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JoVE Journal Cancer Research

Cancer Research

Establishment and Characterization of Three Afatinib-resistant Lung Adenocarcinoma PC-9 Cell Lines Developed with Increasing Doses of Afatinib

Published: June 26, 2019 doi: 10.3791/59473
Automatic Translation
1, 1, 2, 1, 3
1Advanced Cancer Translational Research Institute, Showa University, 2Division of Breast Surgical Oncology, Department of Surgery, Showa University School of Medicine, 3Division of Allergology and Respiratory Medicine, Department of Medicine, Showa University School of Medicine

Summary

A method for establishing afatinib-resistance cell lines from lung adenocarcinoma PC-9 cells was developed, and resistant cells were characterized. The resistant cells can be used to investigate epidermal growth factor receptor tyrosine kinase inhibitor-resistance mechanisms, applicable for patients with non-small cell lung cancer.

Abstract

Acquired resistance to molecular target inhibitors is a severe problem in cancer therapy. Lung cancer remains the leading cause of cancer-related death in most countries. The discovery of "oncogenic driver mutations," such as epidermal growth factor receptor (EGFR)-activating mutations, and subsequent development of molecular targeted agents of EGFR tyrosine kinase inhibitors (TKIs) (gefitinib, erlotinib, afatinib, dacomitinib, and osimertinib) have dramatically altered lung cancer treatment in recent decades. However, these drugs are still not effective in patients with non-small cell lung cancer (NSCLC) carrying EGFR-activating mutations. Following acquired resistance, the systemic progression of NSCLC remains a significant obstacle in treating patients with EGFR mutation-positive NSCLC. Here, we present a stepwise dose escalation method for establishing three independent acquired afatinib-resistant cell lines from NSCLC PC-9 cells harboring EGFR-activating mutations of 15-base pair deletions in EGFR exon 19. Methods for characterizing the three independent afatinib-resistance cell lines are briefly presented. The acquired resistance mechanisms to EGFR TKIs are heterogeneous. Therefore, multiple cell lines with acquired resistance to EGFR-TKIs must be examined. Ten to twelve months are required to obtain cell lines with acquired resistance using this stepwise dose escalation approach. The discovery of novel acquired resistance mechanisms will contribute to the development of more effective and safe therapeutic strategies.

Introduction

Five tyrosine kinase inhibitors, targeting epidermal growth factor receptor (EGFR), including gefitinib, erlotinib, afatinib, dacomitinib, and osimertinib are currently available for treating patients with EGFR mutation-positive non-small cell lung cancer (NSCLC). Over the past decade, therapies for such patients have undergone dramatic development with the discovery of new potential EGFR-TKIs. Among patients with lung adenocarcinoma, somatic mutations in EGFR are identified in approximately 50% of Asian and 15% of Caucasian patients1. The most common mutations in EGFR are an L858R point mutation in EGFR exon 21 and 15 base pair (bp) deletions in EGFR exon 192. In EGFR mutation-positive patients with NSCLC, EGFR-TKIs improve the response rates and clinical outcomes compared to the previous standard of platinum doublet chemotherapy3.

Gefitinib and erlotinib were the first approved small molecule inhibitors and are generally referred to as first-generation EGFR TKIs. These EGFR TKIs block tyrosine kinase activity by competing with ATP and reversibly binding to ATP binding sites4. Afatinib is a second-generation EGFR TKI that irreversibly and covalently binds to the tyrosine kinase domain of EGFR and is characterized as a pan-human EGFR family inhibitor5.

Despite the dramatical benefit of these therapies in patients with NSCLC, acquired resistance is inevitable. The most common resistance mechanism against first- and second-generation EGFR TKIs is the emergence of the T790M mutation in EGFR exon 20, which is present in 50-70% of tumor samples6,7,8. Other resistance mechanisms include bypass signals (to MET, IGF1R, and HER2), transformation to small cell lung cancer, and induction of epithelial-to-mesenchymal transition, which occur pre-clinically and clinically9. The resistance mechanisms to EGFR TKIs are heterogeneous. By identifying novel resistance mechanisms in preclinical studies, it may be possible to develop novel therapeutics to overcome resistance. Optimal sequence therapies that maximize the clinical benefit to patients must consider the resistance mechanisms and therapeutic target.

