Loss of the mismatch repair protein MSH6 in human glioblastomas is associated with tumor progression during temozolomide treatment

Induction of a mismatch repair deficient genotype by tailored chemical mutagenesis in experimental models of cancer

Mismatch repair deficient (MMRd) tumors harbor thousands of somatic mutations enriched for insertion-deletion (indels) conferring high sensitivity to immunotherapy. We sought to reproduce this phenotype using mutagenic agents to engineer an MMRd genotype in immunoresistant cells. The combination of temozolomide (TMZ) and cisplatin led to a rapid accumulation of a high mutational load enriched for indels in murine cell lines resulting from the epigenetic loss of Msh2. Pretreated cells showed sensitivity to PD-1 blockade. Systemic treatment with TMZ, cisplatin, and anti-PD-1 bearing immunoresistant tumor cells led to increased survival, intratumoral T cell infiltration, and downregulation of Msh2 expression without affecting healthy tissues. In a clinical trial with 18 patients with refractory mismatch repair proficient colorectal cancer, no responses were seen, but MMRd signatures emerged in cell-free DNA. These findings show that recapitulating an MMRd genotype through chemical mutagenesis can generate an immunogenic phenotype.

Glioblastoma multiforme: an updated overview of temozolomide resistance mechanisms and strategies to overcome resistance

Glioblastoma (GBM) is an aggressive primary brain tumor with high lethality. The typical treatment regimen includes post-surgical radiotherapy and temozolomide (TMZ) chemotherapy, which helps extend survival. Nevertheless, TMZ resistance occurs in approximately 50% of patients. This resistance is primarily associated with the expression of O6-methylguanine-DNA methyltransferase (MGMT), which repairs O6-methylguanine lesions generated by TMZ and is thought to be the major mechanism of drug resistance. Additionally, the mismatch repair and base excision repair pathways play crucial roles in TMZ resistance. Emerging studies also point to drug transport mechanisms, glioma stem cells, and the heterogeneous tumor microenvironment as additional influences on TMZ resistance in gliomas. A better understanding of these mechanisms is vital for developing new treatments to improve TMZ effectiveness, such as DNA repair inhibitors, inhibitors of multidrug transporting proteins, TMZ analogs, and combination therapies targeting multiple pathways. This article discusses the main resistance mechanisms and potential strategies to counteract resistance in GBM patients, aiming to broaden the understanding of these mechanisms for future research and to explore the therapeutic effects of traditional Chinese medicines and their active components in overcoming TMZ resistance.

Therapy-induced senescence of glioblastoma cells is determined by the p21CIP1-CDK1/2 axis and does not require activation of DREAM

Therapy-induced senescence (TIS) is a major challenge in cancer therapy as senescent cancer cells provoke local and systemic inflammation and might be the cause of recurrences. Elucidation of pathways leading to TIS is of utmost importance for establishing strategies to counteract this. Previously we have shown that temozolomide (TMZ), an alkylating drug used forefront in glioma therapy, causes majorly cellular senescence, which is triggered by the primary damage O6-methylguanine, activating the mismatch repair dependent ATR/ATM-CHK1/CHK2-p53 damage response pathway. The downstream pathways leading to TIS remained to be explored. Here, we show that TMZ-induced TIS in glioma cells does not require activation of the DREAM complex, but is bound on a G2-specific response. We show that the CDK inhibitor p21CIP1 does not interact with CDK4, but with CDK1 and CDK2 causing abrogation of the B-Myb and FOXM1-signaling pathway and subsequently arrest of cells in the G2-phase. The induced G2-arrest is incomplete as DNA synthesis can be resumed leading to endoreduplications. This process, which is inhibited by the CDK4-blocking drug palbociclib, is preceded by reactivation of the G1/S-specific E2F1-signaling pathway due to lack of functional DREAM activation. These findings provide an explanation for the polyploidization and giant cell phenotype of anticancer drug-induced senescent cells. Incomplete DREAM activation may also explain the observation that downregulation of DNA repair is a transient phenomenon, which goes along with the entrance of cells into the senescent state.

New approaches to targeted drug therapy of intracranial tumors

Intracranial tumors encompass a heterogeneous group of neoplasms, including gliomas, meningiomas, pituitary adenomas, schwannomas, craniopharyngiomas, ependymomas, medulloblastomas, and primary central nervous system lymphomas. These tumors present significant challenges due to their diverse molecular characteristics, critical locations, and the unique obstacles posed by the blood-brain barrier (BBB) and blood-tumor barrier (BTB), which limit the efficacy of systemic therapies. Recent advances in molecular biology and genomics have enabled the identification of specific molecular pathways and targets, paving the way for innovative precision therapies. This review examines the current state of targeted therapies for intracranial tumors, including receptor tyrosine kinase (RTK) inhibitors, PI3K/AKT/mTOR inhibitors, RAF/MEK/ERK pathway inhibitors, IDH mutation inhibitors, immune checkpoint inhibitors, and CAR-T cell therapies. Emphasis is placed on the role of the BBB and BTB in modulating drug delivery and therapeutic outcomes. Strategies to overcome these barriers, such as focused ultrasound, nanoparticle-based delivery systems, and convection-enhanced delivery, are also explored. Furthermore, the manuscript reviews clinical trial data, highlighting successes and limitations across different tumor types. It delves into emerging therapeutic approaches, including combination of regimens and personalized treatments based on molecular profiling. By synthesizing the latest research, this article aims to provide a comprehensive understanding of the advancements and ongoing challenges in the targeted treatment of intracranial tumors. The findings underscore the necessity for innovative delivery systems and more extensive clinical trials to optimize therapeutic strategies. This review aspires to inform future research and clinical practices, aiming to improve patient outcomes and quality of life in the management of these complex and life-threatening conditions.

The novel DNA cross-linking agent KL-50 is active against patient-derived models of new and recurrent post-temozolomide mismatch repair-deficient glioblastoma

BACKGROUND

Acquired resistance to temozolomide (TMZ) chemotherapy due to DNA mismatch repair (MMR) enzyme deficiency is a barrier to improving outcomes for isocitrate dehydrogenase (IDH) wild-type glioblastoma (GBM) patients. KL-50 is a new imidazotetrazine-based therapeutic designed to induce DNA interstrand cross-links, and subsequent double-stranded breaks, in an MMR-independent manner in cells with O-6-methylguanine-DNA methyltransferase (MGMT) deficiency. Previous research showed its efficacy against LN229 glioma cells with MMR and MGMT knockdown. Its activity against patient-derived GBM that model post-TMZ recurrent tumors is unclear.

METHODS

We created MMR-deficient GBM patient-derived xenografts through exposure to TMZ, followed by treatment with additional TMZ or KL-50. We also generated isogenic, MSH6 knockout (KO) patient-derived GBM and tested them for sensitivity to TMZ and KL-50.

RESULTS

KL-50 extended the median survival of mice intracranially engrafted with either patient-derived TMZ-naïve GBM6 or TMZ-naïve GBM12 by 1.75-fold and 2.15-fold, respectively (P < 0.0001). A low dose (4 Gy) of fractionated RT further extended the survival of KL-50-treated GBM12 mice (median survival = 80 days for RT + KL-50 vs. 71 days KL-50 alone, P = 0.018). KL-50 also extended the median survival of mice engrafted with post-TMZ, MMR-deficient GBM6R-m185 (140 days for KL-50 vs. 37 days for vehicle, P < 0.0001). MSH6 KO increased TMZ IC50 for GBM6 and GBM12 cultures by >5-fold and >12-fold for cell death and live cell count outputs, respectively. In contrast, MSH6-KO actually decreased KL-50 IC50 by 10-80%.

CONCLUSION

KL-50-based compounds are a promising new strategy for the treatment of MGMT-deficient, MMR-deficient GBM that recurs after frontline TMZ.

Hunting glioblastoma recurrence: glioma stem cells as retrospective targets

Glioblastoma (GBM) remains one of the most aggressive and treatment-resistant brain malignancies in adults. Standard approaches, including surgical resection followed by adjuvant radio- and chemotherapy with temozolomide (TMZ), provide only transient control, as GBM frequently recurs due to its infiltrative nature and the presence of therapy-resistant subpopulations such as glioma stem cells (GSCs). GSCs, with their quiescent state and robust resistance mechanisms, evade conventional therapies, contributing significantly to relapse. Consequently, current treatment methods for GBM face significant limitations in effectively targeting GSCs. In this review, we emphasize the relationship between GBM recurrence and GSCs, discuss the current limitations, and provide future perspectives to overwhelm the challenges associated with targeting GSCs. Eliminating GSCs may suppress recurrence, achieve durable responses, and improve therapeutic outcomes for patients with GBM.

