Antiangiogenic and anti-invasive effects of sunitinib on experimental human glioblastoma

Combining organotypic tissue culture with light-sheet microscopy (OTCxLSFM) to study glioma invasion

Glioblastoma is a very aggressive tumor and represents the most common primary brain malignancy. Key characteristics include its high resistance against conventional treatments, such as radio- and chemotherapy and its diffuse tissue infiltration, preventing complete surgical resection. The analysis of migration and invasion processes in a physiological microenvironment allows for enhanced understanding of these phenomena and can lead to improved therapeutic approaches. Here, we combine two state-of-the-art techniques, adult organotypic brain tissue slice culture (OTC) and light-sheet fluorescence microscopy (LSFM) of cleared tissues in a combined method termed OTCxLSFM. Using this methodology, we can show that glioblastoma tissue infiltration can be effectively blocked through treatment with arsenic trioxide or WP1066, as well as genetic depletion of the tetraspanin, transmembrane receptor CD9, or signal transducer and activator of transcription 3 (STAT3). With our analysis pipeline, we gain single-cell level, three-dimensional information, as well as insights into the morphological appearance of the tumor cells.

Target-Based Anticancer Indole Derivatives for the Development of Anti-Glioblastoma Agents

Glioblastoma (GBM) is the most aggressive and frequent primary brain tumor, with a poor prognosis and the highest mortality rate. Currently, GBM therapy consists of surgical resection of the tumor, radiotherapy, and adjuvant chemotherapy with temozolomide. Consistently, there are poor treatment options and only modest anticancer efficacy is achieved; therefore, there is still a need for the development of new effective therapies for GBM. Indole is considered one of the most privileged scaffolds in heterocyclic chemistry, so it may serve as an effective probe for the development of new drug candidates against challenging diseases, including GBM. This review analyzes the therapeutic benefit and clinical development of novel indole-based derivatives investigated as promising anti-GBM agents. The existing indole-based compounds which are in the pre-clinical and clinical stages of development against GBM are reported, with particular reference to the most recent advances between 2013 and 2022. The main mechanisms of action underlying their anti-GBM efficacy, such as protein kinase, tubulin and p53 pathway inhibition, are also discussed. The final goal is to pave the way for medicinal chemists in the future design and development of novel effective indole-based anti-GBM agents.

Sunitinib efficacy with minimal toxicity in patient-derived retinoblastoma organoids

BACKGROUND

Recurrence of retinoblastoma (RB) following chemoreduction is common and is often managed with local (intra-arterial/intravitreal) chemotherapy. However, some tumors are resistant to even local administration of maximum feasible drug dosages, or effective tumor control and globe preservation may be achieved at the cost of vision loss due to drug-induced retinal toxicity. The aim of this study was to identify drugs with improved antitumor activity and more favorable retinal toxicity profiles via screening of potentially repurposable FDA-approved drugs in patient-derived tumor organoids.

METHODS

Genomic profiling of five RB organoids and the corresponding parental tissues was performed. RB organoids were screened with 133 FDA-approved drugs, and candidate drugs were selected based on cytotoxicity and potency. RNA sequencing was conducted to generate a drug signature from RB organoids, and the effects of drugs on cell cycle progression and proliferative tumor cone restriction were examined. Drug toxicity was assessed with human embryonic stem cell-derived normal retinal organoids. The efficacy/toxicity profiles of candidate drugs were compared with those of drugs in clinical use.

RESULTS

RB organoids maintained the genomic features of the parental tumors. Sunitinib was identified as highly cytotoxic against both classical RB1-deficient and novel MYCN-amplified RB organoids and inhibited proliferation while inducing differentiation in RB. Sunitinib was a more effective suppressor of proliferative tumor cones in RB organoids and had lower toxicity in normal retinal organoids than either melphalan or topotecan.

CONCLUSION

The efficacy and retinal toxicity profiles of sunitinib suggest that it could potentially be repurposed for local chemotherapy of RB.

Phase II trial of concurrent sunitinib, temozolomide, and radiotherapy with adjuvant temozolomide for newly diagnosed MGMT unmethylated glioblastoma

Background

The overall prognosis of glioblastoma (GBM) remains dismal, particularly for patients with unmethylated O6-methylguanine-DNA-methyltransferase (MGMT) promoter. In this phase II trial, we tested the combination of the antiangiogenic agent sunitinib with radiotherapy and temozolomide (TMZ) for newly diagnosed unmethylated MGMT GBM patients.

Methods

We enrolled 37 patients with unmethylated MGMT promoter GBM, age 18-70, and KPS ≥70. Patients received 12.5 mg of daily sunitinib for 7 days, followed by concurrent chemoradiation plus 12.5 mg sunitinib, then adjuvant TMZ. The primary endpoint was progression-free survival (PFS), and secondary endpoints were overall survival (OS), safety, and neutrophil-to-lymphocyte ratio (NLR) biomarker.

Results

At a median follow-up time of 15.3 months (range: 3.1-71.3 months), the median PFS was 7.15 months (95% CI: 5.4-10.5) and the 6-month PFS was 54.0%. Median OS was 15.0 months (95% CI: 13.8-19.4) and 2-year OS rate was 17.1%. Patients receiving >3 cycles of adjuvant TMZ, undergoing surgery at progression, and presenting a post-concurrent NLR ≤6 experienced a significant improved OS with hazard ratios of 0.197 (P = .001), 0.46 (P = .049), and 0.38 (P = .021), respectively, on multivariable analysis. Age >65 years predicted for worse OS with hazard ratio of 3.92 (P = .037). Grade ≥3 thrombocytopenia occurred in 22.9%, grade ≥3 neutropenia in 20%, and grade ≥3 thromboembolic events in 14.3% of patients. There were no grade 5 events.

Conclusion

Our findings suggest a potential benefit of combining sunitinib with chemoradiation in newly diagnosed GBM patients with unmethylated MGMT status and provide a strong rationale to test this combination in future studies.

Brain Invasion and Trends in Molecular Research on Meningioma

Meningiomas are the most common primary brain tumors in adults. The treatment of non-benign meningiomas remains a challenging task, and after the publication of the 2021 World Health Organization classification, the importance of molecular biological classification is emerging. In this article, we introduce the mechanisms of brain invasion in atypical meningioma and review the genetic factors involved along with epigenetic regulation. First, it is important to understand the three major steps for brain invasion of meningeal cells: 1) degradation of extracellular matrix by proteases, 2) promotion of tumor cell migration to resident cells by adhesion molecules, and 3) neovascularization and supporting cells by growth factors. Second, the genomic landscape of meningiomas should be analyzed by major categories, such as germline mutations in NF2 and somatic mutations in non-NF2 genes (TRAF7, KLF4, AKT1, SMO, and POLR2A). Finally, epigenetic alterations in meningiomas are being studied, with a focus on DNA methylation, histone modification, and RNA interference. Increasing knowledge of the molecular landscape of meningiomas has allowed the identification of prognostic and predictive markers that can guide therapeutic decision-making processes and the timing of follow-up.

Role of Sam68 in Sunitinib induced renal cell carcinoma apoptosis

Sunitinib is one of the first-line targeted drugs for metastatic renal cell carcinoma (RCC) with dual effects of antiangiogensis and proapoptosis. Sam68 (Src-associated in mitosis, 68 KDa), is found being involved in cell apoptosis. This article reveals that Sam68 impacts the sensitivity to sunitinib by mediating the apoptosis of RCC cells. Immunohistochemical staining indicated that the Sam68 expression levels in sunitinib sensitive tumor tissues were markedly higher than those in sunitinib resistant tumor tissues. Sunitinib induced RCC cell apoptosis in a concentration-dependent manner and inhibited the expression of total and phosphorylated Sam68 (p-Sam68). Downregulation of Sam68 expression inhibited RCC cell apoptosis induced by sunitinib. While upregulation of Sam68 expression could enhance apoptosis induced by sunitinib. Xenograft models showed that tumors in the Sam68-knockdown group did not shrink as much as those in the control group after treatment with sunitinib for 4 weeks. Together, our results suggest that Sam68 expression is associated with the sensitivity of ccRCC patients to sunitinib. Sam68 may promote cell apoptosis induced by sunitinib, and the Sam68 expression level may be a biomarker for predicting sunitinib sensitivity in ccRCC patients.

