Exploring lung cancer microenvironment: pathways and nanoparticle-based therapies

Abstract

Lung cancer stands out as a significant global health burden, with staggering incidence and mortality rates primarily linked to smoking and environmental carcinogens. The tumor microenvironment (TME) emerges as a critical determinant of cancer progression and treatment outcomes, comprising a complex interplay of cells, signaling molecules, and extracellular matrix. Through a comprehensive literature review, we elucidate current research trends and therapeutic prospects, aiming to advance our understanding of TME modulation strategies and their clinical implications for lung cancer treatment. Dysregulated immune responses within the TME can facilitate tumor evasion, limiting the efficacy of immune checkpoint inhibitors (ICI). Consequently, TME modulation strategies have become potential avenues to enhance therapeutic responses. However, conventional TME-targeted therapies often face challenges. In contrast, nanoparticle (NP)-based therapies offer promising prospects for improved drug delivery and reduced toxicity, leveraging the enhanced permeability and retention (EPR) effect. Despite NP design and delivery advancements, obstacles like poor tumor cell uptake and off-target effects persist, necessitating further optimization. This review underscores the pivotal role of TME in lung cancer management, emphasizing the synergistic potential of immunotherapy and nano-therapy.

Background

According to current projections, lung cancer stands as the leading cause of cancer-related deaths, with an estimated 2.2 million cases diagnosed alongside 1.8 million deaths in 2020. It is estimated that smoking causes 90% of lung cancer cases, with cigarette smoke, air pollution, and various other carcinogens serving as determinants. Nonetheless, the specific processes are not fully known [1, 2]. Tumors are clusters of cancerous cells that disrupt and degrade the functionality and health of various other cells in the body. Both malignant and benign cells impact cancer progression, which can result in poor health and death [3].

Tumor microenvironment (TME) is an increasingly salient component in advancing cancer therapy, either as a source of predictive characteristics to guide therapy or as a therapeutic target in its own right. It comprises a diverse community of cancer and immune cells, signaling mediators, stroma, vasculature, and extracellular matrix (ECM) [4]. Lung cancer patients may have altered or deviated immune cell differentiation due to the existence of a chronic inflammatory milieu. This might lead to a contrast in anti-tumor activity, favoring tumor evasion and eventual suppression of immune checkpoint inhibitors (ICI). In this situation, TME may be a useful source of ICI prognostic biomarkers and a possible target for cutting-edge treatment approaches [5].

TME modulation techniques targeting extracellular interactions between ligands and receptors and downstream mechanisms can increase treatment effectiveness and create long-lasting responses [6, 7]. TME-modulated drugs have demonstrated tentative efficacy in tumor treatment. However, not all people benefit from these medications. There are still several obstacles that targeted anti-cancer medications confront, such as drug resistance, limited efficiency, and high cost, despite the substantial progress that has been gained. To cope with them, several tactics have been employed, including new-generation medications combating drug resistance mutations, combination treatments, multi-target therapies, and drugs targeting cancer stem cells [8, 9]. Furthermore, many individuals have encountered side effects, including gastrointestinal, arthritis, dermatitis, endocrine and hematologic diseases, neuropathy, and acute renal damage [10–12]. In comparison to these medications, nanoparticles (NPs) can increase retention duration and provide targeted distribution, lowering toxicity. Furthermore, NPs might transform the immunosuppressive milieu in TME into an immuno-supportive condition by targeting its key components [13]. They can be administered to tumor, extending the retention duration of transported medications. Because of the leaky vasculature and impaired lymphatic outflow, the enhanced permeability and retention effect (EPR) causes them to collect considerably more in tumors than in normal tissue [14]. Alternatively, modifying their architecture can improve their efficacy and compatibility. NPs, when conjugated with certain ligands, provide targeted delivery to the TME and modify the TME, thereby improving therapeutic effectiveness [15–17]. Nanoplatforms might be used with other treatments to transport multiple medications. Several nanostructures of various compositions, sizes, forms, and functionalities have been produced [18].

Despite considerable advances in reducing off-target adverse reactions [19], the clinical application of NP still confronts poor anti-tumor performance. The analysis of EPR is relatively simplistic since numerous biological processes in the systemic transport of NPs might alter the outcome [20]. The median effectiveness of the delivery of NPs into cancer cells is predicted to be about 0.7% of an administered dosage [21]. It might be difficult to identify the optimal endocytic pathway for specific targeting and to improve NP configuration to enhance absorption through that channel [22]. Another problem is identifying suitable targeting ligands unique to the intended cell type that do not cause immune reactions or toxicity. Even if the NP attaches to the intended cell with excellent selectivity and specificity, the internalization efficiency can also be swayed by the ligand density, shape, size, and surface charge of the NP [23]. In reality, NPs have a lengthy and rough voyage to reach cells in tumors.

Hence, this review aims to underscore the pivotal role of the tumor microenvironment (TME) in the management of lung cancer, particularly focusing on immunotherapy and nano-therapy. Moreover, it seeks to explore the intricate interplay of various relationships, processes, and cellular components within the TME.

Tumor microenvironment (TME)

The biological milieu wherein tumors or cancer stem cells thrive is called the tumor microenvironment (TME). The integrants of this complex include ECM and its degrading enzymes, vascular endothelial cells, immunological cells, tumor cells, and inflammatory and growth factors. It communicates with tumor cells through these, contributing significantly to the development and metastasis of tumors [24].

A developing TME is a complex, dynamic entity with a varied makeup [25]. Lord and co-workers initially suggested the TME. Using an in vitro tumor model, they confirmed the host cell’s impact on tumor [26]. The TME impacts tumor genesis, growth, and progression, and its mechanism is complicated. Cancer stem cells contribute to our knowledge of the TME but also provide important hurdles in cancer diagnosis and therapy. The malignant and non-malignant cell associations form a TME, influencing cancer growth and progression. Non-malignant cells frequently perform a pro-tumorigenic role at all stages of carcinogenesis by encouraging uncontrolled cell proliferation. In contrast, malignant cells infect healthy tissues and travel to other body areas via the circulatory or lymphatic system [3].

Tumor infiltrating lymphocytes (TILs), which were used to construct prediction aids for therapeutic response, was described in several studies as a characteristic of a TME. An independent predictor of a patient's survival is the presence of lymphocytes in the tumor region, with a higher degree of lymphocytic infiltration associated with a longer survival time [27, 28].

Clinical and epidemiological research have found a substantial link between persistent infections, inflammation, and cancer. Chronic inflammation is seen as an enhanced risk factor associated with cancer progression and prognosis, accounting for 15–20% of cancer deaths. The role of inflammation in the development and spread of cancer has been frequently underlined. It is acknowledged that inflammation assists in the many capacities of cancer by providing active chemicals and establishing the TME [29]. Research on non-small cell lung carcinoma (NSCLC) therapeutic targets has changed from researching cancer-cell autonomous capabilities to encompass the TME [30].

Lung cancer-tumor microenvironment relationship

It has been suggested that the tumor microenvironment is not just a silent bystander, but rather an active promoter of cancer progression” [25, 31]. Lung cancer has the greatest fatality rate among all cancer kinds. It is defined by the uncontrolled growth of cells inside the lung, most often epithelial cells [32]. Lung cancer may be classified into several types, the most common of which are small cell lung carcinoma (SCLC) and non-small cell lung carcinoma (NSCLC). NSCLC accounts for about 85% of identified lung tumors and is classified into three histological subtypes: lung adenocarcinomas (LUADs), lung squamous cell carcinomas (LUSCs), and large-cell lung carcinomas (LCLCs). While LUADs are assumed to form from tiny bronchi, bronchioles, or alveolar epithelial cells and are usually peripherally placed, LUSCs and SCLCs normally originate from the large bronchi and are centrally positioned. Each has distinct genetic, cellular, and epigenetic heterogeneity, resulting in patient-specific TMEs [33].

