Towards the preclinical study of magnetic fluid hyperthermia: strategies for determining specific loss power and murine melanoma cell count

Abstract

Magnetic fluid hyperthermia (MFH) is a potential cancer treatment which uses heat from the relaxation of magnetic nanoparticles (MNPs) under an applied alternating magnetic field to damage and kill cancer cells. To plan in vitro MFH treatments, the specific loss power (SLP) of the MNPs must be determined to quantify heating efficiency and the cell counting protocol must be validated to assess viability of the cultures post-treatment. A variety of methods are used to calculate SLP, and there can be differences in equipment and the sample’s environment, all of which contribute to measurement reproducibility. In this study, we compare three common SLP determination methods: the Initial Slope Method (ISM), the Corrected Slope Method (CSM), and the Box-Lucas Method (BLM). The methods differ in the amount of temperature over time data used as an input, their heat transfer assumptions, and the necessity of the post-treatment cooling curve acquisition. ISM uses the initial slope of the heating curve, CSM integrates the cooling curve to correct the heating curve, and BLM fits the heating and cooling curve to global parameters. We ran such measurements on commercial particles RCL-01, Perimag, and Synomag-D and found that the BLM analysis method is optimal for quick and precise screening of MNPs while the CSM method is optimal for precision but is more time-consuming. Additionally, we examined methods of counting B16 murine melanoma cells to measure viability for in vitro MFH experiments. The main obstacles in counting included cell aggregation, pigmentation typical of melanoma, and concentration. Poor performance of an automated cell counter prompted comparison with the hemocytometer and a fluorescence microscope. We concluded that both the automated cell counter and hemocytometer are limited by visibility issues due to melanin darkening cells, leading to further exploration into the fluorescent microscope and other viability assays.