Antitumor Effects of a New Retinoate of the Fungal Cytotoxin Illudin M in Brain Tumor Models

While the fungal metabolite illudin M (1) is indiscriminately cytotoxic in cancer and non-malignant cells, its retinoate 2 showed a greater selectivity for the former, especially in a cerebral context. Illudin M killed malignant glioma cells as well as primary neurons and astrocytes at similarly low concentrations and destroyed their microtubule and glial fibrillary acidic protein (GFAP) networks. In contrast, the ester 2 was distinctly more cytotoxic in highly dedifferentiated U87 glioma cells than in neurons, which were even stimulated to enhanced growth. This was also observed in co-cultures of neurons with U87 cells where conjugate 2 eventually killed them by induction of differentiation based on the activation of nuclear receptors, which bind to retinoid-responsive elements (RARE). Hence, illudin M retinoate 2 appears to be a promising drug candidate.

Lycorine inhibits angiogenesis by docking to PDGFRα

Lycorine (Lyc) is a natural alkaloid derived from medicinal plants of the Amaryllidaceae family. Lyc has been reported to inhibit the recurrence and metastasis of different kinds of tumors. However, Lyc’s effect on angiogenesis and its specific mechanism are still not clear. This study was designed to test the antiangiogenesis effect of Lyc and to explore the possible mechanisms. We performed cell experiments to confirm Lyc’s inhibitory effect on angiogenesis and employed sunitinib as a positive control. Moreover, the synergistic effect of Lyc and sunitinib was also explored. Next, we conducted bioinformatics analyses to predict the potential targets of Lyc and verified them by western blotting and immunofluorescence. Molecular docking, kinase activity assays, Biacore assays and cellular thermal shift assays (CETSAs) were applied to elucidate the mechanism by which Lyc inhibited target activity. Lyc inhibited angiogenesis in human umbilical vein endothelial cells (HUVECs). Employing bioinformatics, we found that Lyc’s target was PDGFRα and that Lyc attenuated PDGFRα phosphorylation. We also found that Lyc inhibited PDGFRα activation by docking to it to restrain its activity. Additionally, Lyc significantly inhibited PDGF-AA-induced angiogenesis. This study provides new insights into the molecular functions of Lyc and indicates its potential as a therapeutic agent for tumor angiogenesis.

Receptor tyrosine kinases as druggable targets in glioblastoma: Do signaling pathways matter?

Glioblastoma (GBM) is the most malignant primary brain tumor without effective therapies. Since bevacizumab was FDA approved for targeting vascular endothelial growth factor receptor 2 (VEGFR2) in adult patients with recurrent GBM, targeted therapy against receptor tyrosine kinases (RTKs) has become a new avenue for GBM therapeutics. In addition to VEGFR, the epidermal growth factor receptor (EGFR), platelet-derived growth factor receptor (PDGFR), hepatocyte growth factor receptor (HGFR/MET), and fibroblast growth factor receptor (FGFR) are major RTK targets. However, results from clinical Phase II/III trials indicate that most RTK-targeting therapeutics including tyrosine kinase inhibitors (TKIs) and neutralizing antibodies lack clinical efficacy, either alone or in combination. The major challenge is to uncover the genetic RTK alterations driving GBM initiation and progression, as well as to elucidate the mechanisms toward therapeutic resistance. In this review, we will discuss the genetic alterations in these 5 commonly targeted RTKs, the clinical trial outcomes of the associated RTK-targeting therapeutics, and the potential mechanisms toward the resistance. We anticipate that future design of new clinical trials with combination strategies, based on the genetic alterations within an individual patient’s tumor and mechanisms contributing to therapeutic resistance after treatment, will achieve durable remissions and improve outcomes in GBM patients.

Guanabenz Sensitizes Glioblastoma Cells to Sunitinib by Inhibiting GADD34-Mediated Autophagic Signaling

Limited therapeutic efficacy of temozolomide (TMZ) against glioblastomas highlights the importance of exploring new drugs for clinical therapy. Sunitinib, a multitargeted receptor tyrosine kinase inhibitor, is currently being tested as therapy for glioblastomas. Unfortunately, sunitinib still has insufficient activity to cure glioblastomas. Our aim was to determine the molecular mechanisms counteracting sunitinib drug sensitivity and find potential adjuvant drugs for glioblastoma therapy. Through in vitro experiments, transcriptome screening by RNA sequencing, and in silico analyses, we found that sunitinib induced glioma apoptotic death, and downregulated genes were enriched in oncogenic genes of glioblastoma. Meanwhile, sunitinib-upregulated genes were highly associated with the protective autophagy process. Blockade of autophagy significantly enhanced sunitinib's cytotoxicity. Growth arrest and DNA damage-inducible protein (GADD) 34 was identified as a candidate involved in sunitinib-promoted autophagy through activating p38-mitogen-activated protein kinase (MAPK) signaling. Higher GADD34 levels predicted poor survival of glioblastoma patients and induced autophagy formation in desensitizing sunitinib cytotoxicity. Guanabenz, an alpha2-selective adrenergic agonist and GADD34 functional inhibitor, was identified to enhance the efficacy of sunitinib by targeting GADD34-induced protective autophagy in glioblastoma cells, TMZ-resistant cells, hypoxic cultured cells, sphere-forming cells, and colony formation abilities. A better combined treatment effect with sunitinib and guanabenz was also observed by using xenograft mice. Taken together, the sunitinib therapy combined with guanabenz in the inhibition of GADD34-enhanced protective autophagy may provide a new therapeutic strategy for glioblastoma.

Sunitinib-Containing Carborane Pharmacophore with the Ability to Inhibit Tyrosine Kinases Receptors FLT3, KIT and PDGFR-β, Exhibits Powerful In Vivo Anti-Glioblastoma Activity

Simple Summary

Glioblastoma is one of the most aggressive central nervous system tumors. Combinations of therapies, such as tyrosine kinase receptor inhibition and boron neutron capture therapy (BNCT), could offer greater patients benefits over single-therapies. The aim of our study was to assess the potential of sunitinib-carborane hybrid compound 1 as an anti-glioblastoma agent. We confirmed for 1 the ability to inhibit tyrosine kinase receptors, which could promote canonical and non-canonical effects, absence of mutagenicity, ability to cross the blood–brain barrier, and powerful in vivo anti-glioblastoma activity. The overall attractive profile of 1 makes it an interesting compound for a bimodal therapeutic strategy against high grade gliomas.

Abstract

Malignant gliomas are the most common malignant and aggressive primary brain tumors in adults, the prognosis being—especially for glioblastomas—extremely poor. There are no effective treatments yet. However, tyrosine kinase receptor (TKR) inhibitors and boron neutron capture therapy (BNCT), together, have been proposed as future therapeutic strategies. In this sense in our ongoing project of developing new anti-glioblastoma drugs, we identified a sunitinib-carborane hybrid agent, 1, with both in vitro selective cytotoxicity and excellent BNCT-behavior. Consequently, we studied the ability of compound 1 to inhibit TKRs, its promotion of cellular death processes, and its effects on the cell cycle. Moreover, we analyzed some relevant drug-like properties of 1, i.e., mutagenicity and ability to cross the blood–brain barrier. These results encouraged us to perform an in vivo anti-glioblastoma proof of concept assay. It turned out to be a selective FLT3, KIT, and PDGFR-β inhibitor and increased the apoptotic glioma-cell numbers and arrested sub-G1-phase cell cycle. Its in vivo activity in immunosuppressed mice bearing U87 MG human glioblastoma evidenced excellent anti-tumor behavior.

Disentangling the therapeutic tactics in GBM: From bench to bedside and beyond

Glioblastoma multiforme (GBM) is one of the most common and malignant form of adult brain tumor with a high mortality rate and dismal prognosis. The present standard treatment comprising surgical resection followed by radiation and chemotherapy using temozolomide can broaden patient's survival to some extent. However, the advantages are not palliative due to the development of resistance to the drug and tumor recurrence following the multimodal treatment approaches due to both intra- and intertumoral heterogeneity of GBM. One of the major contributors to temozolomide resistance is O⁶ -methylguanine-DNA methyltransferase. Furthermore, deficiency of mismatch repair, base excision repair, and cytoprotective autophagy adds to temozolomide obstruction. Rising proof additionally showed that a small population of cells displaying certain stem cell markers, known as glioma stem cells, adds on to the resistance and tumor progression. Collectively, these findings necessitate the discovery of novel therapeutic avenues for treating glioblastoma. As of late, after understanding the pathophysiology and biology of GBM, some novel therapeutic discoveries, such as drug repurposing, targeted molecules, immunotherapies, antimitotic therapies, and microRNAs, have been developed as new potential treatments for glioblastoma. To help illustrate, "what are the mechanisms of resistance to temozolomide" and "what kind of alternative therapeutics can be suggested" with this fatal disease, a detailed history of these has been discussed in this review article, all with a hope to develop an effective treatment strategy for GBM.

