Glioblastoma (GBM) is the most common primary tumor of the central nervous system, with its deadly nature owing to a high rate of invasion and angiogenesis. A key player in the GBM pathogenesis is a distinct subpopulation of tumor cells which are capable of self-renewal, highly angiogenic and possess the potential for extensive proliferation and multi-lineage differentiation. This cell population termed Glioma Stem Cells (GSCs) is highly resistant to the chemo- and radiotherapies and plays an important role in tumor initiation, progression, and recurrence. In response to radiation therapy, GSCs are capable of triggering the activation of multiple signaling pathways including Wnt, Notch, and Hedgehog, and their DNA damage repair system is proactive. Taken together, the efforts to foster therapeutic interventions will prove futile, without first targeting the GSC population. The miRNA network adds a dimension of regulatory control, which serves to maintain pluripotency and reprograms multiple stemness and radioresistance promoting pathways. However, not much information is available that could provide mechanistic insights regarding how specific miRNAs modulate radioresistance pathways. Our initial efforts involving a global screening of microRNA profiles in different GSCs after radiation treatment resulted in identification of multiple microRNAs that were significantly altered in response to radiation. Based on our preliminary data, we selected 7 microRNAs as potential candidates, with each having several targets in Notch, Wnt, PI3K/Akt, and Hedgehog signaling pathways. In order to unfold the role of each of identified microRNAs, we used specific lentiviral constructs to create overexpression/knockdown of each microRNA in GSCs. Using these stable GSC clones, we carried out multiple in vitro studies to analyze the effects of the respective alteration in relation to radioresistance and stemness phenotypes. Other phenotypic studies included growth kinetics, cell proliferation, invasiveness, apoptosis and cell cycle. We also carried out an extensive in silico analysis to identify the potential targets of these microRNAs. This was followed by analyzing various downstream components of the target genes. Additionally, we carried out a context-based assessment of the overall effects to probe if there is an integration of one or more pathways that could lead to radiation sensitivity. Our in vitro findings also revealed their roles in regulating stemness and metastatic ability in vivo. Lastly, our study provides a basis for understanding the role of miRNAs in radioresistance phenotype and furthermore, it may lead towards another tool to inhibit GSC proliferation and/or survival.

Funding: R01CA108633, R01CA169368, RC2CA148190, U10CA180850-01 (NCI), Brain Tumor Funders Collaborative Grant, and The Ohio State University CCC (all to AC).

Citation Format: Rajbir Singh, Kamalakannan Palanichamy, Saikh Jaharul Haque, Arnab Chakravarti. MicroRNA-mediated modulation of radioresistance of glioma stem cells [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 3440. doi:10.1158/1538-7445.AM2017-3440