Minimally cytotoxic doses of temozolomide produce radiosensitization in human glioblastoma cells regardless of MGMT expression

DNA Adducts in Cancer Chemotherapy

DNA adducting drugs, including alkylating agents and platinum-containing drugs, are prominent in cancer chemotherapy. Their mechanisms of action involve direct interaction with DNA, resulting in the formation of DNA addition products known as DNA adducts. While these adducts are well-accepted to induce cancer cell death, understanding of their specific chemotypes and their role in drug therapy response remain limited. This perspective aims to address this gap by investigating the metabolic activation and chemical characterization of DNA adducts formed by the U.S. FDA-approved drugs. Moreover, clinical studies on DNA adducts as potential biomarkers for predicting patient responses to drug efficacy are examined. The overarching goal is to engage the interest of medicinal chemists and stimulate further research into the use of DNA adducts as biomarkers for guiding personalized cancer treatment.

Micro-Vessels-Like 3D Scaffolds for Studying the Proton Radiobiology of Glioblastoma-Endothelial Cells Co-Culture Models

Glioblastoma (GBM) is a devastating cancer of the brain with an extremely poor prognosis. While X-ray radiotherapy and chemotherapy remain the current standard, proton beam therapy is an appealing alternative as protons can damage cancer cells while sparing the surrounding healthy tissue. However, the effects of protons on in vitro GBM models at the cellular level, especially when co-cultured with endothelial cells, the building blocks of brain micro-vessels, are still unexplored. In this work, novel 3D-engineered scaffolds inspired by the geometry of brain microvasculature are designed, where GBM cells cluster and proliferate. The architectures are fabricated by two-photon polymerization (2PP), pre-cultured with endothelial cells (HUVECs), and then cultured with a human GBM cell line (U251). The micro-vessel structures enable GBM in vivo-like morphologies, and the results show a higher DNA double-strand breakage in GBM monoculture samples when compared to the U251/HUVECs co-culture, with cells in 2D featuring a larger number of DNA damage foci when compared to cells in 3D. The discrepancy in terms of proton radiation response indicates a difference in the radioresistance of the GBM cells mediated by the presence of HUVECs and the possible induction of stemness features that contribute to radioresistance and improved DNA repair.

Somatostatin Receptor Subtype-2 Targeting System for Specific Delivery of Temozolomide

Temozolomide (TMZ) is a DNA alkylating agent that produces objective responses in patients with neuroendocrine tumors (NETs) when the DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) is inactivated. At high doses, TMZ therapy exhausts MGMT activity but also produces dose-limiting toxicities. To reduce off-target effects, we converted the clinically approved radiotracer 68Ga-DOTA-TOC into a peptide-drug conjugate (PDC) for targeted delivery of TMZ to somatostatin receptor subtype-2 (SSTR2)-positive tumor cells. We used an integrated radiolabeling strategy for direct quantitative assessment of receptor binding, pharmacokinetics, and tissue biodistribution. In vitro studies revealed selective binding to SSTR2-positive cells with high affinity (5.98 ± 0.96 nmol/L), internalization, receptor-dependent DNA damage, cytotoxicity, and MGMT depletion. Imaging and biodistribution analysis showed preferential accumulation of the PDC in receptor-positive tumors and high renal clearance. This study identified a trackable SSTR2-targeting system for TMZ delivery and utilizes a modular design that could be broadly applied in PDC development.

Reduced YAP1 and FOLR1 in gliomas predict better response to chemotherapeutics

Gliomas harbouring mutations in IDH1 (isocitrate dehydrogenase 1) are characterized by greater sensitivity to chemotherapeutics. These mutants also exhibit diminished levels of transcriptional coactivator YAP1 (yes-associated protein 1). Enhanced DNA damage in IDH1 mutant cells, as evidenced by γH2AX formation (phosphorylation of histone variant H2A.X) and ATM (serine/threonine kinase; ataxia telangiectasia mutated) phosphorylation, was accompanied by reduced FOLR1 (folate receptor 1) expression. Diminished FOLR1, concomitant with heightened γH2AX levels, was also observed in patient-derived IDH1 mutant glioma tissues. Chromatin immunoprecipitation, overexpression of mutant YAP1, and treatment with YAP1-TEAD (TEA domain transcription factors) complex inhibitor verteporfin demonstrated regulation of FOLR1 expression by YAP1 and its partner transcription factor TEAD2. TCGA (The Cancer Genome Atlas) data analysis demonstrated better patient survival with reduced FOLR1 expression. Depletion of FOLR1 rendered IDH1 wild-type gliomas more susceptible to temozolomide-mediated death. Despite heightened DNA damage, IDH1 mutants exhibited reduced levels of IL6 (interleukin 6) and IL8 (interleukin 8) - pro-inflammatory cytokines known to be associated with persistent DNA damage. While both FOLR1 and YAP1 influenced DNA damage, only YAP1 was involved in regulating IL6 and IL8. ESTIMATE and CIBERSORTx analyses revealed the association between YAP1 expression and immune cell infiltration in gliomas. By identifying the influence of YAP1-FOLR1 link in DNA damage, our findings suggest that simultaneous depletion of both could amplify the potency of DNA damaging agents, while concomitantly reducing the release of inflammatory mediators and potentially affecting immune modulation. This study also highlights the novel role of FOLR1 as a probable prognostic marker in gliomas, predicting responsiveness to temozolomide and other DNA damaging agents.

