Resistance to EGFR-TKI can be mediated through multiple signaling pathways converging upon cap-dependent translation in EGFR-wild type NSCLC

The Role of RNA Modifications and RNA-modifying Proteins in Cancer Therapy and Drug Resistance

The advent of new genome-wide sequencing technologies has uncovered abnormal RNA modifications and RNA editing in a variety of human cancers. The discovery of reversible RNA N6-methyladenosine (RNA: m⁶A) by fat mass and obesity-associated protein (FTO) demethylase has led to exponential publications on the pathophysiological functions of m⁶A and its corresponding RNA modifying proteins (RMPs) in the past decade. Some excellent reviews have summarized the recent progress in this field. Compared to the extent of research into RNA: m⁶A and DNA 5-methylcytosine (DNA: m⁵C), much less is known about other RNA modifications and their associated RMPs, such as the role of RNA: m⁵C and its RNA cytosine methyltransferases (RCMTs) in cancer therapy and drug resistance. In this review, we will summarize the recent progress surrounding the function, intramolecular distribution and subcellular localization of several major RNA modifications, including 5' cap N7-methylguanosine (m7G) and 2'-O-methylation (Nm), m⁶A, m⁵C, A-to-I editing, and the associated RMPs. We will then discuss dysregulation of those RNA modifications and RMPs in cancer and their role in cancer therapy and drug resistance.

Intrapatient Molecular and Histologic Heterogeneity After First-generation or Second-generation TKI Therapy of NSCLC Patients: Potential Clinical Impact on Subsequent third-generation TKI Treatment

OBJECTIVES

The discovery of tyrosine kinase inhibitors (TKI) has remarkably improved the clinical course of patients with non-small cell lung cancer driven by Epidermal Growth Factor Receptor (EGFR) mutations. However, virtually in all cases, the disease resurfaces in a TKI-resistant form that is mainly linked to an acquired EGFR-T790M mutation, a MET amplification, or small cell lung cancer (SCLC) transformation. Third-generation TKIs are able to block tumor growth through an irreversible binding to the T790M-mutated receptor. Such new treatments require the diagnostic analysis of new pathologic tissue or a liquid biopsy to detect the presence of the T790M mutation.

MATERIALS AND METHODS

Pre-TKI and post-TKI biopsies from 27 patients with an activating EGFR mutation were collected and analyzed for EGFR-T790M mutation, MET amplification, and SCLC transformation.

RESULTS

The T790M mutation was found in 16 patients (59%) whereas MET gene amplification was found in 2 (10.5%) of 19 evaluated cases. The histologic transformation from adenocarcinoma (ADC) to SCLC was identified in 3 patients (11%). In one of them reversal from SCLC back to adenocarcinoma was observed. One patient had the T790M mutation concordantly detected in 2 synchronous lesions whereas another patient showed T790M positivity only in one of 2 specimens. In 4 patients longitudinal biopsies revealed T790M gains and losses not always according to biological expectations.

CONCLUSIONS

Intrapatient molecular or histologic heterogeneity may be frequently found during routine treatment of non-small cell lung cancer patients. This biological aspect may have profound repercussions on subsequent therapeutic decisions, and therefore requires in-depth investigation.

The regulation of Neuropilin 1 expression by miR-338-3p promotes non-small cell lung cancer via changes in EGFR signaling

Neuropilin 1 (NRP1) is a transmembrane glycoprotein that acts as a co‐receptor for multiple extracellular ligands and typically performs growth‐promoting functions in cancer cells. Accumulating evidence indicates that NRP1 is upregulated, and may be an independent predictor of cancer relapse and poor survival, in many cancer types, including non‐small cell lung cancer (NSCLC). Recent evidence suggests that NRP1 affects tumour cell viability via the epidermal growth factor receptor (EGFR) and Erb‐B2 receptor tyrosine kinase 2 (ErbB2) signalling pathways in venous endothelial cells and in multiple cancer cells. In the present study, we aimed to evaluate the role of NRP1 in NSCLC tumourigenesis and to explore a new post‐transcriptional mechanism of NRP1 regulation via a microRNA that mediates EGFR signalling regulation in lung carcinogenesis. The results showed that miR‐338‐3p is poorly expressed and NRP1 is overexpressed in NSCLC tissues relative to their levels in adjacent noncancerous tissues. Luciferase reporter assays, quantitative real‐time reverse transcription PCR, and Western blot analyses showed that NRP1 is a direct target of miR‐338‐3p. Overexpression of miR‐338‐3p in NSCLC cell lines inhibited cell proliferation in vitro and in vivo. Moreover, cell migration and invasion were inhibited by miR‐338‐3p overexpression. These effects occurred via the EGF signalling pathway. Our data revealed a new post‐transcriptional mechanism by which miR‐338‐3p directly targets NRP1; this mechanism plays a role in enhancing drug sensitivity in EGFR wild‐type patients with NSCLC.

