Lung cancer stem cells: Molecular features and therapeutic targets

The multifaceted role of beta-blockers in overcoming cancer progression and drug resistance: Extending beyond cardiovascular disorders

Beta-blockers are commonly used medications that antagonize β-adrenoceptors, reducing sympathetic nervous system activity. Emerging evidence suggests that beta-blockers may also have anticancer effects and help overcome drug resistance in cancer treatment. This review summarizes the contribution of different isoforms of beta-adrenoceptors in cancer progression, the current preclinical and clinical data on associations between beta-blockers use and cancer outcomes, as well as their ability to enhance responses to chemotherapy and other standard therapies. We discuss proposed mechanisms, including effects on angiogenesis, metastasis, cancer stem cells, and apoptotic pathways. Overall, results from epidemiological studies and small clinical trials largely indicate the beneficial effects of beta-blockers on cancer progression and drug resistance. However, larger randomized controlled trials are needed to firmly establish their clinical efficacy and optimal utilization as adjuvant agents in cancer therapy.

Identification of novel T cell proliferation patterns, potential biomarkers and therapeutic drugs in colorectal cancer

Background: T cells are crucial components of antitumor immunity. A list of genes associated with T cell proliferation was recently identified; however, the impact of T cell proliferation-related genes (TRGs) on the prognosis and therapeutic responses of patients with colorectal cancer (CRC) remains unclear. Methods: 33 TRG expression information and clinical information of patients with CRC gathered from multiple datasets were subjected to bioinformatic analysis. Consensus clustering was used to determine the molecular subtypes associated with T cell proliferation. Utilizing the Lasso-Cox regression, a predictive signature was created and verified in external cohorts. A tumor immune environment analysis was conducted, and potential biomarkers and therapeutic drugs were identified and confirmed via in vitro and in vivo studies. Results: CRC patients were separated into two TRG clusters, and differentially expressed genes (DEGs) were identified. Patient information was divided into three different gene clusters, and the determined molecular subtypes were linked to patient survival, immune cells, and immune functions. Prognosis-associated DEGs in the three gene clusters were used to evaluate the risk score, and a predictive signature was developed. The ability of the risk score to predict patient survival and treatment response has been successfully validated using multiple datasets. To discover more possible biomarkers for CRC, the weighted gene co-expression network analysis algorithm was utilized to screen key TRG variations between groups with high- and low-risk. CDK1, BATF, IL1RN, and ITM2A were screened out as key TRGs, and the expression of key TRGs was confirmed using real-time reverse transcription polymerase chain reaction. According to the key TRGs, 7,8-benzoflavone was identified as the most significant drug molecule, and MTT, colony formation, wound healing, transwell assays, and in vivo experiments indicated that 7,8-benzoflavone significantly suppressed the proliferation and migration of CRC cells. Conclusion: T cell proliferation-based molecular subtypes and predictive signatures can be utilized to anticipate patient results, immunological landscape, and treatment response in CRC. Novel biomarker candidates and potential therapeutic drugs for CRC were identified and verified using in vitro and in vivo tests.

Machine learning-identified stemness features and constructed stemness-related subtype with prognosis, chemotherapy, and immunotherapy responses for non-small cell lung cancer patients

AIM

This study aimed to explore a novel subtype classification method based on the stemness characteristics of patients with non-small cell lung cancer (NSCLC).

METHODS

Based on the Cancer Genome Atlas database to calculate the stemness index (mRNAsi) of NSCLC patients, an unsupervised consensus clustering method was used to classify patients into two subtypes and analyze the survival differences, somatic mutational load, copy number variation, and immune characteristics differences between them. Subsequently, four machine learning methods were used to construct and validate a stemness subtype classification model, and cell function experiments were performed to verify the effect of the signature gene ARTN on NSCLC.

RESULTS

Patients with Stemness Subtype I had better PFS and a higher somatic mutational burden and copy number alteration than patients with Stemness Subtype II. In addition, the two stemness subtypes have different patterns of tumor immune microenvironment. The immune score and stromal score and overall score of Stemness Subtype II were higher than those of Stemness Subtype I, suggesting a relatively small benefit to immune checkpoints. Four machine learning methods constructed and validated classification model for stemness subtypes and obtained multiple logistic regression equations for 22 characteristic genes. The results of cell function experiments showed that ARTN can promote the proliferation, invasion, and migration of NSCLC and is closely related to cancer stem cell properties.

CONCLUSION

This new classification method based on stemness characteristics can effectively distinguish patients' characteristics and thus provide possible directions for the selection and optimization of clinical treatment plans.

Identification of cuproptosis-based molecular subtypes, construction of prognostic signature and characterization of immune landscape in colon cancer

Background

Cuproptosis is a newly discovered form of cell death induced by targeting lipoacylated proteins involved in the tricarboxylic acid cycle. However, the roles of cuproptosis-related genes (CRGs) in the clinical outcomes and immune landscape of colon cancer remain unknown.

Methods

We performed bioinformatics analysis of the expression data of 13 CRGs identified from a previous study and clinical information of patients with colon cancer obtained from The Cancer Genome Atlas and Gene Expression Omnibus databases. Colon cancer cases were divided into two CRG clusters and prognosis-related differentially expressed genes. Patient data were separated into three corresponding distinct gene clusters, and the relationships between the risk score, patient prognosis, and immune landscape were analyzed. The identified molecular subtypes correlated with patient survival, immune cells, and immune functions. A prognostic signature based on five genes was identified, and the patients were divided into high- and low-risk groups based on the calculated risk score. A nomogram model for predicting patient survival was developed based on the risk score and other clinical features.

Results

The high-risk group showed a worse prognosis, and the risk score was related to immune cell abundance, microsatellite instability, cancer stem cell index, checkpoint expression, immune escape, and response to chemotherapeutic drugs and immunotherapy. Findings related to the risk score were validated in the imvigor210 cohort of patients with metastatic urothelial cancer treated with anti-programmed cell death ligand 1.

Conclusion

We demonstrated the potential of cuproptosis-based molecular subtypes and prognostic signatures for predicting patient survival and the tumor microenvironment in colon cancer. Our findings may improve the understanding of the role of cuproptosis in colon cancer and lead to the development of more effective treatment strategies.