One important factor that influences the development of tumors is the TME. Based on the somatic cell composition, the immunological architecture, and the genetic makeup of the tumor, each person will have a unique microenvironment [33, 34]. Due to tissue scarcity, studies regarding NSCLC TME utilizing immunological and histological examinations of the underlying tumor have proven challenging because most patients are diagnosed with advanced conditions and are not candidates for surgery [5]. Understanding the interactions between the various TME components and malignant tumor cells is crucial to understanding the processes behind the advancement of cancer. The microenvironment is also crucial for cancer cells to acquire pleiotropic capacities via activated transcription factors. Because many bacterial metabolites have a role in the host's metabolism and signaling pathway control, alterations in bacterial-derived compounds caused by biological anomalies in the TME may impact both metabolic processes and oncogenic signaling in lung cancer cells. Antibiotic or probiotic aerosolization may alter the lung microbiota, and these changes are related to a reversal of the immunosuppression prevalent in TME [35, 36].

Cancer cells interact with the TME bidirectionally, activating both tumor and accessory stromal cells. These interactions are critical to cancer development. To build a favorable TME, tumor cells communicate with the milieu via a complicated network comprising numerous growth factors, cytokines, chemokines, and their own receptors [37]. Reports show that the modification of TME can diminish the progression of malignancies of the lungs in animal models and lung cancer patients [38, 39]

Tumor cells release a range of proteins, including growth factors and ECM-destroying proteinases, or they drive the host to produce elaborate biomolecules capable of degrading the matrix and its adhesion molecules. Tumor cells produce proteins in the ECM milieu that are important in adhesion to cells, motility, intercellular communication, and invasion. Secreted proteins are particularly interesting because they play a major role in a disease condition or the biological process leading to illness. Their discovery and characterization may help to gain insight into disease patterns [36]. The TME, which is commonly believed to be directly associated with the emergence and growth of tumors, has emerged as one of the fastest-growing fields of cancer research in recent years. It is currently a hot topic in cancer research.

Molecular pathogenesis of lung cancer

Early identification and efficient prevention are critical for minimizing lung cancer. However, numerous large-scale lung cancer chemoprevention measures have had poor, indifferent, or even hazardous outcomes [40, 41]. Initial identification of lung cancer is still in the development stage and is deemed unsatisfactory [42]. The deterrents are partly related to the lack of appropriate molecular targets for assessing the effectiveness of pharmaceuticals in clinical trials [40, 41, 43] and markers for early diagnosis of lesions [44, 45].

The several kinds of lung cancer result from separate and diverse biological pathways, as depicted in Fig. 1. The varied anatomical sites and suspected cells of the various kinds of lung cancer support this notion. There is evidence of multi-step cancer development in several organs, including the skin, lungs, and colon. Learning more about the initial phases of lung cancer pathophysiology can help us determine if the aggressive lung phenotype evolves multi-step or sequentially. The formation of the lung malignant phenotype appears to be caused by the accumulation and combination of genetic and epigenetic abnormalities and progressive, sequence-specific, and multi-stage molecular pathogenesis [33].

Fig. 1.

The different types of lung cancer, their subtypes and their associated main pathways of pathogenesis. Lung cancer is generally classified into NSCLC and SCLC. NSCLC is shown to have different manifestations, most importantly as LUAD and LUSC. The chief causative molecular pathways associated with LUAD are KRAS and EGFR, followed by LUSC related to VEGFR and SOX2. Subsequently, SCLC was also found to be linked to expression of TP53, RB1 and the Hedgehog pathway. Created with BioRender.com. NSCLC, Non-small cell lung carcinoma; SCLC, Small cell lung carcinoma; LUAD, Lung adenocarcinoma; SOX2, Sex-determining region Y-box 2; LUSC, Lung squamous cell carcinoma; KRAS, Kirsten rat sarcoma viral oncogene; TP53, Tumor protein p53; EGFR, Epidermal growth factor receptor; RB1, Retinoblastoma 1; VEGF, Vascular endothelial growth factor receptor

Molecular pathogenesis of lung adenocarcinoma (LUAD)

A vast number of reports implies that lung adenocarcinoma (LUAD) is caused by at least two molecular routes: the Kirsten rat sarcoma viral oncogene (KRAS) and the epidermal growth factor receptor (EGFR) pathways in smokers [46–48] and non-smokers [46, 49–51], respectively.

Atypical alveolar hyperplasia (AAH) is a morphological alteration associated with the development of LUADs, and it is widely agreed that the pathophysiology of many adenocarcinomas is poorly understood [33, 52]. Accumulating data currently clearly supports that surfactant protein C (SPC) articulating alveolar type II (AT2) cells, not clara cells, are the cells of the creation of LUADs [53, 54]. The shared molecular changes between LUADs and AAHs indicate that AAHs are pre-neoplastic lesions in LUAD development. AAH and adenocarcinoma in-situ (AIS) lesions have been shown to have high levels of NK2 homeobox 1 (NKX2-1), which is mostly seen in the terminal lung bronchioles and lung peripherals. NKX2-1 is widely acquired or amplified in LUAD, suggesting a cell-lineage-specific oncogenic role [33].

Around 10–30% of NSCLC patients have alterations in exons 18–21 of the EGFR gene [55]. AAH is also known to emerge from the bronchiolar epithelium and tiny bronchi due to the discovery of driver EGFR mutations in bronchioles close to EGFR mutant LUADs [56, 57]. Clinical and preclinical investigations have shown that the TME of NSCLC patients carrying EGFR alterations has unique properties that may affect the anti-tumor immune response. Preclinical research showed that EGFR mutations cause immune escape via the programmed death-ligand 1 (PD-1/PD-L1) pathway [58]. Mutations in EGFR affect TME components, including myeloid-derived suppressor cells (MDSCs), TILs, tumor-associated macrophages (TAMs), immunoregulatory cytokines, and regulatory T cells (Tregs) [59]. In NSCLC, EGFR activation increases PD-L1 expression, leading to T-cell death and immunological escape. In a genetically modified mouse model of lung cancer with an EGFR mutation, reduced major histocompatibility complex class II (MHC-II) expression, higher interleukin-1 receptor antagonist (IL1RA) expression, along with elevated macrophage phagocytic activity were reported and linked to the M2 macrophage phenotype [60]. An inflamed TME is thought to indicate a good immunotherapy response. Although EGFR-altered NSCLC is usually not linked with inflammatory TME, Tregs and PD-L1 expression levels are elevated in this malignancy [61]. This lowers T-cell functionality and stimulates TME, which favors immunological escape and the advancement of malignancy [60, 62]. The TME in EGFR-mutated tumors has substantial Treg infiltration but little CD8 + T-cell infiltration, blocked by IRF1-mediated C-X-C-motif chemokine ligand 10 (CXCL10) inhibition. In contrast, Treg infiltration is stimulated by JNK/-JUN-mediated CCL22 overexpression. Ultimately, within the EGFR-mutated NSCLC’s TME, significant Treg inroad exists in the setting of the non-inflammatory TME. As a result, EGFR alteration occupies an important role in cell proliferation, survival, and the emergence of immune escape [61].