Overexpression of miR-124 enhances the therapeutic benefit of TMZ treatment in the orthotopic GBM mice model by inhibition of DNA damage repair

Glioblastoma (GBM) is the most common malignant primary brain cancer with poor prognosis due to the resistant to current treatments, including the first-line drug temozolomide (TMZ). Accordingly, it is urgent to clarify the mechanism of chemotherapeutic resistance to improve the survival rate of patients. In the present study, by integrating comprehensive non-coding RNA-seq data from multiple cohorts of GBM patients, we identified that a series of miRNAs are frequently downregulated in GBM patients compared with the control samples. Among them, a high level of miR-124 is closely associated with a favorable survival rate in the clinical patients. In the phenotype experiment, we demonstrated that miR-124 overexpression increases responsiveness of GBM cells to TMZ-induced cell death, and vice versa. In the mechanistic study, we for the first time identified that RAD51, a key functional molecule in DNA damage repair, is a novel and bona fide target of miR-124 in GBM cells. Given that other miR-124-regulated mechanisms on TMZ sensitivity have been reported, we performed recue experiment to demonstrate that RAD51 is essential for miR-124-mediated sensitivity to TMZ in GBM cells. More importantly, our in vivo functional experiment showed that combinational utilization of miR-124 overexpression and TMZ presents a synergetic therapeutic benefit in the orthotopic GBM mice model. Taken together, we rationally explained a novel and important mechanism of the miR-124-mediated high sensitivity to TMZ-induced cell death in GBM and provided evidence to support that miR-124-RAD51 regulatory axis could be a promising candidate in the comprehensive treatment with TMZ in GBM.

Temozolomide Treatment in Refractory Pituitary Adenomas and Pituitary Carcinomas

BACKGROUND

Temozolomide (TMZ), a nonclassical alkylating agent, possesses lipophilic properties that allow it to cross the blood-brain barrier, making it active within the central nervous system. Furthermore, the adverse reactions of the TMZ are relatively mild, which is why it is currently recommended as a first-line chemotherapy drug for refractory pituitary adenomas (RPAs) and pituitary carcinomas (PCs).

SUMMARY

Systematic evaluations indicate a radiological response rate of 41% and a hormonal response rate of 53%, underscoring TMZ clinical efficacy, particularly when combined with radiotherapy. Functional tumors demonstrate a higher response rate compared to nonfunctional tumors. While the optimal duration of TMZ treatment remains undetermined, studies suggest that longer therapy durations may lead to better prognoses. Additionally, prior to TMZ administration, it is advisable to conduct immunohistochemical analysis of O6-methylguanine-DNA methyltransferase, MSH2, MSH6, MLH1, PMS2, and N-methylpurine DNA glycosylase to assess the potential impact of repair mechanisms such as direct repair, mismatch repair pathway, and base excision repair on TMZ treatment. The efficacy of TMZ analogs, combined TMZ therapies, and TMZ with nanomaterials following TMZ treatment failure remains uncertain.

KEY MESSAGES

The involvement of experienced multidisciplinary pituitary teams in all management decisions for RPAs/PCs patients is essential.

The challenges and clinical landscape of glioblastoma immunotherapy

Glioblastoma is associated with a dismal prognosis with the standard of care involving surgery, radiation therapy and temozolomide chemotherapy. This review investigates the features that make glioblastoma difficult to treat and the results of glioblastoma immunotherapy clinical trials so far. There have been over a hundred clinical trials involving immunotherapy in glioblastoma. We report the survival-related outcomes of every Phase III glioblastoma immunotherapy trial with online published results we could find at the time of writing. To date, the DCVax-L vaccine is the only immunotherapy shown to have statistically significant increased median survival compared with standard-of-care in a Phase III trial: 19.3 months versus 16.5 months. However, this trial used an external control group to compare with the intervention which limits its quality of evidence. In conclusion, glioblastoma immunotherapy requires further investigation to determine its significance in improving disease survival.

Genomic Profiling in Glioma Patients to Explore Clinically Relevant Markers

Gliomas are a heterogeneous group of brain tumors, among which the most aggressive subtype is glioblastoma, accounting for 60% of cases in adults. Available systemic treatment options are few and ineffective, so new approaches to therapies for glioblastoma are in high demand. In total, 131 patients with diffuse glioma were studied. Paired tumor–normal samples were sequenced on the Illumina platform; the panel included 812 genes associated with cancer development. Molecular profiles in clinically distinct groups were investigated. In low-grade glioma (LGG) patients (n = 18), the most common mutations were IDH1/2 (78%), ATRX (33%), TP53 (44%), PIK3CA (17%), and co-deletion 1p/19q (22%). In high-grade glioma (HGG) patients (n = 113), more frequently affected genes were CDKN2A/B (33%), TERTp (71%), PTEN (60%), TP53 (27%), and EGFR (40%). The independent predictors of better prognosis were tumor grade and IDH1/2 mutations. In IDH—wildtype glioblastoma patients, a history of other precedent cancer was associated with worse overall survival (OS), while re-operation and bevacizumab therapy increased OS. Also, among genetic alterations, TERTp mutation and PTEN deletion were markers of poor prognosis. Nine patients received molecular targeted therapy, and the results were evaluated. The search for molecular changes associated with tumor growth and progression is important for diagnosis and choice of therapy.

Unraveling the mysteries of MGMT: Implications for neuroendocrine tumors

Neuroendocrine tumors (NETs) are a diverse group of tumors that arise from neuroendocrine cells and are commonly found in various organs. A considerable proportion of NET patients were diagnosed at an advanced or metastatic stage. Alkylating agents are the primary treatment for NET, and O6-methylguanine methyltransferase (MGMT) remains the first-line of defense against DNA damage caused by these agents. Clinical trials have indicated that MGMT promoter methylation or its low/lacked expression can predict a favorable outcome with Temozolomide in NETs. Its status could help select NET patients who can benefit from alkylating agents. Therefore, MGMT status serves as a biomarker to guide decisions on the efficacy of Temozolomide as a personalized treatment option. Additionally, delving into the regulatory mechanisms of MGMT status can lead to the development of MGMT-targeted therapies, benefiting individuals with high levels of MGMT expression. This review aims to explore the polymorphism of MGMT regulation and summarize its clinical implications in NETs, which would help establish the role of MGMT as a biomarker and its potential as a therapeutic target in NETs. Additionally, we explore the benefits of combining Temozolomide and immunotherapy in MGMT hypermethylated subgroups. Future studies can focus on optimizing Temozolomide administration to induce specific immunomodulatory changes.

Temozolomide based treatment in glioblastoma: 6 vs. 12 months

The Stupp regimen remains the standard treatment for newly diagnosed glioblastomas, although the prognosis remains poor. Several temozolomide alternative schedules have been studied, with extended adjuvant treatment (>6 cycles of temozolomide) frequently used, although different trials have indicated contrasting results. Survival data of 87 patients who received 6 ('6C' group) or 12 ('12C' group) cycles of temozolomide were collected between 2012 and 2022. A total of 45 patients were included in the 6C group and 42 patients were included in the 12C group. Data on isocitrate dehydrogenase mutation and methylguanine-DNA-methyltransferase (MGMT) promoter methylation status were also collected. The 12C group exhibited statistically significantly improved overall survival [OS; 22.8 vs. 17.5 months; hazard ratio (HR), 0.47; 95% CI, 0.30-0.73; P=0.001] and progression-free survival (15.3 vs. 9 months; HR, 0.39; 95% CI, 0.25-0.62; P=0.001). However, in the subgroup analysis according to MGMT status, OS in the 12C group was significantly superior to OS in the 6C group only in the MGMT unmethylated tumors. The present data suggested that extended adjuvant temozolomide appeared to be more effective than the conventional six cycles.

Glioblastoma Standard of Care: Effects on Tumor Evolution and Reverse Translation in Preclinical Models

Glioblastoma (GBM) presents a significant public health challenge as the deadliest and most common malignant brain tumor in adults. Despite standard-of-care treatment, which includes surgery, radiation, and chemotherapy, mortality rates are high, underscoring the critical need for advancing GBM therapy. Over the past two decades, numerous clinical trials have been performed, yet only a small fraction demonstrated a benefit, raising concerns about the predictability of current preclinical models. Traditionally, preclinical studies utilize treatment-naïve tumors, failing to model the clinical scenario where patients undergo standard-of-care treatment prior to recurrence. Recurrent GBM generally exhibits distinct molecular alterations influenced by treatment selection pressures. In this review, we discuss the impact of treatment-surgery, radiation, and chemotherapy-on GBM. We also provide a summary of treatments used in preclinical models, advocating for their integration to enhance the translation of novel strategies to improve therapeutic outcomes in GBM.