Investigating the effects of arginine methylation inhibitors on microdissected brain tumour biopsies maintained in a miniaturised perfusion system

Arginine methylation is a post-translational modification that consists of the transfer of one or two methyl (CH3) groups to arginine residues in proteins. Several types of arginine methylation occur, namely monomethylation, symmetric dimethylation and asymmetric dimethylation, which are catalysed by different protein arginine methyltransferases (PRMTs). Inhibitors of PRMTs have recently entered clinical trials to target several types of cancer, including gliomas (NCT04089449). People with glioblastoma (GBM), the most aggressive form of brain tumour, are among those with the poorest quality of life and likelihood of survival of anyone diagnosed with cancer. There is currently a lack of (pre)clinical research on the possible application of PRMT inhibitors to target brain tumours. Here, we set out to investigate the effects of clinically-relevant PRMT inhibitors on GBM biopsies. We present a new, low-cost, easy to fabricate perfusion device that can maintain GBM tissue in a viable condition for at least eight days post-surgical resection. The miniaturised perfusion device enables the treatment of GBM tissue with PRMT inhibitors ex vivo, and we observed a two-fold increase in apoptosis in treated samples compared to parallel control experiments. Mechanistically, we show thousands of differentially expressed genes after treatment, and changes in the type of arginine methylation of the RNA binding protein FUS that are consistent with hundreds of differential gene splicing events. This is the first time that cross-talk between different types of arginine methylation has been observed in clinical samples after treatment with PRMT inhibitors.

Temozolomide – Just a Radiosensitizer?

Radiation concomitant with the DNA methylating drug temozolomide (TMZ) is the gold standard in the treatment of glioblastoma. In this adjuvant setting, TMZ is regarded to be a radiation sensitizer. However, similar to ionising radiation, TMZ induces DNA double-strand breaks and is itself a potent trigger of apoptosis, cellular senescence and autophagy, suggesting that radiation and TMZ act independently. Although cell culture experiments yielded heterogeneous results, some data indicate that the cytotoxic effect of radiation was only enhanced when TMZ was given before radiation treatment. Based on the molecular mechanism of action of TMZ, the importance of specific TMZ and radiation-induced DNA lesions, their repair as well as their interactions, possible scenarios for an additive or synergistic effect of TMZ and radiation are discussed, and suggestions for an optimal timing of radio-chemical treatments are proposed.

Evaluation of Proton-Induced DNA Damage in 3D-Engineered Glioblastoma Microenvironments

Glioblastoma (GBM) is a devastating cancer of the brain with an extremely poor prognosis. For this reason, besides clinical and preclinical studies, novel in vitro models for the assessment of cancer response to drugs and radiation are being developed. In such context, three-dimensional (3D)-engineered cellular microenvironments, compared to unrealistic two-dimensional (2D) monolayer cell culture, provide a model closer to the in vivo configuration. Concerning cancer treatment, while X-ray radiotherapy and chemotherapy remain the current standard, proton beam therapy is an appealing alternative as protons can be efficiently targeted to destroy cancer cells while sparing the surrounding healthy tissue. However, despite the treatment's compelling biological and medical rationale, little is known about the effects of protons on GBM at the cellular level. In this work, we designed novel 3D-engineered scaffolds inspired by the geometry of brain blood vessels, which cover a vital role in the colonization mechanisms of GBM cells. The architectures were fabricated by two-photon polymerization (2PP), cultured with U-251 GBM cells and integrated for the first time in the context of proton radiation experiments to assess their response to treatment. We employed Gamma H2A.X as a fluorescent biomarker to identify the DNA damage induced in the cells by proton beams. The results show a higher DNA double-strand breakage in 2D cell monolayers as compared to cells cultured in 3D. The discrepancy in terms of proton radiation response could indicate a difference in the radioresistance of the GBM cells or in the rate of repair kinetics between 2D cell monolayers and 3D cell networks. Thus, these biomimetic-engineered 3D scaffolds pave the way for the realization of a benchmark tool that can be used to routinely assess the effects of proton therapy on 3D GBM cell networks and other types of cancer cells.

Advanced MRI Protocols to Discriminate Glioma From Treatment Effects: State of the Art and Future Directions

In the follow-up treatment of high-grade gliomas (HGGs), differentiating true tumor progression from treatment-related effects, such as pseudoprogression and radiation necrosis, presents an ongoing clinical challenge. Conventional MRI with and without intravenous contrast serves as the clinical benchmark for the posttreatment surveillance imaging of HGG. However, many advanced imaging techniques have shown promise in helping better delineate the findings in indeterminate scenarios, as posttreatment effects can often mimic true tumor progression on conventional imaging. These challenges are further confounded by the histologic admixture that can commonly occur between tumor growth and treatment-related effects within the posttreatment bed. This review discusses the current practices in the surveillance imaging of HGG and the role of advanced imaging techniques, including perfusion MRI and metabolic MRI.

Double-Strand Breaks: when DNA Repair Events Accidentally Meet

The cellular response to alkylation damage is complex, involving multiple DNA repair pathways and checkpoint proteins, depending on the DNA lesion, the cell type, and the cellular proliferation state. The repair of and response to O-alkylation damage, primarily O⁶-methylguaine DNA adducts (O⁶-mG), is the purview of O⁶-methylguanine-DNA methyltransferase (MGMT). Alternatively, this lesion, if left un-repaired, induces replication-dependent formation of the O⁶-mG:T mis-pair and recognition of this mis-pair by the post-replication mismatch DNA repair pathway (MMR). Two models have been suggested to account for MMR and O⁶-mG DNA lesion dependent formation of DNA double-strand breaks (DSBs) and the resulting cytotoxicity - futile cycling and direct DNA damage signaling. While there have been hints at crosstalk between the MMR and base excision repair (BER) pathways, clear mechanistic evidence for such pathway coordination in the formation of DSBs has remained elusive. However, using a novel protein capture approach, Fuchs and colleagues have demonstrated that DSBs result from an encounter between MMR-induced gaps initiated at alkylation induced O⁶-mG:C sites and BER-induced nicks at nearby N-alkylation adducts in the opposite strand. The accidental encounter between these two repair events is causal in the formation of DSBs and the resulting cellular response, documenting a third model to account for O⁶-mG induced cell death in non-replicating cells. This graphical review highlights the details of this Repair Accident model, as compared to current models, and we discuss potential strategies to improve clinical use of alkylating agents such as temozolomide, that can be inferred from the Repair Accident model.

