Applications of CRISPR-Cas9 Technology to Genome Editing in Glioblastoma Multiforme
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cells Review Applications of CRISPR-Cas9 Technology to Genome Editing in Glioblastoma Multiforme Nadia Al-Sammarraie and Swapan K. Ray * Department of Pathology, Microbiology and Immunology, School of Medicine, University of South Carolina, Columbia, SC 29209, USA; [email protected] * Correspondence: [email protected]; Tel.: +1-803-216-3420; Fax: +1-803-216-3428 Abstract: Glioblastoma multiforme (GBM) is an aggressive malignancy of the brain and spinal cord with a poor life expectancy. The low survivability of GBM patients can be attributed, in part, to its heterogeneity and the presence of multiple genetic alterations causing rapid tumor growth and resistance to conventional therapy. The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-CRISPR associated (Cas) nuclease 9 (CRISPR-Cas9) system is a cost-effective and reliable gene editing technology, which is widely used in cancer research. It leads to novel discoveries of various oncogenes that regulate autophagy, angiogenesis, and invasion and play important role in pathogenesis of various malignancies, including GBM. In this review article, we first describe the principle and methods of delivery of CRISPR-Cas9 genome editing. Second, we summarize the current knowledge and major applications of CRISPR-Cas9 to identifying and modifying the genetic regulators of the hallmark of GBM. Lastly, we elucidate the major limitations of current CRISPR-Cas9 technology in the GBM field and the future perspectives. CRISPR-Cas9 genome editing aids in identifying novel coding and non-coding transcriptional regulators of the hallmarks of GBM particularly in vitro, while work using in vivo systems requires further investigation. Citation: Al-Sammarraie, N.; Ray, S.K. Applications of CRISPR-Cas9 Keywords: glioblastoma multiforme (GBM); CRISPR-Cas9 genome editing; apoptosis; proliferation; Technology to Genome Editing in autophagy; angiogenesis; cell invasion and migration Glioblastoma Multiforme. Cells 2021, 10, 2342. https://doi.org/10.3390/ cells10092342 1. Introduction Academic Editors: Jacques P. Glioblastoma multiforme (GBM) is an aggressive primary tumor, which arises from the Tremblay and Antonella Arcella abnormal astroglial cells in the brain in most cases as well as in the spinal cord in less often cases [1,2]. The incidence of GBM is approximately less than 10 per 100,000 individuals Received: 24 May 2021 worldwide, and a significant number of the GBM patients show a low survival rate of Accepted: 4 September 2021 Published: 7 September 2021 14 months or less [3,4]. The heterogenous nature of the GBM contributes to its therapy- resistance and poor prognosis; hence, identifying genetic regulations of the hallmarks of Publisher’s Note: MDPI stays neutral this malignant disease may help device effective treatments [5,6]. with regard to jurisdictional claims in Almost all GBM patients are presented with the high-grade of the disease, which published maps and institutional affil- is characterized by rapid recurrence after surgery and resistance to radiotherapy and iations. chemotherapy [7,8]. Resistance of GBM to therapies is a major challenge for treatment of the patients and it can result from several mechanisms, which collectively constitute the hallmarks of this malignancy [7,8]. The resistance mechanisms can either accelerate initial tumor growth or potentiate regrowth of the more resistant tumor after the treatment [7,8]. One of the major hallmarks of GBM is the presence of GBM stem cells (GSCs), which are Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. genetically heterogeneous cells with more distinct properties than primary tumor cells, and This article is an open access article they play critical roles in disease recurrence and therapy resistance [9,10]. Sustained prolif- distributed under the terms and erative signals is another major cause of resistance, which results from aberrant expression conditions of the Creative Commons of the growth and trophic factors [11]. Escaping the programed cell death or apoptosis and Attribution (CC BY) license (https:// activating the pro-survival pathways are other major mechanisms of therapy resistance creativecommons.org/licenses/by/ in GBM [12]. Autophagy or recycling of cellular building blocks is also an important 4.0/). survival mechanism that is activated in GBM and it is one of the major causes of therapy Cells 2021, 10, 2342. https://doi.org/10.3390/cells10092342 https://www.mdpi.com/journal/cells Cells 2021, 10, 2342 2 of 18 resistance [13]. Aberrant inflammation and immune response are correlated with rapid Cells 2021, 10, x FOR PEER REVIEW progression and resistance to therapy [14,15]. Angiogenesis or aberrant2 of 18 new blood