It is imperative to choose the right parental cell line, as it is the basis of all the subsequent experiments. The selection strategies begin with clinical relevance; it is necessary to choose a chemotherapy and radiation naïve cell line. Previous chemotherapeutic and/or radiative treatment may induce the alteration of resistance pathways and changes of the expression of drug resistance markers. In this study, PC-9 cells, carrying 15 bp deletions in EGFR exon 19, are employed for the establishment of acquired resistance to afatinib. This cell line was derived from a Japanese NSCLC patient, who did not receive prior chemotherapy and radiation.

Because afatinib is administered orally on a daily basis, continuous in vitro treatment, where the cells are cultured constantly in the presence of afatinib would be clinically relevant. The dose of drugs used in the various steps of the experiment must be optimized for the parental cell line selected. A cytotoxicity assay can be used for determining a suitable drug range, which should be comparable to the pharmacokinetic information of the drug.

Throughout the selection process, the whole population of cells is maintained as a single group; cloning or other separation methods are not used. The cells are first continuously exposed to a low level of the drug. Subsequently, after the cells adapt to grow in the presence of the drug, the dose of the drug is slowly increased to the final optimal dose of drug10,11. Alternatively, a pulse drug-administration or mutagenesis can be used for selecting resistance cells, which are also performed prior to drug treatment 12,13. Unfortunately, cases where drug resistance fails to develop are generally not reported. The selection strategies are developed with the aim of trying to mimic the conditions of cancer patients for rebuilding clinically relevant resistance. Sometimes, to identify molecular changes associated with mechanisms of drug resistance, a high drug concentration is used. This model becomes less clinically relevant.

Here, we describe a method for establishing three independent afatinib-resistant cell lines from PC-9 cells harboring 15 bp deletions in EGFR exon 19 as well as the initial characterization of the afatinib-resistant cell lines.