The KRAS mutations are observed in over 35% of patients of the NSCLC subtype [63, 64], together with significant Treg infiltration, particularly the KRAS^G12D mutation [65]. KRAS mutations raise interleukin-6 (IL-6) levels via NF-κB, activating the signal transducer and activator of the transcription (STAT3) pathway and contributing to the formation of immune-suppressive myeloid-derived suppressor cells (MDSCs). Interestingly, IL-6 has been linked to a Treg/Th17 cell response. As a result, it may re-instruct the lung milieu toward an anti-inflammatory phenotype by macrophage polarization, MDSC induction, and Treg/Th17 boosting [39]. IL-10 has also attracted anti-inflammatory M2 macrophages and Tregs to the tumor [63]. Oncogenic KRAS has been shown in KRAS mutant lung cancer cells to stimulate PD-L1 by increasing PD-L1 mRNA stability via tristetraprolin (TTP). This is controlled via STAT3 and activator protein 1 (AP-1) [66]. A link amongst KRAS alterations increased CD8 + TILs, and PD-L1 expression indicated that KRAS mutations promote anti-inflammatory, immunosuppressive TME, and adaptive immune resistance [67]. Studies in lung cancer indicated that the co-mutation of KRAS and TP53 resulted in enhanced expression of PD-L1 [68].

Molecular pathogenesis of lung squamous cell carcinoma (LUSC)

Lung squamous cell carcinoma (LUSC) is assumed to develop through a series of epithelial transformations, including squamous metaplasia, dysplasia, and carcinoma in-situ (CIS), before progressing to invasive malignancy [69]. The basal cells are thought to serve as progenitors for LUSC [70].

Vascular endothelial growth factor receptors (VEGFR) and isoforms were reported to be higher in bronchial squamous lesions than in normal bronchial epithelia, reinforcing the hypothesis that angiogenesis starts early in lung cancer [71, 72]. The VEGF is not only associated with angiogenesis but also inhibits immune cells and causes immunosuppression in cancer. In NSCLC, an elevated level of VEGF-A and VEGFR-1 co-expression was observed and substantially correlated with the modification of EGFR in exon 21 [73]. Tumor-secreted factors such as VEGF-A, transforming growth factor (TGF-β), and tumor necrosis factor (TNF-α) promote the production of chemo-attractants like S100A9 and S100A8 in Mac1 + myeloid cells and lung endothelial cells [74, 75] that enhance the migration of tumor cells to the pre-metastatic areas by inducing serum amyloid A3 (SAA3). Of particular note, SAA3 activated NF-κB signaling in the macrophages through Toll-like receptor 4 (TLR4) and facilitated metastasis [76].

The sex-determining region Y-box 2 (SOX2) oncogene, which is increased in LUSCs, increases tumor survival through gene amplification [77]. SOX2 is classified as a lineage-specific oncogene since it causes several malignancies, including lung cancer, and guides tumor type to a basal-cell destiny. In a normal lung, SOX2 stimulates multiplication and preserves stem and basal cell integrity, whereas NKX2-1 determines the identity of alveolar cells. SOX2 shows conflicting expression patterns in the two main subtypes of NSCLC. It has been increased in ~ 21% and excessively expressed in > 80% of LUSCs but seldom expressed in LUAD [78]. Furthermore, it was discovered to promote the proliferation of lung tumor and to modulate the stemness in lung cancer stem cells [79, 80]. Notably, SOX2 increase was linked to clinical advancement of high-grade pre-invasive squamous lesions [81].

Molecular pathogenesis of small cell lung carcinoma (SCLC)

Currently, there exists no phenotypically recognizable pre-neoplastic lesion for SCLC. Compared to NSCLC, little has been discovered about SCLC's molecular pathogenesis. There was a considerably greater prevalence of epithelial changes near SCLCs than near NSCLCs [82]. SCLC can grow straight from histologically normal epithelium without going through a more complicated phase. Studies have shown that SCLC progression is operated by silencing of tumor protein p53 (TP53) and retinoblastoma gene (RB1) [83, 84] as well as by activation of the hedgehog pathway [85, 86]. In small cell lung cancer (SCLC), the tumor suppressor genes TP53 and RB1 are almost always inactivated, leading to the loss of key regulators p53 and Rb. This inactivation disrupts essential cell cycle checkpoints and the DNA damage repair pathway, allowing mutations to accumulate unchecked. Without TP53, cells fail to undergo apoptosis in response to DNA damage, while RB1 loss leads to uncontrolled cell proliferation. Together, these alterations promote genomic instability, fueling further oncogenic processes, rapid tumor evolution, and increased treatment resistance in SCLC [87]. Recently, various therapeutic candidates for SCLC have been found, including PARP1 [Poly (ADP-ribose) polymerase 1], DNA repair proteins [88, 89] and lysine demethylase 1 (LMD1) [90]. The functions of the changes and targets in SCLC’s premalignant and normal stages remain insufficiently clarified. In addition to de novo SCLC, there is transformed SCLC, which has comparable pathological appearance, molecular properties, clinical symptoms, and treatment sensitivity. However, de-novo and transformed SCLC have diverse pathophysiology and TMEs [91].

Approaches for the management of tumor microenvironment (TME) in preventing lung cancer

Studies on lung cancer from the standpoint of TME revealed a complicated picture in which tumor angiogenesis, soluble substances, immune suppressive/regulatory components, and TME cells all contribute to tumor progression. Because TME may significantly alter immune response via complicated pathways, its components are interesting targets for experimental therapies, as shown in Fig. 2. Current immuno-oncology research focuses on the connection of established ICI, like anti-PD-L1 and anti-CTLA-4 (cytotoxic T-lymphocyte–associated antigen 4) medicines, with experimental drugs, either deviated towards TME molecules or emerging immune checkpoints [5].

Fig. 2.

The various approaches for managing lung cancer targeting the TME. This figure illustrates the immunotherapeutic approaches and NPs in regulating the TME by negatively impacting its various molecular mechanisms. Created with BioRender.com. TME, Tumor microenvironment; NP, Nanoparticle

Targeting immune suppression

Several immunosuppressive processes govern the immune system, making them potential targets for novel therapies focusing on improving ICI function. Inflammatory and metabolic regulators and immunosuppressive cells in the TME, like Tregs and TAMs, all regulate these processes and pathways worldwide.

Inflammatory regulator manipulation

The NSCLC frequently expresses cyclooxygenase (COX)-2, essential for prostaglandin production and known to generate FoxP3 + Treg cells [92]. COX-2 targeting to decrease Treg cell growth and immunosuppression has been used in various studies. Unfortunately, the outcomes of many such experiments have not reached expectations [5]. Retrospective cohort research found that using COX inhibitors concurrently with ICI treatment for NSCLC patients enhanced their results regarding response and time to progression [93]. In a study, patients with NSCLC were treated with a bifunctional fusion protein that combines the TGF-β receptor II with an anti-PD-L1 to target TGF-β in conjunction with ICI [94].

Metabolic mediator manipulation

Metabolic mediators, like adenosine, tryptophan, and arginine, engaged in various immunoregulatory pathways, often with immunosuppression. Thus, the pathways comprising them constitute a prospective target for immunomodulating therapies. Treg and MDSC cells express CD39/CD73, which are considered possible targets for therapy [95]. Several ongoing clinical trials are investigating antibodies' effectiveness primarily targeting CD39 or CD73, combined with immune checkpoint inhibitors (ICI) or alongside chemotherapy. Notable examples include trials such as NCT04306900 and NCT03884556 [5]. According to the results of the COAST trial, the investigational combination of Durvalumab with Oleclumab (anti-CD73) outperformed Durvalumab alone in terms of both PFS (progression-free survival) and ORR (objective response rate) [96].

The MDSC and neutrophils create arginase, which depletes arginine from the TME. Arginine is necessary for optimum T cell activity, so inhibiting arginase in combination with ICI serves as a beneficial therapeutic strategy in cancer immunotherapy. INCB001158 is a novel arginase inhibitor investigated in a clinical study as a sole entity with ICI combination in advanced tumors [97].

