Metal materials have been used in radiotherapy research for decades. In a pioneering study by Regulla in 1998, it was observed that mouse embryonic fibroblasts irradiated with X-rays on a gold surface exhibited increased biological effects compared to those in a tissue-like environment (9). Further research by Herold et al. revealed enhanced radiation effects in cancer cells with gold particles (10). By 2010, T. Marques et al. demonstrated that gold nanoparticles (GNPs) in tissues could selectively increase radiation doses to target areas, illustrating the potential of metals in refining radiotherapy (11).

Cuihong Wang et al. were the first to use thio-glucose-bound gold nanoparticles (Glu-GNPs) on NSCLC cells. They found that glucose enhances the uptake of Glu-GNPs by A549 cells, leading to their accumulation in vesicular endosomes or lysosomes. Upon X-ray exposure, Glu-GNPs triggered cell apoptosis through the modulation of Bcl-2 family proteins and activation of the mitochondrial apoptotic pathway (12). Tao Li’s team also worked with Glu-GNPs in A549 cells, achieving sensitization enhancement ratios (SER) of 1.41 and 1.15 for 160 kV and 6 MV X-rays, respectively (13). Shokouhozaman’s research indicated increased inhibitory effects of Glu-GNPs on QU-DB lung cancer cells by 64.4% and 32.4% under 100 kV and 6 MV X-rays (14). These findings proposed that Glu-GNPs may possess superior efficacy in combating NSCLC cells under conditions of low-energy radiation. However, the substantiation of these claims is somewhat feeble, primarily due to the omission of in vivo experiments by the researchers.

Additionally, GNPs have demonstrated potential in impeding the migratory capabilities of A549 cells post-radiation therapy, perhaps as a result of alterations in the cytoskeleton affecting overall cellular adhesion (15). Nevertheless, it would behoove the research to consider testing a broader range of dosages, extending beyond the used levels of 2Gy and 5Gy. Moreover, albumin-bound GNPs, known for their favorable biosafety profile, exhibited radiosensitization and anti-tumor activity both in vivo and in vitro experiments, boasting a SER of 1.432 (16). The study could be strengthened by incorporating more tumor models beyond A549 for validation. Zhongli Cai’s team found that the dose enhancement ratio of GNPs was lower in 3D culture models compared to single-monolayer (1.3 vs 1.6) (17). Sherif et al. argued that the common algorithm for calculating the dose enhancement ratio is overly simplistic and fails to consider specific profiles, leading to a decrease in the dose enhancement ratio due to potential rupture and detachment of GNPs’ surface coating (18). Therefore, optimizing the surface coating of GNPs was crucial, although it would certainly be better if the models were more closely aligned with the actual lung environment.

Fatma et al. modified GNPs with Schiff bases derived from galactose, resulting in larger particles that showed greater radiosensitization in A549 cells compared to unmodified GNPs (19). Arvind’s study compared 3.9 and 37.4 nm GNPs in Lewis lung cancer cells, finding significant radiosensitizing effects post-X-ray irradiation with both sizes, but no significant difference between them (20). Both studies might benefit from the inclusion of animal experiments and a broader spectrum of radiotherapy dose configurations.

Table 1 summarizes researches on GNP combined with radiotherapy in NSCLC. These researches are extensive, indicating that particle size, coating, and surface modifiers significantly influence their radiosensitizing effect. Future studies are needed to optimize these factors for better clinical application.

Chemotherapy remains a cornerstone in the treatment of NSCLC and various other cancers. Agents such as platinum, paclitaxel, and pemetrexed have shown to augment radiotherapy’s effectiveness through diverse mechanisms. For instance, cisplatin disrupts the ATM pathway crucial for repairing cellular damage caused by irradiation (47). Paclitaxel (PTX) orchestrates NSCLC cells to pause at the radiosensitive G2/M phase (48), while pemetrexed impedes nucleotide precursor synthesis, impacting DNA repair (49). Nanotechnology’s advent has pioneered the encapsulation and delivery of these radiosensitizing chemotherapeutics directly into lung tumors, forging a novel and synergistic approach in chemotherapy-radiotherapy treatments.

