CBIO-20GLIOBLASTOMA SPECIFIC PROTEINS IDENTIFIED THROUGH COMBINED IN VITRO AND IN VIVO PHAGE DISPLAY BIOPANNING

Abstract

Glioblastomas are the most common and lethal primary brain tumor with conventional therapy offering only palliation. Their resistance to therapy has been hypothesized to be due in part to the cancer stem cell, the target of which the development of safe and effective future therapeutics will be focused on. As phage display technology has been used in cancer to identify, target, and image tumor cells, we employed phage display technology to identify novel proteins specific to the functioning of glioblastoma stem cells (GSCs). We have previously shown that in vivo phage display biopanning against primary glioblastoma cell lines xenografted in immunocompromised mice is an effective strategy for isolating glioma stem cell (GSC) specific peptides sequences. Using this strategy, we identified Vav3, a guanine exchange factor that plays a role in the maintenance of GSCs. In order to further identify novel proteins that may play a role in GSC maintenance, we have employed an in vitro biopanning strategy against GSCs isolated from patient derived glioblastoma cell lines grown in culture. Several peptides isolated using this strategy matched peptides that were separately isolated using the in vivo biopanning technique, validating the ability of these selection strategies to achieve consensus peptide sequences that are specific for GSC binding. In silico analysis of these peptides using a BLAST search as previously described revealed CD48. Analysis of CD48 showed that it is preferentially expressed in glioblastoma cells with a potential role in tumor maintenance. Together, these studies validate the effectiveness of utilizing different phage display biopanning strategies to isolate novel proteins that may play a vital role in maintenance of glioblastomas.