We have proved that the effect of tadalafil capacity of anti-tumor on CRC completely depends on PDE5, a classical target of tadalafil, by cell viability and the relative expression of important genes in amino acid metabolism including GPTA, GGT5, and TAT in tadalafil with pde5 knockdown groups compared with tadalafil-treated groups. This evidence concerns the gene GGT5 and colorectal carcinoma.