Imbalanced nucleotide metabolism sensitises triple negative breast cancer cell lines to standard of care chemotherapies

Deoxythymidylate triphosphate (TTP) is produced by the thymidylate biosynthesis pathway. Thymidylate biosynthesis is unique compared to the pathways which produce the other canonical nucleotides for DNA synthesis (dCTP, dGTP and dATP); requiring additional enzymatic reactions and also having the potential to produce the unwanted intermediate deoxyuridine triphosphate (dUTP) which can be misincorporated into DNA as DNA polymerase cannot distinguish between dUTP and TTP.

Thymidylate metabolism is a demonstrably targetable pathway, with multiple chemotherapies currently used in the clinic targeting the enzyme thymidylate synthase (TS), such as fluoropyrimidines (e.g. 5-FU, FUdR, Capecitabine) and antifolates (Pemetrexed, Raltitrexed, Methotrexate).<br><br>We have identified novel therapeutic opportunities to target the enzymes thymidylate kinase (TMPK) and deoxyuridine 5’-triphosphate nucleotidohydrolase (dUTPase).

TMPK is the subsequent enzyme following TS in the thymidylate biosynthesis pathway and catalyses the phosphorylation of TMP to TDP as part of TTP production. dUTPase catalyses the hydrolytic dephosphorylation of deoxyuridine triphosphate (dUTP) to deoxyuridine monophosphate (dUMP). Therefore, dUTPase is a critical gatekeeper that protects tumour DNA from the genotoxic misincorporation of uracil during DNA synthesis/repair.

Clinical trials are underway, with more planned, evaluating dUTPase inhibitors alongside TS targeting therapies (Capecitabine and S-1).<br><br>We hypothesise that targeting dUTPase or TMPK will cause an imbalanced dUTP to TTP ratio and enhance the effects of standard of care chemotherapies in TNBC.