Green synthesized plant mediated zinc oxide nanoparticles as potential nano phytotherapeutic agents for reactive oxygen species driven anticancer activity in HepG2 liver cancer cells

Green nanotechnology has emerged as a promising approach for the sustainable synthesis of metal oxide nanoparticles with potential applications in cancer therapy. In this study, aqueous extracts of Galinsoga parviflora (GP), Ageratum conyzoides (AC), and Argemone mexicana (AM) were employed as green agents for the biosynthesis of zinc oxide nanoparticles (ZnO-NPs). Characterization confirmed the formation of phase-pure, crystalline ZnO-NPs with a hexagonal wurtzite structure and predominantly spherical morphology. The mean particle sizes were 12.33 ± 5.58 nm (GP-ZnO), 12.05 ± 4.51 nm (AM-ZnO), and 10.32 ± 1.98 nm (AC-ZnO), with the overall observed size range of 5–36 nm. Zeta potentials ranging from −8.2 to −8.6 mV indicated weak electrostatic stabilization and a tendency for some aggregation, as observed in FE-SEM images. FT-IR confirmed ZnO formation with residual surface-associated plant-derived constituents, while XRD exhibited characteristic reflections corresponding to the (100), (002), (101), (102), (103), (110), and (112) crystal planes of wurtzite ZnO. The biosynthesized ZnO-NPs demonstrated favorable biocompatibility, exhibiting minimal haemolysis and negligible cytotoxicity against normal THLE-2 liver cells. GP-ZnO, AM-ZnO, and AC-ZnO-NPs exhibited concentration-dependent cytotoxicity against HepG2 carcinoma cells, with IC 50 values of 60.25 ± 3.2, 68.35 ± 3.4, and 74.15 ± 2.6 μg/mL, respectively. Treatment markedly enhanced intracellular ROS and Annexin V + cells, with GP-ZnO and AM-ZnO-NPs inducing 59.71% and 57.40% Annexin V + cells, respectively, against 50.05% for Doxorubicin (Dox). Despite lower ROS levels than Dox, their higher apoptotic fractions suggest ROS-independent mechanisms may contribute to cytotoxicity. However, lack of PI staining prevented differentiation between late apoptosis and necrosis. Overall, plant-mediated ZnO-NPs show promise as sustainable candidates for further in vivo investigation and translational development in liver cancer nanotherapy.