A folate
antagonist is any of a group of
chemicals which block the formation of
nucleotides that require the presence of folate (
folic acid). The chemicals interfere with key steps in the
biochemical reaction sequence that creates the
nucleotides.
Folate antagonist drugs are often used to treat cancer because fast-growing cancerous cells usually need to use the blocked reactions more than normal cells do.
Some or all of the information in this writeup was taken from the science dictionary at http://biotech.icmb.utexas.edu/; I oversaw the development of the dictionary (the website was mothballed in 1998) and believe I wrote the entry this writeup is partly or wholly based upon.