Correction to: Targeting the epidermal growth factor receptor in non-small cell lung cancer cells: the effect of combining RNA interference with tyrosine kinase inhibitors or cetuximab.

Following publication of the original article [1], the authors reported that there was an error in Figure 9, which contained a misplaced picture. The authors confirm that all of the published results and conclusions of the paper remain unchanged, as well as the figure legends. The authors apologize for any confusion caused. The corrected Figure 9 is shown as follows.

Effect of siRNAs targeting the EGFR T790M mutation in a non-small cell lung cancer cell line resistant to EGFR tyrosine kinase inhibitors and combination with various agents.

The epidermal growth factor receptor (EGFR) is a validated therapeutic target in non-small cell lung cancer (NSCLC). However, some mutations confer resistance to current available agents, especially the frequently occurring T790M mutation. In the current study, we have examined, in a NSCLC cell line H1975 containing both L858R and T790M mutations, the effect of T790M-specific-siRNAs versus other EGFR-specific-siRNAs. T790M-specific-siRNAs were able to inhibit T790M and EGFR mRNA, to reduce EGFR protein expression, as well as to reduce the cell growth and induce cell caspase activity in H1975 cells. However, this effect showed less potency compared to the other EGFR-specific-siRNAs. EGFR-specific-siRNAs strongly inhibited cell growth and induced apoptosis in H358, H1650, H292, HCC827 and also in H1975 cells, which showed weak response to tyrosine kinase inhibitors (TKIs) or cetuximab. The addition of T790M-specific-siRNAs could rescue the sensitivity of T790M mutant H1975 cells to TKIs. The combination of T790M-specific-siRNAs and cetuximab also additively enhanced cell growth inhibition and induction of apoptosis in H1975 cells. Among the anti-EGFR agents tested, the strongest biological effect was observed when afatinib was combined with T790M-specific-siRNAs. Afatinib also offered extra effect when combined with cetuximab in H1975 cells. In conclusion, knock-down of T790M transcript by siRNAs further decreases the cell growth of T790M mutant lung cancer cells that are treated with TKIs or cetuximab. The combination of a potent, irreversible kinase inhibitor such as afatinib, with T790M-specific-siRNAs should be further investigated as a new strategy in the treatment of lung cancer containing the resistant T790M mutation.

Targeting the epidermal growth factor receptor in non-small cell lung cancer cells: the effect of combining RNA interference with tyrosine kinase inhibitors or cetuximab.

BACKGROUND: The epidermal growth factor receptor (EGFR) is a validated therapeutic target in non-small cell lung cancer (NSCLC). However, current single agent receptor targeting does not achieve a maximal therapeutic effect, and some mutations confer resistance to current available agents. In the current study we have examined, in different NSCLC cell lines, the combined effect of RNA interference targeting the EGFR mRNA, and inactivation of EGFR signaling using different receptor tyrosine kinase inhibitors (TKIs) or a monoclonal antibody cetuximab. METHODS: NSCLC cells (cell lines HCC827, H292, H358, H1650, and H1975) were transfected with EGFR siRNA and/or treated with the TKIs gefitinib, erlotinib, and afatinib, and/or with the monoclonal antibody cetuximab. The reduction of EGFR mRNA expression was measured by real-time quantitative RT-PCR. The down-regulation of EGFR protein expression was measured by western blot, and the proliferation, viability, caspase3/7 activity, and apoptotic morphology were monitored by spectrophotometry, fluorimetry, and fluorescence microscopy. The combined effect of EGFR siRNA and different drugs was evaluated using a combination index. RESULTS: EGFR-specific siRNA strongly inhibited EGFR protein expression almost equally in all cell lines and inhibited cell growth and induced cell apoptosis in all NSCLC cell lines studied, albeit with a different magnitude. The effects on growth obtained with siRNA was strikingly different from the effects obtained with TKIs. The effects of siRNA probably correlate with the overall oncogenic significance of the receptor, which is only partly inhibited by the TKIs. The cells which showed weak response to TKIs, such as the H1975 cell line containing the T790M resistance mutation, were found to be responsive to siRNA knockdown of EGFR, as were cell lines with downstream TKI resistance mutations. The cell line HCC827, harboring an exon 19 deletion mutation, was more than 10-fold more sensitive to TKI proliferation inhibition and apoptosis induction than any of the other cell lines. Cetuximab alone had no relevant in vitro activity at concentrations obtainable in the clinic. The addition of EGFR siRNA to either TKIs or cetuximab additively enhanced growth inhibition and induction of apoptosis in all five cell lines, independent of the EGFR mutation status (wild-type or sensitizing mutation or resistant mutation). The strongest biological effect was observed when afatinib was combined with an EGFR-specific siRNA. CONCLUSIONS: EGFR knockdown by siRNA further decreases the cell growth of lung cancer cells that are treated with TKIs or cetuximab alone, confirming that single agent drug targeting does not achieve a maximal biological effect. The siRNA inhibits EGFR oncogenic activity that bypasses downstream "resistance" mutations such as KRAS and PTEN. The combined treatment of siRNA and EGFR inhibitory agents is additive. The combination of a potent, irreversible kinase inhibitor such as afatinib, with EGFR-specific siRNAs should be further investigated as a new strategy in the treatment of lung cancer and other EGFR dependent cancers, including those with downstream resistance mutations.

