Increased EGFR mRNA Expression Levels in Non-Small Cell Lung Cancer

1Department of Medical Genetics, Atatürk University School of Medicine, Erzurum, Turkey 2Department of Medical Biology, Erciyes University School of Medicine, Kayseri, Turkey 3Department of Medical Genetics, Erciyes University School of Medicine, Kayseri, Turkey 4Department of Pathology, Erciyes University School of Medicine, Kayseri, Turkey 5Department of Thoracic Surgery, Erciyes University School of Medicine, Kayseri, Turkey


Introduction
Lung cancer is one of the most common cancers in humans and is the most common cause of death from cancer in the world.Non-small cell lung cancer (NSCLC) constitutes about 85% of lung cancers and it is divided into subgroups as squamous cell carcinoma, adenocarcinoma, large cell carcinoma and others [1].The treatment of lung cancer is planned mainly according to the stage of the cancer, the patient' s performance status and comorbid diseases.A large proportion of patients with NSCLC are diagnosed at stage 3 and stage 4, and chemotherapy is usually recommended as the first-line treatment option [2].Chemotherapy is very toxic, especially for the elderly and patients with poor performance.Therefore, in recent years there are efforts for developing targeted molecular-based drugs.
Epidermal growth factor receptor (EGFR) is a critical oncogenic factor involved in the occurrence and progress of NSCLC.EGFR is overexpressed in the majority of patients with NSCLC and is an important target in the treatment.EGFR is a member of the EGF-related tyrosine kinase receptor family [3].There are two specific EGFR tyrosine kinase inhibitors (TKIs), gefitinib and erlotinib, which are enhanced and used in clinic for the treatment of advanced NSCLC.An objective response rate is about 10% for unselected NSCLC patients.Female patients, non-smokers, East Asians and patients with adenocarcinoma have a much higher response rate [4].Today, molecular markers, which affect the response to EGFR-TKIs, have also been identified.
Many somatic mutations were identified in the EGFR gene in NSCLC.Most of the mutations are localized in the tyrosine kinase domain (exons 18-21) of the EGFR gene.The amino acids 746-753 encoded by exon 19 and the amino acid 858 encoded by exon 21, which comprise more than 80% of all detected mutations, are two mutation hotspots.Sensitivity to EGFR-TKIs has been identified in small frameshift deletions of exon 19 and arginine for leucine substitution at 858th amino acid of exon 21 (L858R) [5][6][7][8].This is the most important molecular mechanism in lung cancer.The seven phase-2 study made with gefitinib or erlotinib showed that response to TKIs are more than 87% and life expectancy is between 7.7 to 14 months without progression in patients with EGFR mutation positive NSCLC [9].This period is much longer than the time that is provided by chemotherapy in unselected patient population and other target therapies (4-6 months).Gene amplification is a mechanism responsible for the overexpression of oncogenes.Increased EGFR copies have been identified in about 30% of NSCLC patients with FISH analysis and this is often associated with poor prognosis [10].Increased EGFR copy is an effective indicator for better treatment response to EGFR-TKIs [5,7].High EGFR copy number is often associated with EGFR somatic mutations [5,8].EGFR mutation rates in American and European patients (10%) are too low when compared to Asian patients (30-50%).Still, a response to EGFR-TKI therapy is received in significant proportion of patients without the EGFR mutation and increased EGFR copy number might be the cause.Japanese patients with EGFR gene amplification do not benefit from gefitinib treatment and there is no known reason for this [11].
EGFR protein expression is very high (40-80%) in patients with NSCLC and is associated with poor prognosis [12].Both positive [7,13] and a negative relationship [14] is found in the literature between the levels of EGFR protein and EGFR TKIs sensitivity.The EGFR protein level is usually associated with EGFR gene copy number [7,10].Both IHC and FISH positive patients can benefit from EGFR-TKIs therapy.
There are significant differences in the prevalence of EGFR gene mutations in patients with lung cancer from different ethnic groups.The frequency of these mutations are 1-10% in the US and European patients [6,15], 19-26% in Southeast Asians patients [16], and about 58% in East Asian women [17].The studies showed that the incidence of EGFR mutations in Middle Eastern society was similar to western society.
While the amplification of the EGFR gene was seen about 30% in East Asian lung cancer patients, it is below 10% in the US and Australian patients.The frequency of EGFR amplification is higher in the Middle Eastern society (16%) than the western population (6-9%) [10].
In this study EGFR mutation frequency and EGFR mRNA and protein expression levels were investigated in Turkish population due to different EGFR mutation, amplification and protein expression rates between communities and their effects in response to the tyrosine kinase inhibitors.This study may determine the molecular predictors in predicting the efficacy of tyrosine kinase inhibitors in the NSCLC patients in Turkish population.