A novel oxidative stress- and ferroptosis-related gene prognostic signature for distinguishing cold and hot tumors in colorectal cancer

Oxidative stress and ferroptosis exhibit crosstalk in many types of human diseases, including malignant tumors. We aimed to develop an oxidative stress- and ferroptosis-related gene (OFRG) prognostic signature to predict the prognosis and therapeutic response in patients with colorectal cancer (CRC). Thirty-four insertion genes between oxidative stress-related genes and ferroptosis-related genes were identified as OFRGs. We then performed bioinformatics analysis of the expression profiles of 34 OFRGs and clinical information of patients obtained from multiple datasets. Patients with CRC were divided into three OFRG clusters, and differentially expressed genes (DEGs) between clusters were identified. OFRG clusters correlated with patient survival and immune cell infiltration. Prognosis-related DEGs in three clusters were used to calculate the risk score, and a prognostic signature was constructed according to the risk score. In this study, patients in the low-risk group had better prognosis, higher immune cell infiltration levels, and better responses to fluorouracil-based chemotherapy and immune checkpoint blockade therapy than high-risk patients; these results were successfully validated with multiple independent datasets. Thus, low-risk CRC could be defined as hot tumors and high-risk CRC could be defined as cold tumors. To further identify potential biomarkers for CRC, the expression levels of five signature genes in CRC and adjacent normal tissues were further verified via an in vitro experiment. In conclusion, we identified 34 OFRGs and constructed an OFRG-related prognostic signature, which showed excellent performance in predicting survival and therapeutic responses for patients with CRC. This could help to distinguish cold and hot tumors in CRC, and the results might be helpful for precise treatment protocols in clinical practice.

PANoptosis-based molecular clustering and prognostic signature predicts patient survival and immune landscape in colon cancer

PANoptosis is a newly-discovered cell death pathway that involves crosstalk and co-ordination between pyroptosis, apoptosis, and necroptosis processes. However, the roles of PANoptosis-related genes (PRGs) in prognosis and immune landscape of colon cancer remain widely unknown. Here, we performed a bioinformatics analysis of expression data of nineteen PRGs identified from previous studies and clinical data of colon cancer patients obtained from TCGA and GEO databases. Colon cancer cases were divided into two PRG clusters, and prognosis-related differentially expressed genes (PRDEGs) were identified. The patient data were then separated into two corresponding distinct gene clusters, and the relationship between the risk score, patient prognosis, and immune landscape was analyzed. The identified PRGs and gene clusters correlated with patient survival and immune system and cancer-related biological processes and pathways. A prognosis signature based on seven genes was identified, and patients were divided into high-risk and low-risk groups based on the calculated risk score. A nomogram model for prediction of patient survival was also developed based on the risk score and other clinical features. Accordingly, the high-risk group showed worse prognosis, and the risk score was related to immune cell abundance, cancer stem cell (CSC) index, checkpoint expression, and response to immunotherapy and chemotherapeutic drugs. Results of quantitative real-time polymerase chain reaction (qRT-PCR) showed that LGR5 and VSIG4 were differentially expressed between normal and colon cancer samples. In conclusion, we demonstrated the potential of PANoptosis-based molecular clustering and prognostic signatures for prediction of patient survival and tumor microenvironment (TME) in colon cancer. Our findings may improve our understanding of the role of PANoptosis in colon cancer, and enable the development of more effective treatment strategies.

Weighted Correlation Network Analysis of Cancer Stem Cell-Related Prognostic Biomarkers in Esophageal Squamous Cell Carcinoma

Background: The role of cancer stem cells in esophageal squamous cell carcinoma (ESCC) remains unclear. Methods: The mRNA stemness index (mRNAsi) of 179 ESCC patients (GSE53625) was calculated using a machine learning algorithm based on their mRNA expression. Stemness-related genes were identified by weighted correlation network analysis (WGCNA) and LASSO regression, whose associations with mutation status, immune cell infiltrations, and potential compounds were also analyzed. The role of these genes in proliferation and their expressions was assessed in ESCC cell lines and 112 samples from our center. Results: The ESCC samples had significantly higher mRNAsi than the normal tissues. Patients with high mRNAsi exhibited higher worse OS. Seven stemness-related genes were identified by WGCNA and LASSO regression, based on which a risk-predicted score model was constructed. Among them, CST1, CILP, PITX2, F2RL2, and RIOX1 were favorable for OS, which were adverse for DPP4 and ZFHX4 in the GSE53625 dataset. However, RIOX1 was unfavorable for OS in patients from our center. In vitro assays showed that CST1, CILP, PITX2, F2RL2, and RIOX1 were pro-proliferated, which were opposite for DDP4 and ZFHX4. In addition, SMARCA4, NOTCH3, DNAH5, and KALRN were more mutated in the low-score group. The low-score group had significantly more memory B cells, monocytes, activated NK cells, and Tregs and less macrophages M2, resting mast cells, and resting dendritic cells. Conclusions: Seven stemness-related genes are significantly related to the prognosis, gene mutations, and immune cell infiltration of ESCC. Some potential anticancer compounds may be favorable for OS.

Polycaprolactone Electrospun Scaffolds Produce an Enrichment of Lung Cancer Stem Cells in Sensitive and Resistant EGFRm Lung Adenocarcinoma

Simple Summary

The culture of lung cancer stem cells (LCSCs) is not possible using traditional flat polystyrene surfaces. The study of these tumor-initiating cells is fundamental due to their key role in the resistance to anticancer therapies, tumor recurrence, and metastasis. Hence, we evaluated the use of polycaprolactone electrospun (PCL-ES) scaffolds for culturing LCSC population in sensitive and resistant EGFR-mutated lung adenocarcinoma models. Our findings revealed that both cell models seeded on PCL-ES structures showed a higher drug resistance, enhanced levels of several genes and proteins related to epithelial-to-mesenchymal process, stemness, and surface markers, and the activation of the Hedgehog pathway. We also determined that the non-expression of CD133 was associated with a low degree of histological differentiation, disease progression, distant metastasis, and worse overall survival in EGFR-mutated non-small cell lung cancer patients. Therefore, we confirmed PCL-ES scaffolds as a suitable three-dimensional cell culture model for the study of LCSC niche.