PTX, known for its poor water solubility, is traditionally dissolved in polyoxyethylated castor oil, a substance linked to allergic reactions and neurotoxicity (50). In 2006, T Negishi and team leveraged NK105, a micellar nanoparticle formulation of PTX, in mice inoculated with Lewis cells. Administering this formulation followed by X-ray irradiation led to enhanced efficacy compared to conventional PTX, notably inducing a higher rate of tumor cell arrest in the G2/M phase (51). The experimental group setup in this study was quite reasonable. However, in the absence of in-vitro experiments to determine the IC50 of NK105, directly using a dose of 45 mg kg⁻¹ in vivo might not be quite suitable. Genexol-PM, another micellar formulation of paclitaxel free from polyoxyethylated castor oil, mirrored NK105’s antitumor effects and radiosensitization properties (52). The study would be improved by incorporating a group that was solely treated with the drugs. Exploring further, Wheemoon et al. developed LOXab NPs by fusing LOX antibodies with PTX, yielding a highly targeted approach against A549 cells, resulting in increased apoptosis and radiosensitization (53). Despite the unirradiated tumor sites not presenting a remarkable abscopal effect, the study which utilized a model of tumors implanted on both sides of mice was well-designed. Additionally, the FDA has approved an albumin-bound form of paclitaxel for NSCLC’s frontline treatment, which will be described in detail in later sections.

In the realm of platinum-based treatments, platinum nanoparticles, particularly those of cisplatin-NPs and carboplatin-NPs, are garnering significant attention. Y Hao and his colleagues observed that cisplatin-NPs and carboplatin-NPs, when administered via inhalation, concentrate more effectively in lung tumors, enhancing radiotherapy’s synergistic effects while minimizing normal tissue toxicity (54). Utilizing liposomes, nanoscale drug carriers, coupled with EGFR antibodies and cisplatin, showed promising results in targeting mouse A549 xenograft tumors and boosting radiosensitivity (55). Joseph et al. crafted cisplatin precursor nanoparticles through alkali-catalyzed sol-gel polymerization and modified them with polyethylene glycol (PEG) to evade mononuclear phagocytic system uptake, resulting in superior performance in vivo and in vitro (56). Maofan Zhang et al. synthesized PEG-PLGA NPs encapsulating etoposide and cisplatin, achieving significant SERs (1.6 and 1.65) in 344SQ and H460 cells without added toxicity (57). Ling-Yu Chen and his team developed albumin-based cisplatin-gold nanoparticles (Au-cisplatin NPs), demonstrating remarkable superiority in tumor control and anti-tumor immunity when combined with radiotherapy (58). The aforementioned five studies each possessed their unique attributes, including features such as inhalation drug delivery and liposome encapsulation. Apart from the first study which did not undertake a safety evaluation, the remaining investigations enhanced efficacy without amplifying toxicity, representing particular value in terms of clinical application utility.

Gemcitabine, a first-line therapy for advanced NSCLC, saw innovation through Ji Liu et al.’s work, who attached RGDc peptides to lipid GNPs loaded with gemcitabine. Activated by near-infrared light, this combination hindered tumor growth and bolstered radiosensitivity by facilitating ROS production in NSCLC cells (59). For advanced NSCLC, doxorubicin (DOX) serves as a second-line treatment. Jing Wang et al. prepared epidermal growth factor-modified adriamycin nanoparticles (EGF@DOX-NPs), targeting cells overexpressing EGFR, significantly heightening A549 cells’ radiosensitivity both in vitro and in vivo (60). Recognizing the high expression of Glucose-regulated protein 78 on NSCLC surfaces, Abhay et al. employed Glucose-regulated protein 78 targeting peptides with DOX liposomes, enhancing drug delivery efficiency and markedly improving radiotherapy efficacy in both A549 and H460 cells (61). These three studies also boasted robust designs. Their future exploration lies in the field of in-situ tumor studies.

There is Table 5 summarizing nano-radiosensitizers loaded with FDA approved chemotherapy drugs in NSCLC.

Olaparib, an FDA-approved poly (ADP-ribose) polymerase inhibitor, plays a pivotal role in inhibiting poly (ADP-ribose) polymerase, essential for repairing radiation-induced DNA damage. It’s widely recognized for its efficacy in treating ovarian, breast, pancreatic cancer and various other cancers (62–64). Min Wu and colleagues innovatively synthesized Olaparib-NPs, which demonstrated a significantly higher SER of 3.81 in A549 cells compared to free Ola’s 1.66, without introducing additional toxicity (65). Similarily, if in-situ tumor research was conducted, it could make their studies more intriguing.

Curcumin (Cum), known for its antitumor properties in lung cancer, faces challenges in clinical use due to low solubility and bioavailability. Overcoming this, Cum-NPs, made by encapsulating Cum with polyvinylpyrrolidone-polycaprolactone, significantly enhanced apoptosis in A549 cells compared to free Cum, thereby enhancing the efficacy of radiotherapy (with a SER at 10% cell survival of 1.55 versus 1.13) (66).