Patients
The study was ethically approved by the local ethics committee of Erciyes University (accession number: 2008/10) in accordance with the ethical standards of Helsinki Declaration and supported by Erciyes University Scientific Research Department with TST-08-399 project number.Written informed consent for study tissue DNA, RNA and protein was obtained from each patient in the study.Clinical data were obtained from patients' medical records.The following criteria were used to classify smoking status: never smokers were defined as those with lifetime exposure of 100 cigarettes or less; former smoker, who had stopped smoking at least 12 months before diagnosis and current smoker, who had stopped smoking 1 to 12 months before diagnosis or current smoking.
Primary cancer tissue and normal tissue samples were obtained from 34 NSCLC patients who had undergone lobectomy at the Erciyes University Department of Thoracic Surgery.RNA was extracted from fresh tissue samples as soon as possible.Tissue samples were collected at -80 C for DNA isolation and isolated together.
L858R (exon 21) mutation analysis by mutation specific PCR Genomic DNA was isolated using Genelute mammalian genomic DNA miniprep kit (Sigma-Aldrich) according to manufacturer' s guidelines.The EGFR gene exon 21 was amplified by PCR.Two specific primer sets were designed for the wild type sequence and the L858R mutation in exon 21 by introducing a wild type or mutated nucleotide at the 3′ terminal end (Table 1).A 20 ul PCR reaction mixture contained 5 ul of 10 PCR buffer, 50 nmol of MgCl 2 , 10 pmol each of sense and antisense primer, 6 nmol of dNTPs, 2 U of Taq polymerase and 100 ng of sample DNA.PCR was performed on Rotorgene Real-Time PCR System (Qiagen, Germany) under the following conditions: 95°C for 10 min, followed by 35 cycles of 94°C for 30s, 64°C for 30s, 72°C for 30s and final extension at 72°C for 5 min.PCR products were electrophoresed in % 2 agarose gels and visualized under UV.
EGFR exon 19 mutation analysis by direct sequencing Sample DNA was amplified by PCR using the primers indicated in Table 1.A 20 ul PCR reaction mixture contained 5 ul of 10 PCR buffer, 50 nmol of MgCl 2 , 10 pmol each of sense and antisense primer, 6 nmol of dNTPs, 2U of Taq polymerase and 100 ng of sample DNA.PCR was performed on Rotorgene Real-Time PCR System (Qiagen, Germany) under the following conditions: 95°C for 5 min, followed by 35 cycles of 95°C for 30 s, 64°C for 45 s, 72°C for 30 s and final extension at 72°C for 10 min.DNA products producing a positive band on agarose gel were used for further steps.Amplified DNA was purified using Genomic DNA purification kit (Fermantas).10 ng of PCR products was applied for the sequencing reaction using a Dye terminator cycle sequencing quick start kit (Beckman Coulter).EGFR exon 19 sequence analysis was performed using CEQTM 8000 Genetic Analysis System (Beckman Coulter).The reference coding sequence of EGFR was obtained from the NCBI (NCBI Reference Sequence: NG_007726.1)[18].

