BMP4 and Temozolomide Synergize in the Majority of Patient-Derived Glioblastoma Cultures.

One of the main causes of poor prognoses in patient with glioblastoma (GBM) is drug resistance to current standard treatment, which includes chemoradiation and adjuvant temozolomide (TMZ). In addition, the concept of cancer stem cells provides new insights into therapy resistance and management also in GBM and glioblastoma stem cell-like cells (GSCs), which might contribute to therapy resistance. Bone morphogenetic protein-4 (BMP4) stimulates astroglial differentiation of GSCs and thereby reduces their self-renewal capacity. Exposure of GSCs to BMP4 may also sensitize these cells to TMZ. A recent phase I trial has shown that local delivery of BMP4 is safe, but a large variation in survival is seen in these treated patients and in features of their cultured tumors. We wanted to combine TMZ and BMP4 (TMZ + BMP4) therapy and assess the inter-tumoral variability in response to TMZ + BMP4 in patient-derived GBM cultures. A phase II trial could then benefit a larger group of patients than those treated with BMP4 only. We first show that simultaneous treatment with TMZ + BMP4 is more effective than sequential treatment. Second, when applying our optimized treatment protocol, 70% of a total of 20 GBM cultures displayed TMZ + BMP4 synergy. This combination induces cellular apoptosis and does not inhibit cell proliferation. Comparative bulk RNA-sequencing indicates that treatment with TMZ + BMP4 eventually results in decreased MAPK signaling, in line with previous evidence that increased MAPK signaling is associated with resistance to TMZ. Based on these results, we advocate further clinical trial research to test patient benefit and validate pathophysiological hypothesis.

AB071. Predictive value of plasma microRNA-10b and microRNA-21 on chemotherapy toxicity, recurrence, and overall survival in high-grade glioma patients treated with temozolomide.

BACKGROUND: The low level of median survival rate after complete therapy (i.e., surgery and concomitant chemotherapy and radiotherapy) in high-grade glioma (HGG) patients reflects the needs for a better understanding about HGG pathogenesis, including the role of epigenetic in glioma. MicroRNA (miRNA), a small chain non-coding RNA, has been increasingly utilized in the management of other oncology cases and might possess an immense potential in HGG. The expression of miRNA-10b and miRNA-21 (i.e., two miRNAs that are frequently studied due to its involvement in glioma) are higher in HGG patients and their role in regulatory mechanism of glioma has been established. However, the influence of those miRNAs in toxicity, recurrence, and overall survival of HGG patients is still unclear. We aim to assess the predictive value of plasma miRNA-10b and miRNA-21 in the chemotherapy toxicity, recurrence, and overall survival of HGG patients. METHODS: This is an observational analytic study using hospital-based mixed cohort approach. The study is conducted in RSUP Dr. Sardjito, Yogyakarta, from January 2021 to December 2024. We prospectively assess the plasma miRNA level from HGG patients who met the inclusive and exclusive criteria. The consecutive sampling is used until the sample size is met. Statistical analysis will be conducted for temozolomide toxicity using Spearman's rank correlation, for recurrence using logistical regression, and for overall survival test. RESULTS: In this ongoing study, we plan to collect samples from 155 HGG patients. As of April 2024, we managed to collect 96 samples (median age of 49 years and 55% of male patients). Most of the patients were diagnosed with World Health Organization (WHO) grade IV tumors (69.3%), with the most common diagnosis was glioblastoma (62%). Most of the patients had unmethylated O6-methylguanine-DNA methyltransferase (MGMT) and wild-type isocitrate dehydrogenase (IDH) status (62% and 57%, respectively). There was no difference in miRNA-21 expression based on MGMT status (methylated or unmethylated), nor IDH status (wild type or mutant), with P=0.39 and P=0.25, respectively. Moreover, we found no significant difference in miRNA-10b expression in both MGMT status and both IDH status (P=0.19 and P=0.09). As for the data regarding toxicity, recurrence, and overall survival was still on the process of data collection. CONCLUSIONS: MiRNA is a promising epigenetic modulator that might be utilized in HGG management. A better understanding on the role of miRNA in HGG patients might be able to improve clinical outcome.

