Fig. 6. In vitro viability studies based on MTT metabolic assays of: (a), (b) and (c) MSN2-CPT-PPz incubated with lung epithelial (BEAS-2B) and lung tumor (A549) cells, for different times, from (d) to (h) MSN3-PPz-control and MSN2-CPT-PPz nanoparticles incubated with A549 lung tumor cells.