Abstract

The establishment of a three-dimensional (3D) cell culture model for lung cancer stem cells (LCSCs) is needed because the study of these stem cells is unable to be done using flat surfaces. The study of LCSCs is fundamental due to their key role in drug resistance, tumor recurrence, and metastasis. Hence, the purpose of this work is the evaluation of polycaprolactone electrospun (PCL-ES) scaffolds for culturing LCSCs in sensitive and resistant EGFR-mutated (EGFRm) lung adenocarcinoma cell models. We performed a thermal, physical, and biological characterization of 10% and 15%-PCL-ES structures. Several genes and proteins associated with LCSC features were analyzed by RT-qPCR and Western blot. Vimentin and CD133 tumor expression were evaluated in samples from 36 patients with EGFRm non-small cell lung cancer through immunohistochemistry. Our findings revealed that PC9 and PC9-GR3 models cultured on PCL-ES scaffolds showed higher resistance to osimertinib, upregulation of ABCB1, Vimentin, Snail, Twist, Sox2, Oct-4, and CD166, downregulation of E-cadherin and CD133, and the activation of Hedgehog pathway. Additionally, we determined that the non-expression of CD133 was significantly associated with a low degree of histological differentiation, disease progression, and distant metastasis. To sum up, we confirmed PCL-ES scaffolds as a suitable 3D cell culture model for the study of the LCSC niche.

Vitamin D affects the Warburg effect and stemness maintenance of non-small-cell lung cancer cells by regulating PI3K/AKT/mTOR signaling pathway

BACKGROUND

Non-small-cell lung cancer (NSCLC) is the most prevalent form of lung cancer, accounting for approximately 85% of all lung cancer cases and resulting in high morbidity and mortality. Previous studies have demonstrated that 1,25-dihydroxy-vitamin-D3 (vitamin D) exhibited anti-cancer activity against breast and prostate cancer.

OBJECTIVES

The aim of the current study is to investigate the effect of vitamin D on NSCLC and its underlying mechanism.

METHODS

The effects of vitamin D on stemness maintenance and the Warburg effect in NSCLC cells were investigated both in vitro and in vivo.

RESULTS & DISCUSSION

In vitro experiments revealed that vitamin D inhibited glycolysis and stemness maintenance in A549 and NCI-H1975 cells. Both in vitro and in vivo experiments indicated that vitamin D attenuated the expression of metabolism-related enzymes associated with the Warburg effect (GLUT1, LDHA, HK2, and PKM2). In addition, vitamin D down-regulated the expression of stemness-related genes (Oct-4, SOX-2, and Nanog) and the expression of PI3K, AKT, and mTOR.

CONCLUSION

Overall, these findings suggest that vitamin D suppresses the Warburg effect and stemness maintenance in NSCLC cells via the inactivation of PI3K/AKT/mTOR signaling, thereby inhibiting the progression of NSCLC. The current study indicates that vitamin D is a potential candidate in therapeutic strategies against NSCLC.

Triple Negative Breast Cancer: A Mountain Yet to Be Scaled Despite the Triumphs

Metastatic progression and tumor recurrence pertaining to TNBC are certainly the leading cause of breast cancer-related mortality; however, the mechanisms underlying TNBC chemoresistance, metastasis, and tumor relapse remain somewhat ambiguous. TNBCs show 77% of the overall 4-year survival rate compared to other breast cancer subtypes (82.7 to 92.5%). TNBC is the most aggressive subtype of breast cancer, with chemotherapy being the major approved treatment strategy. Activation of ABC transporters and DNA damage response genes alongside an enrichment of cancer stem cells and metabolic reprogramming upon chemotherapy contribute to the selection of chemoresistant cells, majorly responsible for the failure of anti-chemotherapeutic regime. These selected chemoresistant cells further lead to distant metastasis and tumor relapse. The present review discusses the approved standard of care and targetable molecular mechanisms in chemoresistance and provides a comprehensive update regarding the recent advances in TNBC management.

Paclitaxel-Based Chemotherapy Targeting Cancer Stem Cells from Mono- to Combination Therapy

Paclitaxel (PTX) is a chemotherapeutical agent commonly used to treat several kinds of cancer. PTX is known as a microtubule-targeting agent with a primary molecular mechanism that disrupts the dynamics of microtubules and induces mitotic arrest and cell death. Simultaneously, other mechanisms have been evaluated in many studies. Since the anticancer activity of PTX was discovered, it has been used to treat many cancer patients and has become one of the most extensively used anticancer drugs. Regrettably, the resistance of cancer to PTX is considered an extensive obstacle in clinical applications and is one of the major causes of death correlated with treatment failure. Therefore, the combination of PTX with other drugs could lead to efficient therapeutic strategies. Here, we summarize the mechanisms of PTX, and the current studies focusing on PTX and review promising combinations.

Identification of cancer stem cell-related biomarkers in lung adenocarcinoma by stemness index and weighted correlation network analysis

BACKGROUND

Accounting for tumor heterogeneity, cancer stem cells (CSC) are involved in tumor metastasis, relapse, and drug resistance. Genes regulating CSC characteristics in lung adenocarcinoma (LUAD) were explored and validated in this study.

METHODS

The mRNA stemness index (mRNAsi) of more than 500 LUAD cases from The Cancer Genome Atlas database were calculated using a one-class logistic regression machine learning algorithm based on the mRNA expression of pluripotent stem cells and their differentiated progeny. mRNAsi-related key genes were identified by weighted correlation network analysis. The expression levels and prognostic roles of key genes were analyzed in Oncomine, PrognoScan, and Kaplan-Meier plotter databases, and validated using data from our center.

RESULTS

The mRNAsi was significantly higher in LUAD compared with normal lung tissues. LUAD patients of advanced stage exhibited a higher mRNAsi and worse overall survival (OS). Eight key genes were identified: heat shock 70 kDa protein 4 (HSPA4), cell division cycle associated 7 (CDCA7), cell division cycle 20 (CDC20), cyclin-dependent kinase 1 (CDK1), CAP-GLY domain containing linker protein 1 (CLIP1), cyclin B1 (CCNB1), H2A histone family, member X (H2AFX), and Bloom syndrome, RecQ helicase-like (BLM). These genes were differentially expressed in various types of malignancies and validated in the LUAD cases. LUAD patients with low expression of CDC20, CDK1, CCNB1, H2AFX, or BLM had a significantly better OS, whereas OS was reduced for patients with low expression of CLIP1. In addition, the expression of CDCA7 did not significantly impact the OS of LUAD patients. The protein-protein interaction networks evaluated by STRING demonstrated strong relationships between these key genes, which were validated in our cases.

CONCLUSIONS

The mRNAsi was significantly higher in LUAD compared with normal samples. Eight mRNAsi-related key genes were associated with prognosis and the cell cycle, and were strongly correlated with each other and differentially expressed in tumor and normal samples. We provide a new strategy for exploring stemness-related genes in LUAD cases.

