IDO1 and neoplasm: IDO1 expression can be downregulated by kushenol E (KS76, DL = 0.59, Caco-2 = 0.58) and kushenol F (KS74, DL = 0.61, Caco-2 = 0.45) to inhibit tumor proliferation (Kwon et al., 2019) and induce apoptosis (Kwon et al., 2020).