Cancer is described as a group of disorders entailing abnormal cell growth with the ability to spread to other organs and tissues in the body. Human lung cancers are divided into small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC), which originates from epithelial cells. NSCLC is very heterogeneous group of cancers and is composed of different histological subtypes including mainly squamous-cell carcinoma, large-cell carcinoma, and adenocarcinoma [1]. Moreover, lung cancer is highly aggressive and challenging neoplasm, with an established 5-years survival rate under 20% ^[2][3][2,3]. At the same time, it should be mentioned that nearly 85% of all diagnosed lung cancers are covered with non-small cell lung cancer cases [4].

Although, currently used anti-cancer therapies including chemo- and radiotherapy have prolonged overall survival among patients, other challenges, such as metastasis and chemoresistance, emerged. These are, up until no, one of the biggest clinical problems that are receiving great attention regarding clinical oncology ^[5][6][5,6]. Currently, the treatment of choice in case of NSCLC is radical surgery; however, only 20–25% of diagnosed patients were allowed to be treated with surgical approaches [7]. Adjuvant cisplatin-based chemotherapy is the gold standard for fully resected NSCLC tumors [8]. At the same time, new generations of drugs that target a specific genes mutations or protein have been approved as personalized treatments in NSCLC patients [9].

A lack of early symptoms and effective early diagnostic methods results in a diagnosis of cancer often in an inoperable, advanced stage of the disease. Therefore, there is an urgent need for novel, effective diagnostic methods and therapies for lung cancer. Activating apoptotic cell death with anti-cancer drugs is one of the major approaches for killing cancer cells. Nevertheless, the efficiency of apoptosis induction in tumors is limited due to the acquired or intrinsic resistance of cancer cells relative to apoptosis ^[10][11][10,11]. Consequently, developing other forms of non-apoptotic cell death opens new therapeutic opportunities for eliminating cancer cells and limiting the survival of drug-resistant clones.

Regarding lung-cancer therapy, graphene was already considered as an attractive material for screening (biosensing) or direct anti-cancer treatment. An interesting approach was presented in a paper written by Chen et al. [12], in which graphene with silver particles was used to fabricate simple, highly sensitive and fast biosensor. This biosensor was calibrated to detect CYFRA21-1 gene of NSCLC patients and was successfully tested during clinical trials, proving that graphene can be considered as a material for the selective and sensitive detection of DNA. Hence, it is possible to introduce graphene-based sensors as an efficient tool for the early diagnosis of NSLC.

2. Ferroptosis

Reactive oxygen species (ROS) ^[13][14][15,16] along with excessive accumulation of iron is one of the ferroptosis pivotal mechanisms. It is worth underlining that ferroptosis is a newly defined programmed cell death process. It is recognized as an efficient mechanism to eliminate malignant cells. It plays an essential role in the inhibition of oncogenic processes by removing cells that are not able to keep nutrients in the environment or cells damaged by infection or stress [9]. Moreover, ferroptosis occurs together with defeated of repair system that are responsible for the removal of lipid peroxidation products in physiological homeostatic conditions. Contrary to healthy cells, cancer cells in majority lack repair systems, which means that they are more vulnerable to oxidative damage and, thus, ferroptosis. Nevertheless, the natural function of ferroptosis in physiological contexts is still not clear. There are some ideas that ferroptosis may serve as a normal tumor suppressive function, including the observation that tumor suppressors p53, fumarase, and BAP1 can drive ferroptosis under specific conditions, and that some negative regulators of ferroptosis, such as SLC7A11, GPX4, and NRF2 are overexpressed or activated in a diversity of tumors ^[15][16][17,18]. It is worth mentioning that ferroptosis can be responsible for a failure of different crucial organs, including, i.e., lungs, heart, or brain (Figure 1). For instance, one can find scientific articles describing ferroptosis-dependent neural diseases, including the following: cerebral stroke, Parkinson’s, or Alzheimer’s disease. Having this in mind, ferrotosis can be considered as an unwanted and dangerous factor affecting human health. However, if properly designed and controlled (using nanomaterial-based approach), it can be also be a useful tool for targeted anticancer remedies. It is well known that tumor cell death is the most desirable effect of any cancer therapy. However, similarly to what was mentioned earlier, available anticancer drugs directed to kill cancer cells through apoptosis have limited effects since acquired resistance to apoptosis occurs ^[17][19]. Therefore, the main goal of ferroptosis-based therapy in cancer is to prevent treatment resistance. Unlike other forms of cell death, ferroptosis is iron- and ROS-dependent. To date, several mechanisms on which ferroptosis can act in tumor cells have been indicated. Researchers described in great detail how the resistance to targeted cancer therapy could be reversed by inducing ferroptosis through iron and lipid metabolism pathways, as well as other signaling pathways. A perfect example of new ferroptosis-based therapeutic strategy in NSCLC is the overcoming of cisplatin resistance within NF-E2 related factor 2 (Nrf2)/light chain of System xc−(xCT) pathway given by Yu Li et al. ^[18][20]. Moreover, it has been recently presented that the inhibition of ferroptosis is engaged in cancer immunotherapy by anti-programmed cell death 1 (PD-1)/programmed death-ligand 1 (PD-L1) treatment resistance [9]. Off these efforts, nanotechnology-based methods are especially remarkable, given their theragnostic approaches. Understanding the specific mechanism of ferroptosis and its relationship with lung cancer could provide significant references regarding cancer therapy ^[20][21][22][22,23,24]. It is well accepted that the occurrence of ferroptosis is iron-dependent and it can be assumed that, i.e., thoughtfully designed graphene oxide ^[23][24][25,26] (very promising 2D carbon-based materials for possible biomedical application) modifications with iron can be used as a new system to induce ferroptosis. Such tailor-made graphene oxide-Fe (graphene oxide-iron) composite could be a good option to induce and further study not only ferroptosis but other molecular changes in cancer cells after extracellular Fe intake. Graphene-based nanomaterials such as as a ferroptosis-inducing agents were already considered by other authors, who paid special attention to graphene quantum dots (GQDs). GQDs are quantum dots smaller than 20 nm and composed of carbon atoms. Two types of GQDs were studied by Wu et al. ^[25][27], namely amino-functionalized and nitrogen-doped graphene dots. The authors concluded that nitrogen-doped GQDs induced ferroptosis by mitochondrial oxidative stress. This phenomenon was associated with the disruption of a morphology of mitochondria, which was additionally translated to redox imbalance and iron overload. Further investigation performed by the same research team bore fruit in the form of even more detailed descriptions of GQDs-triggered ferroptosis mechanism ^[26][28]. The authors stated that key factors responsible for graphene quantum dots ferroptic action is the disruption of calcium homeostasis in microglia. Interestingly, BV2 (microglial cell line) cells exposed to amino-functionalized GQDs were less prone to oxidative stress, which indicate that the surface modification of graphene-based materials can be of crucial importance for triggering specific cellular responses. Understanding the entry mechanism of graphene derivatives relative to cells would be significant for the evaluation of its interaction within cells and further clinical application. Endocytosis, an energy-dependent mechanism, is known to be the entry mechanism of graphene ^[27][29]. Experimental studies have suggested that, due to GO 2D structure, it could be taken up by cancer cells via clathrin-mediated endocytosis (Figure 2). However, another hypothesis is that graphene-based materials are able to penetrate and disrupt the cell membrane mostly thanks to their sharp edges (acting as nano-sized knifes) ^[28][30]. Such nano-knife can damage cell membrane and cause the leakage of phospholipids from cell body. A huge number of scientific publications were written in order to address the biomedical application of graphene family materials, and to date, contradictory arguments are present in this discussion ^{[27][29][30][31]}[29,31,32,33]. The possible explanation could be that the current state of knowledge and scientific tools are not sufficient to fully understand and describe complex biological interactions occurring on the graphene–living cell interface.

