All-trans retinoic acids induce differentiation and sensitize a radioresistant breast cancer cells to chemotherapy
© Yan et al. 2016
Received: 23 September 2015
Accepted: 19 March 2016
Published: 31 March 2016
Radiotherapy is of critical importance in the treatment of breast cancer. However, not all patients derive therapeutic benefit and some breast cancers are resistant to the treatment, and are thus evidenced with prospective distant metastatic spread and local recurrence. In this study, we investigated the potential therapeutic effects of all-trans retinoic acid (ATRA) on radiation-resistant breast cancer cells and the associated invasiveness.
The MCF7/C6 cells with gained radiation resistance after a long term treatment with fractionated ionizing radiation were derived from human breast cancer MCF7 cell line, and are enriched with cells expressing putative breast cancer stem cell biomarker CD44+/CD24-/low/ALDH+. The enhanced invasiveness and the acquired resistances to chemotherapeutic treatments of MCF7/C6 cells were measured, and potential effects of all-trans retinoic acid (ATRA) on the induction of differentiation, invasion and migration, and on the sensitivities to chemotherapies in MCF7/C6 cells were investigated.
MCF7/C6 cells are with enrichment of cancer stem-cell like cells with positive staining of CD44+/CD24-/low, OCT3/4 and NANOG. MCF7/C6 cells showed an increased tumoregensis potential and enhanced aggressiveness of invasion and migration. Treatment with ATRA induces the differentiation in MCF7/C6 cells, resulting in reduced invasiveness and migration, and increased sensitivity to Epirubincin treatment.
Our study suggests a potential clinic impact for ATRA as a chemotherapeutic agent for treatment of therapy-resistant breast cancer especially for the metastatic lesions. The study also provides a rationale for ATRA as a sensitizer of Epirubincin, a first-line treatment option for breast cancer patients.
KeywordsBreast cancer Radiation resistance Cancer stem cell ATRA
Breast cancer is the leading cancer diagnosed in women and is second only to lung cancer in terms of cancer death, causing extensive morbidity and psychological distress to millions globally [1, 2]. Despite the tremendous efforts and progress in breast cancer research and early diagnosis, clinical outcome for breast cancer patients is still disappointing. Resistances to current therapeutic regimen, and as much as 40 % of relapses with recurrent and/or metastatic disease remain to be great challenges in clinical management for breast cancer patients [3–5]. It is also needed to be indicated that, while overall breast cancer mortality rates have decreased over the last several decades , the survival rates for metastatic breast cancer are currently estimated at less than 25 % for 5-year and 5–10 % for 10-year [3, 7–9].
Radiation therapy continues to be an important part of conditioning regimens for breast cancer treatment. Radiation therapy given after surgery in early stage breast cancer patients has shown significant effects of increasing the probability of both local control and survival . The most recent meta-analysis including 10,801 women in 17 clinical trials of radiation or no radiation after lumpectomy showed that radiation reduced the 10-year risk of any recurrence in lymph node-negative women from 31 to 15.6 % and reduced the 15-year risk of death from breast cancer from 20.5 to 17.2 % . However, the rate of totally control of tumor growth by radiotherapy remains unacceptable low, and studies have indicated that breast cancer patients may fail to radiation therapy and cancer cells in these patients become resistant to the treatment [12–15]. Elucidation of mechanism causing tumor radioresistance and definition of effective therapeutic targets to enhance tumor response, especially for the most resistant and aggressive cancer cells in the recurrent and metastatic lesions, are thus urgently needed.