Genetic and epigenetic instability as an underlying driver of progression and aggressive behavior in IDH-mutant astrocytoma

In recent years, the classification of adult-type diffuse gliomas has undergone a revolution, wherein specific molecular features now represent defining diagnostic criteria of IDH-wild-type glioblastomas, IDH-mutant astrocytomas, and IDH-mutant 1p/19q-codeleted oligodendrogliomas. With the introduction of the 2021 WHO CNS classification, additional molecular alterations are now integrated into the grading of these tumors, given equal weight to traditional histologic features. However, there remains a great deal of heterogeneity in patient outcome even within these established tumor subclassifications that is unexplained by currently codified molecular alterations, particularly in the IDH-mutant astrocytoma category. There is also significant intercellular genetic and epigenetic heterogeneity and plasticity with resulting phenotypic heterogeneity, making these tumors remarkably adaptable and robust, and presenting a significant barrier to the design of effective therapeutics. Herein, we review the mechanisms and consequences of genetic and epigenetic instability, including chromosomal instability (CIN), microsatellite instability (MSI)/mismatch repair (MMR) deficits, and epigenetic instability, in the underlying biology, tumorigenesis, and progression of IDH-mutant astrocytomas. We also discuss the contribution of recent high-resolution transcriptomics studies toward defining tumor heterogeneity with single-cell resolution. While intratumoral heterogeneity is a well-known feature of diffuse gliomas, the contribution of these various processes has only recently been considered as a potential driver of tumor aggressiveness. CIN has an independent, adverse effect on patient survival, similar to the effect of histologic grade and homozygous CDKN2A deletion, while MMR mutation is only associated with poor overall survival in univariate analysis but is highly correlated with higher histologic/molecular grade and other aggressive features. These forms of genomic instability, which may significantly affect the natural progression of these tumors, response to therapy, and ultimately clinical outcome for patients, are potentially measurable features which could aid in diagnosis, grading, prognosis, and development of personalized therapeutics.

ATM inhibition exploits checkpoint defects and ATM-dependent double strand break repair in TP53-mutant glioblastoma

Determining the balance between DNA double strand break repair (DSBR) pathways is essential for understanding treatment response in cancer. We report a method for simultaneously measuring non-homologous end joining (NHEJ), homologous recombination (HR), and microhomology-mediated end joining (MMEJ). Using this method, we show that patient-derived glioblastoma (GBM) samples with acquired temozolomide (TMZ) resistance display elevated HR and MMEJ activity, suggesting that these pathways contribute to treatment resistance. We screen clinically relevant small molecules for DSBR inhibition with the aim of identifying improved GBM combination therapy regimens. We identify the ATM kinase inhibitor, AZD1390, as a potent dual HR/MMEJ inhibitor that suppresses radiation-induced phosphorylation of DSBR proteins, blocks DSB end resection, and enhances the cytotoxic effects of TMZ in treatment-naïve and treatment-resistant GBMs with TP53 mutation. We further show that a combination of G2/M checkpoint deficiency and reliance upon ATM-dependent DSBR renders TP53 mutant GBMs hypersensitive to TMZ/AZD1390 and radiation/AZD1390 combinations. This report identifies ATM-dependent HR and MMEJ as targetable resistance mechanisms in TP53-mutant GBM and establishes an approach for simultaneously measuring multiple DSBR pathways in treatment selection and oncology research.

Revolutionizing Glioblastoma Treatment: A Comprehensive Overview of Modern Therapeutic Approaches

Glioblastoma is the most common malignant primary brain tumor in the adult population, with an average survival of 12.1 to 14.6 months. The standard treatment, combining surgery, radiotherapy, and chemotherapy, is not as efficient as we would like. However, the current possibilities are no longer limited to the standard therapies due to rapid advancements in biotechnology. New methods enable a more precise approach by targeting individual cells and antigens to overcome cancer. For the treatment of glioblastoma, these are gamma knife therapy, proton beam therapy, tumor-treating fields, EGFR and VEGF inhibitors, multiple RTKs inhibitors, and PI3K pathway inhibitors. In addition, the increasing understanding of the role of the immune system in tumorigenesis and the ability to identify tumor-specific antigens helped to develop immunotherapies targeting GBM and immune cells, including CAR-T, CAR-NK cells, dendritic cells, and immune checkpoint inhibitors. Each of the described methods has its advantages and disadvantages and faces problems, such as the inefficient crossing of the blood-brain barrier, various neurological and systemic side effects, and the escape mechanism of the tumor. This work aims to present the current modern treatments of glioblastoma.

Revisiting Temozolomide's role in solid tumors: Old is gold?

Temozolomide is an imidazotetrazine with a long history in oncology especially for the high grade malignant glioma and metastatic melanoma. However, last year's new indications for its use are added. Its optimum pharmacodynamic profile, its ability to penetrate the blood-brain barrier, the existence of methylation of MGMT in solid tumors which enhances its efficacy, the identification of new agents that can overcome temozolomide's resistance, the promising role of temozolomide in turning immune cold tumors to hot ones, are leading to expand its use in other solid tumors, giving oncologists an additional tool for the treatment of advanced and aggressive neoplasms.

Rise of oligodendroglioma hypermutator phenotype from a subclone harboring TP53 mutation after TMZ treatment

Oligodendrogliomas characterized and defined by 1p/19q co-deletion are slowly growing tumors showing better prognosis than astrocytomas. TP53 mutation is rare in oligodendrogliomas while the vast majority of astrocytomas harbor the mutation, making TP53 mutation mutually exclusive with 1p/19q codeletion in lower grade gliomas virtually. We report a case of 51-year-old woman with a left fronto-temporal oligodendroglioma that contained a small portion with a TP53 mutation, R248Q, at the initial surgery. On a first, slow-growing recurrence 29 months after radiation and nitrosourea-based chemotherapy, the patient underwent TMZ chemotherapy. The recurrent tumor responded well to TMZ but developed a rapid progression after 6 cycles as a malignant hypermutator tumor with a MSH6 mutation. Most of the recurrent tumor lacked typical oligodendroglioma morphology that was observed in the primary tumor, while it retained the IDH1 mutation and 1p/19q co-deletion. The identical TP53 mutation observed in the small portion of the primary tumor was universal in the recurrence. This case embodied the theoretically understandable clonal expansion of the TP53 mutation with additional mismatch repair gene dysfunction leading to hypermutator phenotype. It thus indicated that TP53 mutation in oligodendroglioma, although not common, may play a critical role in the development of hypermutator after TMZ treatment.

Effects of temozolomide on tumor mutation burden and microsatellite instability in melanoma cells

The efficacy of combination therapy with an immune checkpoint inhibitor (ICI) and cytotoxic chemotherapeutic agents has been investigated in cancer, including melanoma. Before ICIs were introduced, dacarbazine or temozolomide (TMZ) were used to treat melanoma. Several studies using glioma or colorectal cancer cells showed that TMZ can increase the tumor mutation burden (TMB) and induce mismatch repair (MMR) deficiency associated with microsatellite instability (MSI). These could increase immunoreactivity to an ICI, but this has not been evaluated in melanoma cells. We investigated the effects of TMZ on MSI status and TMB in melanoma cells. To evaluate the TMB, we performed whole-exome sequencing using genomic DNA from the human melanoma cell lines Mel18, A375, WM266-4, G361, and TXM18 before and after TMZ treatment. Polymerase chain reaction amplification of five mononucleotide repeat markers, BAT25, BAT26, NR21, NR24, and MONO27, was performed, and we analyzed changes in the MSI status. In all cell lines, the TMB was increased after TMZ treatment (the change amount of TMB with ≤ 5% variant allele frequency [VAF] was 18.0-38.3 mutations per megabase) even in the condition without obvious cytological damage. MSI after TMZ treatment was not observed in any cells. TMZ increased TMB but did not change MSI status in melanoma cells.

Combined Immunotherapy Improves Outcome for Replication-Repair-Deficient (RRD) High-Grade Glioma Failing Anti-PD-1 Monotherapy: A Report from the International RRD Consortium

Immune checkpoint inhibition (ICI) is effective for replication-repair-deficient, high-grade gliomas (RRD-HGG). The clinical/biological impact of immune-directed approaches after failing ICI monotherapy is unknown. We performed an international study on 75 patients treated with anti-PD-1; 20 are progression free (median follow-up, 3.7 years). After second progression/recurrence (n = 55), continuing ICI-based salvage prolonged survival to 11.6 months (n = 38; P < 0.001), particularly for those with extreme mutation burden (P = 0.03). Delayed, sustained responses were observed, associated with changes in mutational spectra and the immune microenvironment. Response to reirradiation was explained by an absence of deleterious postradiation indel signatures (ID8). CTLA4 expression increased over time, and subsequent CTLA4 inhibition resulted in response/stable disease in 75%. RAS-MAPK-pathway inhibition led to the reinvigoration of peripheral immune and radiologic responses. Local (flare) and systemic immune adverse events were frequent (biallelic mismatch-repair deficiency > Lynch syndrome). We provide a mechanistic rationale for the sustained benefit in RRD-HGG from immune-directed/synergistic salvage therapies. Future approaches need to be tailored to patient and tumor biology.

