This work was funded by the Natural Science Foundation of China 81572599, 81773124, and 81972787; Natural Science Foundation of Tianjin City (China) 19JCYBJC27300; Tianjin People&#8217;s Hospital &#38;&#160;Nankai University Collaborative Research Grant 2016rmnk005; Fundamental Research Funds for the Central Universities, Nankai University 63191153.

1. Cell preparation
<ol>
	<li>Cell digestion and neutralization
	<ol>
		<li>Seed tumor cells (such as MDA-MB-231 cells) in a 6 well plate, and culture them in a 37 &#176;C incubator supplied with 5% CO2.</li>
		<li>Harvest cells when their density reaches about 90%. Aspirate the culture medium thoroughly and wash the cells 2x with 3 mL of phosphate buffered saline (PBS). 
		NOTE: To examine the effects of signaling pathway inhibitors (e.g., FRA1 inhibitor), or activators (e.g., STAT3 activator) on stemn...

<ol>
	<li>Reya, T., Morrison, S. J., Clarke, M. F., Weissman, I. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stem+cells,+cancer,+and+cancer+stem+cells.">Stem cells, cancer, and cancer stem cells.</a> Nature. 414 (6859), 105-111 (2001).</li><li>Batlle, E., Clevers, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cancer+stem+cells+revisited.">Cancer stem cells revisited.</a> Nature Medicine. 23 (10), 1124-1134 (2017).</li><li>Eramo, 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=Identification+and+expansion+of+the+tumorigenic+lung+cancer+stem+cell+population.">Identification and expansion of the tumorigenic lung cancer stem cell population.</a> Cell Death &amp; Differentiation. 15 (3), 504-514 (2008).</li><li>Kahlert, U. 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=CD133/CD15+defines+distinct+cell+subpopulations+with+differential+in+vitro+clonogenic+activity+and+stem+cell-related+gene+expression+profile+in+in+vitro+propagated+glioblastoma+multiforme-derived+cell+line+with+a+PNET-like+component.">CD133/CD15 defines distinct cell subpopulations with differential in vitro clonogenic activity and stem cell-related gene expression profile in in vitro propagated glioblastoma multiforme-derived cell line with a PNET-like component.</a> Folia Neuropathologica. 50 (4), 357-368 (2012).</li><li>Bailey, J. 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=DCLK1+marks+a+morphologically+distinct+subpopulation+of+cells+with+stem+cell+properties+in+preinvasive+pancreatic+cancer.">DCLK1 marks a morphologically distinct subpopulation of cells with stem cell properties in preinvasive pancreatic cancer.</a> Gastroenterology. 146 (1), 245-256 (2014).</li><li>Hurt, E. M., Kawasaki, B. T., Klarmann, G. J., Thomas, S. B., Farrar, W. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CD44++CD24(-)+prostate+cells+are+early+cancer+progenitor/stem+cells+that+provide+a+model+for+patients+with+poor+prognosis.">CD44+ CD24(-) prostate cells are early cancer progenitor/stem cells that provide a model for patients with poor prognosis.</a> British Journal of Cancer. 98 (4), 756-765 (2008).</li><li>Al-Hajj, M., Wicha, M. S., Benito-Hernandez, A., Morrison, S. J., Clarke, M. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prospective+identification+of+tumorigenic+breast+cancer+cells.">Prospective identification of tumorigenic breast cancer cells.</a> Proceedings of the National Academy of Science of the United States of America. 100 (7), 3983-3988 (2003).</li><li>Yang, Z. F., 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=Significance+of+CD90++cancer+stem+cells+in+human+liver+cancer.">Significance of CD90+ cancer stem cells in human liver cancer.</a> Cancer Cell. 13 (2), 153-166 (2008).</li><li>Schulenburg, 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=Cancer+stem+cells+in+basic+science+and+in+translational+oncology:+can+we+translate+into+clinical+application.">Cancer stem cells in basic science and in translational oncology: can we translate into clinical application.</a> Journal of Hematology &amp; Oncolcology. 8, 16 (2015).</li><li>Park, J. W., Park, J. M., Park, D. M., Kim, D. Y., Kim, H. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stem+Cells+Antigen-1+Enriches+for+a+Cancer+Stem+Cell-Like+Subpopulation+in+Mouse+Gastric+Cancer.">Stem Cells Antigen-1 Enriches for a Cancer Stem Cell-Like Subpopulation in Mouse Gastric Cancer.</a> Stem Cells. 34 (5), 1177-1187 (2016).</li><li>Goodell, M. A., Brose, K., Paradis, G., Conner, A. S., Mulligan, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+and+functional+properties+of+murine+hematopoietic+stem+cells+that+are+replicating+in+vivo.">Isolation and functional properties of murine hematopoietic stem cells that are replicating in vivo.</a> Journal of Experimental Medicine. 183 (4), 1797-1806 (1996).</li><li>Goodell, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stem+cell+identification+and+sorting+using+the+Hoechst+33342+side+population+(SP).">Stem cell identification and sorting using the Hoechst 33342 side population (SP).</a> Current Protocols in Cytometry. , 18 (2005).</li><li>Begicevic, R. R., Falasca, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ABC+Transporters+in+Cancer+Stem+Cells:+Beyond+Chemoresistance.">ABC Transporters in Cancer Stem Cells: Beyond Chemoresistance.</a> International Journal of Molecular Sciences. 18 (11), 2362 (2017).</li><li>Rabindran, S. K., Ross, D. D., Doyle, L. A., Yang, W., Greenberger, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fumitremorgin+C+reverses+multidrug+resistance+in+cells+transfected+with+the+breast+cancer+resistance+protein.">Fumitremorgin C reverses multidrug resistance in cells transfected with the breast cancer resistance protein.</a> Cancer Research. 60 (1), 47-50 (2000).</li><li>Takara, 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=Differential+effects+of+calcium+antagonists+on+ABCG2/BCRP-mediated+drug+resistance+and+transport+in+SN-38-resistant+HeLa+cells.">Differential effects of calcium antagonists on ABCG2/BCRP-mediated drug resistance and transport in SN-38-resistant HeLa cells.</a> Molecular Medicine Reports. 5 (3), 603-609 (2012).</li><li>Matsson, P., Pedersen, J. M., Norinder, U., Bergstrom, C. A., Artursson, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+novel+specific+and+general+inhibitors+of+the+three+major+human+ATP-binding+cassette+transporters+P-gp,+BCRP+and+MRP2+among+registered+drugs.">Identification of novel specific and general inhibitors of the three major human ATP-binding cassette transporters P-gp, BCRP and MRP2 among registered drugs.</a> Pharmaceutical Research. 26 (8), 1816-1831 (2009).</li><li>Challen, G. A., Little, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+side+order+of+stem+cells:+the+SP+phenotype.">A side order of stem cells: the SP phenotype.</a> Stem Cells. 24 (1), 3-12 (2006).</li><li>Wu, C., Alman, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Side+population+cells+in+human+cancers.">Side population cells in human cancers.</a> Cancer Letters. 268 (1), 1-9 (2008).