CDK9 and esophageal adenocarcinoma: Similarities in effects of transient shCDK9 and CDK9 inhibitors on p-Poll II (surrogate of CDK9 activity) and MCL-1 support our conclusion that cytotoxic effects of CAN 508 and Flavopiridol are at least partly mediated by CDK9 and MCL-1 is a potential target of these inhibitors in esophageal adenocarcinoma cells.