In our previous studies, we observed a breast cancer MCF7 cell population (MCF + FIR) that could survive after a course of clinical fractionated doses of radiation and showed enhanced radioresistance compared to the wild type parental MCF7 cells [16, 17]. With sub-cloning, different clones with varied radiosensitivity were isolated from this radioresistant population . Cells expressing the biomarkers of breast cancer stem cells (BCSCs; e,g., CD44+/CD24-/low/ALDH+) were further sorted and confirmed in one of these clones (MCF7/C6) , indicating that BCSCs can survive long-term fractionated radiation and be responsible tumor repopulation with radiation resistance. In supporting this observation, other studies also demonstrated the enrichment of cancer stem cells during the course of fractionated radiation [20, 21]. In addition, radiation is also shown to be able to reprogram the differentiated breast cancer cells into induced breast cancer stem cells (BCSCs) . These and other results provide the evidence indicating that, while some patients with early-stage breast cancer can benefit from radiation therapy, others may gain resistance to radiotherapy with a potential of increased recurrence and/or distant metastasis due to the enrichment of BCSCs . Thus, targeting BCSCs in patients with radiation resistant breast cancer may impede an important clinical impact for decreasing cancer metastatic potential in these patients.
In this study, we used the MCF + FIR cellular model to investigate the roles of BCSCs in enhanced capability of cancer cell invasion and the acquired resistances to chemotherapy of breast cancer. The potential therapeutic effects of all-trans retinoic acid (ATRA), which has been used in the management of certain hematologic malignancies and solid tumors, including breast cancer , on the induction of differentiation of enriched BCSCS, inhibition of aggressive growth and sensitization to chemotherapeutic agent in MCF/C6 cells. The results indicate that ATRA is a promising candidate to target radioresistant breast cancer cells with enrichment of BCSCs.
ATRA was purchased from Sigma–Aldrich (St. Louis, MO), and was dissolved in dimethylsulphoxide (DMSO) as stock solution. Primary antibodies for Involucrin, Sydencan-3, and E-Cadherin were purchased from Santa Cruz Biotechnology (Santa Cruz, CA). Anti-CD44 antibody was from ABGENT (San Diego, CA). Anti-β-actin antibody was from Cell Signaling Technology (Beverly, MA). siRNA oligos for CD44 and control siRNA-A were also from Santa Cruz Biotech. Inc. Enzymes I-SceI was from New England Biolabs (Ipswich, MA).
Human breast cancer MCF7 cells were from American Type Culture Collection (ATCC, Manassas, VA). Radiation-resistant MCF7/C6 cells were generated from MCF-7 cells by exposure to fractionized ionizing irradiation (FIR) with a total dose of 60 Gy of γ-irradiation (2 Gy per fraction, five times per week for 6 weeks) as previously described . MCF7 and MCF7/C6 cells were maintained in ATCC-formulated RPMI-1640 medium supplemented with 10 % Fetal bovine serum (FBS), 5 % sodium pyruvate, 5 % nonessential amino acid, 100 U/mL of penicillin, and 100 mg/mL streptomycin in a 37 °C incubator (5 % CO2). To maintain the radiation-resistant phenotype, MCF7/C6 cells were also frequently exposed to irradiation (IR) at 2Gy for five times per week and radioresistance was validated before each designated experiment.
Clonogenic survival assay
Cells in log-phase were plated and then immediately treated with indicated treatment. 24 h later, cells were washed twice with pre-warmed medium, and were then maintained in corresponding medium for 10–14 days and stained with crystal violet. Colonies consisting >50 cells were considered as survival colonies and directly scored using an inverted microscope. Average numbers for survival colonies were plotted versus untreated control to determine the survival fractions. When ATRA pretreatment applied, cells were treated 10 μM ATRA for 72 h. Cells were then re-plated and treated with indicated chemodrugs for 24 h, and maintained in corresponding medium for colony formations as described above.
Assays for invasion, migration and wound healing
MCF7 and MCF7/C6 cells in log-phase were trypsinized, and 5 × 104 cells in growth medium containing 1 % FBS were re-seeded in 1× BME (Trevigen, Gaithersburg, MD) coated 8.0-μm pore size cell culture inserts (for 24-well plate, Millipore, Danvers, MA). Complete growth medium containing 10 % FBS was placed outside the chambers, and cells were allowed to invade toward the attractant of full-serum medium. Chamber filter processing and visualization/quantitation of invasion were performed, as previously described . Cells migrated to bottom chamber were also visualized/quantified for migration analysis.
