Assessment of in vivo toxicity to MEK inhibitor PD0325901. (A) Weight change in grams is shown for each PD0325901 (PD) treatment group in the MDA-MB-453 xenograft model. Weight change is the difference between pre- and post-treatment weight in each group. PD0325901 treatments were carried out at 5, 10, 15 and 20 mg/kg/day for 30 days, and daily gavage of carrier solution was used as control. *P < 0.01 for PD-5/PD-10 vs. control groups and PD-5/PD-10 vs. PD-15/PD-20 groups using Mann-Whitney U test. Error bars: ± 2 SEM. (B) Number of days lost due to toxicity is shown for each PD0325901 treatment group in mouse xenograft model explained in Figure 5A. *P < 0.01 for PD-5/PD-10 vs. PD-15/PD-20 groups.