The Phosphorylated Form of the Histone H2AX (γH2AX) in the Brain from Embryonic Life to Old Age

The γ phosphorylated form of the histone H2AX (γH2AX) was described more than 40 years ago and it was demonstrated that phosphorylation of H2AX was one of the first cellular responses to DNA damage. Since then, γH2AX has been implicated in diverse cellular functions in normal and pathological cells. In the first part of this review, we will briefly describe the intervention of H2AX in the DNA damage response (DDR) and its role in some pivotal cellular events, such as regulation of cell cycle checkpoints, genomic instability, cell growth, mitosis, embryogenesis, and apoptosis. Then, in the main part of this contribution, we will discuss the involvement of γH2AX in the normal and pathological central nervous system, with particular attention to the differences in the DDR between immature and mature neurons, and to the significance of H2AX phosphorylation in neurogenesis and neuronal cell death. The emerging picture is that H2AX is a pleiotropic molecule with an array of yet not fully understood functions in the brain, from embryonic life to old age.

Crosstalk between repair pathways elicits double-strand breaks in alkylated DNA and implications for the action of temozolomide

Temozolomide (TMZ), a DNA methylating agent, is the primary chemotherapeutic drug used in glioblastoma treatment. TMZ induces mostly N-alkylation adducts (N7-methylguanine and N3-methyladenine) and some O⁶-methylguanine (O⁶mG) adducts. Current models propose that during DNA replication, thymine is incorporated across from O⁶mG, promoting a futile cycle of mismatch repair (MMR) that leads to DNA double-strand breaks (DSBs). To revisit the mechanism of O⁶mG processing, we reacted plasmid DNA with N-methyl-N-nitrosourea (MNU), a temozolomide mimic, and incubated it in Xenopus egg-derived extracts. We have shown that in this system, MMR proteins are enriched on MNU-treated DNA and we observed robust, MMR-dependent, repair synthesis. Our evidence also suggests that MMR, initiated at O⁶mG:C sites, is strongly stimulated in cis by repair processing of other lesions, such as N-alkylation adducts. Importantly, MNU-treated plasmids display DSBs in extracts, the frequency of which increases linearly with the square of alkylation dose. We suggest that DSBs result from two independent repair processes, one involving MMR at O⁶mG:C sites and the other involving base excision repair acting at a nearby N-alkylation adduct. We propose a new, replication-independent mechanism of action of TMZ, which operates in addition to the well-studied cell cycle-dependent mode of action.

Auger electron therapy of glioblastoma using [125I]5-iodo-2'-deoxyuridine and concomitant chemotherapy - Evaluation of a potential treatment strategy

INTRODUCTION

Treatment of glioblastomas (GBM) using the Auger electron emitting compound [¹²⁵I]5-Iodo-2'-deoxyuridine ([¹²⁵I]I-UdR), combined with the thymidylate synthase inhibitor methotrexate (MTX) and concomitant chemotherapy with temozolomide (TMZ) has recently shown very promising therapeutic effects in vitro and in vivo in animals. The aim of the current study was to investigate if the therapeutic effects of this multimodal treatment strategy could be further increased by the thymidylate synthase inhibitor, 5-fluoro-2'-deoxyuridine (F-UdR), in comparison to MTX, and if the co-treatment should be given in a neoadjuvant or adjuvant setting.

METHODS

A patient-derived GBM cancer stem cell (CSC)-enriched cell line, grown as neurospheres, was employed to evaluate DNA-incorporation of [¹²⁵I]I-UdR, determined by a DNA precipitation assay, using either pre-treatment or co-treatment with MTX or F-UdR. The therapeutic effects in the CSC-enriched cell line after exposure to various combinations of MTX, F-UdR, TMZ and [¹²⁵I]I-UdR were also investigated by a CellTiter-Blue assay.

RESULTS

The highest general increase in [¹²⁵I]I-UdR incorporation was observed with F-UdR co-treatment, which resulted in approx. 2.5-fold increase in the DNA-associated activity. Also the cell viability was significantly decreased when F-UdR was combined with [¹²⁵I]I-UdR compared to [¹²⁵I]I-UdR alone at all activity concentrations tested. MTX was redundant when combined with 400 and 500 Bq/ml [¹²⁵I]I-UdR. TMZ was effective in combination with either [¹²⁵I]I-UdR alone or with both thymidylate synthase inhibitors combined with 50-100 Bq/ml [¹²⁵I]I-UdR.

CONCLUSIONS

Overall, our study revealed a higher incorporation and therapeutic effect of [¹²⁵I]I-UdR when GBM cells were co-treated with F-UdR compared to MTX. The therapeutic effects were further increased when TMZ was combined with [¹²⁵I]I-UdR in combination with the thymidylate synthase inhibitors.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

Auger electron therapy in combination with thymidylate synthase inhibition and concomitant chemotherapy has the potential to become a future therapeutic treatment option for patients with glioblastoma.

siRNA nanoparticle suppresses drug-resistant gene and prolongs survival in an orthotopic glioblastoma xenograft mouse model

Temozolomide (TMZ) is the standard of care chemotherapy drug for treating glioblastomas (GBMs), the most aggressive cancer that affects people of all ages. However, its therapeutic efficacy is limited by the drug resistance mediated by a DNA repair protein, O⁶-methylguanine-DNA methyltransferase (MGMT), which eliminates the TMZ-induced DNA lesions. Here we report the development of an iron oxide nanoparticle (NP) system for targeted delivery of siRNAs to suppress the TMZ-resistance gene (MGMT). We show that our NP is able to overcome biological barriers, bind specifically to tumor cells, and reduce MGMT expression in tumors of mice bearing orthotopic GBM serially-passaged patient-derived xenografts. The treatment with sequential administration of this NP and TMZ resulted in increased apoptosis of GBM stem-like cells, reduced tumor growth, and significantly-prolonged survival as compared to mice treated with TMZ alone. This study introduces an approach that holds great promise to improve the outcomes of GBM patients.