Novel HDAC11 inhibitors suppress lung adenocarcinoma stem cell self-renewal and overcome drug resistance by suppressing Sox2

Non-small cell lung cancer (NSCLC) is known to have poor patient outcomes due to development of resistance to chemotherapy agents and the EGFR inhibitors, which results in recurrence of highly aggressive lung tumors. Even with recent success in immunotherapy using the checkpoint inhibitors, additional investigations are essential to identify novel therapeutic strategies for efficacious treatment for NSCLC. Our finding that high levels of histone deacetylase 11 (HDAC11) in human lung tumor tissues correlate with poor patient outcome and that depletion or inhibition of HDAC11 not only significantly reduces self-renewal of cancer stem cells (CSCs) from NSCLC but also decreases Sox2 expression that is essential for maintenance of CSCs, indicates that HDAC11 is a potential target to combat NSCLC. We find that HDAC11 suppresses Sox2 expression through the mediation of Gli1, the Hedgehog pathway transcription factor. In addition, we have used highly selective HDAC11 inhibitors that not only target stemness and adherence independent growth of lung cancer cells but these inhibitors could also efficiently ablate the growth of drug-insensitive stem-like cells as well as therapy resistant lung cancer cells. These inhibitors were found to be efficacious even in presence of cancer associated fibroblasts which have been shown to contribute in therapy resistance. Our study presents a novel role of HDAC11 in lung adenocarcinoma progression and the potential use of highly selective inhibitors of HDAC11 in combating lung cancers.

β-Adrenergic Signaling in Lung Cancer: A Potential Role for Beta-Blockers

Lung cancer results in more patient deaths each year than any other cancer type. Additional treatment strategies are needed to improve clinical responses to approved treatment modalities and prevent the emergence of resistant disease. Catecholamines including norepinephrine and epinephrine are elevated as a result of chronic stress and mediate their physiological effects through activation of adrenergic receptors on target tissues. Lung cancer cells express β-adrenergic receptors (β-ARs), and numerous preclinical studies indicate that β2-AR signaling on lung cancer cells facilities cellular programs including proliferation, motility, apoptosis resistance, epithelial-to-mesenchymal transition, metastasis, and the acquisition of an angiogenic and immunosuppressive phenotype. Here, we review the preclinical and clinical evidence supporting a potential role for beta-blockers in improving the clinical outcome of lung cancer patients. Graphical Abstract Catecholamines including norepinephrine and epinephrine act of β-ARs expressed on NSCLC tumor cells and activate pathways regulating tumor progression.

Fbxw7 and Skp2 Regulate Stem Cell Switch between Quiescence and Mitotic Division in Lung Adenocarcinoma

BACKGROUND/AIMS

The molecular mechanism of dormancy initiation of cancer stem cells (CSCs) is not clear. This study was to explore the molecular mechanism by which CSCs switch from mitotic division to quiescence.

METHODS

MTT assays, flow cytometry, Western blotting, qRT-PCR, and immunofluorescence staining were used to test cell viability, cell cycle and expression of F-box and WD repeat domain-containing 7 (Fbxw7), c-myc, S phase kinase associated protein-2 (Skp2), cyclin-dependent kinase inhibitor 1B (p27), octamer-binding transcription factor 3/4 (Oct3/4), and β catenin gene in 5-fluorouracil (5-FU)-treated A549 cells. Lung adenocarcinoma xenograft models were employed to detect the effects of Fbxw7 on tumor growth.

RESULTS

5-FU inhibited the proliferation of A549 cells, with a median inhibitory concentration (IC50) of 200 μg/ml after 24 h treatment. 5-FU treatment increased the expressions of Oct3/4, Fbxw7, and p27 and increased the number of A549 cells at G0/G1. 5-FU treatment triggered nuclear translocation of β-catenin, decreased the expression levels of c-myc and Skp2, and decreased the number of A549 cells at S phase. Release from 5-FU decreased the expressions of Oct3/4, Fbxw7 and p27; decreased the percentage of cells in the G0/G1 phase; increased the expressions of Skp2 and c-myc; and increased the proportion of cells in S phase. 5-FU treatment led to high expressions of Oct3/4, c-myc, and p27, with low expressions of Fbxw7 and Skp2. Knockdown of Fbxw7 augmented the expression of c-myc and decreased the proportion of A549 cells in Go/G1 phase. Skp2 siRNA increased the expression of p27 and the percentage of G0/G1 phase cells and reduced the proportion of S phase cells. Fbxw7 overexpression inhibited tumor growth in mouse lung adenocarcinoma xenograft models. When Fbxw7 expression was low, Skp2 expression was higher in lung adenocarcinoma tissues and associated with the differentiation of lung adenocarcinoma.

CONCLUSION

5-FU enriches the CSCs in lung adenocarcinoma cells via increasing Fbxw7 and decreasing Skp2 expression, followed by downregulation of c-myc and upregulation of p27, which switches cells to quiescence.

Inhibitory role of Gi-coupled receptors on cAMP-driven cancers with focus on opioid receptors in lung adenocarcinoma and its stem cells

The development, progression, metastasis and drug resistance of the most common human cancers are driven by cyclic adenosine monophosphate (cAMP)-signaling downstream of beta-adrenergic receptors (β-Ars) coupled to the stimulatory G-protein G_s. Receptors coupled to the inhibitory G-protein G_i inhibit this signaling cascade by blocking the activation of the enzyme adenylyl cyclase that catalyzes the formation of cAMP and function as the physiological inhibitors of this signaling cascade. Members of the G_i-coupled receptor family widely expressed in the mammalian organism are GABA B receptors (GABA_B-Rs) for the inhibitory neurotransmitter γ-aminobutyric acid (GABA), opioid receptors for endogenous opioid peptides and cannabinoid receptors for endogenous cannabinoids. This review summarizes current evidence for the concept that the activation of G_i-receptor signaling by pharmacological and psychological means is a promising tool for the long-term management of cAMP-driven cancers with special emphasis on the inhibitory effects of opioids on lung adenocarcinoma and its stem cells.

Targeting Cancer Stem Cells: A Strategy for Effective Eradication of Cancer

Cancer stem cells (CSCs) are subpopulations of tumor cells with the ability to self-renew, differentiate, and initiate and maintain tumor growth, and they are considered to be the main drivers of intra- and inter-tumoral heterogeneity. While conventional chemotherapy can eradicate the majority of non-CSC tumor cells, CSCs are often drug-resistant, leading to tumor recurrence and metastasis. The heterogeneity of CSCs is the main challenge in developing CSC-targeting therapy; therefore, we and other investigators have focused on developing novel therapeutic strategies that combine conventional chemotherapy with inhibitors of CSC-regulating pathways. Encouraging preclinical findings have suggested that CSC pathway blockade can indeed enhance cellular sensitivity to non-targeted conventional therapy, and this work has led to several ongoing clinical trials of CSC pathway inhibitors. Our studies in bladder cancer and lung adenocarcinoma have demonstrated a crucial role of YAP1, a transcriptional regulator of genes that promote cell survival and proliferation, in regulating CSC phenotypes. Moreover, using cell lines and patient-derived xenograft models, we showed that inhibition of YAP1 enhances the efficacy of conventional therapies by attenuating CSC stemness features. In this review, we summarize the therapeutic strategies for targeting CSCs in several cancers and discuss the potential and challenges of the approach.

