We thank the members of the Institute of Molecular Oncology for their thoughtful comments and helpful advice, and Editage for their assistance with English language editing. This work was supported by the MEXT-supported Program for the Strategic Research Foundation at Private Universities (2012-2016) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. Tohru Ohmori received research funding (2015-2016) from Boehringer-Ingelheim (Ingelheim, Germany).

1. Establish Gefitinib-resistant Cells
<ol>
	<li>Determine the initial gefitinib concentration by 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT) assay.
	<ol>
		<li>Culture PC-9 cells in growth medium (RPMI-1640 medium with 10% FBS and 1% antibiotics (penicillin: 100 U/mL and streptomycin: 100 &#181;g/mL)), in a 5% CO2 incubator at 37 &#176;C.</li>
		<li>Adjust the cells to 1.0 &#215; 105 cells/mL using an automated cell counter (see Table of materials) and seed 50 &#181;L of this in each well of a 96-well plate using the growth medium; the final concentration of cells should be 5.0 &#215; 103 cells/well.</li>
		<li>Incubate the plate overnight at 37 &#176;C.</li>
		<li>Add 50 &#181;L of gefitinib (at 2X final concentration) at different concentrations: 0, 0.002, 0.006, 0.02, 0.06, 0.2, 0.6, 2, 6, and 20 &#181;M to these wells such that the final volume in each well is 100 &#181;L.</li>
		<li>Incubate the plate for 72 h at 37 &#176;C.</li>
		<li>Add 15 &#181;L of the dye solution (see Table of Materials) to each well (use final 13% concentration of the dye solution), and incubate for 4 h at 37 &#176;C.</li>
		<li>Add 100 &#181;L of the solubilization/stop solution (see Table of Materials) for solubilizing the formazan produced by the dye solution (see Table of Materials) in each well, and incubate it overnight at 37 &#176;C.</li>
		<li>Measure the optical density at 570 nm (OD570) using a microplate reader for obtaining the IC50 value by generating a cell-proliferation curve.</li>
		<li>Use a statistical software (see Table of Materials) to graphically display the data, and calculate the IC50 value (Figure 2).</li>
		<li>Prepare 6-12 replicates and repeat the experiments at least three times.</li>
	</ol>
	</li>
	<li>Continuous stepwise dose-escalation of gefitinib for treatment of PC-9 cells.
	<ol>
		<li>Culture PC-9 cells (1 mL in sub-confluent condition) in p100 dishes with 10 mL of growth medium in a 5% CO2 incubator at 37 &#176;C.</li>
		<li>Add one-tenth of the IC50 value of gefitinib into the p100 dish.
		<ol>
			<li>When the cells in the culture medium become sub-confluent, add 1-2 mL of cells to 10 mL of fresh growth medium using a 1-mL pipet with 10-30% higher concentration of gefitinib in the same culture conditions.</li>
		</ol>
		</li>
		<li>Increase the gefitinib concentration progressively by 10-30% with each split until it reaches 1 &#181;M; this might take about 6-12 months. 
		NOTE: When the concentration of gefitinib reaches the IC50 value, the cell proliferation becomes considerably slower, and so, 2-4 mL of cells may be added to 10 mL of the fresh growth medium with higher concentration of gefitinib; reducing the increase in the concentration of gefitinib might solve the problem. Moreover, it would be ideal to store the remaining cells at -80 &#176;C, and reuse them at the previous concentration. As PC-9 cells are in suspension, it is unnecessary to use trypsin for passaging; however, during the process of increasing gefitinib concentration, the cells may attach to the bottom of culture dish. In such a situation, a cell-scraper can be used for detaching the adherent cells.</li>
		<li>Culture the gefitinib-resistant PC-9 cells in the growth medium with 1 &#181;M of gefitinib.</li>
		<li>Perform the MTT assay to confirm the gefitinib-resistance of the cells13; these gefitinib-resistant cells were named PC-9MET1000 (designated as MET1000 cells), because they exhibited increased protein and RNA levels of MET (Figure 3A, Figure 4A, B).</li>
	</ol>
	</li>
</ol>
2. Establish Dual-resistance to Gefitinib and PHA665752
<ol>
	<li>Determine the initial concentration of PHA665752 by MTT assay.
	<ol>
		<li>Culture the MET1000 cells in p100 dishes with 10 mL of growth medium and 1 &#181;M gefitinib in a 5% CO2 incubator at 37 &#176;C.</li>
		<li>Seed the cells into a 96-well plate at 5.0 &#215; 103 cells/well with 50 &#181;L of the growth medium in each well. Adjust the final concentration of the cells to 1.0 &#215; 105 cells/mL using an automated cell counter (see Table of Materials).</li>
		<li>Incubate the plate overnight at 37 &#176;C.</li>
		<li>Add 50 &#181;L of PHA665752, a MET-TKI (at 2X final concentration), to the cells in different concentrations: 0, 0.002, 0.006, 0.02, 0.06, 0.2, 0.6, 2, 6, and 20 &#181;M including 2 &#181;M gefitinib (at 2X final concentration); the final volume in each well should be 100 &#181;L.</li>
		<li>Incubate the plate for 72 h at 37 &#176;C.</li>