Bimodal Therapeutic Agents Against Glioblastoma, One of the Most Lethal Forms of Cancer

About 95 % of people diagnosed with glioblastoma die within five years. Glioblastoma is the most aggressive central nervous system tumour. It is necessary to make progress in the glioblastoma treatment so that advanced chemotherapy drugs or radiation therapy or, ideally, two-in-one hybrid systems should be implemented. Tyrosine kinase receptors-inhibitors and boron neutron capture therapy (BNCT), together, could provide a therapeutic strategy. In this work, sunitinib decorated-carborane hybrids were prepared and biologically evaluated identifying excellent antitumoral- and BNCT-agents. One of the selected hybrids was studied against glioma-cells and found to be 4 times more cytotoxic than sunitinib and 1.7 times more effective than ¹⁰ B-boronophenylalanine fructose complex when the cells were irradiated with neutrons.

Autophagy as a Potential Therapy for Malignant Glioma

Glioma is the most frequent and aggressive type of brain neoplasm, being anaplastic astrocytoma (AA) and glioblastoma multiforme (GBM), its most malignant forms. The survival rate in patients with these neoplasms is 15 months after diagnosis, despite a diversity of treatments, including surgery, radiation, chemotherapy, and immunotherapy. The resistance of GBM to various therapies is due to a highly mutated genome; these genetic changes induce a de-regulation of several signaling pathways and result in higher cell proliferation rates, angiogenesis, invasion, and a marked resistance to apoptosis; this latter trait is a hallmark of highly invasive tumor cells, such as glioma cells. Due to a defective apoptosis in gliomas, induced autophagic death can be an alternative to remove tumor cells. Paradoxically, however, autophagy in cancer can promote either a cell death or survival. Modulating the autophagic pathway as a death mechanism for cancer cells has prompted the use of both inhibitors and autophagy inducers. The autophagic process, either as a cancer suppressing or inducing mechanism in high-grade gliomas is discussed in this review, along with therapeutic approaches to inhibit or induce autophagy in pre-clinical and clinical studies, aiming to increase the efficiency of conventional treatments to remove glioma neoplastic cells.

Porcine arterial ECM hydrogel: Designing an in vitro angiogenesis model for long-term high-throughput research

The field of angiogenesis research provides deep understanding regarding this important process, which plays fundamental roles in tissue development and different abnormalities. In vitro models offer the advantages of low-cost high-throughput research of angiogenesis while sparing animal lives, and enabling the use of human cells. Nevertheless, prevailing in vitro models lack stability and are limited to a few days' assays. This study, therefore, examines the hypothesis that closely mimicking the vascular microenvironment can more reliably support longer angiogenesis processes in vitro. To this end, porcine arterial extracellular matrix (paECM)- a key component of blood vessels-was isolated and processed into a thermally induced hydrogel and characterized in terms of composition, structure, and mechanical properties, thus confirming the preservation of important characteristics of arterial extracellular matrix. This unique hydrogel was further tailored into a three-dimensional model of angiogenesis using endothelial cells and supporting cells, in a configuration that allows high-throughput quantitative analysis of cell viability and proliferation, cell migration, and apoptosis, thus revealing the advantages of paECM over frequently used biomaterials. Markedly, when applied with well-known effectors of angiogenesis, the model measures reflected the expected response, hence validating its efficacy and establishing its potential as a promising tool for the research of angiogenesis.

A new tyrosine kinase inhibitor K905-0266 inhibits proliferation and sphere formation of glioblastoma cancer cells

Glioblastoma (GBM) is the most prevalent malignant tumour of the central nervous system and carries a poor prognosis; average survival time after diagnosis is 14 months. Because of its unfavourable prognosis, novel therapies are needed. The aim of this study was to assess whether inhibition of GBM and GBM-derived cancer stem cells (CSCs) by a new tyrosine kinase inhibitor (TKI), K905-0266, is possible. To do this, we generated GBM (D54 and U87MG) cells expressing luciferase and characterised the inhibitory effects of the TKI with bioluminescent imaging (BLI) and western blot (WB). The effect of the TKI was then evaluated in CSCs. BLI showed significant inhibition of D54 and U87MG cells by TKI treatment. WB showed that the TKI decreased pERK and Bcl-2 level and increased cleaved caspase-3 level. Sphere formation was significantly reduced by the TKI in CSCs. Our results showed that a new TKI, K905-0266, effectively inhibited GBM and CSCs, making this a candidate for GBM therapy.

The Brain Penetrating and Dual TORC1/TORC2 Inhibitor, RES529, Elicits Anti-Glioma Activity and Enhances the Therapeutic Effects of Anti-Angiogenetic Compounds in Preclinical Murine Models

Background. Glioblastoma multiforme (GBM) is a devastating disease showing a very poor prognosis. New therapeutic approaches are needed to improve survival and quality of life. GBM is a highly vascularized tumor and as such, chemotherapy and anti-angiogenic drugs have been combined for treatment. However, as treatment-induced resistance often develops, our goal was to identify and treat pathways involved in resistance to treatment to optimize the treatment strategies. Anti-angiogenetic compounds tested in preclinical and clinical settings demonstrated recurrence associated to secondary activation of the phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR pathway. Aims. Here, we determined the sensitizing effects of the small molecule and oral available dual TORC1/TORC2 dissociative inhibitor, RES529, alone or in combination with the anti-VEGF blocking antibody, bevacizumab, or the tyrosine kinase inhibitor, sunitinib, in human GBM models. Results. We observed that RES529 effectively inhibited dose-dependently the growth of GBM cells in vitro counteracting the insurgence of recurrence after bevacizumab or sunitinib administration in vivo. Combination strategies were associated with reduced tumor progression as indicated by the analysis of Time to Tumor Progression (TTP) and disease-free survival (DSF) as well as increased overall survival (OS) of tumor bearing mice. RES529 was able to reduce the in vitro migration of tumor cells and tubule formation from both brain-derived endothelial cells (angiogenesis) and tumor cells (vasculogenic mimicry). Conclusions. In summary, RES529, the first dual TORC1/TORC2 dissociative inhibitor, lacking affinity for ABCB1/ABCG2 and having good brain penetration, was active in GBM preclinical/murine models giving credence to its use in clinical trial for patients with GBM treated in association with anti-angiogenetic compounds.

Glioblastoma Multiforme: An Overview of Emerging Therapeutic Targets

Glioblastoma multiforme (GBM) is the most common and aggressive malignant primary brain tumour in humans and has a very poor prognosis. The existing treatments have had limited success in increasing overall survival. Thus, identifying and understanding the key molecule(s) responsible for the malignant phenotype of GBM will yield new potential therapeutic targets. The treatment of brain tumours faces unique challenges, including the presence of the blood brain barrier (BBB), which limits the concentration of drugs that can reach the site of the tumour. Nevertheless, several promising treatments have been shown to cross the BBB and have shown promising pre-clinical results. This review will outline the status of several of these promising targeted therapies.

The Distribution Volume of 18F-Albumin as a Potential Biomarker of Antiangiogenic Treatment Efficacy

Objective: 18F-albumin, a vascular imaging agent, may have potential to assess tumor responses to anti-angiogenic therapies. In these studies tumor distribution volume of 18F-albumin were first determined in various human tumor xenografts from biodistribtuion measurments and then one of the tumor type was used to evaluate changes in 18F-albumin uptake in anti-angiognic tumor model. Method: 18F-albumin was synthesized via conjugation of 6-[18F]fluoronicotinic acid-2,3,5,6-tetrafluorophenyl ester, [18F]F-Py-TFP, with rat albumin. From the biodistribution of 18F-albumin in various human tumor xenografts tumor distribution volumes (DVs; tumor%ID/g:blood%ID/g) were first determined at various time points. Then, the ability of 18F-albumin to detect tumor angiogenic inhibition in one of these tumor types (U87MG) following treatment with sunitinib was evaluated by position emission tomography (PET) imaging at 0, 7, 14, and 21 days post treatment. Caliper measurements of tumor dimensions were also made at these same times. At Day 21, following imaging, biodistributions, autoradiography of tumor tissues and tumor blood vessel counts (CD31 IHC) were performed. Results: 18F-albumin retention in various tumors steadily increased over time with U87MG tumor exhibiting the highest uptake (DV) at all times. Significant decreases in 18F-albumin DVs were observed one week post-treatement (-39%) vs. controls whereas tumor caliper volumes were not significantly decreased until days 14 and 21. At day 21 the significant decrease in DVs in the treatment group (-44%) paralleled biodistribution DV measurements and was consistent with autoradiography and CD31 IHC findings. Conclusion: These data suggest that 18F-albumin DVs obtained by imaging may serve as an early biomarker of the effectiveness of anti-angiogenic therapy and thus aid in patient management and treatment planning.