Influence of RT-qPCR primer position on EGFR interference efficacy in lung cancer cells.

BACKGROUND: Real-time quantitative RT-PCR (RT-qPCR) is a "gold" standard for measuring steady state mRNA levels in RNA interference assays. The knockdown of the epidermal growth factor receptor (EGFR) gene with eight individual EGFR small interfering RNAs (siRNAs) was estimated by RT-qPCR using three different RT-qPCR primer sets. RESULTS: Our results indicate that accurate measurement of siRNA efficacy by RT-qPCR requires careful attention for the selection of the primers used to amplify the target EGFR mRNA. CONCLUSIONS: We conclude that when assessing siRNA efficacy with RT-qPCR, more than one primer set targeting different regions of the mRNA should be evaluated and at least one of these primer sets should amplify a region encompassing the siRNA recognition sequence.

Quantification of epidermal growth factor receptor T790M mutant transcripts in lung cancer cells by real-time reverse transcriptase-quantitative polymerase chain reaction.

A simple and sensitive real-time reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) was developed to quantify threonine-to-methionine substitution at amino acid position 790 (T790M) mutant transcripts in a wild-type (wt) epidermal growth factor receptor background. The assay is based on three unmodified oligonucleotides, and both SYBR Green and a Taqman probe can be used. To increase the discrimination between mutant and wt signals, ARMS (amplification refractory mutation system) and LNA (locked nucleic acid) primers were tested, but a benefit was observed only with plasmids and not with cellular complementary DNA. The RT-qPCR assay using transcript-specific primers can detect as few as 1% T790M transcripts in a wt background and, therefore, will be useful in RNA interference studies specifically targeting mutant RNA.

Production of a mono-biotinylated EGFR nanobody in the E. coli periplasm using the pET22b vector.

OBJECTIVE: Our aim was to produce a mono-biotinylated single domain antibody ('nanobody') specific for the epidermal growth factor receptor (EGFR), which is overexpressed in many cancer cells. The binding of the nanobody and its function are tested in cancer cells. The construct could be used to carry variable therapeutic or diagnostic load using biotin-streptavidin bridging. RESULTS: The EGFR-specific 7D12 nanobody was genetically fused to an IgA hinge linker and to a C-terminal biotin ligase acceptor sequence, allowing mono-biotinylation in E. coli. Expression was in strain BL21-DE3 from a T7 RNA polymerase driven pET22b vector. The biotinylated nanobody, isolated from the periplasm, was purified using streptavidin-mutein affinity chromatography. Final yields were up to 5 mg/l of cell culture. We showed that the construct could bind to EGFR expressing A431 epidermoid carcinoma cells, and to transiently transformed EGFR overexpressing HEK293T cells and not to EGFR negative control cells. The specificity for the EGFR was further demonstrated by immunoprecipitation. To test the functionality, PC9 non-small cell lung cancer cells were treated with mono-biotinylated nanobody or with streptavidin-coupled tetravalent nanobodies. Both were able to block mutant EGFR phosphorylation and slow down growth of PC9 cells. Tetravalent nanobodies were able to downregulate AKT phosphorylation.

