Figure 6.

Enhancement of DX cytotoxicity by (A) NAA and (B) NADMA. Six concentrations of DX were tested for cytotoxicity in (•), SHP77 (MDR⁺ + MRP⁺); (▵), SW2R120 (wild type); (□), SW2R160 (MDR⁺), and (○), SW1573 (LRP⁺) cells in the presence and absence of NAA or NADMA. The concentrations required for 50% inhibition of cell growth (IC₅₀ in μM) were determined by the median-effect plot using computer software (23, 24). Fold of increase in efficacy of DX is based on fold of decrease in IC₅₀. NAA or NADMA alone showed little or no cytotoxicity in these cell lines.