## 1 Introduction
We used the polyol method for synthesizing ternary metallic alloy CoNiFe and CoNiZn NPs [17] because it is a significant technique for preparing well-defined NPs with controlled shape and size by managing the precipitation kinetics [18]. Polyol solvents used in the synthesis of these NPs possess a high dielectric constant. Furthermore, it is known that ternary metallic alloy CoNiFe and CoNiZn NPs can elicit synergistic effects due to hybrid characteristics, such as photocatalytic properties and super-magnetism [19]. To the best of our knowledge, there are no data in the literature regarding the cytotoxicity of CoNiFe and CoNiZn NPs in cancer cells. Few works have been conducted to explore the advantages and consequences of CoNiFe and CoNiZn nanoparticles on normal and cancer cell lines for potential use in hyperthermia and electrocatalysis [20]. In fact, CoNiFe and CoNiZn NPs are involved in efficient, targeted killing of cancer cells and theranostics via induction of self-controlled hyperthermia using non-invasive techniques [20]. These ternary metallic alloys are potential thermoseeds, the surface of which can be modified to prevent dissolution, early phagocytosis, and toxicity, as well as to improve the intensity of fluorescent emitted signal and the affinity for target-specific tumor genomic sites with great flexibility [21]. Ternary metallic alloys are also highly effective in killing the cancerous as well as bacterial cells via utilizing their cytotoxic effects. In this regard, biologically synthesized ternary nanoformulation proved to be of greater potential to inhibit cancer cells better than raw plant ingredients or binary AgNPs. The beneficial effects of growth inhibition can be contributed towards the enhanced stabilization and targeted action [22; 23]. Ternary metallic alloys nanocomposite consisting of titanate nanotube (TNT)/CuFe\({}_{2}\)O\({}_{4}\)/Zn-Fe MMO were investigated for their treatment efficacy and cytotoxicity potential. It was concluded that these ternary alloys resulted in increased cellular uptake and followed a receptor-independent delivery mechanism for entrance. Moreover, the intracellular distribution of the tested nanocomposite and the potential toxicity of the tested ternary nanocomposite was dose- and time-dependent, reflecting increased cellular uptake. All these features of the TNT/CuFe\({}_{2}\)O\({}_{4}\)/Zn-Fe were basically proposed to induce cytotoxicity against cancer cells in prostate cancer [22]. As a useful model for in vitro cancer researches, MCF-7 cells have been considered as the first hormone-responding breast cancer cell line and have been widely studied because they retained numerous ideal characteristics particular to the mammary epithelium, including the processing of estrogen, in the form of estradiol, by means of estrogen receptors located in the cell cytoplasm [24]. On the other hand, the human umbilical vein endothelial cells (HUVECs) are commonly used for pharmacological and physiological studies (e.g., angiogenesis, fibrinolysis, macromolecule transport, and blood coagulation). Furthermore, HUVECs were previously used to examine the therapeutic efficacy of modified cationic nanocarriers [25], silicon microparticles [26], and magnetic NPs [27]. Therefore, MCF7 and HUVEC cells are useful in vitro models for cytotoxicity assessments. The current work investigates the potential in vitro toxicity of CoNiFe and CoNiZn NPs on different cell types.