Temozolomide Resistance in Glioblastoma by NRF2: Protecting the Evil

Ultrasound-responsive nanoparticles for imaging and therapy of brain tumors

Central nervous system (CNS) cancers, particularly glioblastoma (GBM), are associated with high mortality and disability rates. Despite aggressive surgical resection, radiotherapy, and chemotherapy, patient survival remains poor. The blood-brain barrier (BBB) significantly impedes therapeutic efficacy, making BBB penetration a critical focus of research. Focused ultrasound (FUS) combined with microbubbles (MBs) can transiently open the BBB through mechanisms such as cavitation, modulation of tight junction protein expression, and enhanced vesicular transport in endothelial cells. This review highlights precision delivery and personalized treatment strategies under ultrasound visualization, including precise control of ultrasound parameters and modulation of the immune microenvironment. We discuss the applications of ultrasound-responsive nanoparticles in brain tumor therapy, including enhanced radiotherapy, gene delivery, immunotherapy, and sonodynamic therapy (SDT), with a particular emphasis on piezoelectric catalytic immunotherapy. Finally, we provide insights into the clinical translation potential of ultrasound-responsive nanoparticles for personalized and precision treatment of brain tumors.

miR-124-mediated temozolomide sensitivity and DNA repair modulation in Glioblastoma Multiforme

Glioblastoma Multiforme (GBM) is the most frequent and invasive primary malignant brain tumor. One approach to improve the effectiveness of GBM treatment is the combination of miRNA-targeted therapy with TMZ. This study aimed to assess the effect of miR-124 overexpression on TMZ resistance in GBM cell lines. Additionally, we examined how miR-124 overexpression affects the expression of genes involved in DNA repair processes. We conducted a bioinformatics prediction for target genes of miR‑124‑3p and then overexpressed miR-124 in U-87 and U-251 cell lines through lentiviral transduction. Sixty genes were identified as potential targets of miR-124-3p, which revealed overlap among 504 target mRNAs and upregulated genes across four GEO datasets. PRRX1, ETS, VIM, and PTBP1 genes were selected based on their contributions to DNA repair and related processes such as autophagy including Beclin-1 and Atg-5. The MTT assay results showed that only the U87 cell line overexpressing miR-124 exhibited significantly greater sensitivity to TMZ treatment. The qRT-PCR analysis revealed a significant reduction in mRNA levels of all DNA repair-related genes and two autophagy-related genes in both cell lines. The results might indicate that after TMZ-induced genomic damage, cells activate the DNA repair pathways, ultimately leading to the development of resistance. In the context of TMZ treatment, autophagy is considered a protective process for cancer cells, and definitive proof of its association with the anti-cancer activity of miR-124 requires further supplementary tests. So, modulating DNA repair pathways with miR-124 could enhance the chemosensitivity of Glioma cells to TMZ.

Role of Glutamate Excitotoxicity in Glioblastoma Growth and Its Implications in Treatment

Glioblastoma is a highly malignant and invasive type of primary brain tumor that originates from astrocytes. Glutamate, a neurotransmitter in the brain plays a crucial role in excitotoxic cell death. Excessive glutamate triggers a pathological process known as glutamate excitotoxicity, leading to neuronal damage. This excitotoxicity contributes to neuronal death and tumor necrosis in glioblastoma, resulting in seizures and symptoms such as difficulty in concentrating, low energy, depression, and insomnia. Glioblastoma cells, derived from astrocytes, fail to maintain glutamate-glutamine homeostasis, releasing excess glutamate into the extracellular space. This glutamate activates ionotropic N-methyl-D-aspartate (NMDA) receptors and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors on nearby neurons, causing hyperexcitability and triggering apoptosis through caspase activation. Additionally, glioblastoma cells possess calcium-permeable AMPA receptors, which are activated by glutamate in an autocrine manner. This activation increases intracellular calcium levels, triggering various signaling pathways. Alkylating agent temozolomide has been used to counteract glutamate excitotoxicity, but its efficacy in directly combating excitotoxicity is limited due to the development of resistance in glioblastoma cells. There is an unmet need for alternative biochemical agents that can have the greatest impact on reducing glutamate excitotoxicity in glioblastoma. In this review, we discuss the mechanism and various signaling pathways involved in glutamate excitotoxicity in glioblastoma cells. We also examine the roles of various receptor and transporter proteins, in glutamate excitotoxicity and highlight biochemical agents that can mitigate glutamate excitotoxicity in glioblastoma and serve as potential therapeutic agents.

