Cytotoxicity analysis of PEI25K and blank HNPs in SUM159, MDA-MB-231, and LM2 cells by the MTT assay. Cells were cultured and treated with PEI25K and various concentrations of HNPs as described in the Experimental Section. The HNP concentrations were calculated on the basis of the concentration of PEI10K. (The amount of PEI10K-CD was converted into that of PEI10K as well.) Results are expressed as mean ± standard deviation (n = 8). *: p < 0.05, compared to 50, 100, 200, 500, and 1000 nM of HNP-treated groups; #: p < 0.05, compared to 50, 100, 200, and 500 nM of HNP-treated groups.