Effect of lomeguatrib-temozolomide combination on MGMT promoter methylation and expression in primary glioblastoma tumor cells

MGMT inhibition regulates radioresponse in GBM, GSC, and melanoma

Radiotherapy is the standard treatment for glioblastoma (GBM), but the overall survival rate for radiotherapy treated GBM patients is poor. The use of adjuvant and concomitant temozolomide (TMZ) improves the outcome; however, the effectiveness of this treatment varies according to MGMT levels. Herein, we evaluated whether MGMT expression affected the radioresponse of human GBM, GBM stem-like cells (GSCs), and melanoma. Our results indicated a correlation between MGMT promoter methylation status and MGMT expression. MGMT-producing cell lines ACPK1, GBMJ1, A375, and MM415 displayed enhanced radiosensitivity when MGMT was silenced using siRNA or when inhibited by lomeguatrib, whereas the OSU61, NSC11, WM852, and WM266-4 cell lines, which do not normally produce MGMT, displayed reduced radiosensitivity when MGMT was overexpressed. Mechanistically lomeguatrib prolonged radiation-induced γH2AX retention in MGMT-producing cells without specific cell cycle changes, suggesting that lomeguatrib-induced radiosensitization in these cells is due to radiation-induced DNA double-stranded break (DSB) repair inhibition. The DNA-DSB repair inhibition resulted in cell death via mitotic catastrophe in MGMT-producing cells. Overall, our results demonstrate that MGMT expression regulates radioresponse in GBM, GSC, and melanoma, implying a role for MGMT as a target for radiosensitization.

Dual-targeted delivery of temozolomide by multi-responsive nanoplatform via tumor microenvironment modulation for overcoming drug resistance to treat glioblastoma

Glioblastoma (GBM) is the most aggressive primary brain tumor with low survival rate. Currently, temozolomide (TMZ) is the first-line drug for GBM treatment of which efficacy is unfortunately hindered by short circulation time and drug resistance associated to hypoxia and redox tumor microenvironment. Herein, a dual-targeted and multi-responsive nanoplatform is developed by loading TMZ in hollow manganese dioxide nanoparticles functionalized by polydopamine and targeting ligands RAP12 for photothermal and receptor-mediated dual-targeted delivery, respectively. After accumulated in GBM tumor site, the nanoplatform could respond to tumor microenvironment and simultaneously release manganese ion (Mn2+), oxygen (O2) and TMZ. The hypoxia alleviation via O2 production, the redox balance disruption via glutathione consumption and the reactive oxygen species generation, together would down-regulate the expression of O6-methylguanine-DNA methyltransferase under TMZ medication, which is considered as the key to drug resistance. These strategies could synergistically alleviate hypoxia microenvironment and overcome TMZ resistance, further enhancing the anti-tumor effect of chemotherapy/chemodynamic therapy against GBM. Additionally, the released Mn2+ could also be utilized as a magnetic resonance imaging contrast agent for monitoring treatment efficiency. Our study demonstrated that this nanoplatform provides an alternative approach to the challenges including low delivery efficiency and drug resistance of chemotherapeutics, which eventually appears to be a potential avenue in GBM treatment.

A hypoxia-dissociable siRNA nanoplatform for synergistically enhanced chemo-radiotherapy of glioblastoma

Glioblastoma (GBM), as the most aggressive adult brain tumor, seriously threatened people's lives with a low survival time. Standard postoperative treatment, chemotherapy combined with radiotherapy (RT), was the major therapeutic strategy for GBM. However, this therapeutic efficacy was hindered by chemoradiotherapy resistance of GBM. Herein, to sensitize temozolomide (TMZ)-based chemotherapy and RT, a hypoxia-radiosensitive nanoparticle for co-delivering TMZ and siMGMT (RDPP(Met)/TMZ/siMGMT) was synthesized in this study. Our nanoparticle could effectively release the encapsulated alkylating agent (TMZ) and small interfering O6-methylguanine-DNA-methyltransferase RNA (siMGMT) in the hypoxic GBM. DNA-damage repair was effectively inhibited by down-regulating MGMT expression and activating cell apoptosis, which obviously enhanced the sensitivity of TMZ as well as RT. In vitro and in vivo experiments showed that RDPP(Met)/TMZ/siMGMT could efficiently penetrate the blood-brain barrier (BBB), accurately target GBM cells and effectively inhibit GBM proliferation. Compared with traditional TMZ combined with RT, RDPP(Met)/TMZ/siMGMT remarkably improved the survival time of orthotopic GBM-bearing mice, which demonstrated that our nanoplatform was an efficient combinatorial GBM therapy.