</li><li>Patrawala, 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=Side+population+is+enriched+in+tumorigenic,+stem-like+cancer+cells,+whereas+ABCG2++and+ABCG2-+cancer+cells+are+similarly+tumorigenic.">Side population is enriched in tumorigenic, stem-like cancer cells, whereas ABCG2+ and ABCG2- cancer cells are similarly tumorigenic.</a> Cancer Research. 65 (14), 6207-6219 (2005).</li><li>Yamada, 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=Nasal+Colivelin+treatment+ameliorates+memory+impairment+related+to+Alzheimer's+disease.">Nasal Colivelin treatment ameliorates memory impairment related to Alzheimer's disease.</a> Neuropsychopharmacology. 33 (8), 2020-2032 (2008).</li><li>Marotta, L. 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=The+JAK2/STAT3+signaling+pathway+is+required+for+growth+of+CD44(+)CD24(-)+stem+cell-like+breast+cancer+cells+in+human+tumors.">The JAK2/STAT3 signaling pathway is required for growth of CD44(+)CD24(-) stem cell-like breast cancer cells in human tumors.</a> Journal of Clinical Investigation. 121 (7), 2723-2735 (2011).</li><li>Zhang, C. H., 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=From+Lead+to+Drug+Candidate:+Optimization+of+3-(Phenylethynyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine+Derivatives+as+Agents+for+the+Treatment+of+Triple+Negative+Breast+Cancer.">From Lead to Drug Candidate: Optimization of 3-(Phenylethynyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine Derivatives as Agents for the Treatment of Triple Negative Breast Cancer.</a> Journal of Medicnal Chemistry. 59 (21), 9788-9805 (2016).</li><li>Tam, W. 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=Protein+kinase+C+alpha+is+a+central+signaling+node+and+therapeutic+target+for+breast+cancer+stem+cells.">Protein kinase C alpha is a central signaling node and therapeutic target for breast cancer stem cells.</a> Cancer Cell. 24 (3), 347-364 (2013).</li><li>Ibrahim, S. F., Diercks, A. H., Petersen, T. W., van den Engh, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetic+analyses+as+a+critical+parameter+in+defining+the+side+population+(SP)+phenotype.">Kinetic analyses as a critical parameter in defining the side population (SP) phenotype.</a> Experimental Cell Research. 313 (9), 1921-1926 (2007).</li><li>Petriz, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flow+cytometry+of+the+side+population+(SP).">Flow cytometry of the side population (SP).</a> Current Protocol in Cytometry. , 23 (2013).</li><li>Hiraga, T., Ito, S., Nakamura, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Side+population+in+MDA-MB-231+human+breast+cancer+cells+exhibits+cancer+stem+cell-like+properties+without+higher+bone-metastatic+potential.">Side population in MDA-MB-231 human breast cancer cells exhibits cancer stem cell-like properties without higher bone-metastatic potential.</a> Oncology Reports. 25 (1), 289-296 (2011).</li><li>Shen, 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=ICAM3+mediates+inflammatory+signaling+to+promote+cancer+cell+stemness.">ICAM3 mediates inflammatory signaling to promote cancer cell stemness.</a> Cancer Letters. 422, 29-43 (2018).</li><li>Koh, S. Y., Moon, J. Y., Unno, T., Cho, S. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Baicalein+Suppresses+Stem+Cell-Like+Characteristics+in+Radio-+and+Chemoresistant+MDA-MB-231+Human+Breast+Cancer+Cells+through+Up-Regulation+of+IFIT2.">Baicalein Suppresses Stem Cell-Like Characteristics in Radio- and Chemoresistant MDA-MB-231 Human Breast Cancer Cells through Up-Regulation of IFIT2.</a> Nutrients. 11 (3), 624 (2019).</li><li>Lee, H., Park, S., Kim, J. B., Kim, J., Kim, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Entrapped+doxorubicin+nanoparticles+for+the+treatment+of+metastatic+anoikis-resistant+cancer+cells.">Entrapped doxorubicin nanoparticles for the treatment of metastatic anoikis-resistant cancer cells.</a> Cancer Letters. 332 (1), 110-119 (2013).</li><li>Ota, 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=ADAM23+is+downregulated+in+side+population+and+suppresses+lung+metastasis+of+lung+carcinoma+cells.">ADAM23 is downregulated in side population and suppresses lung metastasis of lung carcinoma cells.</a> Cancer Science. 107 (4), 433-443 (2016).</li><li>Wei, H., 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=The+mechanisms+for+lung+cancer+risk+of+PM2.5+:+Induction+of+epithelial-mesenchymal+transition+and+cancer+stem+cell+properties+in+human+non-small+cell+lung+cancer+cells.">The mechanisms for lung cancer risk of PM2.5 : Induction of epithelial-mesenchymal transition and cancer stem cell properties in human non-small cell lung cancer cells.</a> Environmental Toxicology. 32 (11), 2341-2351 (2017).</li><li>Prasanphanich, A. F., White, D. E., Gran, M. A., Kemp, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetic+Modeling+of+ABCG2+Transporter+Heterogeneity:+A+Quantitative,+Single-Cell+Analysis+of+the+Side+Population+Assay.">Kinetic Modeling of ABCG2 Transporter Heterogeneity: A Quantitative, Single-Cell Analysis of the Side Population Assay.</a> PLoS Computational Biology. 12 (11), 1005188 (2016).</li><li>Han, H., 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=An+endogenous+inhibitor+of+angiogenesis+inversely+correlates+with+side+population+phenotype+and+function+in+human+lung+cancer+cells.">An endogenous inhibitor of angiogenesis inversely correlates with side population phenotype and function in human lung cancer cells.</a> Oncogene. 33 (9), 1198-1206 (2014).</li><li>Loebinger, M. R., Sage, E. K., Davies, D., Janes, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=TRAIL-expressing+mesenchymal+stem+cells+kill+the+putative+cancer+stem+cell+population.">TRAIL-expressing mesenchymal stem cells kill the putative cancer stem cell population.</a> British Journal of Cancer. 103 (11), 1692-1697 (2010).</li><li>Chiba, 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=Side+population+purified+from+hepatocellular+carcinoma+cells+harbors+cancer+stem+cell-like+properties.">Side population purified from hepatocellular carcinoma cells harbors cancer stem cell-like properties.</a> Hepatology. 44 (1), 240-251 (2006).</li><li>Hirschmann-Jax, C., 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=A+distinct+"side+population"+of+cells+with+high+drug+efflux+capacity+in+human+tumor+cells.">A distinct "side population" of cells with high drug efflux capacity in human tumor cells.</a> Proceedings of the National Academy of Science of the United States of America. 101 (39), 14228-14233 (2004).</li><li>Chen, A. 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There are several key points to keep in mind for the SP assay. The first is the selection of a proper blocker, such as Verapamil or Reserpine, for each cell line, because the &#34;gate&#34; location of the SP cells is determined according to the position at which a large number of SP cells disappear after the addition of the blocker. For the MDA-MB-231 cell line, Reserpine works well. However, for other cell lines, different blockers might work better.
The second is the concentration of Hoechs...

