In recent years, the increasing cancer incidence and mortality rate has posed a significant challenge to scientists to develop novel therapeutic drugs against cancerous cells. One of the investigated techniques for cancer therapeutics is the green synthesis of nanoparticles (NPs). In this study, we reported the green synthesis and characterization of the CuFe2O4@Ag nanocomposite using Spirulina platensis and its cytotoxic activity on two cancer cell lines: human gastric adenocarcinoma (AGS) and Michigan Cancer Foundation-7 (MCF-7) breast cancer. The physical and chemical properties of the biosynthesized nanocomposite were characterized using Fourier-transform infrared spectroscopy, X-ray diffraction, energy-dispersive X-ray analysis, dynamic light scattering, ultraviolet–visible spectroscopy, scanning electron microscopy, transmission electron microscopy, and zeta potential analyses. The anticancer properties of the CuFe2O4@Ag nanocomposite and imatinib drug on both cancer cell lines were evaluated using 3-(4,5-dimethylthiazoyl-2-yl)2,5-diphenyltetrazoliumbromide (MTT) assay. Also, apoptosis induced by the nanocomposite was assessed using annexin V/propidium iodide staining followed by flow cytometry analysis, Hoechst 33432 staining, and caspase-3 activity assay. Finally, the effect of the CuFe2O4@Ag nanocomposite on the expression of BAX and BCL2 genes was assessed by real-time polymerase chain reaction. The result of the MTT test showed an increase in the cellular uptake of CuFe2O4@Ag nanocomposite and cell viability loss in a concentrationdependent manner with the 50% minimum inhibitory concentration (IC50) of 180 and 220 μg/ml for MCF-7 and AGS cell lines, respectively. The mean expression of BAX was significantly higher than that of BCL2 in cells treated with the nanocomposite. The results of flow cytometry, Hoechst 33432 staining, and caspase-3 activity assay indicated the stimulation of apoptosis through an increase in caspase-3 and nucleus fragmentation. In