AB002. DNA methylation-regulated genes contribute to temozolomide (TMZ) resistance by scaffolding paraspeckle proteins.

BACKGROUND: Temozolomide (TMZ) resistance in glioblastoma (GBM) remains a challenge in clinical treatment and the mechanism is largely unknown. Emerging evidence shows that epigenetic modifications including DNA methylation and non-coding RNA were involved in diverse biological processes, including therapeutic resistance. However, the underlying mechanisms by which DNA methylation-mediated non-coding RNA regulates TMZ resistance remain poorly characterized. METHODS: RNA microarray and DNA methylation chips of TMZ-resistant and parental GBM cells were performed for the gain of unreported long non-coding RNA HSD52. Quantitative reverse transcription polymerase chain reaction (PCR) and fluorescence in situ hybridization assays were used to detect HSD52 levels in GBM cells and tissues. The investigation into HSD52's impact on TMZ resistance was conducted utilizing both in vitro assays and intracranial xenograft mouse models. The mechanism of HSD52 expression and its relationships with paraspeckle proteins, non-POU domain-containing octamer-binding protein (NONO) and splicing factor proline/glutamine rich (SFPQ), as well as alpha-thalassemia mental retardation X-linked (ATRX) mRNA were determined by pyrosequencing assay, chromatin immunoprecipitation, chromatin isolation by RNA purification, RNA immunoprecipitation, RNA pulldown, immunofluorescence, and western blot assays. RESULTS: HSD52 was highly expressed in high-grade glioma and TMZ-resistant GBM cells. Phosphorylated p38 mitogen-activated protein kinase (p38 MAPK)/ubiquitin specific peptidase 7 (USP7) axis mediates H3 ubiquitination, impairs the interaction between H3K23ub and DNA methyltransferase 1 (DNMT1) and the recruitment of DNMT1 at the HSD52 promoter to attenuate DNA methylation, which makes the transcription factor 12 (TCF12) more accessible to the promoter region to regulate HSD52 expression. Further analysis showed that HSD52 can serve as a scaffold to promote the interaction between NONO and SFPQ, and then increase the paraspeckle assembly and activate the paraspeckle/ataxia telangiectasia mutated (ATM) kinase pathway in GBM cells. In addition, HSD52 forms an RNA-RNA duplex with ATRX mRNA, and facilitates the association of heteromer of SFPQ and NONO with RNA duplex, thus leading to the increase of ATRX mRNA stability and level. In clinical patients, HSD52 is required for TMZ resistance and GBM recurrence. CONCLUSIONS: Our results reveal that HSD52 in GBM could serve as a therapeutic target to overcome TMZ resistance, enhancing the clinical benefits of TMZ chemotherapy.

Preparation of transferrin-targeted temozolomide nano-micelles and their anti-glioma effect.

Objectives: This study aims to develop brain-targeted temozolomide (TMZ) nanograins using the biodegradable polymer material PEG-PLA as a carrier. The model drug TMZ was encapsulated within the polymer using targeted nanotechnology. Key characteristics such as appearance, particle size, size distribution, drug loading capacity, in vitro release rate, stability, and anti-tumor effects were systematically evaluated through in vitro experiments. Methods: Transmission electron microscopy (TEM) and Malvern size analyzer were employed to observe the morphological and particle size features of the TMZ nanospheres at various time points to assess stability. The effects of TMZ nanograins on glioma cell viability and apoptosis were evaluated using MTT assays and flow cytometry. Results: The targeted TMZ nano-micelles were successfully synthesized. After loading and targeted modifications, the particle size increased from 50.7 to 190 nm, indicating successful encapsulation of TMZ. The average particle size of the nano-micelles remained stable around 145 ± 10 nm at 1 day, 15 days, and 30 days post-preparation. The release rate of the nano-micelles was monitored at 2 h, 12 h, 24 h, and 48 h post-dialysis, ultimately reaching 95.8%. Compared to TMZ alone, the TMZ-loaded PEG-PLA nano-micelles exhibited enhanced cytotoxicity and apoptosis in glioma cells. This was accompanied by increased mitochondrial membrane potential and reactive oxygen species (ROS) levels following treatment with the TMZ nano-micelles. Conclusions: TMZ-loaded nano-micelles demonstrated a gradual release profile and significantly enhanced inhibitory effects on human glioma U251 cells compared to TMZ alone. The findings suggest that TMZ-loaded PEG-PLA nano-micelles may offer a more effective therapeutic approach for glioma treatment.

