Molecular biology of lung cancer: clinical implications

The complexity of thyroid transcription factor 1 with both pro- and anti-oncogenic activities

After the original identification of thyroid transcription factor 1 (TTF-1 or NKX2-1) biochemical activity as a transcriptional regulator of thyroglobulin in 1989, the bulk of the ensuing research has concentrated on elucidating the roles of NKX2-1 in the development of lung and thyroid tissues. Motivated by its specific expression pattern, pathologists adopted the NKX2-1 immunoreactivity to distinguish pulmonary from nonpulmonary nonthyroid adenocarcinomas. Interestingly, the concept of NKX2-1 as an active participant in lung tumorigenesis did not take hold until 2007. This minireview contrasts the recent advancements of NKX2-1-related observations primarily in the realm of pulmonary malignancies.

TGF-beta specifically enhances the metastatic attributes of murine lung adenocarcinoma: implications for human non-small cell lung cancer

Lung cancer is the most frequent and one of the most deadly cancer types and is classified into small cell lung cancer and non-small cell lung cancer (NSCLC). Transforming growth factor beta (TGFβ) regulates a wide array of cell functions and plays a major role in lung diseases, including NSCLC. TGFβ signals through the complex of TGFβ type I and type II receptors, triggering Smad and non-Smad signaling pathways such as PI3K/Akt and MEK1/ERK. We investigated the role of TGFβ1 on the progression of the murine lung adenocarcinoma cell line LP07. Furthermore, we undertook a retrospective study with tissue samples from stage I and II NSCLC patients to assess the clinical pathologic role and prognostic significance of TβRI expression. We demonstrated that although lung cancer cell monolayers responded to TGFβ1 anti-mitogenic effects and TGFβ1 pulse (24 h treatment) delayed tumor growth at primary site; a switch towards malignant progression upon TGFβ1 treatment was observed at the metastatic site. In our model, TGFβ1 modulated in vitro clonogenicity, protected against stress-induced apoptosis and increased adhesion, spreading, lung retention and metastatic outgrowth. PI3K and MEK1 signaling pathways were involved in TGFβ1-mediated metastasis stimulation. Several of these TGFβ responses were also observed in human NSCLC cell lines. In addition, we found that a higher expression of TβRI in human lung tumors is associated with poor patient's overall survival by univariate analysis, while multivariate analysis did not reach statistical significance. Although additional detailed analysis of the endogenous signaling in vivo and in vitro is needed, these studies may provide novel molecular targets for the treatment of lung cancer.

Genome-wide identification of genes with amplification and/or fusion in small cell lung cancer

To obtain a landscape of gross genetic alterations in small cell lung cancer (SCLC), genome-wide copy number analysis and whole-transcriptome sequencing were performed in 58 and 42 SCLCs, respectively. Focal amplification of known oncogene loci, MYCL1 (1p34.2), MYCN (2p24.3), and MYC (8q24.21), was frequently and mutually exclusively detected. MYCL1 and MYC were co-amplified with other regions on either the same or the different chromosome in several cases. In addition, the 9p24.1 region was identified as being amplified in SCLCs without amplification of MYC family oncogenes. Notably, expression of the KIAA1432 gene in this region was significantly higher in KIAA1432 amplified cells than in non-amplified cells, and its mRNA expression showed strong correlations with the copy numbers. Thus, KIAA1432 is a novel gene activated by amplification in SCLCs. By whole-transcriptome sequencing, a total of 60 fusion transcripts, transcribed from 95 different genes, were identified as being expressed in SCLC cells. However, no in-frame fusion transcripts were recurrently detected in ≥2 SCLCs, and genes in the amplified regions, such as PVT1 neighboring MYC and RLF in MYCL1 amplicons, were recurrently fused with genes in the same amplicons or with those in different amplicons on either the same or different chromosome. Thus, it was indicated that amplification and fusion of several genes on chromosomes 1 and 8 occur simultaneously but not sequentially through chromothripsis in the development of SCLC, and amplification rather than fusion of genes plays an important role in its development.

