A recently found natural compound, JBIR-21 (62), isolated from an anamorphic fungus [91], was reported to inhibit TDP1 with an IC50 of 18 μM, to be toxic to cancer cell lines (HeLa, NCI-H2052, HT-29, and Namalva; IC50 values of 9.2, 13, 4.0, and 3.5 μM, respectively), and to exert antitumor activity against HT-29 cells in a mouse xenograft model. The gene discussed is TDP1; the disease is cancer.