GART and neoplasm: Toward KB tumor cells, 4–9 were highly active (IC50’s from 2.11 to 7.19 nM).By metabolite rescue in KB cells and in vitro enzymeassays, de novo purine biosynthesis was identifiedas a targeted pathway (at 5-aminoimidazole-4-carboxamide ribonucleotideformyltransferase (AICARFTase) and glycinamide ribonucleotide formyltransferase(GARFTase)).