Abstract 1258: Therapeutic potential of the cyclin- dependent kinase inhibitor on c-Myc overexpressing esophageal adenocarcinoma
Authors: Hassan Sazzad , Awasthi Niranjan , Schwarz Margaret A. , Schwarz Roderich E. , Holzen Urs V. 
Published: July 2016

Abstract
Introduction: Esophageal adenocarcinoma (EAC) is now the fastest growing cancer in the western world and most EAC patients present with widespread metastatic disease, where current treatment is largely ineffective. Therefore, new therapeutic approaches are urgently needed. The transcription factor proto-oncogene c-Myc is a potent activator of tumorigenesis. Tumors with elevated c-Myc expression often exhibit highly aggressive phenotype. c-Myc amplification has been shown to be frequent in esophageal adenocarcinoma and has been implicated in Barrett's carcinogenesis. Emerging data suggests that synthetic lethal interactions between c-Myc pathway activation and small molecules inhibition involved in cell cycle signaling can be therapeutically exploited to preferentially kill tumor cells. In this study, we therefore investigated whether exploiting a synthetic-lethal approach dependent on elevated c-Myc signaling is effective in treating esophageal cancer with a cyclin-dependent kinase (CDK) inhibitor flavopiridol. Methods: Western blot analysis was done to see the expression of c-Myc and apoptotic signaling pathways in a panel of nine esophageal cancer cell lines. c-Myc overexpression and knockdown were performed using both genetic and novel chemical approaches. Cell viability assays were performed in 96-well plates using the colorimetric WST-1 reagent. Esophageal cancer tumors growth was measured in xenograft and a novel peritoneal disseminated metastatic survival model of immunodeficient mice. Results: Western blot analysis revealed frequent overexpression of c-Myc in EAC cell lines. In this panel of esophageal cancer cell lines tested more than 70% of EAC cell lines showed overexpression of c-Myc. When we tested these cell lines for their ability to form xenograft tumor and peritoneal dissemination, c-Myc overexpression correlated with accelerated EAC tumor growth in xenograft and peritoneal disseminated metastatic survival model of NOD/SCID mice. The xenograft tumor growth rate and formation rate of peritoneal cancer after injection of 5 million cells were highest in OE19 EAC cell line which showed the highest c-Myc expression. In addition, median animal survival with peritoneal dissemination was lowest for OE19 (55 days) whereas OACM5.1 C EAC cell line which had the lowest c-Myc expression didn't form any peritoneal tumor. EAC cell lines with elevated c-Myc expression are preferentially more sensitive to induction of apoptosis by CDK inhibitor flavopiridol compared to EAC cell lines with lower c-Myc expression. When we tested the role of c-Myc expression by upregulation/downregulation in this apoptotic effect we found that this effect is very much dependent on c-Myc expression. Conclusion: These results indicate that CDK inhibitor alone or in combination with other cytotoxic or targeted agents can be a potential therapy for c-Myc overexpressing EAC.
Citation Format: Sazzad Hassan, Niranjan Awasthi, Margaret A. Schwarz, Roderich E. Schwarz, Urs V. Holzen. Therapeutic potential of the cyclin- dependent kinase inhibitor on c-Myc overexpressing esophageal adenocarcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1258.