Combined PDK1 and CHK1 inhibition is required to kill glioblastoma stem-like cells in vitro and in vivo

Molecular Targeted Therapies in Glioblastoma Multiforme: A Systematic Overview of Global Trends and Findings

This systematic review assesses current molecular targeted therapies for glioblastoma multiforme (GBM), a challenging condition with limited treatment options. Using PRISMA methodology, 166 eligible studies, involving 2526 patients (61.49% male, 38.51% female, with a male-to-female ratio of 1.59/1), were analyzed. In laboratory studies, 52.52% primarily used human glioblastoma cell cultures (HCC), and 43.17% employed animal samples (mainly mice). Clinical participants ranged from 18 to 100 years, with 60.2% using combined therapies and 39.8% monotherapies. Mechanistic categories included Protein Kinase Phosphorylation (41.6%), Cell Cycle-Related Mechanisms (18.1%), Microenvironmental Targets (19.9%), Immunological Targets (4.2%), and Other Mechanisms (16.3%). Key molecular targets included Epidermal Growth Factor Receptor (EGFR) (10.8%), Mammalian Target of Rapamycin (mTOR) (7.2%), Vascular Endothelial Growth Factor (VEGF) (6.6%), and Mitogen-Activated Protein Kinase (MEK) (5.4%). This review provides a comprehensive assessment of molecular therapies for GBM, highlighting their varied efficacy in clinical and laboratory settings, ultimately impacting overall and progression-free survival in GBM management.

Identification of CDK1, PBK, and CHEK1 as an Oncogenic Signature in Glioblastoma: A Bioinformatics Approach to Repurpose Dapagliflozin as a Therapeutic Agent

Glioblastoma multiforme (GBM) is the most aggressive and lethal primary brain tumor whose median survival is less than 15 months. The current treatment regimen comprising surgical resectioning, chemotherapy with Temozolomide (TMZ), and adjuvant radiotherapy does not achieve total patient cure. Stem cells' presence and GBM tumor heterogeneity increase their resistance to TMZ, hence the poor overall survival of patients. A dysregulated cell cycle in glioblastoma enhances the rapid progression of GBM by evading senescence or apoptosis through an over-expression of cyclin-dependent kinases and other protein kinases that are the cell cycle's main regulatory proteins. Herein, we identified and validated the biomarker and predictive properties of a chemoradio-resistant oncogenic signature in GBM comprising CDK1, PBK, and CHEK1 through our comprehensive in silico analysis. We found that CDK1/PBK/CHEK1 overexpression drives the cell cycle, subsequently promoting GBM tumor progression. In addition, our Kaplan-Meier survival estimates validated the poor patient survival associated with an overexpression of these genes in GBM. We used in silico molecular docking to analyze and validate our objective to repurpose Dapagliflozin against CDK1/PBK/CHEK1. Our results showed that Dapagliflozin forms putative conventional hydrogen bonds with CDK1, PBK, and CHEK1 and arrests the cell cycle with the lowest energies as Abemaciclib.

Systematic Review of Molecular Targeted Therapies for Adult-Type Diffuse Glioma: An Analysis of Clinical and Laboratory Studies

Gliomas are the most common brain tumor in adults, and molecularly targeted therapies to treat gliomas are becoming a frequent topic of investigation. The current state of molecular targeted therapy research for adult-type diffuse gliomas has yet to be characterized, particularly following the 2021 WHO guideline changes for classifying gliomas using molecular subtypes. This systematic review sought to characterize the current state of molecular target therapy research for adult-type diffuse glioma to better inform scientific progress and guide next steps in this field of study. A systematic review was conducted in accordance with PRISMA guidelines. Studies meeting inclusion criteria were queried for study design, subject (patients, human cell lines, mice, etc.), type of tumor studied, molecular target, respective molecular pathway, and details pertaining to the molecular targeted therapy-namely the modality, dose, and duration of treatment. A total of 350 studies met the inclusion criteria. A total of 52 of these were clinical studies, 190 were laboratory studies investigating existing molecular therapies, and 108 were laboratory studies investigating new molecular targets. Further, a total of 119 ongoing clinical trials are also underway, per a detailed query on clinicaltrials.gov. GBM was the predominant tumor studied in both ongoing and published clinical studies as well as in laboratory analyses. A few studies mentioned IDH-mutant astrocytomas or oligodendrogliomas. The most common molecular targets in published clinical studies and clinical trials were protein kinase pathways, followed by microenvironmental targets, immunotherapy, and cell cycle/apoptosis pathways. The most common molecular targets in laboratory studies were also protein kinase pathways; however, cell cycle/apoptosis pathways were the next most frequent target, followed by microenvironmental targets, then immunotherapy pathways, with the wnt/β-catenin pathway arising in the cohort of novel targets. In this systematic review, we examined the current evidence on molecular targeted therapy for adult-type diffuse glioma and discussed its implications for clinical practice and future research. Ultimately, published research falls broadly into three categories-clinical studies, laboratory testing of existing therapies, and laboratory identification of novel targets-and heavily centers on GBM rather than IDH-mutant astrocytoma or oligodendroglioma. Ongoing clinical trials are numerous in this area of research as well and follow a similar pattern in tumor type and targeted pathways as published clinical studies. The most common molecular targets in all study types were protein kinase pathways. Microenvironmental targets were more numerous in clinical studies, whereas cell cycle/apoptosis were more numerous in laboratory studies. Immunotherapy pathways are on the rise in all study types, and the wnt/β-catenin pathway is increasingly identified as a novel target.

DNA Repair and Therapeutic Strategies in Cancer Stem Cells

First-line cancer treatments successfully eradicate the differentiated tumour mass but are comparatively ineffective against cancer stem cells (CSCs), a self-renewing subpopulation thought to be responsible for tumour initiation, metastasis, heterogeneity, and recurrence. CSCs are thus presented as the principal target for elimination during cancer treatment. However, CSCs are challenging to drug target because of numerous intrinsic and extrinsic mechanisms of drug resistance. One such mechanism that remains relatively understudied is the DNA damage response (DDR). CSCs are presumed to possess properties that enable enhanced DNA repair efficiency relative to their highly proliferative bulk progeny, facilitating improved repair of double-strand breaks induced by radiotherapy and most chemotherapeutics. This can occur through multiple mechanisms, including increased expression and splicing fidelity of DNA repair genes, robust activation of cell cycle checkpoints, and elevated homologous recombination-mediated DNA repair. Herein, we summarise the current knowledge concerning improved genome integrity in non-transformed stem cells and CSCs, discuss therapeutic opportunities within the DDR for re-sensitising CSCs to genotoxic stressors, and consider the challenges posed regarding unbiased identification of novel DDR-directed strategies in CSCs. A better understanding of the DDR mediating chemo/radioresistance mechanisms in CSCs could lead to novel therapeutic approaches, thereby enhancing treatment efficacy in cancer patients.

Perspective on the Use of DNA Repair Inhibitors as a Tool for Imaging and Radionuclide Therapy of Glioblastoma

Simple Summary

The current routine treatment for glioblastoma (GB), the most lethal high-grade brain tumor in adults, aims to induce DNA damage in the tumor. However, the tumor cells might be able to repair that damage, which leads to therapy resistance. Fortunately, DNA repair defects are common in GB cells, and their survival is often based on a sole backup repair pathway. Hence, targeted drugs inhibiting essential proteins of the DNA damage response have gained momentum and are being introduced in the clinic. This review gives a perspective on the use of radiopharmaceuticals targeting DDR kinases for imaging in order to determine the DNA repair phenotype of GB, as well as for effective radionuclide therapy. Finally, four new promising radiopharmaceuticals are suggested with the potential to lead to a more personalized GB therapy.