		<li>Add 15 &#181;L of the dye solution (see Table of Materials) to each well, and incubate for 4 h at 37 &#176;C.</li>
		<li>Add 100 &#181;L of the solubilization/stop Solution for solubilizing the formazan produced by the dye solution (see Table of Materials) to each well, and again incubate overnight at 37 &#176;C.</li>
		<li>Measure the optical density at 570 nm (OD570) using a microplate reader for obtaining the IC50 value by generating a cell-proliferation curve.</li>
		<li>Use a statistical software (see Table of Materials) to graphically display the data, and calculate the IC50 value of PHA665752 in the presence of gefitinib (Figure 3B).</li>
		<li>Prepare 6-12 replicates and repeat the experiments at least three times.</li>
	</ol>
	</li>
	<li>Establish the dual-resistance in MET1000 cells to gefitinib and PHA665752.
	<ol>
		<li>Culture the MET1000 cells in p100 dishes with 10 mL of growth medium, and 1 &#181;M gefitinib in a 5% CO2 incubator at 37 &#176;C.</li>
		<li>Add one-tenth of the IC50 value of PHA665752 into the growth medium in the presence of 1 &#181;M of gefitinib with the same culture conditions.</li>
		<li>Increase the PHA665752 concentration progressively by 10-30% with each split until it reaches 1 &#181;M. This might take about 6-12 months. 
		NOTE: When the concentration of PHA665752 reaches the IC50 value, the cell proliferation becomes considerably slower, and so, 2-4 ml of cells may be added using a 1-mL pipet to 10 mL of the fresh growth medium with higher concentration of PHA665752; reducing the increase in the concentration of PHA665752 might solve the problem. Moreover, it would be ideal to store the remaining cells at -80 &#176;C, and reuse them at the previous concentration. It is unnecessary to use trypsin for passaging; however, during the increase of PHA665752 concentration, the cells may attach to the bottom of the culture dish. In such situations, a cell-scraper can be used to detach the cells.</li>
		<li>Finally, culture the PC-9 cells resistant to both gefitinib and PHA665752 in the growth medium with 1 &#181;M each of gefitinib and PHA665752 in a 5% CO2 incubator at 37 &#176;C.</li>
		<li>Perform the MTT assay to confirm that the cells are dual-resistant to gefitinib and PHA66575213, and that they are not sensitive to PHA665752 in the presence of gefitinib; these dual-resistance cells were named PC-9DR (designated as DR cells) (Figure 5).</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Lynch, T. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activating+mutations+in+the+epidermal+growth+factor+receptor+underlying+responsiveness+of+non-small-cell+lung+cancer+to+gefitinib.">Activating mutations in the epidermal growth factor receptor underlying responsiveness of non-small-cell lung cancer to gefitinib.</a> N Engl J Med. 350 (21), 2129-2139 (2004).</li><li>Paez, J. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=EGFR+mutations+in+lung+cancer:+correlation+with+clinical+response+to+gefitinib+therapy.">EGFR mutations in lung cancer: correlation with clinical response to gefitinib therapy.</a> Science. 304 (5676), 1497-1500 (2004).</li><li>Pao, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=EGF+receptor+gene+mutations+are+common+in+lung+cancers+from+"never+smokers"+and+are+associated+with+sensitivity+of+tumors+to+gefitinib+and+erlotinib.">EGF receptor gene mutations are common in lung cancers from "never smokers" and are associated with sensitivity of tumors to gefitinib and erlotinib.</a> Proc Natl Acad Sci U S A. 101 (36), 13306-13311 (2004).</li><li>Mitsudomi, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mutations+of+the+epidermal+growth+factor+receptor+gene+predict+prolonged+survival+after+gefitinib+treatment+in+patients+with+non-small-cell+lung+cancer+with+postoperative+recurrence.">Mutations of the epidermal growth factor receptor gene predict prolonged survival after gefitinib treatment in patients with non-small-cell lung cancer with postoperative recurrence.</a> J Clin Oncol. 23 (11), 2513-2520 (2005).</li><li>Sequist, L. V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genotypic+and+histological+evolution+of+lung+cancers+acquiring+resistance+to+EGFR+inhibitors.">Genotypic and histological evolution of lung cancers acquiring resistance to EGFR inhibitors.</a> Sci Transl Med. 3 (75), 75ra26 (2011).</li><li>Engelman, J. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MET+amplification+leads+to+gefitinib+resistance+in+lung+cancer+by+activating+ERBB3+signaling.">MET amplification leads to gefitinib resistance in lung cancer by activating ERBB3 signaling.</a> Science. 316 (5827), 1039-1043 (2007).</li><li>Schmidt, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+mutations+of+the+MET+proto-oncogene+in+papillary+renal+carcinomas.">Novel mutations of the MET proto-oncogene in papillary renal carcinomas.</a> Oncogene. 18 (14), 2343-2350 (1999).