AB045. E2F6 promotes temozolomide resistance in glioblastoma by enrichment in CARD6 and POSTN promoter region.

BACKGROUND: Glioblastoma (GBM) is the most aggressive primary malignant brain tumor. Temozolomide (TMZ) is the most used first-line chemotherapeutic agent for GBM after surgery, but acquired resistance to TMZ frequently leads to treatment failure and is a major challenge in the clinical treatment of GBM. Increasing evidence suggests that E2F transcription factor 6 (E2F6) is associated with a variety of tumor malignant biological behaviors and drug resistance, but its biological function and underlying molecular mechanisms in GBM are unknown. METHODS: The study investigated the levels of E2F6 in both TMZ-sensitive and TMZ-resistant GBM cells and tissues using Western blotting and immunofluorescence assays. In vitro experiments were conducted to explore the impact of E2F6 on TMZ resistance and glioma stem cell stemness. These experiments included Western blotting, colony formation assay, flow cytometry assay, and TdT-mediated dUTP nick-end labeling (TUNEL) assay. Bioinformatic analyses were conducted to investigate the mechanism behind the high expression of E2F6 in TMZ-resistant cells and its correlation with caspase recruitment domain 6 (CARD6) and disulfide-linked cell adhesion protein (POSTN). The study employed bioinformatic analyses, messenger RNA (mRNA) sequencing, chromatin immunoprecipitation sequencing assay, immunofluorescence, quantitative real-time polymerase chain reaction (qRT-PCR), and Western blotting. To examine the function of E2F6, an intracranial xenograft tumor mouse model was used for in vivo experiments. RESULTS: It was found that CARD6 and POSTN were significantly associated with TMZ resistance and survival of GBM patients. E2F6 was up-regulated in TMZ-resistant cells and tissues. Knockdown of E2F6 down-regulated the expression of CARD6, promoted TMZ-induced apoptosis, and enhanced chemo-sensitivity, whereas its overexpression significantly increased TMZ resistance in vitro and in vivo. In addition, E2F6 can promote TMZ resistance through stem-like properties acquisition. We identified a signaling pathway related to E2F6 and POSTN, which maintains the self-renewal of GBM stem cells (GSCs). E2F6 concentrates in the promoter region of POSTN, thereby regulating the expression of GSCs-related genes cluster of differentiation 133 (CD133), Nestin, and sex-determining region Y-box 2 (SOX2), which may be involved in tumor metabolism and drug resistance processes. Down-regulation of E2F6 down-regulated the expression of POSTN and inhibited tumor growth in nude mice. CONCLUSIONS: These results suggest that the E2F6-CARD6/POSTN signaling axis regulates the malignant biological behaviors of GBM and TMZ resistance. These findings are expected to provide promising therapeutic targets for CARD6 overcoming GBM TMZ resistance.

Use of surface-modified porous silicon nanoparticles to deliver temozolomide with enhanced pharmacokinetic and therapeutic efficacy for intracranial glioblastoma in mice.

Glioblastoma (GBM) is one of the most common and fatal primary brain tumors, with a 5-year survival rate of 7.2%. The standard treatment for GBM involves surgical resection followed by chemoradiotherapy, and temozolomide (TMZ) is currently the only approved chemotherapeutic agent for the treatment of GBM. However, hydrolytic instability and insufficient drug accumulation are major challenges that limit the effectiveness of TMZ chemotherapy. To overcome these limitations, we have developed a drug delivery platform utilizing porous silicon nanoparticles (pSiNPs) to improve the stability and blood-brain barrier penetration of TMZ. The pSiNPs are synthesized via electrochemical etching and functionalized with octadecane. The octadecyl-modified pSiNP (pSiNP-C18) demonstrates the superiority of loading efficiency, in vivo stability, and brain accumulation of TMZ. Treatment of intracranial tumor-bearing mice with TMZ-loaded pSiNP-C18 results in a decreased tumor burden and a corresponding increase in survival compared with equivalent free-drug dosing. Furthermore, the mice treated with TMZ-loaded nanoparticles do not exhibit in vivo toxicity, thus underscoring the preclinical potential of the pSiNP-based platform for the delivery of therapeutic agents to gliomas.