EGFR mRNA expression by relative quantitative reverse transcription PCR (qRT-PCR)
Total RNA was isolated using UltraClean tissue RNA isolation kit (MO BIO) following the manufacturer' s protocol.The cDNA was transcripted by using Transcriptor first strand cDNA synthesis kit with random hexamers (Roche; Germany).We prepared four PCR tubes for each patient to quantify the expression of EGFR-GAPDH in tumor samples and EGFR-GAPDH in normal samples.PCR reactions in a final volume of 25 μl: 2 μl cDNA, 18 μl distilled water, 1 ul MgCl 2 , 2 μl LightCycler faststart DNA master SYBR green I mix (Roche Diagnostics) and 2 μl primers for each EGFR and GAPDH gene (Table 1).
For each cDNA sample, expression levels of EGFR and the reference gene (GAPDH) were analyzed using the Rotorgene Real-Time PCR System (Qiagen, Germany).Cycle conditions of the relative qRT-PCR were preincubated at 95°C for 10 min, followed by 45 amplification cycles of 95°C for 8 s, 62°C for 15 s, 72°C for 10 s, and a melting curve analysis, which ran Melt (65-95°c), at 95°C hold 0 sec, at 65°C hold 15 secs and at 95°C hold 0 sec.qRT-PCR analysis and calculation of quantification cycle (Cq) values for relative quantification were performed by the Rotorgene Real-Time PCR software (Qiagen, Germany).
The gene expression of EGFR gene was normalized with GAPDH.The relative quantification of EGFR gene was calculated using the following formula [19] and the expression ratio greater than one is considered as overexpression (positive).agreement, 0-0.20 as slight, 0.21-0.40 as fair, 0.41-0.60 as moderate, 0.61-0.80 as substantial, and 0.81-1 as almost perfect agreement) [20].