The pivotal role of IKKα in the development of spontaneous lung squamous cell carcinomas

Here, we report that kinase-dead IKKα knockin mice develop spontaneous lung squamous cell carcinomas (SCCs) associated with IKKα downregulation and marked pulmonary inflammation. IKKα reduction upregulated the expression of p63, Trim29, and keratin 5 (K5), which serve as diagnostic markers for human lung SCCs. IKKα(low)K5(+)p63(hi) cell expansion and SCC formation were accompanied by inflammation-associated deregulation of oncogenes, tumor suppressors, and stem cell regulators. Reintroducing transgenic K5.IKKα, depleting macrophages, and reconstituting irradiated mutant animals with wild-type bone marrow (BM) prevented SCC development, suggesting that BM-derived IKKα mutant macrophages promote the transition of IKKα(low)K5(+)p63(hi) cells to tumor cells. This mouse model resembles human lung SCCs, sheds light on the mechanisms underlying lung malignancy development, and identifies targets for therapy of lung SCCs.

TPL2 kinase is a suppressor of lung carcinogenesis

Lung cancer is a heterogeneous disease at both clinical and molecular levels, posing conceptual and practical bottlenecks in defining key pathways affecting its initiation and progression. Molecules with a central role in lung carcinogenesis are likely to be targeted by multiple deregulated pathways and may have prognostic, predictive, and/or therapeutic value. Here, we report that Tumor Progression Locus 2 (TPL2), a kinase implicated in the regulation of innate and adaptive immune responses, fulfils a role as a suppressor of lung carcinogenesis and is subject to diverse genetic and epigenetic aberrations in lung cancer patients. We show that allelic imbalance at the TPL2 locus, up-regulation of microRNA-370, which targets TPL2 transcripts, and activated RAS (rat sarcoma) signaling may result in down-regulation of TPL2 expression. Low TPL2 levels correlate with reduced lung cancer patient survival and accelerated onset and multiplicity of urethane-induced lung tumors in mice. Mechanistically, TPL2 was found to antagonize oncogene-induced cell transformation and survival through a pathway involving p53 downstream of cJun N-terminal kinase (JNK) and be required for optimal p53 response to genotoxic stress. These results identify multiple oncogenic pathways leading to TPL2 deregulation and highlight its major tumor-suppressing function in the lung.

Genotyping and genomic profiling of non-small-cell lung cancer: implications for current and future therapies

Substantial advances have been made in understanding critical molecular and cellular mechanisms driving tumor initiation, maintenance, and progression in non-small-cell lung cancer (NSCLC). Over the last decade, these findings have led to the discovery of a variety of novel drug targets and the development of new treatment strategies. Already, the standard of care for patients with advanced-stage NSCLC is shifting from selecting therapy empirically based on a patient's clinicopathologic features to using biomarker-driven treatment algorithms based on the molecular profile of a patient's tumor. This approach is currently best exemplified by treating patients with NSCLC with first-line tyrosine kinase inhibitors when their cancers harbor gain-of-function hotspot mutations in the epidermal growth factor receptor (EGFR) gene or anaplastic lymphoma kinase (ALK) gene rearrangements. These genotype-based targeted therapies represent the first step toward personalizing NSCLC therapy. Recent technology advances in multiplex genotyping and high-throughput genomic profiling by next-generation sequencing technologies now offer the possibility of rapidly and comprehensively interrogating the cancer genome of individual patients from small tumor biopsies. This advance provides the basis for categorizing molecular-defined subsets of patients with NSCLC in whom a growing list of novel molecularly targeted therapeutics are clinically evaluable and additional novel drug targets can be discovered. Increasingly, practicing oncologists are facing the challenge of determining how to select, interpret, and apply these new genetic and genomic assays. This review summarizes the evolution, early success, current status, challenges, and opportunities for clinical application of genotyping and genomic tests in therapeutic decision making for NSCLC.

Human lung epithelial cells progressed to malignancy through specific oncogenic manipulations

We used CDK4/hTERT-immortalized normal human bronchial epithelial cells (HBEC) from several individuals to study lung cancer pathogenesis by introducing combinations of common lung cancer oncogenic changes (p53, KRAS, and MYC) and followed the stepwise transformation of HBECs to full malignancy. This model showed that: (i) the combination of five genetic alterations (CDK4, hTERT, sh-p53, KRAS(V12), and c-MYC) is sufficient for full tumorigenic conversion of HBECs; (ii) genetically identical clones of transformed HBECs exhibit pronounced differences in tumor growth, histology, and differentiation; (iii) HBECs from different individuals vary in their sensitivity to transformation by these oncogenic manipulations; (iv) high levels of KRAS(V12) are required for full malignant transformation of HBECs, however, prior loss of p53 function is required to prevent oncogene-induced senescence; (v) overexpression of c-MYC greatly enhances malignancy but only in the context of sh-p53+KRAS(V12); (vi) growth of parental HBECs in serum-containing medium induces differentiation, whereas growth of oncogenically manipulated HBECs in serum increases in vivo tumorigenicity, decreases tumor latency, produces more undifferentiated tumors, and induces epithelial-to-mesenchymal transition (EMT); (vii) oncogenic transformation of HBECs leads to increased sensitivity to standard chemotherapy doublets; (viii) an mRNA signature derived by comparing tumorigenic versus nontumorigenic clones was predictive of outcome in patients with lung cancer. Collectively, our findings show that this HBEC model system can be used to study the effect of oncogenic mutations, their expression levels, and serum-derived environmental effects in malignant transformation, while also providing clinically translatable applications such as development of prognostic signatures and drug response phenotypes.