Gastrodin Liposomes Block Crosstalk between Astrocytes and Glioma Cells via Downregulating Cx43 to Improve Antiglioblastoma Efficacy of Temozolomide.

The crosstalk between glioma cells and astrocytes plays a crucial role in developing temozolomide (TMZ) resistance of glioblastomas, together with the existence of the BBB contributing to the unsatisfactory clinical treatment of glioblastomas. Herein, we developed a borneol-modified and gastrodin-loaded liposome (Bo-Gas-LP), with the intent of enhancing the efficacy of TMZ therapy after intranasal administration. The results showed that Bo-Gas-LP improved GL261 cells' sensitivity to TMZ and prolonged survival of GL261-bearing mice by blocking the crosstalk between astrocytes and glioblastoma cells with the decrease of Cx43. Our study showed that intranasal Bo-Gas-LP targeting the crosstalk in glioblastoma microenvironments proposed a promising targeted therapy idea to overcome the current therapeutic limitations of TMZ-resistant glioblastomas.

Injectable Dendrimer Hydrogel Delivers Melphalan in Both Conjugated and Free Forms for Retinoblastoma.

We report the successful synthesis of an injectable dendrimer hydrogel (DH) carrying melphalan, a clinical drug for retinoblastoma treatment, in both conjugated and free forms. Polyamidoamine (PAMAM) dendrimer generation 5 (G5) is surface-modified with an acid-sensitive acetal-dibenzocyclooctyne linker and then undergoes azide-alkyne cycloaddition with melphalan-PEG-N3 conjugate to form G5-acetal-melphalan. During the DH gelation between G5-acetal-melphalan and PEG-diacrylate, free melphalan is added, resulting in a hydrogel (G5-acetal-melphalan-DH/melphalan) that carries the drug in both conjugated and free forms. Melphalan is slowly released from G5-acetal-melphalan-DH/melphalan, with the conjugated melphalan released more quickly at pH 5.3 due to acid-triggered acetal bond cleavage. The formulation's in vitro safety and efficacy were established on human corneal epithelia (HCE-2) and retinoblastoma cells (Y79). In an in vivo Y79 tumor xenograft model of retinoblastoma, intratumorally injected G5-melphalan-DH formulation prolonged tumor suppression. This injectable, multimodal, pH-responsive formulation shows promise for intravitreal injection to treat retinoblastoma.

Stanniocalcin-1 promotes temozolomide resistance of glioblastoma through regulation of MGMT.

Temozolomide (TMZ) resistance is a major challenge in the treatment of glioblastoma (GBM). Tumour reproductive cells (TRCs) have been implicated in the development of chemotherapy resistance. By culturing DBTRG cells in three-dimensional soft fibrin gels to enrich GBM TRCs and performing RNA-seq analysis, the expression of stanniocalcin-1 (STC), a gene encoding a secreted glycoprotein, was found to be upregulated in TRCs. Meanwhile, the viability of TMZ-treated TRC cells was significantly higher than that of TMZ-treated 2D cells. Analysis of clinical data from CGGA (Chinese Glioma Genome Atlas) database showed that high expression of STC1 was closely associated with poor prognosis, glioma grade and resistance to TMZ treatment, suggesting that STC1 may be involved in TMZ drug resistance. The expression of STC1 in tissues and cells was examined, as well as the effect of STC1 on GBM cell proliferation and TMZ-induced DNA damage. The results showed that overexpression of STC1 promoted and knockdown of STC1 inhibited TMZ-induced DNA damage. These results were validated in an intracranial tumour model. These data revealed that STC1 exerts regulatory functions on MGMT expression in GBM, and provides a rationale for targeting STC1 to overcome TMZ resistance.

Molecular Iodine Improves the Efficacy and Reduces the Side Effects of Metronomic Cyclophosphamide Treatment against Mammary Cancer Progression.

