Bavachinin Induces G2/M Cell Cycle Arrest and Apoptosis via the ATM/ATR Signaling Pathway in Human Small Cell Lung Cancer and Shows an Antitumor Effect in the Xenograft Model

Lung cancer is grouped into small cell lung cancer (SCLC) and non-SCLC (NSCLC). SCLC exhibits a poor prognosis, and the current anticancer treatment remains unsatisfactory. Bavachinin, present in the seed of Psoralea corylifolia, shows anti-inflammatory effects, immune modulation, and anticancer potency. This study aims to investigate the antitumor effect of bavachinin on SCLC and its underlying mechanism. The SCLC cell line H1688 was treated with different concentrations of bavachinin and showed decreased viability with arrested G2/M and sub-G1 phase cell accumulation at a concentration as low as 25 μM. Expression levels of caspase-3, -8, and -9, as well as Fas, FasL, and Bax, increased with the concentration of bavachinin. The accumulated sub-G1 cells and annexin V confirmed increasing apoptotic cancer cells after treatment. The accumulated G2/M phase cells with increasing levels of phosphorylated CDC25C, CDC2, ATM/ATR, and CHK2/CHK1 confirmed the arrested cell cycle caused by bavachinin via a dose-dependent manner. This phenomenon can be reversed by an ATM/ATR inhibitor, caffeine. Following the administration of bavachinin to xenograft mice with SCLC, the tumor burden decreased without impairing hematologic or hepatorenal functions. Bavachinin induces SCLC apoptosis via intrinsic and extrinsic pathways and causes cancer cell cycle arrest via the ATM/ATR signaling pathway.