Magnetic thermoablation stimuli alter BCL2 and FGF-R1 but not HSP70 expression profiles in BT474 breast tumors

Abstract

Magnetically induced heating of magnetic nanoparticles (MNP) in an alternating magnetic field (AMF) is a promising minimal invasive tool for localized tumor treatment that eradicates tumor cells by applying thermal stress. While temperatures between 42°C and 45°C induce apoptosis and sensitize the cells for chemo- and radiation therapies when applied for at least 30 minutes, temperatures above 50°C, so-called thermoablative temperatures, rapidly induce irreversible cell damage resulting in necrosis. Since only little is known concerning the protein expression of anti-apoptotic B-cell lymphoma 2 (BCL2), fibroblast growth factor receptor 1 (FGF-R1), and heat shock protein (HSP70) after short-time magnetic thermoablative tumor treatment, these relevant tumor proteins were investigated by immunohistochemistry (IHC) in a human BT474 breast cancer mouse xenograft model. In the investigated sample groups, the application of thermoablative temperatures (<2 minutes) led to a downregulation of BCL2 and FGF-R1 on the protein level while the level of HSP70 remained unchanged. Coincidently, the tumor tissue was damaged by heat, resulting in large apoptotic and necrotic areas in regions with high MNP concentration. Taken together, thermoablative heating induced via magnetic methods can reduce the expression of tumor-related proteins and locally inactivate tumor tissue, leading to a prospectively reduced tumorigenicity of cancerous tissues. The presented data allow a deeper insight into the molecular mechanisms in relation to magnetic thermoablative tumor treatments with the aim of further improvements.

Keywords: breast cancer tumor; in vivo; magnetic nanoparticles (MNP); mouse model; thermoablation.

Figure 1

(A) Experimental set-up, (B) temperature curves, and (C) X-ray image during magnetic thermoablation. Notes: (A) Scheme of the used experimental set-up. Nanoparticles are indicated by orange spots. (B) Representative temperature curves of different tumor regions during treatment. Body temperature was observed by thermal measurement via the rectum. Higher temperatures in the central tumor region correlate with the distribution of the administered magnetic material. After reaching ablative temperatures of approximately 65°C, the AMF was shut-off. (C) X-ray images of mice were used to control MNP relocalization and the localization of thermocouples for thermal treatment. Abbreviations: AMF, alternating magnetic field; MNP, magnetic nanoparticles.

Figure 2

Effect of magnetic thermoablation on the BCL2, HSP70, and FGF-R1 protein expression pattern in BT474 tumors. Notes: Representative pictures after IHC staining of BCL2, HSP70, and FGF-R1 were chosen. Blue: nuclei, red: protein-specific antibody, scale bar: 100 μm. Relative semi-quantitative expression of investigated proteins is depicted in diagrams. In diagrams, bars represent the relative number of slides with a specific protein expression normalized to the total number of all slides in the specific treatment group. Bar colors represent the amount of specifically stained area within the viable tumor region: unstained/negative (light gray), less than 50% of vital area stained (dark grey), more than 50% of vital area stained (black). Whereas a downregulation of BCL2 and FGF-R1 can be assumed, HSP70 expression remained unchanged. Abbreviations: BCL2, B-cell lymphoma 2; HSP70, heat shock protein; FGF-R1, fibroblast growth factor receptor 1; IHC, immunohistochemistry; MNP, magnetic nanoparticles; AMF, alternating magnetic field.