Linrodostat is a small molecule effectively and specifically inhibits IDO1, preventing Trp from being converted into the immunosuppressive Kyn [60] to lower serum Kyn levels and inhibit tumor, IDO1's heme is particularly labile, and linrodostat inhibits IDO1 by binding to the heme-free (apo) form of the enzyme [60, 61]. The gene discussed is IDO1; the disease is neoplasm.