Indoleamine 2,3‐dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase 2 (TDO2) facilitate the kynurenine pathway, which leads to the formation of dendritic cells and Treg through the tryptophan inhibition in TME, whilst the kynurenines exhibit lethality on cytotoxic T cells [98, 99]. Various unions of anti-PD-1 with IDO-1 inhibitors (such as NLG-919, BMS-986205, and Navoximod/GDC-0919), dual IDO/TDO inhibitors (like RG70099 and IOM-D), and Indoximod are undergoing clinical development. Prominent trials include NCT03322540, NCT02298153, and NCT03562871 [5].

Immunoregulatory cell manipulation

One approach to enhancing the immune response to tumors is to modulate immunoregulatory cells within the TME, specifically targeting immunosuppressive cells, either by directly controlling them or by inhibiting their growth. Given that Treg cells are commonly associated with resistance to ICI, there has been interest in exploring the targeting possibility of Treg alongside ICI. One proposed approach involves anti-CD25 (cluster of differentiation 25) antibodies to reduce Tregs in cancer. Preclinical investigations of ADCT-301/Camidanlumab Tesirine (anti-CD25) indicated that this drug would efficiently deplete Treg and cause immunogenic cell death while simultaneously increasing the amount of tumor-infiltrating CD8 + T effector cells [100].

Colony-stimulating factor-1 receptor (CSF1R) signaling enhances TAM mobilization and activation and is related to low numbers of cytotoxic cells, favoring an immunosuppressive microenvironment [101]. At the same time, CD40 enhances T-cell activation while encouraging a proinflammatory milieu, including macrophage polarization toward M1 [102]. Recently, the findings of a clinical trial employing Sotigalimab (CD40 agonist) and Cabiralizumab, a CSF1R inhibitor, were reported. The combination was widely tolerated, and the reported global outcomes urge additional investigation into combinations targeted to shift TME into a pro-inflammatory pattern [103].

Chemokine receptor type 4 (CCR4) can also be a viable therapeutic target. CCR4 is known to encourage Treg enrollment, promoting an immunosuppressive TME. Therefore, blocking CCR4 may cause Treg inhibiting and a return to an immunogenic milieu. In two preliminary phase trials, Mogamulizumab (anti-CCR4 antibody) was tested with anti-CTLA-4 or anti-PD-1/PD-L1. Chemokine receptor type 4 (CCR4) stimulates the Treg enrolment. So, inhibiting CCR4 may lead to Treg inhibiting and reversion to an immunogenic microenvironment [104, 105].

Immune checkpoints targeting

Numerous new immune checkpoints have been found recently, with lymphocyte activation gene 3 (LAG-3), T cell immunoglobulin and mucin-domain containing-3 (TIM-3), B7 Homolog 3 (B7-H3), and T-cell immunoreceptors with Ig and ITIM domains (TIGIT) emerging as promising molecules. LAG-3 targeting is being employed in NSCLC through a recombinant LAG-3. This recombinant LAG-3 stimulates dendritic cells via MHC class II molecules and elicits an immune response when combined with anti-PD-1 therapy (NCT03625323). Alternative strategies involve antibodies targeting both LAG-3 and PD-1 (NCT03219268; NCT04140500), as opposed to single-agent compounds (NCT03849469; NCT03250832) [5]. Relatlimab, an anti-LAG-3 antibody, has been evaluated in a randomized experiment wherein 714 patients with metastatic melanoma were randomly assigned either Nivolumab with Relatlimab or Nivolumab plus placebo. The median PFS was considerably extended in the combination than in the control [106].

In addition to CTL, natural killer cells (NK), and Treg, TIM-3 is expressed in macrophages and dendritic cells [107]. Monoclonal antibodies fixated on TIM-3, singly or combined with anti-PD-1, are implicated in several tumors (NCT02608268; NCT03652077). Furthermore, the antibodies that can bind to PD-1 and TIM-3 are being investigated in current trials, including NSCLC patients (NCT04931654; NCT03708328) [5]. In separate research, 33 patients (17 NSCLC and 16 melanoma) who were progressing following PD1/PD-L1 inhibition were given Spartalizumab (anti-PD-1) and MBG453 (anti-TIM-3). The combination was usually safe but had minimal effect [108]. Other findings suggest that the unified administration of TSR-022 (anti-TIM-3) with TSR-042 (anti-PD-1) has demonstrated efficacy in NSCLC, advancing on prior anti-PD-1 treatment [107]. Single-agent therapy with anti-TIM-3 agent LY3321367 produced > 20% tumor shrinkage in two individuals; one of these patients had SCLC, which was later verified to have a partial response [109].

The B7-H3 is a transmembrane protein that tumors often produce. It is thought to be an immune checkpoint molecule that tumors use to evade immune system identification. It was proposed that B7-H3 expression may contribute to NSCLC resistance to anti-PD-1/PD-L1 inhibition [110]. There are three clinical studies (NCT03729596; NCT02475213; NCT02381314) to evaluate the potential antibody use for targeting B7-H3 in conjunction with anti-CTLA-4 or anti-PD-1 in pre-treated cancers [5].

CD8 + and CD4 + T cells, NK, and Treg express TIGIT, suppressing innate and adaptive immunity [111]. Although TIGIT's exact mode of action is still unknown, it is known that the molecule binds CD155, blocking CD226—an immune activator receptor—and inhibiting the activity of NK and T cells. Moreover, TIGIT has been shown to promote the differentiation of M2 macrophages [112]. Tiraglobumab is now the most promising anti-TIGIT therapy for NSCLC. This medication has recently been assessed in the CITYSCAPE study in conjunction with Atezolizumab [113]. In 30 NSCLC patients who have already received treatment, a clinical study is presently being conducted to determine the safety and effectiveness of the combination of Domvanalimab (anti-TIGIT), Zimberelimab (anti-PD-1), and Etrumadenant (A2A and A2B adenosine receptor) (NCT04791839) [5]. This is an intriguing strategy to lessen immunological checkpoint-induced inhibition of T and NK cells and adenosine-mediated immunosuppression.

CAR T-cell therapy

Chimeric antigen receptor T-cell (CAR T-cell) therapy is a form of immunotherapy where T cells are genetically engineered using CARs to confer a particular tumor-killing capacity [114]. It turned out that chemokine (C–C motif) ligand 20 (CCL20) was a chemokine receptor 6 (CCR6) ligand. Therefore, CAR T-cells targeting the EGFR (epidermal growth factor receptor) and overexpressing CCR6 were more likely to traffic to LUAD cells due to their high production of CCL20 [115]. Cherkassky generated mesothelin-CAR-T cells lacking intracellular signaling domains using a dominant-negative PD-1 receptor in a study. In mesothelioma and lung cancer mice models, this receptor substantially increased the survival and anti-tumor activity of CAR-T cells by blocking PD-L1 or PD-L2 on tumor cells [116].