Cancer stem cells (CSCs) are subsets of cells with self-renewal ability and multiple differentiation potential, which play a vital role in tumor growth, metastasis, and recurrence1,2. Currently, CSCs have been identified to exist in a variety of malignant tumors, including lung, brain, pancreas, prostate, breast, and liver cancers3,4,5,6,7,8,9. Identification of CSCs in these tumors is mainly based on the presence of surface marker proteins, such as high and/or low expression of CD44, CD24, CD133, and Sca-19,10, but a unique marker that can distinguish CSCs from non-CSCs has not been reported so far. Currently, several techniques are used to identify and purify CSCs in tumor tissue or tumor cell lines. These techniques are designed based on the specific properties of CSCs. Among them, assays and sorting of side population (SP) cells are two of the commonly used methods.
SP cells were originally discovered by Goodell et al.11, when they characterized hematopoietic stem cells in mouse bone marrow cells. When the mouse bone marrow cells were labeled with the fluorescent dye Hoechst 33342, a small group of Hoechst 33342 dimly-stained cells appeared in the two-dimensional dot plot of a flow cytometry assay. Hoechst 33342 is a DNA-binding dye and has at least two binding modes that lead to different spectral characteristics. When viewing fluorescence emission at two wavelengths at the same time, multiple populations can be revealed12. In their assay, the Hoechst 33342 was excited at 350 nm and the fluorescence was measured by using the 450/20 nm band-pass (BP) filter and 675 nm edge filter long-pass (EFLP)11. Compared with whole population of bone marrow cells, this group of cells was enriched with hematopoietic stem cells called SP cells11. SP cells are capable of rapidly expelling Hoechst 33342. The efflux of this dye is related to ATP-binding cassette (ABC) transporters13, which can be inhibited by some agents such as Fumitremorgin C14, Verapamil and Reserpine15,16. After that, different proportions of SP cells were detected in a variety of tissues, organs, tumor tissues, and tumor cell lines17,18,19. These SP cells have many characteristics of stem cells17,19.
This manuscript describes Hoechst 33342 labeling and staining of cultured tumor cells and the analysis of SP cells by flow cytometry. Moreover, optimization of the Hoechst 33342 concentration and the proper blocker selection for a specific tumor cell line using this approach are shown. Finally, the effects of stemness promotion or inhibition signals on the proportion of SP in tumor cells are demonstrated. The experimental examples demonstrate that analysis of SP can be used to explore the effects of various signals, such as gene expression, small inhibitors, activators, cytokines, and chemokines, on tumor stemness. Compared to other methods for isolation and purification of CSCs, such as sorting of CD44+/CD24&#8211; population, aldehyde dehydrogenase (ALDH) analysis, and tumor sphere formation assays, this method is easier for manipulation and is cost-effective.