Pimozide Suppresses the Growth of Brain Tumors by Targeting STAT3-Mediated Autophagy

Brain tumors are considered as one of the most aggressive and incurable forms of cancer. The majority of the patients with brain tumors have a median survival rate of 12%. Brain tumors are lethal despite the availability of advanced treatment options such as surgical removal, chemotherapy, and radiotherapy. In this study, we have evaluated the anti-cancer effects of pimozide, which is a neuroleptic drug used for the treatment of schizophrenia and chronic psychosis. Pimozide significantly reduced the proliferation of U-87MG, Daoy, GBM 28, and U-251MG brain cancer cell lines by inducing apoptosis with IC₅₀ (Inhibitory concentration 50) ranging from 12 to 16 μM after 48 h of treatment. Our Western blotting analysis indicated that pimozide suppressed the phosphorylation of STAT3 at Tyr705 and Src at Tyr416, and it inhibited the expression of anti-apoptotic markers c-Myc, Mcl-1, and Bcl-2. Significant autophagy induction was observed with pimozide treatment. LC3B, Beclin-1, and ATG5 up-regulation along with autolysosome formation confirmed the induction of autophagy with pimozide treatment. Inhibiting autophagy using 3-methyladenine or LC3B siRNA significantly blocked the apoptosis-inducing effects of pimozide, suggesting that pimozide mediated its apoptotic effects by inducing autophagy. Oral administration of 25 mg/kg pimozide suppressed the intracranially implanted U-87MG tumor growth by 45% in athymic nude mice. The chronic administration of pimozide showed no general signs of toxicity, and the behavioral activity of the mice remained unchanged. Taken together, these results indicate that pimozide inhibits the growth of brain cancer by autophagy-mediated apoptosis.

Developing a clinically relevant radiosensitizer for temozolomide-resistant gliomas

The prognosis for patients with glioblastoma (GB) remains grim. Concurrent temozolomide (TMZ) radiation—the cornerstone of glioma control—extends the overall median survival of GB patients by only a few months over radiotherapy alone. While these survival gains could be partly attributed to radiosensitization, this benefit is greatly minimized in tumors expressing O⁶-methylguanine DNA methyltransferase (MGMT), which specifically reverses O⁶-methylguanine lesions. Theoretically, non-O⁶-methylguanine lesions (i.e., the N-methylpurine adducts), which represent up to 90% of TMZ-generated DNA adducts, could also contribute to radiosensitization. Unfortunately, at concentrations attainable in clinical practice, the alkylation capacity of TMZ cannot overwhelm the repair of N-methylpurine adducts to efficiently exploit these lesions. The current therapeutic application of TMZ therefore faces two main obstacles: (i) the stochastic presence of MGMT and (ii) a blunted radiosensitization potential at physiologic concentrations. To circumvent these limitations, we are developing a novel molecule called NEO212—a derivatization of TMZ generated by coupling TMZ to perillyl alcohol. Based on gas chromatography/mass spectrometry and high-performance liquid chromatography analyses, we determined that NEO212 had greater tumor cell uptake than TMZ. In mouse models, NEO212 was more efficient than TMZ at crossing the blood-brain barrier, preferentially accumulating in tumoral over normal brain tissue. Moreover, in vitro analyses with GB cell lines, including TMZ-resistant isogenic variants, revealed more potent cytotoxic and radiosensitizing activities for NEO212 at physiologic concentrations. Mechanistically, these advantages of NEO212 over TMZ could be attributed to its enhanced tumor uptake presumably leading to more extensive DNA alkylation at equivalent dosages which, ultimately, allows for N-methylpurine lesions to be better exploited for radiosensitization. This effect cannot be achieved with TMZ at clinically relevant concentrations and is independent of MGMT. Our findings establish NEO212 as a superior radiosensitizer and a potentially better alternative to TMZ for newly diagnosed GB patients, irrespective of their MGMT status.

Purine metabolism regulates DNA repair and therapy resistance in glioblastoma

Intratumoral genomic heterogeneity in glioblastoma (GBM) is a barrier to overcoming therapy resistance. Treatments that are effective independent of genotype are urgently needed. By correlating intracellular metabolite levels with radiation resistance across dozens of genomically-distinct models of GBM, we find that purine metabolites, especially guanylates, strongly correlate with radiation resistance. Inhibiting GTP synthesis radiosensitizes GBM cells and patient-derived neurospheres by impairing DNA repair. Likewise, administration of exogenous purine nucleosides protects sensitive GBM models from radiation by promoting DNA repair. Neither modulating pyrimidine metabolism nor purine salvage has similar effects. An FDA-approved inhibitor of GTP synthesis potentiates the effects of radiation in flank and orthotopic patient-derived xenograft models of GBM. High expression of the rate-limiting enzyme of de novo GTP synthesis is associated with shorter survival in GBM patients. These findings indicate that inhibiting purine synthesis may be a promising strategy to overcome therapy resistance in this genomically heterogeneous disease.

Targeting genotype-independent abnormalities may overcome therapy resistance in glioblastoma despite intratumoral genomic heterogeneity. Here, the authors show that glioblastoma radiation resistance is promoted by purine metabolism and can be overcome by inhibitors of purine synthesis.

On the Critical Issues in Temozolomide Research in Glioblastoma: Clinically Relevant Concentrations and MGMT-independent Resistance

The current standard first-line treatment for adult patients with newly diagnosed glioblastoma includes concurrent radiotherapy and daily oral temozolomide (TMZ), followed by adjuvant TMZ. As a prodrug, TMZ undergoes spontaneous hydrolysis generating a methylating agent. O⁶-methylguanine is considered the most preponderant toxic damage mechanism at therapeutically relevant TMZ doses, whereas MGMT, which encodes the O⁶-methylguanine-DNA methyltransferase DNA repair enzyme, is the most relevant resistance mechanism. Speculations on clinically relevant TMZ concentrations, cytotoxic and cytostatic effects of TMZ, and resistance mechanisms exist in the literature. Here, we raise the following principal issues: What are the clinically relevant TMZ concentrations in glioma patients, and which TMZ-induced molecular lesion(s) and corresponding resistance mechanism(s) are important for TMZ therapeutic effects at clinically relevant concentrations? According to clinical data from patients with glioblastoma, the mean peak TMZ concentrations in the peritumoral tissue might be much lower (around 5 µM) than usually used in in vitro research, and may represent only 20% of systemic drug levels. According to in vitro reports, single-dose TMZ at concentrations around 5 µM have minimal, if any, effect on apoptosis and/or senescence of glioblastoma cell lines. However, the clinically relevant concentrations of TMZ are sufficient to radiosensitize both MGMT-positive and -negative cell lines in vitro. It is speculated that a single DNA repair protein, MGMT, is highly efficient in protecting cells against TMZ toxicity. However, an endogenous level of MGMT protein expression is not universally correlated with TMZ responsiveness, and MGMT-independent mechanisms of TMZ resistance exist.

