Nolatrexed dihydrochloride is primarily used in the field of oncology as a thymidylate synthase inhibitor. It is applied in the treatment of various cancers, particularly solid tumors, by disrupting the synthesis of DNA, which is crucial for cancer cell proliferation. The compound works by blocking the enzyme thymidylate synthase, thereby preventing the formation of thymidine, a necessary component for DNA replication. This inhibition leads to the cessation of cancer cell growth and can induce apoptosis, or programmed cell death, in malignant cells. Clinical trials have explored its efficacy in treating liver cancer, colorectal cancer, and other malignancies, often in combination with other chemotherapeutic agents to enhance its therapeutic impact. Its application is carefully monitored due to potential side effects and the need for precise dosing to maximize anti-cancer activity while minimizing harm to healthy tissues.