Co-treatment with exogenous ceramide or TMZ or irradiation shows additive but not synergistic effects in vitro.

<p>(A) LNT-229 or (B) T98G wt cells were treated with increasing concentrations of TMZ or C2- or C6-ceramide or co-treated with TMZ and C2- or C6-ceramide for 24 h and clonogenicity was assessed 2–3 weeks later. (C) LNT-229 or (D) T98G wt cells were treated with increasing concentrations of C2- or C6-ceramide for 24 h and increasing doses of irradiation (RT) or co-treated with C2- or C6-ceramide and irradiation and clonogenicity data were obtained 2–3 weeks later. (E) LNT-229 or (F) T98G wt cells were treated with a single dose of C2-ceramide (12 µM), C6-ceramide (12 µM) or TMZ (LNT-229: 12 µM; T98G: 125 µM) for 72 h or RT (8 Gy) or co-treated with C2- or C6-ceramide and TMZ or RT and cell density measured with crystal violet 72 h later. Predicted values, assessed using the fractional product method, are displayed in grey bars, observed values are highlighted by blank bars. Statistically significant changes compared to untreated cells are marked with asterisks (*, <i>p</i><0.05; **, <i>p</i><0.01; <i>t</i>-test).