</li><li>Olivero, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+mutation+in+the+ATP-binding+site+of+the+MET+oncogene+tyrosine+kinase+in+a+HPRCC+family.">Novel mutation in the ATP-binding site of the MET oncogene tyrosine kinase in a HPRCC family.</a> Int J Cancer. 82 (5), 640-643 (1999).</li><li>Janne, P. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=AZD9291+in+EGFR+inhibitor-resistant+non-small-cell+lung+cancer.">AZD9291 in EGFR inhibitor-resistant non-small-cell lung cancer.</a> N Engl J Med. 372 (18), 1689-1699 (2015).</li><li>Bean, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MET+amplification+occurs+with+or+without+T790M+mutations+in+EGFR+mutant+lung+tumors+with+acquired+resistance+to+gefitinib+or+erlotinib.">MET amplification occurs with or without T790M mutations in EGFR mutant lung tumors with acquired resistance to gefitinib or erlotinib.</a> Proc Natl Acad Sci U S A. 104 (52), 20932-20937 (2007).</li><li>. NCT02468661 - ClinicalTrials.gov Available from: <a target="_blank" href="https://clinicaltrials.gov/ct2/show/NCT02468661">https://clinicaltrials.gov/ct2/show/NCT02468661</a> (2017)</li><li>Yamaoka, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Acquired+Resistance+Mechanisms+to+Combination+Met-TKI/EGFR-TKI+Exposure+in+Met-Amplified+EGFR-TKI-Resistant+Lung+Adenocarcinoma+Harboring+an+Activating+EGFR+Mutation.">Acquired Resistance Mechanisms to Combination Met-TKI/EGFR-TKI Exposure in Met-Amplified EGFR-TKI-Resistant Lung Adenocarcinoma Harboring an Activating EGFR Mutation.</a> Mol Cancer Ther. 15 (12), 3040-3054 (2016).</li><li>Mosmann, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+colorimetric+assay+for+cellular+growth+and+survival:+application+to+proliferation+and+cytotoxicity+assays.">Rapid colorimetric assay for cellular growth and survival: application to proliferation and cytotoxicity assays.</a> J Immunol Methods. 65 (1-2), 55-63 (1983).</li><li>Cifone, M. A., Fidler, I. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correlation+of+patterns+of+anchorage-independent+growth+with+in+vivo+behavior+of+cells+from+a+murine+fibrosarcoma.">Correlation of patterns of anchorage-independent growth with in vivo behavior of cells from a murine fibrosarcoma.</a> Proc Natl Acad Sci U S A. 77 (2), 1039-1043 (1980).</li><li>Ercan, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amplification+of+EGFR+T790M+causes+resistance+to+an+irreversible+EGFR+inhibitor.">Amplification of EGFR T790M causes resistance to an irreversible EGFR inhibitor.</a> Oncogene. 29 (16), 2346-2356 (2010).</li><li>Ogino, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Emergence+of+epidermal+growth+factor+receptor+T790M+mutation+during+chronic+exposure+to+gefitinib+in+a+non+small+cell+lung+cancer+cell+line.">Emergence of epidermal growth factor receptor T790M mutation during chronic exposure to gefitinib in a non small cell lung cancer cell line.</a> Cancer Res. 67 (16), 7807-7814 (2007).</li><li>Ando, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhancement+of+sensitivity+to+tumor+necrosis+factor+alpha+in+non-small+cell+lung+cancer+cells+with+acquired+resistance+to+gefitinib.">Enhancement of sensitivity to tumor necrosis factor alpha in non-small cell lung cancer cells with acquired resistance to gefitinib.</a> Clin Cancer Res. 11 (24 Pt 1), 8872-8879 (2005).</li><li>Suda, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reciprocal+and+complementary+role+of+MET+amplification+and+EGFR+T790M+mutation+in+acquired+resistance+to+kinase+inhibitors+in+lung+cancer.">Reciprocal and complementary role of MET amplification and EGFR T790M mutation in acquired resistance to kinase inhibitors in lung cancer.</a> Clin Cancer Res. 16 (22), 5489-5498 (2010).</li><li>Shien, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Acquired+resistance+to+EGFR+inhibitors+is+associated+with+a+manifestation+of+stem+cell-like+properties+in+cancer+cells.">Acquired resistance to EGFR inhibitors is associated with a manifestation of stem cell-like properties in cancer cells.</a> Cancer Res. 73 (10), 3051-3061 (2013).</li><li>Sagawa, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Establishment+of+three+cisplatin-resistant+endometrial+cancer+cell+lines+using+two+methods+of+cisplatin+exposure.">Establishment of three cisplatin-resistant endometrial cancer cell lines using two methods of cisplatin exposure.</a> Tumour Biol. 32 (2), 399-408 (2011).</li><li>Ritter, C. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+breast+cancer+cells+selected+for+resistance+to+trastuzumab+in+vivo+overexpress+epidermal+growth+factor+receptor+and+ErbB+ligands+and+remain+dependent+on+the+ErbB+receptor+network.">Human breast cancer cells selected for resistance to trastuzumab in vivo overexpress epidermal growth factor receptor and ErbB ligands and remain dependent on the ErbB receptor network.</a> Clin Cancer Res. 13 (16), 4909-4919 (2007).</li></ol>