Targeting angiogenesis

Cancer therapies have predominantly relied on anti-angiogenic agents. Several compounds, including antibodies (Bevacizumab, Ramucirumab) and multi-targeted agents (Nintedanib, Sunitinib, and others) that are both active on angiogenesis and different molecular pathways, have been approved for use against multiple malignancies. Nowadays, acting on VEGF and its receptors is the foundation of anti-angiogenic molecules. A lot of interest has grown in the utilization of ICI and anti-angiogenic treatment combinations. An important challenge with this strategy is balancing while manipulating blood vessel development. Tumor cell-induced neo-angiogenesis is usually disordered and comprises twisted, disorganized blood vessels with high permeability. This leads to heightened interstitial fluid pressure and decreased perfusion and oxygenation. If this process is interfered with, blood circulation may briefly return to normal, promoting the influx of lymphocytes. However, when anti-angiogenesis effects continue, leucocytes find it harder to enter the tumor mass, which may decrease TILs [117]. In particular, elevated VEGF production has also been linked to increased immature dendritic cells, which support immunological tolerance and Treg. Moreover, VEGF may play a role in polarizing macrophages to an M2 phenotype [117, 118]. In a phase Ia/Ib study, the combination of Pembrolizumab and anti-VEGFR2 (Ramucirumab) was assessed in NSCLC patients [119]. In a randomized study, the unified dosage of Bevacizumab with Atezolizumab, Paclitaxel, and Carboplatin was investigated [120]. Another novel strategy focused on VEGF in NSCLC examined the potential curative benefit of AK112 (PD-1/VEGF bispecific antibody) [121].

Targeting cancer cell death

An intriguing treatment strategy is to inhibit the Poly (ADP-ribose) polymerases (PARPs), which would cause cell death when combined with ICI. Nevertheless, there are currently little published data on NSCLC. Pembrolizumab with Niraparib effectively treated NSCLC with high PD-L1 expression [122]. There is still a dearth of published data regarding PARP inhibitors and ICI, but several clinical trials are being conducted and might yield intriguing findings in the coming months. In patients with stage IV NSCLC who do not advance following a course of platinum-based chemotherapy plus Durvalumab, an ORION study (NCT03775486) is now assessing the safety and effectiveness of a regimen consisting of Durvalumab and Olaparib in comparison to Durvalumab alone. Other studies (NCT03976323, NCT03976362) also assess the combination of Olaparib and Pembrolizumab in NSCLC [5].

Nanoparticle-based therapies

Despite the initial effectiveness of immunotherapeutic medicines, their therapeutic benefits have been limited due to poor drug retention time in TME. Surgery, chemotherapy, and radiotherapy are the only remedies for advanced NSCLC, but they are substandard [123]. Lung carcinoma patients frequently develop resistance following targeted treatment, chemotherapy, and radiation. Although ICI treatment has improved lung cancer patients' survival rates, immune resistance and resistance to PD-1 blocking have been outlined, resulting in a lower immune response in patients [124]. So, new studies have begun to scrutinize lung cancer from the TME’s perspective and develop more therapeutic targets [125].

Compared with traditional drug delivery, nanoparticles (NPs) with unique properties and designs can efficiently penetrate TME and specifically deliver to the major elements in TME [15–17]. Nano-carriers have been modified to liberate the drug, increase its duration, and protect it from early deterioration [126]. The respiratory system is ideal for targeted medication delivery since it bypasses the first stage of metabolism and promotes fast therapeutic activity [127]. The development of NPs has opened new possibilities in drug delivery. Small size, large surface area, and ability to amend the surface properties are a few benefits of NPs in contrast to other delivery systems. The sustained release capability of NPs may assist in sustaining drug concentrations at tumor sites for longer durations [128, 129]. NPs facilitate a regulated drug release, reducing the dosage frequency and improving patient compliance [130]. A study by Yang et al. has summarized the major components of TME and the current targeted delivery of NPs to these components [131]. Figure 3 illustrates the benefits of nanoparticle-based therapy over conventional therapy in treating lung cancer focusing on the TME.

Fig. 3.

The benefits of NP-based therapy over conventional therapy in treating lung cancer focusing on the TME. The figure addresses how the different NPs used for lung cancer therapy contribute to improved drug delivery and better drug response than conventional therapy. These include targeted delivery, improved bioavailability, drug release regulation, increased retention of drugs and immunomodulation. Created with BioRender.com. TME Tumor microenvironment, NP Nanoparticle

A study on developing reduction-sensitive NPs for docetaxel (DTX) delivery to lung cancer focuses on the synthesis and characterization of cross-linked lipoic acid NPs (LANPs). The LANPs were designed to prevail over the limitations of conventional drug carriers and to enhance the anti-tumor potency of DTX. The reduction-sensitive drug release mechanism of LANPs in response to the TME, their cellular uptake, in vitro cytotoxicity, in vivo tumor targeting and anti-tumor efficacy have been highlighted. Key findings of the study include the efficient encapsulation of DTX by LANPs, a significant increase in intracellular DTX uptake, higher potency in inhibiting A549 cell growth, and increased tumor targeting and low toxicity anti-tumor efficacy in in-vivo experiments [132]. Another study was found on developing glutathione GSH-triggered NPs for targeted cancer therapy, specifically based on enhancing chemotherapy by reprogramming the TME. The NPs were designed to release the drug rapidly upon exposure to elevated GSH concentrations, mimicking the GSH gradient between neoplastic and healthy tissues. Additionally, the NPs featured a tumor-homing peptide for dual targeting of TAMs and tumor cells, resulting in enhanced cytotoxicity and tumor suppression [133]. Researchers synthesized some transition metal oxide (CuO, NiO, and Fe₂O₃) NPs and investigated their cytotoxic potential in a heterogeneous TME. They found that the NPs effectively compromised lung cancer cells’ cell viability in both normoxia and hypoxia. Additionally, they also demonstrated that ROS generation contributed to cellular toxicity in CuO, but not in NiO and Fe₂O₃. The study’s findings shed light on the potential of transition metal oxide NPs as therapeutic agents for lung cancer in both normoxic and hypoxic conditions [134]. The safety and effectiveness of some nanoparticle-based therapies in treating lung cancer with the association of TME have been highlighted in Table 1 by analyzing their particle size, and data about the possible mechanism of action for use as a treatment for lung cancer [132–155].

Table 1.

Effectiveness of nanoparticle-based therapies for lung cancer associated with regulation of the tumor microenvironment (TME)

