Comparative analysis of the biological effects on U87 and FaDu 3D spheroids after their exposure to different hyperthermia modes

Abstract

Objective: To systematically compare the impact of four hyperthermia (HT) modalities, water bath (WB), amplitude-modulated and non-modulated radiofrequency electromagnetic fields (AMRF and RF), and magnetic nanoparticles (MNP) in 3D tumor spheroid models, and to evaluate how different thermal doses influence treatment outcomes and translational relevance. Methods: 3D spheroids of U87 glioblastoma and FaDu squamous carcinoma cells were exposed to thermal doses of 15, 30 and 120 CEM43 corresponding to 42 °C (60 min), 43 °C (30 min), and 45 °C (30 min), accounting for modality-dependent heating rates. Cell viability was assessed immediately after treatment and seven days later. Morphological changes, TUNEL staining, and apoptosis were evaluated in FaDu spheroids, while BRCA2 protein levels were analyzed in both spheroid types to investigate potential effects on homologous recombination-mediated DNA repair. Results: Immediately after treatment, U87 spheroids showed up to a 40% reduction in viability, while FaDu spheroids exhibited moderate sensitivity. By day 7, viability had largely recovered across most heating modalities and doses. However, U87 spheroids treated with MNP heating at 45 °C displayed sustained cytotoxicity, with viability reduced to 29%. In FaDu spheroids, morphological alterations, TUNEL positivity, and apoptosis correlated with increasing thermal dose. Reduced BRCA2 protein levels suggested possible impairment of homologous recombination repair, though functional validation was not conducted. At moderate thermal doses, all modalities produced comparable biological effects, whereas high-dose MNP heating resulted in enhanced cytotoxicity. Conclusions: Our findings indicate that at moderate thermal doses, all tested HT-modalities produced comparable biological responses in both 3D spheroid models, while high-dose MNP-mediated heating markedly enhanced cytotoxicity, likely due to combined nanoparticle-specific and thermal effects. These results highlight the usefulness of 3D spheroid models for assessing modality-dependent HT responses and may help guide the design of clinically relevant thermal therapies.