Orientin inhibits cyclin E/A-CDK2 to induce senescence and G0/G1 arrest in gastric cancer cells

Gastric cancer (GC) remains a significant global health challenge, characterized by high malignancy and poor prognosis. Current therapeutic strategies often face limitations, including resistance and systemic toxicity. A key hallmark of cancer is uncontrolled cell proliferation, often driven by dysregulation of the cell cycle. Inducing cellular senescence, a state of irreversible growth arrest, or restoring proper cell cycle control, particularly at the G0/G1 phase, represents a promising therapeutic avenue to halt tumor progression. This study investigates Orientin's potential to modulate these critical pathways in GC.

Researchers investigated Orientin's effects on human gastric cancer cell lines (AGS and HGC-27) in vitro and in an unspecified in vivo tumor model. In vitro, cells were treated with varying concentrations of Orientin to determine IC50 values and assess proliferation inhibition. They used flow cytometry to analyze cell cycle distribution and western blotting to quantify expression levels of cell cycle regulators like CDK2, CCNA2, CCNE1, CCNE2, p16, p21, and phosphorylated retinoblastoma (p-Rb). Senescence was evaluated via senescence-associated β-galactosidase staining. In vivo, Orientin was administered to assess its impact on tumor progression and the expression of key cell cycle proteins.

Orientin demonstrated significant anti-proliferative effects on gastric cancer cells. The IC50 values for Orientin were 24.33 μM in AGS cells and 39.28 μM in HGC-27 cells, indicating dose-dependent inhibition. Molecular docking studies predicted strong binding affinities, with Orientin docking to CDK2 at -9.1 kcal/mol, CCNA2 at -7.5 kcal/mol, CCNE1 at -7.2 kcal/mol, and CCNE2 at -8.3 kcal/mol. This inhibition translated into a promotion of G0/G1 phase arrest in GC cells.

Orientin significantly enhanced senescence-associated β-galactosidase staining intensity, indicative of induced cellular senescence. Furthermore, Orientin upregulated the expression of tumor suppressor proteins p16 and p21, while concomitantly downregulating phosphorylated retinoblastoma (p-Rb) and the expression of CDK2, CCNA2, CCNE1, and CCNE2. In the in vivo model, Orientin also suppressed tumor progression, mirroring the in vitro findings by promoting p16 and p21 expression and inhibiting CCNE/CCNA-CDK2 signaling.