Metronomic chemotherapy with cyclophosphamide (Cpp) has shown promising results in cancer protocols. These lower and prolonged doses have antiangiogenic, pro-cytotoxic, and moderate secondary effects. Molecular iodine (I2) reduces the viability of cancer cells and, with chemotherapeutic agents, activates the antitumoral immune response and diminishes side effects. The present work evaluates the adjuvant of oral I2 with Cpp using a murine model of mammary cancer. Female Sprague Dawley rats with 7,12-dimethylbenzantracene-induced tumors received Cpp intraperitoneal (50 and 70 mg/kg two times/week, iCpp50 and iCpp70) and oral (0.03%; 50 mg/Kg; oCpp50) doses. I2 (0.05%, 50 mg/100 mL) and oCpp50 were offered in drinking water for three weeks. iCpp70 was the most efficient antitumoral dose but generated severe body weight loss and hemorrhagic cystitis (HC). I2 prevented body weight loss, exhibited adjuvant actions with Cpp, decreasing tumor growth, and canceled HC mechanisms, including decreases in vascular endothelial growth factor (VEGF) and Survivin expression. oCpp50 + I2 diminished angiogenic signals (CD34, vessel-length, and VEGF content) and proinflammatory cytokines (interleukin-10 and tumor necrosis factor-alpha) and increased cytotoxic (lymphocytic infiltration, CD8+ cells, Tbet, and interferon-gamma) and antioxidant markers (nuclear erythroid factor-2 and glutathione peroxidase). I2 enhances the effectiveness of oCpp, making it a compelling candidate for a clinical protocol.

Modelling glioblastoma resistance to temozolomide. A mathematical model to simulate cellular adaptation in vitro.

Drug resistance is one of the biggest challenges in the fight against cancer. In particular, in the case of glioblastoma, the most lethal brain tumour, resistance to temozolomide (the standard of care drug for chemotherapy in this tumour) is one of the main reasons behind treatment failure and hence responsible for the poor prognosis of patients diagnosed with this disease. In this work, we combine the power of three-dimensional in vitro experiments of treated glioblastoma spheroids with mathematical models of tumour evolution and adaptation. We use a novel approach based on internal variables for modelling the acquisition of resistance to temozolomide that was observed in experiments for a group of treated spheroids. These internal variables describe the cell's phenotypic state, which depends on the history of drug exposure and affects cell behaviour. We use model selection to determine the most parsimonious model and calibrate it to reproduce the experimental data, obtaining a high level of agreement between the in vitro and in silico outcomes. A sensitivity analysis is carried out to investigate the impact of each model parameter in the predictions. More importantly, we show how the model is useful for answering biological questions, such as what is the intrinsic adaptation mechanism, or for separating the sensitive and resistant populations. We conclude that the proposed in silico framework, in combination with experiments, can be useful to improve our understanding of the mechanisms behind drug resistance in glioblastoma and to eventually set some guidelines for the design of new treatment schemes.

TRAbectedin in adVanced rEtroperitoneal well differentiated/dedifferentiated Liposarcoma and Leiomyosarcoma (TRAVELL): results of a phase II study from the Italian Sarcoma Group.

BACKGROUND: This is a multicentre, single-arm, phase II study aimed at further exploring the activity of trabectedin as second-/further-line treatment in retroperitoneal leiomyosarcoma (LMS) and well-differentiated/dedifferentiated liposarcoma (LPS). MATERIALS AND METHODS: The primary endpoint was the growth modulation index (GMI) defined as the ratio between PFS under trabectedin (PFS) and during previous chemotherapy treatment: time to progression (TTP-1). Secondary endpoints were objective response rate (ORR) and PFS. As per protocol, patients were considered responders if the GMI was >1.33, non-responders if <0.75 and neither if 0.76-1.32. RESULTS: Overall 91 patients were assessable for the primary endpoint (32 patients with LMS and 59 patients with LPS): the median number of cycles received was 6.0 (Q1-Q3 3.0-12.0), and the main reason for treatment discontinuation was disease progression in 72% of patients. The median PFS was 6.0 months, while the median TTP1 was 7.5 months (8.1 and 6.4 months for LMS and LPS, respectively). Thirty-three patients [52%, 95% confidence interval (CI) 36% to 58%, P = 0.674, odds of response 1.1] had a GMI >1.33 (LMS 46%, 95% CI 26% to 67%, odds of response 0.85; LPS 56%, 95% CI 40% to 72%, odds of response 1.3). Overall, in LPS we observed 15/47 patients with a GMI <0.5 and 15/47 patients with a GMI >2. Among LMS patients, 9/26 had a GMI <0.5 and 10/26 had a GMI >2. Overall, ORR (complete response + partial response) was 16% (24% for LMS and 12% for LPS). CONCLUSIONS: While the primary endpoint of the study was not met, we noticed a subgroup of patients with a markedly discrepant TTP with trabectedin in comparison to previous therapy (GMI <0.5 or >2, the latter including some patients with a long TTP with trabectedin). A mismatch between PFS and overall survival was observed, possibly due to the natural history of the two different histologies and the availability of further lines in LMS.