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Protocol

1. Establishment of Three Independent Afatinib-resistant PC-9 Cell Lines

  1. Determination of the initial afatinib exposure concentration for PC-9 cells using the 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT) assay
    1. Culture PC-9 cells in growth medium containing fetal bovine serum (10%), penicillin (100 U/mL), and streptomycin (100 µg/mL) in a cell-culture treated 10-cm dish in a 5% CO2 incubator at 37 °C.
    2. Resuspend PC-9 cells at 4 x 104 cells/mL in growth medium and then seed at 50 µL/well in a 96-well microplate. The final concentration of cells is 2.0 x 103 cells/50 µL/well. Incubate overnight in a 5% CO2 incubator at 37°C.
    3. Add 50 µL of afatinib solution at different concentrations: 0, 0.002, 0.006, 0.02, 0.06, 0.2, 0.6, 2, 6, and 20 µM to the wells containing the growth medium (50 µL). The final volume and concentrations of afatinib are 100 µL and 0, 0.001, 0.003, 0.01, 0.03, 0.1, 0.3, 1, 3, and 10 µM, respectively.
    4. Incubate the 96-well plate for 96 h in a 5% CO2 incubator at 37 °C.
    5. Add 15 µL of the dye solution (see Table of Materials) to each well and incubate for 4 h in a 5% CO2 incubator at 37 °C, and then add 100 µL of solubilization/stop-solution (see Table of Materials) to each well and incubate overnight in a 5% CO2 incubator at 37 °C.
    6. Measure the optical density at 570 nm (OD570) using a microplate reader (see Table of Materials). Prepare 6-12 replicates and repeat the experiments at least three times.
    7. Use statistical software (see Table of Materials) to graphically plot these data as a semi-log graph and calculate the IC50 value, which is the drug concentration that reduces response to 50% of its maximum (see Table of Materials).
  2. Continuous exposure of PC-9 cells to the irreversible EGFR-TKI, afatinib, by stepwise dose escalation in three independent 10 cm dishes
    1. Culture PC-9 cells in p100 dishes containing 10 mL of growth medium. When the PC-9 cells reach the sub-confluent stage, transfer 1 mL of cell suspension into three new p100 dishes, with 9 mL of growth medium. The 1:10 diluted PC-9 cells become sub-confluent in 3-4 days, with a cell number of approximately 4-5 x 105 cells/mL.
    2. On the next day, add 1/10 of the IC50 value of afatinib into each of the three p100 dishes.
      NOTE: Afatinib is reconstituted in DMSO at stock concentrations of 1 μM, 10 µM, 100 µM, 1 mM, and 5 mM. 1 to 10 µL of afatinib-solution is added into 10 mL of growth medium in the culture, as per the required final concentrations.
    3. When the cells in the afatinib-containing p100 dishes become sub-confluent, mix well by aspiration with a 1 mL pipette and add 1 mL of the cell suspension to 9 mL of fresh growth medium in a new p100 dish. Next, add 10-20% higher concentrations of afatinib to the new culture.
    4. Increase the afatinib concentration of 0.1 nM to 1 μM in the medium by the stepwise dose escalation with the afatinib concentration increased by 10-20% at each step over the period of 10-12 months.
      NOTE: When the afatinib concentration approaches the IC50 value, cell growth becomes quite slow. If the cells are split 1:9, they may not grow, as these cells are killed by higher concentrations of afatinib. Therefore, at higher afanitib concentrations, the cells can be split at a ratio of 1:2. The most resistant cells were grown in afatinib-contained medium for 3-14 days, and the medium was not changed until the resistant cells needed to be passaged.
    5. Culture the afatinib-resistant cells for 2-3 months in 1 µM afatinib-containing growth medium. At an afatinib concentration of 1 µM, 10-12 months are required for developing resistance to afatinib in this model. Perform the MTT assay to confirm that the cells are resistant to afatinib. The three independently established afatinib resistance cell lines were named AFR1, AFR2, and AFR3.

