1. Introduction
Glioblastoma (GBM), also known as Grade IV astrocytoma, is the most common and aggressive form of primary brain tumor in adults, accounting for approximately 15% of all brain tumors and 54% of all gliomas [
1,
2]. GBM presents a unique complexity in terms of its molecular heterogeneity, aggressive growth, and resistance to conventional therapies [
3,
4]. Its incidence rate in the United States and Europe is 3-4 per 100,000 adults per year, and its median survival rate remains dismally low, at about 15 months, with a five-year survival rate of less than 10%[
5,
6]. The male-to-female ratio is approximately 3:2, and the median age of diagnosis is around 64 years [
7,
8].
Histologically, GBM is characterized by cellular pleomorphism, nuclear atypia, high mitotic activity, microvascular proliferation, and necrosis, making its invasive nature often render complete surgical resection challenging, if not impossible [
9,
10]. The complexity of GBM stems from its genetic and epigenetic diversity, with multiple mutations and alterations in signaling pathways contributing to its aggressive behavior [
11,
12]. Common alterations include mutations in the genes encoding epidermal growth factor receptor (EGFR), TP53, and isocitrate dehydrogenase 1 (IDH1) [
13,
14]. Epigenetically, alterations in DNA methylation, histone modifications, and microRNAs are observed, leading to the classification of GBM into different subtypes, namely Classical, Mesenchymal, Neural, and Proneural, each with distinct genetic profiles and clinical outcomes [
15,
16].
Type of Tumor (WHO Grade) |
5-Year Relative Survival Rate |
Age |
20–44 |
45–54 |
55–64 |
Anaplastic astrocytoma (III) |
58% |
29% |
15% |
Glioblastoma (IV) |
22% |
9% |
6% |
Anaplastic oligodendroglioma (III) |
76% |
67% |
45% |
The standard treatment for GBM consists of maximal safe surgical resection followed by radiation therapy and chemotherapy, particularly with the alkylating agent temozolomide (TMZ) (
Figure 1) [
17,
18]. Despite these aggressive interventions, recurrence is nearly universal due to the tumor's resistance to conventional therapies [
19,
20]. The extent of resection correlates with survival, but the infiltrative nature often hinders complete removal [
21]. Postoperative radiation is standard, but it can lead to adverse effects like cognitive decline [
22]. TMZ is the most used chemotherapeutic agent, often in conjunction with radiation, but resistance is common [
23]. Despite multiple clinical trials, targeted therapies have largely failed to provide significant improvements, highlighting the need for innovative approaches [
24]. Some promise has been seen with immune checkpoint inhibitors, but results are inconsistent [
25,
26].
GBM's complexity, combined with its heterogeneity and resistance to current therapeutic strategies, creates an urgent need for novel and personalized therapeutic approaches [
27]. Understanding the intricate role of transcription factors in epigenetic regulation presents a promising frontier in the fight against this devastating disease [
28]. The need to transcend conventional methodologies and embrace a multidimensional and individualized strategy is evident, underscoring the gravity and challenge of battling one of the most insidious malignancies known to mankind [
29].
Transcription factors are proteins that control the rate of transcription of genetic information from DNA to mRNA, playing a crucial role in gene regulation. In cancer, including GBM, aberrant transcription factor activity can lead to uncontrolled cell proliferation, invasion, metastasis, and resistance to therapy [
30,
31]. Transcription factors like MYC and STAT3 are often found to be dysregulated in various cancers [
32,
33]. Overexpression of MYC has been associated with uncontrolled cell growth, while STAT3 dysregulation can drive inflammatory pathways that promote tumorigenesis [
34,
35]. Factors such as TWIST1 and SNAI2 regulate epithelial-to-mesenchymal transition (EMT), a crucial process in cancer invasion and metastasis [
36,
37]. Altered expression of these factors can lead to enhanced migratory and invasive capabilities of tumor cells [
38]. The aberrant activity of transcription factors like NF-kB has been linked to resistance to chemotherapy and radiation [
39]. These factors can activate survival pathways, making cancer cells less responsive to treatments [
40]. Transcription factors also affect the interaction between cancer cells and the surrounding microenvironment, impacting immune response, angiogenesis, and stromal interactions [
41]. For example, HIF-1α controls angiogenesis through the regulation of VEGF expression [
42].