<table>
	<tbody>
		<tr>
			<td>6 well cell culture plate</td>
			<td>CORNING</td>
			<td>3516</td>
			<td>9.5 cm2 (approx.)</td>
		</tr>
		<tr>
			<td>Colivelin</td>
			<td>MCE</td>
			<td>HY-P1061A</td>
			<td>Ser-Ala-Leu-Leu-Arg-Ser-Ile-Pro-Ala-Pro-Ala-Gly-Ala-Ser-Arg-Leu-Leu-Leu-Leu-Thr-Gly-Glu-Ile-Asp-Leu-Pro</td>
		</tr>
		<tr>
			<td>Fetal bovine serum (FBS)</td>
			<td>Biological Industries (BIOIND)</td>
			<td>04-001-1ACS</td>
			<td></td>
		</tr>
		<tr>
			<td>Flow cytometer</td>
			<td>BD Biosciences</td>
			<td>BD LSRFortessa</td>
			<td></td>
		</tr>
		<tr>
			<td>Flow cytometer software</td>
			<td>BD Biosciences</td>
			<td>FACSDiva</td>
			<td></td>
		</tr>
		<tr>
			<td>Flow cytometry analysis software</td>
			<td>BD Biosciences</td>
			<td>FlowJo</td>
			<td></td>
		</tr>
		<tr>
			<td>Hoechst33342</td>
			<td>Sigma-Aldrich</td>
			<td>B2261</td>
			<td>bisBenzimide H 33342 trihydrochloride</td>
		</tr>
		<tr>
			<td>Polystyrene round bottom test tube</td>
			<td>CORNING</td>
			<td>352054</td>
			<td>12 x 75 mm, 5mL</td>
		</tr>
		<tr>
			<td>Propidium iodide (PI)</td>
			<td>Sigma-Aldrich</td>
			<td>P4170</td>
			<td>3,8-Diamino-5-[3-(diethylmethylammonio)propyl]-6-phenylphenanthridinium diiodide</td>
		</tr>
		<tr>
			<td>Reserpine</td>
			<td>Sigma-Aldrich</td>
			<td>83580</td>
			<td>(3&#946;, 16&#946;, 17&#945;, 18&#946;, 20&#945;)-11,17-Dimethoxy-18-[(3,4,5-trimethoxybenzoyl)oxy]yohimban-16-carboxylic acid methyl ester</td>
		</tr>
		<tr>
			<td>SKLB816</td>
			<td>Provided by Dr. Shengyong Yang, Sichuan University</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin-EDTA (0.25%), phenol red</td>
			<td>Gibco</td>
			<td>25200072</td>
			<td></td>
		</tr>
		<tr>
			<td>Verapamil hydrochloride</td>
			<td>Sigma-Aldrich</td>
			<td>V4629</td>
			<td>5-[N-(3,4-Dimethoxyphenylethyl)methylamino]-2-(3,4-dimethoxyphenyl)-2-isopropylvaleronitrile hydrochloride</td>
		</tr>
	</tbody>
</table>

analysis of side population in solid tumor cell lines

Cancer stem cells (CSCs) are an important cause of tumor growth, metastasis, and recurrence. Isolation and identification of CSCs are of great significance for tumor research. Currently, several techniques are used for the identification and purification of CSCs from tumor tissues and tumor cell lines. Separation and analysis of side population (SP) cells are two of the commonly used methods. The methods rely on the ability of CSCs to rapidly expel fluorescent dyes, such as Hoechst 33342. The efflux of the dye is associated with the ATP-binding cassette (ABC) transporters and can be inhibited by ABC transporter inhibitors. Methods for staining cultured tumor cells with Hoechst 33342 and analyzing the proportion of their SP cells by flow cytometry are described. This assay is convenient, fast, and cost-effective. Data generated in this assay can contribute to a better understanding of the effect of genes or other extracellular and intracellular signals on the stemness properties of tumor cells.