vessel formation is also correlated with rapid progression and therapy resistance in GBM [15,16]. Finally, interaction between tumor cells and the surrounding microenvironment potentiates thetherapy migratory resistance and in GBM invasive [12]. Autophagy properties or recycling of the tumorof cellular cells, building contributing blocks is also to rapid relapse of GBMan important and poor survival outcome mechanism [17 that–19 is]. activated in GBM and it is one of the major causes of therapyGenetic resistance knockout, [13]. Aberrant knock inflammation in, and overexpression and immune response have been are correlated widely used to screen for with rapid progression and resistance to therapy [14,15]. Angiogenesis or aberrant new theblood molecular vessel formation pathways is also correlated that govern with rapid the hallmarksprogression and of GBMtherapy and resistance to study in the function of variousGBM [15,16 genes]. Finally, in pathogenesis interaction and between progression tumor ofcells this malignantand the surrounding disease [20 –23]. In the past, scientistsmicroenvironment used ‘gene potentiates targeting’ the migratory for changing and invasive the genome properties in of the the specifictumor cells, places with addition orcontributing deletion to ofrapid either relapse entire of GBM genes and poor or singleoutcome bases. [17–19]. Although gene targeting has highly Genetic knockout, knock in, and overexpression have been widely used to screen for beenthe molecular useful pathways in understanding that govern the the hallmarks function of GBM of specific and to study genes, the thisfunction technology of takes long timevarious to genes make in pathogenesis a mutant geneand progression and it is of expensive. this malignant Subsequently, disease [20–23]. In several the ‘gene editing’ technologiespast, scientists used such ‘gene as Transcriptiontargeting’ for changing Activator-Like the genome Effectorin the specific Nucleases places with (TALENs) and Zinc- Fingeraddition Nucleasesor deletion of (ZFNs) either entire have genes been or discoveredsingle bases. Although to improve gene thetargeting gene has targeting to a great extent.highly been Still useful scientists in understanding were looking the function for of a specific cheaper genes, and this quicker technology gene takes editing technology long time to make a mutant gene and it is expensive. Subsequently, several ‘gene editing’ thantechnologies TALENs such andas Transcription ZNFs. The Activator Clustered-Like Effector Regularly Nucleases Interspaced (TALENs) Short and Zinc Palindromic- Repeat (CRISPR)-CRISPRFinger Nucleases (ZFNs) associated have been discovered (Cas) nuclease to improve 9 (CRISPR-Cas9)the gene targeting to system a great is the latest gene editingextent. Still technology scientists were [20 looking], which for standsa cheaper out and as quicker the fastest, gene editing cheapest, technology highly than versatile, and most reliableTALENs geneand ZNFs editing. The tool Clustered for using Regularly widely Interspaced to discover Short genetic Palindromic alterations, Repeat oncogenic targets, (CRISPR)-CRISPR associated (Cas) nuclease 9 (CRISPR-Cas9) system is the latest gene andediting epigenetic technology regulation.[20], which stands Currently, out as the CRISPR-Cas9 fastest, cheapest, system highly isversatile, the number and one choice for editingmost reliable genes gene or editing genome tool for in using various widely cancers to disc includingover genetic GBMalterations, [21– oncogenic24]. targets,In and this epigenetic article, weregulation. will first Currently, briefly CRISPR discuss-Cas9 the system basic principleis the number of CRISPR-Cas9one system (Figurechoice for1 editing) and itsgenes application or genome in to various GBM cancers in revealing including the GBM function [21–24]. of genes that contribute to maintainingIn this article, we tumor will first cell briefly growth discuss and the stemness, basic principle escaping of CRISPR the-Cas9 programmed system cell death or (Figure 1) and its application to GBM in revealing the function of genes that contribute to apoptosis,maintaining tumor inducing cell growth autophagy, and stemness, promoting escaping angiogenesis, the programmed deregulating cell death or immune response andapoptosis, inflammation, inducing autophagy, and potentiating promoting angiogenesi cell invasions, deregulating and metastasis immune (Figure response2 ). Finally, we will discussand inflammation, the pitfalls and andpotentiating current cell limitations invasion and of metastasis CRISPR-Cas9 (Figure gene2). Finally, editing we systems in GBM researchwill discuss and the futurepitfalls and prospective. current limitations of CRISPR-Cas9 gene editing systems in GBM research and future prospective. Figure 1. 1.PrinciplePrinciple