The authors have no conflicts of interest to disclose.

The protocol described here can be used for the establishment of acquired dual-resistance in cancer cells using a 2-step dose-escalation method in vitro. Many research papers have reported that PC-9 cells developed EGFR-TKI (gefitinib or erlotinib) resistance through T790M EGFR mutations15,16. However, we did not detect T790M mutations in exon 20 of our PC-9MET1000 cells by direct sequencing (Figure 4C). Moreover, MET amplif...

Oncogenic mutations in the epidermal growth factor receptor (EGFR) are found in a subset of patients with non-small cell lung cancer (NSCLC) and are important predictive biomarkers of this disease1,2. These activating EGFR mutations most commonly occur as either an in-frame deletion in exon 19 (delE746-A750) or a point mutation replacing leucine with arginine at codon 858 of exon 21 (L858R) in the EGFR tyrosine kinase domain3,4. Treatment with EGFR-tyrosine kinase inhibitors (TKIs) is a clinically effective therapy for patients with NSCLC harboring EGFR mutations. However, this therapy is limited by the inevitable acquisition of resistance to EGFR-TKIs such as gefitinib and erlotinib. The most common acquired resistance occurs through a secondary T790M mutation in exon 20 of EGFR, which was detected in approximately 60% of patients who acquired EGFR-TKI (gefitinib or erlotinib) resistance. Other molecular mechanisms associated with acquired resistance to EGFR-TKIs are activation of bypass signaling caused by MET amplification, transformation of small-cell lung cancers, and epithelial-to-mesenchymal transition5,6. The receptor for the hepatocyte growth factor, encoded by the MET gene, which is dysregulatedin many tumors, has been reported to be an important candidate for targeted therapies7,8.
Strategies for overcoming the acquired resistance to EGFR-TKIs are now undergoing clinical evaluation. Preclinical and clinical studies have shown that third-generation EGFR inhibitors such as osimertinib are effective for patients with the T790M mutation9. In addition, the growth of EGFR-mutant cancers with MET amplification can be inhibited by combined treatment with EGFR- and MET-TKIs6,10. Clinical trials assessing a combination of MET and EGFR inhibitors in patients with acquired resistance to gefitinib and erlotinib are underway now11.
To study the molecular mechanism of acquired resistance to chemotherapeutic agents, cell lines that initially respond to inhibitors are treated continuously with these inhibitors. Two methods are available to establish acquired resistance in cell lines. One is stepwise dose-escalation, and the other is high-concentration exposure. The stepwise escalation method has been more commonly used, because it has a higher success rate. The cells are first exposed to low concentrations of the inhibitors, nearly a tenth of the half-maximal inhibitory concentration (IC50) value, and the concentration is then gradually increased by 10-30% until the target concentration is achieved. The high-concentration exposure method involves exposing the cells to the final dose of inhibitor in the culture medium, which is more than the IC50 value, so the parental cells are almost completely killed. This high-concentration exposure method has much a lower success rate than the stepwise escalation method.
In a previous study, combined treatment with EGFR-TKI and MET-TKI was shown to be effective in an in vitro system. Acquired resistance to an EFGR-TKI, gefitinib, was established through stepwise escalation for 12 months, along with MET-amplification, and thus, a gefitinib-resistant cell line called PC-9MET1000 was generated12.
The protocol presented here is a two-step dose-escalation procedure for obtaining EGFR-mutated NSCLC PC-9 cells with dual resistance to the EGFR-TKI, gefitinib, and a MET-TKI, PHA665752 (Figure 1). This method for establishing acquired resistant in cell lines is relatively easy to perform, with a high success rate. The described protocol can be modified for application with inhibitors of other molecular target drugs and cytotoxic agents as well.