Abstract

Despite numerous innovative treatment strategies, the treatment of glioblastoma (GB) remains challenging. With the current state-of-the-art therapy, most GB patients succumb after about a year. In the evolution of personalized medicine, targeted radionuclide therapy (TRT) is gaining momentum, for example, to stratify patients based on specific biomarkers. One of these biomarkers is deficiencies in DNA damage repair (DDR), which give rise to genomic instability and cancer initiation. However, these deficiencies also provide targets to specifically kill cancer cells following the synthetic lethality principle. This led to the increased interest in targeted drugs that inhibit essential DDR kinases (DDRi), of which multiple are undergoing clinical validation. In this review, the current status of DDRi for the treatment of GB is given for selected targets: ATM/ATR, CHK1/2, DNA-PK, and PARP. Furthermore, this review provides a perspective on the use of radiopharmaceuticals targeting these DDR kinases to (1) evaluate the DNA repair phenotype of GB before treatment decisions are made and (2) induce DNA damage via TRT. Finally, by applying in-house selection criteria and analyzing the structural characteristics of the DDRi, four drugs with the potential to become new therapeutic GB radiopharmaceuticals are suggested.

Therapeutic Opportunities of Disrupting Genome Integrity in Adult Diffuse Glioma

Adult diffuse glioma, particularly glioblastoma (GBM), is a devastating tumor of the central nervous system. The existential threat of this disease requires on-going treatment to counteract tumor progression. The present outcome is discouraging as most patients will succumb to this disease. The low cure rate is consistent with the failure of first-line therapy, radiation and temozolomide (TMZ). Even with their therapeutic mechanism of action to incur lethal DNA lesions, tumor growth remains undeterred. Delivering additional treatments only delays the inescapable development of therapeutic tolerance and disease recurrence. The urgency of establishing lifelong tumor control needs to be re-examined with a greater focus on eliminating resistance. Early genomic and transcriptome studies suggest each tumor subtype possesses a unique molecular network to safeguard genome integrity. Subsequent seminal work on post-therapy tumor progression sheds light on the involvement of DNA repair as the causative contributor for hypermutation and therapeutic failure. In this review, we will provide an overview of known molecular factors that influence the engagement of different DNA repair pathways, including targetable vulnerabilities, which can be exploited for clinical benefit with the use of specific inhibitors.

Targeting Cell Cycle Checkpoint Kinases to Overcome Intrinsic Radioresistance in Brain Tumor Cells

Simple Summary

As cell cycle checkpoint mechanisms maintain genomic integrity, the inhibition of enzymes involved in these control mechanisms may increase the sensitivity of the cells to DNA damaging treatments. In this review, we summarize the knowledge in the field of brain tumor treatment with radiation therapy and cell cycle checkpoint inhibition via targeting ATM, ATR, CHK1, CHK2, and WEE1 kinases.

Abstract

Radiation therapy is an important part of the standard of care treatment of brain tumors. However, the efficacy of radiation therapy is limited by the radioresistance of tumor cells, a phenomenon held responsible for the dismal prognosis of the most aggressive brain tumor types. A promising approach to radiosensitization of tumors is the inhibition of cell cycle checkpoint control responsible for cell cycle progression and the maintenance of genomic integrity. Inhibition of the kinases involved in these control mechanisms can abolish cell cycle checkpoints and DNA damage repair and thus increase the sensitivity of tumor cells to radiation and chemotherapy. Here, we discuss preclinical progress in molecular targeting of ATM, ATR, CHK1, CHK2, and WEE1, checkpoint kinases in the treatment of brain tumors, and review current clinical phase I-II trials.

DDRugging glioblastoma: understanding and targeting the DNA damage response to improve future therapies

Glioblastoma is the most frequently diagnosed type of primary brain tumour in adults. These aggressive tumours are characterised by inherent treatment resistance and disease progression, contributing to ~ 190 000 brain tumour-related deaths globally each year. Current therapeutic interventions consist of surgical resection followed by radiotherapy and temozolomide chemotherapy, but average survival is typically around 1 year, with < 10% of patients surviving more than 5 years. Recently, a fourth treatment modality of intermediate-frequency low-intensity electric fields [called tumour-treating fields (TTFields)] was clinically approved for glioblastoma in some countries after it was found to increase median overall survival rates by ~ 5 months in a phase III randomised clinical trial. However, beyond these treatments, attempts to establish more effective therapies have yielded little improvement in survival for patients over the last 50 years. This is in contrast to many other types of cancer and highlights glioblastoma as a recognised tumour of unmet clinical need. Previous work has revealed that glioblastomas contain stem cell-like subpopulations that exhibit heightened expression of DNA damage response (DDR) factors, contributing to therapy resistance and disease relapse. Given that radiotherapy, chemotherapy and TTFields-based therapies all impact DDR mechanisms, this Review will focus on our current knowledge of the role of the DDR in glioblastoma biology and treatment. We also discuss the potential of effective multimodal targeting of the DDR combined with standard-of-care therapies, as well as emerging therapeutic targets, in providing much-needed improvements in survival rates for patients.

PDK1 Inhibitor BX795 Improves Cisplatin and Radio-Efficacy in Oral Squamous Cell Carcinoma by Downregulating the PDK1/CD47/Akt-Mediated Glycolysis Signaling Pathway

Background: Oral squamous cell carcinoma (OSCC) has a high prevalence and predicted global mortality rate of 67.1%, necessitating better therapeutic strategies. Moreover, the recurrence and resistance of OSCC after chemo/radioresistance remains a major bottleneck for its effective treatment. Molecular targeting is one of the new therapeutic approaches to target cancer. Among a plethora of targetable signaling molecules, PDK1 is currently rising as a potential target for cancer therapy. Its aberrant expression in many malignancies is observed associated with glycolytic re-programming and chemo/radioresistance. Methods: Furthermore, to better understand the role of PDK1 in OSCC, we analyzed tissue samples from 62 patients with OSCC for PDK1 expression. Combining in silico and in vitro analysis approaches, we determined the important association between PDK1/CD47/LDHA expression in OSCC. Next, we analyzed the effect of PDK1 expression and its connection with OSCC orosphere generation and maintenance, as well as the effect of the combination of the PDK1 inhibitor BX795, cisplatin and radiotherapy in targeting it. Results: Immunohistochemical analysis revealed that higher PDK1 expression is associated with a poor prognosis in OSCC. The immunoprecipitation assay indicated PDK1/CD47 binding. PDK1 ligation significantly impaired OSCC orosphere formation and downregulated Sox2, Oct4, and CD133 expression. The combination of BX795 and cisplatin markedly reduced in OSCC cell’s epithelial-mesenchymal transition, implying its synergistic effect. p-PDK1, CD47, Akt, PFKP, PDK3 and LDHA protein expression were significantly reduced, with the strongest inhibition in the combination group. Chemo/radiotherapy together with abrogation of PDK1 inhibits the oncogenic (Akt/CD47) and glycolytic (LDHA/PFKP/PDK3) signaling and, enhanced or sensitizes OSCC to the anticancer drug effect through inducing apoptosis and DNA damage together with metabolic reprogramming. Conclusions: Therefore, the results from our current study may serve as a basis for developing new therapeutic strategies against chemo/radioresistant OSCC.

Bioactive Compounds with Antiglioma Activity from Marine Species

The search for new chemical compounds with antitumor pharmacological activity is a necessary process for creating more effective drugs for each specific malignancy type. This review presents the outcomes of screening studies of natural compounds with high anti-glioma activity. Despite significant advances in cancer therapy, there are still some tumors currently considered completely incurable including brain gliomas. This review covers the main problems of the glioma chemotherapy including drug resistance, side effects of common anti-glioma drugs, and genetic diversity of brain tumors. The main emphasis is made on the characterization of natural compounds isolated from marine organisms because taxonomic diversity of organisms in seawaters significantly exceeds that of terrestrial species. Thus, we should expect greater chemical diversity of marine compounds and greater likelihood of finding effective molecules with antiglioma activity. The review covers at least 15 classes of organic compounds with their chemical formulas provided as well as semi-inhibitory concentrations, mechanisms of action, and pharmacokinetic profiles. In conclusion, the analysis of the taxonomic diversity of marine species containing bioactives with antiglioma activity is performed noting cytotoxicity indicators and to the tumor cells in comparison with similar indicators of antitumor agents approved for clinical use as antiglioblastoma chemotherapeutics.