SIGNIFICANCE

Hypermutant RRD-HGG are susceptible to checkpoint inhibitors beyond initial progression, leading to improved survival when reirradiation and synergistic immune/targeted agents are added. This is driven by their unique biological and immune properties, which evolve over time. Future research should focus on combinatorial regimens that increase patient survival while limiting immune toxicity. This article is featured in Selected Articles from This Issue, p. 201.

Glioblastoma vaccines: past, present, and opportunities

Glioblastoma (GBM) is one of the most lethal central nervous systems (CNS) tumours in adults. As supplements to standard of care (SOC), various immunotherapies improve the therapeutic effect in other cancers. Among them, tumour vaccines can serve as complementary monotherapy or boost the clinical efficacy with other immunotherapies, such as immune checkpoint blockade (ICB) and chimeric antigen receptor T cells (CAR-T) therapy. Previous studies in GBM therapeutic vaccines have suggested that few neoantigens could be targeted in GBM due to low mutation burden, and single-peptide therapeutic vaccination had limited efficacy in tumour control as monotherapy. Combining diverse antigens, including neoantigens, tumour-associated antigens (TAAs), and pathogen-derived antigens, and optimizing vaccine design or vaccination strategy may help with clinical efficacy improvement. In this review, we discussed current GBM therapeutic vaccine platforms, evaluated and potential antigenic targets, current challenges, and perspective opportunities for efficacy improvement.

Plasma ctDNA enables early detection of temozolomide resistance mutations in glioma

Background

Liquid biopsy based on circulating tumor DNA (ctDNA) is a novel tool in clinical oncology, however, its use has been limited in glioma to date, due to low levels of ctDNA. In this study, we aimed to demonstrate that sequencing techniques optimized for liquid biopsy in glioma patients can detect ctDNA in plasma with high sensitivity and with potential clinical utility.

Methods

We investigated 10 glioma patients with tumor tissue available from at least 2 surgical operations, who had 49 longitudinally collected plasma samples available for analysis. Plasma samples were sequenced with CAPP-seq (AVENIO) and tissue samples with TSO500.

Results

Glioma-derived ctDNA mutations were detected in 93.8% of plasma samples. 25% of all mutations detected were observed in plasma only. Mutations of the mismatch repair (MMR) genes MSH2 and MSH6 were the most frequent circulating gene alterations seen after temozolomide treatment and were frequently observed to appear in plasma prior to their appearance in tumor tissue at the time of surgery for recurrence.

Conclusions

This pilot study suggests that plasma ctDNA in glioma is feasible and may provide sensitive and complementary information to tissue biopsy. Furthermore, plasma ctDNA detection of new MMR gene mutations not present in the initial tissue biopsy may provide an early indication of the development of chemotherapy resistance. Additional clinical validation in larger cohorts is needed.

Lynch Syndrome-Associated Glioblastoma Treated With Concomitant Chemoradiotherapy and Immune Checkpoint Inhibitors: Case Report and Review of Literature

Lynch syndrome (LS) is an autosomal dominant disorder caused by mutations in mismatch repair (MMR) genes and is also known to be associated with glioblastomas. The efficacy of immunotherapy for LS-associated glioblastomas remains unknown. Herein, we report a rare case of LS-associated glioblastoma, treated with chemotherapy using immune checkpoint inhibitors (ICI). A 41-year-old female patient presented with headaches and sensory disturbances in the right upper limb for 6 weeks. She had been treated for rectal cancer and had a family history of LS. MRI revealed two ring-enhancing lesions in the left precentral gyrus. She underwent subtotal resection, leading to a pathological diagnosis of isocitrate dehydrogenase wild-type glioblastoma. She received daily administration of (temozolomide, 75 mg/m²) and concurrent radiotherapy (60 Gy) postoperatively. However, the tumor recurred 1 year after the initial treatment. A molecular genetic study showed high microsatellite instability (MSI), and she was treated with pembrolizumab therapy. Disease progression occurred despite six cycles of pembrolizumab therapy and radiotherapy at the dose of 40 Gy. She died due to glioblastoma progression 19 months after the initial treatment. The present case demonstrates that some LS-associated glioblastomas may be resistant to ICI despite high MSI, possibly because of intratumor heterogeneity related to MMR deficiency.

NEO212, temozolomide conjugated to NEO100, exerts superior therapeutic activity over temozolomide in preclinical chemoradiation models of glioblastoma

Background

The chemotherapeutic standard of care for patients with glioblastoma (GB) is radiation therapy (RT) combined with temozolomide (TMZ). However, during the twenty years since its introduction, this so-called Stupp protocol has revealed major drawbacks, because nearly half of all GBs harbor intrinsic treatment resistance mechanisms. Prime among these are the increased expression of the DNA repair protein O6-guanine-DNA methyltransferase (MGMT) and cellular deficiency in DNA mismatch repair (MMR). Patients with such tumors receive very little, if any, benefit from TMZ. We are developing a novel molecule, NEO212 (TMZ conjugated to NEO100), that harbors the potential to overcome these limitations.

Methods

We used mouse models that were orthotopically implanted with GB cell lines or primary, radioresistant human GB stem cells, representing different treatment resistance mechanisms. Animals received NEO212 (or TMZ for comparison) without or with RT. Overall survival was recorded, and histology studies quantified DNA damage, apoptosis, microvessel density, and impact on bone marrow.

Results

In all tumor models, replacing TMZ with NEO212 in a schedule designed to mimic the Stupp protocol achieved a strikingly superior extension of survival, especially in TMZ-resistant and RT-resistant models. While NEO212 displayed pronounced radiation-sensitizing, DNA-damaging, pro-apoptotic, and anti-angiogenic effects in tumor tissue, it did not cause bone marrow toxicity.

Conclusions

NEO212 is a candidate drug to potentially replace TMZ within the standard Stupp protocol. It has the potential to become the first chemotherapeutic agent to significantly extend overall survival in TMZ-resistant patients when combined with radiation.

Aggressive and Metastatic Pituitary Neuroendocrine Tumors: Therapeutic Management and Off-Label Drug Use

Pituitary neuroendocrine tumors (PitNETs) are the most common pituitary tumors and the second most common brain tumors. Although the vast majority (>90%) are benign, a small percentage (<2%) are aggressive. These aggressive PitNETs (AgPitNETs) are defined by the presence of radiological invasion, a high rate of cell proliferation, resistance to conventional treatments, and/or a high propensity for recurrence. Lastly, there are the rare pituitary carcinomas, also known as metastatic PitNETs (MetPitNETs), which account for only 0.2% of cases and are defined by the presence of craniospinal or distant metastases. At present, there are no definitive factors that allow us to predict with certainty the aggressive behavior of PitNETs, making the therapeutic management of AgPitNETs a real challenge. Surgery is considered the first-line treatment for AgPitNETs and MetPitNETs. Radiation therapy can be effective in controlling tumor growth and regulating hormone hypersecretion. Currently, there are no approved non-endocrine medical therapies for the management of AgPitNETs/MetPitNETs, mainly due to the lack of randomized controlled clinical trials. As a result, many of the medical therapies used are off-label drugs, and several are under investigation. Temozolomide (TMZ) is now recognized as the primary medical treatment following the failure of standard therapy (medical treatment, surgery, and radiotherapy) in AgPitNETs/MetPitNETs due to its ability to improve overall and progression-free survival rates in responding patients over 5 years. Other therapeutic options include pituitary-targeted therapies (dopamine agonists and somatostatin analogs), hormonal antisecretory drugs, non-hormonal targeted therapies, radionuclide treatments, and immunotherapy. However, the number of patients who have undergone these treatments is limited, and the results obtained to date have been inconsistent. As a result, it is imperative to expand the cohort of patients undergoing treatment to better determine the therapeutic efficacy and safety of these drugs for individuals with AgPitNETs/MetPitNETs.

Temozolomide, Procarbazine and Nitrosoureas in the Therapy of Malignant Gliomas: Update of Mechanisms, Drug Resistance and Therapeutic Implications

The genotoxic methylating agents temozolomide (TMZ) and procarbazine and the chloroethylating nitrosourea lomustine (CCNU) are part of the standard repertoire in the therapy of malignant gliomas (CNS WHO grade 3 and 4). This review describes the mechanisms of their cytotoxicity and cytostatic activity through apoptosis, necroptosis, drug-induced senescence, and autophagy, interaction of critical damage with radiation-induced lesions, mechanisms of glioblastoma resistance to alkylating agents, including the alkyltransferase MGMT, mismatch repair, DNA double-strand break repair and DNA damage responses, as well as IDH-1 and PARP-1. Cyclin-dependent kinase inhibitors such as regorafenib, synthetic lethality using PARP inhibitors, and alternative therapies including tumor-treating fields (TTF) and CUSP9v3 are discussed in the context of alkylating drug therapy and overcoming glioblastoma chemoresistance. Recent studies have revealed that senescence is the main trait induced by TMZ in glioblastoma cells, exhibiting hereupon the senescence-associated secretory phenotype (SASP). Strategies to eradicate therapy-induced senescence by means of senolytics as well as attenuating SASP by senomorphics are receiving increasing attention, with therapeutic implications to be discussed.