COX-2 Inhibition in Glioblastoma Cells Counteracts Resistance to Temozolomide by Inducing Oxidative Stress

Oxidative stress critically influences the pathophysiology of glioblastoma (GBM), a deadly and aggressive brain tumor. Reactive oxygen species (ROS) regulate cancer cell homeostasis, influencing the treatment response. The transcription factor Nuclear Factor Erythroid 2-Related Factor 2 (Nrf2) activates antioxidant defenses, protecting GBM cells from therapy-induced oxidative stress and contributing to Temozolomide (TMZ) resistance. Cyclooxygenase-2 (COX-2) plays a key role in GBM chemoresistance by modulating the tumor microenvironment and supporting a pro-survival phenotype. The impact of COX-2 inhibition by celecoxib (CXB), a selective COX-2 inhibitor, combined with TMZ on oxidative stress modulation linked to resistance was investigated in GBM primary cultures and cell lines. The drug combination CXB+TMZ was tested on TMZ-sensitive and -resistant cells, and ROS levels and Nrf2 activation were evaluated via a DCFH-DA probe and Western blotting, respectively. The oxidative stress marker malondialdehyde and antioxidant enzymes were assayed using standard methods. COX-2 inhibition combined with TMZ significantly increased ROS, while TMZ alone induced a compensatory antioxidant response, sustaining resistance. Drug combination reduced this response, restoring oxidative stress even in TMZ-resistant cells. Prostaglandin E2 reversed these effects, confirming the role of the COX-2/PGE2 axis in redox balance. Drug combination increased ROS, disrupted redox homeostasis and overcame TMZ resistance, supporting COX-2 inhibition as a promising GBM therapy strategy.

Inhibition of Thioredoxin-Reductase by Auranofin as a Pro-Oxidant Anticancer Strategy for Glioblastoma: In Vitro and In Vivo Studies

Reactive oxygen species (ROS) play a key role in cancer progression and antitumor therapy. Glioblastoma is a highly heterogeneous tumor with different cell populations exhibiting various redox statuses. Elevated ROS levels in cancer cells promote tumor growth and simultaneously make them more sensitive to anticancer drugs, but further elevation leads to cell death and apoptosis. Meanwhile, various subsets of tumor cells, such a glioblastoma stem cells (GSC) or the cells in tumor microenvironment (TME), demonstrate adaptive mechanisms to excessive ROS production by developing effective antioxidant systems such as glutathione- and thioredoxin-dependent. GSCs demonstrate higher chemoresistance and lower ROS levels than other glioma cells, while TME cells create a pro-oxidative environment and have immunosuppressive effects. Both subpopulations have become an attractive target for developing therapies. Increased expression of thioredoxin reductase (TrxR) is often associated with tumor progression and poor patient survival. Various TrxR inhibitors have been investigated as potential anticancer therapies, including nitrosoureas, flavonoids and metallic complexes. Gold derivatives are irreversible inhibitors of TrxR. Among them, auranofin (AF), a selective TrxR inhibitor, has proven its effectiveness as a drug for the treatment of rheumatoid arthritis and its efficacy as an anticancer agent has been demonstrated in preclinical studies in vitro and in vivo. However, further clinical application of AF could be challenging due to the low solubility and insufficient delivery to glioblastoma. Different delivery strategies for hydrophobic drugs could be used to increase the concentration of AF in the brain. Combining different therapeutic approaches that affect the redox status of various glioma cell populations could become a new strategy for treating brain tumor diseases.