Autophagic and Apoptotic Pathways as Targets for Chemotherapy in Glioblastoma

Glioblastoma multiforme is the most malignant and aggressive type of brain tumor, with a mean life expectancy of less than 15 months. This is due in part to the high resistance to apoptosis and moderate resistant to autophagic cell death in glioblastoma cells, and to the poor therapeutic response to conventional therapies. Autophagic cell death represents an alternative mechanism to overcome the resistance of glioblastoma to pro-apoptosis-related therapies. Nevertheless, apoptosis induction plays a major conceptual role in several experimental studies to develop novel therapies against brain tumors. In this review, we outline the different components of the apoptotic and autophagic pathways and explore the mechanisms of resistance to these cell death pathways in glioblastoma cells. Finally, we discuss drugs with clinical and preclinical use that interfere with the mechanisms of survival, proliferation, angiogenesis, migration, invasion, and cell death of malignant cells, favoring the induction of apoptosis and autophagy, or the inhibition of the latter leading to cell death, as well as their therapeutic potential in glioma, and examine new perspectives in this promising research field.

EphB4 mediates resistance to antiangiogenic therapy in experimental glioma

INTRODUCTION

Alterations in vascular morphogenesis are hallmarks of antiangiogenesis-resistant tumor vessels. Vascular morphogenesis is regulated by ephrinB2-EphB4 system which may induce different biological effects depending on the oncological and molecular contexts. It was the aim of the current study to characterize the influence of EphB4 on tumor microcirculation after antiangiogenic treatment using different SF126 glioma models.

MATERIALS AND METHODS

Using an ecotropic transfection system, empty vector (pLXSN) or EphB4 (EphB4^OE) overexpressing Phoenix-ECO cells were coimplanted with SF126 glioma cells subcutaneously (dorsal skinfold chamber, DSC) and orthotopically (cranial window, CW). Tumor volume was assessed by MRI. Intravital microscopy (IVM) allowed microcirculatory analysis (total {TVD} and functional vessel density {FVD}, diameter {D}, and permeability index {PI}) before and after antiangiogenic treatment (Sunitinib: DSC: 40 mg/kg BW, 6 days; CW: 80 mg/kg BW, 4 days). Immunohistochemistry included Pecam-Desmin, Ki67, TUNEL, and Caspase 3 stainings.

RESULTS

EphB4^OE induced large and treatment-resistant tumor vessels (FVD: Control/Su: 110 ± 23 cm/cm² vs. EphB4^OE/Su: 103 ± 42 cm/cm²). Maintenance of pericyte-endothelial cell interactions (Control: 80 ± 12 vs. Control/Su: 47 ± 26%; EphB4^OE: 88 ± 9 vs. EphB4^OE/Su: 74 ± 25%) and reduced antiproliferative (Control: 637 ± 80 vs. Control/Su: 110 ± 22; EphB4^OE: 298 ± 108 vs. EphB4^OE/Su: 213 ± 80) and proapoptotic responses (Control: 196 ± 25 vs. Control / Su: 404 ± 60; EphB4^OE: 183 ± 20 vs. EphB4^OE/Su: 270 ± 66) were observed under EphB4 overexpression.

CONCLUSION

EphB4 overexpression leads to vascular resistance by altering vascular morphogenesis, pericyte coverage, and cellular proliferation/apoptosis in experimental SF126 glioma models.

The pancreatic niche inhibits the effectiveness of sunitinib treatment of pancreatic cancer

Current treatments for pancreatic ductal adenocarcinoma (PDA) are ineffective, making this the 4^th leading cause of cancer deaths. Sunitinib is a broad-spectrum inhibitor of tyrosine kinase receptors mostly known for its anti-angiogenic effects. We tested the therapeutic effects of sunitinib in pancreatic cancer using the Ela-myc transgenic mouse model. We showed that Ela-myc pancreatic tumors express PDGFR and VEGFR in blood vessels and epithelial cells, rendering these tumors sensitive to sunitinib by more than only its anti-angiogenic activity. However, sunitinib treatment of Ela-myc mice with either early or advanced tumor progression had no impact on either survival or tumor burden. Further histopathological characterization of these tumors did not reveal differences in necrosis, cell differentiation, angiogenesis, apoptosis or proliferation. In stark contrast, in vitro sunitinib treatment of Ela-myc– derived cell lines showed high sensitivity to the drug, with increased apoptosis and reduced proliferation. Correspondingly, subcutaneous tumors generated from these cell lines completely regressed in vivo after sunitinib treatments. These data point at the pancreatic tumor microenvironment as the most likely barrier preventing sunitinib treatment efficiency in vivo. Combined treatments with drugs that disrupt tumor fibrosis may enhance sunitinib therapeutic effectiveness in pancreatic cancer treatment.

Real-Time Apoptosis and Viability High-Throughput Screening of 3D Multicellular Tumor Spheroids Using the Celigo Image Cytometer

Three-dimensional tumor spheroid models have been increasingly used to investigate and characterize cancer drug compounds. Previously, the Celigo image cytometer has demonstrated its utility in a high-throughput screening manner for evaluating potential drug candidates in a 3D multicellular tumor spheroid (MCTS) primary screen. In addition, we have developed real-time kinetic caspase 3/7 apoptosis and propidium iodide viability 3D MCTS assays, both of which can be used in a secondary screen to better characterize the hit compounds. In this work, we monitored the kinetic apoptotic and cytotoxic effects of 14 compounds in 3D MCTS produced from the glioblastoma cell line U87MG in 384-well plates for 9 days. The kinetic results allowed the categorization of the effects from 14 drug compounds into early and late cytotoxic, apoptotic, cytostatic, and no effects. The real-time apoptosis and viability screening method can serve as an improved secondary screen to better understand the mechanism of action of these potential drug candidates identified from the primary screen, allowing one to identify a more qualified drug candidate and streamline the drug discovery process of research and development.

The novel CXCR4 antagonist, PRX177561, reduces tumor cell proliferation and accelerates cancer stem cell differentiation in glioblastoma preclinical models

Glioblastoma is the most frequent and the most lethal primary brain tumor among adults. Standard of care is the association of radiotherapy with concomitant or adjuvant temozolomide. However, to date, recurrence is inevitable. The CXCL12/CXCR4 pathway is upregulated in the glioblastoma tumor microenvironment regulating tumor cell proliferation, local invasion, angiogenesis, and the efficacy of radio-chemotherapy. In this study, we evaluated the effects of the novel CXCR4 antagonist, PRX177561, in preclinical models of glioblastoma. CXCR4 expression and PRX177561 effects were assessed on a panel of 12 human glioblastoma cells lines and 5 patient-derived glioblastoma stem cell cultures. Next, the effect of PRX177561 was tested in vivo, using subcutaneous injection of U87MG, U251, and T98G cells as well as orthotopic intrabrain inoculation of luciferase-transfected U87MG cells. Here we found that PRX177561 impairs the proliferation of human glioblastoma cell lines, increases apoptosis, and reduces CXCR4 expression and cell migration in response to stromal cell-derived factor 1alpha in vitro. PRX177561 reduced the expression of stem cell markers and increased that of E-cadherin and glial fibrillary acidic protein in U87MG cells consistent with a reduction in cancer stem cells. In vivo, PRX177561 reduced the weight and increased the time to progression of glioblastoma subcutaneous tumors while increasing disease-free survival and overall survival of mice bearing orthotopic tumors. Our findings suggest that targeting stromal cell-derived factor 1 alpha/CXCR4 axis by PRX177561 might represent a novel therapeutic approach against glioblastoma and support further investigation of this compound in more complex preclinical settings in order to determine its therapeutic potential.

