The inhibition of proliferation and migration of glioma spheroids exposed to temozolomide is less than additive if combined with irradiation

The aim of this study was to investigate the effect of temozolomide (TZM) in combination with X-rays on proliferation and migration in human glioma spheroids. Multicellular spheroids were derived from GaMg and U87 cell lines. Spheroids were treated with various concentrations of TZM (5 μmol, 0.025 mmol, 0.05 mmol) and irradiation (RT). Proliferation and migration assays were performed. For GaMg spheroids, the proliferation inhibition was 30% (RT), 71%, 79%, 85% (for various TZM concentrations) and 78%, 83%, 90% following RT+TZM. For U87 spheroids, the inhibition of proliferation was 52% (RT), 62%, 78%, 88% (TZM), and 73%, 87%, 92% (RT+TZM). Inhibition of migration for GaMg was 30% (RT), 37%, 63%, 78% (TZM), and 56%, 75%, 84% (RT+TZM). For U87, migration inhibition was 29% (RT), 48%, 52%, 67% (TZM), and 62%, 67%, 73% (RT+TZM). Radiotherapy enhancement ratio (RER) of GaMg/U87 spheroid proliferation was 1.4/1.7 (5 μmol TZM), 1.3/1.8 (0.025 mmol TZM), and 1.4/1.4 (0.05 mmol TZM). RER for migration of GaMg/U87 was 2.2/1.9 (5 μmol TZM), 1.7/1.8 (0.025 mmol TZM), and 1.5/1.4 (0.05 mmol TZM). In terms of inhibition of proliferation and migration, irradiation can lead to an enhancement of the TZM effect in human glioma spheroids, which is less than additive.