Oncotarget

Research Papers:

Investigating the role of Hedgehog/GLI1 signaling in glioblastoma cell response to temozolomide

Jilian R. Melamed, Joshua T. Morgan, Stephen A. Ioele, Jason P. Gleghorn, Jennifer Sims-Mourtada and Emily S. Day _

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Oncotarget. 2018; 9:27000-27015. https://doi.org/10.18632/oncotarget.25467

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Abstract

Jilian R. Melamed1, Joshua T. Morgan2, Stephen A. Ioele1, Jason P. Gleghorn1,3, Jennifer Sims-Mourtada4 and Emily S. Day1,4,5

1Biomedical Engineering, University of Delaware, Newark, DE, USA

2Bioengineering, University of California, Riverside, CA, USA

3Biological Sciences, University of Delaware, Newark, DE, USA

4Helen F. Graham Cancer Center and Research Institute, Newark, DE, USA

5Materials Science and Engineering, University of Delaware, Newark, DE, USA

Correspondence to:

Emily S. Day, email: emilyday@udel.edu

Keywords: glioblastoma; hedgehog; GLI1; temozolomide; chemoresistance

Received: June 08, 2017     Accepted: May 08, 2018     Published: June 05, 2018

ABSTRACT

Resistance to chemotherapy substantially hinders successful glioblastoma (GBM) treatment, contributing to an almost 100% mortality rate. Resistance to the frontline chemotherapy, temozolomide (TMZ), arises from numerous signaling pathways that are deregulated in GBM, including Hedgehog (Hh) signaling. Here, we investigate suppression of Hh signaling as an adjuvant to TMZ using U87-MG and T98G cell lines as in vitro models of GBM. We found that silencing GLI1 with siRNA reduces cell metabolic activity by up to 30% in combination with TMZ and reduces multidrug efflux activity by 2.5-fold. Additionally, pharmacological GLI inhibition modulates nuclear p53 levels and decreases MGMT expression in combination with TMZ. While we surprisingly found that silencing GLI1 does not induce apoptosis in the absence of TMZ co-treatment, we discovered silencing GLI1 without TMZ co-treatment induces senescence as evidenced by a significant 2.3-fold increase in senescence associated β-galactosidase staining, and this occurs in a loss of PTEN-dependent manner. Finally, we show that GLI inhibition increases apoptosis in glioma stem-like cells by up to 6.8-fold in combination with TMZ, and this reduces the size and number of neurospheres grown from glioma stem-like cells. In aggregate, our data warrant the continued investigation of Hh pathway inhibitors as adjuvants to TMZ chemotherapy and highlight the importance of identifying signaling pathways that determine whether co-treatment will be successful.


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