<table width="970">
	<tbody>
		<tr height="21">
			<td height="21" style="width:365px;height:21px;">RPMI-1640</td>
			<td style="width:177px;">Wako</td>
			<td style="width:119px;">189-02025</td>
			<td style="width:309px;">with L-Glutamine and Phenol Red</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CellTiter 96</td>
			<td style="width:177px;">Promega</td>
			<td style="width:119px;">G4100</td>
			<td>Non-Radioactive Cell Proliferation Assay</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:365px;height:21px;">FBS</td>
			<td style="width:177px;">gibco</td>
			<td style="width:119px;">26140-079</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:365px;height:21px;">Pen Strep</td>
			<td style="width:177px;">gibco</td>
			<td style="width:119px;">15140-163</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:365px;height:21px;">gefitinib</td>
			<td style="width:177px;">Selleck</td>
			<td style="width:119px;">S1025</td>
			<td>stocked 10 mM/EMSO at -20&#186;C</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:365px;height:21px;">PHA665752</td>
			<td style="width:177px;">Selleck</td>
			<td style="width:119px;">S1070</td>
			<td>stocked 10 mM/EMSO at -20&#186;C</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:365px;height:21px;">96-well plate</td>
			<td style="width:177px;">IWAKI</td>
			<td style="width:119px;">860-096</td>
			<td>flat bottom with lid, low evaporation type</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:365px;height:21px;">TC10 Automated Cell Counter</td>
			<td style="width:177px;">BIO RAD</td>
			<td>#1450010</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="width:365px;height:26px;">CellTiter 96 Non-Radioactive Cell Proliferation Assay</td>
			<td style="width:177px;">Promega</td>
			<td style="width:119px;">G4100</td>
			<td style="width:309px;">Dye Solution and Solubilization/Stop Solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Powerscan HT microplate reader</td>
			<td>BioTek</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="width:365px;height:26px;">GraphPad Prism v.5.0 software</td>
			<td style="width:177px;">GraphPad Inc.</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="width:365px;height:26px;">PC-9</td>
			<td style="width:177px;">Riken BioResource Center</td>
			<td style="width:119px;">RCB4455</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:365px;height:21px;">P100 dish</td>
			<td style="width:177px;">FALCON</td>
			<td align="right" style="width:119px;">353003</td>
			<td></td>
		</tr>
	</tbody>
</table>

establishing dual resistance to egfr-tki and met-tki in lung adenocarcinoma cells in vitro with a 2-step dose-escalation procedure

Drug resistance is a major challenge in cancer therapy. The generation of resistant sublines in vitro is necessary for discovering novel mechanisms to overcome this challenge. Here, a 2-step dose-escalation method for establishing dual-resistance to an epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI), gefitinib, and a MET-TKI, PHA665752, is described. This method is based on simple stepwise dose-escalation of inhibitors for inducing acquired resistance in cell lines. The alternate method for generating resistant sublines involves exposing the cells to high concentrations of the inhibitor in one step. The stepwise dose-escalation method has a higher possibility of successfully inducing acquired resistance than this method. Activating EGFR mutations are biomarkers of a response to treatment with EGFR-TKI, which is an applied first-line treatment for non-small cell lung cancers (NSCLC) that harbor these mutations. However, despite reports of effective responses, the use of EGFR-TKI is limited because tumors inevitably acquire resistance. The major mechanisms behind EGFR-TKI resistance include a secondary mutation at the gatekeeper site, T790M in exon 20 of EGFR, and a bypass signal of MET. Thus, a potential solution for this issue would be a combination of EGFR-TKI and MET-TKI. This combined treatment has been shown to be effective in an in vitro study model. Acquired gefitinib-resistance was established through MET-amplification by stepwise dose-escalation of gefitinib for 12 months, and a cell line named PC-9MET1000 was generated in a previous study. To further investigate the mechanisms of acquired MET-TKI and EGFR-TKI resistance, a MET-TKI, PHA665752, was administered to these cells with stepwise dose-escalation in the presence of gefitinib for 12 months. This protocol has also been successfully applied for a number of combination therapies to establish acquired resistance to other inhibitor molecules.

The overview of the protocol presented in this manuscript is shown in Figure 1, including the induction of acquired dual-resistance to gefitinib and PHA665752 in PC-9 cells by a 2-step dose-escalation procedure. Figure 2 shows a decrease in the proliferation of parental PC-9 cells as the concentration of gefitinib increases. This indicates that the PC-9 cells became sensitive to gefitinib after the dose-escalation procedure was p...

Watch this Scientific Journal Video about Establishing Dual Resistance to EGFR-TKI and MET-TKI in Lung Adenocarcinoma Cells In Vitro with a 2-step Dose-escalation Procedure at JoVE.com

Establishing Dual Resistance to EGFR-TKI and MET-TKI in Lung Adenocarcinoma Cells In Vitro with a 2-step Dose-escalation Procedure

An in vitro method for establishing dual resistance to an EGFR-TKI and a MET-TKI in cancer cells is described. This method is useful for developing treatments for patients with EGFR-mutations, who exhibit disease progression despite EGFR-TKI treatment with MET-amplification. It can also be modified for inhibitors targeting other molecules.

Establishing Dual Resistance to EGFR-TKI and MET-TKI in Lung Adenocarcinoma Cells In Vitro with a 2-step Dose-escalation Procedure

Drug resistance is a major challenge in cancer therapy. The generation of resistant sublines in vitro is necessary for discovering novel mechanisms to ...

