Abstract #1080: Brain tumor stem cell marker: Distinct populations of tumor-initiating cells expressing surface antigens derived from cancer stem cells mediates chemo and radio resistance
Authors: Kamalakannan Palanichamy, Howard Colman, Arnab Chakravarti
Journal: Cancer Research (2009)

Introduction: Resistance to treatment represents a major obstacle to recovery. It is becoming better understood that Radiation Resistance may be secondary to a self-renewing sub-population of cells in the bulk of tumor capable of forming Neurospheres referred to as CSCs. Not all CSCs exhibit treatment resistance, it is only a sub-population of CSCs exhibit Chemo-/Radio- resistance. For the first time here we have identified a set of surface antigens whose expression encodes chemo-/radio-resistant subpopulation in Glioma CSCs. Results: We demonstrate with this work that these cells possessed higher tumorigenicity and metastatic potential and could be a potential marker to isolate chemo-/radio-resistant CSCs. The treatment resistance subpopulation of CSCs expresses higher levels of ABC family genes in addition to stem cell genes such as Nanog, Sox2, Oct4, etc. They also have a higher expression of TERT, Chemokine receptors and IAP family proteins. We have generated brain tumor spheroid cultures of primary GBM and this sub-population of CSCs are consistently capable of inducing tumors upon xenotransplantation that resemble the original malignancies, both in morphology and marker expression. We have also elucidated that a single cancer cell is pluripotent and has the capacity to generate a differentiated astrocytes, oligodentrocytes, and neurons, through a series of single-cell-cloning experiments. Using single-cell sorting of spheroid cells by flow cytometry we established that 1 in 15 cells has the capacity to induce a monoclonal culture as judged by the successful formation of spheroids, whereas in negative population about 1 in 350 cells have the same ability. Next we tested whether clonogenicity by FACS depositing a single GFP-transduced spheroid cell into different amounts of GFP+/- Antigen +/- cells from the same culture. This invariably resulted in Antigen+ spheres. Further this antigen specificity in identifying treatment resistant sub-population was tested in a panel of MD Anderson CSCs. To fully ascertain that this is also true for directly isolated tumor cells, we used a third primary GBM and initiated single cell cultures with purified Antigen+ cells directly ex-patient. Also in this setting the Antigen+ cell fraction generated single cell derived spheroids, whereas the Antigen- cells were incapable of doing so. This clearly confirmed that the clonogenic potential of our spheroid cultures resides in the Antigen+ cells. Conclusion: Taken together, the Antigen+ cells have not only stem cell properties, but also the ability to resist chemotherapeutic agents and radiation. The presence of such CSCs has important clinical implications for brain tumor treatment. Further characterization is underway by silencing this antigen in CSCs to gain new insights for novel therapeutic targets and prognostic markers.  Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 1080.