Genetic Landscape Of Glioma Reveals Defective Neuroactive Ligand Receptor Interaction Pathway As A Poor Prognosticator In Glioblastoma Patients

Glioblastoma (GBM; grade IV), is highly proliferative, infiltrative and treatment refractory. Hence, understanding the complete genetic alteration profile of GBM would help us in identifying molecules or pathways that have strong implications in GBM pathogenesis, thus opening up avenues for targeted therapy. Recent large scale studies suggest that three pathways - receptor-tyrosine kinase, TP53 and RB, are significantly altered in GBM. However, even with the tremendous increase in our understanding of the tumor, advancement in therapeutics is minimal and the median survival still remains at 15 months. Hence, we need to elucidate novel altered molecules and pathways in GBM progression such that more effective therapeutic options can be explored. Here, we have carried out whole exome sequencing of grade II, grade III and GBM samples which revealed the mutation spectrum of glioma from our patient set. Further, we performed integrative analysis of mutated genes from our patient cohort as well as TCGA cohort (The Cancer Genome Atlas) to find out mutated pathways that predict survival in GBM patients. The most significant pathway - neuroactive ligand-receptor interaction pathway was explored further. Patients with mutations in one or more genes of this pathway had poor survival. The pathway comprises of G-protein coupled receptors, ion channels and ligands which functions in modulation of neural plasticity, memory processes, behavior etc. Of the enriched genes belonging to this pathway, Calcitonin Receptor (CALCR), which was highest mutated in GBM (2.75%), was taken up for further investigation. CALCR was found to be downregulated in GBM and mutation or downregulation of the gene was found to predict poor survival in patients. Functional studies through cell-line based experiments revealed CALCR is a tumor suppressor in GBM. The peptide hormone calcitonin (CT), a high affinity CALCR ligand, inhibited proliferation, migration and anchorage-independent growth of glioma cells expressing CALCR with a concomitant decrease in the phosphorylation levels of ERK, AKT and JNK signaling molecules. However, CT failed to do these functions in CALCR silenced glioma cells. Exogenous overexpression of CALCR in glioma cells expressing low levels of the receptor was found to inhibit proliferation, migration and anchorage independent growth and this effect was further augmented when CT was added. Further, introduction of tumor-derived mutations in CALCR led to the abrogation of its tumor suppressor function. Studies are ongoing to demonstrate the tumor suppressive nature of CALCR using in vitro astrocyte transformation and intracranial orthotopic mouse glioma model. Thus, our study finds CT-CALCR signaling axis is an important tumor suppressor pathway in glioma development and underscores the importance of using CT as a novel therapeutic molecule for GBM treatment. Citation Format: Jagriti Pal, Vikas Patil, Anupam Kumar, Kavneet Kaur, Chitra Sarkar, Kumaravel Somasundaram. Genetic landscape of glioma reveals defective neuroactive ligand receptor interaction pathway as a poor prognosticator in glioblastoma patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2454. doi:10.1158/1538-7445.AM2017-2454