Standing the test of time: targeting thymidylate biosynthesis in cancer therapy

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Over the past 60 years, chemotherapeutic agents that target thymidylate biosynthesis and the enzyme thymidylate synthase (TS) have remained among the most-successful drugs used in the treatment of cancer. Fluoropyrimidines, such as 5-fluorouracil and capecitabine, and antifolates, such as methotrexate and pemetrexed, induce a state of thymidylate deficiency and imbalances in the nucleotide pool that impair DNA replication and repair. TS-targeted agents are used to treat numerous solid and haematological malignancies, either alone or as foundational therapeutics in combination treatment regimens. We overview the pivotal discoveries that led to the rational development of thymidylate biosynthesis as a chemotherapeutic target, and highlight the crucial contribution of these advances to driving and accelerating drug development in the earliest era of cancer chemotherapy. The function of TS as well as the mechanisms and consequences of inhibition of this enzyme by structurally diverse classes of drugs with distinct mechanisms of action are also discussed. In addition, breakthroughs relating to TS-targeted therapies that transformed the clinical landscape in some of the most-difficult-to-treat cancers, such as pancreatic, colorectal and non-small-cell lung cancer, are highlighted. Finally, new therapeutic agents and novel mechanism-based strategies that promise to further exploit the vulnerabilities and target resistance mechanisms within the thymidylate biosynthesis pathway are reviewed.

Key Points

  • Since the 1940s, inhibitors of thymidylate biosynthesis have remained among the most effective chemotherapies used in the treatment of cancer

  • The enzyme thymidylate synthase (TS) is a key metabolic bottleneck in the synthesis of thymidine monophosphate required for DNA replication in tumour cells and, therefore, represents an important therapeutic target

  • The molecular consequences of TS inhibition can be complex and vary depending on the type of inhibitor, the tumour type and the expression levels of enzymes involved in drug metabolism

  • Inhibitors of TS fall into two major classes, the fluoropyrimidines and antifolates; these TS-targeted therapies remain the foundation of many combination chemotherapies used in patients with difficult-to-treat cancers

  • The application of existing TS-targeted agents continues to expand, with new approvals of these drugs for the treatment of solid tumours

  • New combination therapeutic strategies have emerged and are entering clinical trials, such as those targeting dUTPase to exploit the uracil-misincorporation pathway and defective DNA repair that occurs during TS inhibition

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Figure 1: Historical development and breakthroughs in targeting thymidylate biosynthesis and TS in cancer chemotherapy.
Figure 2: The thymidylate biosynthesis pathway.
Figure 3: Mechanism of action of fluoropyrimidines and antifolates.
Figure 4: dUTPase protects tumour cells from mechanisms of cytotoxicity during TS inhibition.


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P.M.W., P.V.D. and R.D.L. researched data for the manuscript, and P.M.W. wrote the article. All authors made substantial contributions to discussion of content, and reviewed and edited the manuscript before submission.

Correspondence to Robert D. Ladner.

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H.-J.L. has received clinical trial support from Taiho and Roche. The other authors declare no competing interests.

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Wilson, P., Danenberg, P., Johnston, P. et al. Standing the test of time: targeting thymidylate biosynthesis in cancer therapy. Nat Rev Clin Oncol 11, 282–298 (2014) doi:10.1038/nrclinonc.2014.51

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