Ricolinostat enhances the in vivo antimyeloma activity of JQ1. (A) Ricolinostat enhances the antimyeloma activity of JQ1 in vivo. RPMI-8226 tumors were established in nude mice. Mice were treated with 50 mg/kg JQ1, 50 mg/kg ricolinostat, or the combination of both agents once per day for 5 days per week for 3 weeks. Tumor volume was measured twice per week. Data are shown as mean ± standard error of the mean; n = 10. (B) JQ1 and ricolinostat are well tolerated in mice. RPMI-8226 tumors were established in nude mice, and mice were treated as described above. Mouse body weight was measured twice per week. Data are shown as mean ± SD; n = 10. No significant weight loss was observed in any of the treatment groups compared with vehicle control. (C) Tumors were collected at the end of study, and levels of c-MYC, BCL-2, PCNA, and cleaved caspase-3 were measured by immunohistochemistry. Scale bars, 50 μm. (D) Immunohistochemical analysis shows that administration of JQ1 and ricolinostat effectively reduces c-MYC and BCL-2 expression, decreases PCNA⁺ cells, and induces significant caspase-3⁺ cells. Quantification of immunohistochemical analysis of c-MYC and BCL-2 was determined by densitometry (relative expression). PCNA and active caspase-3–positive cells were determined by manual counting. Data are shown as mean ± SD; n = 5 random fields. *Indicates a significant difference compared with vehicle; **indicates either single-agent treatment. P < .05.