3. Nanomaterial Based Ferroptosis Inducers in NSCLC

A literature analysis of ferroptosis inducers (including small molecules and nanomaterials) is presented to define their design, action mechanisms, and anticancer applications; however, there are still many questions about mechanisms governing the killing activity of cancer cells through ferroptosis and its implications at molecular levels. The mechanisms of action of apoptosis or necroptosis are reliant on caspases or can be inhibited by their activity. It should be mentioned that ferroptosis appears to have advanced independent and very little known yet direct molecular cross-talk to other pathways of regulated cell death ^[32][34]. Specially designed nanomaterials (NMs) are known to be able to penetrate the human body through respiratory systems, oral ingestion, or a skin. Furthermore, NMs are capable to cross the plasma membrane in order to start cell death processes. Nanoparticles are considered as a novel ferroptosis inducer with possible therapeutic effects in a wide range of cancer types, including NSCLC. It is widely known that the distraction of cell-death homeostasis is related to various diseases, including neurodegenerative diseases, immune disorders, diabetes, and cancer. Available data indicate that iron- or iron-oxide-based NMs can be considered as a good approach to study ferroptosis and its implications in cancer. Mechanisms of iron-based NPs and non-iron NPs for ferroptosis-based cancer therapy are similar. Both types of NPs can be incorporated into cells through endocytosis and release iron in lysosomes. Furthermore, they can be involved in the Fenton reaction to produce reactive oxygen species (ROS) and, as a consequence, induce ferroptosis. Moreover, the drugs carried by nanoparticles can facilitate the production of ROS, which is caused by excess iron. β-lapachone (β-lap), a novel anticancer drug, has shown significant cancer specificity by increasing (ROS) stress in cancer cells. A 10-fold increase in ROS stress was detected in β-lap-exposed cells pretreated with iron oxide nanoparticle over cells treated with β-lap alone in A549 cells, which also correlates with significantly increased cell death ^[33][35]. Regardless of the nanomaterials’ size and origin, the overriding conclusion drawn by the authors of the manuscripts provided in Table 1 was that this theranostic approach is very promising. The results of their work clearly showed that nanomaterials can be implemented as an efficient tool for anticancer therapy. Interestingly, different types of cancer models were investigated, including inter alia breast, lung, colorectal, cervical, pancreatic, colon, and leukemia. All of the cited publications underlined that the utilization of nanoparticles enabled the triggering of ferroptosis. Hence, it can be hypothesized that nanomaterials can be considered as a future cancer remedy. However, a lot of work still has to be performed in order to fully understand and describe underlying ferroptosis mechanisms activated by nanomaterials.