Biological effects of CDK7 inhibitors on pancreatic cancer cells
Pancreatic cancer is often diagnosed at a late stage, and the current standard of care treatments are only able to moderately improve the outcomes of patients, extending their lives by only 2-3 months. c-MYC is a key oncogene in the pathogenesis of pancreatic cancer, and the overexpression of c-MYC leads to increased resistance to chemotherapeutics. Cyclin Dependent Kinase 7 (CDK7) is a component of the Transcription Factor IIH (TFIIH) and regulates cell cycle progression via phosphorylation of RNA Polymerase II (RNA Pol II) and other CDKs. CDK7 has been shown to also regulate the expression of super-enhancer controlled oncogenes such as c-MYC in cancer cells. Therefore, inhibition of CDK7 kinase activity has the potential to decrease the level of phosphorylation of RNA Pol II and downregulate the c-MYC expression leading to better chemotherapeutic susceptibility. We sought to develop novel CDK7 inhibitors that can downregulate RNA Pol II phosphorylation and c-MYC expression, which, as a result, leads to the inhibition of pancreatic cancer cell growth. In this study, sulforhodamine B (SRB) assay was first used to determine the IC50 values for four novel CDK7 inhibitors in two pancreatic cancer cell lines (PSN1 and MIA PaCa2). Two concentrations for each inhibitor based on the IC50 values were then used to treat both cell lines to determine the effects of the drug treatment on RNA Pol II phosphorylation and c-MYC expression. Proteins from the samples were separated using Western blotting probed with antibodies against phospho RNA Pol II (pRpbII), total RNA Pol II (RpbII), c-MYC, and β actin, which served as a loading control. It was observed that the phospho RNA Pol II and c-MYC levels were reduced after drug treatment in some of the samples, which indicates that CDK7 was being successfully inhibited at those drug concentrations. Further testing with additional drug concentrations and in more cell lines needs to be done to validate these results. In the future, combinations of the current standard of care therapies and the CDK7 inhibitors can be tested to determine if there is a greater inhibitory effect on pancreatic tumor growth in vitro and in vivo.
