It revealed that Lactucin inhibits the cell cycle at the G0/G1 phase, Figure 2A. It was further supported by the western blot (WB) analysis of Lactucin-treated (24 h) adenocarcinoma (A549 and H2347) cell’s protein, Figure 2B. Both cyclins (cyclin B1 and cyclin D1) and cyclin-dependent protein kinases (CDKs) (CDK2 and CDK4), which regulate the cell cycle through mutual interactions, were dose-dependently downregulated, Figure 2C,D. The gene discussed is CCND1; the disease is adenocarcinoma.