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JoVE Journal

Cancer Research

8.7K Views.  Showa University. An in vitro method for establishing dual resistance to an EGFR-TKI and a MET-TKI in cancer cells is described. This method is useful for developing treatments for patients with EGFR-mutations, who exhibit disease progression despite EGFR-TKI treatment with MET-amplification. It can also be modified for inhibitors targeting other molecules.

Video: Establishing Dual Resistance to EGFR-TKI and MET-TKI in Lung Adenocarcinoma Cells In Vitro with a 2-step Dose-escalation Procedure

Long-term High-Resolution Intravital Microscopy in the Lung with a Vacuum Stabilized Imaging Window

Metastasis to secondary sites such as the lung, liver and bone is a traumatic event with a mortality rate of approximately 90% 1. Of these sites, the lung is the most difficult to assess using intravital optical imaging due to its enclosed position within the body, delicate nature and vital role in sustaining proper physiology. While clinical modalities (positron emission tomography (PET), magnetic resonance imaging (MRI) and computed tomography (CT)) are capable of providing noninvasive images of this tissue, they lack the resolution necessary to visualize the earliest seeding events, with a single pixel consisting of nearly a thousand cells. Current models of metastatic lung seeding postulate that events just after a tumor cell&#39;s arrival are deterministic for survival and subsequent growth. This means that real-time intravital imaging tools with single cell resolution 2 are required in order to define the phenotypes of the seeding cells and test these models. While high resolution optical imaging of the lung has been performed using various ex vivo preparations, these experiments are typically single time-point assays and are susceptible to artifacts and possible erroneous conclusions due to the dramatically altered environment (temperature, profusion, cytokines, etc.) resulting from removal from the chest cavity and circulatory system 3. Recent work has shown that time-lapse intravital optical imaging of the intact lung is possible using a vacuum stabilized imaging window 2,4,5 however, typical imaging times have been limited to approximately 6 hr. Here we describe a protocol for performing long-term intravital time-lapse imaging of the lung utilizing such a window over a period of 12 hr. The time-lapse image sequences obtained using this method enable visualization and quantitation of cell-cell interactions, membrane dynamics and vascular perfusion in the lung. We further describe an image processing technique that gives an unprecedentedly clear view of the lung microvasculature.

This protocol describes the use of multiphoton microscopy to perform long-term high-resolution, single cell imaging of the intact lung in real time using a vacuum stabilized imaging window.

Metastasis to secondary sites such as the lung, liver and bone is a traumatic event with a mortality rate of approximately 90% 1. Of these sites, the lung ...

Using RNA-sequencing to Detect Novel Splice Variants Related to Drug Resistance in In Vitro Cancer Models

Drug resistance remains a major problem in the treatment of cancer for both hematological malignancies and solid tumors. Intrinsic or acquired resistance can be caused by a range of mechanisms, including increased drug elimination, decreased drug uptake, drug inactivation and alterations of drug targets. Recent data showed that other than by well-known genetic (mutation, amplification) and epigenetic (DNA hypermethylation, histone post-translational modification) modifications, drug resistance mechanisms might also be regulated by splicing aberrations. This is a rapidly growing field of investigation that deserves future attention in order to plan more effective therapeutic approaches. The protocol described in this paper is aimed at investigating the impact of aberrant splicing on drug resistance in solid tumors and hematological malignancies. To this goal, we analyzed the transcriptomic profiles of several in vitro models through RNA-seq and established a qRT-PCR based method to validate candidate genes. In particular, we evaluated the differential splicing of DDX5 and PKM transcripts. The aberrant splicing detected by the computational tool MATS was validated in leukemic cells, showing that different DDX5 splice variants are expressed in the parental vs. resistant cells. In these cells, we also observed a higher PKM2/PKM1 ratio, which was not detected in the Panc-1 gemcitabine-resistant counterpart compared to parental Panc-1 cells, suggesting a different mechanism of drug-resistance induced by gemcitabine exposure.

Using RNA-sequencing to Detect Novel Splice Variants Related to Drug Resistance in In Vitro Cancer Models

Here we describe a protocol aimed at investigating the impact of aberrant splicing on drug resistance in solid tumors and hematological malignancies. To this goal, we analyzed the transcriptomic profiles of parental and resistant in vitro models through RNA-seq and established a qRT-PCR based method to validate candidate genes.

Drug resistance remains a major problem in the treatment of cancer for both hematological malignancies and solid tumors. Intrinsic or acquired resistance ...