Dysregulated ENPP1 increases the malignancy of human lung cancer by inducing epithelial-mesenchymal transition phenotypes and stem cell features

Induction of cancer stem cell (CSC) characters and epithelial mesenchymal transition (EMT) features are crucial in tumor initiation, progression and metastasis. However, underlying mechanisms remain incompletely understood. Here, we showed that ENPP1 plays an important role in inducing and maintaining EMT phenotypes and CSC features in lung cancer. ENPP1 is upregulated in lung cancer cells. ENPP1-knockdown in lung cancer HCC827 cells and A549 cells resulted in suppressed colonogenic formation, anchorage-independent growth in vitro, and tumorigenicity in vivo. ENPP1-knockdown also reduced expression of CSC makers, including ABCG2, SOX2, NANOG, and CD44. Moreover, ENPP1-knockdown reversed TGFβ-induced EMT phenotypes, including cell migration, E-cadherin repression and vimentin induction. Finally, upregulated ENPP1 was identified in majority of human lung tumor tissues compared to adjacent normal lung tissues. Taken together, our study demonstrates that dysregulated ENPP1 contributes to increased malignancy of human lung cancer by inducing CSC-features, and EMT-like phenotypes.

TRPM7 overexpression enhances the cancer stem cell-like and metastatic phenotypes of lung cancer through modulation of the Hsp90α/uPA/MMP2 signaling pathway

Background

Waixenicin A, a bioactive extract of soft coral Sarcothelia edmondsoni, has been shown to be anti-neoplastic. However, its mechanisms of action remain unclear. Cancer stem cells (CSCs) and associated stemness factors are implicated in lung cancer. Here, we investigated the role of Waixenicin A on CSCs-like and metastatic lung cancer cells.

Methods

We demonstrated and compared TRPM7 expression in the non-tumor lung tissues or bronchial epithelial 16-HBE cell line. TRPM7 was aberrantly expressed in the cancer tissues and SPCA-1, NCI-H520, SK-MES-1, A549 and 95D cell lines.

Results

Increased TRPM7 expression was associated with enhanced SOX2, KLF4, and CD133, Hsp90α, uPA, and MMP2 expression in lung cancer cells. TRPM7-silencing inhibited epithelial-to-mesenchymal transition (EMT), suppressed stemness markers and phenotypes, concomitantly suppressed Hsp90α/uPA/MMP2 axis. Coincidently, Waixenicin A treatment downregulated TRPM7 and oncogenic markers; Waixenicin A also attenuated the ability of lung cancer cells to form tumorspheres, in vitro. In validation, our clinicopathological analyses showed that a higher TRPM7 expression was positively correlated with the larger tumor size (p = 0.007), positive lymph node metastasis (p = 0.005) and disease grade (p = 0.003).

Conclusions

Through its ability to inhibit Hsp90α/uPA/MMP2 signaling and suppress TRPM7 expression, we showed that Waixenicin A is a potential anticancer therapeutic agent for treating malignant lung cancer.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-5050-x) contains supplementary material, which is available to authorized users.

Histone demethylase JARID1B/KDM5B promotes aggressiveness of non-small cell lung cancer and serves as a good prognostic predictor

Background

Lung cancer is the leading cause of cancer death worldwide. Recently, epigenetic dysregulation has been known to promote tumor progression and therefore may be a therapeutic target for anticancer therapy. JARID1B, a member of histone demethylases, has been found to be related to tumorigenesis in certain kinds of cancers. However, its biological roles in non-small cell lung cancer (NSCLC) remain largely unclear.

Methods

We firstly examined the expression of JARID1B in surgical specimens and six NSCLC cell lines. Then, we evaluated the relationship between JARID1B expression and clinicopathologic parameters in 72 NSCLC patients, thereby established its prognostic importance. We subsequently studied the functional roles of JARID1B in tumorigenesis to verify its clinicopathologic significance.

Results

Our results showed that JARID1B was overexpressed in NSCLC cells and JARID1B overexpression was associated with tumor size, lymph node metastasis, advanced stages, and poor overall survival in NSCLC patients. JARID1B overexpression resulted in increased cell proliferation and formation of tumorspheres and correlated positively with the expression of cancer stem cells (CSCs) and epithelial-mesenchymal transition (EMT) markers, while the c-Met signaling pathway was actively involved. It also correlated with the strength of resistance to cisplatin and doxorubicin. On the contrary, downregulation of JARID1B expression by applying shRNA or JARID1B inhibitor PBIT reversed these phenomena.

Conclusions

JARID1B worsens prognosis of NSCLC patients by promotion of tumor aggressiveness through multiple biological facets which were associated with activation of the c-Met signaling, and can be a novel prognostic biomarker and therapeutic target for NSCLC.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0533-9) contains supplementary material, which is available to authorized users.

Utilization of lung cancer cell lines for the study of lung cancer stem cells

Lung cancer is one of the most lethal types of cancer, and its poor prognosis is primarily due to drug resistance and cancer recurrence. As it is associated with a low five-year survival rate, lung cancer stem cells (LCSCs) have been the subject of numerous recent studies. For these studies of LCSCs, lung cancer cell lines are more commonly used than lung cancer tissues obtained from patients, as they are easier to acquire. The methods utilized for the identification of LCSCs from lung cancer cell lines include fluorescence activated cell sorting (FACS), magnetic activated cell sorting (MACS), sphere-forming assay and bacterial surface display library screening. As LCSCs have certain proteins expressed on the surface (CD133, CD44 and CD24) or in the cytoplasm (ALDH and ABCG2), which may act as specific markers, the most frequently used technique to identify and obtain LCSCs is FACS. The current lack of recognized biomarkers in LCSCs makes the identification of LCSCs problematic. Furthermore, the various proportions of LCSCs in specific cell lines, as revealed by numerous previous studies, may cause the LCSC model to be questioned with regard to whether the utilization of certain lung cancer cell lines is dependable for LCSC studies. The current review focuses on lung cancer cell lines that are used for the study of LCSCs and the methods available to identify LCSCs with various markers. The present study also aimed to determine the proportion of LCSCs present in specific cell lines reported by various studies, and to discuss the suitability of specific lung cancer cell lines for the study of LCSCs.