Nrf2/Keap1/ARE regulation by plant secondary metabolites: a new horizon in brain tumor management

Brain cancer is regarded as one of the most life-threatening forms of cancer worldwide. Oxidative stress acts to derange normal brain homeostasis, thus is involved in carcinogenesis in brain. The Nrf2/Keap1/ARE pathway is an important signaling cascade responsible for the maintenance of redox homeostasis, and regulation of anti-inflammatory and anticancer activities by multiple downstream pathways. Interestingly, Nrf2 plays a somewhat, contradictory role in cancers, including brain cancer. Nrf2 has traditionally been regarded as a tumor suppressor since its cytoprotective functions are considered to be the principle cellular defense mechanism against exogenous and endogenous insults, such as xenobiotics and oxidative stress. However, hyperactivation of the Nrf2 pathway supports the survival of normal as well as malignant cells, protecting them against oxidative stress, and therapeutic agents. Plants possess a pool of secondary metabolites with potential chemotherapeutic/chemopreventive actions. Modulation of Nrf2/ARE and downstream activities in a Keap1-dependant manner, with the aid of plant-derived secondary metabolites exhibits promise in the management of brain tumors. Current article highlights the effects of Nrf2/Keap1/ARE cascade on brain tumors, and the potential role of secondary metabolites regarding the management of the same.

The role of chaperone-mediated autophagy in drug resistance

In the search for alternatives to overcome the challenge imposed by drug resistance development in cancer treatment, the modulation of autophagy has emerged as a promising alternative that has achieved good results in clinical trials. Nevertheless, most of these studies have overlooked a novel and selective type of autophagy: chaperone-mediated autophagy (CMA). Following its discovery, research into CMA's contribution to tumor progression has accelerated rapidly. Therefore, we now understand that stress conditions are the primary signal responsible for modulating CMA in cancer cells. In turn, the degradation of proteins by CMA can offer important advantages for tumorigenesis, since tumor suppressor proteins are CMA targets. Such mutual interaction between the tumor microenvironment and CMA also plays a crucial part in establishing therapy resistance, making this discussion the focus of the present review. Thus, we highlight how suppression of LAMP2A can enhance the sensitivity of cancer cells to several drugs, just as downregulation of CMA activity can lead to resistance in certain cases. Given this panorama, it is important to identify selective modulators of CMA to enhance the therapeutic response.

NRF2 mutation enhances the immune escape of hepatocellular carcinoma by reducing STING activation

The nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor usually hyperactivated in hepatocellular carcinoma (HCC). In addition, about 14 % of HCC patients carry mutation in NRF2 or Kelch-like ECH-associated protein 1 (Keap1), a NRF2 inhibitor, both of which lead to constitutive activation of NRF2. It has been widely reported that NRF2 plays important roles in the proliferation, differentiation and metastasis of tumor cells. But as an important gene involved in antioxidation and anti-inflammation, little studies have focused on its role in tumor immune escape. Here we found that NRF2 gain-of-function mutation leads to reduced expression of STING and decreased infiltration of peripheral immune cells through which way it helps the tumor cells to evade from immune surveillance. This phenomenon can be reversed by STING overexpression. Our study also revealed that NRF2 mutation greatly reduced the effect of STING activating based immunotherapy. It is important to simultaneously inhibit the activity of NRF2 when using STING agonist for the treatment of HCC patients carrying NRF2 mutation.