A novel protein encoded by circCOPA inhibits the malignant phenotype of glioblastoma cells and increases their sensitivity to temozolomide by disrupting the NONO-SFPQ complex.

Glioblastoma (GBM) represents a primary malignant brain tumor. Temozolomide resistance is a major hurdle in GBM treatment. Proteins encoded by circular RNAs (circRNAs) can modulate the sensitivity of multiple tumor chemotherapies. However, the impact of circRNA-encoded proteins on GBM sensitivity to temozolomide remains unknown. Herein, we discover a circRNA (circCOPA) through the circRNA microarray profile in GBM samples, which can encode a novel 99 amino acid protein (COPA-99aa) through its internal ribosome entry site. Functionally, circCOPA overexpression in GBM cells inhibits cell proliferation, migration, and invasion in vitro and growth in vivo. Rather than itself, circCOPA mainly functions as a suppressive effector by encoding COPA-99aa. Moreover, we reveal that circCOPA is downregulated in GBM tissues and high expression of circCOPA is related to a better prognosis in GBM patients. Mechanistically, a heteromer of SFPQ and NONO is required for double-strand DNA break repair. COPA-99aa disrupts the dimerization of NONO and SFPQ by separately binding with the NONO and SFPQ proteins, thus resulting in the inhibition of proliferation or invasion and the increase of temozolomide-induced DNA damage in GBM cells. Collectively, our data suggest that circCOPA mainly contributes to inhibiting the GBM malignant phenotype through its encoded COPA-99aa and that COPA-99aa increases temozolomide-induced DNA damage by interfering with the dimerization of NONO and SFPQ. Restoring circCOPA or COPA-99aa may increase the sensitivity of patients to temozolomide.

Overcoming High Trabectedin Resistance of Soft-tissue Sarcoma With Recombinant Methioninase: A Potential Solution of a Recalcitrant Clinical Problem.

BACKGROUND/AIM: Drug resistance has been a recalcitrant problem for sarcoma patients for many decades. Trabectedin is a second-line chemotherapy for soft-tissue sarcoma that often leads to resistance and death of the patients. The objective of the present study was to address the issue of trabectedin-chemoresistance in HT1080 fibrosarcoma cells by combining recombinant methioninase (rMETase) with trabectedin and examining their efficacy on trabectedin-resistant fibrosarcoma cells in vitro. MATERIALS AND METHODS: Trabectedin-resistant HT1080 (TR-HT1080) cells were generated by subjecting HT1080 human fibrosarcoma cells to increasing trabectedin concentrations (3.3-8 nM). IC50 values for trabectedin and rMETase were compared for HT1080 and TR-HT1080 cells. TR-HT 1080 cells were placed into four groups to determine synergy of rMETase and trabectedin on TR-HT1080 cells: a control group with no treatment; a group treated with trabectedin (3.3 nM); a group treated with rMETase (0.75 U/ml); and a group treated with both trabectedin (3.3 nM) and rMETase (0.75 U/ml). RESULTS: The IC50 value of trabectedin- on TR-HT1080 cells was 42.9 nM, whereas the IC50 value of trabectedin on the parental HT1080 cells was 3.3 nM, indicating a 13-fold increase. The combination of rMETase (0.75 U/ml) and trabectedin (3.3 nM) was synergistic on TR-HT1080 cells resulting in an inhibition of 64.2% compared to trabectedin alone (5.7%) or rMETase alone (50.5%) (p<0.05). rMETase increased the efficacy of trabectedin 11-fold on trabectedin-resistant fibrosarcoma cells. CONCLUSION: The combined administration of trabectedin and rMETase was synergistic on the viability of TR-HT1080 cells in vitro. The combination of rMETase and trabectedin has promising clinical potential for overcoming chemo-resistance of soft-tissue sarcoma.