Epigenetic changes, including DNA methylation, histone modifications, and non-coding RNA regulation, have been found to play vital roles in cancer development and progression [
43,
44]. Hypermethylation of tumor suppressor genes can lead to their silencing, promoting oncogenesis [
45]. Conversely, hypomethylation can lead to oncogene activation [
46]. Alterations in histone acetylation and methylation can change chromatin structure, affecting gene expression [
47]. Histone deacetylase (HDAC) inhibitors are being explored as potential cancer therapies [
48]. MicroRNAs (miRNAs) and long non-coding RNAs (lncRNAs) can act as oncogenes or tumor suppressors [
49]. Dysregulation of miRNAs has been implicated in GBM progression [
50].
With the complexity and heterogeneity of tumors, personalized immunotherapy has emerged as a promising approach [
51,
52]. Several reasons justify this focus. Personalized immunotherapy considers the unique genetic and epigenetic landscape of each patient's tumor, enabling more targeted and effective treatment [
53]. Identification of patient-specific neoantigens allows the development of vaccines or cellular therapies targeting these unique tumor markers, enhancing treatment specificity [
54]. By targeting the specific mechanisms of resistance in individual tumors, personalized immunotherapy may overcome the limitations of traditional therapies [
55]. Combining personalized immunotherapy with existing treatments like chemotherapy or radiation may provide synergistic effects, enhancing therapeutic efficacy [
56].
In conclusion, transcription factors and epigenetic regulation are at the nexus of many critical cancer pathways [
57]. Their study offers innovative therapeutic avenues, particularly in personalized immunotherapy [
58]. Understanding and harnessing these mechanisms may lead to unprecedented advancements in GBM treatment, providing more effective, targeted, and individualized interventions [
59]. The fusion of transcriptional and epigenetic insights with immunotherapeutic strategies offers a multifaceted approach to tackling GBM, signifying an era where personalized medicine not only enhances current therapeutic paradigms but also paves the way for groundbreaking innovations [
60].
The burgeoning complexity of glioblastoma (GBM) and the intricate interplay between its genetic and epigenetic landscape present both opportunities and challenges for therapeutic advancement [
61]. The overarching aim of this review is to provide an exhaustive and nuanced exploration of the critical role that transcription factors play in GBM's epigenetic regulation and the subsequent implications for personalized immunotherapy [
62]. The specific objectives are as follows: to scrutinize the function and significance of transcription factors, such as SNAI2, FOXA1, YAP1, TWIST1, ZEB1, and NF-kB, that have been implicated in the epigenetic regulation of GBM [
63,
64]; to delve into the multifaceted world of epigenetic regulation in GBM, encompassing DNA methylation, histone modifications, and non-coding RNA regulation, elucidating how these mechanisms interact with transcription factors and contribute to GBM's heterogeneity and complexity [
65,
66].
By presenting a comprehensive overview of the subject, this review seeks to foster interdisciplinary collaboration between oncologists, geneticists, immunologists, and other stakeholders involved in GBM research and treatment [
67]. In synthesizing existing knowledge, presenting recent advancements, and suggesting future research directions, this review aspires to contribute substantively to the scientific community's understanding of GBM [
68]. Through the lens of transcription factors and epigenetic regulation, it aims to illuminate new paths toward personalized and effective therapeutic strategies for one of the most challenging and devastating forms of brain cancer [
69].