A Novel Multiparametric Drug-Scoring Method for High-Throughput Screening of 3D Multicellular Tumor Spheroids Using the Celigo Image Cytometer

Three-dimensional (3D) tumor models have been increasingly used to investigate and characterize cancer drug compounds. The ability to perform high-throughput screening of 3D multicellular tumor spheroids (MCTS) can highly improve the efficiency and cost-effectiveness of discovering potential cancer drug candidates. Previously, the Celigo Image Cytometer has demonstrated a novel method for high-throughput screening of 3D multicellular tumor spheroids. In this work, we employed the Celigo Image Cytometer to examine the effects of 14 cancer drug compounds on 3D MCTS of the glioblastoma cell line U87MG in 384-well plates. Using parameters such as MCTS diameter and invasion area, growth and invasion were monitored for 9 and 3 d, respectively. Furthermore, fluorescent staining with calcein AM, propidium iodide, Hoechst 33342, and caspase 3/7 was performed at day 9 posttreatment to measure viability and apoptosis. Using the kinetic and endpoint data generated, we created a novel multiparametric drug-scoring system for 3D MCTS that can be used to identify and classify potential drug candidates earlier in the drug discovery process. Furthermore, the combination of quantitative and qualitative image data can be used to delineate differences between drugs that induce cytotoxic and cytostatic effects. The 3D MCTS-based multiparametric scoring method described here can provide an alternative screening method to better qualify tested drug compounds.

Synthetic miR-145 Mimic Enhances the Cytotoxic Effect of the Antiangiogenic Drug Sunitinib in Glioblastoma

Although aggressive therapeutic regimen has been applied in the treatment of Glioblastoma (GBM), the prognosis of patients with GBM remains poor. Preclinical studies have demonstrated the efficacy of Suntinib in GBM both in vitro and in vivo. In this study, we showed that the cytotoxicity was enhanced by transfection with miR-145 mimic. In addition, we suggested that the enhanced cytotoxicity of Sunitinib by miR-145 mimic was mediated by inhibition of both P-gp and Bcrp.

The brain-penetrating CXCR4 antagonist, PRX177561, increases the antitumor effects of bevacizumab and sunitinib in preclinical models of human glioblastoma

Background

Glioblastoma recurrence after treatment with the anti-vascular endothelial growth factor (VEGF) antibody bevacizumab is characterized by a highly infiltrative and malignant behavior that renders surgical excision and chemotherapy ineffective. It has been demonstrated that anti-VEGF/VEGFR therapies control the invasive phenotype and that relapse occurs through the increased activity of CXCR4. We therefore hypothesized that combining bevacizumab or sunitinib with the novel CXCR4 antagonist, PRX177561, would have superior antitumor activity.

Methods

The effects of bevacizumab, sunitinib, and PRX177561 were tested alone or in combination in subcutaneous xenografts of U87MG, U251, and T98G cells as well as on intracranial xenografts of luciferase tagged U87MG cells injected in CD1-nu/nu mice. Animals were randomized to receive vehicle, bevacizumab (4 mg/kg iv every 4 days), sunitinib (40 mg/kg po qd), or PRX177561 (50 mg/kg po qd).

Results

The in vivo experiments demonstrated that bevacizumab and sunitinib increase the in vivo expression of CXCR4, SDF-1α, and TGFβ1. In addition, we demonstrate that the co-administration of the novel brain-penetrating CXCR4 antagonist, PRX177561, with bevacizumab or sunitinib inhibited tumor growth and reduced the inflammation. The combination of PRX177561 with bevacizumab resulted in a synergistic reduction of tumor growth with an increase of disease-free survival (DSF) and overall survival (OS), whereas the combination of PRX177561 with sunitinib showed a mild additive effect.

Conclusions

The CXC4 antagonist PRX177561 may be a valid therapeutic complement to anti-angiogenic therapy, particularly when used in combination with VEGF/VEGFR inhibitors. Therefore, this compound deserves to be considered for future clinical evaluation.

Limited Tumor Tissue Drug Penetration Contributes to Primary Resistance against Angiogenesis Inhibitors

Resistance mechanisms against antiangiogenic drugs are unclear. Here, we correlated the antitumor and antivascular properties of five different antiangiogenic receptor tyrosine kinase inhibitors (RTKIs) (motesanib, pazopanib, sorafenib, sunitinib, vatalanib) with their intratumoral distribution data obtained by matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI). In the first mouse model, only sunitinib exhibited broad-spectrum antivascular and antitumor activities by simultaneously suppressing vascular endothelial growth factor receptor-2 (VEGFR2) and desmin expression, and by increasing intratumoral hypoxia and inhibiting both tumor growth and vascularisation significantly. Importantly, the highest and most homogeneous intratumoral drug concentrations have been found in sunitinib-treated animals. In another animal model, where - in contrast to the first model - vatalanib was detectable at homogeneously high intratumoral concentrations, the drug significantly reduced tumor growth and angiogenesis. In conclusion, the tumor tissue penetration and thus the antiangiogenic and antitumor potential of antiangiogenic RTKIs vary among the tumor models and our study demonstrates the potential of MALDI-MSI to predict the efficacy of unlabelled small molecule antiangiogenic drugs in malignant tissue. Our approach is thus a major technical and preclinical advance demonstrating that primary resistance to angiogenesis inhibitors involves limited tumor tissue drug penetration. We also conclude that MALDI-MSI may significantly contribute to the improvement of antivascular cancer therapies.

Quantitative Evaluation of Tumor Early Response to a Vascular-Disrupting Agent with Dynamic PET

PURPOSE

The purpose of this study is to evaluate the early response of tumors to a vascular-disrupting agent (VDA) VEGF121/recombinant toxin gelonin (rGel) using dynamic [(18)F]FPPRGD2 positron emission tomography (PET) and kinetic parameter estimation.

PROCEDURES

Two tumor xenograft models: U87MG (highly vascularized) and A549 (moderately vascularized), were selected, and both were randomized into treatment and control groups. Sixty-minute dynamic PET scans with [(18)F]FPPRGD2 that targets to integrin αvβ3 were performed at days 0 (baseline), 1, and 3 since VEGF121/rGel treatment started. Dynamic PET-derived binding potential (BPND) and parametric maps were compared with tumor uptake (%ID/g) and the static PET image at 1 h after the tracer administration.

RESULTS

The growth of U87MG tumor was obviously delayed upon VEGF121/rGel treatment. A549 tumor was not responsive to the same treatment. BPND of treated U87MG tumors decreased significantly at day 1 (p < 0.05), and the difference was more significant at day 3 (p < 0.01), compared with the control group. However, the tracer uptake (%ID/g) derived from static images at 1-h time point did not show significant difference between the treated and control tumors until day 3. Little difference in tracer uptake (%ID/g) or BPND was found between treated and control A549 tumors. Considering the tracer retention in tumor and the slower clearance due to damaged tumor vasculature after treatment, BPND representing the actual specific binding portion appears to be more sensitive and accurate than the semiquantitative parameters (such as %ID/g) derived from static images to assess the early response of tumor to VDA treatment.

CONCLUSIONS

Quantitative analysis based on dynamic PET with [(18)F]FPPRGD2 shows advantages in distinguishing effective from ineffective treatment during the course of VEGF121/rGel therapy at early stage and is therefore more sensitive in assessing therapy response than static PET.

Optimization of Early Response Monitoring and Prediction of Cancer Antiangiogenesis Therapy via Noninvasive PET Molecular Imaging Strategies of Multifactorial Bioparameters

Objective: Antiangiogenesis therapy (AAT) has provided substantial benefits regarding improved outcomes and survival for suitable patients in clinical settings. Therefore, the early definition of therapeutic effects is urgently needed to guide cancer AAT. We aimed to optimize the early response monitoring and prediction of AAT efficacy, as indicated by the multi-targeted anti-angiogenic drug sunitinib in U87MG tumors, using noninvasive positron emission computed tomography (PET) molecular imaging strategies of multifactorial bioparameters.

