CFZ-loaded ZnO NCs preserved the drug mechanism of action in MM cell lines, the interconnection between simulations and experiments played a central role in predicting and optimizing NCs-drug interactions. This approach demonstrates the potential of computational simulations in minimizing trial-and-error in the nanoconstruct development process, ultimately streamlining the creation and validation of more effective nanoparticle-based drug delivery systems.

Keywords: carfilzomib; coarse grained models; drug delivery; molecular dynamics simulations; small-angle X-ray scattering; surface functionalization; zinc oxide.

Scheme 1. Representation of the Experimental–Computational Approach Followed in This Study, Enabling a Holistic Approach toward the Design and Production of Effective Drug Delivery Nanosystems

Figure 1

DLS measurements of (a, d) ZnO, (b, e) ZnO_OLA, and (c, f) ZnO_OLA_APTMS NCs in double distilled water and ethanol. The upper row reports the size distributions in % intensity, while the lower row reports the distributions in % number.

Figure 2

(a) Field emission scanning electron microscopy (FESEM) image of the synthesized ZnO_OLA_APTMS NCs; (b) high-resolution transmission electron microscopy (HR-TEM) image of ZnO_OLA_APTMS NCs; (c) X-ray diffraction pattern of the analyzed ZnO_OLA_APTMS NCs; (d) SAXS profiles (symbols) of ZnO nanocrystals without and with functionalizations together with their best fits (black lines). Red squares, ZnO-Fe NCs; orange triangles, ZnO_oleic acid (ZnO_OLA); green circles, ZnO_OLA_APTMS. ZnO_OLA_APTMS and ZnO_OLA_APTMS_CFZ are represented with an incremental multiplication factor of 5 for better visibility.

Figure 3

CFZ molecule (purple) plus ZnO surface functionalized with (a) APTMS, (b) APTMS and OLA, (c) L-APTMS, (d) APTMS and OLA. (e) Densities of APTMS, L-APTMS, and OLA as a function of the distance from the surface.

Figure 4

SAXS profiles (symbols) of ZnO nanocrystals with functionalizations upon CFZ loading together with the best fit (black line). The dashed black drives the eye showing the slope of the data at low q-vector values, related to NCs fractal dimension.

Figure 5

Free energy of adsorption of one CFZ on the ZnO surface (a) in water and (b) in ethanol.

Figure 6

Comparison of the cytotoxic effect of the NCs administered at 5 and 10 μg/mL with and without the drug loaded on their surface on (a) AMO-1 and (b) KMS-28BM cell lines.

Figure 7

(a) GFP+ mean fluorescence signal of AMO-1 Ub-G76V-GFP with increasing concentration of CFZ (0–1.25–2.5–5 nM) and two different concentrations of ZnO-OLA_APTMS NCs (5 and 10 μg/mL) with and without CFZ (washed three times) at 12, 24, and 48 h post-treatment. Every value was normalized to the respective untreated sample at the indicated time point. (b) Cell viability of AMO-1 Ub-G76V-GFP with increasing concentration of CFZ (0–1.25–2.5–5 nM) and two different concentrations of ZnO-OLA_APTMS NCs (5 and 10 μg/mL) with and without CFZ (washed three times) at 12, 24, and 48 h post-treatment.