The complexities of PKCα signaling in cancer

Protein kinase C α (PKCα) is a ubiquitously expressed member of the PKC family of serine/threonine kinases with diverse functions in normal and neoplastic cells. Early studies identified anti-proliferative and differentiation-inducing functions for PKCα in some normal tissues (e.g., regenerating epithelia) and pro-proliferative effects in others (e.g., cells of the hematopoietic system, smooth muscle cells). Additional well documented roles of PKCα signaling in normal cells include regulation of the cytoskeleton, cell adhesion, and cell migration, and PKCα can function as a survival factor in many contexts. While a majority of tumors lose expression of PKCα, others display aberrant overexpression of the enzyme. Cancer-related mutations in PKCα are uncommon, but rare examples of driver mutations have been detected in certain cancer types (e. g., choroid gliomas). Here we review the role of PKCα in various cancers, describe mechanisms by which PKCα affects cancer-related cell functions, and discuss how the diverse functions of PKCα contribute to tumor suppressive and tumor promoting activities of the enzyme. We end the discussion by addressing mutations and expression of PKCα in tumors and the clinical relevance of these findings.

Deregulated expression of the imprinted DLK1-DIO3 region in glioblastoma stemlike cells: tumor suppressor role of lncRNA MEG3

Background

Glioblastoma (GBM) stemlike cells (GSCs) are thought to be responsible for the maintenance and aggressiveness of GBM, the most common primary brain tumor in adults. This study aims at elucidating the involvement of deregulations within the imprinted delta-like homolog 1 gene‒type III iodothyronine deiodinase gene (DLK-DIO3) region on chromosome 14q32 in GBM pathogenesis.

Methods

Real-time PCR analyses were performed on GSCs and GBM tissues. Methylation analyses, gene expression, and reverse-phase protein array profiles were used to investigate the tumor suppressor function of the maternally expressed 3 gene (MEG3).

Results

Loss of expression of genes and noncoding RNAs within the DLK1-DIO3 region was observed in GSCs and GBM tissues compared with normal brain. This downregulation is mainly mediated by epigenetic silencing. Kaplan–Meier analysis indicated that low expression of MEG3 and MEG8 long noncoding (lnc)RNAs significantly correlated with short survival in GBM patients. MEG3 restoration impairs tumorigenic abilities of GSCs in vitro by inhibiting cell growth, migration, and colony formation and decreases in vivo tumor growth, reducing infiltrative growth. These effects were associated with modulation of genes involved in cell adhesion and epithelial-to-mesenchymal transition (EMT).

Conclusion

In GBM, MEG3 acts as a tumor suppressor mainly regulating cell adhesion, EMT, and cell proliferation, thus providing a potential candidate for novel GBM therapies.

Role of glioblastoma stem cells in cancer therapeutic resistance: a perspective on antineoplastic agents from natural sources and chemical derivatives

Glioblastoma (GBM) is the highest-grade form of glioma, as well as one of the most aggressive types of cancer, exhibiting rapid cellular growth and highly invasive behavior. Despite significant advances in diagnosis and therapy in recent decades, the outcomes for high-grade gliomas (WHO grades III-IV) remain unfavorable, with a median overall survival time of 15–18 months. The concept of cancer stem cells (CSCs) has emerged and provided new insight into GBM resistance and management. CSCs can self-renew and initiate tumor growth and are also responsible for tumor cell heterogeneity and the induction of systemic immunosuppression. The idea that GBM resistance could be dependent on innate differences in the sensitivity of clonogenic glial stem cells (GSCs) to chemotherapeutic drugs/radiation prompted the scientific community to rethink the understanding of GBM growth and therapies directed at eliminating these cells or modulating their stemness. This review aims to describe major intrinsic and extrinsic mechanisms that mediate chemoradioresistant GSCs and therapies based on antineoplastic agents from natural sources, derivatives, and synthetics used alone or in synergistic combination with conventional treatment. We will also address ongoing clinical trials focused on these promising targets. Although the development of effective therapy for GBM remains a major challenge in molecular oncology, GSC knowledge can offer new directions for a promising future.

G-quadruplex ligand RHPS4 radiosensitizes glioblastoma xenograft in vivo through a differential targeting of bulky differentiated- and stem-cancer cells

BACKGROUND

Glioblastoma is the most aggressive and most lethal primary brain tumor in the adulthood. Current standard therapies are not curative and novel therapeutic options are urgently required. Present knowledge suggests that the continued glioblastoma growth and recurrence is determined by glioblastoma stem-like cells (GSCs), which display self-renewal, tumorigenic potential, and increased radio- and chemo-resistance. The G-quadruplex ligand RHPS4 displays in vitro radiosensitizing effect in GBM radioresistant cells through the targeting and dysfunctionalization of telomeres but RHPS4 and Ionizing Radiation (IR) combined treatment efficacy in vivo has not been explored so far.

METHODS

RHPS4 and IR combined effects were tested in vivo in a heterotopic mice xenograft model and in vitro in stem-like cells derived from U251MG and from four GBM patients. Cell growth assays, cytogenetic analysis, immunoblotting, gene expression and cytofluorimetric analysis were performed in order to characterize the response of differentiated and stem-like cells to RHPS4 and IR in single and combined treatments.

RESULTS

RHPS4 administration and IR exposure is very effective in blocking tumor growth in vivo up to 65 days. The tumor volume reduction and the long-term tumor control suggested the targeting of the stem cell compartment. Interestingly, RHPS4 treatment was able to strongly reduce cell proliferation in GSCs but, unexpectedly, did not synergize with IR. Lack of radiosensitization was supported by the GSCs telomeric-resistance observed as the total absence of telomere-involving chromosomal aberrations. Remarkably, RHPS4 treatment determined a strong reduction of CHK1 and RAD51 proteins and transcript levels suggesting that the inhibition of GSCs growth is determined by the impairment of the replication stress (RS) response and DNA repair.

CONCLUSIONS

We propose that the potent antiproliferative effect of RHPS4 in GSCs is not determined by telomeric dysfunction but is achieved by the induction of RS and by the concomitant depletion of CHK1 and RAD51, leading to DNA damage and cell death. These data open to novel therapeutic options for the targeting of GSCs, indicating that the combined inhibition of cell-cycle checkpoints and DNA repair proteins provides the most effective means to overcome resistance of GSC to genotoxic insults.

A patent update on PDK1 inhibitors (2015-present)

INTRODUCTION

3-Phosphoinositide-dependent kinase 1 (PDK1), the 'master kinase of the AGC protein kinase family', plays a key role in cancer development and progression. Although it has been rather overlooked, in the last decades a growing number of molecules have been developed to effectively modulate the PDK1 enzyme.

AREAS COVERED

This review collects different PDK1 inhibitors patented from October 2014 to December 2018. The molecules have been classified on the basis of the chemical structure/type of inhibition, and for each general structure, examples have been discussed in extenso.

EXPERT OPINION

The role of PDK1 in cancer development and progression as well as in metastasis formation and in chemoresistance has been confirmed by many studies. Therefore, the pharmaceutical discovery in both public and private institutions is still ongoing despite the plentiful molecules already published. The majority of the new molecules synthetized interact with binding sites different from the ATP binding site (i.e. PIF pocket or DFG-out conformation). However, many researchers are still looking for innovative PDK1 modulation strategy such as combination of well-known inhibitory agents or multitarget ligands, aiming to block, together with PDK1, other different critical players in the wide panorama of proteins involved in tumor pathways.