Lomeguatrib Increases the Radiosensitivity of MGMT Unmethylated Human Glioblastoma Multiforme Cell Lines

Background: Treatment resistance of glioblastoma multiforme to chemo- and radiotherapy remains a challenge yet to overcome. In particular, the O⁶-methylguanine-DNA-methyltransferase (MGMT) promoter unmethylated patients have only little benefit from chemotherapy treatment using temozolomide since MGMT counteracts its therapeutic efficacy. Therefore, new treatment options in radiotherapy need to be developed to inhibit MGMT and increase radiotherapy response. Methods: Lomeguatrib, a highly specific MGMT inhibitor, was used to inactivate MGMT protein in vitro. Radiosensitivity of established human glioblastoma multiforme cell lines in combination with lomeguatrib was investigated using the clonogenic survival assay. Inhibition of MGMT was analyzed using Western Blot. Cell cycle distribution and apoptosis were investigated to determine the effects of lomeguatrib alone as well as in combination with ionizing radiation. Results: Lomeguatrib significantly decreased MGMT protein and reduced radiation-induced G2/M arrest. A radiosensitizing effect of lomeguatrib was observed when administered at 1 µM and increased radioresistance at 20 µM. Conclusion: Low concentrations of lomeguatrib elicit radiosensitization, while high concentrations mediate a radioprotective effect.

DNA Repair Mechanisms and Therapeutic Targets in Glioma

PURPOSE OF REVIEW

This review discusses current and investigative strategies for targeting DNA repair in the management of glioma.

RECENT FINDINGS

Recent strategies in glioma treatment rely on the production of overwhelming DNA damage and inhibition of repair mechanisms, resulting in lethal cytotoxicity. Many strategies are effective in preclinical glioma models while clinical feasibility remains under investigation. The presence of glioma biomarkers, including IDH mutation and/or MGMT promoter methylation, may confer particular susceptibility to DNA damage and inhibition of repair. These biomarkers have been adopted as eligibility criteria in the design of multiple ongoing clinical trials. Targeting DNA repair mechanisms with novel agents or therapeutic combinations is a promising approach to the treatment of glioma. Further investigations are underway to optimize this approach in the clinical setting.

Personalized therapy and stem cell transplantation for pro-inflammatory modulation of cancer stem cells microenvironment in glioblastoma: Review

Glioblastoma multiforme (GBM) is one of the most aggressive types of brain tumor in humans. The prognosis for patients with GBM is unfavorable and treatment is largely ineffective, where modern treatment regimens typically increase survival by 15 months. GBM relapse and progression are associated with cancer stem cells (CSCs). The present review provides a critical analysis of the primary reasons underlying the lack of effectiveness of modern CSC management methods. An emphasis is placed on the role of the blood-brain barrier in the development of treatment resistance. The existing methods for increasing the efficiency of antitumor genotoxic therapy are also described, and a strategy for personalized regulation of CSC based on post-genome technologies is suggested. The hypothesis that GBM cells employ a special mechanism for DNA repair based on their interactions with normal stem cells, is presented and the function of the tumor microenvironment in fulfilling the antitumor potential of normal stem cells is explained. Additionally, the mechanisms by which cancer stem cells regulate glioblastoma progression and recurrence are described based on novel biomedical technologies.

A novel enhancer regulates MGMT expression and promotes temozolomide resistance in glioblastoma

Temozolomide (TMZ) was used for the treatment of glioblastoma (GBM) for over a decade, but its treatment benefits are limited by acquired resistance, a process that remains incompletely understood. Here we report that an enhancer, located between the promoters of marker of proliferation Ki67 (MKI67) and O6-methylguanine-DNA-methyltransferase (MGMT) genes, is activated in TMZ-resistant patient-derived xenograft (PDX) lines and recurrent tumor samples. Activation of the enhancer correlates with increased MGMT expression, a major known mechanism for TMZ resistance. We show that forced activation of the enhancer in cell lines with low MGMT expression results in elevated MGMT expression. Deletion of this enhancer in cell lines with high MGMT expression leads to a dramatic reduction of MGMT and a lesser extent of Ki67 expression, increased TMZ sensitivity, and impaired proliferation. Together, these studies uncover a mechanism that regulates MGMT expression, confers TMZ resistance, and potentially regulates tumor proliferation.

Synthesis of novel imidazopyridines and their biological evaluation as potent anticancer agents: A promising candidate for glioblastoma

Novel imidazopyridine derivatives were synthesized according to a very simple protocol and then subjected to cytotoxicity testing against LN-405 cells. Two of the compounds exhibited antiproliferative effects on LN-405 cells at 10 and 75 µM and were selected as lead compounds for further study. Safety experiment for lead compounds on WS1 was carried out and IC₅₀ values were calculated as 480 and 844 µM. LN-405 cell line were incubated with the lead compounds and then tested for DNA damage by comet assay and effects on cell cycle using flow cytometry. The results of these two tests showed that both lead compounds affected the G0/G1 phase and did not allow the cells to reach the synthesis phase. The log BB (blood-brain barrier) and Caco-2 permeability of the synthesized molecules were calculated and it was shown that imidazopyridine derivatives taken orally are likely to pass through gastrointestinal membrane and the blood-brain barrier.

