Pemetrexed anti-cancer drug. Molecular model of the chemotherapy drug pemetrexed, marketed under the brand name Alimta. This drug is used to treat lung cancers, specifically mesothelioma and non- small cell lung cancer. Pemetrexed is a folate antimetabolite. The molecule's structure resembles folic acid (vitamin B9), and it interferes with cancer cells during their production of the nucleotide bases that make up DNA, leading to the cells' death. Patients taking the drug must also take folic acid and vitamin B12 supplements. Atoms in this molecule are shown as spheres and are colour coded: carbon (green), hydrogen (white), oxygen (red) and nitrogen (blue).