Design and Synthesis of 7-Oxabicyclo[2.2.1]heptane-2,3-dicarboxylic Acid Derivatives as PP5 Inhibitors To Reverse Temozolomide Resistance in Glioblastoma Multiforme.

The serine/threonine phosphatase family is important in tumor progression and survival. Due to the high conserved catalytic domain, designing selective inhibitors is challenging. Herein, we obtained compound 28a with 38-fold enhanced PP5 selectivity (PP2A/5 IC50 = 33.8/0.9 µM) and improved drug-like properties (favorable stability and safety, F = 82.0%) by rational drug design based on a phase II PP2A/5 dual target inhibitor LB-100. Importantly, we found the spatial conformational restriction of the 28a indole fragment was responsible for the selectivity of PP5. Thus, 28a activated p53 and downregulated cyclin D1 and MGMT, which showed potency in cell cycle arrest and reverse temozolomide (TMZ) resistance in the U87 MG cell line. Furthermore, oral administration of 28a and TMZ was well tolerated to effectively inhibit tumor growth (TGI = 87.7%) in the xenograft model. Collectively, these results implicate 28a could be a drug candidate by reversing TMZ resistance with a selective PP5 inhibition manner.

Accidental Encounter of Repair Intermediates in Alkylated DNA May Lead to Double-Strand Breaks in Resting Cells.

In clinics, chemotherapy is often combined with surgery and radiation to increase the chances of curing cancers. In the case of glioblastoma (GBM), patients are treated with a combination of radiotherapy and TMZ over several weeks. Despite its common use, the mechanism of action of the alkylating agent TMZ has not been well understood when it comes to its cytotoxic effects in tumor cells that are mostly non-dividing. The cellular response to alkylating DNA damage is operated by an intricate protein network involving multiple DNA repair pathways and numerous checkpoint proteins that are dependent on the type of DNA lesion, the cell type, and the cellular proliferation state. Among the various alkylating damages, researchers have placed a special on O6-methylguanine (O6-mG). Indeed, this lesion is efficiently removed via direct reversal by O6-methylguanine-DNA methyltransferase (MGMT). As the level of MGMT expression was found to be directly correlated with TMZ efficiency, O6-mG was identified as the critical lesion for TMZ mode of action. Initially, the mode of action of TMZ was proposed as follows: when left on the genome, O6-mG lesions form O6-mG: T mispairs during replication as T is preferentially mis-inserted across O6-mG. These O6-mG: T mispairs are recognized and tentatively repaired by a post-replicative mismatched DNA correction system (i.e., the MMR system). There are two models (futile cycle and direct signaling models) to account for the cytotoxic effects of the O6-mG lesions, both depending upon the functional MMR system in replicating cells. Alternatively, to explain the cytotoxic effects of alkylating agents in non-replicating cells, we have proposed a "repair accident model" whose molecular mechanism is dependent upon crosstalk between the MMR and the base excision repair (BER) systems. The accidental encounter between these two repair systems will cause the formation of cytotoxic DNA double-strand breaks (DSBs). In this review, we summarize these non-exclusive models to explain the cytotoxic effects of alkylating agents and discuss potential strategies to improve the clinical use of alkylating agents.

S-p-bromobenzyl-glutathione cyclopentyl diester (BBGC) as novel therapeutic strategy to enhance trabectedin anti-tumor effect in soft tissue sarcoma preclinical models.

