With human indoleamine 2,3-dioxygenase upregulated in key human tissues (i.e., small intestine and lung), and a number of cancers (i.e., acute myeloid leukemia, ovarian, and colorectal carcinoma), knowledge that aplysinopsins are substrates, and yield potent Michael acceptors, could inform future development of this pharmacophore. Here, IDO2 is linked to cancer.