FDA-Approved Therapy |
YearApproved |
Mechanism |
Application |
Dosage |
Common Toxicities |
Overall Survival |
Other Notes |
Lomustine (CCNU) |
1976 |
Nonspecific alkylating agent that causes crosslinking of DNA and RNA |
Oral |
80–110 mg/m2 every 6 weeks |
Hematologic toxicity (49.7%) |
11.5 months |
No benefit compared to RT alone |
Carmustine (BCNU) |
1977 |
Nonspecific alkylating agent that causes crosslinking of DNA and RNA in dividing cells; also binds to and modifies glutathione reductase |
IV |
150–200 mg/m2 every 6 weeks |
Pulmonary toxicity (<30%), ocular toxicity (>10%) and bone marrow suppression (>10%) |
11.75 months |
No benefit compared to RT alone |
Carmustine wafer implants (BCNU wafers) |
1996 & 2003 |
Nonspecific alkylating agent that causes crosslinking of DNA and RNA in dividing cells; also binds to and modifies glutathione reductase |
Directly applied during surgery |
8 wafers: 61.6 mg |
Wound healing complications (12%), intracranial infection (1–10%), and cerebral edema (1–10%) |
13.9 months |
High complication rate (42.7%) and expensive |
Temozolomide (TMZ) |
2005 |
Nonspecific alkylating agent that causes mismatch repair in DNA by methylation at the O6 position of guanine |
Oral |
75 mg/m2 per day with RT, 150–200 mg/m2 per day |
Hematologic toxicity (16%): thrombocytopenia (12%), leukopenia (7%), and neutropenia (7%) |
14.6–16.1 months |
Standard of Care |
Bevacizumab (BVZ) |
2009 |
Targeted therapeutic antibody that binds and inhibits VEGF protein in tumor cells |
IV |
10 mg/kg every 2 weeks |
Hypertension (5.5–11.4%), thromboembolic events (3.2–11.9%), gastrointestinal perforation (1.5–5.4%), cerebral bleeding (2–5.3%), wound healing complications (0.8–3.3%), and proteinuria (2.7–11.4%) |
9.3 months (recurrent) |
Used to treat symptomatic edema and radiation necrosis |
Optune device (TTFields) |
2011 & 2015 |
Low-intensity (1–3 V/cm), intermediate-frequency (200 kHz) alternating electric fields that disrupt mitosis in tumor cells |
Portal device, electrodes on scalp |
Greater than 18 h a day for >4 weeks |
Skin toxicity (43%) and seizures (7%) |
20.5–20.9 months |
Not SOC because of marginal survival benefits, expensive costs, and inconvenience for patients |
2. Transcription Factors and Epigenetic Regulation in GBM:
Transcription factors (TFs) are specialized proteins that recognize and bind to specific DNA sequences, thereby regulating the transcription of genetic information from DNA to RNA. They play an indispensable role in the orchestration of gene expression, controlling various cellular processes like growth, differentiation, and response to environmental stimuli.
In the context of GBM, TFs have a profound impact on epigenetic regulation, contributing to the disease's complexity and heterogeneity.
Control of Gene Expression: TFs act as master regulators of gene expression, controlling both activation and repression. They can interact with chromatin modifiers, such as histone acetyltransferases (HATs) and histone deacetylases (HDACs), to modulate chromatin structure, thereby affecting gene accessibility (Lee et al., 1993; Struhl, 1998).
Regulation of Epigenetic Landscape: Epigenetic modifications, including DNA methylation and histone modifications, are controlled by TFs. They act as a bridge between signaling pathways and chromatin, integrating extracellular signals into precise gene expression patterns (Spitz & Furlong, 2012).
Involvement in Oncogenic Pathways: In GBM, certain TFs are found to be dysregulated, contributing to oncogenic pathways. For example, overexpression of STAT3 is associated with poor prognosis and tumor progression (Brantley et al., 2008).
Target for Therapeutics: TFs offer potential therapeutic targets. Inhibition of TFs like c-MYC has shown promise in preclinical GBM models (Wang et al., 2011).
Impact on Cellular Processes: TFs like TWIST1 and SNAI2 are involved in epithelial-to-mesenchymal transition (EMT), a process that enhances tumor invasion and metastasis in GBM (Siegfried et al., 2014).
Transcription factors play a multifaceted role in the epigenetic regulation of GBM. Understanding their function and dysregulation can unlock novel diagnostic, prognostic, and therapeutic avenues. Their central role in linking genetic information with environmental signals makes them a pivotal component of GBM's intricate molecular landscape.