C-type lectin domain family 5, member A (CLEC5A, MDL-1) promotes brain glioblastoma tumorigenesis by regulating PI3K/Akt signalling

OBJECTIVES

Glioblastoma is the most common malignant glioma of all brain tumours. It is difficult to treat because of its poor response to chemotherapy and radiotherapy and high recurrence rate after treatment. The aetiology of glioblastoma is a result of disorders of multiple factors. Depending on cell signal transduction, these glioblastoma-associated factors lead to cell proliferation, differentiation and apoptosis. Therefore, investigation of the potential factors which involved in the development of glioblastoma could provide a new target for the treatment of glioblastoma.

MATERIALS AND METHODS

We analysed the transcript expression of CLEC5A in glioblastoma by accessing The Cancer Genome Atlas (TCGA). qRT-PCR was performed to detect the RNA expression of genes in cells and tissues, and Western blot was used to measure the protein levels (Cyclin D1, Bcl-2, BAX, PCNA, MMP2, MMP9, Akt and Akt phosphorylation) in tissues and cells. Cell proliferation, migration, invasion, cycle and apoptosis were measured by CCK-8, transwell and flow cytometry assays, respectively. Ki67 level and lung metastasis were determined by immunochemistry and H&E staining.

RESULTS

In this study, we found that CLEC5A was highly upregulated in glioblastoma compared to normal brain tissues, which had an opposite relation with the overall patient survival. Downregulation of CLEC5A could inhibit cell proliferation, migration and invasion via promoting apoptosis and G1 arrest. In contrast, overexpression of CLEC5A stimulated cell proliferation, migration and invasion. In addition, we found that CLEC5A level was positively correlated with Akt phosphorylation level. Akt inhibitor or agonist could reverse the modulation effects of CLEC5A in glioblastoma. Moreover, In vivo results suggested that inhibition of CLEC5A significantly reduced tumour size, weight, cell proliferation ability and lung metastasis via inhibition of phosphorylation Akt.

CONCLUSION

Both in vitro and in vivo evidences supported that CLEC5A was involved in glioblastoma pathogenesis via regulation of PI3K/Akt pathway. Thus, CLEC5A might serve as a potential therapeutic target in the treatment of glioblastoma in the future.

Drug resistance in glioblastoma and cytotoxicity of seaweed compounds, alone and in combination with anticancer drugs: A mini review

BACKGROUND

Glioblastomas (GBM) are one of the most aggressive tumor of the central nervous system with an average life expectancy of only 1-2 years after diagnosis, even with the use of advanced treatments with surgery, radiation, and chemotherapy. There are several anticancer drugs with alkylating properties that have been used in the therapy of malignant gliomas. Temozolomide (TMZ) is one of them, widely used even in combination with ionizing radiation. However, the main disadvantage of using these types of drugs in the treatment of GBM is the development of cancer drug resistance. Research of bioactive compounds with anticancer activity has been heavily explored.

PURPOSE

This review focuses on a carotenoid and a phlorotannin present in seaweed, namely fucoxanthin and phloroglucinol, and their anticancer activity against glioblastoma. The combination of natural compounds with conventional drugs is also discussed.

CONCLUSION

Several natural compounds existing in seaweeds, such as fucoxanthin and phoroglucinol, have shown cytotoxic activity in models in vitro and in vivo, acting through different molecular mechanisms, such as antioxidant, antiproliferative, DNA damage/DNA repair, proapoptotic, antiangiogenic and antimetastic. Within the scope of interactions with conventional drugs, there are evidences that some seaweed compounds could be used to potentiate the action of anticancer drugs. However, their effects and mechanisms of action, alone or in combination with anticancer drugs, namely TMZ, in glioblastoma cell, still few explored and require more attention due to the unquestionable high potential of these marine compounds.

Inhibition of autophagy increases susceptibility of glioblastoma stem cells to temozolomide by igniting ferroptosis

The role of autophagy in cancer onset and progression appears still controversial. On one hand, autophagy allows cancer cell to survive in unfavorable environmental conditions, on the other hand, once internal energy resources are exhausted, it leads to cell death. In addition, autophagy interpheres with cell cycle progression, de facto exerting a cytostatic activity. Hence, it represents an important target for anticancer therapy. For example, temozolomide (TMZ), of use for glioblastoma (GBM) treatment, appears as capable of inducing autophagy partially inhibiting cancer cell proliferation. However, GBM, a very aggressive brain tumor with poor prognosis even after surgery and radio-chemotherapy, invariably recurs and leads to patient death. Since cancer stem cells have been hypothesized to play a role in refractory/relapsing cancers, in the present work we investigated if autophagy could represent a constitutive cytoprotection mechanism for glioblastoma stem-like cells (GSCs) and if the modulation of autophagic process could affect GBM growth and survival. Thus, in the present study we first evaluated the relevance of autophagy in GBM tumor specimens, then its occurrence in GSCs and, finally, if modulation of autophagy could influence GSC response to TMZ. Our results suggested that, in vitro, the impairing autophagic process with quinacrine, a compound able to cross the blood-brain barrier, increased GSC susceptibility to TMZ. Death of GSCs was apparently due to the iron dependent form of programmed cell death characterized by the accumulation of lipid peroxides called ferroptosis. These results underscore the relevance of the modulation of autophagy in the GSC survival and death and suggest that triggering of ferroptosis in GSCs could represent a novel and important target for the management of glioblastoma.

New Multitarget Approaches in the War Against Glioblastoma: A Mini-Perspective

Glioblastoma multiforme (GBM) is the most common tumor of the CNS, and the deadliest form of brain cancer. The rapid progression, the anatomic location in the brain and a deficient knowledge of the pathophysiology, often limit the effectiveness of therapeutic interventions. Current pillars of GBM therapies include surgical resection, radiotherapy and chemotherapy, but the low survival rate and the short life expectation following these treatments strongly underline the urgency to identify innovative and more effective therapeutic tools. Frequently, patients subjected to a mono-target therapy, such as Temozolomide (TMZ), develop drug resistance and undergo relapse, indicating that targeting a single cellular node is not sufficient for eradication of this disease. In this context, a multi-targeted therapeutic approach aimed at using compounds, alone or in combination, capable of inhibiting more than one specific molecular target, offers a promising alternative. Such strategies have already been well integrated into drug discovery campaigns, including in the field of anticancer drugs. In this miniperspective, we will discuss the recent progress in the treatment of GBM focusing on innovative and effective preclinical strategies, which are based on a multi-targeted approach.

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.

STK3 is a therapeutic target for a subset of acute myeloid leukemias

Acute myeloid leukemia (AML) is characterized by uncontrolled proliferation and accumulation of immature myeloblasts, which impair normal hematopoiesis. While this definition categorizes the disease into a distinctive group, the large number of different genetic and epigenetic alterations actually suggests that AML is not a single disease, but a plethora of malignancies. Still, most AML patients are not treated with targeted medication but rather by uniform approaches such as chemotherapy. The identification of novel treatment options likely requires the identification of cancer cell vulnerabilities that take into account the different genetic and epigenetic make-up of the individual tumors. Here we show that STK3 depletion by knock-down, knock-out or chemical inhibition results in apoptotic cells death in some but not all AML cell lines and primary cells tested. This effect is mediated by a premature activation of cyclin dependent kinase 1 (CDK1) in presence of elevated cyclin B1 levels. The anti-leukemic effects seen in both bulk and progenitor AML cells suggests that STK3 might be a promising target in a subset of AML patients.

