Thymidine rescues ATR kinase inhibitor-induced deoxyuridine contamination in genomic DNA, cell death, and interferon-α/β expression.

Abstract

ATR kinase is a central regulator of the DNA damage response (DDR) and cell cycle checkpoints. ATR kinase inhibitors (ATRi's) combine with radiation to generate CD8+ Tcell-dependent responses in mouse models of cancer. We show that ATRi's induce cyclin-dependent kinase 1 (CDK1)-dependent origin firing across active replicons in CD8+ Tcells activated exvivo while simultaneously decreasing the activity of rate-limiting enzymes for nucleotide biosynthesis. These pleiotropic effects of ATRi induce deoxyuridine (dU) contamination in genomic DNA, R loops, RNA-DNA polymerase collisions, and interferon-α/β (IFN-α/β). Remarkably, thymidine rescues ATRi-induced dU contamination and partially rescues death and IFN-α/β expression in proliferating CD8+ Tcells. Thymidine also partially rescues ATRi-induced cancer cell death. We propose that ATRi-induced dU contamination contributes to dose-limiting leukocytopenia and inflammation in the clinic and CD8+ Tcell-dependent anti-tumor responses in mouse models. We conclude that ATR is essential to limit dU contamination in genomic DNA and IFN-α/β expression.