Abstract 202: Functional heterogeneity in glioblastoma: cell-cell communication regulates temporospatial events in tumor recurrence
Authors: Woolard Kevin D. , Huang Patrick , Sears Thomas K. , Settles Matthew 
Published: August 2018

Abstract
Patients with glioblastoma frequently develop progressive disease following treatment. This is believed to occur because of an inherent or acquired resistance to chemo- and radiotherapy within residual tumor burden. However, how discrete tumor subpopulations coordinate tumor recurrence and progression is still poorly understood. Here, we describe the isolation of glioma stem cells (GSCs) from a patient prior to treatment (0203), and then from multiple sites in the brain following tumor recurrence. These sites include the recurrent tumor at the primary site (T3/T4), as well as disseminated tumor cells in the contralateral hemisphere (T6/T7). Whole exome sequencing identifies loss of all unique genomic signatures within the original tumor cells (0203) following treatment, suggesting eradication of the original tumor bulk. Moreover, genomic signatures of the recurrent tumor (T3/T4) clusters alongside disseminated subpopulations of tumor cells isolated from the contralateral hemisphere (T6/T7), suggesting that tumor recurrence is driven by repopulation of the original tumor location. Copy number variants (CNVs) between the original tumor (0203), the recurrent tumor (T3/T4), and distant tumor sites (T6/T7), identify a more primordial genome in distant tumor sites (T6/T7), which lack canonical CNVs found in the original tumor and in other subpopulations (deletion of PTEN or amplification of EGFR). Thus, tumor dissemination likely occurs early in disease development. We are able to model the patient's disease progression by using co-culture techniques and orthotopic xenograft studies. Our data indicates that 0203 cells actively suppress migration of disseminated tumor sub-populations (T6/T7) in vitro and in vivo, which is replicated by using cell-free conditioned media. In stark contrast, the induction of apoptosis in 0203 cells (or treating with conditioned media from apoptotic 0203 cells) rapidly recruits migration of disseminated cells (T6/T7) in a co-culture system. Co-culture of disseminated GSCs (T6/T7) with viable 0203 cells also results in suppression of pathways implicated in glioma migration, such as AKT, CXCR4, TrkA, and CLCN3; suppression that is reversed upon induction of apoptosis in 0203 cells. These data indicate that while widespread tumor dissemination occurs early in glioblastoma, a dominant subpopulation may actively suppress proliferation of separate, disseminated subpopulations. Moreover, abrogating this suppression following therapy triggers migration and proliferation of specific, distant tumor sub-populations, resulting in tumor recurrence. This suggests that glioblastoma recurrence may not be as simple as selection of radioresistant cells, rather it may result from the active recruitment of disseminated subpopulations, which migrate to the original tumor microenvironment.
Citation Format: Kevin D. Woolard, Patrick Huang, Thomas K. Sears, Matthew Settles. Functional heterogeneity in glioblastoma: cell-cell communication regulates temporospatial events in tumor recurrence [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 202.