Methods: U87MG tumor mice were treated via intragastric injections of sunitinib (80 mg/kg) or vehicle for 7 consecutive days. Longitudinal MicroPET/CT scans with ¹⁸F-FDG, ¹⁸F-FMISO, ¹⁸F-ML-10 and ¹⁸F-Alfatide II were acquired to quantitatively measure metabolism, hypoxia, apoptosis and angiogenesis on days 0, 1, 3, 7 and 13 following therapy initiation. Tumor tissues from a dedicated group of mice were collected for immunohistochemical (IHC) analysis of key biomarkers (Glut-1, CA-IX, TUNEL, α_νβ₃ and CD31) at the time points of PET imaging. The tumor sizes and mouse weights were measured throughout the study. The tumor uptake (ID%/g_max), the ratios of the tumor/muscle (T/M) for each probe, and the tumor growth ratios (TGR) were calculated and used for statistical analyses of the differences and correlations.

Results: Sunitinib successfully inhibited U87MG tumor growth with significant differences in the tumor size from day 9 after sunitinib treatment compared with the control group (P < 0.01). The uptakes of ¹⁸F-FMISO (reduced hypoxia), ¹⁸F-ML-10 (increased apoptosis) and ¹⁸F-Alfatide II (decreased angiogenesis) in the tumor lesions significantly changed during the early stage (days 1 to 3) of sunitinib treatment; however, the uptake of ¹⁸F-FDG (increased glucose metabolism) was significantly different during the late stage. The PET imaging data of each probe were all confirmed via ex vivo IHC of the relevant biomarkers. Notably, the PET imaging of ¹⁸F-Alfatide II and ¹⁸F-FMISO was significantly correlated (all P < 0.05) with TGR, whereas the imaging of ¹⁸F-FDG and ¹⁸F-ML-10 was not significantly correlated with TGR.

Conclusion: Based on the tumor uptake of the PET probes and their correlations with MVD and TGR, ¹⁸F-Alfatide II PET may not only monitor the early response but also precisely predict the therapeutic efficacy of the multi-targeted, anti-angiogenic drug sunitinib in U87MG tumors. In conclusion, it is feasible to optimize the early response monitoring and efficacy prediction of cancer AAT using noninvasive PET molecular imaging strategies of multifactorial bioparameters, such as angiogenesis imaging with ¹⁸F-Alfatide II, which represents an RGD-based probe.

Human iPSC-derived endothelial cell sprouting assay in synthetic hydrogel arrays

Activation of vascular endothelial cells (ECs) by growth factors initiates a cascade of events during angiogenesis in vivo consisting of EC tip cell selection, sprout formation, EC stalk cell proliferation, and ultimately vascular stabilization by support cells. Although EC functional assays can recapitulate one or more aspects of angiogenesis in vitro, they are often limited by undefined substrates and lack of dependence on key angiogenic signaling axes. Here, we designed and characterized a chemically-defined model of endothelial sprouting behavior in vitro using human induced pluripotent stem cell-derived endothelial cells (iPSC-ECs). We rapidly encapsulated iPSC-ECs at high density in poly(ethylene glycol) (PEG) hydrogel spheres using thiol-ene chemistry and subsequently encapsulated cell-dense hydrogel spheres in a cell-free hydrogel layer. The hydrogel sprouting array supported pro-angiogenic phenotype of iPSC-ECs and supported growth factor-dependent proliferation and sprouting behavior. iPSC-ECs in the sprouting model responded appropriately to several reference pharmacological angiogenesis inhibitors of vascular endothelial growth factor, NF-κB, matrix metalloproteinase-2/9, protein kinase activity, and β-tubulin, which confirms their functional role in endothelial sprouting. A blinded screen of 38 putative vascular disrupting compounds from the US Environmental Protection Agency's ToxCast library identified six compounds that inhibited iPSC-EC sprouting and five compounds that were overtly cytotoxic to iPSC-ECs at a single concentration. The chemically-defined iPSC-EC sprouting model (iSM) is thus amenable to enhanced-throughput screening of small molecular libraries for effects on angiogenic sprouting and iPSC-EC toxicity assessment.

STATEMENT OF SIGNIFICANCE

Angiogenesis assays that are commonly used for drug screening and toxicity assessment applications typically utilize natural substrates like Matrigel(TM) that are difficult to spatially pattern, costly, ill-defined, and may exhibit lot-to-lot variability. Herein, we describe a novel angiogenic sprouting assay using chemically-defined, bioinert poly(ethylene glycol) hydrogels functionalized with biomimetic peptides to promote cell attachment and degradation in a reproducible format that may mitigate the need for natural substrates. The quantitative assay of angiogenic sprouting here enables precise control over the initial conditions and can be formulated into arrays for screening. The sprouting assay here was dependent on key angiogenic signaling axes in a screen of angiogenesis inhibitors and a blinded screen of putative vascular disrupting compounds from the US-EPA.

Therapeutic application of anti-angiogenic nanomaterials in cancers

Angiogenesis, the formation of new blood vessels from pre-existing vasculature, plays a vital role in physiological and pathological processes (embryonic development, wound healing, tumor growth and metastasis). The overall balance of angiogenesis inside the human body is maintained by pro- and anti-angiogenic signals. The processes by which drugs inhibit angiogenesis as well as tumor growth are called the anti-angiogenesis technique, a most promising cancer treatment strategy. Over the last couple of decades, scientists have been developing angiogenesis inhibitors for the treatment of cancers. However, conventional anti-angiogenic therapy has several limitations including drug resistance that can create problems for a successful therapeutic strategy. Therefore, a new comprehensive treatment strategy using antiangiogenic agents for the treatment of cancer is urgently needed. Recently researchers have been developing and designing several nanoparticles that show anti-angiogenic properties. These nanomedicines could be useful as an alternative strategy for the treatment of various cancers using anti-angiogenic therapy. In this review article, we critically focus on the potential application of anti-angiogenic nanomaterial and nanoparticle based drug/siRNA/peptide delivery systems in cancer therapeutics. We also discuss the basic and clinical perspectives of anti-angiogenesis therapy, highlighting its importance in tumor angiogenesis, current status and future prospects and challenges.

Hypoxia imaging in gliomas with 18F-fluoromisonidazole PET: toward clinical translation

There is significant interest in the development of improved image-guided therapy for neuro-oncology applications. Glioblastomas (GBM) in particular present a considerable challenge because of their pervasive nature, propensity for recurrence, and resistance to conventional therapies. MRI is routinely used as a guide for planning treatment strategies. However, this imaging modality is not able to provide images that clearly delineate tumor boundaries and affords only indirect information about key tumor pathophysiology. With the emergence of PET imaging with new oncology radiotracers, mapping of tumor infiltration and other important molecular events such as hypoxia is now feasible within the clinical setting. In particular, the importance of imaging hypoxia levels within the tumoral microenvironment is gathering interest, as hypoxia is known to play a central role in glioma pathogenesis and resistance to treatment. One of the hypoxia radiotracers known for its clinical utility is (18)F-fluoromisodazole ((18)F-FMISO). In this review, we highlight the typical causes of treatment failure in gliomas that may be linked to hypoxia and outline current methods for the detection of hypoxia. We also provide an overview of the growing body of studies focusing on the clinical translation of (18)F-FMISO PET imaging, strengthening the argument for the use of (18)F-FMISO hypoxia imaging to help optimize and guide treatment strategies for patients with glioblastoma.

VB-111: a novel anti-vascular therapeutic for glioblastoma multiforme

Glioblastoma multiforme (GBM) is among the most highly vascularized of solid tumors, contributing to the infiltrative nature of the disease, and conferring poor outcome. Due to the critical dependency of GBM on growth of new endothelial vasculature, we evaluated the preclinical activity of a novel adenoviral gene therapy that targets the endothelium within newly formed blood vessels for apoptosis. VB-111, currently in phase II clinical trials, consists of a non-replicating Adenovirus 5 (El deleted) carrying a proapoptotic human Fas-chimera (transgene) under the control of a modified murine promoter (PPE-1-3×) which specifically targets endothelial cells within the tumor vasculature. Here we report that a single intravenous dose of 2.5 × 10(11) or 1 × 10(11) VPs was sufficient to extend survival in nude rats bearing U87MG-luc2 or nude mice bearing U251-luc, respectively. Bioluminescence imaging of nude rats showed that VB-111 effectively inhibited tumor growth within four weeks of treatment. This was confirmed in a select group of animals by MRI. In our mouse model we observed that 3 of 10 nude mice treated with VB-111 completely lost U251 luciferase signal and were considered long term survivors. To assess the antiangiogenic effects of VB-111, we evaluated the tumor-associated microvaculature by CD31, a common marker of neovascularization, and found a significant decrease in the microvessel density by IHC. We further assessed the neovasculature by confocal microscopy and found that VB-111 inhibits vascular density in two separate mouse models bearing U251-RFP xenografts. Collectively, this study supports the clinical development of VB-111 as a treatment for GBM.