Four experimental SP analyses were performed according to this method. In the first one, we detected the proportion of SP cells in MDA-MB-231, which is a triple negative human breast cancer cell line, under normal conditions. After cell counting, Hoechst 33342 was added into one tube containing 1 x 106 cells to a final concentration of 3 &#181;g/mL. Reserpine and Hoechst 33342 were added to another tube to&#160;final concentrations of 40 &#181;M and 3 &#181;g/mL, respectively. PI was added to both tubes. The d...

Watch this Scientific Journal Video about Analysis of Side Population in Solid Tumor Cell Lines at JoVE.com

Analysis of Side Population in Solid Tumor Cell Lines

A convenient, fast, and cost-effective method to measure the proportion of side population cells in solid tumor cell lines is presented.

Cancer stem cells (CSCs) are an important cause of tumor growth, metastasis, and recurrence. Isolation and identification of CSCs are of great ...

Analysis of side population cells is one of the commonly used methods to isolate and identify cancer stem cells from tumor tissues and tumor cell lines. This assay is convenient, fast, and cost-effective. This method can contribute to a better understanding of the effect of genes or other extracellular and intracellular signals on stemness properties of tumor cells.Many factors can influence the percentage of SP cells in this analysis, so it is critical to explore the proper conditions before the formal experiment. Seed tumor cells in a six-well plate, and incubate them in a 37-degree Celsius incubator supplied with 5%carbon dioxide. When the cell density reaches about 90%aspirate the culture medium, and wash the cells twice with three milliliters of PBS.Then, add 500 microliters of 0.25%trypsin-EDTA to each well, and incubate the plate at 37 degrees Celsius for one to three minutes. Gently tap the plate to detach the cells, add three milliliters of PBS supplemented with 2%FBS to each well, and pipette the cells up and down three to five times to disperse the cell clumps. Examine the cell suspension under the microscope.If cell clumps are present, pass the suspension through a 70-micrometer strainer. Transfer the cells to a 15-milliliter centrifuge tube, and centrifuge them at 200 times g for five minutes. Remove the supernatant, and resuspend the cells in three milliliters of PBS supplemented with 2%FBS, pipetting the cells up and down three to five times to mix.Count cells under the microscope using a hemocytometer, and dilute them in PBS supplemented with 2%FPS to a final concentration of one times 10 to the six cells per milliliter. Prepare two five-milliliter, polystyrene, round-bottom test tubes, and add one milliliter of the cell suspension to each tube. Label one tube as a test tube and the other as a blocker control tube.Prepare a solution of blocker by diluting it to the appropriate concentration. Add it to the blocker control tube and mix well, then incubate the tube at 37 degrees Celsius for 30 minutes. Shake the tube every 10 minutes.Prepare a solution of Hoechst 33342 by diluting it to the appropriate concentration. Add it to the test tube and blocker control tube separately and mix well, then incubate the tubes at 37 degrees Celsius for 60 minutes. Shake the tubes every 10 minutes.After the incubation, centrifuge the cells for five minutes at 200 times g and four degrees Celsius, then carefully aspirate the supernatant. Resuspend the cells in each tube with one milliliter of ice-cold PBS supplemented with 2%FBS, then pipette the cells up and down to mix. Add one microliter of one-milligram-per-milliliter propidium iodide, or PI, to each tube and mix.Click the Parameters tab in the flow cytometer software. First, choose the parameters of FSC, SSC, Hoechst Blue, Hoechst Red, and PI, respectively. Second, choose the logarithmic scale for the PI parameter.Finally, choose area and width scales for the FSC, SSC, Hoechst Blue, Hoechst Red, and PI parameters, respectively. Run the cells from the test tube first, then run the cells from the blocker control tube using the same voltages and gates. Collect 20 to 100, 000 events from each sample to analyze the percentage of SP cells.This method was used to detect the proportion of SP cells in the MDA-MB-231 human breast cancer cell line. The dot plot of FSC-A versus PI-A showed a population of dead cells, cell debris, and the main population of PI negative cells, which was subjected to further analysis. A single cell population gated from the dot plot of FSC-A versus FSC-W and the dot plot of SSC-A versus SSC-W was used to analyze the proportion of SP cells, which was about 0.9%in untreated cells and about 0.09%in cells treated with reserpine.Different staining concentrations of Hoechst 33342 were tested on MDA-MB-435 cells, and it was determined that two micrograms per milliliter was optimal for SP analysis. Low concentrations made it difficult to distinguish SP cells from other populations, while high concentrations caused SP cells to disappear. Verapamil and reserpine were tested to determine the proper blocker for the MDA-MB-435 cells.About 0.4%of cells expelled the dye after verapamil treatment, but the ratio dropped to about 0.1%after reserpine treatment, demonstrating that reserpine is a more appropriate blocker for this cell line. This protocol was also used to determine the proportion of SP cells in A549 human lung adenocarcinoma cells treated with STAT3 activator colivelin and in T47D human breast cancer cells treated with FRA1 inhibitor SKLB816. This assay provides clues to the regulatory effect of signaling pathways on the features of cancer stem cells and facilitates the discovery of new mechanisms, which can ultimately guide the targeted therapy of tumors.

analysis-of-side-population-in-solid-tumor-cell-lines

Research

JoVE Journal

Cancer Research

4.2K ビュー.  Nankai University. 側の集団細胞の分析は、腫瘍組織および腫瘍細胞株から癌幹細胞を単離し、同定するために一般的に使用される方法の1つである。このアッセイは、便利で、高速で、費用対効果が高い。この方法は、腫瘍細胞の幹細胞性に対する遺伝子または他の細胞外および細胞内シグナルの影響をよりよく理解するのに役立つ。この分析では、多くの要因がSP細胞の割合に影響?...

