Assessment of Rapamycin effect on apoptosis in MCF-7 breast cancer cell line

Background: Rapamycin was the first inhibitor of mTOR (mechanistic previously named mammalian target of rapamycin, also known as FRAP or RAFT 1) to be discovered and studied as a therapy for a wide variety of diseases. Since the phosphoinositide 3 kinase (PI3K)/Akt (protein kinase B) /mTOR (PAM) pathway is frequently activated/dysregulated in breast cancer, rapamycin was explored as an effective target therapy in breast cancer, however the mode of its action remains unclear, therefore our study aimed at understanding the antitumor effect of rapamycin, using MCF-7 breast cancer cells.
Methods: Trypan blue dye exclusion method and MTT assay were performed to determine the IC50 value of rapamycin. Trypan blue dye exclusion method was also used to determine cell growth in untreated versus rapamycin treated MCF-7 cells, these cells were examined for morphological changes using inverted phase microscope.
Results: Rapamycin showed inhibitory activity on MCF-7 cell line via cell growth inhibition as determined by the IC50 value. The IC50 value was determined as 75μg/ml measured by trypan blue dye exclusion method and confirmed by MTT assay. Treatment of MCF-7 cells with rapamycim at IC50 resulted in induction of apoptosis up to 41% as determined by both Annexin-V/Propidium iodide dual staining assay and flowcytometry. Direct examination by inverted phase microscope showed that MCF-7 cells treated with rapamycin at IC50 for 72 hrs. resulted in characteristic morphological changes in the form of cell shrinkage and loss of cell contacts, also the cells became rounded and some of them were floating in the medium.
Conclusions: This study demonstrated that rapamycin acts as an anticancer drug via inhibition of cell growth in a dose dependent manner as well as induction of apoptosis .However further studies are needed to characterize the mode of action of rapamycin as an anticancer agent