Nanoparticles	Particle Size	Possible mechanism of action	References
Docetaxel loaded lipoic acid nanoparticles (DTX-LANPs)	110 nm	Reduction-sensitive drug release in the TME Caveolae-mediated endocytosis	[132]
Paclitaxel loaded GSH sensitive nanoparticles	100.17 ± 0.21 nm	Response to elevated GSH concentrations Dual targeting of TAMs and tumor cells	[133]
Transition metal oxide (CuO, NiO, Fe2O3) nanoparticles	< 100 nm	ROS generation, cell cycle arrest and caspase-independent programmed necrotic death PARP1 mediated apoptosis Cell cycle perturbations and programmed cell death in both normoxia and hypoxia	[134]
CLip-PC@CO-LC nanoparticles	193.6 ± 0.97 nm	pH-triggered charge-conversion Inhibition of glycolysis Prevention of microtubule depolymerisation	[135]
7C1 nanoparticles	50 nm	Activation of KRAS gene by siRNAs Stimulation of p53-related responses by miRNA34a	[136]
VEGF- siRNAs loaded magnetic mesoporous silica nanoparticles	~ 50 nm	Silencing of VEGF gene expression	[137]
Zero-valent-iron nanoparticles (ZVI-NP)	ZVI@Ag, 97.1 ± 19.3 nm; ZVI@CMC, 78.8 ± 19.8 nm	Degradation of Nrf2 by GSK3/β-TrCP through AMPK/mTOR activation Shifting of pro-tumor M2 macrophages to anti-tumor M1	[138]
Ce6- DOX (Doxorubicin)-GNCs- MMP2 polypeptide nanoparticles (CDGM NPs)	85.2 nm	Enhanced cellular uptake efficiency of DOX and Ce6 enabling the chemo photodynamic therapy	[139]
Manganese dioxide nanoparticles (MnO2 NPs)	15 nm	Tilting TAM polarization from the M2 phenotype to a tumor-inhibiting M1 phenotype Improving tumor oxygen level by reacting with endogenous hydrogen peroxide under hypoxic conditions Downregulation of HIF-1α and VEGF	[140]
Manganese dioxide nanoparticles (MnO2 NPs)	49.81 nm	GSH-responsive dissolution Enhanced MR imaging	[141]
LPT peptide-conjugated nanoparticles (LPT-NP-PTX)	112 nm	Functionalization with specific peptides, such as LinTT1 and TAT, to enhance affinity to TME	[142]
Di-iron hexacarbonyl compound loaded nanoparticles (FeCORM NPs)	∼ 60 nm	CDT and ICD-induced immunotherapy	[143]
Multi-walled carbon nanotube (MWNT) with iRGD-PEI-MWNT-SS-CD/pAT2 complexes	10–20 nm	RAS dysregulation by synergistic conduction of AT1R and AT2R pathway	[144]
siRNA-loaded PEGylated pSiNPs	110 nm	Downregulation of PKM2 mRNA and protein expression	[145]
SGT-53 nanocomplex	114.4 ± 8.4 nm	Sensitization of the anti-PD1 treatment	[146]
AZD1080 silicasomes	160.9 ± 6.3 nm	Reduction of PD1 expression and release of CD8 + T cells	[147]
Cisplatin nanoparticles (P-Cis)	14.40 nm	Promotion of the anti-PD1/PD-L1 blockade	[148]
D-peptide Au infinite covalent polymer cow milk extracellular vesicles (DPAICP@ME)	13.4 nm	Elevation of p53 activation Augmentation of anti-PD1 immunotherapy	[149]
Superparamagnetic iron oxide nanoparticles (SPIO NPs)	158.2 nm	Maintenance of the half-life of the anti-PD-L1 peptides T-cell reactivation and tumor growth inhibition	[150]
NBTXR3 nanoparticles	-	TME modulation involving regulation of the T cell receptor repertoire, increasing CD8 + T cells, and activating immunological signaling pathways Overcoming the anti-PD1 resistance	[151]
Antigen Release Agent and Checkpoint Inhibitor (ARAC)	90 nm	Volasertib and PD-L1 antibody effectiveness decreased due to CD8 + T cell modification Increased effect of PD-L1 inhibitors	[152]
Nanodiamond-polyglycerol-doxorubicin conjugates (Nano-DOX)	83.9 ± 32.3 nm	Enhancement of immunogenicity of tumor cells Reactivation of TAM into M1 phenotype via RAGE/ NF- κB regulation Induction of PD-L1 in tumor cells and TAMs	[153]
Met and SN38 self-assembled nanodrug (MS NPs)	50 nm	Improving immunotherapy by suppressing PD-L1 expression levels Retardation of tumor metastasis by enhancing immune surveillance and altering the ECM	[154]
Gold nano prisms (GNPs@PSS/PDADMAC-siRNA)	98.5 ± 4.6 nm	Inhibition of PD-L1 expression Serving as a photothermal agent for theranostic properties	[155]

TAM Tumor-associated macrophage, AT1R Angiotensin II type 1 receptor, HIF-1α Hypoxia-inducible factor-1α, AT2R Angiotensin II type 2 receptor; GSH Glutathione, Nrf2 Nuclear factor-E2-related factor 2, VEGF Vascular endothelial growth factor, DOX Doxorubicin, Ce6 Chlorin e6; PARP1 Poly (ADP-ribose) polymerase 1, PKM2 Pyruvate kinase M2, RAS Renin-angiotensin system, CDT Chemodynamic therapy, ICD Immunogenic cell death, MR Magnetic resonance, PD-L1 Programmed death-ligand 1, RAGE Receptor for advanced glycation end-products, ROS Reactive oxygen species, KRAS Kirsten rat sarcoma viral oncogene, siRNA Small interfering RNA, ECM Extracellular matrix, NF- κB Nuclear factor kappa B, AMPK Adenosine monophosphate-activated protein kinase, mTOR Mammalian target of rapamycin, miRNA34a MicroRNA 34a, GSK3 Glycogen synthase kinase-3, β-TrCP Beta-transducin repeat-containing protein, LinTT1 Linear TT1, TAT Trans-activator of transcription

Exosomes, small extracellular vesicles derived from various cell types, hold unique properties that make them promising tools for lung cancer diagnosis and treatment. They have the potential to carry therapeutic cargo such as chemotherapeutic pharmaceuticals, siRNAs, and immune-modulating agents directly to cancerous cells, thanks to their ability to cross biological barriers. Furthermore, modified exosomes containing specific targeting molecules exhibit a precise delivery pathway to cancer cells while limiting off-target effects. Notably, exosomes, which contain a wide range of components including proteins, nucleic acids, and metabolites, are an excellent source of biomarkers. Evaluating the contents of exosomes, particularly the genetic alterations, microRNAs, and proteins, helps unravel the molecular profiles of lung cancers and aids in diagnosis. Moreover, stem cell-derived exosomes are known to have anti-inflammatory, immunomodulatory, and antifibrotic capabilities, which have the potential to be used in the treatment of numerous inflammatory and chronic respiratory disorders [156, 157]

Modulation strategies to overcome the barriers in the tumor microenvironment

To a large extent, drug delivery using NPs is impeded by tumor heterogeneity, including atypical vasculature, stiff ECM, excessively generated glutathione (GSH), hypoxia, acidic pH, immune suppression, and their association with the TME [13, 158]. Some TME properties, like high interstitial solid and fluid pressure, can impede drug delivery to deep tumor areas for NP-mediated anticancer treatment. In contrast, some TME features, like hypoxia and acidity, might impair the anti-tumor impact and potentially cause drug tolerance and metastasis [159]. To give improved insight into future pharmaceutical administration directions, a thorough understanding of the developing TME is required. To increase the movement efficiency and therapeutic value of NPs in TME, the biological barriers—such as abnormal vasculature, rigid ECM, acidic pH, hypoxia, irregular enzyme levels, changed metabolic pathway, and immunosuppression—must be addressed [101]. In this regard, we present an overview of a few potential ways for modulating the TME, as explained in Fig. 4.

Fig. 4.

The strategies to best the barriers in the TME and improve the drug delivery process. Great improvement has been made in TME-targeting drug delivery utilizing the modulation methods, especially the feasible aspects like remodeling of vasculature, stroma regulation, hypoxia and pH manipulation, and reshaping of the immune microenvironment. A better understanding of the TME and its related modulation techniques can ameliorate the drug delivery efficiency and antitumor response. Created with BioRender.com. TME Tumor microenvironment, NP Nanoparticle

Remodeling the vascular networks

Two techniques are discovered based on distinct reasoning to improve the extravasation of NPs within the TME, namely vascular disruption and normalization [160]. Vascular disruption was offered to destroy neo-vessels, significantly decreasing blood flow and tumor necrosis. Several vascular disrupting drugs, including combretastatin A4 phosphate (CA4P) and 5,6-dimethylxanthenone-4-acetic acid (DMXAA), have demonstrated the feasibility of this method. Following injection, CA4, emerging through CA4P, suppresses tubulin polymerization and degrades the endothelial cells [161, 162]. In one study, CA4-nano drugs (CA4-NPs) were utilized for damaging blood vessels, which increased MMP-9 levels in tumors. Then, an MMP9-activated doxorubicin prodrug was given, which increased the selective release [163]. Other studies coupled this medication with photothermal treatment (PTT), a hypoxia-sensitive medicine, and other substances [164–167]. Furthermore, physical techniques like ultrasound, radiation, and near-infrared (NIR) therapy might cause vascular disturbance [168, 169]. When heated with NIR light, hollow copper sulfide NPs laden with vinyl azide targeted tumor vasculature and produced nitrogen bubbles. The bubbles burst and damaged the neo vessels, resulting in ischemia and tumor necrosis [170].