Rhizochalinin Exhibits Anticancer Activity and Synergizes with EGFR Inhibitors in Glioblastoma In Vitro Models

Rhizochalinin (Rhiz) is a recently discovered cytotoxic sphingolipid synthesized from the marine natural compound rhizochalin. Previously, Rhiz demonstrated high in vitro and in vivo efficacy in various cancer models. Here, we report Rhiz to be highly active in human glioblastoma cell lines as well as in patient-derived glioma-stem like neurosphere models. Rhiz counteracted glioblastoma cell proliferation by inducing apoptosis, G2/M-phase cell cycle arrest, and inhibition of autophagy. Proteomic profiling followed by bioinformatic analysis suggested suppression of the Akt pathway as one of the major biological effects of Rhiz. Suppression of Akt as well as IGF-1R and MEK1/2 kinase was confirmed in Rhiz-treated GBM cells. In addition, Rhiz pretreatment resulted in a more pronounced inhibitory effect of γ-irradiation on the growth of patient-derived glioma-spheres, an effect to which the Akt inhibition may also contribute decisively. In contrast, EGFR upregulation, observed in all GBM neurospheres under Rhiz treatment, was postulated to be a possible sign of incipient resistance. In line with this, combinational therapy with EGFR-targeted tyrosine kinase inhibitors synergistically increased the efficacy of Rhiz resulting in dramatic inhibition of GBM cell viability as well as a significant reduction of neurosphere size in the case of combination with lapatinib. Preliminary in vitro data generated using a parallel artificial membrane permeability (PAMPA) assay suggested that Rhiz cannot cross the blood brain barrier and therefore alternative drug delivery methods should be used in the further in vivo studies. In conclusion, Rhiz is a promising new candidate for the treatment of human glioblastoma, which should be further developed in combination with EGFR inhibitors.

Molecular and clonal evolution in vivo reveal a common pathway of distant relapse gliomas

The evolutionary trajectories of genomic alterations underlying distant recurrence in glioma remain largely unknown. To elucidate glioma evolution, we analyzed the evolutionary trajectories of matched pairs of primary tumors and relapse tumors or tumor in situ fluid (TISF) based on deep whole-genome sequencing data (ctDNA). We found that MMR gene mutations occurred in the late stage in IDH-mutant glioma during gene evolution, which activates multiple signaling pathways and significantly increases distant recurrence potential. The proneural subtype characterized by PDGFRA amplification was likely prone to hypermutation and distant recurrence following treatment. The classical and mesenchymal subtypes tended to progress locally through subclonal reconstruction, trunk genes transformation, and convergence evolution. EGFR and NOTCH signaling pathways and CDNK2A mutation play an important role in promoting tumor local progression. Glioma subtypes displayed distinct preferred evolutionary patterns. ClinicalTrials.gov, NCT05512325.

PD-L1 Expression in Pituitary Neuroendocrine Tumors/Pituitary Adenomas

BACKGROUND AND AIM

About a third of Pituitary Neuroendocrine Tumors (PitNETs) may show aggressive behavior. Many efforts have been performed for identifying possible predictive factors to early determine the future behavior of PitNETs. Programmed cell death ligand 1 (PD-L1) expression was associated with a more aggressive biology in different solid tumors, but its role in PitNET is not well-established yet. Our study aims to analyze PD-L1 expression in a surgical cohort of PitNETs to determine its association with radiological invasion and pathology findings, as well as with long-term recurrence rates.

METHODS

We performed a retrospective analysis in a series of 86 PitNETs. Clinical presentation and radiological features of the preoperative period were collected, as well as pathological data and follow-up data. The rate of PD-L1 expression was immunohistochemically evaluated and expressed as a tumor proportion score (TPS). We assessed its relationship with cavernous sinus invasion and Trouillas' classification as primary outcomes. Secondary outcomes included the TPS' relationship with histopathological markers of proliferation, hormonal expression, tumor size and long-term recurrence rates. We calculated the optimal cut-point for the primary outcomes while maximizing the product of the sensitivity and specificity and then we evaluated the significance of secondary outcomes with logistic regression analysis.

RESULTS

Eighty-six patients were included in the analysis; 50 cases were non-functional PitNETs. The TPS for PD-L1 showed a highly right-skewed distribution in our sample, as 30.2% of patients scored 0. Using Trouillas' classification, we found that "proliferative" cases have a significantly higher probability to express PD-L1 in more than 30% of tumor cells (OR: 5.78; CI 95%: 1.80-18.4). This same cut-point was also associated with p53 expression. A positive association was found between PD-L1 expression and GH expression (p = 0.001; OR: 5.44; CI 95%: 1.98-14.98), while an inverse relationship was found with FSH/LH expression (p = 0.014; OR = 0.27, CI 95%: 0.10-0.76). No association was found with CS invasion, tumor size, bone erosion or dura invasion. We could not find any association between PD-L1 expression and recurrence.

CONCLUSIONS

PD-L1 expression was associated with proliferative grades of Trouillas' classification and p53 expression. We also confirmed a higher expression of PD-L1 in somatotroph tumors. Larger studies are necessary to investigate the relationship between PD-L1 expression and aggressive behaviors.

Improved Pathologic response to chemoradiation in MGMT methylated locally advanced rectal cancer

BACKGROUND AND PURPOSE

With the growing interest in total neoadjuvant treatment for locally advanced rectal adenocarcinoma (LARC) there is an urgent unmet need to identify predictive markers of response to long-course neoadjuvant concurrent chemoradiotherapy (LCRT). O6-Methylguanine (O6-MG)-DNA-methyltransferase (MGMT) gene methylation has been associated in some malignancies with response to concurrent chemoradiotherapy. We attempted to find if pathologic response to LCRT was associated with MGMT promoter hypermethylation (MGMTh).

MATERIALS AND METHODS

Patients were identified with LARC, available pre-treatment biopsy specimens, and at least 1 year of follow-up who received LCRT followed by surgical resection within 6 months. Biopsies were tested for MGMTh using a Qiagen pyrosequencing kit (Catalog number 970061). The primary outcome of LCRT responsiveness was based on tumor regression grade (TRG), with grades of 0-1 considered to have excellent response and grades of 2-3 considered to be non-responders. Secondary outcomes included overall survival (OS) and recurrence free survival (RFS).

RESULTS

Of 96 patients who met inclusion criteria, 76 had samples which produced reliable assay results. MGMTh corresponded with higher grade and age of the biopsy specimen. The percentage of responders to LCRT was higher amongst the MGMTh patients than the MGMTn patients (60.0% vs 27.5%, p value = 0.0061). MGMTh was not significantly associated with improved OS (2-year OS of 96.0% vs 98.0%, p = 0.8102) but there was a trend for improved RFS (2-year RFS of 87.6% vs 74.2%, p = 0.0903).

CONCLUSION

Significantly greater tumor regression following LCRT was seen in MGMTh LARC. Methylation status may help identify good candidates for close observation without surgery following LCRT.

Pakistan National Guidelines for Pediatric High-Grade Gliomas

Pediatric high-grade glioma (pHGG) is highly malignant central nervous system tumor and constitute 10% of the pediatric gliomas. Effective treatment needs a functioning multi-disciplinary team including pediatric neuro oncologist, neurosurgeon, neuroradiologist, neuropathologist and radiation oncologist. Despite surgical resection, radiotherapy and chemotherapy, most HGG will recur resulting in early death. A significant proportion of HGG occurs in context of cancer predisposition syndromes like Constitutional Mismatch Repair Deficiency (CMMRD) also known as Biallelic Mismatch Repair Deficiency (bMMRD) characterized by high mutational burden. The incidence of HGG with CMMRD is one per million patients. bMMRD is caused by homozygous germline mutations in one of the four Mis Match Repair (MMR) genes (PMS2, MLH1, MSH2, and MSH6). The use of TMZ is now avoided in CMMRD related HGG due to its limited response and known ability to increase the accumulation of somatic mutations in these patients, increasing the risk of secondary tumors. HGG should be managed under the care of multidisciplinary team to receive optimum treatment. This is particularly important for low middle-income countries (LMIC) with limited resources like Pakistan.