The enhancement of siPLK1 penetration across BBB and its anti glioblastoma activity in vivo by magnet and transferrin co-modified nanoparticle

In order to enhance the penetration of small interference RNA against the polo-like kinase I (siPLK1) across BBB to treat glioblastoma (GBM), transferrin (Tf) modified magnetic nanoparticle (Tf-PEG-PLL/MNP@siPLK1) was prepared. The in vitro experiments indicated that Tf-PEG-PLL/MNP@siPLK1 enhanced the cellular uptake of siPLK1, which resulted in an increase of gene silencing effect and cytotoxicity of Tf-PEG-PLL/MNP@siPLK1 on U87 cells. Besides, Tf-PEG-PLL/MNP@siPLK1 significantly inhibited the growth of U87 glioblastoma spheroids and markedly increased the BBB penetration efficiency of siPLK1 with the application of external magnetic field in in-vitro BBB model. The in vivo experiments indicated that siPLK1 selectively accumulated in the brain tissue, and markedly reduced tumor volume and prolonged the survival time of GBM-bearing mice after Tf-PEG-PLL/MNP@siPLK1 was injected to GBM-bearing mice via tail vein. The above data indicated that magnet and transferrin co-modified nanoparticle enhanced siPLK1 penetration across BBB and increased its anti GBM activity in vivo.

UCN-01 enhances cytotoxicity of irinotecan in colorectal cancer stem-like cells by impairing DNA damage response

Colorectal cancer (CRC) is one of the most common and lethal cancers worldwide. Despite recent progress, the prognosis of advanced stage CRC remains poor, mainly because of cancer recurrence and metastasis. The high morbidity and mortality of CRC has been recently ascribed to a small population of tumor cells that hold the potential of tumor initiation, i.e. cancer stem cells (CSCs), which play a pivotal role in cancer recurrence and metastasis and are not eradicated by current therapy. We screened CRC-SCs in vitro with a library of protein kinase inhibitors and showed that CRC-SCs are resistant to specific inhibition of the major signaling pathways involved in cell survival and proliferation. Nonetheless, broad-spectrum inhibition by the staurosporin derivative UCN-01 blocks CRC-SC growth and potentiates the activity of irinotecan in vitro and in vivo CRC-SC-derived models. Reverse-Phase Protein Microarrays (RPPA) revealed that, albeit CRC-SCs display individual phospho-proteomic profiles, sensitivity of CRC-SCs to UCN-01 relies on the interference with the DNA damage response mediated by Chk1. Combination of LY2603618, a specific Chk1/2 inhibitor, with irinotecan resulted in a significant reduction of CRC-SC growth in vivo, confirming that irinotecan treatment coupled to inhibition of Chk1 represents a potentially effective therapeutic approach for CRC treatment.

Targeting PDK1 for Chemosensitization of Cancer Cells

Despite the rapid development in the field of oncology, cancer remains the second cause of mortality worldwide, with the number of new cases expected to more than double in the coming years. Chemotherapy is widely used to decelerate or stop tumour development in combination with surgery or radiation therapy when appropriate, and in many cases this improves the symptomatology of the disease. Unfortunately though, chemotherapy is not applicable to all patients and even when it is, there are many cases where a successful initial treatment period is followed by chemotherapeutic drug resistance. This is caused by a number of reasons, ranging from the genetic background of the patient (innate resistance) to the formation of tumour-initiating cells (acquired resistance). In this review, we discuss the potential role of PDK1 in the development of chemoresistance in different types of malignancy, and the design and application of potent inhibitors which can promote chemosensitization.

Claspin functions in cell homeostasis-A link to cancer?

Cancer remains one of the leading causes of mortality worldwide. Most cancers present high degrees of genomic instability. DNA damage and replication checkpoints function as barriers to halt cell cycle progression until damage is resolved, preventing the perpetuation of errors. Activation of these checkpoints is critically dependent on Claspin, an adaptor protein that mediates the phosphorylation of the effector kinase Chk1 by ATR. However, Claspin also performs other roles related to the protection and maintenance of cell and genome integrity. For instance, following DNA damage and checkpoint activation, Claspin bridges checkpoint responses to DNA repair or to apoptosis. During DNA replication, Claspin acts a sensor and couples DNA unwinding to strand polymerization, and may also indirectly regulate replication initiation at firing origins. As Claspin participates in several processes that are vital to maintenance of cell homeostasis, its function is tightly regulated at multiple levels. Nevertheless, little is known about its role in cancer. Accumulating evidence suggests that Claspin inactivation could be an essential event during carcinogenesis, indicating that Claspin may function as a tumour suppressor. In this review, we will examine the functions of Claspin and how its deregulation may contribute to cancer initiation and progression. To conclude, we will discuss means by which Claspin can be targeted for cancer therapy.

Chemical Proteomic Approaches Targeting Cancer Stem Cells: A Review of Current Literature

Cancer stem cells (CSCs) have been proposed as central drivers of tumor initiation, progression, recurrence, and therapeutic resistance. Therefore, identifying stem-like cells within cancers and understanding their properties is crucial for the development of effective anticancer therapies. Recently, chemical proteomics has become a powerful tool to efficiently determine protein networks responsible for CSC pathophysiology and comprehensively elucidate molecular mechanisms of drug action against CSCs. This review provides an overview of major methodologies utilized in chemical proteomic approaches. In addition, recent successful chemical proteomic applications targeting CSCs are highlighted. Future direction of potential CSC research by integrating chemical genomic and proteomic data obtained from a single biological sample of CSCs are also suggested in this review.

DNA Repair

Cellular chromosomal DNA is the principal target through which ionising radiation exerts it diverse biological effects. This chapter summarises the relevant DNA damage signalling and repair pathways used by normal and tumour cells in response to irradiation. Strategies for tumour radiosensitisation are reviewed which exploit tumour-specific DNA repair deficiencies or signalling pathway addictions, with a special focus on growth factor signalling, PARP, cancer stem cells, cell cycle checkpoints and DNA replication. This chapter concludes with a discussion of DNA repair-related candidate biomarkers of tumour response which are of crucial importance for implementing precision medicine in radiation oncology.

Translational research in radiation-induced DNA damage signaling and repair

Radiotherapy is an effective tool in the fight against cancer. It is non-invasive and painless, and with advanced tumor imaging and beam control systems, radiation can be delivered to patients safely, generally with minor or no adverse side effects, accounting for its increasing use against a broad range of tumors. Tumors and normal cells respond to radiation-induced DNA damage by activating a complex network of DNA damage signaling and repair pathways that determine cell fate including survival, death, and genome stability. DNA damage response (DDR) proteins represent excellent targets to augment radiotherapy, and many agents that inhibit key response proteins are being combined with radiation and genotoxic chemotherapy in clinical trials. This review focuses on how insights into molecular mechanisms of DDR pathways are translated to small animal preclinical studies, to clinical studies of naturally occurring tumors in companion animals, and finally to human clinical trials. Companion animal studies, under the umbrella of comparative oncology, have played key roles in the development of clinical radiotherapy throughout its >100-year history. There is growing appreciation that rapid translation of basic knowledge of DNA damage and repair systems to improved radiotherapy practice requires a comprehensive approach that embraces the full spectrum of cancer research, with companion animal clinical trials representing a critical bridge between small animal preclinical studies, and human clinical trials.

EMAP-II sensitize U87MG and glioma stem-like cells to temozolomide via induction of autophagy-mediated cell death and G2/M arrest

Despite the fact that temozolomide (TMZ) has been widely accepted as the key chemotherapeutic agent to prolong the survival of patients with glioblastoma, failure and recurrence cases can still be observed in clinics. Glioma stem-like cells (GSCs) are thought to be responsible for the drug resistance. In this study, we investigate whether endothelial monocyte-activating polypeptide-II (EMAP-II), a pro-inflammatory cytokine, can enhance TMZ cytotoxicity on U87MG and GSCs or not. As described in prior research, GSCs have been isolated from U87MG and maintained in the serum-free DMEM/F12 medium containing EGF, b-FGF, and B27. TMZ and/or EMAP-II administration were performed for 72 h, respectively. The results showed that TMZ combined with EMAP-II inhibit the proliferation of U87MG and GSCs by a larger measure than TMZ single treatment by decreasing the IC₅₀. EMAP-II also enhanced TMZ-induced autophagy-mediated cell death and G2/M arrest. Moreover, we found that EMAP-II functioned a targeted suppression on mTOR, which may involve in the anti-neoplasm mechanism. The results suggest that EMAP-II could be considered as a combined chemotherapeutic agent against glioblastoma by sensitizing U87MG and GSCs to TMZ.

