We next tested the efficacy of PLX4720 (a sister compound of PLX4032) (Tsai et al., 2008) to inhibit tumor progression and phosphorylated ERK signaling in vivo. D4M.3A cells were injected intradermally into B6 mice (300 000 cells, per mouse). When tumors reached 5 mm in diameter (8 days post-injections), mice were either given drug-amixed chow containing PLX4720 (Plexxikon, Berkeley, CA) or control chow. Tumors were measured 4 and 7 days after the start of treatment and tumor volumes were calculated. After 7 days of treatment, mice that were fed the PLX4720 chow had significantly smaller tumors than mice that were fed the control chow (Figure 3B, P < 0.05). Mice injected with