Vascular normalization has become known as a viable solution to the biological problems associated with NP delivery. Anti-angiogenic medications, including Bevacizumab, Cediranib, Sunitinib, and DC101, have reduced vascular leakiness and increased vascular functioning [171, 172]. Tumor vascular normalization is intimately connected with immunostimulatory mechanisms, giving a novel avenue to affect tumor growth [173]. This was demonstrated in a recent work in which a dinitrosyl iron complex (DNIC) was enclosed in lipid-poly (lactic-co-glycolic acid) (PLGA) NPs (NanoNO). Human umbilical vein endothelial cells impaired three proangiogenic genes (VEGFA, ANGPT2, and EGF) while increasing two vascular maturation-related genes (S1PR1 and ANGPT1) after treatment with free DNIC [174].

In lung cancer, ADAM9 (a disintegrin and metalloproteinase 9) was found to induce vascular remodeling by upregulating the levels of VEGFA, angiopoietin 2 (ANGPT2), and plasminogen activator tissue type (PLAT) [175]. The HGF/c-MET pathway also promotes VEGFR inhibitor resistance and vascular remodeling in NSCLC [176].

Regulating stroma

The stroma is a strong barrier, increasing solid stress, compressing blood vessels, and inhibiting medication diffusion. As a result, two strategies have been investigated to increase medication delivery: modifying the ECM and engaging cancer-associated fibroblasts (CAFs) [177].

The ECM may be controlled in three ways: suppressing ECM synthesis, distorting the ECM, and imitating the ECM. Prolyl-4-hydroxylase inhibitor [178, 179], deferoxamine and siRNA silencing heat shock protein 47 [180] may disrupt collagen formation, whilst 4-methylumbelliferone can impede the synthesis of hyaluronic acid [181, 182]. Physical techniques (like PTT and ultrasound), enzymes (like collagenase and hyaluronidase), and chemical agents (like cyclopamine, nitric oxide, and relaxin) can be utilized to increase ECM breakdown and NP permeability into tumors [101]. Using nitric oxide to activate matrix metalloprotease (MMP) production and dissolve collagen increased mesoporous silica NPs' dispersion throughout tumors [183]. But, reinforcing the ECM rather than destroying it could tackle tumor metastasis because the above two tactics may enhance the odds of tumor cells migrating and spreading [184]. Addressing this, a laminin-imitating peptide (BP-KLVFFK-GGDGR-YIGSR) was also created. This ECM-simulating technique successfully reduced lung metastasis in melanoma and breast tumor specimens [185].

CAFs act as essential arbitrators in the ECM, contributing to restricted drug delivery. So, directly interrupting CAFs might increase delivery. This notion was tested using fibroblast activation protein-targeting NPs, docetaxel-coupled NPs, and the introduction of TNF-related factor-expressing plasmids into CAFs [186–188]. Notably, direct CAF inhibition may enhance tumor development and metastasis [189, 190]. One study found that encapsulating quercetin in lipid/calcium/phosphate NPs significantly decreased wingless-related integration site 16 (Wnt16) expression, inhibited α-SMA⁺ CAFs development, and reduced collagen [191]. In NSCLC, integrin α11β1, a stromal cell-specific mediator for fibrillar collagens, controls cancer stromal stiffness and drives tumorigenesis and metastasis [192].

Hypoxia and pH manipulation

Hypoxia, an important feature of malignancies, has lately received a lot of attention since it inhibits angiogenesis, metastasis, and the ineffectiveness of other therapies, such as photodynamic therapy (PDT) and chemotherapy. There are numerous approaches to ameliorating the hypoxic condition: boosting blood flow, supplying oxygen, in-situ oxygen generation, and reducing oxygen use [193]. Effective PDT can be achieved by delivering substances such as MnO₂, CaO₂, and catalase into tumors [194–196], which can activate various chemical processes and physical mechanisms [197] and in-situ-produced oxygen. However, in-situ oxygen synthesis is often limited by inadequate penetration of large NPs, inorganic materials that are difficult to degrade, and low oxygen production efficiency. Inhibiting oxygen consumption is another effective technique for treating hypoxia. To improve PDT efficacy, verteporfin (PDT drug) and atovaquone were encapsulated in PLGA NPs, with atovaquone impeding electron transport in the mitochondrial respiratory chain. During hypoxia, the NPs demonstrated more cytotoxicity compared to PDT alone. This approach can relieve hypoxia in poorly vascularized areas and overcome resistance to oxygen-dependent treatment [198].

Hypoxia is typically supported by an acidic microenvironment, which promotes tumor development and metastasis. The options for managing acidosis incorporate mitigating acidity with buffers and tampering with pH-regulating enzymes [199]. Sodium bicarbonate, lysine, and imidazoles were added to function as acidity buffers and inhibit tumor aggressiveness. Proton pump inhibitors can block H⁺/K⁺-ATPase while increasing extracellular pH. The monocarboxylate transporter (MCT) inhibitors like AZD3965, which attack lactate synthesis-derived H + ions, are an appealing technique to regulate pH [200]. CAIX is associated with a bad prognosis of hypoxic malignancies. A study using a CA inhibitor with a self-assembled motif (N-pepABS) demonstrated the impact of controlling CAIX enzymes upon acidic pH and hypoxia. N-pepABS regulates extracellular pH and inhibits cell motility. They were internalized into tumors through CAIX enzymes and later prevented autophagy [201]. In the tumor-associated stroma of NSCLC, the occurrence of secreted protein acidic and rich in cystein (SPARC)/Osteonectin was connected with hypoxia/acidity indicators [202].

Reshaping the immune microenvironment

The TAMs, Tregs, and MDSCs are regulatory cells that limit T and NK cells' anti-tumor immune responses. M2-type TAMs emanate immunosuppressive cytokines, like IL-10, PGE-2, and TGF-β, as well as minor levels of pro-inflammatory cytokines like IL-6 and TNF-α, leading to immune suppression through evasion [203]. CSF-1R and bisphosphonates can directly reduce macrophage survival and proliferation. However, direct TAM inhibition can dispatch M1-like macrophages. Thus, numerous ligands have been changed to boost the M2-targeting capabilities, like anti-CD204 immunotoxin and M2pep [204]. Metal NPs can enhance reactive oxygen species (ROS) within TAMs, activating M1-like macrophages [205, 206]. There are three sorts of tactics for Tregs: inhibition [207, 208], function inhibition with anti-CTLA-4 and regulating Tregs by STAT 3/5 pathway [209]. Some research demonstrated that STAT3 enhance the release of Th2 cytokines, inhibiting the Th1 response and increasing Tregs survival [210].

Soluble mediators, including indoleamine 2, 3 dioxygenase (IDO), MMP, TGF-β, and C-X-C-motif chemokine ligand 12 (CXCL12), not only target immune cells but also contribute to an immunosuppressive milieu. Thus, administration of these inhibitors is seen as a promising method of immune regulation. IDO can prompt the conversion of tryptophan to kynurenine. A low tryptophan content reduces the lifespan and functioning of cytotoxic T cells. When paired with other therapeutics, IDO inhibitors like NLG919 and indoximod, with nanocarriers provide a powerful immune reaction against malignancies [211–213]. Tumor and mesenchymal cells secrete chemokines, which activate and attract immunosuppressive cells into the TME. Small-molecule inhibitors like AMD 3100 or monoclonal antibodies can prevent the impact of CXCL12 [214].