Immunomodulating and Immunoresistance Properties of Cancer-Initiating Cells: Implications for the Clinical Success of Immunotherapy

Cancer-initiating cells (CICs) represent a relatively rare subpopulation of cells endowed with self-renewal, stemness properties, tumorigenicity in immunodeficient mice, and resistance to standard therapies as well as to immunotherapy. Here, we review the biological and immunological characteristics of CICs with special focus on the immunomodulating mechanisms they utilize to escape from immunosurveillance. The recently developed immunotherapeutic strategies have yielded remarkable clinical results in many types of tumors, indicating that indeed a patient's immune system can mount an immune response, which is effective in controlling tumor growth. However, a high proportion of patients is resistant or acquires resistance to these therapeutic strategies. The latter findings may reflect, at least in some cases, the inability of the immunotherapeutic strategies used to eradicate CICs. The CICs that escape immune recognition and destruction may give rise to new tumors in the same organ site or through the metastatic colonization in other anatomic sites. Identification of novel therapeutic approaches that can eradicate CICs is a major challenge in the cancer therapy area. An improved understanding of the interactions of CICs with immune system and with tumor microenvironment may contribute to optimize the available therapies and to design novel combination treatments for cancer therapy.

ABBREVIATIONS

ALDH, aldehyde dehydrogenase; APC, antigen-presenting cells; APM, antigen-processing machinery; CAR: chimeric antigen receptor; CHK1, checkpoint serine/threonine protein kinase; CIC, cancer-initiating cell; CRC, colorectal cancer; CTLA-4, cytotoxic T lymphocyte antigen-4; GBM, glioblastoma multiforme; GDF-15, growth differentiation factor-15; CSPG4: chondroitin sulfate proteoglycan-4; IFN, interferon; IL-4, interleukin-4; IL-10, interleukin-10; IL-13, interleukin-13; IL-13α2, α2 chain of IL-13 receptor; mAb, monoclonal antibody; MDSC, myeloid-derived suppressor cell; MHC, major histocompatibility complex; PD-1, programmed death-1; PD-L1 programmed death ligand-1; PDK, 3-phosphoinositide-dependent protein kinase-1; PGE2, prostaglandin E2; STAT3, signal transducer and activator of transcription 3; TGFB-1, transforming growth factor beta-1; Treg, T regulatory cell.

Human mesenchymal stromal cells inhibit tumor growth in orthotopic glioblastoma xenografts

BACKGROUND

Mesenchymal stem/stromal cells (MSCs) represent an attractive tool for cell-based cancer therapy mainly because of their ability to migrate to tumors and to release bioactive molecules. However, the impact of MSCs on tumor growth has not been fully established. We previously demonstrated that murine MSCs show a strong tropism towards glioblastoma (GBM) brain xenografts and that these cells are able to uptake and release the chemotherapeutic drug paclitaxel (PTX), maintaining their tropism towards the tumor. Here, we address the therapy-relevant issue of using MSCs from human donors (hMSCs) for local or systemic administration in orthotopic GBM models, including xenografts of patient-derived glioma stem cells (GSCs).

METHODS

U87MG or GSC1 cells expressing the green fluorescent protein (GFP) were grafted onto the striatum of immunosuppressed rats. Adipose hMSCs (Ad-hMSCs), fluorescently labeled with the mCherry protein, were inoculated adjacent to or into the tumor. In rats bearing U87MG xenografts, systemic injections of Ad-hMSCs or bone marrow (BM)-hMSCs were done via the femoral vein or carotid artery. In each experiment, either PTX-loaded or unloaded hMSCs were used. To characterize the effects of hMSCs on tumor growth, we analyzed survival, tumor volume, tumor cell proliferation, and microvascular density.

RESULTS

Overall, the AD-hMSCs showed remarkable tropism towards the tumor. Intracerebral injection of Ad-hMSCs significantly improved the survival of rats with U87MG xenografts. This effect was associated with a reduction in tumor growth, tumor cell proliferation, and microvascular density. In GSC1 xenografts, intratumoral injection of Ad-hMSCs depleted the tumor cell population and induced migration of resident microglial cells. Overall, PTX loading did not significantly enhance the antitumor potential of hMSCs. Systemically injected Ad- and BM-hMSCs homed to tumor xenografts. The efficiency of hMSC homing ranged between 0.02 and 0.5% of the injected cells, depending both on the route of cell injection and on the source from which the hMSCs were derived. Importantly, systemically injected PTX-loaded hMSCs that homed to the xenograft induced cytotoxic damage to the surrounding tumor cells.

CONCLUSIONS

hMSCs have a therapeutic potential in GBM brain xenografts which is also expressed against the GSC population. In this context, PTX loading of hMSCs seems to play a minor role.

Hypoxia-responsive ionizable liposome delivery siRNA for glioma therapy

Here, we report the hypoxia-responsive ionizable liposomes to deliver small interference RNA (siRNA) anticancer drugs, which can selectively enhance cellular uptake of the siRNA under hypoxic and low-pH conditions to cure glioma. For this purpose, malate dehydrogenase lipid molecules were synthesized, which contain nitroimidazole groups that impart hypoxia sensitivity and specificity as hydrophobic tails, and tertiary amines as hydrophilic head groups. These malate dehydrogenase molecules, together with DSPE-PEG2000 and cholesterol, were self-assembled into O'1,O1-(3-(dimethylamino)propane-1,2-diyl) 16-bis(2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethyl) di(hexadecanedioate) liposomes (MLP) to encapsulate siRNA through electrostatic interaction. Our study showed that the MLP could deliver polo-like kinase 1 siRNA (siPLK1) into glioma cells and effectively enhance the cellular uptake of MLP/siPLK1 because of increased positive charges induced by hypoxia and low pH. Moreover, MLP/siPLK1 was shown to be very effective in inhibiting the growth of glioma cells both in vitro and in vivo. Therefore, the MLP is a promising siRNA delivery system for tumor therapy.

Dual Inhibition of PDK1 and Aurora Kinase A: An Effective Strategy to Induce Differentiation and Apoptosis of Human Glioblastoma Multiforme Stem Cells

The poor prognosis of glioblastoma multiforme (GBM) is mainly attributed to drug resistance mechanisms and to the existence of a subpopulation of glioma stem cells (GSCs). Multitarget compounds able to both affect different deregulated pathways and the GSC subpopulation could escape tumor resistance and, most importantly, eradicate the stem cell reservoir. In this respect, the simultaneous inhibition of phosphoinositide-dependent kinase-1 (PDK1) and aurora kinase A (AurA), each one playing a pivotal role in cellular survival/migration/differentiation, could represent an innovative strategy to overcome GBM resistance and recurrence. Herein, the cross-talk between these pathways was investigated, using the single-target reference compounds MP7 (PDK1 inhibitor) and Alisertib (AurA inhibitor). Furthermore, a new ligand, SA16, was identified for its ability to inhibit the PDK1 and the AurA pathways at once, thus proving to be a useful tool for the simultaneous inhibition of the two kinases. SA16 blocked GBM cell proliferation, reduced tumor invasiveness, and triggered cellular apoptosis. Most importantly, the AurA/PDK1 blocker showed an increased efficacy against GSCs, inducing their differentiation and apoptosis. To the best of our knowledge, this is the first report on combined targeting of PDK1 and AurA. This drug represents an attractive multitarget lead scaffold for the development of new potential treatments for GBM and GSCs.

