(A and B) – Cytotoxicity of dendrimer/siRNA complexes (A) and of acetylated dendrimers (B). U-87 cells were exposed to dendrimer/siRNA complexes (siRNA concentration = 100 nM) or to dendrimers (0.005 or 0.01 mM) for 4 hours in OptiMEM medium prior to MTS viability assay. MTS absorbance measurements were normalized to cells receiving a mock treatment of OptiMEM medium only (100%). The unmodified, generation 5 dendrimer has 128 primary amines. Data represent mean ± SEM (n = 2 experiments, each measured in triplicate).