Moving Upwards: A Simple and Flexible In Vitro Three-dimensional Invasion Assay Protocol

Although 3D invasion assays have been developed, the challenge remains to study cells without affecting the integrity of their microenvironment. Traditional 3D assays such as the Boyden Chamber require that cells are displaced from the original culture location and moved to a new environment. Not only does this disrupt the cellular processes that are intrinsic to the microenvironment, but it often results in a loss of cells. These problems are especially challenging when dealing with cells that are either rare, or extremely sensitive to their microenvironment. Here, we describe the development of a 3D invasion assay that avoids both concerns. In this assay, cells are plated within a small well and an ECM matrix containing a chemoattractant is laid atop the cells. This requires no cell displacement, and allows the cells to invade upwards into the matrix. In this assay, cell invasion as well as cell morphology can be assessed within the collagen gel. Using this assay, we characterize the invasive capacity of rare and sensitive cells; the hybrid cells resulting from fusion between breast cancer cells MCF7 and mesenchymal/multipotent stem/stroma cells (MSCs).

Moving Upwards: A Simple and Flexible In Vitro Three-dimensional Invasion Assay Protocol

This protocol describes an inverted vertical invasion assay that could be used to quantify the migration and invasion capabilities of cells in a three-dimensional setting while preserving the cell microenvironment. This assay is suitable for rare and/or sensitive cells.

Although 3D invasion assays have been developed, the challenge remains to study cells without affecting the integrity of their microenvironment. ...

Phosphopeptide Enrichment Coupled with Label-free Quantitative Mass Spectrometry to Investigate the Phosphoproteome in Prostate Cancer

Phosphoproteomics involves the large-scale study of phosphorylated proteins. Protein phosphorylation is a critical step in many signal transduction pathways and is tightly regulated by kinases and phosphatases. Therefore, characterizing the phosphoproteome may provide insights into identifying novel targets and biomarkers for oncologic therapy. Mass spectrometry provides a way to globally detect and quantify thousands of unique phosphorylation events. However, phosphopeptides are much less abundant than non-phosphopeptides, making biochemical analysis more challenging. To overcome this limitation, methods to enrich phosphopeptides prior to the mass spectrometry analysis are required. We describe a procedure to extract and digest proteins from tissue to yield peptides, followed by an enrichment for phosphotyrosine (pY) and phosphoserine/threonine (pST) peptides using an antibody-based and/or titanium dioxide (TiO2)-based enrichment method. After the sample preparation and mass spectrometry, we subsequently identify and quantify phosphopeptides using liquid chromatography-mass spectrometry and analysis software.

This protocol describes a procedure to extract and enrich phosphopeptides from prostate cancer cell lines or tissues for an analysis of the phosphoproteome via mass spectrometry-based proteomics.

Phosphoproteomics involves the large-scale study of phosphorylated proteins. Protein phosphorylation is a critical step in many signal transduction ...

Orthotopic Transplantation of Syngeneic Lung Adenocarcinoma Cells to Study PD-L1 Expression

The use of mouse models is indispensable for studying the pathophysiology of various diseases. With respect to lung cancer, several models are available, including genetically engineered models as well as transplantation models. However, genetically engineered mouse models are time-consuming and expensive, whereas some orthotopic transplantation models are difficult to reproduce. Here, a non-invasive intratracheal delivery method of lung tumor cells as an alternative orthotopic transplantation model is described. The use of mouse lung adenocarcinoma cells and syngeneic graft recipients allows studying tumorigenesis under the presence of a fully active immune system. Furthermore, genetic manipulations of tumor cells before transplantation makes this model an attractive time-saving approach to study the impact of genetic factors on tumor growth and tumor cell gene expression profiles under physiological conditions. Using this model, we show that lung adenocarcinoma cells express increased levels of the T-cell suppressor programmed death-ligand 1 (PD-L1) when grown in their natural environment as compared to cultivation in vitro.

Here we describe a minimally invasive syngeneic orthotopic transplantation model of mouse lung adenocarcinoma cells as a time- and cost-reducing model to study non-small cell lung cancer.

The use of mouse models is indispensable for studying the pathophysiology of various diseases. With respect to lung cancer, several models are available, ...

Mesenchymal Stem Cell Isolation from Pulp Tissue and Co-Culture with Cancer Cells to Study Their Interactions

Cancer as a multistep process and complicated disease is not only regulated by individual cell proliferation and growth but also controlled by tumor environment and cell-cell interactions. Identification of cancer and stem cell interactions, including changes in extracellular environment, physical interactions, and secreted factors, might enable the discovery of new therapy options. We combine known co-culture techniques to create a model system for mesenchymal stem cells (MSCs) and cancer cell interactions. In the current study, dental pulp stem cells (DPSCs) and PC-3 prostate cancer cell interactions were examined by direct and indirect co-culture techniques. Condition medium (CM) obtained from DPSCs and 0.4 &#181;m pore sized trans-well membranes were used to study paracrine activity. Co-culture of different cell types together was performed to study direct cell-cell interaction. The results revealed that CM increased cell proliferation and decreased apoptosis in prostate cancer cell cultures. Both CM and trans-well system increased cell migration capacity of PC-3 cells. Cells stained with different membrane dyes were seeded into the same culture vessels, and DPSCs participated in a self-organized structure with PC-3 cells under this direct co-culture condition. Overall, the results indicated that co-culture techniques could be useful for cancer and MSC interactions as a model system.