Adaptation to antiangiogenic therapy in neurological tumors

Because tumors require a vascular supply for their survival and growth, angiogenesis is considered an important therapeutic target in most human cancers including cancer of the central nervous system. Antiangiogenic therapy has focused on inhibitors of the vascular endothelial growth factor (VEGF) signaling pathway. VEGF pathway-targeted drugs have shown therapeutic efficacy in several CNS tumors and have been tried most frequently in glioblastoma. These therapies, however, have been less effective than anticipated as some patients do not respond to therapy and some receive only modest benefit. Underlying this suboptimal response are multiple mechanisms of drug resistance involving changes in both tumor cells and their microenvironment. In this review, we discuss the multiple proposed mechanisms by which neurological tumors evolve to become resistant to antiangiogenic therapies. A better understanding of these mechanisms, their context, and their interplay will likely facilitate improvements in pharmacological strategies for the targeted treatment of neurological tumors.

Molecularly targeted therapies for recurrent glioblastoma: current and future targets

OBJECT

Glioblastoma is the most aggressive and diffusely infiltrative primary brain tumor. Recurrence is expected and is extremely difficult to treat. Over the past decade, the accumulation of knowledge regarding the molecular and genetic profile of glioblastoma has led to numerous molecularly targeted therapies. This article aims to review the literature and highlight the mechanisms and efficacies of molecularly targeted therapies for recurrent glioblastoma.

METHODS

A systematic search was performed with the phrase "(name of particular agent) and glioblastoma" as a search term in PubMed to identify all articles published up until 2014 that included this phrase in the title and/or abstract. The references of systematic reviews were also reviewed for additional sources. The review included clinical studies that comprised at least 20 patients and reported results for the treatment of recurrent glioblastoma with molecular targeted therapies.

RESULTS

A total of 42 articles were included in this review. In the treatment of recurrent glioblastoma, various targeted therapies have been tested over the past 10-15 years. The targets of interest include epidermal growth factor receptor, vascular endothelial growth factor receptor, platelet-derived growth factor receptor, Ras pathway, protein kinase C, mammalian target of rapamycin, histone acetylation, and integrins. Unfortunately, the clinical responses to most available targeted therapies are modest at best. Radiographic responses generally range in the realm of 5%-20%. Progression-free survival at 6 months and overall survival were also modest with the majority of studies reporting a 10%-20% 6-month progression-free survival and 5- to 8-month overall survival. There have been several clinical trials evaluating the use of combination therapy for molecularly targeted treatments. In general, the outcomes for combination therapy tend to be superior to single-agent therapy, regardless of the specific agent studied.

CONCLUSIONS

Recurrent glioblastoma remains very difficult to treat, even with molecular targeted therapies and anticancer agents. The currently available targeted therapy regimens have poor to modest activity against recurrent glioblastoma. As newer agents are actively being developed, combination regimens have provided the most promising results for improving outcomes. Targeted therapies matched to molecular profiles of individual tumors are predicted to be a critical component necessary for improving efficacy in future trials.

Microglia and astrocytes attenuate the replication of the oncolytic vaccinia virus LIVP 1.1.1 in murine GL261 gliomas by acting as vaccinia virus traps

Background

Oncolytic virotherapy is a novel approach for the treatment of glioblastoma multiforme (GBM) which is still a fatal disease. Pathologic features of GBM are characterized by the infiltration with microglia/macrophages and a strong interaction between immune- and glioma cells. The aim of this study was to determine the role of microglia and astrocytes for oncolytic vaccinia virus (VACV) therapy of GBM.

Methods

VACV LIVP 1.1.1 replication in C57BL/6 and Foxn1^nu/nu mice with and without GL261 gliomas was analyzed. Furthermore, immunohistochemical analysis of microglia and astrocytes was investigated in non-, mock-, and LIVP 1.1.1-infected orthotopic GL261 gliomas in C57BL/6 mice. In cell culture studies virus replication and virus-mediated cell death of GL261 glioma cells was examined, as well as in BV-2 microglia and IMA2.1 astrocytes with M1 or M2 phenotypes. Co-culture experiments between BV-2 and GL261 cells and apoptosis/necrosis studies were performed. Organotypic slice cultures with implanted GL261 tumor spheres were used as additional cell culture system.

Results

We discovered that orthotopic GL261 gliomas upon intracranial virus delivery did not support replication of LIVP 1.1.1, similar to VACV-infected brains without gliomas. In addition, recruitment of Iba1⁺ microglia and GFAP⁺ astrocytes to orthotopically implanted GL261 glioma sites occurred already without virus injection. GL261 cells in culture showed high virus replication, while replication in BV-2 and IMA2.1 cells was barely detectable. The reduced viral replication in BV-2 cells might be due to rapid VACV-induced apoptotic cell death. In BV-2 and IMA 2.1 cells with M1 phenotype a further reduction of virus progeny and virus-mediated cell death was detected. Application of BV-2 microglial cells with M1 phenotype onto organotypic slice cultures with implanted GL261 gliomas resulted in reduced infection of BV-2 cells, whereas GL261 cells were well infected.

Conclusion

Our results indicate that microglia and astrocytes, dependent on their activation state, may preferentially clear viral particles by immediate uptake after delivery. By acting as VACV traps they further reduce efficient virus infection of the tumor cells. These findings demonstrate that glia cells need to be taken into account for successful GBM therapy development.

Sunitinib malate (SU-11248) reduces tumour burden and lung metastasis in an intratibial human xenograft osteosarcoma mouse model

Osteosarcoma is a rare type of cancer that commonly occurs as a primary bone tumour in children and adolescents and is associated with a poor clinical outcome. Despite complex treatment protocols, including chemotherapy combined with surgical resection, the prognosis for patients with osteosarcoma and metastases remains poor and more effective therapies are required. In this study, we evaluated the therapeutic efficacy of sunitinib malate, a wide-spectrum tyrosine kinase inhibitor, in a preclinical mouse model of osteosarcoma. Sunitinib significantly inhibited proliferation, provoked apoptosis and induced G2/M cell cycle arrest in the human osteosarcoma cell lines SaOS-2 and 143B in vitro. Importantly, sunitinib treatment significantly reduced tumour burden, microvessel density and suppressed pulmonary metastasis in a 143B cell-derived intratibial osteosarcoma model in SCID mice. Sunitinib significantly decreased primary tumor tissue proliferation and reduced tumor vasculature. Our study indicates that sunitinib has potential for effective treatment of metastasizing osteosarcoma and provides the framework for future clinical trials with sunitinib alone or in combination with conventional and other novel therapeutics aiming at increased treatment efficacy and improved patient outcome.

Increasing feasibility and utility of (18)F-FDOPA PET for the management of glioma

INTRODUCTION

Despite radical treatment therapies, glioma continues to carry with it a uniformly poor prognosis. Patients diagnosed with WHO Grade IV glioma (glioblastomas; GBM) generally succumb within two years, even those with WHO Grade III anaplastic gliomas and WHO Grade II gliomas carry prognoses of 2-5 and 2 years, respectively. PET imaging with (18)F-FDOPA allows in vivo assessment of the metabolism of glioma relative to surrounding tissues. The high sensitivity of (18)F-DOPA imaging grants utility for a number of clinical applications.

METHODS

A collection of published work about (18)F-FDOPA PET was made and a critical review was discussed and written.

RESULTS

A number of research papers have been published demonstrating that in conjunction with MRI, (18)F-FDOPA PET provides greater sensitivity and specificity than these modalities in detection, grading, prognosis and validation of treatment success in both primary and recurrent gliomas. In further comparisons with (11)C-MET, (18)F-FLT, (18)F-FET and MRI, (18)F-FDOPA has shown similar or better efficacy. Recently synthesis cassettes have become available, making (18)F-FDOPA more accessible.

CONCLUSIONS

According to the available data, (18)F-FDOPA PET is a viable radiotracer for imaging and treatment planning of gliomas.

ADVANCES IN KNOWLEDGE AND IMPLICATION FOR PATIENT CARE

(18)F-FDOPA PET appears to be a viable radiopharmaceutical for the diagnosis and treatment planning of gliomas cases, improving on that of MRI and (18)F-FDG PET.