Oncogenic kinases and perturbations in protein synthesis machinery and energetics in neoplasia

Notwithstanding that metabolic perturbations and dysregulated protein synthesis are salient features of cancer, the mechanism underlying coordination of cellular energy balance with mRNA translation (which is the most energy consuming process in the cell) is poorly understood. In this review, we focus on recently emerging insights in the molecular underpinnings of the cross-talk between oncogenic kinases, translational apparatus and cellular energy metabolism. In particular, we focus on the central signaling nodes that regulate these processes (e.g. the mechanistic/mammalian target of rapamycin MTOR) and the potential implications of these findings on improving the anti-neoplastic efficacy of oncogenic kinase inhibitors.

Eukaryotic translation initiation factor 3 subunit C is associated with acquired resistance to erlotinib in non-small cell lung cancer

The acquisition of resistance to EGFR tyrosine kinase inhibitors (EGFR-TKIs) is one of the major problems in the pharmacotherapy against non-small cell lung cancers; however, molecular mechanisms remain to be fully elucidated. Here, using a newly-established erlotinib-resistant cell line, PC9/ER, from PC9 lung cancer cells, we demonstrated that the expression of translation-related molecules, including eukaryotic translation initiation factor 3 subunit C (eIF3c), was upregulated in PC9/ER cells by proteome analyses. Immunoblot analyses confirmed that eIF3c protein increased in PC9/ER cells, compared with PC9 cells. Importantly, the knockdown of eIF3c with its siRNAs enhanced the drug sensitivity in PC9/ER cells. Mechanistically, we found that LC3B-II was upregulated in PC9/ER cells, while downregulated by the knockdown of eIF3c. Consistently, the overexpression of eIF3c increased the number of autophagosomes, proposing the causality between eIF3c expression and autophagy. Moreover, chloroquine, an autophagy inhibitor, restored the sensitivity to erlotinib. Finally, immunohistochemical analyses of biopsy samples showed that the frequency of eIF3c-positive cases was higher in the patients with EGFR-TKI resistance than those prior to EGFR-TKI treatment. Moreover, the eIF3c-positive cases exhibited poor prognosis in EGFR-TKI treatment. Collectively, the upregulation of eIF3c could impair the sensitivity to EGFR-TKI as a novel mechanism of the drug resistance.

Targeting EIF4F complex in non-small cell lung cancer cells

Non-small cell lung cancer (NSCLC) accounts for about 85–90% of lung cancer cases, which represents the leading cause of cancer-related death in the world. The majority of lung cancer patients doesn't respond well to conventional chemo-/radio-therapeutic regimens and have a poor prognosis. The recent introduction of targeted therapy and immunotherapy gives new hopes to NSCLC patients, but their outcome/prognosis is far from satisfactory. The translation initiation EIF4F complex has been shown to play important roles in cancer progression, but its functional role and therapeutic effect in lung cancers especially NSCLC remain largely unknown. In this current review, we summarize recent findings regarding the role of EIF4F complex in NSCLC progression and targeted therapy potentials. We also discuss the unanswered questions and future directions in this field.

NRF2 Promotes Tumor Maintenance by Modulating mRNA Translation in Pancreatic Cancer

Pancreatic cancer is a deadly malignancy that lacks effective therapeutics. We previously reported that oncogenic Kras induced the redox master regulator Nfe2l2/Nrf2 to stimulate pancreatic and lung cancer initiation. Here, we show that NRF2 is necessary to maintain pancreatic cancer proliferation by regulating mRNA translation. Specifically, loss of NRF2 led to defects in autocrine epidermal growth factor receptor (EGFR) signaling and oxidation of specific translational regulatory proteins, resulting in impaired cap-dependent and cap-independent mRNA translation in pancreatic cancer cells. Combined targeting of the EGFR effector AKT and the glutathione antioxidant pathway mimicked Nrf2 ablation to potently inhibit pancreatic cancer ex vivo and in vivo, representing a promising synthetic lethal strategy for treating the disease.