For wound healing analysis, 5 × 104 cells were grown in monolayers in triplicate in 24-well plates for 72 h. The confluent monolayer was then scraped with a sterile tip. The migration into the wounded monolayer was assessed by microscopy. When siRNA transfection applied, cells were transiently transfected with SiRNA-CD44 or SiRNA-Control-A, and then maintained in complete medium for 72 h until confluent monolayer formed for wound healing analysis, or re-seeded in BME-precoated cell culture inserts for invasion/migration assays.
Flow cytometry analysis
After treatments, cells were detached by using stempro® accutase (Life Technologies, Grand Island, NY), and washed twice with PBS. Cells were then stained with PE-conjugated anti-Sox2, anti-Oct3/4, and anti-NANOG antibodies, or co-stained with PE-conjugated anti-CD24 and FITC-conjugated anti-CD44 antibodies (BD Biosciences, San Jose, CA). In the process for staining of Sox 2, Oct3/4 and Nanog, BD Perm/WashTM buffer was also used per manufacture’s instruction. PE- or FITC-positive cells were quantified by flow cytometric analysis on Flow Cytometer LSRII (BD Biosciences, San Jose, CA). Up to 5 × 104 cells were counted during flow cytometry analysis. For cell cycle analysis, cells were collected and fixed with 75 % ethanol, stained with propidium iodide and analyzed by flow cytometry with 5 × 104 events counting per run, as described previously . The percentage of cells in the G1, S, and G2/M phases of the cell cycle were determined by using Flowjo software (Flowjo data analysis software, OR).
Cell lysates were prepared in RIPA buffer with mild sonication, and subjected to SDS-PAGE gel for immunoblot assays. β-actin was included to determine equivalent protein loading.
in vivo end-joining assay
in vivo end-joining assay was based on the reactivation of linearized plasmid as previously reported . Briefly, cells were treated with 10 μM of ATRA, or DMSO as control, for 72 h, 1 × 105 cells were then co-transfected with 1.2 μg linearized EJ5-GFP substrates (linearized with I-SceI) and 0.5 μg circular pDsReD-Express2-N1 (as transfection control) by using electroporation (Gene Pulse Xcell, Bio-Rad, Hercules, CA). After transfection, cells were plated and cultured in fresh complete medium for 72 h. In ATRA experiment, 10 μM ATRA was added into culture medium after transfections and DMSO was included as control. Flow cytometry analysis was performed with Fortessa Flow Cytometer (Fluofarma, Princeton, NJ). Up to 5 × 104 cells were counted. The ratio of GFP-positive cells to DsRed-positive cells was used as a measure of end-joining efficiencies.
Tumor initiating test
Tumor initiating test was conducted following the described methods [19, 28] and the protocol was reviewed and approved by the Chancellor’s Animal Research Committee (ARC) at the University of California Los Angeles (ARC #2009–063–13). Six weeks old female NOD/SCID mice (Jackson Lab, Bar Harbor, ME) were pretreated for 5 days with estrogen pellets (Innovative Research of America, Sarasota FL) and freshly prepared MCF7 and MCF7/C6 cells were resuspended in serum-free PBS/Matrigel mixture (1:1 V/V), and 1×103 cells were inoculated subcutaneously to bilateral franks of same animal. Tumorigenesis was assessed twice a week with palpation. Tumor sizes were determined from caliper measurements of tumor length (L) and width (W) according to the formula (LxW2)/2.
Statistical analyses were performed using the Student’s t-test. A p value <0.05 was considered as significant (*).
Enhanced cancer cell invasiveness and migration of radiation-resistant MCF7/C6 cells
It has been previously shown that HER2-positive cells in MCF7/C6 were with increased invasiveness . In an attempt to test whether MCF7/C6 cells have overall changes in cancer cell invasiveness and migration, we performed the assays in MCF7 and MCF7/C6 cells. We observed that the capabilities of cancer cell invasion/migration were dramatically enhanced in MCF7/C6 cells versus parental MCF7 cells. MCF7/C6 cells also showed increased ability for wound healing (Fig. 1c, d). In addition, a substantial amount of E-cadherin, a protein prominently associated with tumor invasiveness and metastatic dissemination , was found to be reduced in the MCF7/C6 cells (Fig. 1e).
