Lometrexol hydrate is primarily used in research and experimental settings to study its effects on folate metabolism, particularly in inhibiting the enzyme glycinamide ribonucleotide formyltransferase (GARFT). This inhibition disrupts the synthesis of purines, which are essential for DNA and RNA production, making it a compound of interest in cancer research. It has been explored for its potential as an antineoplastic agent, targeting rapidly dividing cancer cells by limiting their ability to replicate. Additionally, its role in folate-dependent pathways has been investigated in the context of autoimmune diseases and inflammatory conditions, where modulating cell proliferation could provide therapeutic benefits. However, its clinical application has been limited due to challenges such as toxicity and the need for precise dosing strategies. Ongoing studies aim to optimize its use, potentially in combination with other therapies, to enhance efficacy while minimizing adverse effects.