Figure 2.

Schematic of intracellular pharmacokinetics and pharmacodynamics of methotrexate (MTX). Following transporter‐mediated uptake, MTX is reversibly metabolized to form a series of polyglutamated metabolites (MTX‐Glu_n). MTX inhibits the enzymatic conversion of folic acid (FA) to dihydrofolate (DHF), and DHF to tetrahydrofolate (THF), resulting in the depletion of cellular methylene‐THF (CH₂THF), methenyl‐THF (CH=THF), and 5‐methyl‐THF (5mTHF). Depletion of the reduced cellular folate pool by MTX and inhibition of folate‐dependent enzymes by MTX‐Glu_n results in inhibition of purine, pyrimidine, and methionine biosynthesis.