Two-stage induced differentiation of OCT4+/Nanog+ stem-like cells in lung adenocarcinoma

Stem-like cells in solid tumors are purported to contribute to cancer development and poor treatment outcome. The abilities to self-renew, differentiate, and resist anticancer therapies are hallmarks of these rare cells, and steering them into lineage commitment may be one strategy to curb cancer development or progression. Vitamin D is a prohormone that can alter cell growth and differentiation and may induce the differentiation cancer stem-like cells. In this study, octamer-binding transcription factor 4 (OCT4)-positive/Nanog homeobox (Nanog)- positive lung adenocarcinoma stem-like cells (LACSCs) were enriched from spheroid cultured SPC-A1 cells and differentiated by a two-stage induction (TSI) method, which involved knockdown of hypoxia-inducible factor 1-alpha (HIF1α) expression (first stage) followed by sequential induction with 1alpha,25-dihydroxyvitamin D3 (1,25(OH)₂D₃, VD3) and suberoylanilide hydroxamic acid (SAHA) treatment (second stage). The results showed the HIF1α-knockdowned cells displayed diminished cell invasion and clonogenic activities. Moreover, the TSI cells highly expressed tumor suppressor protein p63 (P63) and forkhead box J1 (FOXJ1) and lost stem cell characteristics, including absent expression of OCT4 and Nanog. These cells regained sensitivity to cisplatin in vitro while losing tumorigenic capacity and decreased tumor cell proliferation in vivo. Our results suggest that induced transdifferentiation of LACSCs by vitamin D and SAHA may become novel therapeutic avenue to alter tumor cell phenotypes and improve patient outcome.

SPC25 upregulation increases cancer stem cell properties in non-small cell lung adenocarcinoma cells and independently predicts poor survival

In this study, we investigated the functional role and prognostic value of spindle pole body component 25 (SPC25) in non-small cell lung cancer (NSCLC). SPC25 expression profile in lung adenocarcinoma (LUAD), lung squamous cell carcinoma (LUSC) and normal lung tissues was examined by using data from the Cancer Genome Atlas (TCGA) and the Human Protein Atlas (HPA). LUAD A549 cells and LUSC H520 cells were used to investigate the influence of SPC25 on cancer stem cell (CSC) properties in terms of the proportion of CD133⁺ cells, tumorsphere formation and CSC markers, including CD133, ALDH1 and Sox2. Data mining was also performed in the Kaplan-Meier plotter and TCGA-NSCLC to assess the independent prognostic value of SPC25. Results showed SPC25 was significantly upregulated in LUAD and LUSC tissues compared with normal lung tissues. SPC25 overexpression significantly increased the CSC properties and invasion of A549 cells, but not H520 cells. In comparison, SPC25 knockdown impaired the CSC properties and invasion of A549 cells, but not H520 cells. Univariate and multivariate analysis confirmed that high SPC25 expression was an independent prognostic factor for poor overall survival (OS) (HR: 1.622, 95%CI: 1.207-2.178, p = .001) and recurrence-free survival (RFS) (HR: 1.726, 95%CI: 1.242-2.399, p = .001) in LUAD patients. However, no independent prognostic value of SPC25 was observed in LUSC patients even under the best cut-off model. Based on these findings, we infer that SPC25 upregulation can increase CSC properties in LUAD and independently predict poor survival in this histological subtype.

[Research Progress in the Therapeutic Strategy Based on Targeting at Lung Cancer Stem Cell]

With high morbidity and mortality, lung cancer is a major threat to human health and one of the focuses of tumor researches. Lung cancer stem cells (LCSCs) are regarded as a subpopulation of cells within lung cancer tissues with the capacity of self-renewal and differentiation, and might be related to tumorigenesis and heterogeneity of lung cancer. Tumor recurrence, metastasis and drug resistance of lung cancers could be clarified by LCSC hypothesis. Thus it's therapeutically prospective to target at these cells. This review summarizes the biomarkers of LCSCs and their aberrant signal pathways, as well as the therapeutic strategies targeting at LCSCs.

MiR-410 induces stemness by inhibiting Gsk3β but upregulating β-catenin in non-small cells lung cancer

Our previous research indicated miR-410 played a critical role in promoting the tumorigenesis and development of NSCLC (non-small cells lung cancer). MiR-410 has been recently reported to be crucial for development and differentiation of embryonic stem cells. But it remains elusive whether miR-410 stimulates the stemness of cancer until now. Herein, we identify miR-410 induces the stemness and is associated with the progression of NSCLC. We demonstrate miR-410 increases the levels of stem cells marker Sox2, Oct4, Nanog, CXCR4 as well as lung cancer stem cells surface marker CD44 and CD166. MiR-410 promotes stem cells-like properties such as proliferation, sphere formation, metastasis and chemoresistance. Moreover, Gsk3β is directly targeted and post-transcriptionally downregulated by miR-410. Also, the expression levels of miR-410 and Gsk3β may be correlated to clinicopathological differentiation in NSCLC tumor specimens. Additionally, we demonstrate miR-410 induces stemness through inhibiting Gsk3β but increasing Sox2, Oct4, Nanog and CXCR4, which binds to β-catenin signaling. In conclusion, our findings identify the miR-410/Gsk3β/β-catenin signaling axis is a novel molecular circuit in inducing stemness of NSCLC.

Lung cancer-associated brain metastasis: Molecular mechanisms and therapeutic options

BACKGROUND

Lung cancer is the most common cause of cancer-related mortality in humans. There are several reasons for this high rate of mortality, including metastasis to several organs, especially the brain. In fact, lung cancer is responsible for approximately 50% of all brain metastases, which are very difficult to manage. Understanding the cellular and molecular mechanisms underlying lung cancer-associated brain metastasis brings up novel therapeutic promises with the hope to ameliorate the severity of the disease. Here, we provide an overview of the molecular mechanisms underlying the pathogenesis of lung cancer dissemination and metastasis to the brain, as well as promising horizons for impeding lung cancer brain metastasis, including the role of cancer stem cells, the blood-brain barrier, interactions of lung cancer cells with the brain microenvironment and lung cancer-driven systemic processes, as well as the role of growth factor/receptor tyrosine kinases, cell adhesion molecules and non-coding RNAs. In addition, we provide an overview of current and novel therapeutic approaches, including radiotherapy, surgery and stereotactic radiosurgery, chemotherapy, as also targeted cancer stem cell and epithelial-mesenchymal transition (EMT)-based therapies, micro-RNA-based therapies and other small molecule or antibody-based therapies. We will also discuss the daunting potential of some combined therapies.

