Abstract 1779: Bromodomain inhibitor JQ1 inhibits cholangiocarcinoma tumor growth in patient-derived xenograft models

Cholangiocarcinoma (CCA) is a lethal malignancy of the biliary epithelium that can arise in any part of the biliary tree. Surgery is the only curative treatment for CCA, but only ∼30% of patients present with resectable disease. The remaining 70% of patients present with advanced or metastatic disease and, if eligible, undergo systemic chemotherapy with the first-line combination of gemcitabine and cisplatin. This combination was shown in a phase II clinical trial to significantly increase median survival from 8.1 to 11.7 months, compared to gemcitabine alone. In order to improve on current treatment, pre-clinical evaluation of novel therapeutics is essential to improving outcome. Unfortunately, the paucity of data describing characteristics common to CCA make development of targeted therapy difficult. However, as is true for other types of solid tumors, c-Myc expression likely contributes to CCA phenotype: c-Myc expression has been observed in 95% of CCA tumors, and experimental down-regulation of c-Myc decreases the invasive potential of CCA cells in vitro. Recently it has become possible to inhibit expression of c-Myc using BET inhibitors. Therefore, we evaluated the efficacy of the bromodomain (BET) inhibitor JQ1 using in vivo models of CCA. The five patient-derived xenograft (PDX) models of CCA that we developed are the first such models to be reported. These models retain the heterogeneity, architecture and specific genetic characteristics of the primary tumors from which they were derived. We used three of these models to examine whether the BET inhibitor JQ1 inhibited CCA tumor growth and generated expression profiles of vehicle- and drug-treated tumors. We administered 50 mg/kg of JQ1 i.p. daily for 20 days and monitored tumor growth. This treatment regimen was well tolerated by tumor-bearing mice, without apparent toxicity. Our data demonstrate that JQ1 suppressed tumor growth in two of the three models, compared to vehicle control treated mice. The data also showed that JQ1-treated tumors had lower levels of c-Myc RNA (↓5-fold) and protein and of RNA encoding multiple transcriptional targets downstream of this oncogenic transcription factor. We conclude that BET inhibitors such as JQ1 warrant further investigation as potentially effective drugs for the treatment of CCA. Citation Format: Patrick L. Garcia, Aubrey L. Miller, Kelly Kreitzburg, Tracy L. Gamblin, Leona N. Council, John D. Christein, Pablo Arnoletti, Marty Heslin, Sushanth Reddy, Joseph H. Richardson, Eddy S. Yang, Jun Qi, James E. Bradner, Karina J. Yoon. Bromodomain inhibitor JQ1 inhibits cholangiocarcinoma tumor growth in patient-derived xenograft models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1779. doi:10.1158/1538-7445.AM2015-1779