Cannabinoids, active compounds in cannabis, are able to inhibit tumor growth. Wilfred and his team attached cannabinoids to ‘nanoparticle drones’ using gold nanoparticles, targeting lung tumors in a transgenic mouse NSCLC model. Administered by inhalation, these drones improved radiosensitivity while minimizing side effects (67).

Maytansinoid DM1, an alkaloid with cancer-fighting properties linked to maytansine, has been further optimized by Shi Gao’s group. They nitrosylated DM1 to produce DM1-NO and then loaded it onto PLGA-βPEG nanoparticles, creating DM1-NO PLGA-NPs that targeted NSCLC effectively. X-ray irradiation breaks the drug’s S-N bond, releasing DM1 and nitric oxide (NO), which interacts with ROS to form free radicals and block cells in the G2/M phase, enhancing radiosensitizing effect on H1299 cells (68).

Baicalein, an active anticancer agent derived from Scutellaria baicalensis, suffers from low bioavailability. This challenge was addressed by formulating it into solid lipid NPs. Applied to A549 cells, solid lipid NPs increased ROS and apoptosis, sensitizing them to radiotherapy, while also providing radioprotection in normal cells (69).

Absolutely, natural anti-tumor substances extracted from plants in nature have advantages such as being inexpensive and readily available. Figuring out how to better deliver them to tumors, enhance anti-tumor effects, and reduce toxic side effects presents a significant area of research. The studies above have provided good examples.

Presented below is Table 6 , summarizing nano-radiosensitizers that encapsulate FDA-approved chemotherapy drugs for various tumor treatments and natural anti-tumor compounds.

Jinghui Zhang’s team discovered that H1299 cells, which survived repeated X-ray irradiation, exhibit high expression of ALDH1 and CD133 proteins. Notably, in the ALDH1⁺ CD133⁺ NSCLC cell subset, miR-21 and miR-95 levels were significantly elevated compared to the ALDH1^- CD133^- group. Addressing this, the researchers used calcium carbonate nanoparticles to deliver anti-miR21 and anti-miR95 to NSCLC cells. This approach markedly inhibited tumor growth and enhanced radiosensitivity in H1299 cells, potentially by upregulating PTEN, SNX1, and SGPP1, while concurrently suppressing the PI3K-Akt pathway (70).

The overexpression of the MUC1-C subunit, commonly found in NSCLC tumors, led Alexandre et al. to develop MUC1-C antibody-conjugated Gd-based nanoparticles. These nanoparticles achieved a SER of 1.86 in H460 cells and showed prolonged retention in tumor models, boosting the effectiveness of fractionated radiotherapy (71).

Specificity protein 1 (SP1), often overexpressed in NSCLC, was targeted by GNPs-siSP1, comprising siSP1 and gold nanoparticles. GNPs-siSP1, easily internalized by A549 cells, reduced SP1 expression, upregulated granzyme B, and arrested cells in the G2/M phase, thereby enhancing radiosensitivity with SERs of 2.09 and 2.13 at 10 nM and 20 nM concentrations, respectively (72).

KRAS is a member of the human Ras gene family, with KRAS mutations present in 20% -25% of NSCLCs. Linlin Yang et al. engineered EGFR_apt-3WJ-siKRAS^G12C nanoparticles targeting KRAS mutations, effectively reducing KRAS^G12C expression in H2122, H2030, and H1299 cells. This innovation inhibited the downstream MAPK pathway and amplified the tumor-suppressive impact of radiotherapy (73).

HPNAS-4 has been recognized as a pro-apoptotic gene. When plasmids carrying the HPNAS-4 gene were delivered to NSCLC cells using liposomes, there was a notable overexpression of the hPNAS-4 protein. This led to increased apoptosis in A549 and Lewis cells, significantly enhancing the efficacy of radiotherapy (74).

In another study, Chang’s team developed plasmids that combined radiation-responsive Egr1 promoters with hypoxia-responsive enhancers. These plasmids, when introduced into A549 cells via liposomes, triggered the overexpression of the pro-apoptotic protein Smac. This intervention promoted apoptosis and caused G2/M phase arrest in the cells, ultimately improving the radiosensitivity of A549 cells under hypoxic conditions (75).

Nowadays, people can initially select the research targets by screening the genes that are differentially expressed in normal tissues and tumor tissues from the public database. How to further screen the preliminary data to pinpoint the specific molecules and design rigorous experiments around them is a topic worthy of deep investigation.