CONCLUSIONS

The identification of molecular mechanisms underlying lung cancer metastasis has opened up new avenues towards their eradication and provides interesting opportunities for future research aimed at the development of novel targeted therapies.

SOX9 Regulates Cancer Stem-Like Properties and Metastatic Potential of Single-Walled Carbon Nanotube-Exposed Cells

Engineered nanomaterials hold great promise for the future development of innovative products but their adverse health effects are a major concern. Recent studies have indicated that certain nanomaterials, including carbon nanotubes (CNTs), may be carcinogenic. However, the underlying mechanisms behind their potential malignant properties remain unclear. In this study, we linked SOX9, a stem cell associated transcription factor, to the neoplastic-like properties of human lung epithelial cells chronically exposed to a low-dose of single-walled carbon nanotubes (SWCNTs). We found that SOX9 is upregulated in SWCNT-exposed cells, which is consistent with their abilities to induce tumor formation and metastasis in vivo. We therefore hypothesized that SOX9 overexpression may be responsible for the neoplastic-like phenotype observed in our model. Indeed, SOX9 knockdown inhibited anchorage-independent cell growth in vitro and lung colonization in vivo in a mouse xenograft model. SOX9 depletion also suppressed the formation of cancer stem-like cells (CSCs), as determined by tumor sphere formation and aldehyde dehydrogenase (ALDH) activity (Aldefluor) assays. Furthermore, SOX9 knockdown suppressed tumor metastasis and the expression of the stem cell marker ALDH1A1. Taken together, our findings provide a mechanistic insight into SWCNT-induced carcinogenesis and the role of SOX9 in CSC regulation and metastasis.

A potent indolylquinoline alleviates growth of human lung cancer cell tumorspheres

To fight cancer at its roots by targeting cancer stem cells is a promising approach for therapy. Previously, an indolylquinoline derivative, 3-((7-ethyl-1H-indol-3-yl)-methyl)-2-methylquinoline (EMMQ), was reported effectively inhibiting the growth of lung cancer cells through impairment of cellular mitochondria functions. To address more on drug efficiency, the study further exploited if EMMQ can impede the propagation of tumorspheres stemmed from non-small cell lung cancer cells. EMMQ inhibited proliferation of spheroids in culture. In animal models, administration of the drug attenuated the spheroid tumorigenicity. The activated apoptosis alleviated growth of xenograft tumors in immune-deficient mice as established by the enriched tumorspheres. More evidence suggested that the reduced stemness of the spheroid tumors is attributed to apoptotic death. The findings supported that EMMQ is an eligible approach to eradicate the minor but tumorigenic lung cancer tumorspheres.

Cullin7 is required for lung cancer cell proliferation and is overexpressed in lung cancer

Ubiquitin ligase Cullin7 has been identified as an oncogene in some malignant diseases such as choriocarcinoma and neuroblastoma. However, the role of Cullin7 in lung cancer carcinogenesis remains unclear. In this study, we explored the functional role of Cullin7 in lung cancer cell proliferation and tumorigenesis and determined its expression profile in lung cancer. Knocking down Cullin7 expression by small interfering RNA (siRNA) in lung cancer cells inhibited cell proliferation and elevated the expression of p53, p27, and p21 proteins. The enhanced p53 expression resulted from activation of the DNA damage response pathway. Cullin7 knockdown markedly suppressed xenograft tumor growth in vivo in mice. Moreover, Cullin7 expression was increased in primary lung cancer tissues of humans. Thus, Cullin7 is required for sustained proliferation and survival of tumor cells in vitro and in vivo, and its aberrant expression may contribute to the pathogenesis of lung cancer. Thus, our study provided evidence that Cullin7 functions as a novel oncogene in lung cancer and may be a potential therapeutic target for lung cancer management.

PAK1 confers chemoresistance and poor outcome in non-small cell lung cancer via β-catenin-mediated stemness

PAK1 confers resistance to the estrogen antagonist tamoxifen in breast cancer. However, a role for PAK1 remains to be elucidated for chemoresistance and prognosis in non-small cell lung cancer (NSCLC). We provide evidence that PAK1 confers cisplatin resistance by increasing β-catenin expression through ERK/GSK3β signaling. The increased β-catenin expression promotes sphere cell formation and expression of stemness markers and this β-catenin-induced stemness is responsible for PAK1-mediated cisplatin resistance. We enrolled 87 NSCLC patients who had received cisplatin-based chemotherapy to confirm the association between PAK1 expression and response to chemotherapy and outcomes. PAK1 expression, evaluated by immunohistochemistry, was positively correlated with pERK and β-catenin expression in lung tumors. Patients with high-PAK1, high-pERK, and high-nuclear β-catenin tumors more frequently showed an unfavorable response to cisplatin-based chemotherapy when compared to their counterparts. Kaplan-Meier and Cox regression analysis also indicated a poorer overall survival (OS) and relapse free survival (RFS) in patients with high-PAK1, high-pERK, and high-nuclear β-catenin tumors. In conclusion, PAK1 confers cisplatin resistance in NSCLC via β-catenin-mediated stemness. Therefore, we suggest that clinical use of a combination of the MEK/ERK inhibitor AZD6244 and cisplatin might improve sensitivity to cisplatin-based chemotherapy and outcomes in NSCLC patients who harbor high-PAK1-expressing tumors.

YAP1 Regulates OCT4 Activity and SOX2 Expression to Facilitate Self-Renewal and Vascular Mimicry of Stem-Like Cells

Non-small cell lung cancer (NSCLC) is highly correlated with smoking and has very low survival rates. Multiple studies have shown that stem-like cells contribute to the genesis and progression of NSCLC. Our results show that the transcriptional coactivator yes-associated protein 1 (YAP1), which is the oncogenic component of the Hippo signaling pathway, is elevated in the stem-like cells from NSCLC and contributes to their self-renewal and ability to form angiogenic tubules. Inhibition of YAP1 by a small molecule or depletion of YAP1 by siRNAs suppressed self-renewal and vascular mimicry of stem-like cells. These effects of YAP1 were mediated through the embryonic stem cell transcription factor, Sox2. YAP1 could transcriptionally induce Sox2 through a physical interaction with Oct4; Sox2 induction occurred independent of TEAD2 transcription factor, which is the predominant mediator of YAP1 functions. The binding of Oct4 to YAP1 could be detected in cell lines as well as tumor tissues; the interaction was elevated in NSCLC samples compared to normal tissue as seen by proximity ligation assays. YAP1 bound to Oct4 through the WW domain, and a peptide corresponding to this region could disrupt the interaction. Delivery of the WW domain peptide to stem-like cells disrupted the interaction and abrogated Sox2 expression, self-renewal, and vascular mimicry. Depleting YAP1 reduced the expression of multiple epithelial-mesenchymal transition genes and prevented the growth and metastasis of tumor xenografts in mice; overexpression of Sox2 in YAP1 null cells rescued these functions. These results demonstrate a novel regulation of stem-like functions by YAP1, through the modulation of Sox2 expression.

