(ai–di) JQ1 suppressed the growth of tumors derived from THJ-16T ATC cells in a xenograft mouse model. An equal number of THJ-16T cells (5 × 106) were injected into the flanks of mice before treatment. When tumors started to develop (average tumor size reached 100 mm3), JQ1 or vehicle was administered intraperitoneally on day 40 (50 mg/kg/d). JQ1 treatment decreased (ai) tumor growth, (bi) growth rate, (ci) tumor size, and (di) tumor weight. (ei) JQ1 treatment altered the protein abundance of key cell regulators. (ei-i) Western blot analysis was carried out as described in the Materials and Methods section. The proteins analyzed were marked. (ei-ii) The band intensities were determined, and the quantitative data indicated that JQ1 treatment decreased MYC and elevated p21 protein levels to decrease p-Rb/total Rb ratios and E2F-3 without significantly affecting CDK4 and cyclin D1. Six tumors derived from vehicle-treated mice and seven tumors derived from JQ1-treated mice were used in the Western blot analysis for the vehicle- and JQ1-treated mice. P values are indicated. (aii-dii) JQ1 suppressed the growth of tumors derived from ATC THJ-11T cells in a xenograft mouse model. An equal number of THJ-11T cells (5 × 106) were injected into the flanks of mice before treatment. When tumors started to develop (average tumor size reached 100 mm3), JQ1 or vehicle was administered intraperitoneally on day 20 (50 mg/kg per mouse twice per day). JQ1 treatment decreased (aii) tumor growth, (bii) growth rate, (cii) tumor size, and (dii) tumor weight. (eii) JQ1 treatment altered the protein abundance of key cell regulators. (eii-i) Western blot analysis was carried out as described in the Materials and Methods section. The proteins analyzed were marked. (eii-ii) The band intensities from the Western blots shown in eii-i were determined. The quantitative data indicated that JQ1 elevated p21 to decrease p-Rb/total Rb ratios and E2F-3 without significantly affecting CDK4 and cyclin D1. Five tumors each from vehicle- and JQ1-treated mice were used in the Western blot analysis. P values are shown.