Glioblastoma Therapy: Past, Present and Future

Glioblastoma (GB) stands out as the most prevalent and lethal form of brain cancer. Although great efforts have been made by clinicians and researchers, no significant improvement in survival has been achieved since the Stupp protocol became the standard of care (SOC) in 2005. Despite multimodality treatments, recurrence is almost universal with survival rates under 2 years after diagnosis. Here, we discuss the recent progress in our understanding of GB pathophysiology, in particular, the importance of glioma stem cells (GSCs), the tumor microenvironment conditions, and epigenetic mechanisms involved in GB growth, aggressiveness and recurrence. The discussion on therapeutic strategies first covers the SOC treatment and targeted therapies that have been shown to interfere with different signaling pathways (pRB/CDK4/RB1/P16ink4, TP53/MDM2/P14arf, PI3k/Akt-PTEN, RAS/RAF/MEK, PARP) involved in GB tumorigenesis, pathophysiology, and treatment resistance acquisition. Below, we analyze several immunotherapeutic approaches (i.e., checkpoint inhibitors, vaccines, CAR-modified NK or T cells, oncolytic virotherapy) that have been used in an attempt to enhance the immune response against GB, and thereby avoid recidivism or increase survival of GB patients. Finally, we present treatment attempts made using nanotherapies (nanometric structures having active anti-GB agents such as antibodies, chemotherapeutic/anti-angiogenic drugs or sensitizers, radionuclides, and molecules that target GB cellular receptors or open the blood-brain barrier) and non-ionizing energies (laser interstitial thermal therapy, high/low intensity focused ultrasounds, photodynamic/sonodynamic therapies and electroporation). The aim of this review is to discuss the advances and limitations of the current therapies and to present novel approaches that are under development or following clinical trials.

Involvement of Cyclooxygenase-2 in Establishing an Immunosuppressive Microenvironment in Tumorspheres Derived from TMZ-Resistant Glioblastoma Cell Lines and Primary Cultures

Glioblastoma (GBM) is characterized by an immunosuppressive tumor microenvironment (TME) strictly associated with therapy resistance. Cyclooxygenase-2 (COX-2) fuels GBM proliferation, stemness, and chemoresistance. We previously reported that COX-2 upregulation induced by temozolomide (TMZ) supported chemoresistance. Also, COX-2 transfer by extracellular vesicles released by T98G promoted M2 polarization in macrophages, whereas COX-2 inhibition counteracted these effects. Here, we investigated the COX-2 role in the stemness potential and modulation of the GBM immunosuppressive microenvironment. The presence of macrophages U937 within tumorspheres derived from GBM cell lines and primary cultures exposed to celecoxib (COX-2 inhibitor) with or without TMZ was studied by confocal microscopy. M2 polarization was analyzed by TGFβ-1 and CD206 levels. Osteopontin (OPN), a crucial player within the TME by driving the macrophages' infiltration, and CD44 expression was assessed by Western blot. TMZ strongly enhanced tumorsphere size and induced the M2 polarization of infiltrating macrophages. In macrophage-infiltrated tumorspheres, TMZ upregulated OPN and CD44 expression. These TMZ effects were counteracted by the concurrent addition of CXB. Remarkably, exogenous prostaglandin-E2 restored OPN and CD44, highlighting the COX-2 pivotal role in the protumor macrophages' state promotion. COX-2 inhibition interfered with TMZ's ability to induce M2-polarization and counteracted the development of an immunosuppressive TME.

Novel Tetrazole Derivatives Targeting Tubulin Endowed with Antiproliferative Activity against Glioblastoma Cells

Increasing awareness of the structure of microtubules has made tubulin a relevant target for the research of novel chemotherapies. Furthermore, the particularly high sensitivity of glioblastoma multiforme (GBM) cells to microtubule disruption could open new doors in the search for new anti-GBM treatments. However, the difficulties in developing potent anti-tubulin drugs endowed with improved pharmacokinetic properties necessitates the expansion of medicinal chemistry campaigns. The application of an ensemble pharmacophore screening methodology helped to optimize this process, leading to the development of a new tetrazole-based tubulin inhibitor. Considering this scaffold, we have synthesized a new family of tetrazole derivatives that achieved remarkable antimitotic effects against a broad panel of cancer cells, especially against GBM cells, showing high selectivity in comparison with non-tumor cells. The compounds also exerted high aqueous solubility and were demonstrated to not be substrates of efflux pumps, thus overcoming the main limitations that are usually associated with tubulin binding agents. Tubulin polymerization assays, immunofluorescence experiments, and flow cytometry studies demonstrated that the compounds target tubulin and arrest cells at the G2/M phase followed by induction of apoptosis. The docking experiments agreed with the proposed interactions at the colchicine site and explained the structure-activity relationships.