Interdisciplinary Initiatives Program Round 4 – 2008

Stephen Skirboll, Neurosurgery
Patrick Brown, Biochemistry

A subpopulation of cells within cancers behave as “cancer stem cells”(CSC), which are the only cells enriched for the ability to form tumors following transplantation.  CSCs have been demonstrated in human leukemia, breast cancer, and colon cancer using cell surface markers that distinguish CSC from the other cancer cells.  CD133 has been reported to be a marker for CSCs in human malignant gliomas (MGs).  However, the work by others and here at Stanford with CD133 has not corroborated this finding and CD133 is not expressed in up to one-third of MGs.  Thus, we believe the complete or a more complete phenotypic signature of CSCs in most MGs is currently unknown.  Since there many possible CSC cell surface markers, it is critical that a powerful screening approach be developed to better identify several markers before initiating laborious in vivo mouse xenograft assays.  Currently there is no such approach that can screen hundreds of cell surface markers on living tumor cells to identify CSC subpopulations within MGs or any other cancer. 

We are developing such an approach that combines an antibody-cell microarray with a soft agar assay which can screen over 1600 cell surface markers on living MG cells and identify those that enrich for colony formation in vitro.  This novel assay, called the Colony-Forming Antibody Cell Array (CFACA), will be used to study MG surgical specimens and cell lines and even CD133(+) sorted subpopulations of MG cells.  The CFACA is allowing us to study subpopulations of cells expressing several cell surface markers and offer a more complete cell surface phenotype for candidate CSCs in human MGs.  The antibody cell array portion of the CFACA will also allow us to further characterize the cell surface phenotype of CD133(+) vs. CD133(-) cells using a differential capture assay.  The CFACA-derived markers will be used to sort cells for implantation into mice and validate the CFACA as a screening assay to identify a more complete cell surface phenotype for CSC in MGs.   This project has progressed only because of a productive collaboration between Dr. Skirboll and Dr. Brown, since it utilizes the expertise, resources, and specific interests that are unique to each investigator and simply could not be done as two independent projects.   Dr. Skirboll has applied Dr. Brown’s expertise and resources with the antibody cell array to the development of the CFACA and the identification of CSCs in human cancers.  With the progress that we have made thus far, we are confident that the identification of CSC in MGs by using the CFACA will provide insights into glioma pathogenesis and establish previously unidentified cellular target(s) for more effective GBM therapies.  While the focus of this grant proposal is studying MGs, the CFACA can be applied to identify CSCs of any human cancer and can even be applied to identify stem cells of any normal human tissue.