Trabectedin, approved for the treatment of soft tissue sarcoma (STS), interferes with cell division and genetic transcription processes. Due to its strong anti-tumor activity in only certain histotypes, several studies on trabectedin combinations are currently ongoing to improve its efficacy. In this study, we aimed to investigate novel potential therapeutic strategies to enhance the anti-tumor effect of trabectedin using integrated in silico, in vitro, and in vivo approaches. For in silico analysis, we screened two public datasets, GSEA M5190 and TCGA SARC. Fibrosarcoma, leiomyosarcoma, dedifferentiated, and myxoid liposarcoma cell lines were used for in vitro studies. For in vivo experiments, fibrosarcoma orthotopic murine model was developed. In silico analysis identified Glo1 as the only druggable target upregulated after trabectedin treatment and correlated with poor prognosis. The specific Glo1 inhibitor, S-p-bromobenzylglutathione cyclopentyl diester (BBGC), increased trabectedin cytotoxicity in STS cells, and restored drug sensitivity in myxoid liposarcoma cells resistant to trabectedin. Moreover, the combined treatment with BBGC and trabectedin had a synergistic antitumor effect in vivo without any additional toxicity to mice. Based on these results, we believe that BBGC warrants further investigation to evaluate its potential clinical use in combination with trabectedin.

Human translesion DNA polymerases ι and κ mediate tolerance to temozolomide in MGMT-deficient glioblastoma cells.

Glioblastoma (GBM) is a highly aggressive brain tumor associated with poor patient survival. The current standard treatment involves invasive surgery, radiotherapy, and chemotherapy employing temozolomide (TMZ). Resistance to TMZ is, however, a major challenge. Previous work from our group has identified candidate genes linked to TMZ resistance, including genes encoding translesion synthesis (TLS) DNA polymerases iota (PolÉ©) and kappa (Polκ). These specialized enzymes are known for bypassing lesions and tolerating DNA damage. Here, we investigated the roles of PolÉ© and Polκ in TMZ resistance, employing MGMT-deficient U251-MG glioblastoma cells, with knockout of either POLI or POLK genes encoding PolÉ© and Polκ, respectively, and assess their viability and genotoxic stress responses upon subsequent TMZ treatment. Cells lacking either of these polymerases exhibited a significant decrease in viability following TMZ treatment compared to parental counterparts. The restoration of the missing polymerase led to a recovery of cell viability. Furthermore, knockout cells displayed increased cell cycle arrest, mainly in late S-phase, and lower levels of genotoxic stress after TMZ treatment, as assessed by a reduction of γH2AX foci and flow cytometry data. This implies that TMZ treatment does not trigger a significant H2AX phosphorylation response in the absence of these proteins. Interestingly, combining TMZ with Mirin (double-strand break repair pathway inhibitor) further reduced the cell viability and increased DNA damage and γH2AX positive cells in TLS KO cells, but not in parental cells. These findings underscore the crucial roles of PolÉ© and Polκ in conferring TMZ resistance and the potential backup role of homologous recombination in the absence of these TLS polymerases. Targeting these TLS enzymes, along with double-strand break DNA repair inhibition, could, therefore, provide a promising strategy to enhance TMZ's effectiveness in treating GBM.

MEN1 Deficiency-Driven Activation of the ß-Catenin-MGMT Axis Promotes Pancreatic Neuroendocrine Tumor Growth and Confers Temozolomide Resistance.

O6-methylguanine DNA methyltransferase (MGMT) removes alkyl adducts from the guanine O6 position (O6-MG) and repairs DNA damage. High MGMT expression results in poor response to temozolomide (TMZ). However, the biological importance of MGMT and the mechanism underlying its high expression in pancreatic neuroendocrine tumors (PanNETs) remain elusive. Here, it is found that MGMT expression is highly elevated in PanNET tissues compared with paired normal tissues and negatively associated with progression-free survival (PFS) time in patients with PanNETs. Knocking out MGMT inhibits cancer cell growth in vitro and in vivo. Ectopic MEN1 expression suppresses MGMT transcription in a manner that depends on ß-Catenin nuclear export and degradation. The Leucine 267 residue of MEN1 is crucial for regulating ß-Catenin-MGMT axis activation and chemosensitivity to TMZ. Interference with ß-Catenin re-sensitizes tumor cells to TMZ and significantly reduces the cytotoxic effects of high-dose TMZ treatment, and MGMT overexpression counteracts the effects of ß-Catenin deficiency. This study reveals the biological importance of MGMT and a new mechanism by which MEN1 deficiency regulates its expression, thus providing a potential combinational strategy for treating patients with TMZ-resistant PanNETs.