The Effect of Cell Cluster Size on Intracellular Nanoparticle-Mediated Hyperthermia: Is It Possible to Treat Microscopic Tumors?

Abstract

Aim To compare the measured surface temperature of variable size ensembles of cells heated by intracellular magnetic fluid hyperthermia with heat diffusion model predictions. Materials & methods Starch-coated Bionized NanoFerrite (Micromod Partikeltechnologie GmbH, Rostock, Germany) iron oxide magnetic nanoparticles were loaded into cultured DU145 prostate cancer cells. Cell pellets of variable size were treated with alternating magnetic fields. The surface temperature of the pellets was measured in situ and the associated cytotoxicity was determined by clonogenic survival assay. Results & conclusion For a given intracellular nanoparticle concentration, a critical minimum number of cells was required for cytotoxic hyperthermia. Above this threshold, cytotoxicity increased with increasing cell number. The measured surface temperatures were consistent with those predicted by a heat diffusion model that ignores intercellular thermal barriers. These results suggest a minimum tumor volume threshold of approximately 1 mm3, below which nanoparticle-mediated heating is unlikely to be effective as the sole cytotoxic agent.

Effective particle magnetic moment of multi-core particles

“…The particles are supplied as suspension in water. The BNF particles are widely used in hyperthermia studies for cancer treatment [6][7][8] and show interesting properties as contrast agent for magnetic resonance imaging [9]. The FeraSpin R particle system from nanoPET is also an iron oxide multi-core particle system with a median particle size of about 70 nm.…”

Magnetic hyperthermia enhances cell toxicity with respect to exogenous heating

“…12,19 To determine the minimum number of cells required for attaining the target temperatures in the hyperthermia region (T < 42°C), we compared several cell pellets containing were investigated by increasing the T from a starting permissive set point of 37°C. At subhyperthermic temperatures of 37 and 40°C, the required amplitude of the AMF was quite small.…”

Magnetic nanoparticles for cancer therapy

“…In their study, Hedayati et al defined the minimum size of a tumor for efficient hyperthermia with an alternating magnetic field. They determined a minimum tumor volume of 1 mm 3 consisting of cells that had incorporated magnetic nanoparticles to facilitate hyperthermia effects [77] . It is of interest to note that Asin et al found no increase in temperature with the application of an alternating magnetic field in vitro .…”