Enrichment of stem cell-like cancer cells in MCF7/C6 cells
Knocking-down CD44 expression inhibited the aggressive growth of MCF7/FIR C6 cells
ATRA induces differentiation and inhibits cancer cell invasion in MCF-7/C6 cells
ATRA enhances sensitivity of MCF7/C6 FIR cells to radiation treatment
ATRA enhances sensitivity of MCF7/C6 cells to chemotherapy
Radioresistance of cancer cells may arise from self-repair mechanisms (mainly DNA damage repair) or repopulation of radioresistant cancer stem cells, or both . Data presented here indicate that the radioresistant MCF7/C6 population derived from long-term fractionated doses of radiation is with enrichment of BCSCs and enhanced capability of NHEJ repair. Compared to parental MCF7 cells, MCF7/C6 cells are aggressive with increased capacity of invasiveness and migration, and inhibition of CD44 expression could effectively reduce cancer cell invasiveness and migration in MCF7/C6 cells. Most important, our data demonstrated that treatment with ATRA can induce differentiation of the enriched BCSCs in MCF7/C6 cell population and sensitized them to chemotherapeutic agent epirubincin.
More than 60 % cancer patients worldwide use radiotherapy for the control of tumor growth during the course of their disease. However, in spite of significant advancements in tumor imaging and precise of tumor dose calculation and delivery, the rate of total tumor growth control by radiotherapy remains disappointing. Although radiation therapy can decrease the risk of local cancer recurrence and improves survival, clinical evidence has shown the detrimental effect of treatment interruptions on tumor control in breast cancer patients . Interestingly, radiation can also induce a BCSC phenotype in differentiated breast cancer cells [21, 22], and CSCs-mediated tumor innate resistance to cytotoxic agents thus become major clinical challenges towards the complete eradication of minimal residual disease in cancer patients . CSCs are also likely to play essential roles in the metastatic spread of primary tumors because of their self-renewal capability and their potential to give rise to differentiated progenies that can adapt to different target organ microenvironments [51–54]. Preclinical study has suggested differentiation therapy to be one of the promising strategies for targeting BCSCs in breast cancer . Thus, targeting these enriched putative BCSCs in breast cancer cells after sublethal doses of radiation treatment may have important clinical impact for breast cancer patients. To this setting, radioresistant MCF7/C6 used in this study is a useful experimental model to mimic the radioresistant lesions in the clinic, especially for the therapy-resistant phenotype of metastatic tumors. MCF7/C6 cells were derived from MCF7 cells after fractionized ionizing radiation and are with developed radiation resistance [16, 19, 56]. Characterization and elucidation of the mechanistic insights and potential therapeutic target to this unique radioresistant, BCSCs-enriched population which is highly relevant to the clinic recurrent/metastatic lesions, will generate informative data for the benefit of breast cancer patients. Our present work demonstrates the increases of putative CSCs populations in MCF7/C6 cells. Compared to parental MCF7 cells, MCF7/C6 cells also exhibited enhanced capabilities for cancer cell invasion and migration, indicating increased potential for metastasis. Thus, radioresistant MCF7/C6 with BCSCs enrichment is a useful experimental model to mimic the radioresistant lesions in the clinic, especially for the therapy-resistant phenotype of metastatic tumors. Preclinical study has suggested differentiation therapy to be one of the promising strategies for targeting BCSCs in breast cancer . Our data also showed that inhibition of CD44 expression could effectively reduce cancer cell invasiveness and migration in MCF7/C6 cells (Fig. 3).
