Class 1 Histone Deacetylases and Ataxia-Telangiectasia Mutated Kinase Control the Survival of Murine Pancreatic Cancer Cells upon dNTP Depletion

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive disease with a dismal prognosis. Here, we show how an inhibition of de novo dNTP synthesis by the ribonucleotide reductase (RNR) inhibitor hydroxyurea and an inhibition of epigenetic modifiers of the histone deacetylase (HDAC) family affect short-term cultured primary murine PDAC cells. We used clinically relevant doses of hydroxyurea and the class 1 HDAC inhibitor entinostat. We analyzed the cells by flow cytometry and immunoblot. Regarding the induction of apoptosis and DNA replication stress, hydroxyurea and the novel RNR inhibitor COH29 are superior to the topoisomerase-1 inhibitor irinotecan which is used to treat PDAC. Entinostat promotes the induction of DNA replication stress by hydroxyurea. This is associated with an increase in the PP2A subunit PR130/PPP2R3A and a reduction of the ribonucleotide reductase subunit RRM2 and the DNA repair protein RAD51. We further show that class 1 HDAC activity promotes the hydroxyurea-induced activation of the checkpoint kinase ataxia-telangiectasia mutated (ATM). Unlike in other cell systems, ATM is pro-apoptotic in hydroxyurea-treated murine PDAC cells. These data reveal novel insights into a cytotoxic, ATM-regulated, and HDAC-dependent replication stress program in PDAC cells.