Afatinib and Temozolomide combination inhibits tumorigenesis by targeting EGFRvIII-cMet signaling in glioblastoma cells

Background

Glioblastoma (GBM) is an aggressive brain tumor with universal recurrence and poor prognosis. The recurrence is largely driven by chemoradiation resistant cancer stem cells (CSCs). Epidermal growth factor receptor (EGFR) and its mutant EGFRvIII are amplified in ~ 60% and ~ 30% of GBM patients, respectively; however, therapies targeting EGFR have failed to improve disease outcome. EGFRvIII-mediated cross-activation of tyrosine kinase receptor, cMET, regulates GBM CSC maintenance and promote tumor recurrence. Here, we evaluated the efficacy of pan-EGFR inhibitor afatinib and Temozolomide (TMZ) combination on GBM in vitro and in vivo.

Methods

We analyzed the effect of afatinib and temozolomide (TMZ) combination on GBM cells U87MG and U251 engineered to express wild type (WT) EGFR, EGFRvIII or EGFRvIII dead kinase, CSCs isolated from U87 and U87EGFRvIII in vitro. The therapeutic utility of the drug combination was investigated on tumor growth and progression using intracranially injected U87EGFRvIII GBM xenografts.

Results

Afatinib and TMZ combination synergistically inhibited the proliferation, clonogenic survival, motility, invasion and induced senescence of GBM cells compared to monotherapy. Mechanistically, afatinib decreased U87EGFRvIII GBM cell proliferation and motility/invasion by inhibiting EGFRvIII/AKT, EGFRvIII/JAK2/STAT3, and focal adhesion kinase (FAK) signaling pathways respectively. Interestingly, afatinib specifically inhibited EGFRvIII-cMET crosstalk in CSCs, resulting in decreased expression of Nanog and Oct3/4, and in combination with TMZ significantly decreased their self-renewal property in vitro. More interestingly, afatinib and TMZ combination significantly decreased the xenograft growth and progression compared to single drug alone.

Conclusion

Our study demonstrated significant inhibition of GBM tumorigenicity, CSC maintenance in vitro, and delayed tumor growth and progression in vivo by combination of afatinib and TMZ. Our results warrant evaluation of this drug combination in EGFR and EGFRvIII amplified GBM patients.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1264-2) contains supplementary material, which is available to authorized users.

Sensitization of Cancer Cells to Radiation and Topoisomerase I Inhibitor Camptothecin Using Inhibitors of PARP and Other Signaling Molecules

Radiation and certain anticancer drugs damage DNA, resulting in apoptosis induction in cancer cells. Currently, the major limitations on the efficacy of such therapies are development of resistance and adverse side effects. Sensitization is an important strategy for increasing therapeutic efficacy while minimizing adverse effects. In this manuscript, we review possible sensitization strategies for radiation and anticancer drugs that cause DNA damage, focusing especially on modulation of damage repair pathways and the associated reactions.

The clinical value of patient-derived glioblastoma tumorspheres in predicting treatment response

Background

Advances from glioma stemlike cell (GSC) research, though increasing our knowledge of glioblastoma (GBM) biology, do not influence clinical decisions yet. We explored the translational power of GSC-enriched cultures from patient-derived tumorspheres (TS) in predicting treatment response.

Methods

The relationship between TS growth and clinical outcome was investigated in 52 GBMs treated with surgical resection followed by radiotherapy and temozolomide (TMZ). The effect on TS of radiation (6 to 60 Gy) and of TMZ (3.9 μM to 1 mM) was related with patients' survival.

Results

Generation of TS was an independent factor for poor overall survival (OS) and poor progression-free survival (PFS) (P < .0001 and P = .0010, respectively). Growth rate and clonogenicity of TS predicted poor OS. In general, TS were highly resistant to both radiation and TMZ. Resistance to TMZ was stronger in TS with high clonogenicity and fast growth (P < .02). Shorter PFS was associated with radiation LD50 (lethal dose required to kill 50% of TS cells) >12 Gy of matched TS (P = .0484). A direct relationship was found between sensitivity of TS to TMZ and patients' survival (P = .0167 and P = .0436 for OS and PFS, respectively). Importantly, values for TMZ half-maximal inhibitory concentration <50 μM, which are in the range of plasma levels achieved in vivo, identified cases with longer OS and PFS (P = .0020 and P = .0016, respectively).

Conclusions

Analysis of TS holds translational relevance by predicting the response of parent tumors to radiation and, particularly, to TMZ. Dissecting the clonogenic population from proliferating progeny in TS can guide therapeutic strategies to a more effective drug selection and treatment duration.

Sorafenib inhibits cell growth but fails to enhance radio- and chemosensitivity of glioblastoma cell lines

BACKGROUND

Glioblastomas (GBM) are the most common malignant type of primary brain tumor. GBM are intensively treated with surgery and combined radiochemotherapy using X-irradiation and temozolomide (TMZ) but they are still associated with an extremely poor prognosis, urging for the development of new treatment strategies. To improve the outcome of GBM patients, the small molecule multi-kinase inhibitor sorafenib has moved into focus of recent research. Sorafenib has already been shown to enhance the radio- and radiochemosensitivity of other tumor entities. Whether sorafenib is also able to sensitize GBM cells to radio- and chemotherapy is still an unsolved question which we have addressed in this study.

METHODS

The effect of sorafenib on signaling, proliferation, radiosensitivity, chemosensitivity and radiochemosensitivity was analyzed in six glioblastoma cell lines using Western blot, proliferation- and colony formation assays.