In this study, we demonstrated the potential therapeutic effects of ATRA on MCF7/C6 cells. Retinoids and its derivatives such as ATRA are promising anti-neoplastic agents endowed with both therapeutic and chemo-preventive potential because they are able to regulate cell growth, differentiation and apoptosis [57–59]. We previously have showed the inhibitory effects of ATRA on proliferation and cancer cell migration of breast cancer cells . ATRA has also been recently demonstrated of the ability to induce cancer stem cell differentiation . We showed here that ATRA can induce differentiation of enriched BCSCs in MCF7/C6 cells, and inhibit cancer cell invasiveness/migration and increase the sensitivities of cells to radiation treatment and to the treatments of epirubincin and 5-Fu of this cell population. These results thus not only indicate potential clinic impacts of differentiation treatment with ATRA as single agent for BCSCs in therapy-resistant breast cancers, but also suggest approaches with combination of ATRA and epirubincin, or other standard-anti-breast cancer chemotherapy, as novel therapeutic strategy for clinic management aiming to minimize the risk of recurrent/metastasis, the major life-threatening tumors in many cancer patients .
Our study suggests a potential clinic impact of ATRA as a chemotherapeutic agent for treatment of radiation-resistant breast cancer. The study also provides a rationale for ATRA as a sensitizer of Epirubincin, a first-line treatment option for breast cancer patients.
Availability of data and materials
This work was supported by National Natural Science Foundation of China (No. 81272399) to YW, and by National Institutes of Health RO1 Grants CA152313 to JL. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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- Edwards BK, Noone AM, Mariotto AB, Simard EP, Boscoe FP, et al. Annual Report to the Nation on the status of cancer, 1975–2010, featuring prevalence of comorbidity and impact on survival among persons with lung, colorectal, breast, or prostate cancer. Cancer. 2014;120:1290–314.View ArticlePubMedPubMed CentralGoogle Scholar
- Owens TW, Naylor MJ. Breast cancer stem cells. Front Physiol. 2013;4:225.View ArticlePubMedPubMed CentralGoogle Scholar
- Cardoso F, Fallowfield L, Costa A, Castiglione M, Senkus E. Locally recurrent or metastatic breast cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Ann Oncol. 2011;22 Suppl 6:vi25–30.PubMedGoogle Scholar
- Peto R, Davies C, Godwin J, Gray R, Pan HC, et al. Comparisons between different polychemotherapy regimens for early breast cancer: meta-analyses of long-term outcome among 100,000 women in 123 randomised trials. Lancet. 2012;379:432–44.View ArticlePubMedGoogle Scholar
- Castano Z, Tracy K, McAllister SS. The tumor macroenvironment and systemic regulation of breast cancer progression. Int J Dev Biol. 2011;55:889–97.View ArticlePubMedGoogle Scholar
- Society AC. Breast Cancer Facts & Figures 2011–2012. 2013.Google Scholar
- Beaumont T, Leadbeater M. Treatment and care of patients with metastatic breast cancer. Nurs Stand. 2011;25:49–56.View ArticlePubMedGoogle Scholar
- Clements MS, Roder DM, Yu XQ, Egger S, O’Connell DL. Estimating prevalence of distant metastatic breast cancer: a means of filling a data gap. Cancer Causes Control. 2012;23:1625–34.View ArticlePubMedGoogle Scholar
- Institute NC. SEER Stat Fact Sheets: Breast. 2013.Google Scholar
