Stephanthraniline A (STA) is a C21 steroidal aglycone isolated from the stem of Stephanotis mucronata (Blanco) Merr. that exerts growth inhibition in human colon cancer cells. However, the intracellular molecular mechanisms whereby this occurs have not been well characterized. In this study, we found that STA significantly inhibits the growth of HCT116 colon cancer cells in a time- and concentration-dependent manner. The inhibitory effect of STA on cell growth was related to the induction of apoptosis. Activated caspase-3, caspase-8 and caspase-9, along with a decreased Bcl-2/Bcl-x ratio and loss of mitochondrial membrane potential (Δψm), were observed in response to STA treatment. Furthermore, treatment of HCT116 cells with STA resulted in G0/G1 phase cell cycle arrest accompanied by decreased mRNA levels of cyclin-dependent kinase 4 (CDK4), p21 and c-myc. Additionally, the inhibition of Akt signaling and activation of p38 signaling were observed after treatment with STA in HCT116 cells. These findings indicate that STA inhibits HCT116 cell growth by promoting apoptosis, the dysregulation of mitochondrial function, and cell cycle arrest.
Keywords: Apoptosis; C21 steroidal aglycone; Cell cycle arrest; Colon cancer.