Tumor-stroma interaction in glioma through proteomic approaches
Kumar Somasundaram, Microbiology and Cell Biology, Indian Institute of Science, Bangalore 12, India
During the last two decades, the neuro-oncology community is witnessing an explosion of knowledge about these extremely complex brain tumors. However, the median life expectancy of glioblastoma (the most common primary adult tumor) patients remains at 15-17 months (Stupp et al., 2005). Hence, there is a pressing need to develop more comprehensive approaches to understand the biology of glioma in order to develop markers that could help diagnose glioma early, molecular stratification with respect to patient prognostication and treatment response prediction and in developing novel therapeutic methods. We have a comprehensive approach covering various aspects like genetic and epigenetic alterations in glioma, serum biomarkers using high-throughput proteomics, genome-wide shRNA screening for temozolomide sensitivity and exome sequencing to understand the glioma biology.
While the role of genetic and epigenetic alterations in tumor cells have been investigated extensively, the importance of the tumor stromal components in GBM development and progression has only been recognized recently. Since the interaction between tumor cells and stromal cells is more likely to involve secreted proteins and the fact that secreted proteins are more likely to be present in serum, we chose to analyse the glioma patient serum to begin with. We used various proteomic platforms like 2-DE, 2-DE DIGE, antibody microarrays, bead arrays and iTRAQ-LC MS/MS to answer some of the above questions.
In this presentation, I will present our recent work on identification and validation of a serum cytokine signature for distinguishing glioma patient sera from normal healthy individual sera. I will also present data related to validation and functional characterization of one of the cytokines, Macrophage Colony Stimulating Factor 1 (MCSF1). Unlike what is known in the literature, we found tumor secreted MCSF1 did not have effect either on tumor cells in an autocrine fashion or a role in M2 polarization of microglial cells in a paracrine fashion even though we found a huge infiltration of M2 polarized macrophages in the glioma stroma. MCSF1 induced angiogenesis through its action on macrophages. SILAC experiment based investigation of macrophage/microglial secretome identified several novel factors as mediators of MCSF1-induced angiogenesis. These results are particularly intersecting as bevacizumab, a VEGF targeting antibody approved by FDA, failed to show any significant improvement in overall and progression free survival in the recently conducted trails. These studies point to the possible presence of factors other than VEGF that may promote angiogenesis and cancer stem cell derived endothelial cells through transdifferentiation. In conclusion, our study identified a cytokine signature for distinguishing glioma sera from that of healthy individuals and identified novel proteins in the microglia secretome as novel mediator of MCSF-induced tumor angiogenesis with a potential of developing a targeted therapy.