- Jagsi R. Progress and controversies: Radiation therapy for invasive breast cancer. CA Cancer J Clin. 2013;64(2):135-52.Google Scholar
- Darby S, McGale P, Correa C, Taylor C, Arriagada R, et al. Effect of radiotherapy after breast-conserving surgery on 10-year recurrence and 15-year breast cancer death: meta-analysis of individual patient data for 10,801 women in 17 randomised trials. Lancet. 2011;378:1707–16.View ArticlePubMedGoogle Scholar
- Cuzick J, Stewart H, Peto R, Baum M, Fisher B, et al. Overview of randomized trials of postoperative adjuvant radiotherapy in breast cancer. Cancer Treat Rep. 1987;71:15–29.PubMedGoogle Scholar
- Cuzick J, Stewart H, Rutqvist L, Houghton J, Edwards R, et al. Cause-specific mortality in long-term survivors of breast cancer who participated in trials of radiotherapy. J Clin Oncol. 1994;12:447–53.PubMedGoogle Scholar
- Buchholz TA, Strom EA, Perkins GH, McNeese MD. Controversies regarding the use of radiation after mastectomy in breast cancer. Oncologist. 2002;7:539–46.View ArticlePubMedGoogle Scholar
- Langlands FE, Horgan K, Dodwell DD, Smith L. Breast cancer subtypes: response to radiotherapy and potential radiosensitisation. Br J Radiol. 2013;86:20120601.View ArticlePubMedPubMed CentralGoogle Scholar
- Li Z, Xia L, Lee LM, Khaletskiy A, Wang J, et al. Effector genes altered in MCF-7 human breast cancer cells after exposure to fractionated ionizing radiation. Radiat Res. 2001;155:543–53.View ArticlePubMedGoogle Scholar
- Guo G, Yan-Sanders Y, Lyn-Cook BD, Wang T, Tamae D, et al. Manganese superoxide dismutase-mediated gene expression in radiation-induced adaptive responses. Mol Cell Biol. 2003;23:2362–78.View ArticlePubMedPubMed CentralGoogle Scholar
- Ahmed KM, Dong S, Fan M, Li JJ. Nuclear factor-kappaB p65 inhibits mitogen-activated protein kinase signaling pathway in radioresistant breast cancer cells. Mol Cancer Res. 2006;4:945–55.View ArticlePubMedGoogle Scholar
- Duru N, Fan M, Candas D, Menaa C, Liu HC, et al. HER2-associated radioresistance of breast cancer stem cells isolated from HER2-negative breast cancer cells. Clin Cancer Res. 2012;18:6634–47.View ArticlePubMedPubMed CentralGoogle Scholar
- Diehn M, Cho RW, Lobo NA, Kalisky T, Dorie MJ, et al. Association of reactive oxygen species levels and radioresistance in cancer stem cells. Nature. 2009;458:780–3.View ArticlePubMedPubMed CentralGoogle Scholar
- Lagadec C, Vlashi E, Della Donna L, Meng Y, Dekmezian C, et al. Survival and self-renewing capacity of breast cancer initiating cells during fractionated radiation treatment. Breast Cancer Res. 2010;12:R13.View ArticlePubMedPubMed CentralGoogle Scholar
- Lagadec C, Vlashi E, Della Donna L, Dekmezian C, Pajonk F. Radiation-induced reprogramming of breast cancer cells. Stem Cells. 2012;30:833–44.View ArticlePubMedPubMed CentralGoogle Scholar
- Geng SQ, Alexandrou AT, Li JJ. Breast cancer stem cells: Multiple capacities in tumor metastasis. Cancer Lett. 2014;349:1–7.View ArticlePubMedPubMed CentralGoogle Scholar
- Garattini E, Paroni G, Terao M. Retinoids and breast cancer: new clues to increase their activity and selectivity. Breast Cancer Res. 2012;14:111.View ArticlePubMedPubMed CentralGoogle Scholar
- Chan CH, Lee SW, Li CF, Wang J, Yang WL, et al. Deciphering the transcriptional complex critical for RhoA gene expression and cancer metastasis. Nat Cell Biol. 2010;12:457–67.View ArticlePubMedGoogle Scholar
- Chen X, Shen B, Xia L, Khaletzkiy A, Chu D, et al. Activation of nuclear factor kappaB in radioresistance of TP53-inactive human keratinocytes. Cancer Res. 2002;62:1213–21.PubMedGoogle Scholar