2.1. Examples of Transcription Factors Implicated in GBM
2.1.1. SNAI2
SNAI2, also known as Slug, is a member of the Snail family of zinc-finger transcription factors. It plays a vital role in embryogenesis, particularly in the epithelial-to-mesenchymal transition (EMT), a process critical for embryonic development and tissue repair. In cancer, including GBM, SNAI2 has been linked to various processes that contribute to tumor aggressiveness and progression.
Role of SNAI2 in GBM:
EMT Regulation: SNAI2 is known to induce EMT, leading to the loss of cell adhesion, increased cell motility, and invasiveness. In GBM, this can facilitate tumor cell invasion into the surrounding brain tissue (Hajra et al., 2002).
Therapeutic Resistance: Overexpression of SNAI2 has been associated with resistance to therapy in various cancer types, including GBM. It can promote survival pathways, making tumor cells less responsive to conventional treatments (Vega et al., 2004).
Interaction with HDACs: In some contexts, SNAI2 has been found to recruit histone deacetylases (HDACs) to the promoters of specific target genes. HDACs remove acetyl groups from histones, leading to chromatin condensation and repression of gene transcription. This SNAI2-HDAC complex may lead to the silencing of tumor suppressor genes, contributing to GBM's malignancy (Peinado et al., 2004).
SNAI2 and HDACs as Therapeutic Targets:
Targeting SNAI2: Inhibiting SNAI2 may reverse EMT, reduce invasiveness, and sensitize GBM cells to therapy. Small molecule inhibitors and RNA interference techniques targeting SNAI2 are under investigation.
HDAC Inhibition: HDAC inhibitors, such as Vorinostat, are being studied as potential treatments for various cancers, including GBM. By inhibiting HDACs, these drugs can reverse gene silencing mediated by the SNAI2-HDAC complex, potentially restoring the expression of tumor suppressor genes (Marks et al., 2001).
Combined Approach: A combined strategy targeting both SNAI2 and HDACs may offer a synergistic effect, attacking the tumor on multiple fronts and overcoming resistance mechanisms.
SNAI2, in coordination with HDACs, represents a pivotal molecular nexus in the pathogenesis of GBM, influencing processes like EMT, invasion, and therapy resistance. The insights into the SNAI2-HDAC interaction offer promising therapeutic avenues and underline the complexity of the epigenetic regulation in GBM. This relationship further emphasizes the need for integrated approaches in both understanding and targeting GBM at the molecular level.
2.1.2. FOXA1: Role in Cell Differentiation and Links to GBM
Function and Epigenetic Influence: FOXA1 serves as a pioneer factor in chromatin remodeling, allowing other transcription factors to bind DNA. It participates in histone modifications and methylation processes, leading to either activation or repression of gene expression.
Implication in GBM: FOXA1's dysregulation in GBM may lead to aberrant epigenetic landscapes that affect cell differentiation and proliferation. It has been associated with maintaining BTSCs' stem-like properties, impacting GBM's heterogeneity, and therapeutic resistance (Zhang et al., 2016).
Potential Therapeutic Approaches: Targeting FOXA1 can lead to the restoration of proper differentiation pathways, offering a new avenue for GBM treatment.
2.1.3. YAP1: Implications in GBM Progression and Tumor-Suppressive Signaling
Function and Epigenetic Role: YAP1 acts as a transcriptional co-activator and is a part of the Hippo pathway. It plays a role in regulating chromatin accessibility and is involved in various epigenetic processes, such as histone methylation and acetylation.
GBM Involvement: In GBM, YAP1's dysregulation can lead to the activation of oncogenes or suppression of tumor suppressor genes through epigenetic mechanisms. It may act both as an oncogene or a tumor suppressor, depending on its interaction with other signaling pathways (Orr et al., 2011).
Therapeutic Implications: Understanding YAP1's dual role in GBM may lead to targeted epigenetic therapies, either inhibiting or enhancing its activity, depending on the context.
2.1.4. TWIST1: Involvement in Epithelial-to-Mesenchymal Transition (EMT)
Function and Epigenetic Connection: TWIST1 is involved in the repression of E-cadherin and other genes by recruiting chromatin-modifying enzymes, including HDACs. It affects DNA methylation patterns and histone modifications that underlie EMT.
