# Recent Progress and Challenges Regarding Magnetic-Based Nanoparticles for Targeted Drug Delivery
### Assumptions of Targeted Drug Delivery Systems
In many cases, such a reaction is generated by the increased concentration of glutathione, often observed in cancer cells, which is the basis for the design of target carriers sensitive to this factor. On the other hand, enzyme-responsive DDSs require a component sensitive to a specific enzyme present in a targeted location. Nanocarriers constitute a particular group of DDSs, as they allow for reducing the dose of drugs, increasing the therapeutic response, or combining highly targeted with prolonged and sustained release. Typical nanocarriers include nanoparticles, nanospheres, nanocapsules, nanofibers, carbon nanotubes, nanoemulsions, hydrogels, liposomes, exosomes, micelles, or dendrimers. Nanocarriers containing magnetite nanoparticles can also occur in various forms. These nanosystems primarily consist of a magnetite core and organic units/shells, defining their intended application in biomedicine [13]. However, Fe\({}_{3}\)O\({}_{4}\) NPs can also be located inside liposomes, micelles, hydrogels, mesoporous silica, or dendrimers [23]. In hydrogels, magnetite NPs and active agents (drugs) are dispersed in polymers. The drug release occurs upon contact with water, but the process can be supported by exposition to alternating magnetic field or NIR laser irradiation. Dendrimers(e.g., polyamidoamine, PAMAM) with three-dimensional structures are composed of repeating monomers. The structure develops as a tree from the core and contains reactive functional groups at the terminal. On the other hand, micelles with lipophilic core could be used for entrapment of magnetite NPs loaded with hydrophobic drugs. External stimuli (AMF, temperature) force the release of the drug from such systems. In turn, liposomes with a lipid bilayer can be used for the entrapment of drug-loaded Fe\({}_{3}\)O\({}_{4}\) NPs. This procedure is applied to eliminate poor drug encapsulation efficiency and thermal disruption of micelles. Additionally, mesoporous silica is also often used to load drugs into its pores. The combination of high efficiency of drug encapsulation in silica with the properties of the magnetic core allows for more effective targeting and control of drug release by external factors. Targeted delivery mainly applies to drugs used in cancer treatment due to the high toxicity of the active substances to both cancer and healthy cells. However, the clinical use of a given system may be significantly limited by its toxicity [24]. Moreover, poor knowledge of their interactions with cells has primarily contributed to the failure of clinical trials conducted so far with their participation [25]. Each year, scientists provide research results on materials based on magnetite nanoparticles for potential use as drug delivery systems in cancer therapy. Based on the Scopus database, since 2015, the number of original articles in this area has been at least 100 (Figure 1). Upon reviewing the most recent literature reports (2021-2023), it is evident that research areas can be categorized into various subgroups. Much attention is still paid to the design of new nanocarriers; hence, many original papers emphasize synthesis procedures, while research aimed at application in cancer therapy is less advanced. On the other hand, numerous publications describe using magnetite-based systems carrying the active substance in treating a specific cancer. Crucially, many reports highlight multifunctional systems capable of performing functions beyond targeted drug delivery, such as those related to hyperthermia or magnetic resonance imaging. The current review aims to analyze the latest literature reports from the last three years (2021-2023) regarding possible progress in synthetic procedures and targeting new systems based on magnetite nanoparticles (MNPs) in treating specific cancers. Additionally, the focus is on advancements in employing various techniques to monitor the interactions of these nanocarriers with cells, bringing the potential for their use in clinical trials closer to realization.