RESULTS

In half of the cell lines sorafenib clearly inhibited MAPK signaling. We also observed a strong blockage of proliferation, which was, however, not associated with MAPK pathway inhibition. Sorafenib had only minor effects on cell survival when administered alone. Most importantly, sorafenib treatment failed to enhance GBM cell killing by irradiation, TMZ or combined treatment, and instead rather caused resistance in some cell lines.

CONCLUSION

Our data suggest that sorafenib treatment may not improve the efficacy of radiochemotherapy in GBM.

A ruthenium polypyridyl intercalator stalls DNA replication forks, radiosensitizes human cancer cells and is enhanced by Chk1 inhibition

Ruthenium(II) polypyridyl complexes can intercalate DNA with high affinity and prevent cell proliferation; however, the direct impact of ruthenium-based intercalation on cellular DNA replication remains unknown. Here we show the multi-intercalator [Ru(dppz)2(PIP)](2+) (dppz = dipyridophenazine, PIP = 2-(phenyl)imidazo[4,5-f][1,10]phenanthroline) immediately stalls replication fork progression in HeLa human cervical cancer cells. In response to this replication blockade, the DNA damage response (DDR) cell signalling network is activated, with checkpoint kinase 1 (Chk1) activation indicating prolonged replication-associated DNA damage, and cell proliferation is inhibited by G1-S cell-cycle arrest. Co-incubation with a Chk1 inhibitor achieves synergistic apoptosis in cancer cells, with a significant increase in phospho(Ser139) histone H2AX (γ-H2AX) levels and foci indicating increased conversion of stalled replication forks to double-strand breaks (DSBs). Normal human epithelial cells remain unaffected by this concurrent treatment. Furthermore, pre-treatment of HeLa cells with [Ru(dppz)2(PIP)](2+) before external beam ionising radiation results in a supra-additive decrease in cell survival accompanied by increased γ-H2AX expression, indicating the compound functions as a radiosensitizer. Together, these results indicate ruthenium-based intercalation can block replication fork progression and demonstrate how these DNA-binding agents may be combined with DDR inhibitors or ionising radiation to achieve more efficient cancer cell killing.

Optimization of combined temozolomide and peptide receptor radionuclide therapy (PRRT) in mice after multimodality molecular imaging studies

BACKGROUND

Successful treatments of patients with somatostatin receptor (SSTR)-overexpressing neuroendocrine tumours (NET) comprise somatostatin-analogue lutetium-177-labelled octreotate ((177)Lu-TATE) treatment, also referred to as peptide receptor radionuclide therapy (PRRT), and temozolomide (TMZ) treatment. Their combination might result in additive effects. Using MRI and SPECT/CT, we studied tumour characteristics and therapeutic responses after different (combined) administration schemes in a murine tumour model in order to identify the optimal treatment schedule for PRRT plus TMZ.

METHODS

We performed molecular imaging studies in mice bearing SSTR-expressing H69 (humane small cell lung cancer) tumours after single intravenous (i.v.) administration of 30 MBq (177)Lu-TATE or TMZ (oral 50 mg/kg daily for 14 days). Tumour perfusion was evaluated weekly by dynamic contrast-enhanced MRI (DCE-MRI), whereas tumour uptake of (111)In-octreotide was quantified using SPECT/CT until day 39 after treatment. Based on these results, seven different (177)Lu-octreotate and TMZ combination schemes were evaluated for therapy response, varying the order and time interval of the two therapies and compared with single treatments.

RESULTS

PRRT and TMZ both resulted in tumour size reduction, accompanied by significant changes in MRI characteristics such as an enhanced tumour perfusion. Moreover, TMZ treatment also resulted in increased uptake of the SST analogue (111)In-octreotide until day 13. In the subsequent therapy study, 90 % of animals receiving (177)Lu-TATE at day 14 after TMZ treatment showed complete response, being the best anti-tumour results among groups.

CONCLUSIONS

Molecular imaging studies indicated that PRRT after TMZ treatment could induce optimal therapeutic effects because of enhanced tumour uptake of radioactivity after TMZ, which was confirmed by therapy responses. Therefore, clinical translation of TMZ treatment prior to PRRT might increase tumour responses in NET patients as well.

Effect of Concomitant Radiochemotherapy on Invasion Potential of Glioblastoma

Glioblastoma (GBM) is the most common primary brain tumor in adults with inevitable recurrence after oncotherapy. The insufficient effect of "gold standard" temozolomide-based concomitant radiochemotherapy may be due to the inability to prevent tumor cell invasion. Peritumoral infiltration depends mainly on the interaction between extracellular matrix (ECM) components and cell membrane receptors. Changes in invasive behaviour after oncotherapy can be evaluated at the molecular level by determining the RNA expression and protein levels of the invasion-related ECM components. The expression of nineteen ECM molecules was determined at both RNA and protein levels in thirty-one GBM samples. Fifteen GBM samples originated from the first surgical procedure on patients before oncotherapy, and sixteen GBM samples were collected at the second surgery due to local recurrence after concomitant chemoirradiation. RNA expressions were measured with qRT-PCR, and protein levels were determined by quantitative analysis of Western blots. Only MMP-9 RNA transcript level was reduced (p < 0.05) whereas at protein level, eight molecules showed changes concordant with RNA expression with significant decrease in brevican only. The results suggest that concomitant radiochemotherapy does not have sufficient impact on the expression of invasion-related ECM components of glioblastoma, oncotherapy does not significantly affect its invasive behavior. To avoid the spread of tumors into the brain parenchyma, supplementation of antiproliferative treatment with anti-invasive agents may be worth consideration in oncotherapy for glioblastoma.

