Dose response for mitoxantrone in malignant cell lines. (a) PC3-TR, (b) PC3 human prostate cancer cells, and (c) Panc-1 pancreatic cancer cells. Single-agent treatments are shown as "dark grey diamonds" and combination treatments with 10 ng/mL of TRAIL are shown as "light grey squares". Asterisks (*) and (**) indicate p-values < 0.05 and < 0.01, respectively. (d) molecular structure of mitoxantrone. Arrows indicate the concentrations at which the enhancement in viability reduction is the greatest. Data are presented on a logarithmic scale and the lines connecting data points are for visualization only.