Table 2.

Examples of recently developed metal-based drug delivery systems for cancer therapy.

Material	Morphology	Carried Drug	Properties	Results	Ref.
Gold	PEG-modified nanospheres (with Arg-Gly-Asp (RGD) peptide as targeting agent)	L-asparaginase	▪Average size: 29.24 ± 5.38 nm	▪NPs improved drug bioavailability and anticancer activity ▪Significant antioxidant effects ▪High tumor-targeting efficacy and distribution in MCF-7 cells ▪Initiation of apoptosis and promotion of cell cycle arrest at the G2/M ▪Upregulated pro-apoptotic p53, while downregulating antiapoptotic Bcl-2	[131]
Silver	Nanospheres	Paclitaxel	▪Average size: ~10 nm	▪Nontoxic to noncancerous HUVEC cells ▪More effective than paclitaxel alone in all tested cells (i.e., MDA-MB-231, MCF-7, 4T1, Saos-2) ▪Saos-2 cells were ~10 times more sensitive to paclitaxel-bonded Ag NPs that to the bare drug	[132]
Silver	Nanospheres (coated with starch)	Euphorbia dracunculoides Lam. (EDL) plant extract	▪Average size: 42.5 ± 1.54 nm ▪Loading capacity: up to 82.5% ▪Encapsulation efficiency: up to 85% ▪Zeta potential: −29.64 ± 0.09 mV	▪The surface modification increased biocompatibility ▪pH-triggered drug release ▪Enhanced antioxidant potential ▪Accumulation in cancer cells and induction of early and late apoptosis in RAW264.7 and SCC7 cells	[133]
Magnetite	Nanospheres (coated with polyvinyl alcohol-zinc/aluminum-layered double hydroxide)	Sorafenib	▪Average size: ~95 nm ▪Saturation magnetization: 57 emu/g ▪Remanent magnetization: 2.706 emu/g	▪No cytotoxicity against 3T3 fibroblasts ▪More potent than bare drug against HepG2 liver cancer cells ▪The drug was more easily released under an acidic environment	[134]
Magnetite	Nanospheres (surface modified with Pluronic F127 and branched polyethylenimine)	Doxorubicin	▪Size range: 10–20 nm ▪Zeta potential: −20.5–4.87 mV ▪Saturation magnetization: 54.5–65.5 emu/g	▪pH-/thermo-responsive drug delivery system ▪Sufficient magnetic strength to allow navigation towards the desired site ▪Enhanced the therapeutic effect of the drug	[135]
Maghemite	Hollow nanospheres (functionalized with polyethylene glycol)	Doxorubicin	▪Average hydrodynamic size: ~175 nm ▪Specific surface area: 266.1 m2/g ▪Saturation magnetization: 16.3 emu/g	▪Highly sensitive to alternating magnetic field and pH ▪Precise drug release to desired tissues	[136]
Nickel oxide	Honeycomb-structured nanoparticles (coated with folic acid-decorated polydopamine)	Quercetin	▪Average size: 35 nm ▪Average pore volume: 0.312 cm3/g ▪Average pore size: 11.44 nm ▪Loading capacity: up to 51% ▪Encapsulation efficiency: 51%	▪Surface modification increased biocompatibility and reduced hemolysis ▪Highly controlled drug release in physiological system compared to TME ▪Strong anticancer activity at very low concentration ▪Cytotoxic effects against Vero cells and MDA-MB-231 in a dose-dependent manner	[137]
Zinc oxide	Hexagonal shaped nanoparticles	Quercetin	▪Average size: 21–39 nm	▪pH-dependent drug-release, with higher releasing rate in acidic medium ▪Stable under physiological pH, indicating that the nanosystem can be retained in the blood stream up to particular time point without causing considerable side effects ▪High biocompatibility with 3T3-L1 cells ▪Effective inhibition of breast cancer cells (MCF-7) growth	[138]
Cobalt ferrite	Polygonal nanoparticles (coated with chitosan)	Doxorubicin	▪Average size: 38 nm ▪Saturation magnetization: 50 emu/g ▪Drug loading: up to ~89%	▪Excellent biocompatibility ▪Non-toxic nanosystem ▪High drug-release at the pH of cancer tissue ▪Good cell death rates in breast cancer cell line MCF-7 cells	[139]
Copper oxide	Nanospheres (coated with bovine serum albumin)	Methotrexate	▪Average size: 23.78 ± 1.52 nm ▪Loading efficiency: 8.70 ± 2.11%	▪Significant cytotoxicity against MDA-MB-231 cell line ▪Faster drug release in the presence of proteinase K enzyme	[140]