The Fluorescent Cell Line SW620-GFP Is a Valuable Model to Monitor Magnetic Hyperthermia

Abstract

In this work, the cell line SW620-GFP has been used in a complete magnetic hyperthermia assay, from the preparation of the ferrofluid with folate-coated iron oxide nanoparticles to in vivo experiments. The physical and chemical characterization of the nanoparticles evidenced their superparamagnetic behaviour, an average diameter of 12 ± 4 nm, a 2 nm coat thickness, and a high-power loss density. The main innovation of the work is the exclusive capability of viable SW620-GFP cells to emit fluorescence, enabling fast analysis of both, cell viability in vitro with an epifluorescence microscope and tumour size and shape in vivo in a non-invasive manner using the iBox technology. Moreover, with this imaging technique, it was possible to demonstrate the successful tumour size reduction in mice applying magnetic hyperthermia three times a week over 3 weeks.

Keywords: fluorescence; hyperthermia; nanoparticles.

Figure 1

(a) XRD spectra of the magnetite nanoparticles (black line) and SPIONs (blue line); (b) TEM micrograph of the SPIONs; and (c) the statistics on size distribution.

Figure 2

(a) FTIR spectra of the magnetite (black line), folate (green line), and SPIONs (red line); (b) TGA analysis of magnetite (black line) and SPIONs (red line); and (c) Zeta potential of the ferrofluid with SPIONs.

Figure 3

(a) VSM measurements of magnetite (black line) and SPIONs (red line); (b) their corresponding ZFC-FC traces; and (c) calorimetric measurements of the ferrofluid with SPIONs irradiating a magnetic field of 530 kHz frequency and amplitudes from 10 to 25 mT.

Figure 4

(a) RCV of SW620-GFP cells after 24 h of incubation with different concentrations of SPIONs and (b) RCV of SW620-GFP cells exposed to 2 mg/mL and heated by magnetic field irradiation from 39 up to 48 °C.

Figure 5

(a) Image of the mock control of SW620-GFP cells exposed to SPIONs but kept at 37 °C, and cells heated to 43 °C (b) and 48 °C (c) by magnetic field irradiation. (d–f) The corresponding images obtained using an epifluorescence microscope with a green filter to observe the expression of GFP.

Figure 5

(a) Image of the mock control of SW620-GFP cells exposed to SPIONs but kept at 37 °C, and cells heated to 43 °C (b) and 48 °C (c) by magnetic field irradiation. (d–f) The corresponding images obtained using an epifluorescence microscope with a green filter to observe the expression of GFP.

Figure 6

Infrared images during the irradiation procedure: (a) after 4 min and (b) after 16 min of irradiation.

Figure 7

Relative average volumes (RAVs) of the tumours over time and different treatments (1 SPIONs + MH; 2 SPIONs; 3. neg. control), using (a) the calliper and (b) iBox technology. Error bars indicate standard deviation (SD).

Figure 8

The sequence of images of one mouse from each group (1 SPIONs + MH; 2 SPIONs; 3. neg. control) at the beginning and after every seventh day. The evolution of the tumour sizes over time can be visually followed.

Figure 8

The sequence of images of one mouse from each group (1 SPIONs + MH; 2 SPIONs; 3. neg. control) at the beginning and after every seventh day. The evolution of the tumour sizes over time can be visually followed.

Figure 9

iBox images from mice after 2 weeks of MH treatment: Top view of mouse from group 1 (a), group 2 (b), and group 3 (c), as well as lateral view of the same mice: group 1 (d), group 2 (e), and group 3 (f).

Figure 10

Fluorescence images of tumours extirpated from a mouse of (a) group 3, (b) group 2, and (c) group 1.

Figure 11

Measurements of the extirpated tumour volumes obtained by three different procedures. Error bars indicate SD.