Temozolomide nanoparticles for targeted glioblastoma therapy

Glioblastoma (GBM) is a deadly and debilitating brain tumor with an abysmal prognosis. The standard therapy for GBM is surgery followed by radiation and chemotherapy with Temozolomide (TMZ). Treatment of GBMs remains a challenge, largely because of the fast degradation of TMZ, the inability to deliver an effective dose of TMZ to tumors, and a lack of target specificity that may cause systemic toxicity. Here, we present a simple method for synthesizing a nanoparticle-based carrier that can protect TMZ from rapid degradation in physiological solutions and can specifically deliver them to GBM cells through the mediation of a tumor-targeting peptide chlorotoxin (CTX). Our nanoparticle, namely NP-TMZ-CTX, had a hydrodynamic size of <100 nm, exhibited sustained stability in cell culture media for up to 2 weeks, and could accommodate stable drug loading. TMZ bound to nanoparticles showed a much higher stability at physiological pH, with a half-life 7-fold greater than that of free TMZ. NP-TMZ-CTX was able to target GBM cells and achieved 2-6-fold higher uptake and a 50-90% reduction of IC50 72 h post-treatment as compared to nontargeted NP-TMZ. NP-TMZ-CTX showed great promise in its ability to deliver a large therapeutic dose of TMZ to GBM cells and could serve as a template for targeted delivery of other therapeutics.

Repair mechanisms help glioblastoma resist treatment

Glioblastoma multiforme (GBM) is a malignant and incurable glial brain tumour. The current best treatment for GBM includes maximal safe surgical resection followed by concomitant radiotherapy and adjuvant temozolomide. Despite this, median survival is still only 14-16 months. Mechanisms that lead to chemo- and radio-resistance underpin treatment failure. Insights into the DNA repair mechanisms that permit resistance to chemoradiotherapy in GBM may help improve patient responses to currently available therapies.

Redox-responsive magnetic nanoparticle for targeted convection-enhanced delivery of O6-benzylguanine to brain tumors

Resistance to temozolomide (TMZ) based chemotherapy in glioblastoma multiforme (GBM) has been attributed to the upregulation of the DNA repair protein O(6)-methylguanine-DNA methyltransferase (MGMT). Inhibition of MGMT using O(6)-benzylguanine (BG) has shown promise in these patients, but its clinical use is hindered by poor pharmacokinetics that leads to unacceptable toxicity. To improve BG biodistribution and efficacy, we developed superparamagnetic iron oxide nanoparticles (NP) for targeted convection-enhanced delivery (CED) of BG to GBM. The nanoparticles (NPCP-BG-CTX) consist of a magnetic core coated with a redox-responsive, cross-linked, biocompatible chitosan-PEG copolymer surface coating (NPCP). NPCP was modified through covalent attachment of BG and tumor targeting peptide chlorotoxin (CTX). Controlled, localized BG release was achieved under reductive intracellular conditions and NPCP-BG-CTX demonstrated proper trafficking of BG in human GBM cells in vitro. NPCP-BG-CTX treated cells showed a significant reduction in MGMT activity and the potentiation of TMZ toxicity. In vivo, CED of NPCP-BG-CTX produced an excellent volume of distribution (Vd) within the brain of mice bearing orthotopic human primary GBM xenografts. Significantly, concurrent treatment with NPCP-BG-CTX and TMZ showed a 3-fold increase in median overall survival in comparison to NPCP-CTX/TMZ treated and untreated animals. Furthermore, NPCP-BG-CTX mitigated the myelosuppression observed with free BG in wild-type mice when administered concurrently with TMZ. The combination of favorable physicochemical properties, tumor cell specific BG delivery, controlled BG release, and improved in vivo efficacy demonstrates the great potential of these NPs as a treatment option that could lead to improved clinical outcomes.

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

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

Differential expression of miR200a-3p and miR21 in grade II-III and grade IV gliomas: evidence that miR200a-3p is regulated by O⁶-methylguanine methyltransferase and promotes temozolomide responsiveness

Glioblastoma multiforme (GBM) is the most common primary brain tumor and is among the deadliest of human cancers. Dysregulation of microRNAs (miRNAs) expression is an important step in tumor progression as miRNAs can act as tumor suppressors or oncogenes and may affect cell sensitivity to chemotherapy. Whereas the oncogenic miR21 has been shown to be overexpressed in gliomas, the expression and function of the tumor-supressor miR200a in GBMs remains unknown. In this study, we show that miR21 is upregulated in grade IV (GBMs) vs. grade II-III (LGs) gliomas, confirming that miR21 expression level is correlated with tumor grade, and that it may be considered as a marker of tumor progression. Conversely, miR200a is demonstrated for the first time to be downregulated in GBMs compared with LGs, and overexpression of miR200a in GBM cells is shown to promote TMZ-sensitivity. Interestingly, miR200a but not miR21 expression level is significantly higher in TMZ-responsive vs. -unresponsive tumoral glial cells in primary culture. Furthermore, miR200a appears negatively correlated with the expression of the DNA repair enzyme O (6)-methylguanine methyltransferase (MGMT), and the inhibition of MGMT activity results in an increase of miR200a expression in GBM cells. Taken together, these data strongly suggest that miR200a is likely to act as a crucial antitumoral factor regarding glioma progression. Interplay between miR200a and MGMT should be considered as potential mechanism involved in therapeutic response.

Enhancing radiation therapy for patients with glioblastoma

Radiation therapy has been the foundation of therapy following maximal surgical resection in patients with newly diagnosed glioblastoma for decades and the primary therapy for unresected tumors. Using the standard approach with radiation and temozolomide, however, outcomes are poor, and glioblastoma remains an incurable disease with the majority of recurrences and progression within the radiation treatment field. As such, there is much interest in elucidating the mechanisms of resistance to radiation therapy and in developing novel approaches to overcoming this treatment resistance.

