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Stem Cells - Cancer - Cancer Stem Cells
Keynote Speaker: Malcolm R. Alison, Barts and The London School of Medicine and Dentistry, London, UK
Cancer Stem Cells: A matter of phenotype or function? Over the past decade, the number of studies addressing cancer cell subpopulations with cancer stem cell (CSC) or cancer stem-like properties in solid tumors has exponentially increased. The literature, however, often remains obscure using a variable / inaccurate terminology, disputable surrogate markers and/or ambiguous analytical endpoints. Despite the uncertainties in nomenclature there is indeed experimental evidence for a circumscribed fraction of cancer cells in various solid tissues with a particular potential to survive that could be considered as root of the disease and/or as driving force of tumor recurrence. Since conventional therapies do not seem to suffice in killing the entire spectrum of tumor cells, one may speculate that the targeting of CSCs could indeed more successfully eradicate cancer. This view, however, is already adapting, mainly because new models of stemness begin to consider plasticity in cancer cells. Cancer cells thus may be reprogrammed into CSC phenotypes depending on the environmental conditions. In this session, we will discuss the CSC hypothesis and we will highlight challenges associated with the identification of cell populations that really are best defined by their function.
A brief introduction to navigate through the foggy sea of cancer stem cell research
OncoRay - National Center for Radiation Research in Oncology, TU Dresden, Germany;
One of the most active and competitive areas in oncology research relates to the cancer stem cell paradigm. Unfortunately, communication in the field is hampered by subtle differences in semantics, and also the power of experimental data is often overinterpreted in the literature. An introduction will thus be given as a compass for the audience to navigate through the sometimes foggy sea of terminology in cancer stem cell research and to become aware of the potential and limitations of functional assays as well as current controversies in the use of biomarkers and theragnostic tools. Challenges of the cancer stem cell concept in light of phenomena such as phenotypic plasticity of stemness and dynamics of microenvironmental niches will briefly be stressed.
Recent developments in cancer stem cells: implications in the clinical setting
Barts and The London School of Medicine and Dentistry, United Kingdom;
Many if not all tumours contain a sub-population of self-renewing and expanding stem cells known as cancer stem cells (CSCs). The symmetric division of CSCs is one mechanism enabling expansion in their numbers as tumours grow, while epithelial mesenchymal transition (EMT) is another mechanism to generate further CSCs endowed with a more invasive and metastatic phenotype. Putative CSCs are prospectively isolated using methods based on either a surface marker (e.g. CD44, CD133) or an intracellular enzyme activity (e.g. ALDH, ABC transporter) [1,2]; subsequently assessed either by a ‘sphere-forming’ assay in non-adherent culture and/or by their ability to initiate new tumour growth when xenotransplanted into immunocompromised mice. Cell sub-populations enriched for tumour-initiating ability have also been found in murine tumours countering the argument that xenografting human cells merely selects human cells with an ability to grow in mice. Cancer progression can be viewed as an evolutionary process that generates new/multiple clones with a fresh identity; this may be a major obstacle to successful cancer stem cell eradication if treatment targets only a single type of stem cell .
In this lecture, I firstly briefly discuss evidence that cancer can originate from normal stem cells or closely related progenitors. I then outline the attributes of CSCs and review studies in which they have been identified in various cancers. Very recently it has become clear that the tumour stroma is not a mere bystander, being an important modulator of CSC behaviour. Finally, I discuss the implications of these findings for successful cancer therapies, concentrating on irradiation, the self-renewal pathways (Wnt, Notch, Hedgehog, PTEN/Akt) [3,4,5], aldehyde dehydrogenase activity, EMT, miRNAs and other epigenetic modifiers as potential targets for therapeutic manipulation. Many and varied therapeutic approaches to target CSCs are being evaluated and some have entered clinical trials.
1. Alison MR, Lim SM, Nicholson LJ. Cancer stem cells; problems for therapy? J Pathol 2011; 223: 147-161.
2. Alison MR, Guppy NJ, Lim SM, Nicholson LJ. Finding cancer stem cells: are aldehyde dehydrogenases fit for purpose? J Pathol. 2010; 222: 335-344.
3. Takebe N, Harris PJ, Warren RQ, Ivy SP. Targeting cancer stem cells by inhibiting Wnt, Notch, and Hedgehog pathways. Nat Rev Clin Oncol. 2011;8(2):97-106.
4. Mas C, Ruiz i Altaba A. Small molecule modulation of HH-GLI signaling: current leads, trials and tribulations. Biochem Pharmacol. 2010;80(5):712-723.