Regulation of nonsmall-cell lung cancer stem cell like cells by neurotransmitters and opioid peptides

Nonsmall-cell lung cancer (NSCLC) is the leading type of lung cancer and has a poor prognosis. We have shown that chronic stress promoted NSCLC xenografts in mice via stress neurotransmitter-activated cAMP signaling downstream of beta-adrenergic receptors and incidental beta-blocker therapy was reported to improve clinical outcomes in NSCLC patients. These findings suggest that psychological stress promotes NSCLC whereas pharmacologically or psychologically induced decreases in cAMP may inhibit NSCLC. Cancer stem cells are thought to drive the development, progression and resistance to therapy of NSCLC. However, their potential regulation by stress neurotransmitters has not been investigated. In the current study, epinephrine increased the number of cancer stem cell like cells (CSCs) from three NSCLC cell lines in spheroid formation assays while enhancing intracellular cAMP and the stem cell markers sonic hedgehog (SHH), aldehyde dehydrogenase-1 (ALDH-1) and Gli1, effects reversed by GABA or dynorphin B via Gαi -mediated inhibition of cAMP formation. The growth of NSCLC xenografts in a mouse model of stress reduction was significantly reduced as compared with mice maintained under standard conditions. Stress reduction reduced serum levels of corticosterone, norepinephrine and epinephrine while the inhibitory neurotransmitter γ-aminobutyric acid (GABA) and opioid peptides increased. Stress reduction significantly reduced cAMP, VEGF, p-ERK, p-AKT, p-CREB, p-SRc, SHH, ALDH-1 and Gli1 in xenograft tissues whereas cleaved caspase-3 and p53 were induced. We conclude that stress neurotransmitters activate CSCs in NSCLC via multiple cAMP-mediated pathways and that pharmacologically or psychologically induced decreases in cAMP signaling may improve clinical outcomes in NSCLC patients.

MRI virtual biopsy and treatment of brain metastatic tumors with targeted nanobioconjugates: nanoclinic in the brain

Differential diagnosis of brain magnetic resonance imaging (MRI) enhancement(s) remains a significant problem, which may be difficult to resolve without biopsy, which can be often dangerous or even impossible. Such MRI enhancement(s) can result from metastasis of primary tumors such as lung or breast, radiation necrosis, infections, or a new primary brain tumor (glioma, meningioma). Neurological symptoms are often the same on initial presentation. To develop a more precise noninvasive MRI diagnostic method, we have engineered a new class of poly(β-l-malic acid) polymeric nanoimaging agents (NIAs). The NIAs carrying attached MRI tracer are able to pass through the blood-brain barrier (BBB) and specifically target cancer cells for efficient imaging. A qualitative/quantitative "MRI virtual biopsy" method is based on a nanoconjugate carrying MRI contrast agent gadolinium-DOTA and antibodies recognizing tumor-specific markers and extravasating through the BBB. In newly developed double tumor xenogeneic mouse models of brain metastasis this noninvasive method allowed differential diagnosis of HER2- and EGFR-expressing brain tumors. After MRI diagnosis, breast and lung cancer brain metastases were successfully treated with similar tumor-targeted nanoconjugates carrying molecular inhibitors of EGFR or HER2 instead of imaging contrast agent. The treatment resulted in a significant increase in animal survival and markedly reduced immunostaining for several cancer stem cell markers. Novel NIAs could be useful for brain diagnostic MRI in the clinic without currently performed brain biopsies. This technology shows promise for differential MRI diagnosis and treatment of brain metastases and other pathologies when biopsies are difficult to perform.

Targeting lung cancer through inhibition of checkpoint kinases

Inhibitors of checkpoint kinases ATR, Chk1, and Wee1 are currently being tested in preclinical and clinical trials. Here, we review the basic principles behind the use of such inhibitors as anticancer agents, and particularly discuss their potential for treatment of lung cancer. As lung cancer is one of the most deadly cancers, new treatment strategies are highly needed. We discuss how checkpoint kinase inhibition in principle can lead to selective killing of lung cancer cells while sparing the surrounding normal tissues. Several features of lung cancer may potentially be exploited for targeting through inhibition of checkpoint kinases, including mutated p53, low ERCC1 levels, amplified Myc, tumor hypoxia and presence of lung cancer stem cells. Synergistic effects have also been reported between inhibitors of ATR/Chk1/Wee1 and conventional lung cancer treatments, such as gemcitabine, cisplatin, or radiation. Altogether, inhibitors of ATR, Chk1, and Wee1 are emerging as new cancer treatment agents, likely to be useful in lung cancer treatment. However, as lung tumors are very diverse, the inhibitors are unlikely to be effective in all patients, and more work is needed to determine how such inhibitors can be utilized in the most optimal ways.

Tumor heterogeneity and resistance to EGFR-targeted therapy in advanced nonsmall cell lung cancer: challenges and perspectives

Lung cancer, mostly nonsmall cell lung cancer, continues to be the leading cause of cancer-related death worldwide. With the development of tyrosine kinase inhibitors that selectively target lung cancer-related epidermal growth factor receptor mutations, management of advanced nonsmall cell lung cancer has been greatly transformed. Improvements in progression-free survival and life quality of the patients were observed in numerous clinical studies. However, overall survival is not prolonged because of later-acquired drug resistance. Recent studies reveal a heterogeneous subclonal architecture of lung cancer, so it is speculated that the tumor may rapidly adapt to environmental changes via a Darwinian selection mechanism. In this review, we aim to provide an overview of both spatial and temporal tumor heterogeneity as potential mechanisms underlying epidermal growth factor receptor tyrosine kinase inhibitor resistance in nonsmall cell lung cancer and summarize the possible origins of tumor heterogeneity covering theories of cancer stem cells and clonal evolution, as well as genomic instability and epigenetic aberrations in lung cancer. Moreover, investigational measures that overcome heterogeneity-associated drug resistance and new assays to improve tumor assessment are also discussed.