Our studies demonstrate a marked decrease in the expressions of cyclins D1, D2 and E, and Cdk2, Cdk4 and Cdk6 in both A549 and H1299 cells dose-dependently on GSPs treatment suggests the disruption of the uncontrolled cell cycle progression of human NSCLC cells (Figure 5) and that the GSPs-induced G1 arrest is mediated through the up-regulation of cyclin-dependent kinase inhibitory proteins, Cip1/p21 and Kip1/p27, which enhances the formation of heterotrimeric complexes with the G1/S Cdks and cyclins thereby resulting in inhibition of their activity. This evidence concerns the gene PCNA and non-small cell lung carcinoma.