5. Wang Z, Li Y, Ahmad A, Azmi AS, Banerjee S, Kong D, Sarkar FH. Targeting Notch signaling pathway to overcome drug resistance for cancer therapy. Biochim Biophys Acta. 2010;1806(2):258-267.
ALDH1+ Glioblastoma cells mediate TMZ-resistance and recurrence
1Institute of Reconstructive Neurobiology, University of Bonn, Germany; 2Department of Neurosurgery, University of Bonn, Germany; 3Department of Neuropathology, University of Bonn, Germany; 4Division of Neurological Research, Department of Neurosurgery, University of Heidelberg, Germany;
One of the major implications of the recently coined cancer stem cell (CSC) hypothesis is that a circumscribed population of tumor cells is responsible for disease maintenance and therapy resistance. In this study, we present evidence for the occurrence of a distinct ALDH1+ subpopulation of CSCs within human glioblastoma (GBM) that shows a strong propensity to survive temozolomide (TMZ)-based chemotherapy regimens.
Using a tissue-microarray of 283 paraffin-embedded glioma specimens, we could demonstrate that the frequency of ALDH1+ cells correlates inversely with the PFS/OS of particularly those GBM patients that were treated with TMZ during recurrence of disease. We furthermore show that the frequency of ALDH1+ cells increases in recurrent GBM samples compared to tissue derived from the respective patient's primary manifestation. Using long-term TMZ application schemes, we could mimic this observation in vitro. ALDH1+ cells could be enriched from a series of previously characterized primary GBM cultures by a factor of 5-10x. These cells are tumorigenic and multipotent, show an increase in self-renewal, and their genomic profiles largely overlap with the original tumor. Various in vitro TMZ re-challenge paradigms confirmed their increased cellular resistance levels, which could be blocked irreversibly by application of DEAB, a selective ALDH-inhibitor. Our findings add creditability to the cancer stem cell hypothesis with a particular emphasis on therapy-related phenotype occurrence.
*Tumorigenicity of colorectal cancer cell lines with distinct CD133 and CD44 antigen pattern*
Tumor Pathophysiology, OncoRay – National Center for Radiation Research in Oncology, Medical Faculty Carl Gustav Carus, Dresden University of Technology, Dresden, Germany;
Background & Aim
Various surface antigens, in particular CD133 and CD44, have been described as surrogate biomarkers to enrich colorectal cancer cell (CRC) subpopulations from primary tissue with enhanced tumorigenic potential. However, the relevance of these markers to define similar subpopulations in established CRC cell lines seems ambiguous. We showed earlier, that CD133 expression does not define a highly tumorigenic subpopulation in microsatellite-instable HCT-116 cells. In the present project we aimed to relate marker expression and tumorigenic capacity of microsatellite-stable, aneuploid CRC cell lines and to further evaluate the usefulness of CD133/CD44 antigen profiles for the identification of tumorigenic subpopulations.
Materials & Methods
Cell lines containing subpopulations with different CD133/CD44 antigen pattern were studied as verified by flow cytometry and Western blotting. Xenograft formation and growth were monitored after injection of CRC cell lines into the hind limbs of NMRI(nu/nu) mice with Matrigel. Cell numbers of 10,000, 500, 100 and as low as 10 cells were applied per injection site and mouse, respectively. Subpopulations from two cell lines were separated by fluorescence-activated cell sorting (FACS) and analyzed for their tumorigenic potential and marker expression in the resulting xenograft tumors.
Results & Perspectives
HT29, SW620, SW480, LS513, LS1034 and SW837 CRC cells show different CD133/CD44 expression pattern in vitro but all produced xenograft tumors after injecting ≥ 500 cells per site. Cell injections of 10 cells led to tumor formation from both HT29 and SW620. In contrast to literature data, we did not observe any difference in tumor formation capacity of CD133-negative/low vs. CD133-positive HT29 populations and found CD133-negative cells to rapidly reexpress CD133. The same was true for SW620 cells which also contained a clear CD44-negative/low subfraction. Here, all subpopulations defined by the CD133/CD44 expression profile showed similar xenograft formation capacities. The conclusion that CD44 is as irrelevant for in vivo engraftment of CRC cell lines is not yet valid, because SW620 cells turned out to be negative in CD44 Western blot analysis. This phenomenon is under further investigation and the search for CRC cell lines with limited tumorigenic potential and respective subpopulations of cancer cells is ongoing.
This work was supported by DFG grant KU 971/7-1.