ビデオ: Analysis of Side Population in Solid Tumor Cell Lines

Harnessing the DNA Dye-triggered Side Population Phenotype to Detect and Purify Cancer Stem Cells from Biological Samples

Cancer is a stem cell-driven disease and eradication of these cells has become a major therapeutic goal. Deciphering vulnerabilities of Cancer Stem Cells (CSCs) and identifying suitable molecular targets relies on methods that allow their specific discrimination in heterogeneous samples such as cell lines and ex vivo tumor tissue. Flow cytometry/FACS is a powerful technology to multi-parametrically dissect biological samples at the single cell level and is to date the method of choice to recover live cells for downstream analyses. Surface markers such as CD44 and CD133 as well as detection of aldehyde dehydrogenase enzymatic activity have often been used to define and sort out CSCs from tumor samples by FACS. A complementary approach, depicted here in methodological detail, makes use of functional dye extrusion by ABC drug transporters, which identifies a distinct population of fluorescence-dim cells commonly referred to as side population (SP). SP&#160;cancer cells exhibit canonical stem cell characteristics and can be abrogated and functionally confirmed using agents that inhibit the dye-extruding drug transporter (most frequently ABCB1/P-glycoprotein/MDR1/CD243 and ABCG2/Bcrp1/CD338). Moreover, the SP&#160;assay is compatible with other flow cytometric evaluations such as staining of surface antigens, aldehyde dehydrogenase detection and dead cell discrimination (e.g., with 7-AAD or propidium iodide (PI)). Thus, we describe a valuable and broadly applicable method for CSC identification, isolation and sub-characterization mechanistically based on a functional, rather than a phenotypic parameter. Although originally performed with Hoechst 33342 as triggering dye, we here focus on the more recent Violet dye-based SP phenotype that is resolvable on any flow cytometer equipped with a violet laser source.

Methods allowing the characterization and isolation of stem cell populations from biological samples are critical for the advance of stem cell-targeted treatments in cancer and beyond. Here, we provide a detailed protocol for cancer stem cell isolation using the dye-triggered side population phenotype.

Cancer is a stem cell-driven disease and eradication of these cells has become a major therapeutic goal. Deciphering vulnerabilities of Cancer Stem Cells ...

Conditional Knockdown of Gene Expression in Cancer Cell Lines to Study the Recruitment of Monocytes/Macrophages to the Tumor Microenvironment

siRNA and shRNA-mediated knock down (KD) methods of regulating gene expression are invaluable tools for understanding gene and protein function. However, in the case that the KD of the protein of interest has a lethal effect on cells or the anticipated effect of the KD is time-dependent, unconditional KD methods are not appropriate. Conditional systems are more suitable in these cases and have been the subject of much interest. These include Ecdysone-inducible overexpression systems, Cytochrome P-450 induction system1, and the tetracycline regulated gene expression systems. 
The tetracycline regulated gene expression system enables reversible control over protein expression by induction of shRNA expression in the presence of tetracycline. In this protocol, we present an experimental design using functional Tet-ON system in human cancer cell lines for conditional regulation of gene expression. We then demonstrate the use of this system in the study of tumor cell-monocyte interaction.

This protocol serves as a scheme for setting up a functional Tet-ON system in cancer cell lines and its subsequent use, in particular for studying the role of tumor cell-derived proteins in recruitment of monocytes/macrophages to the tumor microenvironment.

siRNA and shRNA-mediated knock down (KD) methods of regulating gene expression are invaluable tools for understanding gene and protein function. However, ...

Establishment of Gastric Cancer Patient-derived Xenograft Models and Primary Cell Lines

The use of preclinical models to advance our understanding of tumor biology and investigate the efficacy of therapeutic agents is key to cancer research. Although there are many established gastric cancer cell lines and many conventional transgenic mouse models for preclinical research, the disadvantages of these in vitro and in vivo models limit their applications. Because the characteristics of these models have changed in culture, they no longer model tumor heterogeneity, and their responses have not been able to predict responses in humans. Thus, alternative models that better represent tumor heterogeneity are being developed. Patient-derived xenograft (PDX) models preserve the histologic appearance of cancer cells, retain intratumoral heterogeneity, and better reflect the relevant human components of the tumor microenvironment. However, it usually takes 4-8 months to develop a PDX model, which is longer than the expected survival of many gastric patients. For this reason, establishing primary cancer cell lines may be an effective complementary method for drug response studies. The current protocol describes methods to establish PDX models and primary cancer cell lines from surgical gastric cancer samples. These methods provide a useful tool for drug development and cancer biology research.

The current protocol describes methods to establish patient-derived xenograft (PDX) models and primary cancer cell lines from surgical gastric cancer samples. The methods provide a useful tool for drug development and cancer biology research.