Therapeutic HDAC inhibition in hypermutant diffuse intrinsic pontine glioma

Constitutional mismatch repair deficiency (CMMRD) is a cancer predisposition syndrome associated with the development of hypermutant pediatric high-grade glioma, and confers a poor prognosis. While therapeutic histone deacetylase (HDAC) inhibition of diffuse intrinsic pontine glioma (DIPG) has been reported; here, we use a clinically relevant biopsy-derived hypermutant DIPG model (PBT-24FH) and a CRISPR-Cas9 induced genetic model to evaluate the efficacy of HDAC inhibition against hypermutant DIPG. We screened PBT-24FH cells for sensitivity to a panel of HDAC inhibitors (HDACis) in vitro, identifying two HDACis associated with low nanomolar IC50s, quisinostat (27 nM) and romidepsin (2 nM). In vivo, quisinostat proved more efficacious, inducing near-complete tumor regression in a PBT-24FH flank model. RNA sequencing revealed significant quisinostat-driven changes in gene expression, including upregulation of neural and pro-inflammatory genes. To validate the observed potency of quisinostat in vivo against additional hypermutant DIPG models, we tested quisinostat in genetically-induced mismatch repair (MMR)-deficient DIPG flank tumors, demonstrating that loss of MMR function increases sensitivity to quisinostat in vivo. Here, we establish the preclinical efficacy of quisinostat against hypermutant DIPG, supporting further investigation of epigenetic targeting of hypermutant pediatric cancers with the potential for clinical translation. These findings support further investigation of HDAC inhibitors against pontine high-grade gliomas, beyond only those with histone mutations, as well as against other hypermutant central nervous system tumors.

macroH2A2 antagonizes epigenetic programs of stemness in glioblastoma

Self-renewal is a crucial property of glioblastoma cells that is enabled by the choreographed functions of chromatin regulators and transcription factors. Identifying targetable epigenetic mechanisms of self-renewal could therefore represent an important step toward developing effective treatments for this universally lethal cancer. Here we uncover an epigenetic axis of self-renewal mediated by the histone variant macroH2A2. With omics and functional assays deploying patient-derived in vitro and in vivo models, we show that macroH2A2 shapes chromatin accessibility at enhancer elements to antagonize transcriptional programs of self-renewal. macroH2A2 also sensitizes cells to small molecule-mediated cell death via activation of a viral mimicry response. Consistent with these results, our analyses of clinical cohorts indicate that high transcriptional levels of this histone variant are associated with better prognosis of high-grade glioma patients. Our results reveal a targetable epigenetic mechanism of self-renewal controlled by macroH2A2 and suggest additional treatment approaches for glioblastoma patients.

An overview of glioblastoma multiforme and temozolomide resistance: can LC-MS-based proteomics reveal the fundamental mechanism of temozolomide resistance?

Glioblastoma multiforme (GBM) is a primary type of lethal brain tumor. Over the last two decades, temozolomide (TMZ) has remained the primary chemotherapy for GBM. However, TMZ resistance in GBM constitutes an underlying factor contributing to high rates of mortality. Despite intense efforts to understand the mechanisms of therapeutic resistance, there is currently a poor understanding of the molecular processes of drug resistance. For TMZ, several mechanisms linked to therapeutic resistance have been proposed. In the past decade, significant progress in the field of mass spectrometry-based proteomics has been made. This review article discusses the molecular drivers of GBM, within the context of TMZ resistance with a particular emphasis on the potential benefits and insights of using global proteomic techniques.

Mechanical nanosurgery of chemoresistant glioblastoma using magnetically controlled carbon nanotubes

Glioblastoma (GBM) is the most common and aggressive primary brain cancer. Despite multimodal treatment including surgery, radiotherapy, and chemotherapy, median patient survival has remained at ~15 months for decades. This situation demands an outside-the-box treatment approach. Using magnetic carbon nanotubes (mCNTs) and precision magnetic field control, we report a mechanical approach to treat chemoresistant GBM. We show that GBM cells internalize mCNTs, the mobilization of which by rotating magnetic field results in cell death. Spatiotemporally controlled mobilization of intratumorally delivered mCNTs suppresses GBM growth in vivo. Functionalization of mCNTs with anti-CD44 antibody, which recognizes GBM cell surface-enriched antigen CD44, increases mCNT recognition of cancer cells, prolongs mCNT enrichment within the tumor, and enhances therapeutic efficacy. Using mouse models of GBM with upfront or therapy-induced resistance to temozolomide, we show that mCNT treatment is effective in treating chemoresistant GBM. Together, we establish mCNT-based mechanical nanosurgery as a treatment option for GBM.

Using comprehensive genomic and functional analyses for resolving genotype-phenotype mismatches in children with suspected CMMRD in Lebanon: an IRRDC study

Constitutional mismatch repair deficiency (CMMRD) is an aggressive and highly penetrant cancer predisposition syndrome. Because of its variable clinical presentation and phenotypical overlap with neurofibromatosis, timely diagnosis remains challenging, especially in countries with limited resources. Since current tests are either difficult to implement or interpret or both we used a novel and relatively inexpensive functional genomic assay (LOGIC) which has been recently reported to have high sensitivity and specificity in diagnosing CMMRD. Here we report the clinical and molecular characteristics of nine patients diagnosed with cancer and suspected to have CMMRD and highlight the challenges with variant interpretation and immunohistochemical analysis that led to an uncertain interpretation of genetic findings in 6 of the 9 patients. Using LOGIC, we were able to confirm the diagnosis of CMMRD in 7 and likely exclude it in 2 patients, resolving ambiguous result interpretation. LOGIC also enabled predictive testing of asymptomatic siblings for early diagnosis and implementation of surveillance. This study highlights the varied manifestations and practical limitations of current diagnostic criteria for CMMRD, and the importance of international collaboration for implementing robust and low-cost functional assays for resolving diagnostic challenges.

Genetic and pharmacological modulation of DNA mismatch repair heterogeneous tumors promotes immune surveillance

Patients affected by colorectal cancer (CRC) with DNA mismatch repair deficiency (MMRd), often respond to immune checkpoint blockade therapies, while those with mismatch repair-proficient (MMRp) tumors generally do not. Interestingly, a subset of MMRp CRCs contains variable fractions of MMRd cells, but it is unknown how their presence impacts immune surveillance. We asked whether modulation of the MMRd fraction in MMR heterogeneous tumors acts as an endogenous cancer vaccine by promoting immune surveillance. To test this hypothesis, we use isogenic MMRp (Mlh1^+/+) and MMRd (Mlh1^-/-) mouse CRC cells. MMRp/MMRd cells mixed at different ratios are injected in immunocompetent mice and tumor rejection is observed when at least 50% of cells are MMRd. To enrich the MMRd fraction, MMRp/MMRd tumors are treated with 6-thioguanine, which leads to tumor rejection. These results suggest that genetic and pharmacological modulation of the DNA mismatch repair machinery potentiate the immunogenicity of MMR heterogeneous tumors.

Potential risks associated with the use of ionizing radiation for imaging and treatment of colorectal cancer in Lynch syndrome patients

The aim of this review is to investigate the literature pertaining to the potential risks of low-dose ionizing radiation to Lynch syndrome patients by use of computed tomography (CT), either diagnostic CT colonography (CTC), standard staging CT or CT surveillance. Furthermore, this review explores the potential risks of using radiotherapy for treatment of rectal cancer in these patients. No data or longitudinal observational studies of the impact of radiation exposure on humans with Lynch syndrome were identified. Limited experimental studies utilizing cell lines and primary cells exposed to both low and high radiation doses have been carried out to help determine radio-sensitivity associated with DNA mismatch repair gene deficiency, the defining feature of Lynch syndrome. On balance, these studies suggest that mismatch repair deficient cells may be relatively radio-resistant (particularly for low dose rate exposures) with higher mutation rates, albeit no firm conclusions can be drawn. Mouse model studies, though, showed an increased risk of developing colorectal tumors in mismatch repair deficient mice exposed to radiation doses around 2 Gy. With appropriate ethical approval, further studies investigating radiation risks associated with CT imaging and radiotherapy relevant doses using cells/tissues derived from confirmed Lynch patients or genetically modified animal models are urgently required for future clinical guidance.

LncRNA as potential biomarker and therapeutic target in glioma

Glioma is the most frequent type of malignant tumor in the central nervous system, accounting for about 80% of primary malignant brain tumors, usually with a poor prognosis. A number of studies have been conducted on the molecular abnormalities in glioma to further understand its pathogenesis, and it has been found that lncRNAs (long non-coding RNA) play a key role in angiogenesis, tumor growth, infiltration and metastasis of glioma. Since specific lncRNAs have an aberrant expression in brain tissue, cerebrospinal fluid as well as peripheral circulation of glioma patients, they are considered to be potential biomarkers. This review focuses on the biological characteristics of lncRNA and its value as a biomarker for glioma diagnosis and prognosis. Moreover, in view of the role of lncRNAs in glioma proliferation and chemoradiotherapy resistance, we discussed the feasibility for lncRNAs as therapeutic targets. Finally, the persisting deficiencies and future prospects of using lncRNAs as clinical biomarkers and therapeutic targets were concluded.

