6-Thioguanine is a nucleotide analog of guanine that exhibits anticancer chemotherapeutic, immunosuppressive, and anti-parasitic activities. 6-Thioguanine is incorporated into DNA, altering stability of the topoisomerase II-DNA cleavage complex and increasing DNA fragmentation; these actions result in growth arrest and inhibition of proliferation across many cancer cell lines. In acute lymphoblastic leukemia (ALL) cells, 6-thioguanine increases mitochondrial dysfunction and generation of ROS, inducing a cytotoxic effect. In other in vitro models, 6-thioguanine decreases expression of TNF-related apoptosis-inducing ligand (TRAIL). Additionally, this compound inhibits growth of Toxoplasma gondii.