Targeting Polo-like kinase 1 and TRAIL enhances apoptosis in non-small cell lung cancer.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can selectively induce apoptosis in cancer cells without causing damage to normal cells. However, some tumors are resistant to TRAIL monotherapy and clinical studies assessing targeted agents towards the TRAIL receptor have failed to show robust therapeutic activity. Evidence has shown that standard anti-mitotic drugs can induce synergistic apoptosis upon combination with TRAIL via cell cycle arrest. Polo like kinase-1 (PLK1) plays a critical role in different stages of cell cycle progression and mitosis. A number of investigations have demonstrated that PLK1 inhibition causes cell cycle arrest and mitotic catastrophe in non-small cell lung cancer (NSCLC), and we thus postulated that PLK1 inhibition could enhance TRAIL-induced apoptosis. We demonstrate that the combination of a TRAIL receptor agonist and a PLK1 inhibitor synergistically reduces cell viability, and strongly increases apoptosis in NSCLC cellular models. Consistent with our in vitro observations, this drug combination also significantly reduces tumor growth in vivo. Our data additionally reveal that G2/M cell cycle arrest and downregulation of Mcl-1 and signal transducer and activator of transcription 3 (STAT3) activity following PLK1 inhibition may contribute to the sensitization of TRAIL-induced apoptosis in NSCLC. Together, these data support the further exploration of combined TRAIL and PLK1 inhibition in the treatment of NSCLC.

Combined inhibition of rho-associated protein kinase and EGFR suppresses the invasive phenotype in EGFR-dependent lung cancer cells.

INTRODUCTION: Lung cancer remains the leading cause of cancer-related mortality worldwide, with metastatic disease frequently a prominent feature at the time of diagnosis. The role of NSCLC-derived EGFR mutations in cancer cell proliferation and survival has been widely reported, but little is known about the function of these mutations in invasive growth and metastasis. In this study, we sought to evaluate the intrinsic invasive properties of NSCLC cells with differing EGFR status and examine possible therapeutic targets that can abrogate invasive growth. MATERIALS AND METHODS: Collagen-based assays and 3D cell cultures were used to assess morphological features, actin cytoskeleton dynamics and the invasive capacity of NSCLC cell lines with differing EGFR status. The role of the RhoA/ROCK/MYPT1 and EGFR/HER pathways in NSCLC-related invasion was investigated by pharmacological inhibition and RNA interference techniques. RESULTS: We demonstrate a positive correlation between EGFR mutational/amplification status and invasive capacity. Knockdown of wild-type and mutant EGFR leads to depletion of active and total MYPT1 levels. Combined pharmacological inhibition or genetic ablation of ROCK/EGFR suppresses the hallmarks of cancer cells and abrogates the invasive phenotype in EGFR-dependent NSCLC cells. CONCLUSIONS: These observations suggest that combined targeting of the ROCK and EGFR/HER pathways may be a potential therapeutic approach in limiting invasive growth in NSCLC.

Combined targeting of EGFR/HER promotes anti-tumor efficacy in subsets of KRAS mutant lung cancer resistant to single EGFR blockade.

KRAS is a frequently mutated oncogene in lung cancer and among the most refractory to EGFR targeted therapy. Recently, preclinical evidence in pancreatic cancer has demonstrated that mutant KRAS can be regulated by EGFR. However, the distinct correlation between the EGFR/HER family members and mutant KRAS has not been investigated. Here, we show that non-small cell lung cancer cell lines harboring differing isoforms of mutant KRAS, can be broadly divided into EGFR/HER dependent and EGFR/HER independent groups. Combined therapeutic targeting of EGFR, HER2 and HER3 in isoforms regulated by extracellular growth signals promotes in vitro and in vivo efficacy. We also provide evidence that depletion of EGFR via RNA interference specifically abolishes the EGFR/KRAS interaction in the dependent subset. Taken together, these findings suggest that upstream inhibition of the EGFR/HER receptors may be effective in treating a subset of KRAS mutant lung cancers.

RNA extraction for quantitative enterovirus RT-PCR: comparison of three methods.