Hypofractionated intensity modulated radiotherapy with temozolomide in newly diagnosed glioblastoma multiforme

We conducted a phase I study to determine (a) the maximum tolerated dose of peri-radiation therapy temozolomide (TMZ) and (b) the safety of a selected hypofractionated intensity modulated radiation therapy (HIMRT) regimen in glioblastoma multiforme (GBM) patients. Patients with histological diagnosis of GBM, Karnofsky performance status (KPS)≥ 60 and adequate bone marrow function were eligible for the study. All patients received peri-radiation TMZ; 1 week before the beginning of radiation therapy (RT), 1 week after RT and for 3 weeks during RT. Standard 75 mg/m(2)/day dose was administered to all patients 1 week post-RT. Dose escalation was commenced at level I: 50mg/m(2)/day, level II: 65 mg/m(2)/day and level III: 75 mg/m(2)/day for 4 weeks. HIMRT was delivered at 52.5 Gy in 15 fractions to the contrast enhancing lesion (or surgical cavity) plus the surrounding edema plus a 2 cm margin. Six men and three women with a median age of 67 years (range, 44-81) and a median KPS of 80 (range, 80-90) were enrolled. Three patients were accrued at each TMZ dose level. Median follow-up was 10 months (range, 1-15). Median progression free survival was 3.9 months (95% confidence interval [CI]: 0.9-7.4; range, 0.9-9.9 months) and the overall survival 12.7 months (95% CI: 2.5-17.6; range, 2.5-20.7 months). Time spent in a KPS ≥ 70 was 8.1 months (95% CI: 2.4-15.6; range, 2.4-16 months). No instance of irreversible grade 3 or higher acute toxicity was noted. HIMRT at 52.5 Gy in 15 fractions with peri-RT TMZ at a maximum tolerated dose of 75 mg/m(2)/day for 5 weeks is well tolerated and is able to abate treatment time for these patients.

Repair of 3-methyladenine and abasic sites by base excision repair mediates glioblastoma resistance to temozolomide

Alkylating agents have long played a central role in the adjuvant therapy of glioblastoma (GBM). More recently, inclusion of temozolomide (TMZ), an orally administered methylating agent with low systemic toxicity, during and after radiotherapy has markedly improved survival. Extensive in vitro and in vivo evidence has shown that TMZ-induced O(6)-methylguanine (O(6)-meG) mediates GBM cell killing. Moreover, low or absent expression of O(6)-methylguanine-DNA methyltransferase (MGMT), the sole human repair protein that removes O(6)-meG from DNA, is frequently associated with longer survival in GBMs treated with TMZ, promoting interest in developing inhibitors of MGMT to counter resistance. However, the clinical efficacy of TMZ is unlikely to be due solely to O(6)-meG, as the agent produces approximately a dozen additional DNA adducts, including cytotoxic N3-methyladenine (3-meA) and abasic sites. Repair of 3-meA and abasic sites, both of which are produced in greater abundance than O(6)-meG, is mediated by the base excision repair (BER) pathway, and occurs independently of removal of O(6)-meG. These observations indicate that BER activities are also potential targets for strategies to potentiate TMZ cytotoxicity. Here we review the evidence that 3-meA and abasic sites mediate killing of GBM cells. We also present in vitro and in vivo evidence that alkyladenine-DNA glycosylase, the sole repair activity that excises 3-meA from DNA, and Ape1, the major human abasic site endonuclease, mediate TMZ resistance in GBMs and represent potential anti-resistance targets.

O(6)-methylguanine-DNA methyltransferase in glioma therapy: promise and problems

Gliomas are the most frequent adult primary brain tumor, and are invariably fatal. The most common diagnosis glioblastoma multiforme (GBM) afflicts 12,500 new patients in the U.S. annually, and has a median survival of approximately one year when treated with the current standard of care. Alkylating agents have long been central in the chemotherapy of GBM and other gliomas. The DNA repair protein O(6)-methylguanine-DNA methyltransferase (MGMT), the principal human activity that removes cytotoxic O(6)-alkylguanine adducts from DNA, promotes resistance to anti-glioma alkylators, including temozolomide and BCNU, in GBM cell lines and xenografts. Moreover, MGMT expression assessed by immunohistochemistry, biochemical activity or promoter CpG methylation status is associated with the response of GBM to alkylator-based therapies, providing evidence that MGMT promotes clinical resistance to alkylating agents. These observations suggest a role for MGMT in directing adjuvant therapy of GBM and other gliomas. Promoter methylation status is the most clinically tractable measure of MGMT, and there is considerable enthusiasm for exploring its utility as a marker to assign therapy to individual patients. Here, we provide an overview of the biochemical, genetic and biological characteristics of MGMT as they relate to glioma therapy. We consider current methods to assess MGMT expression and discuss their utility as predictors of treatment response. Particular emphasis is given to promoter methylation status and the methodological and conceptual impediments that limit its use to direct treatment. We conclude by considering approaches that may improve the utility of MGMT methylation status in planning optimal therapies tailored to individual patients.

Temozolomide for corticotroph pituitary adenomas refractory to standard therapy

To highlight the potential of temozolomide (TMZ) to induce rapid tumor regression in patients with aggressive corticotroph adenomas (CA) that are refractory to surgery and radiation therapy and to review use of TMZ in other pituitary tumors. We present a case of a 56-year-old male with a 3 cm CA treated with transphenoidal surgery (TSS) and conventional radiotherapy in the same year. His hypercortisolemia recurred 11 years later with rapid tumor growth (to 4.2 × 2.5 cm) and he underwent a second TSS with good resection. The tumor recurred 6 months later with ophthalmoplegia. Over 16 months he underwent an additional three surgeries (two TSS, one craniotomy) and repeated conventional radiotherapy. Ki67 staining index on surgical specimens was 5-6%. Temozolomide is an oral alkylating agent approved for glioblastoma multiforme treatment that has only recently shown promise in treating some pituitary tumors. In this patient TMZ was started at 150 mg/m²/day, titrated to 200 mg/m²/day, taken 5 days per month. The only significant side effect was moderate nausea. After 10 weeks, the tumor showed a remarkable 60% regression with objective improvement in ophthalmoplegia. Treatment of aggressive CAs represents a therapeutic challenge and in some cases surgical debulking and radiotherapy are of limited success. Few reports of CAs responsive to TMZ have been reported in the literature. To our knowledge, this case represents the most rapid robust CA shrinkage response reported to date. Further randomized clinical trials of TMZ in the treatment of aggressive pituitary adenomas are warranted.