2. Characterization of Three Independent Afatinib-resistant Cells

  1. Determination of the growth curve of parental PC-9 cells and establishment of afatinib-resistant cells
    1. Culture the PC-9, AFR1, AFR2, and AFR3 cells in growth medium in a 5% CO2 incubator at 37 °C.
    2. Resuspend the cells at 5 x 103 cells/mL with growth medium, and seed 100 µL/well into a 96-well microplate, such that the final concentration of cells is 500 cells/100 µL/well.
      NOTE: The MTT assay is performed to measure the OD570 values at 0, 1, 2, 3, 5, and 7 days. Six 96-well microplates are required for each day.
    3. Perform the MTT assay every 24 h and then on days 0, 1, 2, 3, 5, and 7. Measure the OD570 values and prepare 6-12 replicates; repeat the experiments at least three times, and graphically plot the results using a statistical software (see Table of Materials).
  2. Identification of the genomic DNA alterations in EGFR by real-time PCR
    NOTE: Afatinib is a small molecule inhibitor that targets EGFR tyrosine kinase. The EGFR expression status is determined at the DNA and protein levels.
    1. Genomic DNA is isolated using a DNA purification kit (see Table of Materials) following the manufacturer's instructions. Measure the concentration of the isolated genomic DNA with a spectrophotometer (see Table of Materials) and adjust all genomic DNA samples to 25 ng/ µL.
    2. Amplify 50 ng of genomic DNA, which is equivalent to 2 µL of the 25 ng/µL stocks, using a SYBR Green master mix (see Table of Materials) and analyze the results using a fluorescence-based RT-PCR-detection system (see Table of Materials).
      NOTE: PCR cycling conditions began with an initial denaturation step at 95 °C for 20 s, followed by 40 cycles of 95 °C denaturation for 3 s, 60 °C annealing for 30 s. The specific primer sets are as follows: EGFR F: 5′-CAAGGCCATGGAATCTGTCA-3′, R: 5′-CTGGAATGAGGTGGAGGAACA-3′. Normalization gene LINE-1 F: 5′-AAAGCCGCTCAACTACATGG-3′, R: 5′-TGCTTTGAATGCGTCCCAGAG-3′.
  3. Evaluation of the effect of protein alterations on the EGFR level by western blot analysis
    1. Treat the cells with afatinib continuously prior to experiments for 24 h. Wash PC-9, AFR1, AFR2, and AFR3 cells twice with PBS and then seed them in growth media without afatinib. Wash PC-9, AFR1, AFR2, and AFR3 cells twice with 5 mL of ice-cold PBS.
    2. Lyse the cells in RIPA buffer containing 1% protease inhibitor cocktail (see Table of Materials) and phosphatase inhibitor cocktail II and III (see Table of Materials) and incubate this solution at 4 °C for 30 min. Centrifuge the lysates for 10 min at 100 x g and 4 °C and collect the cleared lysates.
    3. Determine protein concentrations using the bicinchoninic acid assay (see Table of Materials), adjust all protein samples to 0.5 or 1 µg/µL using 4x sample buffer (500 mM Tris (PH 6.8), 40% glycerol, 8% SDS, 20% H2O, 0.02% bromophenol blue) and boil at 96 °C for 5 min. Store these protein samples at -80 °C until western blot analysis is performed.
    4. Separate equal amounts of protein samples, preferably 20-30 µL, by 8% SDS-page and transfer the proteins to a polyvinylidene fluoride (PVDF) membrane.
      NOTE: Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) is commonly used in the lab for the separation of proteins based on their molecular weight.
      1. Clean glass plates with ethanol and assemble the glass plate and spacers. Prepare 8% poly-acrylamide gels containing 1.5 M Tris-HCl, pH 8.8, 40% Bis-acrylamide, 10% SDS, 10% APS, and TEMED. Polymerize for 30 min at room temperature.
      2. Subsequently, prepare a stacking gel containing 0.5 M Tris-HCl, pH 6.8, 40% bis-acrylamide, 10% SDS, 10% APS, and TEMED. Add the stacking gel solution, insert the comb, and polymerize the gel for 20-30 min at room temperature.
      3. Place the gels in the electrophoresis apparatus and fill the tank with running buffer (0.25 M Tris, 1.92 M glycine, and 1% SDS). Load equal amount of protein samples (20-30 µL) and run the gel at 180 V. Stop electrophoresis once the dye front flows out of the gel, after approximately 60 min.
      4. Wash the gel for 1-2 min with TBST and then transfer the proteins on to a PVDF membrane by semi-dry blotting (see Table of Materials) for 1.5 h at a constant current of 300 mA.
    5. Block the membranes with 5% of nonfat dry milk (see Table of Materials) diluted with TBST solution (see Table of Materials) for 1 h at room temperature, and then probe the membranes with anti-EGFR, anti-phospho-EGFR (Y1068), anti-HER2, anti-HER3, anti-MET, and anti-actin antibodies (diluted 1:3,000 in TBST) (see Table of Materials) at 4 °C overnight.
    6. Wash the membranes with TBST three times for 10 min, and then expose the membranes to the secondary antibody (diluted 1:200 in TBST) for 1-1.5 h at room temperature. Wash the membranes five times with TBST for 10 min at room-temperature, expose them to the ECL solution (see Table of Materials), and visualize the signals using films.
  4. Analysis of EGFR mutations by sequencing
    1. Amplify genomic DNA using specific primers for EGFR exons 19-21. The PCR cycling conditions begin with an initial denaturation step at 94 °C for 1 min, followed by 30 cycles of denaturation at 98 °C for 10 s, annealing at 55 °C for 30 s, and extension at 72 °C for 1 min.
      NOTE: The specific primers for EGFR exon 19: F: 5′-GCAATATCAGCCTTAGGTGCGGCTC-3′ R: 5′-CATAGAAAGTGAACATTTAGGATGTG-3′, exon 20: F: 5′-CCATGAGTACGTATTTTGAAACTC-3′, R: 5′-CATATCCCCATGGCAAACTCTTGC-3′, and exon 21: F: 5′-ATGAACATGACCCTGAATTCGG-3′, R: 5′-GCTCACCCAGAATGTCTGGAGA-3′.
    2. Purify the amplified PCR products using a PCR purification kit (see Table of Materials) and sequence the amplicons.