Systemic miRNA-7 delivery inhibits tumor angiogenesis and growth in murine xenograft glioblastoma

Tumor-angiogenesis is the multi-factorial process of sprouting of endothelial cells (EC) into micro-vessels to provide tumor cells with nutrients and oxygen. To explore miRNAs as therapeutic angiogenesis-inhibitors, we performed a functional screen to identify miRNAs that are able to decrease EC viability. We identified miRNA-7 (miR-7) as a potent negative regulator of angiogenesis. Introduction of miR-7 in EC resulted in strongly reduced cell viability, tube formation, sprouting and migration. Application of miR-7 in the chick chorioallantoic membrane assay led to a profound reduction of vascularization, similar to anti-angiogenic drug sunitinib. Local administration of miR-7 in an in vivo murine neuroblastoma tumor model significantly inhibited angiogenesis and tumor growth. Finally, systemic administration of miR-7 using a novel integrin-targeted biodegradable polymeric nanoparticles that targets both EC and tumor cells, strongly reduced angiogenesis and tumor proliferation in mice with human glioblastoma xenografts. Transcriptome analysis of miR-7 transfected EC in combination with in silico target prediction resulted in the identification of OGT as novel target gene of miR-7. Our study provides a comprehensive validation of miR-7 as novel anti-angiogenic therapeutic miRNA that can be systemically delivered to both EC and tumor cells and offers promise for miR-7 as novel anti-tumor therapeutic.

A rationally designed combined treatment with an alphavirus-based cancer vaccine, sunitinib and low-dose tumor irradiation completely blocks tumor development

The clinical efficacy of therapeutic cancer vaccines remains limited. For effective immunotherapeutic responses in cancer patients, multimodal approaches capable of both inducing antitumor immune responses and bypassing tumor-mediated immune escape seem essential. Here, we report on a combination therapy comprising sunitinib (40 mg/kg), single low-dose (14 Gy) tumor irradiation and immunization with a therapeutic cancer vaccine based on a Semliki Forest virus vector encoding the oncoproteins E6 and E7 of human papillomavirus (SFVeE6,7). We previously demonstrated that either low-dose irradiation or sunitinib in single combination with SFVeE6,7 immunizations enhanced the intratumoral ratio of antitumor effector cells to myeloid-derived suppressor cells (MDSCs). On the basis of these results we designed a triple treatment combinatorial regimen. The trimodal sunitinib, low-dose irradiation and SFVeE6,7 immunization therapy resulted in stronger intratumoral MDSC depletion than sunitinib alone. Concomitantly, the highest levels of intratumoral E7-specific CD8⁺ T cells were attained after triple treatment. Approximately 75% of these cells were positive for the early activation marker CD69. The combination of sunitinib, low-dose tumor irradiation and SFVeE6,7 immunization dramatically changed the intratumoral immune compartment. Whereas control tumors contained 0.02 E7-specific CD8⁺ T cells per MDSC, triple treatment tumors contained more than 200 E7-specific CD8⁺ T cells per MDSC, a 10,000-fold increased ratio. As a result, the triple treatment strongly enhanced the immunotherapeutic antitumor effect, blocking tumor development altogether and leading to 100% tumor-free survival of tumor-bearing mice. This study demonstrates that this multimodal approach elicits superior antitumor effects and should be considered for clinical applications.

Sunitinib impedes brain tumor progression and reduces tumor-induced neurodegeneration in the microenvironment

Malignant gliomas can be counted to the most devastating tumors in humans. Novel therapies do not achieve significant prolonged survival rates. The cancer cells have an impact on the surrounding vital tissue and form tumor zones, which make up the tumor microenvironment. We investigated the effects of sunitinib, a small molecule multitargeted receptor tyrosine kinase inhibitor, on constituents of the tumor microenvironment such as gliomas, astrocytes, endothelial cells, and neurons. Sunitinib has a known anti-angiogenic effect. We found that sunitinib normalizes the aberrant tumor-derived vasculature and reduces tumor vessel pathologies (i.e. auto-loops). Sunitinib has only minor effects on the normal, physiological, non-proliferating vasculature. We found that neurons and astrocytes are protected by sunitinib against glutamate-induced cell death, whereas sunitinib acts as a toxin towards proliferating endothelial cells and tumor vessels. Moreover, sunitinib is effective in inducing glioma cell death. We determined the underlying pathways by which sunitinib operates as a toxin on gliomas and found vascular endothelial growth factor receptor 2 (VEGFR2, KDR/Flk1) as the main target to execute gliomatoxicity. The apoptosis-inducing effect of sunitinib can be mimicked by inhibition of VEGFR2. Knockdown of VEGFR2 can, in part, foster the resistance of glioma cells to receptor tyrosine kinase inhibitors. Furthermore, sunitinib alleviates tumor-induced neurodegeneration. Hence, we tested whether temozolomide treatment could be potentiated by sunitinib application. Here we show that sunitinib can amplify the effects of temozolomide in glioma cells. Thus, our data indicate that combined treatment with temozolomide does not abrogate the effects of sunitinib. In conclusion, we found that sunitinib acts as a gliomatoxic agent and at the same time carries out neuroprotective effects, reducing tumor-induced neurodegeneration. Thus, this report uncovered sunitinib's actions on the brain tumor microenvironment, revealing novel aspects for adjuvant approaches and new clinical assessment criteria when applied to brain tumor patients.

AXL as a modulator of sunitinib response in glioblastoma cell lines

Receptor tyrosine kinase (RTK) targeted therapy has been explored for glioblastoma treatment. However, it is unclear which RTK inhibitors are the most effective and there are no predictive biomarkers available. We recently identified the RTK AXL as a putative target for the pan-RTK inhibitors cediranib and sunitinib, which are under clinical trials for glioblastoma patients. Here, we provide evidence that AXL activity can modulate sunitinib response in glioblastoma cell lines. We found that AXL knockdown conferred lower sensitivity to sunitinib by rescuing migratory defects and inhibiting apoptosis in cells expressing high AXL basal levels. Accordingly, overactivation of AXL by its ligand GAS6 rendered AXL positive glioblastoma cells more sensitive to sunitinib. AXL knockdown induced a cellular rewiring of several growth signaling pathways through activation of RTKs, such as EGFR, as well as intracellular pathways such as MAPK and AKT. The combination of sunitinib with a specific AKT inhibitor reverted the resistance of AXL-silenced cells to sunitinib. Together, our results suggest that sunitinib inhibits AXL and AXL activation status modulates therapy response of glioblastoma cells to sunitinib. Moreover, it indicates that combining sunitinib therapy with AKT pathway inhibitors could overcome sunitinib resistance.

Sunitinib depletes myeloid-derived suppressor cells and synergizes with a cancer vaccine to enhance antigen-specific immune responses and tumor eradication

The high efficacy of therapeutic cancer vaccines in preclinical studies has yet to be fully achieved in clinical trials. Tumor immune suppression is a critical factor that hampers the desired antitumor effect. Here, we analyzed the combined effect of a cancer vaccine and the receptor tyrosine kinase inhibitor sunitinib. Sunitinib was administered intraperitoneally, alone or in combination with intramuscular immunization using a viral vector based cancer vaccine composed of Semliki Forest virus replicon particles and encoding the oncoproteins E6 and E7 (SFVeE6,7) of human papilloma virus (HPV). We first demonstrated that treatment of tumor-bearing mice with sunitinib alone dose-dependently depleted myeloid-derived suppressor cells (MDSCs) in the tumor, spleen and in circulation. Concomitantly, the number of CD8⁺ T cells increased 2-fold and, on the basis of CD69 expression, their activation status was greatly enhanced. The intrinsic immunosuppressive activity of residual MDSCs after sunitinib treatment was not changed in a dose-dependent fashion. We next combined sunitinib treatment with SFVeE6,7 immunization. This combined treatment resulted in a 1.5- and 3-fold increase of E7-specific cytotoxic T lymphocytes (CTLs) present within the circulation and tumor, respectively, as compared to immunization only. The ratio of E7-specific CTLs to MDSCs in blood thereby increased 10- to 20-fold and in tumors up to 12.5-fold. As a result, the combined treatment strongly enhanced the antitumor effect of the cancer vaccine. This study demonstrates that sunitinib creates a favorable microenvironment depleted of MDSCs and acts synergistically with a cancer vaccine resulting in enhanced levels of active tumor-antigen specific CTLs, thus changing the balance in favor of antitumor immunity.