ATM, ATR, CHK1, CHK2 and WEE1 inhibitors in cancer and cancer stem cells

DNA inevitably undergoes a high number of damages throughout the cell cycle. To preserve the integrity of the genome, cells have developed a complex enzymatic machinery aimed at sensing and repairing DNA lesions, pausing the cell cycle to provide more time to repair, or induce apoptosis if damages are too severe. This so-called DNA-damage response (DDR) is yet considered as a major source of resistance to DNA-damaging treatments in oncology. Recently, it has been hypothesized that cancer stem cells (CSC), a sub-population of cancer cells particularly resistant and with tumour-initiating ability, allow tumour re-growth and cancer relapse. Therefore, DDR appears as a relevant target to sensitize cancer cells and cancer stem cells to classical radio- and chemotherapies as well as to overcome resistances. Moreover, the concept of synthetic lethality could be particularly efficiently exploited in DDR. Five kinases play pivotal roles in the DDR: ATM, ATR, CHK1, CHK2 and WEE1. Herein, we review the drugs targeting these proteins and the inhibitors used in the specific case of CSC. We also suggest molecules that may be of interest for preclinical and clinical researchers studying checkpoint inhibition to sensitize cancer and cancer stem cells to DNA-damaging treatments.

Combination of lentivirus-mediated silencing of PPM1D and temozolomide chemotherapy eradicates malignant glioma through cell apoptosis and cell cycle arrest

Temozolomide (TMZ) is approved for use as first-line treatment for glioblastoma multiforme (GBM). However, GBM shows chemoresistance shortly after the initiation of treatment. In order to detect whether silencing of human protein phosphatase 1D magnesium dependent (PPM1D) gene could increase the effects of TMZ in glioma cells, glioma cells U87-MG were infected with lentiviral shRNA vector targeting PPM1D silencing. After PPM1D silencing was established, cells were treated with TMZ. The multiple functions of human glioma cells after PPM1D silencing and TMZ chemotherapy were detected by flow cytometry and MTT assay. Significantly differentially expressed genes were distinguished by microarray-based gene expression profiling and analyzed by gene pathway enrichment analysis and ontology assessment. Western blotting was used to establish the protein expression of the core genes. PPM1D gene silencing improves TMZ induced cell proliferation and induces cell apoptosis and cell cycle arrest. When PPM1D gene silencing combined with TMZ was performed in glioma cells, 367 genes were upregulated and 444 genes were downregulated compared with negative control. The most significant differential expression pathway was pathway in cancer and IGFR1R, PIK3R1, MAPK8 and EP300 are core genes in the network. Western blotting showed that MAPK8 and PIK3R1 protein expression levels were upregulated and RB1 protein expression was decreased. It was consistent with that detected in gene expression profiling. In conclusion, PPM1D gene silencing combined with TMZ eradicates glioma cells through cell apoptosis and cell cycle arrest. PIK3R1/AKT pathway plays a role in the multiple functions of glioma cells after PPM1D silencing and TMZ chemotherapy.

AKT/GSK3β Signaling in Glioblastoma

Glioblastoma (GBM) is the most aggressive of primary brain tumors. Despite the progress in understanding the biology of the pathogenesis of glioma made during the past decade, the clinical outcome of patients with GBM remains still poor. Deregulation of many signaling pathways involved in growth, survival, migration and resistance to treatment has been implicated in pathogenesis of GBM. One of these pathways is phosphatidylinositol-3 kinases (PI3K)/protein kinase B (AKT)/rapamycin-sensitive mTOR-complex (mTOR) pathway, intensively studied and widely described so far. Much less attention has been paid to the role of glycogen synthase kinase 3 β (GSK3β), a target of AKT. In this review we focus on the function of AKT/GSK3β signaling in GBM.

Locking PDK1 in DFG-out conformation through 2-oxo-indole containing molecules: Another tools to fight glioblastoma

The phosphoinositide-dependent kinase-1 (PDK1) is one of the main components of the PI3K/Akt pathway. Also named the "master kinase" of the AGC family, PDK1 plays a critical role in tumorigenesis, by enhancing cell proliferation and inhibiting apoptosis, as well as in cell invasion and metastasis formation. Although there have been done huge efforts in discovering specific compounds targeting PDK1, nowadays no PDK1 inhibitor has yet entered the clinic. With the aim to pick out novel and potent PDK1 inhibitors, herein we report the design and synthesis of a new class of molecules obtained by merging the 2-oxo-indole nucleus with the 2-oxo-pyridonyl fragment, two moieties with high affinity for the PDK1 hinge region and its DFG-out binding site, respectively. To this purpose, a small series of compounds were synthesised and a tandem application of docking and Molecular Dynamic (MD) was employed to get insight into their mode of binding. The OXID-pyridonyl hybrid 8, possessing the lower IC50 (IC50 = 112 nM), was also tested against recombinant kinases involved in the PI3K/PDK1/Akt pathway and was subjected to vitro studies to evaluate the cytotoxicity and the inhibition of tumour cell migration. All together the results let us to consider 8, as a lead compound of a new generation of PDK1 inhibitors and encourage us to further studies in this direction.

Overexpression of PIK3CA in murine head and neck epithelium drives tumor invasion and metastasis through PDK1 and enhanced TGFβ signaling

Head and neck squamous cell carcinoma (HNSCC) patients have a poor prognosis, with invasion and metastasis as major causes of mortality. The phosphatidylinositol 3-kinase (PI3K) pathway regulates a wide range of cellular processes crucial for tumorigenesis, and PIK3CA amplification and mutation are among the most common genetic alterations in human HNSCC. Compared to the well-documented roles of the PI3K pathway in cell growth and survival, the roles of the PI3K pathway in tumor invasion and metastasis have not been well delineated. We generated a PIK3CA-genetically engineered mouse model (PIK3CA-GEMM) in which wildtype PIK3CA is overexpressed in head and neck epithelium. Although PIK3CA overexpression alone was not sufficient to initiate HNSCC formation, it significantly increased tumor susceptibility in an oral-carcinogenesis mouse model. PIK3CA overexpression in mouse oral epithelium increased tumor invasiveness and metastasis by increasing epithelial-mesenchymal transition and by enriching a cancer stem cell phenotype in tumor epithelial cells. In addition to these epithelial alterations, we also observed marked inflammation in tumor stroma. AKT is a central signaling mediator of the PI3K pathway. However, molecular analysis suggested that progression of PIK3CA-driven HNSCC is facilitated by PDK1 and enhanced TGFβ signaling rather than by AKT. Examination of human HNSCC clinical samples revealed that both PIK3CA and PDK1 protein levels correlated with tumor progression, highlighting the significance of this pathway. In summary, our results offer significant insight into how PIK3CA-overexpression drives HNSCC invasion and metastasis, providing a rationale for targeting PI3K/PDK1 and TGFβ signaling in advanced HNSCC patients with PIK3CA amplification.

Metabolic/Proteomic Signature Defines Two Glioblastoma Subtypes With Different Clinical Outcome

Glioblastoma (GBM) is one of the deadliest human cancers. Because of the extremely unfavorable prognosis of GBM, it is important to develop more effective diagnostic and therapeutic strategies based on biologically and clinically relevant subclassification systems. Analyzing a collection of seventeen patient-derived glioblastoma stem-like cells (GSCs) by gene expression profiling, NMR spectroscopy and signal transduction pathway activation, we identified two GSC clusters, one characterized by a pro-neural-like phenotype and the other showing a mesenchymal-like phenotype. Evaluating the levels of proteins differentially expressed by the two GSC clusters in the TCGA GBM sample collection, we found that SRC activation is associated with a GBM subgroup showing better prognosis whereas activation of RPS6, an effector of mTOR pathway, identifies a subgroup with a worse prognosis. The two clusters are also differentiated by NMR spectroscopy profiles suggesting a potential prognostic stratification based on metabolic evaluation. Our data show that the metabolic/proteomic profile of GSCs is informative of the genomic/proteomic GBM landscape, which differs among tumor subtypes and is associated with clinical outcome.