Mismatch repair protein mutations in isocitrate dehydrogenase (IDH)-mutant astrocytoma and IDH-wild-type glioblastoma

Background

Mutations in mismatch repair (MMR) genes (MSH2, MSH6, MLH1, and PMS2) are associated with microsatellite instability and a hypermutator phenotype in numerous systemic cancers, and germline MMR mutations have been implicated in multi-organ tumor syndromes. In gliomas, MMR mutations can function as an adaptive response to alkylating chemotherapy, although there are well-documented cases of germline and sporadic mutations, with detrimental effects on patient survival.

Methods

The clinical, pathologic, and molecular features of 18 IDH-mutant astrocytomas and 20 IDH-wild-type glioblastomas with MMR mutations in the primary tumor were analyzed in comparison to 361 IDH-mutant and 906 IDH-wild-type tumors without MMR mutations. In addition, 12 IDH-mutant astrocytomas and 18 IDH-wild-type glioblastomas that developed MMR mutations between initial presentation and tumor recurrence were analyzed in comparison to 50 IDH-mutant and 104 IDH-wild-type cases that remained MMR-wild-type at recurrence.

Results

In both IDH-mutant astrocytoma and IDH-wild-type glioblastoma cohorts, the presence of MMR mutation in primary tumors was associated with significantly higher tumor mutation burden (TMB) (P < .0001); however, MMR mutations only resulted in worse overall survival in the IDH-mutant astrocytomas (P = .0069). In addition, gain of MMR mutation between the primary and recurrent surgical specimen occurred more frequently with temozolomide therapy (P = .0073), and resulted in a substantial increase in TMB (P < .0001), higher grade (P = .0119), and worse post-recurrence survival (P = .0022) in the IDH-mutant astrocytoma cohort.

Conclusions

These results suggest that whether present initially or in response to therapy, MMR mutations significantly affect TMB but appear to only influence the clinical outcome in IDH-mutant astrocytoma subsets.

BET protein inhibition sensitizes glioblastoma cells to temozolomide treatment by attenuating MGMT expression

Bromodomain and extra-terminal tail (BET) proteins have been identified as potential epigenetic targets in cancer, including glioblastoma. These epigenetic modifiers link the histone code to gene transcription that can be disrupted with small molecule BET inhibitors (BETi). With the aim of developing rational combination treatments for glioblastoma, we analyzed BETi-induced differential gene expression in glioblastoma derived-spheres, and identified 6 distinct response patterns. To uncover emerging actionable vulnerabilities that can be targeted with a second drug, we extracted the 169 significantly disturbed DNA Damage Response genes and inspected their response pattern. The most prominent candidate with consistent downregulation, was the O-6-methylguanine-DNA methyltransferase (MGMT) gene, a known resistance factor for alkylating agent therapy in glioblastoma. BETi not only reduced MGMT expression in GBM cells, but also inhibited its induction, typically observed upon temozolomide treatment. To determine the potential clinical relevance, we evaluated the specificity of the effect on MGMT expression and MGMT mediated treatment resistance to temozolomide. BETi-mediated attenuation of MGMT expression was associated with reduction of BRD4- and Pol II-binding at the MGMT promoter. On the functional level, we demonstrated that ectopic expression of MGMT under an unrelated promoter was not affected by BETi, while under the same conditions, pharmacologic inhibition of MGMT restored the sensitivity to temozolomide, reflected in an increased level of γ-H2AX, a proxy for DNA double-strand breaks. Importantly, expression of MSH6 and MSH2, which are required for sensitivity to unrepaired O6-methylguanine-lesions, was only briefly affected by BETi. Taken together, the addition of BET-inhibitors to the current standard of care, comprising temozolomide treatment, may sensitize the 50% of patients whose glioblastoma exert an unmethylated MGMT promoter.

Temozolomide in aggressive pituitary tumours and pituitary carcinomas

Survival for patients with aggressive pituitary tumours (APT) and pituitary carcinomas (PC) has significantly improved following the increasing use of temozolomide (TMZ) since the first reports of response in 2006. TMZ was established as first line chemotherapy for APT/PC in the 2018 ESE guidelines on the management of APT/PC. There is no controversy over its use as salvage therapy however there is increasing interest in exploring TMZ use earlier in the treatment algorithm for APT/PC. Overall response rates as reported in systematic reviews are around 40% but stable disease in another 25% illustrates the clinical effectiveness of TMZ. Response is higher among functional compared to non-functional tumours. Where maximal radiation thresholds have not been reached in a patient, combination radiotherapy and TMZ appears more effective. Whether combination TMZ and capecitabine (CAPTEM) offers increased benefit remains uncertain particularly given added toxicity. O6-methyl guanine DNA methyl transferase (MGMT) status is important in determining response to treatment, although examination via immunohistochemistry versus PCR-based promoter-methylation analysis remains somewhat controversial. Optimal duration of TMZ treatment has still not been determined although longer treatment courses have been associated with increased progression-free survival. Treatment options following disease progression after TMZ remain unclear but include a second course of TMZ, immunotherapy and targeted oncological agents such as bevacizumab and lapatinib as well as peptide receptor radionuclide treatment (PRRT). An experienced pituitary multidisciplinary team is essential to all management decisions in patients with APT/PC.

Modeling Therapy-Driven Evolution of Glioblastoma with Patient-Derived Xenografts

Adult-type diffusely infiltrating gliomas, of which glioblastoma is the most common and aggressive, almost always recur after treatment and are fatal. Improved understanding of therapy-driven tumor evolution and acquired therapy resistance in gliomas is essential for improving patient outcomes, yet the majority of the models currently used in preclinical research are of therapy-naïve tumors. Here, we describe the development of therapy-resistant IDH-wildtype glioblastoma patient-derived xenografts (PDX) through orthotopic engraftment of therapy naïve PDX in athymic nude mice, and repeated in vivo exposure to the therapeutic modalities most often used in treating glioblastoma patients: radiotherapy and temozolomide chemotherapy. Post-temozolomide PDX became enriched for C>T transition mutations, acquired inactivating mutations in DNA mismatch repair genes (especially MSH6), and developed hypermutation. Such post-temozolomide PDX were resistant to additional temozolomide (median survival decrease from 80 days in parental PDX to 42 days in a temozolomide-resistant derivative). However, temozolomide-resistant PDX were sensitive to lomustine (also known as CCNU), a nitrosourea which induces tumor cell apoptosis by a different mechanism than temozolomide. These PDX models mimic changes observed in recurrent GBM in patients, including critical features of therapy-driven tumor evolution. These models can therefore serve as valuable tools for improving our understanding and treatment of recurrent glioma.

The Role of PARP Inhibitors in Patients with Primary Malignant Central Nervous System Tumors

OPINION STATEMENT

Primary malignant central nervous (CNS) tumors are a devastating group of diseases with urgent need for improved treatment options. Surgery, radiation, and cytotoxic chemotherapy remain the primary standard treatment modalities, with molecularly targeted therapies having proven efficacy in only small subsets of cases. Poly(ADP-ribose) polymerase (PARP) inhibitors, which have had immense success in the treatment of extracranial cancers with homologous recombination deficiency (HRD), are emerging as a potential targeted treatment for various CNS tumors. Although few primary CNS tumors display canonical BRCA gene defects, preclinical evidence suggests that PARP inhibitors may benefit certain CNS tumors with functional HRD or elevated replication stress. In addition, other preclinical studies indicate that PARP inhibitors may synergize with standard therapies used for CNS tumors including radiation and alkylating agents and may prevent or overcome drug resistance. Thus far, initial clinical trials with early-generation PARP inhibitors, typically as monotherapy or in the absence of selective biomarkers, have shown limited efficacy. However, the scientific rationale remains promising, and many clinical trials are ongoing, including investigations of more CNS penetrant or more potent inhibitors and of combination therapy with immune checkpoint inhibitors. Early phase trials are also critically focusing on determining active drug CNS penetration and identifying biomarkers of therapy response. In this review, we will discuss the preclinical evidence supporting use of PARP inhibitors in primary CNS tumors and clinical trial results to date, highlighting ongoing trials and future directions in the field that may yield important findings and potentially impact the treatment of these devastating malignancies in the coming years.