Metabolic glycoengineering sensitizes drug-resistant pancreatic cancer cells to tyrosine kinase inhibitors erlotinib and gefitinib

Metastatic human pancreatic cancer cells (the SW1990 line) that are resistant to the EGFR-targeting tyrosine kinase inhibitor drugs (TKI) erlotinib and gefitinib were treated with 1,3,4-O-Bu3ManNAc, a 'metabolic glycoengineering' drug candidate that increased sialylation by ∼2-fold. Consistent with genetic methods previously used to increase EGFR sialylation, this small molecule reduced EGF binding, EGFR transphosphorylation, and downstream STAT activation. Significantly, co-treatment with both the sugar pharmacophore and the existing TKI drugs resulted in strong synergy, in essence re-sensitizing the SW1990 cells to these drugs. Finally, 1,3,4-O-Bu3ManNAz, which is the azido-modified counterpart to 1,3,4-O-Bu3ManNAc, provided a similar benefit thereby establishing a broad-based foundation to extend a 'metabolic glycoengineering' approach to clinical applications.

Pim-1 kinase is a target of miR-486-5p and eukaryotic translation initiation factor 4E, and plays a critical role in lung cancer

Background

Pim-1 kinase is a proto-oncogene and its dysregulation contributes to tumorigenesis and progression of a variety of malignancies. Pim-1 was suggested as a therapeutic target of cancers. The functional relevance of Pim-1 and the mechanism underlying its dysregulation in lung tumorigenesis remained unclear. This study aimed to investigate if Pim-1 has important functions in non-small-cell lung cancer (NSCLC) by: 1) evaluating the clinicopathologic significance of Pim-1 through analysing its expression in 101 human NSCLCs tissues using quantitative PCR, Western Blot and immunohistochemical studies, 2) determining its role in NSCLC and drug resistance using in vitro assays, and 3) investigating the regulatory mechanism of Pim-1 dysregulation in lung tumorigenesis.

Results

Pim-1 was upregulated in 66.2% of the lung tumor tissues and its expression was significantly related to advanced stage (P = 0.019) and lymph node metastasis (P = 0.026). Reduced Pim-1 expression suppressed NSCLC cell growth, cell cycle progression and migration in vitro. Pim-1 was a novel target of miR-486-5p determined by luciferase report assay, and ectopic miR-486-5p expression in cancer cells reduced Pim-1 expression. Furthermore, eukaryotic translation initiation factor 4E (eIF4E) controlled the synthesis of Pim-1 in NSCLC cells, and its expression was positively associated with that of Pim-1 in NSCLC tissue specimens (r = 0.504, p < 0.001). The downregulated miR-486-5p and upregulated eIF4E in NSCLC cells led to the overexpression of Pim-1 by relieving the inhibitory effect of the 3′-UTR or 5′-UTR of Pim-1 mRNA, respectively. Moreover, Pim-1 knockdown sensitized NSCLC cells to cisplatin and EGFR tyrosine kinase inhibitor, gefitinib.

Conclusions

Pim-1 kinase could be a critical survival signaling factor in NSCLC, and regulated by miR-486-5p and eIF4E. Pim-1 kinase may provide a potential target for diagnosis and treatment for lung cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-240) contains supplementary material, which is available to authorized users.

EGFR inhibitors and autophagy in cancer treatment

Epidermal growth factor receptor (EGFR) inhibitor treatment is a strategy for cancer therapy. However, innate and acquired resistance is a major obstacle of the efficacy. Autophagy is a self-digesting process in cells, which is considered to be associated with anti-cancer drug resistance. The activation of EGFR can regulate autophagy through multiple signal pathways. EGFR inhibitors can induce autophagy, but the specific function of the induction of autophagy by EGFR inhibitors remains biphasic. On the one hand, autophagy induced by EGFR inhibitors acts as a cytoprotective response in cancer cells, and autophagy inhibitors can enhance the cytotoxic effects of EGFR inhibitors. On the other hand, a high level of autophagy after treatment of EGFR inhibitors can also result in autophagic cell death lacking features of apoptosis, and the combination of EGFR inhibitors with an autophagy inducer might be beneficial. Thus, autophagy regulation represents a promising approach for improving the efficacy of EGFR inhibitors in the treatment of cancer patients.