Low-dose tetrandrine does not affect cell viability. Data are representative of values from at least three independent experiments. The MDA-MB-231, MCF-7, and Hela cancer cells, as well as immortalized nonmalignant cells HFF, were treated with rapamycin or tetrandrine alone for 24 hours. Cells were then counted using a hemocytometer with trypan blue staining. Cell viability was calculated based on the proportion of cells without trypan blue staining compared to the total number of cells. DMSO treatment was used as a control.