- Chen X, Radany EH, Wong P, Ma S, Wu K, et al. Suberoylanilide hydroxamic acid induces hypersensitivity to radiation therapy in acute myelogenous leukemia cells expressing constitutively active FLT3 mutants. PLoS One. 2013;8:e84515.View ArticlePubMedPubMed CentralGoogle Scholar
- Al-Hajj M, Clarke MF. Self-renewal and solid tumor stem cells. Oncogene. 2004;23:7274–82.View ArticlePubMedGoogle Scholar
- Willers H, Dahm-Daphi J, Powell SN. Repair of radiation damage to DNA. Br J Cancer. 2004;90:1297–301.View ArticlePubMedPubMed CentralGoogle Scholar
- Lieber MR. The mechanism of double-strand DNA break repair by the nonhomologous DNA end-joining pathway. Annu Rev Biochem. 2010;79:181–211.View ArticlePubMedPubMed CentralGoogle Scholar
- Onder TT, Gupta PB, Mani SA, Yang J, Lander ES, et al. Loss of E-cadherin promotes metastasis via multiple downstream transcriptional pathways. Cancer Res. 2008;68:3645–54.View ArticlePubMedGoogle Scholar
- Al-Hajj M, Wicha MS, Benito-Hernandez A, Morrison SJ, Clarke MF. Prospective identification of tumorigenic breast cancer cells. Proc Natl Acad Sci U S A. 2003;100:3983–8.View ArticlePubMedPubMed CentralGoogle Scholar
- Phillips TM, McBride WH, Pajonk F. The response of CD24(−/low)/CD44+ breast cancer-initiating cells to radiation. J Natl Cancer Inst. 2006;98:1777–85.View ArticlePubMedGoogle Scholar
- de Jong J, Looijenga LH. Stem cell marker OCT3/4 in tumor biology and germ cell tumor diagnostics: history and future. Crit Rev Oncog. 2006;12:171–203.View ArticlePubMedGoogle Scholar
- Carina V, Zito G, Pizzolanti G, Richiusa P, Criscimanna A, et al. Multiple pluripotent stem cell markers in human anaplastic thyroid cancer: the putative upstream role of SOX2. Thyroid. 2013;23:829–37.View ArticlePubMedPubMed CentralGoogle Scholar
- Wang ML, Chiou SH, Wu CW. Targeting cancer stem cells: emerging role of Nanog transcription factor. Onco Targets Ther. 2013;6:1207–20.PubMedPubMed CentralGoogle Scholar
- Jothy S. CD44 and its partners in metastasis. Clin Exp Metastasis. 2003;20:195–201.View ArticlePubMedGoogle Scholar
- Birzele F, Voss E, Nopora A, Honold K, Heil F, et al. CD44 isoform status predicts response to treatment with anti-CD44 antibody in cancer patients. Clin Cancer Res. 2015; 21(12):2753-62.Google Scholar
- Orian-Rousseau V. CD44, a therapeutic target for metastasising tumours. Eur J Cancer. 2010;46:1271–7.View ArticlePubMedGoogle Scholar
- Naor D, Sionov RV, Ish-Shalom D. CD44: structure, function, and association with the malignant process. Adv Cancer Res. 1997;71:241–319.View ArticlePubMedGoogle Scholar
- Tallman MS, Andersen JW, Schiffer CA, Appelbaum FR, Feusner JH, et al. All-trans-retinoic acid in acute promyelocytic leukemia. N Engl J Med. 1997;337:1021–8.View ArticlePubMedGoogle Scholar
- Karsy M, Albert L, Tobias ME, Murali R, Jhanwar-Uniyal M. All-trans retinoic acid modulates cancer stem cells of glioblastoma multiforme in an MAPK-dependent manner. Anticancer Res. 2010;30:4915–20.PubMedGoogle Scholar
- Gudas LJ, Wagner JA. Retinoids regulate stem cell differentiation. J Cell Physiol. 2011;226:322–30.View ArticlePubMedPubMed CentralGoogle Scholar
- Ginestier C, Wicinski J, Cervera N, Monville F, Finetti P, et al. Retinoid signaling regulates breast cancer stem cell differentiation. Cell Cycle. 2009;8:3297–302.View ArticlePubMedPubMed CentralGoogle Scholar