Role in GBM: In GBM, TWIST1-mediated EMT enhances tumor invasion and therapeutic resistance. Its overexpression may alter the epigenetic landscape, driving a more aggressive phenotype (Elias et al., 2005).
Potential Therapies: Targeting TWIST1 or its downstream epigenetic effectors could lead to the reversal of EMT in GBM, hampering invasion and potentially sensitizing tumors to conventional therapies.
2.1.5. ZEB1: Role in GBM Invasiveness, Link with DNA Methylation
Function and Epigenetic Aspects: ZEB1, like TWIST1, is involved in EMT by repressing E-cadherin. It also influences the methylation of DNA by interacting with DNA methyltransferases, leading to the silencing of specific genes.
Implication in GBM: ZEB1's impact on DNA methylation adds complexity to the epigenetic regulation in GBM. Its role in promoting invasion and contributing to a stem-like phenotype makes it a promising therapeutic target (Siebzehnrubl et al., 2013).
Therapeutic Strategies: Strategies to inhibit ZEB1 or modify its epigenetic effects may reverse malignant phenotypes, reduce invasiveness, and increase sensitivity to treatment.
2.1.6. NF-kB: Impact on Immune Evasion, Inflammation in GBM
Function and Epigenetic Influence: NF-kB controls genes involved in immune response and inflammation. Its activation may lead to changes in chromatin structure, DNA methylation patterns, and histone modifications, influencing the transcriptional output.
GBM Involvement: NF-kB contributes to the inflammatory microenvironment in GBM and impacts immune evasion. Its activation correlates with aggressive tumor behavior and may affect the epigenetic programming of immune cells within the tumor (Nagai et al., 2002).
Potential Targeting Approaches: Targeting NF-kB's epigenetic influence may modulate the immune response and inflammation in GBM, presenting new opportunities for immunotherapy.
These transcription factors contribute significantly to the epigenetic landscape of GBM. Their diverse roles in controlling gene expression, chromatin structure, and DNA methylation provide insights into GBM's complexity. Understanding their epigenetic mechanisms opens opportunities for innovative therapeutic strategies, including targeted epigenetic
2.2. Challenges in Targeting Transcription Factors
2.2.1. Structural Challenges
Lack of Defined Binding Pockets: Transcription factors have long been considered "undruggable" primarily due to the absence of well-defined small-molecule binding pockets. Conventional drug design strategies often target enzymes or receptors that have a clear, pocket-like binding domain. However, transcription factors frequently defy this structural categorization, necessitating alternative strategies for drug design (Bullock et al., 2011).
Conformational Flexibility: Transcription factors are not static entities; they often undergo conformational changes to interact with DNA or other proteins. This dynamic nature introduces considerable difficulty in developing inhibitors that are both specific and effective. The ever-changing structure limits the applicability of static models often used in computational drug design (Lambert et al., 2018).
Complex Protein-Protein Interactions: Targeting transcription factors often involves interrupting their interactions with other proteins. However, protein-protein interactions (PPIs) are generally less well-defined than enzyme-substrate or receptor-ligand interactions. Furthermore, these interactions are crucial for many cellular processes, which raises the risk of unintended consequences when trying to disrupt them (Wells & McClendon, 2007).
2.2.2. Functional Challenges
Pleiotropic Effects: Transcription factors are often implicated in multiple signaling pathways, making them particularly challenging to target without eliciting off-target effects. Due to their diverse roles in cellular functions, inhibiting a single transcription factor may lead to unpredictable and even deleterious outcomes (Wang et al., 2013).
Cell- and Context-specific Roles: Another layer of complexity arises from the fact that transcription factors can play different roles depending on the cellular or biological context. This makes it particularly challenging to develop a one-size-fits-all therapeutic strategy, thus necessitating context-specific approaches for different cancer types or even individual tumors (Spitz & Furlong, 2012).
Feedback Mechanisms: Many cellular processes have built-in feedback loops to maintain homeostasis. Inhibiting one transcription factor can, paradoxically, activate others or even the same factor via alternative pathways, effectively negating the therapeutic effects (Chen et al., 2016).
