Physalin A interferes with cell cycle in human oral squamous carcinoma cells via DNA topoisomerase II/ATM/ATR/Chk signaling for G2/M phase arrest.

In recent years, oral squamous cell carcinoma (OSCC) has been a clinically aggressive disease with a high mortality rate and recurrence/metastasis rate of 45.7% of patients. Physalin A (PA), a natural withanolide isolated from Physalis angulata, inhibits cell proliferation in OSCC. In this study, we analyze one of the anticancer mechanisms of PA in vitro using OSCC cell lines. Experimental results showed that PA decreased cell viability, induced DNA damage, and increased cleaved PARP and γ-H2AX levels in HSC-3 cells. PA-induced G2-M cell cycle arrests and decreased Cyclin A, B1, D1, E, and CDK1, 2, but increased Chk1-p(ser317), Chk2-p(Thr68), p-p53, p-p21, and Wee1 protein expressions. PA decreased p-PI3k, p-Akt, p-TOR, topo IIα, topo IIβ, p-ATM, p-ATR, but increased γ-H2AX, cleaved PARP, Nrf2, HO-1, SOD1, and Catalase in HSC-3 cells. The protein-ligand docking models indicate that PA interferes with topoisomerase II alpha/beta (Topo IIα/β) and DNA, and with ataxia telangiectasia mutated/Ataxia telangiectasia and Rad3-related protein (ATM/ATR)- mediated DNA damage responses in HSC-3 cells. In animal experiments, we found that PA down-regulated hyperplasia, dysplasia, papilloma formation, invasion, mitoses, and epidermal layer thickness. In summary, PA binds to human DNA Topoisomerase IIα/β, then induces Topo/ATM/ATR/CHK signaling pathways, which cleave PARP and γ-H2AX, leading to p-p53 activation and cell cycle arrest at the G2/M phase in HSC-3 cells. It is suggested that PA could develop a novel therapeutic agent against OSCC cells in the future.