- Chou SC, Azuma Y, Varia MA, Raleigh JA. Evidence that involucrin, a marker for differentiation, is oxygen regulated in human squamous cell carcinomas. Br J Cancer. 2004;90:728–35.View ArticlePubMedPubMed CentralGoogle Scholar
- Pfander D, Swoboda B, Kirsch T. Expression of early and late differentiation markers (proliferating cell nuclear antigen, syndecan-3, annexin VI, and alkaline phosphatase) by human osteoarthritic chondrocytes. Am J Pathol. 2001;159:1777–83.View ArticlePubMedPubMed CentralGoogle Scholar
- Li L, Bhatia R. Stem cell quiescence. Clin Cancer Res. 2011;17:4936–41.View ArticlePubMedPubMed CentralGoogle Scholar
- Duru N, Candas D, Jiang G, Li JJ. Breast cancer adaptive resistance: HER2 and cancer stem cell repopulation in a heterogeneous tumor society. J Cancer Res Clin Oncol. 2014;140:1–14.View ArticlePubMedPubMed CentralGoogle Scholar
- Bese NS, Sut PA, Ober A. The effect of treatment interruptions in the postoperative irradiation of breast cancer. Oncology. 2005;69:214–23.View ArticlePubMedGoogle Scholar
- Sampieri K, Fodde R. Cancer stem cells and metastasis. Semin Cancer Biol. 2012;22:187–93.View ArticlePubMedGoogle Scholar
- Kang Y. Analysis of cancer stem cell metastasis in xenograft animal models. Methods Mol Biol. 2009;568:7–19.View ArticlePubMedGoogle Scholar
- Baccelli I, Trumpp A. The evolving concept of cancer and metastasis stem cells. J Cell Biol. 2012;198:281–93.View ArticlePubMedPubMed CentralGoogle Scholar
- Sheridan C, Kishimoto H, Fuchs RK, Mehrotra S, Bhat-Nakshatri P, et al. CD44+/CD24- breast cancer cells exhibit enhanced invasive properties: an early step necessary for metastasis. Breast Cancer Res. 2006;8:R59.View ArticlePubMedPubMed CentralGoogle Scholar
- Takebe N, Warren RQ, Ivy SP. Breast cancer growth and metastasis: interplay between cancer stem cells, embryonic signaling pathways and epithelial-to-mesenchymal transition. Breast Cancer Res. 2011;13:211.View ArticlePubMedPubMed CentralGoogle Scholar
- Pham PV, Phan NL, Nguyen NT, Truong NH, Duong TT, et al. Differentiation of breast cancer stem cells by knockdown of CD44: promising differentiation therapy. J Transl Med. 2011;9:209.View ArticlePubMedPubMed CentralGoogle Scholar
- Guo L, Xiao Y, Fan M, Li JJ, Wang Y. Profiling global kinome signatures of the radioresistant MCF-7/C6 breast cancer cells using MRM-based targeted proteomics. J Proteome Res. 2015;14:193–201.View ArticlePubMedPubMed CentralGoogle Scholar
- Garattini E, Gianni M, Terao M. Cytodifferentiation by retinoids, a novel therapeutic option in oncology: rational combinations with other therapeutic agents. Vitam Horm. 2007;75:301–54.View ArticlePubMedGoogle Scholar
- Zanardi S, Serrano D, Argusti A, Barile M, Puntoni M, et al. Clinical trials with retinoids for breast cancer chemoprevention. Endocr Relat Cancer. 2006;13:51–68.View ArticlePubMedGoogle Scholar
- Arisi MF, Starker RA, Addya S, Huang Y, Fernandez SV. All trans-retinoic acid (ATRA) induces re-differentiation of early transformed breast epithelial cells. Int J Oncol. 2014;44:1831–42.PubMedPubMed CentralGoogle Scholar
- Wang B, Yan Y, Zhou J, Zhou Q, Gui S, et al. A novel all-trans retinoid acid derivatives inhibits the migration of breast cancer cell lines MDA-MB-231 via myosin light chain kinase involving p38-MAPK pathway. Biomed Pharmacother. 2013;67:357–62.View ArticlePubMedGoogle Scholar
- Szakacs G, Paterson JK, Ludwig JA, Booth-Genthe C, Gottesman MM. Targeting multidrug resistance in cancer. Nat Rev Drug Discov. 2006;5:219–34.View ArticlePubMedGoogle Scholar