2.2.3. Contextual Challenges in GBM
Tumor Heterogeneity: Glioblastoma (GBM) is notoriously heterogeneous, both between patients (inter-tumor) and within a single tumor (intra-tumor). This complicates the task of identifying universally applicable drug targets among transcription factors, as their expression and function can vary significantly across different regions of the tumor (Patel et al., 2014).
Blood-Brain Barrier Penetration: Developing therapies for GBM is further complicated by the blood-brain barrier, a highly selective semipermeable membrane that prevents many potential therapeutics from reaching the tumor site (Pardridge, 2019).
Integration with Current Therapies: Adding to the complexities are the existing treatment modalities for GBM, which may interact unpredictably with new transcription factor-targeting therapies. Thus, there is an urgent need to find synergistic or complementary strategies that can maximize efficacy while minimizing toxicity (Stupp et al., 2005).
2.2.4. Research Gaps
In-depth Understanding of Mechanisms: The intricacies of the relationships between transcription factors and epigenetic regulators in GBM remain poorly understood. A more comprehensive mechanistic understanding would enable more effective and specific therapeutic interventions.
Development of Selective Inhibitors: The focus has been shifting towards developing highly selective inhibitors that can effectively modulate transcription factor activity without causing significant off-target effects. However, these strategies are still in their infancy and require extensive validation.
Clinical Validation: Despite the promise shown in pre-clinical models, few transcription factor-targeting agents have advanced to clinical trials specifically for GBM, underlining the urgency for translational research in this area (Lu et al., 2015).
In summary, targeting transcription factors in GBM is an endeavor fraught with challenges, both structural and functional, that are compounded by the unique characteristics of GBM itself. Overcoming these obstacles necessitates a multidisciplinary approach, involving computational biology, medicinal chemistry, and clinical oncology, among other fields. Only through concerted efforts can we hope to translate the increasing understanding of these transcription factors into clinically actionable strategies.
5. Conclusion
In grappling with Glioblastoma multiforme (GBM), one of the most enigmatic and lethal forms of brain cancer, therapeutic avenues have remained disappointingly narrow despite scientific strides in understanding its molecular mechanics. This comprehensive review underscores the intricate and multi-layered nature of GBM, while also illuminating promising routes for research and treatment. As such, the outlook for GBM therapy is not as grim as current clinical outcomes may indicate.
Our main findings encompass the pivotal role of transcription factors (TFs) like FOXA1, YAP1, TWIST1, ZEB1, and NF-kB, which are intrinsically tied to the course of GBM, including its progression, immune escape mechanisms, and invasive properties. Further, the epigenetic roles of SNAI2 and HDACs have been highlighted as compelling therapeutic targets. On the treatment front, the advent of targeted therapies and CRISPR/Cas9 technologies, as well as the use of epigenetic modifiers and HDAC inhibitors to influence transcription factors, are exciting albeit challenging directions. The burgeoning field of personalized immunotherapy, particularly the development of neoantigen-based vaccines, has also shown encouraging potential. This is augmented by current research focusing on linking genetic variations to personalized treatments and delving into the impact of TFs on neoantigen presentation.
However, the path ahead is fraught with challenges, including the molecular diversity and functional redundancy of transcription factors, ethical quandaries in genetic manipulation through techniques like CRISPR/Cas9, and the yawning gap between clinical trials and real-world implementation. Given that many ongoing trials are yet to reach conclusive endpoints, translating research breakthroughs into tangible clinical benefits remains a colossal task.
As for future research, there's a pressing need for a multi-modal therapeutic strategy that combines surgery, radiation, chemotherapy, immunotherapy, and targeted therapies for a synergistic impact. Global collaborations that bring together expertise from diverse fields could accelerate the validation and implementation of GBM interventions. Additionally, the move toward precision medicine mandates the development of predictive models that integrate genetic, epigenetic, and clinical data for individualized treatment plans. Finally, devising reliable markers for early detection, monitoring treatment response, and predicting recurrence is indispensable for more effective GBM management.
To sum up, while the challenges are considerable, the synthesis of advancements in molecular understanding, emerging technologies like AI and machine learning, and collaborative global efforts points to a transformative phase in the battle against GBM.