Enhanced proteasomal activity is essential for long term survival and recurrence of innately radiation resistant residual glioblastoma cells.

Jacinth Rajendra,Sanket Desai,Harsha Gowda,Nilesh Gardi,Kiran Kumar,Ketaki Patkar,Rahul Thorat,Amit Dutt,Ekjot Kaur,Sheikh Burhan Ud Din Farooqee,Keshava K Datta,Sameer Salunkhe,Jyothi Nair,Aliasgar Moiyadi,Jayant Sastri Goda,Prasanna Venkatraman,Shilpee Dutt

doi:10.18632/oncotarget.25351

Abstract

Therapy resistance and recurrence in Glioblastoma is due to the presence of residual radiation resistant cells. However, because of their inaccessibility from patient biopsies, the molecular mechanisms driving their survival remain unexplored. Residual Radiation Resistant (RR) and Relapse (R) cells were captured using cellular radiation resistant model generated from patient derived primary cultures and cell lines. iTRAQ based quantitative proteomics was performed to identify pathways unique to RR cells followed by in vitro and in vivo experiments showing their role in radio-resistance. 2720 proteins were identified across Parent (P), RR and R population with 824 and 874 differential proteins in RR and R cells. Unsupervised clustering showed proteasome pathway as the most significantly deregulated pathway in RR cells. Concordantly, the RR cells displayed enhanced expression and activity of proteasome subunits, which triggered NFkB signalling. Pharmacological inhibition of proteasome activity led to impeded NFkB transcriptional activity, radio-sensitization of RR cells in vitro, and significantly reduced capacity to form orthotopic tumours in vivo. We demonstrate that combination of proteasome inhibitor with radio-therapy abolish the inaccessible residual resistant cells thereby preventing GBM recurrence. Furthermore, we identified first proteomic signature of RR cells that can be exploited for GBM therapeutics.

Highlights

Glioblastoma is the most common and lethal primary brain tumour
We have previously reported development of a cellular model of radiation resistance using primary cultures from patient samples, which recapitulate the clinical scenario of resistance and enable us to capture residual radiation resistant (RR) cells [9] and understand their molecular mechanism of survival
To capture and understand the survival mechanisms of residual resistant cells of GBM, that are diagnostically undetectable post treatment, we generated in vitro radiation resistant model derived from cell lines and patient samples [9] (Figure 1A)

Summary

Introduction

Glioblastoma is the most common and lethal primary brain tumour. Despite the multimodal therapy, tumour recurrence is major challenge in glioblastoma with patient survival less than 6 months post recurrence [1,2,3,4]. Till date majority of proteomics studies in glioblastoma have focused on identification of differential proteins amongst different GBM cell lines, patient samples or within the same tumour to investigate the heterogeneity of glioblastoma, mechanism of chemoresistance and identification of diagnostic biomarkers [14,15,16,17,18,19,20,21,22,23,24,25,26] None of these studies could identify survival mechanism of innately resistant cells due to their unavailability. Our proteomics data has delineated proteasomal pathway as one of the plausible targetable mechanisms that significantly contribute to the survival of innate radiation residual cells via the NFkB signalling cascade

Methods

Results

Conclusion