Optically and magnetically active hybrid
F
e
P
t/
S
i
O
2/
A
u nanoparticles are internalized into normal and cancer urothelial cells
Authors: Hudoklin Samo , Kostevšek Nina , Romih Rok , Rožman Kristina Žužek , Šturm Sašo , Kreft Mateja Erdani 
Published: December 2016

Introduction

Nanomedical approaches in cancer treatment have the potential to enhance the effectiveness of localized therapy while minimizing side effects on the surrounding healthy tissue. The aim of our study was the development of a novel hybrid nanoparticles (hNPs) based on magnetic core (FePt) and photothermaly active shell (SiO
2
/Au) for targeting of cancer tissue. hNPs should enable controlled triggering of photothermic drug release, followed by extraction of hNPs from the body using an external magnetic field. We established biomimetic
in vitro
models of normal and cancer urothelial cells for testing proof‐of‐concept, biocompatibility, targeting, release, photothermic effects and extraction capabilities.

Materials, methods

Superparamagnetic SiO
2
‐coated FePt nanoparticles have been used as seeds for the growth of the Au shells [1]. Au nanoshells were coated with polyethylene glycol (PEG), because of its known biocompatibility, and improved
in vivo
stability. Finally, for the sterilization of the final suspension the sterile filters were used (sterile Millex‐GP syringe filter unit). Normal porcine urothelial cells – (NPU), low‐grade (RT4) – and high‐grade (T24) cancer urothelial cells ‐ were grown on plastic petri dishes in growth media with different basic ingredients (UroM or A‐DMEM/F12) at 37 °C in CO
2
‐incubator for up to 3 weeks [2]. To determine cytotoxic effects, hNPs were added to the culture media (100 µg/mL) for 2h in the presence and absence of the magnetic field (a Nd‐Fe‐B permanent magnet m
0
H=0.3 T measured right at the top of the magnet)). The viability was measured by counting trypan‐blue stained cells. The cellular distribution of hNPs was determined by TEM. Cells were fixed with 4% FA + 2% GA in 0.1M cacodilate buffer for 3h at 4°C, post‐fixed with 1% OsO
4
for 1h at 4°C, dehydrated in ethanol and embedded in Epon. Ultrathin sections were observed under transmission electron microscope (TEM, Philips CM100) running at 80kV.

Results
Schematic representation and a TEM image of hNPs are shown in Figure 1. The survival of urothelial cells, which were exposed to hNPs, has been >85 % in the absence as well as presence of the magnetic field. TEM showed hNP on the apical plasma membrane and in endocytotic structures of urothelial cells. While hNPs were primarily distributed individually or in small clusters (>20 particles) on the apical surface of the urothelial cells, they were also found individually or accumulated in the endosomal compartments of the urothelial cells (Figure 2). High‐grade cancer urothelial cells showed higher intensity of endocytosis compared to low‐grade cancer and normal urothelial cells.

Discussion and Conclusion

We have (i) optimized the culture conditions for long‐term growth and differentiation of normal and cancer urothelial cells and therefore established relevant biomimetic
in vitro
models of normal and cancer urothelial cells, (ii) shown that used hNPs are biocompatible in the presence and absence of magnetic field, and (iii) that hNPs could be internalized into the endosomal compartments of the cells. Our study confirmed proof‐of‐concept and provides a foundation for the next stage studies of hybrid nanomaterials, aiming at the development of smart diagnostic, targeted drug delivery and stimuli‐responsive release system.