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Representative Results

The schema for establishing three afatinib-resistance cell lines from PC-9 cells using a stepwise dose-escalation procedure is shown in Figure 1. Figure 2 shows a decrease in cell proliferation of parental PC-9 cells as the concentration of afatinib is increased, indicating that PC-9 cells are sensitive to afatinib exposure. Figure 3 shows the afatinib-resistance of the three cell lines. None of the three afatinib-resistant cell lines, AFR1, AFR2, and AFR3, showed suppression of cell proliferation under afatinib exposure. Figure 4 shows the cell-proliferation curves for PC-9, AFR1, AFR2, and AFR3 cells. The three afatinib-resistant cell lines exhibited significantly slower growth than the parental PC-9 cells. Figure 5 shows the expression levels of EGFR gDNA in PC-9 and the three afatinib-resistant cells, which indicate that afatinib-resistant cells expressed significantly higher levels of EGFR gDNA than the parental PC-9 cells. Figure 6 shows the protein expression of EGFR in PC-9 and afatinib-resistant cells. At comparable gDNA expression levels, EGFR protein expression was higher in resistant cells than in parental PC-9 cells. Figure 7 shows that the sequencing results of EGFR exons 19 and 20 in PC-9, AFR1, AFR2, and AFR3 cells. PC-9 cells showed 15 bp deletions in EGFR exon 19 and wild-type EGFR in exon 20. However, AFR1 and AFR2 cells exhibited amplification of wild-type EGFR exon 19. AFR3 cells contained 15 bp deletions in EGFR exon 19 as in PC-9 cells, but the point mutation T790M was observed in EGFR exon 20.

Figure 1
Figure 1: Schema of the process used to establish three afatinib-resistant cell lines from PC-9. First, PC-9 cells were separated into three p100 dishes and exposed to afatinib at 1/10 of the IC50 value. Next, afatinib concentrations in the growth medium were increased by stepwise dose escalation to 1 µM. After 10-12 months, three independent afatinib-resistant cell lines were established and named AFR1, AFR2, and AFR3. Please click here to view a larger version of this figure.

Figure 2
Figure 2: Parental PC-9 cells are sensitive to the irreversible EGFR TKI, afatinib. Cells were seeded into a 96-well microplate at 2 x 103 cells/well/50 µL of growth medium, and preincubated overnight. The cells were treated with the indicated concentrations of afatinib for 96 h. An MTT assay was performed, OD570 values were measured using a microplate reader (see Table of Materials) and expressed as a percentage of the value obtained for the control cells. Data are presented as mean ± SEM of values from 6-12 replicate wells. Please click here to view a larger version of this figure.

Figure 3
Figure 3: Established cells exhibited resistance to irreversible EGFR TKI, afatinib. Cells were seeded into a 96-well microplate at 2 x 103 cells/well/50 µL of growth medium and preincubated overnight. The cells were treated with the indicated concentrations of afatinib for 96 h. An MTT assay was performed, OD570 values were measured using a microplate reader (see Table of Materials) and expressed as a percentage of the value obtained for the control cells. Data are presented as mean ± SEM of values from 6-12 replicate wells. Please click here to view a larger version of this figure.