Cellular Pathways in Response to Ionizing Radiation and Their Targetability for Tumor Radiosensitization

During the last few decades, improvements in the planning and application of radiotherapy in combination with surgery and chemotherapy resulted in increased survival rates of tumor patients. However, the success of radiotherapy is impaired by two reasons: firstly, the radioresistance of tumor cells and, secondly, the radiation-induced damage of normal tissue cells located in the field of ionizing radiation. These limitations demand the development of drugs for either radiosensitization of tumor cells or radioprotection of normal tissue cells. In order to identify potential targets, a detailed understanding of the cellular pathways involved in radiation response is an absolute requirement. This review describes the most important pathways of radioresponse and several key target proteins for radiosensitization.

Mechanisms of tumour resistance against chemotherapeutic agents in veterinary oncology

Several classes of chemotherapy drugs are used as first line or adjuvant treatment of the majority of tumour types in veterinary oncology. However, some types of tumour are intrinsically resistant to several anti-cancer drugs, and others, while initially sensitive, acquire resistance during treatment. Chemotherapy often significantly prolongs survival or disease free interval, but is not curative. The exact mechanisms behind intrinsic and acquired chemotherapy resistance are unknown for most animal tumours, but there is increasing knowledge on the mechanisms of drug resistance in humans and a few reports on molecular changes in resistant canine tumours have emerged. In addition, approaches to overcome or prevent chemotherapy resistance are becoming available in humans and, given the overlaps in molecular alterations between human and animal tumours, these may also be relevant in veterinary oncology. This review provides an overview of the current state of research on general chemotherapy resistance mechanisms, including drug efflux, DNA repair, apoptosis evasion and tumour stem cells. The known resistance mechanisms in animal tumours and the potential of these findings for improving treatment efficacy in veterinary oncology are also explored.

The role of glioma stem cells in chemotherapy resistance and glioblastoma multiforme recurrence

Glioma stem cells (GSCs) constitute a slow-dividing, small population within a heterogeneous glioblastoma. They are able to self-renew, recapitulate a whole tumor, and differentiate into other specific glioblastoma multiforme (GBM) subpopulations. Therefore, they have been held responsible for malignant relapse after primary standard therapy and the poor prognosis of recurrent GBM. The failure of current therapies to eliminate specific GSC subpopulations has been considered a major factor contributing to the inevitable recurrence in GBM patients after treatment. Here, we discuss the molecular mechanisms of chemoresistance of GSCs and the reasons why complete eradication of GSCs is so difficult to achieve. We will also describe the targeted therapies currently available for GSCs and possible mechanisms to overcome such chemoresistance and avoid therapeutic relapse.

Targeting lung cancer through inhibition of checkpoint kinases

Inhibitors of checkpoint kinases ATR, Chk1, and Wee1 are currently being tested in preclinical and clinical trials. Here, we review the basic principles behind the use of such inhibitors as anticancer agents, and particularly discuss their potential for treatment of lung cancer. As lung cancer is one of the most deadly cancers, new treatment strategies are highly needed. We discuss how checkpoint kinase inhibition in principle can lead to selective killing of lung cancer cells while sparing the surrounding normal tissues. Several features of lung cancer may potentially be exploited for targeting through inhibition of checkpoint kinases, including mutated p53, low ERCC1 levels, amplified Myc, tumor hypoxia and presence of lung cancer stem cells. Synergistic effects have also been reported between inhibitors of ATR/Chk1/Wee1 and conventional lung cancer treatments, such as gemcitabine, cisplatin, or radiation. Altogether, inhibitors of ATR, Chk1, and Wee1 are emerging as new cancer treatment agents, likely to be useful in lung cancer treatment. However, as lung tumors are very diverse, the inhibitors are unlikely to be effective in all patients, and more work is needed to determine how such inhibitors can be utilized in the most optimal ways.

Localized RNAi therapeutics of chemoresistant grade IV glioma using hyaluronan-grafted lipid-based nanoparticles

Glioblastoma multiforme (GBM) is one of the most infiltrating, aggressive, and poorly treated brain tumors. Progress in genomics and proteomics has paved the way for identifying potential therapeutic targets for treating GBM, yet the vast majority of these leading drug candidates for the treatment of GBM are ineffective, mainly due to restricted passages across the blood-brain barrier. Nanoparticles have been emerged as a promising platform to treat different types of tumors due to their ability to transport drugs to target sites while minimizing adverse effects. Herein, we devised a localized strategy to deliver RNA interference (RNAi) directly to the GBM site using hyaluronan (HA)-grafted lipid-based nanoparticles (LNPs). These LNPs having an ionized lipid were previously shown to be highly effective in delivering small interfering RNAs (siRNAs) into various cell types. LNP's surface was functionalized with hyaluronan (HA), a naturally occurring glycosaminoglycan that specifically binds the CD44 receptor expressed on GBM cells. We found that HA-LNPs can successfully bind to GBM cell lines and primary neurosphers of GBM patients. HA-LNPs loaded with Polo-Like Kinase 1 (PLK1) siRNAs (siPLK1) dramatically reduced the expression of PLK1 mRNA and cumulated in cell death even under shear flow that simulate the flow of the cerebrospinal fluid compared with control groups. Next, a human GBM U87MG orthotopic xenograft model was established by intracranial injection of U87MG cells into nude mice. Convection of Cy3-siRNA entrapped in HA-LNPs was performed, and specific Cy3 uptake was observed in U87MG cells. Moreover, convection of siPLK1 entrapped in HA-LNPs reduced mRNA levels by more than 80% and significantly prolonged survival of treated mice in the orthotopic model. Taken together, our results suggest that RNAi therapeutics could effectively be delivered in a localized manner with HA-coated LNPs and ultimately may become a therapeutic modality for GBM.

Detection of phosphorylated insulin receptor in colorectal adenoma and adenocarcinoma: implications for prognosis and clinical outcome

Colorectal carcinoma remains among the most frequent causes of cancer death. Besides the well-known genetic predisposition, a key role in colorectal adenoma and adenocarcinoma etio-pathogenesis, mainly in sporadic cases, is played by definite risk factors, such as obesity, type 2 diabetes, insulin resistance, hyper-insulinemia, and insulin therapy. These epidemiological data motivated us to determine, by means of immunohistochemistry, the amount of activated (phosphorylated) insulin receptor in archival samples from 22 colorectal adenoma and 117 adenocarcinoma patients, with the objective to estimate the role of this factor in colorectal epithelium transformation and cancer progression. Statistical analysis of the results clearly showed that positive staining for phosphorylated insulin receptor was significantly more frequent in adenomas than adenocarcinomas (P < 0.0001) and, within the adenocarcinoma cohort, it was more frequent in low-grade tumors (P = 0.005). In adenomas, staining was exclusively cytoplasmic, while in adenocarcinomas it was cytoplasmic and/or nuclear (P < 0.0001). Interestingly, disease-free survival in colorectal adenocarcinoma patients pointed out a significantly better prognosis for those bearing a positive staining for phosphorylated insulin receptor (P = 0.02). From these data, we can argue that activated insulin receptor plays a fundamental role at the early stages of tumorigenesis, where late stages could be characterized by a shift toward more active oncogenic drivers. Determining the amount of phosphorylated insulin receptor could thus represent a novel prognostic/predictive tool in colorectal adenocarcinoma patients.

Cancer stem cells--important players in tumor therapy resistance

Resistance to tumor therapy is an unsolved problem in cancer treatment. A plethora of studies have attempted to explain this phenomenon and many mechanisms of resistance have been suggested over recent decades. The concept of cancer stem cells (CSCs), which describes tumors as hierarchically organized, has added a new level of complexity to therapy failure. CSCs are the root of cancers and resist chemo- and radiotherapy, explaining cancer recurrence even many years after therapy is ended. This review discusses briefly CSCs in cancers, gives an overview of the role of CSCs in therapy resistance, and discusses the potential means of targeting these therapy-resistant tumor cells.