Discussion
There are significant differences in the prevalence of EGFR gene mutations in patients with lung cancer from different ethnic groups.
The studies showed that the incidence of EGFR mutations in Middle Eastern society was similar to western society.The frequency of EGFR amplification is higher in the Middle Eastern society than the western population [6,10,15,17].EGFR gene mutation, amplification and expression studies in the literature in NSCLC patients and our study are shown in Table 6.
In the majority of publications, EGFR mutations were identified by sequence and mutation specific PCR + gel electrophoresis; gene amplification by FISH and qPCR and EGFR protein expression was evaluated by IHC method.EGFR protein expression positivity (with IHC method) varies between 40-80% of NSCLC tumors as shown in Table 6.Different results may be because of different detection methods used in measuring EGFR pro- In this study for determining mRNA expression, the EGFR expression in tumor tissue was compared with normal tissue in the same patient (TEGFR/TGAPDH/ NEGFR/ NGAPDH).This method led to the identification of the exact expression results for each patient because EGFR expression normally seen in non-tumor tissue of the patients were excluded (background expression).The differences between initial mRNA amounts of different patients are balanced with the usage of GAPDH as an internal control.This analysis method was used in the study of Brabender et al. [21] for the evaluation of EGFR and HER2-neu mRNA expression in patients with NSCLC, Mafune et al. [22] for expression evaluation in squamous cell esophagus carcinomas and Bong et al. [23] for identifying the expression of colorectal carcinoma.
The frequency of EGFR molecular pathologies change among societies.Evaluation of the usage of molecular pathology targeted drugs in different societies or development of molecular pathology targeted drugs are needed.In our study, EGFR gene changes, which are common in the etiology of NSCLC, are planned to be investigated in the NSCLC patients of Turkish society for predicting the effectiveness of TKIs and for determining the molecular changes that can be used for the response to EGFR therapy.
In our study, about 80% of EGFR gene muta-   tions in the literature were checked and no mutation detected.
The reason for this negativity may be the number of our patients, only three female patients, and three non-smoker patients, two of whom have tandoori story more than 20 years.With this study, the average mutation rate of the Turkish population (267 case, 58 cases have mutated) is 22% between 0-48% [24][25][26][27][28][29].The frequencies of these mutations are 1-10% in America and Europe [6,15].EGFR mutations are rare in Middle Eastern patients, similar to the rates in the Western society (%3).Significantly increased EGFR amplification rates (15%) have shown the need to determine the changes of gene copy number in response to anti-EGFR therapy in the Middle East patients [30].Increased EGFR mRNA and protein expression levels were stated in patients with EGFR mutations when compared to patients without gene mutations [31].Many publications have shown that EGFR mutations are associated with increased EGFR gene copy number and EGFR expression.EGFR gene mutations and increased amplification were found to be the best parameter in determining clinical progression in the Korean patients treated with erlotinib [32] and in Japanese patients treated with gefitinib [5].In addition, researchers have suggested investigating the effects of these molecular markers in different ethnic groups.Similar assessment could not be done in our study due to absence of mutations.In our study, no correlation was found between clinic-pathological characteristics of patients and the expression levels of mRNA and protein.
EGFR mRNA and protein overexpression were detected in 44% and 47% of patients, respectively.The agreement between EGFR mRNA and protein expression indicated a fair level (k = 0.348).EGFR protein overexpression was found in 67% of patients who increased mRNA expression.Although the remaining 33% of the patients increased EGFR mRNA expression, the increase in the protein expression was not detected.The reasons for this may be grading differences in the absence of objective evaluation criteria in IHC method, tumor cell contamination in the normal tissue or normal cell contamination in the tumor tissue.mRNA can also be impaired or translation can be blocked due to post-transcriptional events such as miRNA mechanisms.
In this study, even though approximately 85% of the mutations indicated in the literature were studied, no mutation detected.The mutation rates in European and Middle Eastern societies are about 1-10% and lower than East Asia community [6,15].The EGFR protein expression is between 16-80% in other communities and 46-54% [29,36,37] in Turkish society; we found a ratio of 47% in our study consistent with the literature.EGFR gene amplification has been identified in many different rates such as 9-45% by FISH and 7-51% by qPCR.EGFR mRNA expression was found 22-34% in the literature, which is lower than our positive rate of 44%.Based on the hypothesis that in general, increased gene amplification is associated with increased gene expression, our positive mRNA expression rates are higher than amplification rates measured by FISH and qPCR and higher when compared to European society, but shows compliance with East Asian societies.
In conclusion, markedly increased EGFR mRNA expression ratios in the absence of activating mutations show that identifying an increase in the EGFR mRNA expressions for the prediction of response to EGFR tyrosine kinase inhibitors may be significant in Turkish population.Further studies of patients treated with EGFR inhibitors would be necessary to estimate the influence of EGFR mRNA expression on the response to therapy in Turkish population.

Table 3 .
EGFR expression ratios of the 16 patients are bigger than one.
and percentage of IHC staining cells.The staining pattern was cytoplasmic and membranous.The intensity score was defined as follows: Score 0, no staining; score +1, faint staining; score +2 moderate staining (nearly at the same staining level as observed in the normal bronchial epithelium); score3, strong staining.The total score was calculated by multiplying formed by using the Fisher exact test or the x 2 test.A p value equal or less than 0.05 was considered statistically significant.EGFR mRNA expression and protein expression were compared by kappa, using the Landis and Koch criteria.EGFR protein expression assed by immunohistochemistryExamples of the staining intensity values of +1, +2, +3 used for evaluation of the measure-ment of EGFR protein expression in patients are shown in Figure1.Fifteen samples that exhibited grade 3 immunostaining scored as overexpression are shown in Table3.The level of agreement for EGFR protein expression determined by immunohistochemical analysis and EGFR mRNA expression determined by qPCR demonstrate a Κ of 0.348 (Table 5).A Κ of 0.348 indicates a fair level of agreement according to Landis and Koch criteria (values < 0 as indicating no

Table 1 .
Primers for exon 21 PCR, exon 19 sequence analysis and expression of EGFR gene

Table 2 .
Clinical patient characteristics

Table 3 .
Clinical patient characteristics and study results

Table 4 .
Characteristics of clinical patient according to EGFR mRNA and EGFR protein expression

Table 5 .
Correlation between expression level of EGFR protein and mRNA