Figure 4
Figure 4: Afatinib-resistant cell lines showed slower proliferation than parental PC-9 cells. Cells were seeded into 96-well microplates at 5 x 102 cells/100 µL/well. MTT assay was performed, and OD570 values were measured on days 0, 1, 2, 3, 5, and 7 using a microplate reader (see Table of Materials) and expressed as a percentage of the value obtained for the control cells. Data are presented as mean ± SEM of values from 6-12 replicate wells. Please click here to view a larger version of this figure.

Figure 5
Figure 5: Gene copy number of EGFR was elevated in afatinib-resistant cells. The elevation of the EGFR gene copy number was measured by quantitative PCR of genomic DNA isolated from PC-9, AFR1, AFR2, and AFR3 cells. Please click here to view a larger version of this figure.

Figure 6
Figure 6: Basal level of EGFR protein was increased in afatinib-resistant cells. Western blot analysis of phospho-EGFR, EGFR, HER2, HER3, and MET expression in PC-9, AFR1, AFR2, and AFR3 cells. β-Actin was used as a loading control. Please click here to view a larger version of this figure.

Figure 7
Figure 7: DNA sequence reads in EGFR exons 19 and 20. Genomic DNA of PC-9, AFR1, AFR2, and AFR3 was amplified with specific primers for EGFR exon 19 and 21, and purified for sequencing. Please click here to view a larger version of this figure.

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Discussion

Here, we described a method for establishing three independent afatinib-resistant cell lines and characterized these cells by comparison to parental PC-9 cells. By stepwise dose escalation exposure, the parental PC-9 cells acquired resistance to afatinib over a period of 10-12 months. Clinically, the resistance mechanisms to EGFR TKIs are heterogeneous, and therefore, after the initial treatment with afatinib, PC-9 cells were divided into three independent p100 dishes and exposed further to afatinib. Initially, cell growth was not significantly slowed, but as the drug concentration approached the IC50 value, cell proliferation was slowed. This is a critical step for obtaining cells with acquired resistance to inhibitors. The proliferating cells should be split and transferred to new p100 dishes at a ratio of 1:10 or 1:5. When PC-9 cells were cultured in a p100 dish, some adherence was observed, but most cells grew in suspension. As the concentration of afatinib was increased, the cells adhered to the bottom of the tissue culture treated dishes. If most cells are adherent, they can be detached with a cell-scraper. The final concentration of afatinib was 1 µM, which is about 5 times the maximum serum concentration (Cmax)14. To obtain clear differences between parental and resistance clones, the final concentration was set to be higher than Cmax.

One serious concern during the procedure is bacterial contamination, even though RPMI-1640 contains penicillin and streptomycin. To avoid this, two p100 dishes containing fresh growth medium can be prepared when the cells are split. When the cells reach the sub-confluent stage, the cells in one p100 dish can be further split, while the cells in the other p100 dish can be stored at -80 °C in cryopreservation medium (see Table of Materials) as a backup, such that if one line is contaminated, the stored line can be used.

It would be difficult to completely reproduce the acquisition of afatinib resistance in humans using cell culture. The emergence of the T790M mutation in EGFR exon 20 was reported as the dominant cause of resistance to afatinib. In our report, one resistant clone contained the T790M mutation11. Furthermore, the increase in wild-type EGFR, such as in AFR1 and AFR2 cells, has been reported by us and other groups15,16. The loss of the EGFR mutation and increase in wild type EGFR is also reported in clinical samples from patients with acquired resistance to EGFR-TKIs 17,18. Therefore, in vitro studies of our current model may reflect the molecular profiles of clinical specimens with acquired resistance.