Table 7 presents an overview of nano-radiosensitizers encapsulating drugs specifically aimed at targeting highly expressed biomarkers or genes in NSCLC.

The exceptional targeting and loading capacity of nanoparticles allow for the efficient delivery of increased drug quantities to tumors. Jyothi et al. developed multifunctional dual drug loaded nanoparticles, encapsulating the DNA-PK inhibitor NU7441 and gemcitabine in superparamagnetic iron oxide nanoparticles, and augmented them with folate for targeting folate receptors, which are overexpressed in various cancers, including NSCLC. These folate-coupled MDNPs demonstrated prolonged retention in NSCLC compared to their uncoupled counterparts. Upon reaching tumors, multifunctional dual drug loaded nanoparticles underwent vesicle-mediated endocytosis, releasing their contents in the acidic environment of endosomes or lysosomes, thereby exerting cytotoxic effects and enhancing the radiosensitivity of A549 and H460 cells (76). Roshni and his colleagues co-loaded NU7441 and cisplatin into nanoparticles, attaching them to antibodies targeting the Ephrin receptor A2, prevalent in NSCLC. These Ephrin-coupled NPs significantly increased A549 cells’ radiosensitivity (77). Kin et al. crafted diblock copolymer nanoparticles for the sequential release of warfarin and docetaxel into H460 cells, which, when combined with radiotherapy, outperformed other treatment modalities (78).

Moataz’s team developed C-siPLK1-NPs carrying cetuximab, an EGFR-targeting monoclonal antibody, and siPLK1, an siRNA targeting the mitotic regulator PLK1. These nanoparticles effectively targeted A549 and H460 cells, reduced PLK1 expression, induced G2/M blockade, and acted as radiosensitizers (79). Shuzhen Chen et al. utilized Fe₃O₄ magnetic NPs to carry SiBIRC5 and BIRC5 antisense oligodeoxynucleotides, addressing the upregulated anti-apoptotic protein BIRC5 in NSCLC. These magnetic NPs enhanced drug uptake in A549 and H460 cells, diminished BIRC5 expression, and increased death receptor 5 expression, thereby improving radiotherapy’s therapeutic effect. Moreover, Magnetic field guidance further amplified drug enrichment in tumors (80). Jinghua Han’s team engineered nanoparticles loaded with DOX and 5-aminolevulinic acid, a radiosensitizer, coupled with a neurotensin receptor 1 ligand to target neurotensin receptor 1-high-expressing H1299 cells. The acidic tumor environment triggered DOX release for cytotoxic impact, while 5-aminolevulinic acid targeted mitochondria, enhancing radiation-induced oxidative stress and the overall efficacy of radiation therapy in treating H1299 cells (81).

Packaging two types of drugs into nanoparticles, one being an FDA-approved chemotherapy drug and the other a radiosensitizer, has become the choice of many researchers. On the basis of guaranteeing precision in tumor targeting and releasing medications in the optimal order, this approach is capable of amalgamating traditional drugs, consequently contributing to a more efficacious anti-cancer impact.

XIAP, an inhibitor of apoptotic protease-3, plays a crucial role in cellular apoptosis. By using liposomes to transport siXIAP into both p53 wild-type and mutant H1299 cells, researchers significantly enhanced radiosensitivity, particularly in p53-mutant cells (82). This study also lacked in vivo experiments.

Survivin, known as a radioresistance factor, can be counteracted by mS-T34A, a plasmid that prevents survivin from binding to activated caspase-9. Qing-Zhong’s team used liposomes to create Lip-mS, effectively increasing cell apoptosis, inhibiting tumor angiogenesis, and enhancing radiosensitivity in Lewis cells (83).

The DNA double-strand repair inhibitor KU55933, known for inhibiting DNA double-strand break repair in H460 cells, saw improved radiosensitizing effects when loaded onto nano-lipid polymers by Xi Tian and his colleagues (84).

Radiotherapy of primary tumors in concert with immunoadjuvants can lead to regression of tumors out of the radiation field, which is called as abscopal effect (85). Yao Hao et al. used biodegradable nanopolymers encapsulated with anti-CD40 antibody to significantly enhance radiotherapy’s effect in Lewis cells, slowing tumor growth both within and outside irradiated fields and improving mice survival (86).

All three studies mentioned above were deficient in drug safety evaluations. There was room for enhancement in this area.

