A water soluble antifolate with anti-proliferative activity. Pelitrexol inhibits activity of glycinamide ribonucleotide formyltransferase (GARFT), the first folate-dependent enzyme of the de novo purine synthesis pathway essential for cell proliferation. Enzyme inhibition reduces the purine nucleotides pool required for DNA replication and RNA transcription. As a result, this agent causes cell cycle arrest in S-phase, and ultimately inhibits tumor cell proliferation.