We provide protocols for evaluation of mesenchymal stem cells isolated from dental pulp and prostate cancer cell interactions based on direct and indirect co-culture methods. Condition medium and trans-well membranes are suitable to analyze indirect paracrine activity. Seeding differentially stained cells together is an appropriate model for direct cell-cell interaction.

Cancer as a multistep process and complicated disease is not only regulated by individual cell proliferation and growth but also controlled by tumor ...

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

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.

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.

Acquired resistance to molecular target inhibitors is a severe problem in cancer therapy. Lung cancer remains the leading cause of cancer-related death in ...

In Vitro Assay to Study Tumor-macrophage Interaction

Tumor associated macrophages (TAMs) account for a large percentage of cells in the tumor mass for different types of cancers. Glioblastoma (GBM), a malignant brain tumor with no cure, has up to a half the tumor mass TAMs. TAMs can be pro-tumoral or anti-tumoral, depending on the activation of specific genes in the cells. Genetic mutations in the tumors, through regulating cytokine expression, can affect recruitment of TAMs to the tumor microenvironment. Here, we describe a quantitative cell-based assay to assess macrophage recruitment by the conditioned medium from the tumor cells. This assay uses the human macrophage cell line MV-4-11 to study macrophage attraction by the conditioned medium from glioblastoma, allowing for high reproducibility and low variability. Data generated with this assay can contribute to a better understanding of the interaction between the tumor and the tumor microenvironment. Similar assay can be used to assess interaction between the tumor cells and other immune cells, including T cells and natural killer (NK) cells.

This article represents a useful in vitro assay to evaluate the capability of conditioned medium from tumor cells to attract macrophages.

Tumor associated macrophages (TAMs) account for a large percentage of cells in the tumor mass for different types of cancers. Glioblastoma (GBM), a ...

Radiosensitivity of Cancer Stem Cells in Lung Cancer Cell Lines

The presence of cancer stem cells (CSCs) has been associated with relapse or poor outcomes after radiotherapy. Studying radioresistant CSCs may provide clues to overcoming radioresistance. Voltage-gated calcium channel &#945;2&#948;1 subunit isoform 5 has been reported as a marker for radioresistant CSCs in non-small cell lung cancer (NSCLC) cell lines. Using calcium channel &#945;2&#948;1 subunit as an example of a CSC marker, methods to study the radiosensitivity of CSCs in NSCLC cell lines are presented. CSCs are sorted with putative markers by flow cytometry, and the self-renewal capacity of sorted cells is evaluated by sphere formation assay. Colony formation assay, which determines how many cells lose the ability to generate descendants forming the colony after a certain dose of radiation, is then performed to assess the radiosensitivity of sorted cells. This manuscript provides initial steps for studying the radiosensitivity of CSCs, which establishes the basis for further understanding of the underlying mechanisms.

The presence of cancer stem cells have been associated with relapse or poor outcomes after radiotherapy. This manuscript describes the methods to study the radiosensitivity of cancer stem cells in lung cancer cell lines.

The presence of cancer stem cells (CSCs) has been associated with relapse or poor outcomes after radiotherapy. Studying radioresistant CSCs may provide ...

In Vitro Evaluation of Oncogenic Transformation in Human Mammary Epithelial Cells

Tumorigenesis is a multi-step process in which cells acquire capabilities&#160;that allow their growth, survival, and dissemination under hostile conditions. Different tests seek to identify and quantify these hallmarks of cancerous cells; however, they often focus on a single aspect of cellular transformation and, in fact, multiple tests are required for their proper characterization. The purpose of this work is to provide researchers with a set of tools to assess cellular transformation in vitro from a broad perspective, thereby making it possible to draw sound conclusions.
A sustained proliferative signaling activation is the major feature of tumoral tissues and can be easily monitored under in vitro conditions by calculating the number of population doublings achieved over time. Besides, the growth of cells in 3D cultures allows their interaction with surrounding cells, resembling what occurs in vivo. This enables the evaluation of cellular aggregation and, together with immunofluorescent labeling of distinctive cellular markers, to obtain information on another relevant feature of tumoral transformation: the loss of proper organization. Another remarkable characteristic of transformed cells is their capacity to grow without attachment to other cells and to the extracellular matrix, which can be evaluated with the anchorage assay.
Detailed experimental procedures to evaluate cell growth rate, to perform immunofluorescent labeling of cell lineage markers in 3D cultures, and to test anchorage-independent cell growth in soft agar are provided. These methodologies are optimized for Breast Primary Epithelial Cells (BPEC) due to its relevance in breast cancer; however, procedures can be applied to other cell types after some adjustments.

This protocol provides experimental in vitro tools to evaluate the transformation of human mammary cells. Detailed steps to follow-up cell proliferation rate, anchorage-independent growth capacity, and distribution of cell lineages in 3D cultures with basement membrane matrix are described.