This stepwise dose escalation method is considered the most reliable for obtaining acquired resistant cells lines. However, initial high-dose afatinib exposure in cultured cells would likely better reflect the effects of afatinib treatment in patients with cancer, although establishing resistant cells is more difficult. Not only floating cell lines, such as PC-9 but also adherent cell lines, such as HCC827, 11-18, or HCC4006, can be employed for this method. This stepwise dose escalation method is also useful for establishing clones resistant to other inhibitors, using other cell lines, representing other types of cancer.

Exposure of parental cells to mutagenic agents, such as N-ethyl-N-nitrosourea, followed by selection of cells resistant to afatinib or osimertinib treatment has been reported to enable rapid acquisition of resistant clones 19,20. However, this artificial method tends to cause specific base substitutions, such as GC to AT transitions and AT to TA transversions. Moreover, EGFR TKI is not a mutagenic agent in patients with NSCLC. Therefore, the method of stepwise dose escalation is more representative than using mutagenic agents.

Although EGFR TKIs are initially effective, cells eventually develop resistance to such single-target drugs, making it difficult to cure cancer. Inhibitors that target multiple molecules are therefore essential to develop. To this end, it is necessary to obtain cells with acquired resistance to multi-target inhibitors and evaluate the mechanisms underlying drug resistance.

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Disclosures

The authors have nothing to disclose.

Acknowledgments

We thank the member of the Advanced Cancer Translational Research Institute for their thoughtful comments and Editage for their assistance with English language editing. This work was supported by JSPS KAKENHI (grant number: 16K09590 to T.Y.).

Materials

Name Company Catalog Number Comments
afatinib Selleck S1011
anti-EGFR monoclonal antibody cell signaling technology 4267S
bicinchoninc acid assay sigma B9643
cell-culture treated 10 cm dish Violamo 2-8590-03
CELL BANKER1  TakaRa CB011 cryopreservation media
CellTiter 96 Promega  G4100  Non-Radioactive Cell Proliferation Assay; Dye solution and Solubilization/Stop solution
DMSO Wako 043-07216
ECL solution Perkin Elmer NEL105001EA
FBS gibco 26140-079
GeneAmp 5700 Applied Biosystems fluorescence-based RT-PCR-detection system 
GraphPad Prism v.7 software  GraphPad, Inc. a statistical software
NanoDrop Lite spectrophotometer Thermo spectrophotometer
Nonfat dry milk cell signaling technology 9999S
Pen Strep gibco 15140-163
phosphatase inhibitor cocktail 2 sigma P5726
phosphatase inhibitor cocktail 3 sigma P0044
Powerscan HT microplate reader BioTek
 Power SYBR Green master mix  Applied Biosystems SYBR Green master mix
protease inhibitor cocktail sigma P8340
QIAamp DNA Mini kit Qiagen 51306 DNA purification kit
QIAquick PCR Purification Kit QIAGEN PCR purification kit
RPMI-1640  Wako 189-02025 with L-Glutamine and Phenol Red
TBST powder sigma T9039
Trans-Blot SD Semi-Dry Electrophoretic Transfer cell Bio-Rad semi-dry t4ransfer apparatus
96 well microplate Thermo 130188

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References

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Afatinib-resistant Lung Adenocarcinoma PC-9 Cell Lines Acquired Resistance Therapeutic Strategies Drug Resistance Dose Escalation Method Afatinib-resistance Concentration Culture PC-9 Cells Growth Medium Cell Suspension Microplate Afatinib Solution MTT Dye Optical Density
Establishment and Characterization of Three Afatinib-resistant Lung Adenocarcinoma PC-9 Cell Lines Developed with Increasing Doses of Afatinib
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Cite this Article

Yamaoka, T., Ohba, M., Matsunaga,… More

Yamaoka, T., Ohba, M., Matsunaga, Y., Tsurutani, J., Ohmori, T. Establishment and Characterization of Three Afatinib-resistant Lung Adenocarcinoma PC-9 Cell Lines Developed with Increasing Doses of Afatinib. J. Vis. Exp. (148), e59473, doi:10.3791/59473 (2019).

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