The use of preclinical models to advance our understanding of tumor biology and investigate the efficacy of therapeutic agents is key to cancer research. ...

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 ...

Evaluating Cell Death Using Cell-Free Supernatant of Probiotics in Three-Dimensional Spheroid Cultures of Colorectal Cancer Cells

This manuscript describes a protocol to evaluate cancer cell deaths in three dimensional (3D) spheroids of multicellular types of cancer cells using supernatants from Lactobacillus fermentum cell culture, considered as probiotics cultures. The use of 3D cultures to test Lactobacillus cell-free supernatant (LCFS) are a better option than testing in 2D monolayers, especially as L. fermentum can produce anti-cancer effects within the gut. L. fermentum supernatant was identified to possess increased anti-proliferative effects against several colorectal cancer (CRC) cells in 3D culture conditions. Interestingly, these effects were strongly related to the culture model, demonstrating the notable ability of L. fermentum to induce cancer cell death. Stable spheroids were generated from diverse CRCs (colorectal cancer cells) using the protocol presented below. This protocol of generating 3D spheroid is time saving and cost effective. This system was developed to easily investigate the anti-cancer effects of LCFS in multiple types of CRC spheroids. As expected, CRC spheroids treated with LCFS strongly induced cell death during the experiment and expressed specific apoptosis molecular markers as analyzed by qRT-PCR, western blotting, and FACS analysis. Therefore, this method is valuable for exploring cell viability and evaluating the efficacy of anti-cancer drugs.

Here methods are presented to understand anti-cancer effects of Lactobacillus cell-free supernatant (LCFS). Colorectal cancer cell lines show cell deaths when treated with LCFS in 3D cultures. The process of generating spheroids can be optimized depending on the scaffold and the analysis methods presented are useful for evaluating the involved signaling pathways.

This manuscript describes a protocol to evaluate cancer cell deaths in three dimensional (3D) spheroids of multicellular types of cancer cells using ...

Circulating Tumor Cell Lines: an Innovative Tool for Fundamental and Translational Research

Metastasis is a leading cause of cancer death. Despite improvements in treatment strategies, metastatic cancer has a poor prognosis. We thus face an urgent need to understand the mechanisms behind metastasis development, and thus to propose efficient treatments for advanced cancer. Metastatic cancers are hard to treat, as biopsies are invasive and inaccessible. Recently, there has been considerable interest in liquid biopsies including both cell-free circulating deoxyribonucleic acid (DNA) and circulating tumor cells from peripheral blood and we have established several circulating tumor cell lines from metastatic colorectal cancer patients to participate in their characterization. Indeed, to functionally characterize these rare and poorly described cells, the crucial step is to expand them. Once established, circulating tumor cell (CTC) lines can then be cultured in suspension or adherent conditions. At the molecular level, CTC lines can be further used to assess the expression of specific markers of interest (such as differentiation, epithelial or cancer stem cells) by immunofluorescence or cytometry analysis. In addition, CTC lines can be used to assess drug sensitivity to gold-standard chemotherapies as well as to targeted therapies. The ability of CTC lines to initiate tumors can also be tested by subcutaneous injection of CTCs in immunodeficient mice.
Finally, it is possible to test the role of specific genes of interest that might be involved in cancer dissemination by editing CTC genes, by short hairpin ribonucleic acid (shRNA) or Crispr/Cas9. Modified CTCs can thus be injected into immunodeficient mouse spleens, to experimentally mimic part of the metastatic development process in vivo.
In conclusion, CTC lines are a precious tool for future research and for personalized medicine, where they will allow prediction of treatment efficiency using the very cells that are originally responsible for metastasis.

Culturing CTCs allows a deeper functional characterization of cancer, through assaying specific marker expression, and assessing drug resistance and the ability to colonize the liver among other possibilities. Overall, CTC culture could be a promising clinical tool for personalized medicine to improve patient outcome.

Metastasis is a leading cause of cancer death. Despite improvements in treatment strategies, metastatic cancer has a poor prognosis. We thus face an ...

Analytical Determination of Mitochondrial Function of Excised Solid Tumor Homogenates

Mitochondria are essential to the onset and progression of cancer through energy production, reactive oxygen species regulation, and macromolecule synthesis. Genetic and functional adaptations of mitochondria to the tumor environment drive proliferative and metastatic potential. The advent of DNA and RNA sequencing removed critical barriers to the evaluation of genetic mediators of tumorigenesis. However, to date, methodological approaches to evaluate tumor mitochondrial function remain elusive and require technical proficiency limiting the feasibility, ultimately diminishing diagnostic and prognostic value in both experimental and clinical settings. Here, we&#160;outline a simple and rapid method to quantify rates of oxidative phosphorylation (OXPHOS) and electron transfer (ET) capacity in freshly excised solid tumor homogenates using high-resolution respirometry. The protocol can be reproducibly applied across species and tumor types as well as adapted to evaluate a diversity of mitochondrial ET pathways. Using this protocol, we demonstrate that mice bearing a luminal B mammary cancer exhibit defective nicotinamide adenine dinucleotide-linked respiration and reliance on succinate to generate adenosine triphosphate via OXPHOS.

We developed a practical protocol and analytical approach to evaluate mitochondrial oxidative phosphorylation and electron transfer capacity in fresh tumor homogenates. This protocol can be easily adapted to survey various mitochondrial functions that contribute to cancer initiation, progression, and treatment response.