Lung cancer in women

Recent biological advances in tumor research provide clear evidence that lung cancer in females is different from that in males. These differences appear to have a direct impact on the clinical presentation, histology, and outcomes of lung cancer. Women are more likely to present with lung adenocarcinoma, tend to receive a diagnosis at an earlier age, and are more likely to be diagnosed with localized disease. Women may also be more predisposed to molecular aberrations resulting from the carcinogenic effects of tobacco, but do not appear to be more susceptible than men to developing lung cancer. The gender differences found in female lung cancer make it mandatory that gender stratification is used in clinical trials in order to improve the survival rates of patients with lung cancer.

Monoclonal antibodies in lung cancer

INTRODUCTION

Lung cancer is the leading cause of cancer death worldwide. As clinical benefits to conventional cancer therapies are still formidable, there is an urgent need for novel agents and approaches to improve the overall clinical outcomes for patients with lung cancer.

AREAS COVERED

This article reviews the current understanding of targeted therapy for lung cancer with monoclonal antibodies (mAbs), mainly bevacizumab and cetuximab. The results from several key clinical trials validating the effectiveness and safety of bevacizumab and cetuximab, the relation of cancer biomarkers, the polymorphic correlation of targeted genes with the therapeutic outcome of mAb-based treatment, as well as the impact of Biomarker-integrated Approaches of Targeted Therapy for Lung Cancer Elimination (BATTLE) trial on personalised treatment of lung cancer are discussed.

EXPERT OPINION

The addition of bevacizumab or cetuximab to chemotherapy has shown promising benefits to the patients with non-small-cell lung cancer. However, the overall benefits of mAb-based targeted therapy to lung cancer patients vary among individuals. It is therefore necessary to define reliable predictive biomarkers in an effort to better identify patients who are most likely to benefit from treatment with these novel agents in lung cancer.

Oncogenic KRAS-induced epiregulin overexpression contributes to aggressive phenotype and is a promising therapeutic target in non-small-cell lung cancer

KRAS mutations are one of the most common driver mutations in non-small-cell lung cancer (NSCLC) and finding druggable target molecules to inhibit oncogenic KRAS signaling is a significant challenge in NSCLC therapy. We recently identified epiregulin (EREG) as one of several putative transcriptional targets of oncogenic KRAS signaling in both KRAS-mutant NSCLC cells and immortalized bronchial epithelial cells expressing ectopic mutant KRAS. In the current study, we found that EREG is overexpressed in NSCLCs harboring KRAS, BRAF or EGFR mutations compared with NSCLCs with wild-type KRAS/BRAF/EGFR. Small interfering RNAs (siRNAs) targeting mutant KRAS, but not an siRNA targeting wild-type KRAS, significantly reduced EREG expression in KRAS-mutant and EREG-overexpressing NSCLC cell lines. In these cell lines, EREG expression was downregulated by MEK and ERK inhibitors. Importantly, EREG expression significantly correlated with KRAS expression or KRAS copy number in KRAS-mutant NSCLC cell lines. Further expression analysis using 89 NSCLC specimens showed that EREG was predominantly expressed in NSCLCs with pleural involvement, lymphatic permeation or vascular invasion and in KRAS-mutant adenocarcinomas. In addition, multivariate analysis revealed that EREG expression is an independent prognostic marker and EREG overexpression in combination with KRAS mutations was associated with an unfavorable prognosis for lung adenocarcinoma patients. In KRAS-mutant and EREG overexpressing NSCLC cells, siRNA-mediated EREG silencing inhibited anchorage-dependent and -independent growth and induced apoptosis. Our findings suggest that oncogenic KRAS-induced EREG overexpression contributes to an aggressive phenotype and could be a promising therapeutic target in oncogenic KRAS-driven NSCLC.