Lonidamine, an oxidative phosphorylation inhibitor, was innovatively combined with mitochondria-targeted triphenylphosphine cation and encapsulated in liposomes by Saijun Wang’s team to form TPP- Lonidamine@Lip, which activated AMP-dependent protein kinase through oxidative phosphorylation inhibition, reduced PD-L1 expression, and bolstered anti-tumor immunity. Additionally, it reversed tumor hypoxia, making A549 cells more radiosensitive (87). While this research was quite comprehensive, it would be more beneficial if an in-situ tumor model was utilized.

Presented below, Table 8 enumerates various nano-radiosensitizers designed to carry other types of drugs or multiple drugs.

Wensha Yang and his colleagues utilized polyethylene glycol-coated, amine-functionalized semiconductor nanocrystals (QDs), which, under X-ray irradiation, excited photons to activate photosensitizers. Applied to H460 cells, these QD-photosensitizer conjugates, in conjunction with radiotherapy, were more effective in cell destruction compared to other treatments (88).

Jun Ma’s team developed Ce6/PTX 2-NP/G@NHs, polymer nanoparticles composed of the paclitaxel prodrug and photosensitizer Ce6. These nanoparticles were readily uptaken by NSCLC cells, with Ce6 promoting ROS production and creating a hypoxic environment under laser irradiation. This induced PTX release, directly killing cancer cells and inactivating the PI3K/AKT pathway. As a result, the nanoparticles increased apoptosis in A549 cells, especially when combined with radiotherapy (89).

Cypate (Cyp), an indocyanine green derivative, generates heat under near-infrared light irradiation. Cyp-polymethylmethacrylic acid-Fe@MSCs, comprising polymethylmethacrylic acid nanoparticles loaded with iron and Cyp, encapsulated in mesenchymal stem cell membranes, were more effective in targeting Lewis cells, leading to significant tumor shrinkage under laser and X-ray irradiation (90).

Magnetic nanoparticle clusters (MNCs), wrapped with polyacrylic acid for biocompatibility, generated heat in an alternating magnetic field and were used for cancer thermotherapy. Jia Ma et al. found that MNCs-treated H460 cells showed increased expression of Hsp70 and caspase-3 under alternating magnetic field and radiotherapy, significantly suppressing tumors more than other treatments (91).

Mn-Zn ferrite magnetic nanoparticles, similar to MNCs, were integrated into PEG-β-PCL block copolymer micelles and modified with hyaluronic acid targeting A549 cells. In tumors, Mn-Zn ferrite magnetic NPs not only generated heat, but also raised oxygenation levels under alternating magnetic field, thereby enhancing A549 cells’ radiosensitivity (92).

Tsl-MTX, comprising 1-methylxanthine and temperature-sensitive liposomes, released its contents upon local heating of tumors, achieving pronounced tumor regression, particularly when combined with radiotherapy (93).

Yun Hu’s team explored the potential of hafnium oxide nanoparticles NBTXR3 in an anti-PD1 resistant lung cancer model 344SQR. Only the group receiving NBTXR3 with high and low-dose irradiation (12Gy*3F and 1Gy*2F) plus immunotherapy (anti-PD1 and anti-CTLA-4) exhibited significant CD8⁺ T cell/Treg cell ratio improvement and tumor regression, highlighting NBTXR3’s synergy with radiation and immunotherapy (94). In further studies, combining NBTXR3 with radiotherapy and inhibitors of TIGIT and LAG3, the team demonstrated a significantly enhanced treatment effect, supporting the clinical translation of NBTXR3 (95).

Ying Wang et al. found that cisplatin-loaded nanoparticles induced CXCL10 secretion in tumors. Post-irradiation, there was increased CD8⁺ T cell infiltration in both irradiated and unirradiated tumors. Combining this with anti-PD1 therapy resulted in significantly greater tumor regression, illustrating cisplatin-loaded NPs’ role in boosting anti-tumor immunity post-radiotherapy and achieving an abscopal effect (96).

Leveraging nanotechnology to enhance radiation sensitization, and pairing it with phototherapy or thermotherapy could significantly improve the tumor-targeting ability and anti-cancer efficacy of drugs. Moreover, immunotherapy has emerged as one of the most promising research fields in oncology in recent years, suggesting that boosting anti-cancer immunity holds substantial potential for exploration. By integrating the use of nanomedicine, it allows us to combine differing methods of cancer treatment, thus offering profound clinical implications.

Presented next is Table 9 , showcasing nano-radiosensitizers that are employed in combination with radiotherapy plus phototherapy, thermotherapy, or immunotherapy.