The Effect of Β-Arrestin2 Overexpression Regarding Viability and Temozolomide Treatment in High-Grade Glioma Cells

The β-arrestins (β-arr) family are proteins that regulate the signaling and trafficking of various G protein-coupled receptors. Out of the four members, β-arr 1 and 2 have been proven as essential actors behind different processes that lead to the progression of cancer as cell proliferation, migration, invasion and metastasis. In addition to this, these proteins are also capable of transmitting anti-apoptotic signals, influence tumor growth rate and drug resistance. Several studies have demonstrated that β-arr 2 overexpression corelates with an impaired overall survival and also showed that it may mediate multidrug resistance in certain types of cancer. In the current study we analyzed the effect of β-arr 2 overexpression on proliferation and how it affects Temozolomide (TMZ) response on the CL2:6 High Grade Glioma (HGG) cell line. We observed contradictory results after transfection, with β-arr 2 overexpressing cells having a superior proliferation rate after 24 and 48h, when compared to untransfected cells, while the opposite was noted after 72h. In terms of response to TMZ, we observed a similar contradictory pattern with modest differences between doses being observed at 24h, while the smallest and largest doses in our experiment produced opposite effects after 48h and 72h. This further underscores the scarcity of information regarding the exact roles and the importance of β-arrs in the intrinsic mechanisms which govern cancer cells.

Lung cancer with brain metastases remaining in continuous complete remission due to pembrolizumab and temozolomide: a case report

Background

Immunotherapy has been shown to improve the overall survival (OS) in patients with advanced or metastatic non-small cell lung cancer (NSCLC) without driver gene mutations. However, monotherapy with immunotherapy alone or combined with chemotherapy in NSCLC patients with untreated brain metastases (BM) is still under debate. Data regarding treatment of BM with immunotherapy and temozolomide (TMZ) in patients with NSCLC is rare.

Case Presentation

A 60-year-old male due to cough and expectoration presented in our hospital. Chest computed tomography (CT), brain magnetic resonance imaging (MRI) and immunohistochemistry of a mediastinal lymph node biopsy were administered, he was diagnosed with stage IIIB lung adenocarcinoma. Without driver gene mutations, he was treated with platinum-based chemotherapy because he refused to accept concurrent radiation therapy (RT). Heavy cough companied with hemoptysis and chest CT scan both revealed progressive disease (PD) after 6 cycles of chemotherapy. Immunotherapy was consequently considered, while two metastatic lesions in the brain were confirmed after combined treatment of pembrolizumab with docetaxel. TMZ was administered in combination with pembrolizumab (200 mg, day 1). A new metastasis in the right occipital lobe was detected on a scan 1 month later, though the other 2 lesions continued to shrink. The treatment was continued, MRI and CT scans suggested complete response (CR) was achieved for both the BM and lung lesions after 3 cycles. Consolidation therapy with TMZ and pembrolizumab (100 mg) per month was considered for another 7 months. Maintenance monotherapy with pembrolizumab (100 mg) was selected because of his stable CR status. At 59 months since diagnosis, the patient remains alive, with CR for both the primary lesions and BM. The patient experienced slight numbness on each side of his feet. There was no occurrence of adverse effects greater than grade 3.

Conclusions

The data indicates that immunotherapy combined with TMZ for untreated BM in NSCLC patients maybe an efficient and safe decision making therapeutic choice. Despite the encouraging efficacy of the combination, it is an isolated case and the speculation of synergism need to be proved in further pharmacokinetic/pharmacodynamic studies even in large randomized controlled trials.

Impact of cancer evolution on immune surveillance and checkpoint inhibitor response

Intratumour heterogeneity (ITH) is pervasive across all cancers studied and may provide the evolving tumour multiple routes to escape immune surveillance. Immune checkpoint inhibitors (CPIs) are rapidly becoming standard of care for many cancers. Here, we discuss recent work investigating the influence of ITH on patient response to immune checkpoint inhibitor (CPI) therapy. At its simplest, ITH may confound the diagnostic accuracy of predictive biomarkers used to stratify patients for CPI therapy. Furthermore, ITH is fuelled by mechanisms of genetic instability that can both engage immune surveillance and drive immune evasion. A greater appreciation of the interplay between ITH and the immune system may hold the key to increasing the proportion of patients experiencing durable responses from CPI therapy.

Immunotherapy for Aggressive and Metastatic Pituitary Neuroendocrine Tumors (PitNETs): State-of-the Art

Background: Aggressive and metastatic PitNETs are challenging conditions. Immune checkpoint inhibitors (ICIs) are currently considered in cases resistant to temozolomide (TMZ). However, clinical experience is essentially limited to case reports, with variable outcomes. Material and Methods: The effects of ICIs on 12 aggressive/metastatic PitNETs from the literature were reviewed and analyzed according to tumor characteristics, with the additional description of a silent-Pit1 metastatic tumor responding to pembrolizumab. Results: Most cases were metastatic (10/13: 6 corticotroph, 3 lactotroph, 1 silent Pit1); 3 were aggressive (2 corticotroph, 1 lactotroph). ICIS was used either as monotherapy or in combination. At last follow-up on ICI, a complete response (CR) was present in 3 cases and a partial response (PR) in 2 cases (4/5 metastatic). One sustained stable disease (SD) was reported. Progressive disease (PD) was observed in 7 cases, 3 of them after initial SD (n = 1) or PR (n = 3), with 2 reported deaths. PDL1 expression was studied in 10 cases and was high (>95%) in 2 Pit1-derived metastatic PitNETs (1 CR and 1 remarkable PR) but absent/low (<1%) in the remaining cases (including 1 CP and 2 PR). Elevated tumor mutation burden could be informative in corticotroph PitNETs, especially in mismatch repair-deficient tumors. Conclusion: Significant benefits from ICIs were documented in about half of TMZ-resistant PitNETS. High PDL1 expression was associated with remarkable responses but may be dispensable. Based on their acceptable tolerance and awaiting recognized predictors of response, ICIs may be considered a valuable option for such patients.

Complete Response of a Patient With a Mismatch Repair Deficient Aggressive Pituitary Adenoma to Immune Checkpoint Inhibitor Therapy: A Case Report

BACKGROUND AND IMPORTANCE

Aggressive pituitary adenomas (APAs) are pituitary tumors that are refractory to standard treatments and carry a poor prognosis. Current treatment guidelines are not standardized but combine surgical resection, radiation therapy, and chemotherapy. Temozolomide is the only chemotherapeutic agent with documented effectiveness and is recommended for APA in European Society of Endocrinology clinical guidelines.

CLINICAL PRESENTATION

A 57-year-old man presented with visual deterioration and bitemporal hemianopsia. MRI of the brain demonstrated a sellar mass suspected to be pituitary macroadenoma with displacement of the stalk and optic nerve impingement. The patient underwent stereotactic endoscopic transsphenoidal resection of the mass. Postoperative MRI demonstrated gross total resection. Pathology revealed a sparsely granulated corticotroph adenoma with malignant transformation. Immunohistochemistry showed loss of expression of MLH1 and PMS2 in the tumor cells. Proton therapy was recommended given an elevated Ki67 index and p53 positivity. Before radiotherapy, there was no radiographic evidence of residual tumor. Temozolomide therapy was initiated after surveillance MRI showed recurrence at 16 months postoperatively. However, MRI demonstrated marked progression after 3 cycles. Next-generation sequencing using the MSK-IMPACT platform identified somatic mutations in MLH1 Y548lfs*9 and TP53 R337C . Immunotherapy with ipilimumab/nivolumab was initiated, and MRI demonstrated no residual tumor burden 34 months postoperatively.

CONCLUSION

APA is a tumor with frequent recurrence and a short median expected length of survival. Here, we demonstrate the utility of immunotherapy in a single case report of APA, with complete resolution of recurrent APA and improved survival compared with life expectancy.

Overcoming Temozolomide Resistance in Glioblastoma via Enhanced NAD+ Bioavailability and Inhibition of Poly-ADP-Ribose Glycohydrolase

Glioblastoma multiforme (GBM) is an incurable brain cancer with an average survival of approximately 15 months. Temozolomide (TMZ) is a DNA alkylating agent for the treatment of GBM. However, at least 50% of the patients treated with TMZ show poor response, primarily due to elevated expression of the repair protein O6-methylguanine-DNA methyltransferase (MGMT) or due to defects in the mismatch repair (MMR) pathway. These resistance mechanisms are either somatic or arise in response to treatment, highlighting the need to uncover treatments to overcome resistance. We found that administration of the NAD+ precursor dihydronicotinamide riboside (NRH) to raise cellular NAD+ levels combined with PARG inhibition (PARGi) triggers hyperaccumulation of poly(ADP-ribose) (PAR), resulting from both DNA damage-induced and replication-stress-induced PARP1 activation. Here, we show that the NRH/PARGi combination enhances the cytotoxicity of TMZ. Specifically, NRH rapidly increases NAD+ levels in both TMZ-sensitive and TMZ-resistant GBM-derived cells and enhances the accumulation of PAR following TMZ treatment. Furthermore, NRH promotes hyperaccumulation of PAR in the presence of TMZ and PARGi. This combination strongly suppresses the cell growth of GBM cells depleted of MSH6 or cells expressing MGMT, suggesting that this regimen may improve the efficacy of TMZ to overcome treatment resistance in GBM.