Abstract
Here, the various types of naturally synthesized metallic nanoparticles, which are essentially composed of Ce, Ag, Au, Pt, Pd, Cu, Ni, Se, Fe, or their oxides, are presented, based on a literature analysis. The synthesis methods used to obtain them most often involve the reduction of metallic ions by biological materials or organisms, i.e., essentially plant extracts, yeasts, fungus, and bacteria. The anti-tumor activity of these nanoparticles has been demonstrated on different cancer lines. They rely on various mechanisms of action, such as heat, the release of chemotherapeutic drugs under a pH variation, nanoparticle excitation by radiation, or apoptotic tumor cell death. Among these natural metallic nanoparticles, one type, which consists of iron oxide nanoparticles produced by magnetotactic bacteria called magnetosomes, has been purified to remove endotoxins and abide by pharmacological regulations. It has been tested in vivo for anti-tumor efficacy. For that, purified and stabilized magnetosomes were injected in intracranial mouse glioblastoma tumors and repeatedly heated under the application of an alternating magnetic field, leading to the full disappearance of these tumors. As a whole, the results presented in the literature form a strong basis for pursuing the efforts towards the use of natural metallic nanoparticles for cancer treatment first pre-clinically and then clinically.
Highlights
Many studies have reported the potential of metallic nanoparticles (NP) of different compositions, e.g., Pt, Pd, Au, Fe, Ag, Ni, Cu, Se, or their oxides, for cancer treatments, through various mechanisms of action, such as the local production of heat [1], controlled drug release [2], or an enhancement of the effect of radiation [3]
Whereas anti-tumor activity of the majority of natural metallic NP was assessed in vitro, in vivo anti-tumor efficacy was demonstrated with magnetosomes, which are iron oxide nanoparticles that are synthesized by magnetotactic bacteria
The anti-tumor activity of metallic NP composed of Ni/NiO2 [64,65], ZnO [66], Ag [67], Au [68,69,70], iron oxide [71], and Se [35] has been demonstrated on liver, colon, breast, skin, and hepatoma cancer cells [35,65,66,67,68,69,70,71,72], highlighting the potential of these bio-synthesized metallic NP for the treatment of various cancers
Summary
Many studies have reported the potential of metallic nanoparticles (NP) of different compositions, e.g., Pt, Pd, Au, Fe, Ag, Ni, Cu, Se, or their oxides, for cancer treatments, through various mechanisms of action, such as the local production of heat [1], controlled drug release [2], or an enhancement of the effect of radiation [3]. Most of them report results that are obtained with nanoparticles that were chemically synthesized using methods, such as precipitation, sonication, ball milling, thermal decomposition, spray pyrolysis, thermal hydrolysis, and sol–gel [4,5] These chemical syntheses suffer from drawbacks, such as the uses of toxic solvents/reagents, high temperature/pressure, or additives needing to be added for metallic NP stabilization during the reaction of metallic NP formation. The methods of nanoparticle chemical synthesis are not always reproducible, i.e., the same nanoparticle parameters, such as nanoparticle sizes, distributions in sizes, geometry, shapes, cannot always be obtained from one batch to another This is rarely described in the literature, such variations can be due to the use of containers made of different materials or with different volumes or to local changes in temperatures or pressures at the nanometer scale that are not observable with standard sensors [6]. It was shown that the administration of magnetosomes inside intracranial GBM mouse tumors followed by the repetitive heating of these tumors under alternating magnetic field application leads to full tumor disappearance
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