DDAH1 and cancer: Many literatures suggest that miR‐21 expression is highly associated with its downstream genes including Akt1, Bcl2, Ddah1, Pdcd4, Pd‐l1, and Pten, and inhibiting miR‐21 would greatly induce cancer cell apoptosis by regulating its downstream genes.[13, 17, 18, 19, 20] In KB and A549 cells, AM21 consistently induced Akt1 downregulation, Ddah1 upregulation, and PD‐L1 upregulation in free solution, lipofectamine, and QTsome formulation (Figure 2B,C).