Investigating a signature of temozolomide resistance in GBM cell lines using metabolomics

Glioblastoma multiforme (GBM) is the most common form of malignant glioma. Current therapeutic approach to treat this malignancy involves a combination of surgery, radiotherapy and chemotherapy with temozolomide. Numerous mechanisms contributing to inherent and acquired resistance to this chemotherapeutic agent have been identified and can lead to treatment failure. This study undertook a metabolomics-based approach to characterize the metabolic profiles observed in temozolomide-sensitive and temozolomide-resistant GBM cell lines as well as in a small sub-set of primary GBM tumors. This approach was also utilized to explore the metabolic changes modulated upon cell treatment with temozolomide and lomeguatrib, an MGMT inhibitor with temozolomide-sensitizing potential. Metabolites previously explored for their potential role in chemoresistance including glucose, citrate and isocitrate demonstrated elevated levels in temozolomide-resistant GBM cells. In addition, a signature of metabolites comprising alanine, choline, creatine and phosphorylcholine was identified as up-regulated in sensitive GBM cell line across different treatments. These results present the metabolic profiles associated with temozolomide response in selected GBM models and propose interesting leads that could be leveraged for the development of therapeutic or diagnostic tools to impact temozolomide response in GBMs.

Design and synthesis of a MAO-B-selectively activated prodrug based on MPTP: a mitochondria-targeting chemotherapeutic agent for treatment of human malignant gliomas

Malignant gliomas, including glioblastomas, are extremely difficult to treat. The median survival for glioblastoma patients with optimal therapeutic intervention is 15 months. We developed a novel MAO-B-selectively activated prodrug, N,N-bis(2-chloroethyl)-2-(1-methyl-1,2,3,6-tetrahydropyridin-4-yl)propanamide (MP-MUS), for the treatment of gliomas based on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The design of neutral MP-MUS involved the use of a seeker molecule capable of binding to mitochondrial MAO-B, which is up-regulated ≥fourfold in glioma cells. Once the binding occurs, MP-MUS is converted into a positively charged moiety, P(+) -MUS, which accumulates inside mitochondria at a theoretical maximal value of 1000:1 gradient. The LD50 of MP-MUS against glioma cells is 75 μM, which is two- to threefold more potent than temozolomide, a primary drug for gliomas. Importantly, MP-MUS was found to be selectively toxic toward glioma cells. In the concentration range of 150-180 μM MP-MUS killed 90-95 % of glioma cells, but stimulated the growth of normal human astrocytes. Moreover, maturation of MP-MUS is highly dependent on MAO-B, and inhibition of MAO-B activity with selegiline protected human glioma cells from apoptosis.

Progression of O⁶-methylguanine-DNA methyltransferase and temozolomide resistance in cancer research

Temozolomide (TMZ) is an alkylating agent that is widely used in chemotherapy for cancer. A key mechanism of resistance to TMZ is the overexpression of O(6)-methylguanine-DNA methyltransferase (MGMT). MGMT specifically repairs the DNA O(6)-methylation damage induced by TMZ and irreversibly inactivates TMZ. Regulation of MGMT expression and research regarding the mechanism of TMZ resistance will help rationalize the clinical use of TMZ. In this review, we provide an overview of recent advances in the field, with particular emphasis on MGMT structure, function, expression regulation, and the association between MGMT and resistance to TMZ.

Chemotherapeutic resistance in anaplastic astrocytoma cell lines treated with a temozolomide-lomeguatrib combination

The treatment of anaplastic astrocytoma (AA) is controversial. New chemotherapeutic approaches are needed for AA treatment. Temozolomide (TMZ) is one of the chemotherapeutic drugs for the treatment of AA. The cytotoxic effects of TMZ can be removed by the MGMT (O(6)-methylguanine-DNA methyltransferase) enzyme. Then, chemotherapeutic resistance to TMZ occurs. MGMT inhibition by MGMT inactivators (such as lomeguatrib) is an important anticancer therapeutic approach to circumvent TMZ resistance. We aim to investigate the effect of TMZ-lomeguatrib combination on MGMT expression and TMZ sensitivity of SW1783 and GOS-3 AA cell lines. The sensitivity of SW1783 and GOS-3 cell lines to TMZ and to the combination of TMZ and lomeguatrib was determined by a cytotoxicity assay. MGMT methylation was detected by MS-PCR. MGMT and p53 expression were investigated by real-time PCR after drug treatment, and the proportion of apoptotic cells was analyzed by flow cytometry. When the combination of TMZ-lomeguatrib (50 μM) was used in AA cell lines, IC50 values were reduced compared to only using TMZ. MGMT expression was decreased, p53 expression was increased, and the proportion of apoptotic cells was induced in both cell lines. The lomeguatrib-TMZ combination did not have any effect on the cell cycle and caused apoptosis by increasing p53 expression and decreasing MGMT expression. Our study is a pilot study investigating a new therapeutic approach for AA treatment, but further research is needed.