Clinical trials related to tumor microenvironment

The clinicaltrials.gov repository was utilized to look for clinical research on the tumor microenvironment (TME) in lung cancer. A retrospective case–control study was performed to evaluate the curative effects of cancer immunotherapy in patients with lung adenocarcinoma. Another study collected biological specimens from people experiencing therapeutic procedures for suspected or known cancer to discover therapeutic targets and study the intra-tumoral immune landscape. In another retrospective cohort study, TME was surveyed on SCLC patients with synchronic liver metastases who were administered Atezolizumab plus etoposide and platinum-based chemotherapy. The clinical aspects of the TME in treating lung cancer as a result of extensive experience and ongoing research have been highlighted in several studies and tabulated in Table 2 [215–223].

Table 2.

Summary of clinical trial investigation of tumor microenvironment associated with lung cancer

Trial identifier	Title	Details	Status	References
NCT05982574	Tumor Microenvironment in Lung Adenocarcinoma	The aim of the study is to analyze the cytokine profile and the tumor immune infiltrate in the TME and to investigate its prognostic significance in patients with radically resected lung adenocarcinoma	Active, not recruiting	[215]
NCT04887545	Immune- and Microenvironment- Proteogenomics Profiling for Classifying Lung Cancer Patients	The study intends to provide a more specific and sensitive diagnostic technique for detecting diseases related with pleural fluid build-up	Unknown	[216]
NCT05600933	Prospective Procurement of Tumor Tissue to Identify Novel Therapeutic Targets and Study the Tumor Microenvironment	The researchers undertook this study to gather tissues and blood samples from people undergoing diagnostic or therapeutic procedures for suspected or known cancer in order to uncover novel therapeutic targets and investigate the intra-tumoral immune landscape	Enrolling by invitation	[217]
NCT05636605	Analysis of the Microenvironment of Lung Cancer and Exploration of the Mechanism of Resistance to Immunotherapy	The investigators conducted a multiomics analysis of tumor and blood for analyzing the tumor heterogeneity, mapping the TME map of lung cancer and exploring the mechanism of anti-PD1/PD-L1 resistance	Recruiting	[218]
NCT05055999	Tumor Microenvironment Surveillance on Simultaneous Liver Metastases Extensive Stage Small Cell Lung Cancer Who Treated with Atezolizumab Plus Etoposide and Platinum Based Chemotherapy	The trial detects TME on patients of extensive stage SCLC with coincident liver tumors who are handled with atezolizumab plus etoposide and platinum-based chemotherapy	Completed	[219]
NCT05857800	Exploring the Neo-Adjuvant Therapy Effects on Lung Cancer Through Monitoring and Assessment of Tumor Environment (NAT-LungMate)	The researchers intend to explore how neoadjuvant treatment affects lung carcinoma patients by tracking rapid modifications in the TME	Recruiting	[220]
NCT04880382	Integrative Analysis of the Tumor Microenvironment and Optimization of the Immunotherapy Duration in Non-small Cell Lung Cancer Patients. OPTIMUNE-LUNG Study	The researchers examined the benefits of PD-1 inhibition in individuals with NSCLC who had a response to ICI (PD1/PDL-1 blocking therapy)	Recruiting	[221]
NCT01687439	Effect of Endostar Combined with Chemotherapy and Radiotherapy on Blood Vessels and Microenvironment of Tumor for Non-small Cell Lung Cancer	The investigators examined how well endostar combined with chemotherapy and radiotherapy normalizes NSCLC	Completed	[222]
NCT04405661	Correlation Between Specific Gene Mutation and Local Immune Microenvironment and Immunotherapy Efficacy in NSCLC	This study investigated the relationship between gene mutation, immunological microenvironment, and treatment outcome in primary NSCLC	Unknown	[223]

NCT National clinical trial number, TME Tumor Microenvironment, PD1 Programmed death-1, PDL-1 Programmed death-ligand 1, SCLC Small Cell Lung Cancer; NSCLC Non-small Cell Lung Cancer

Clinical trials related to tumor microenvironment involving nano-therapy

The clinicaltrials.gov repository was available to search for clinical research involving using nanoparticles in the TME in lung cancer. A phase I trial investigated the optimal dose and adverse effects of NBTXR3 when combined with radiation therapy for the treatment of NSCLC that cannot be treated surgically and has recurring issues. NBTXR3 is a radio-enhancer used as an NP intervention to increase the radiotherapy dose deposition inside tumors. Radiation therapy and NBTXR3 may improve radiation-dependent tumor cell elimination while minimizing exposure to healthy tissues. Another study investigates the impact of immunotherapy on the TME and blood of chest cancer patients. Collection of tumor tissues and peripheral blood samples before and after immunotherapy was done along with multiplex immunohistochemistry, single-cell RNA sequencing, and flow cytometry. The investigators analyze the proportion of T-cell subpopulations before and after therapy and seek biological markers to predict immunotherapy. The clinical aspects of the mentioned studies using NP-based therapy targeting the TME in lung cancer due to ongoing research have been tabulated in Table 3 [224, 225].

Table 3.

Summary of clinical trial investigation associated with nano-therapy involving the TME of lung cancer

Trial identifier	Title	Details	Nanoparticle Interventions	Status	References
NCT04505267	NBTXR3 and Radiation Therapy for the Treatment of Inoperable Recurrent Non-small Cell Lung Cancer	The researchers investigated the dose and complications of NBTXR3 when co-administered with radiation therapy for the management of NSCLC that are inoperable and has come back	Hafnium oxide-containing Nanoparticles NBTXR3	Recruiting	[224]
NCT05789498	Investigating the Biomarkers in Tumor and Peripheral Blood to Evaluate the Efficacy of Cancer Immunotherapy in Chest Cancer Patients	This study examined the influence of immunotherapy on TME and blood of chest cancer patients	In-vitro stimulation of Pbmc with tumor antigen nanoparticles	Recruiting	[225]

NCT, National clinical trial number, TME, Tumor Microenvironment, NSCLC, Non-small Cell Lung Cancer

Conclusion

In conclusion, the tumor microenvironment (TME) is a dynamic landscape of cellular interactions and molecular signals that profoundly influence lung cancer progression and treatment response. Modulating the TME through innovative approaches, including nanoparticle-based therapies, holds potential for enhancing treatment efficacy by offering greater specificity, reducing toxicity, and improving overall therapeutic outcomes. While conventional TME-targeting strategies have had limited success due to off-target effects and modest efficacy, nanoparticle-mediated delivery systems show promise in overcoming these limitations by enabling more precise targeting of TME components. Strategies such as vascular remodeling, stromal regulation, manipulation of hypoxia and pH, and reshaping the immune microenvironment present encouraging pathways to address barriers within the TME. However, challenges like low tumor uptake, off-target effects, and potential resistance remain, underlining the need for further refinement in nanoparticle design and delivery systems. Moreover, exploring metabolic mediators, immunoregulatory cells, and emerging immune checkpoints could enhance TME modulation strategies. This review underscores the importance of advancing TME-targeted approaches, though significant limitations and gaps in translational research persist. A multi-pronged approach—including combined therapies, personalized medicine, immune modulation, and efforts to overcome resistance—will be essential for translating preclinical insights into clinically meaningful interventions, ultimately aiming for more effective, individualized lung cancer treatments.

Author contributions

AA: Initial investigation, Design, Literature review, Writing – original draft; PB: Literature review, Writing – original draft; BKD: Conceptualization, Search strategy development, Software, Validation, Writing – review and editing, and Supervision. All the authors have read and approved the final manuscript.

Funding

Not applicable.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

Not applicable.

Competing interests

The authors declare no competing interests.