Manilkara zapota (L.) P. Royen Leaf Extract Derived Silver Nanoparticles Induce Apoptosis in Human Colorectal Carcinoma Cells Without Affecting Human Lymphocytes or Erythrocytes

Plant-derived synthesis of silver nanoparticles (AgNPs) has found wide biomedical applications including cancer cure. This report deals with biosynthesis of silver nanoparticles (MZLAgNPs) employing leaf extracts of Manilkara zapota (L.) under optimized conditions. Characterization of MZLAgNPs using UV-Vis spectroscopy, FTIR, XRD, and FESEM analyses revealed that the particles were predominantly spherical averaging 24 nm in size. Their cellular effects were assessed by MTT assay, fluorescence, and scanning electron microscopy of cells stained with propidium iodide, acridine orange/ethidium bromide, and annexin V-FITC to visualize signs of apoptosis. Evaluation of cell proliferation by clonogenic assay, wound healing ability by scratch assay and cell cycle distribution by flow-cytometry was also carried out. Apoptosis-related gene expressions were analyzed by RTq-PCR and western blot analysis. MZLAgNPs selectively inhibited growth of colorectal carcinoma HCT116, HeLa, and non-small lung carcinoma A549 cells, dose-dependently with IC 50 concentrations of 8, 16, and 29 μg/mL respectively, following 72-h treatment, without affecting growth of normal human lymphocytes and erythrocytes. Apoptosis induction was observed by fluorescence and scanning electron microscopy. Overproduction of reactive oxygen species (ROS), reduction of mitochondrial membrane potential, upregulation of apoptotic-related genes - PUMA, cas-3, cas-8, cas-9, and BAX, expression of caspase 3, and occurrence of PARP cleavage were observed in MZLAgNPs/cisplatin treated cells. Taken together, our results clearly demonstrate the therapeutic potential of biogenic MZLAgNPs as an effective agent for killing colorectal carcinoma cells by apoptosis induction.