Quantification of virus-like RNA sequences in biological fluids, like serum and cerebrospinal fluid, requires an RNA extraction method that is both reproducible and fast. Three RNA extraction methods were tested on enteroviruses: (1) the acid guanidine thiocyanate-phenol/chloroform (AGPC) method; (2) a method based on differential precipitation of the RNA and (3) a 'bind-wash-elute' system based on silica-gel membrane binding. The latter two methods yielded a comparable detection limit as measured by RT-PCR ELISA. The detection limit for the AGPC method was 10 times higher. The relative standard deviation for the bind-wash-elute method (3%) was superior to that of the other methods tested (both 20%) and provides a reliable and fast method to extract (viral) RNA from biological fluids for quantification by RT-PCR.

Synergistic effect of afatinib with su11274 in non-small cell lung cancer cells resistant to gefitinib or erlotinib.

Epidermal growth factor receptor (EGFR) and c-MET receptors are expressed on many non-small cell lung cancer (NSCLC) cells. Current single agent therapeutic targeting of a mutant EGFR has a high efficacy in the clinic, but is not curative. Here, we investigated the combination of targeting EGFR and c-MET pathways in NSCLC cells resistant to receptor tyrosine kinase inhibitors (TKIs), using RNA interference and inhibition by TKIs. Different NSCLC cell lines with various genomic characteristics (H358, H1650 and H1975) were transfected with EGFR-specific-siRNA, T790M-specific-siRNA, c-MET siRNA or the combination. Subsequently EGFR TKIs (gefitinib, erlotinib or afatinib) or monoclonal antibody cetuximab were combined respectively with the c-MET-specific TKI su11274 in NSCLC cell lines. The cell proliferation, viability, caspase-3/7 activity and apoptotic morphology were monitored by spectrophotometry, fluorimetry and fluorescence microscopy. The combined effect of EGFR TKIs, or cetuximab and su11274, was evaluated using a combination index. The results showed that the cell lines that were relatively resistant to EGFR TKIs, especially the H1975 cell line containing the resistance T790M mutation, were found to be more sensitive to EGFR-specific-siRNA. The combination of EGFR siRNA plus c-MET siRNA enhanced cell growth inhibition, apoptosis induction and inhibition of downstream signaling in EGFR TKI resistant H358, H1650 and H1975 cells, despite the absence of activity of the c-MET siRNA alone. EGFR TKIs or cetuximab plus su11274 were also consistently superior to either agent alone. The strongest biological effect was observed when afatinib, an irreversible pan-HER blocker was combined with su11274, which achieved a synergistic effect in the T790M mutant H1975 cells. In a conclusion, our findings offer preclinical proof of principle for combined inhibition as a promising treatment strategy for NSCLC, especially for patients in whom current EGFR-targeted treatments fail due to the presence of the T790M-EGFR-mutation or high c-MET expression.

miR-146a inhibits cell growth, cell migration and induces apoptosis in non-small cell lung cancer cells.

Aberrant expression of microRNA-146a (miR-146a) has been reported to be involved in the development and progression of various types of cancers. However, its role in non-small cell lung cancer (NSCLC) has not been elucidated. The aim of this study was to investigate the contribution of miR-146a to various aspects of the malignant phenotype of human NSCLCs. In functional experiments, miR-146a suppressed cell growth, induced cellular apoptosis and inhibited EGFR downstream signaling in five NSCLC cell lines (H358, H1650, H1975, HCC827 and H292). miR-146a also inhibited the migratory capacity of these NSCLC cells. On the other hand, miR-146a enhanced the inhibition of cell proliferation by drugs targeting EGFR, including both TKIs (gefitinib, erlotinib, and afatinib) and a monoclonal antibody (cetuximab). These effects were independent of the EGFR mutation status (wild type, sensitizing mutation or resistance mutation), but were less potent compared to the effects of siRNA targeting of EGFR. Our results suggest that these effects of miR-146a are due to its targeting of EGFR and NF-κB signaling. We also found, in clinical formalin fixed paraffin embedded (FFPE) lung cancer samples, that low expression of miR-146a was correlated with advanced clinical TNM stages and distant metastasis in NSCLC (P<0.05). The patients with high miR-146a expression in their tumors showed longer progression-free survival (25.6 weeks in miR-146a high patients vs. 4.8 weeks in miR-146a low patients, P<0.05). miR-146a is therefore a strong candidate prognostic biomarker in NSCLC. Thus inducing miR-146a might be a therapeutic strategy for NSCLC.