Mitochondria are essential to the onset and progression of cancer through energy production, reactive oxygen species regulation, and macromolecule ...

Generation and Expansion of Primary, Malignant Pleural Mesothelioma Tumor Lines

Current methodologies for the expansion of primary tumor cell lines from rare tumor types are lacking. This protocol describes methods to expand primary tumor cells from surgically resected, malignant pleural mesothelioma (MPM) by providing a complete overview of the process from digestion to enrichment, expansion, cryopreservation, and phenotypic characterization. In addition, this protocol introduces concepts for tumor generation that may be useful for multiple tumor types such as differential trypsinization and the impact of dissociation methods on the detection of cell surface markers for phenotypic characterization. The major limitation of this study is the selection of tumor cells that will expand in a two-dimensional (2D) culture system. Variations to this protocol, including three-dimensional (3D) culture systems, media supplements, plate coating to improve adhesion, and alternate disaggregation methods, could improve this technique and the overall success rate of establishing a tumor line. Overall, this protocol provides a base method for establishing and characterizing tumor cells from this rare tumor.

The goal of this method paper is to demonstrate a robust and reproducible methodology for the enrichment, generation, and expansion of primary tumor cell lines from surgically resected pleural mesothelioma.

Current methodologies for the expansion of primary tumor cell lines from rare tumor types are lacking. This protocol describes methods to expand primary ...

Multiparametric Tumor Organoid Drug Screening Using Widefield Live-Cell Imaging for Bulk and Single-Organoid Analysis

Patient-derived tumor organoids (PDTOs) hold great promise for preclinical and translational research and predicting the patient therapy response from ex vivo drug screenings. However, current adenosine triphosphate (ATP)-based drug screening assays do not capture the complexity of a drug response (cytostatic or cytotoxic) and intratumor heterogeneity that has been shown to be retained in PDTOs due to a bulk readout. Live-cell imaging is a powerful tool to overcome this issue and visualize drug responses more in-depth. However, image analysis software is often not adapted to the three-dimensionality of PDTOs, requires fluorescent viability dyes, or is not compatible with a 384-well microplate format. This paper describes a semi-automated methodology to seed, treat, and image PDTOs in a high-throughput, 384-well format using conventional, widefield, live-cell imaging systems. In addition, we developed viability marker-free image analysis software to quantify growth rate-based drug response metrics that improve reproducibility and correct growth rate variations between different PDTO lines. Using the normalized drug response metric, which scores drug response based on the growth rate normalized to a positive and negative control condition, and a fluorescent cell death dye, cytotoxic and cytostatic drug responses can be easily distinguished, profoundly improving the classification of responders and non-responders. In addition, drug-response heterogeneity can by quantified from single-organoid drug response analysis to identify potential, resistant clones. Ultimately, this method aims to improve the prediction of clinical therapy response by capturing a multiparametric drug response signature, which includes kinetic growth arrest and cell death quantification.

This protocol describes a semi-automated method for medium- to high-throughput organoid drug screenings and microscope-agnostic, automated image analysis software to quantify and visualize multiparametric, single-organoid drug responses to capture intratumor heterogeneity.

Patient-derived tumor organoids (PDTOs) hold great promise for preclinical and translational research and predicting the patient therapy response from ex ...

Transmitochondrial Cybrid Generation From Suspension-Growing Cancer Cells

Transmitochondrial Cybrid Generation Using Cancer Cell Lines

In recent years, the number of studies dedicated to ascertaining the connection between mitochondria and cancer has significantly risen. However, more efforts are still needed to fully understand the link involving alterations in mitochondria and tumorigenesis, as well as to identify tumor-associated mitochondrial phenotypes. For instance, to evaluate the contribution of mitochondria in tumorigenesis and metastasis processes, it is essential to understand the influence of mitochondria from tumor cells in different nuclear environments. For this purpose, one possible approach consists of transferring mitochondria into a different nuclear background to obtain the so-called cybrid cells. In the traditional cybridization techniques, a cell line lacking mtDNA (&#961;0, nuclear donor cell) is repopulated with mitochondria derived from either enucleated cells or platelets. However, the enucleation process requires good cell adhesion to the culture plate, a feature that is partially or completely lost in many cases in invasive cells. In addition, another difficulty found in the traditional methods is achieving complete removal of the endogenous mtDNA from the mitochondrial-recipient cell line to obtain pure nuclear and mitochondrial DNA backgrounds, avoiding the presence of two different mtDNA species in the generated cybrid. In this work, we present a mitochondrial exchange protocol applied to suspension-growing cancer cells based on the repopulation of rhodamine 6G-pretreated cells with isolated mitochondria. This methodology allows us to overcome the limitations of the traditional approaches, and thus can be used as a tool to expand the comprehension of the mitochondrial role in cancer progression and metastasis.

Author Spotlight: Transmitochondrial Cybrid Generation Using Cancer Cell Lines  

This protocol describes a technique for cybrid generation from suspension-growing cancer cells as a tool to study the role of mitochondria in the tumorigenic process.

In recent years, the number of studies dedicated to ascertaining the connection between mitochondria and cancer has significantly risen. However, more ...