Preferential susceptibility of brain tumors to the antiangiogenic effects of an alpha(v) integrin antagonist

Interaction of integrin αvβ3 and fibronectin under fluid shear forces: implications for tumor cell adhesion and migration

The interaction between integrin αvβ3 and fibronectin enables tumor cell adherence to endothelial layers under diverse hydrodynamic blood flow conditions, particularly in low shear stress regions. Understanding the mechanical binding characteristics between integrin αvβ3 and fibronectin under different hydrodynamic environments can provide insights into tumor cell invasion and proliferation. Here, the adhesive behavior of fibronectin-functionalized microspheres on integrin αvβ3-coated substrates under various wall fluid shear forces (0.1-0.7 dyn/cm2) was assessed using a parallel plate flow chamber system. The bond lifetimes of integrin αvβ3-fibronectin initially increased and then decreased, indicating transition from a "catch bond" to "slip bond." Upon perfusion of fibronectin-coated microspheres into flow chambers with high-density integrin αvβ3 coating, the rolling velocity of the microspheres increased with increasing shear force. Additionally, the mean stop time and stop frequency exhibited a force-dependent biphasic pattern, initially increasing and then decreasing with shear force, demonstrating a nuanced response to mechanical forces. Thus, the integrin αvβ3-fibronectin interaction displays a "catch bond" property, influencing cell distribution in varying fluid shear forces by promoting optimal adhesion in specific shear sites. These insights enhance our understanding of tumor cell adhesion and migration in hydrodynamic environments and may aid the design of integrin αvβ3-targeted therapies.

Family-Wide Photoproximity Profiling of Integrin Protein Social Networks in Cancer

Integrin family transmembrane receptors mediate dynamic interactions between cells and their extracellular microenvironment. The heterogeneous interaction partners of integrins directly regulate cell adhesion, motility, proliferation, and intracellular signaling. Despite the recognized importance of protein-protein interactions and the formation of signaling hubs around integrins, the ability to detect and quantify these dynamic binding partners with high spatial and temporal resolution remains challenging. Here, we developed an integrin-family-directed quantitative photoproximity protein interaction (PhotoPPI) profiling method to detect and quantify native integrin-centered protein social networks on live cells and tissues without the need for genetic manipulation, antibodies, or non-physiologic cell culture conditions. We drafted quantitative maps of integrin-centered protein social networks, highlighting conserved and unique binding partners between different cell types and cellular microenvironments. Comparison of integrin social networks in cancer cell lines of diverse tissue of origin and disease state identified specific AND-gate binding partners involved cell migration, microenvironmental interactions and proliferation that serve as markers of tumor cell metastatic state. Finally, we identified unique combinations - or barcodes - of integrin-proximal proteins on the surface of pre- and post-metastatic triple negative breast cancer (TNBC) cells whose expression strongly correlate with both positive and negative disease progression and outcomes in TNBC patients. Taken together, these data provide the first family-wide high-resolution maps of native protein interactors on live cells and identify dynamic integrin-centered social networks as potential AND-gate markers of cell identity, microenvironmental context and disease state.

Novel Pharmacological Treatment Options in Pediatric Glioblastoma-A Systematic Review

BACKGROUND

Pediatric glioblastoma (GBM) is an aggressive central nervous system tumor in children that has dismal prognosis. Standard of care is surgery with subsequent irradiation and temozolomide. We aimed to outline currently available data on novel pharmacological treatments for pediatric GBM.

METHODS

We conducted a systematic literature search in PubMed and Embase, including reports published in English from 2010 to 2021. We included randomized trials, cohort studies and case series. Phase I trials were not analyzed. We followed PRISMA guidelines, assessed the quality of the eligible reports using the Newcastle-Ottawa scale (NOS) and the RoB-2 tool and registered the protocol on PROSPERO.

RESULTS

We included 6 out of 1122 screened reports. All six selected reports were prospective, multicenter phase II trials (five single-arm and one randomized controlled trial). None of the investigated novel treatment modalities showed any benefit regarding overall or progression free survival.

CONCLUSIONS

To date, the role of pharmacological approaches regarding pediatric GBM remains unclear, since no novel treatment approach could provide a significant impact on overall or progression free survival. Further research should aim to combine different treatment strategies in large international multicenter trials with central comprehensive diagnostics regarding subgrouping. These novel treatment approaches should include targeted and immunotherapeutic treatments, potentially leading to a more successful outcome.

Pulsed Microwave-Induced Thermoacoustic Shockwave for Precise Glioblastoma Therapy with the Skin and Skull Intact

Glioblastoma has a dismal prognosis and is a critical and urgent health issue that requires aggressive research and determined clinical efforts. Due to its diffuse and infiltrative growth in the brain parenchyma, complete neurosurgical resection is rarely possible. Here, pulsed microwave-induced thermoacoustic (MTA) therapy is proposed as a potential alternative modality to precisely and effectively eradicate in vivo orthotopic glioblastoma. A nanoparticle composed of polar amino acids and adenosine-based agonists is constructed with high microwave absorbance and selective penetration of the blood-brain barrier (BBB) at the tumor site. This nanoparticle can activate the adenosine receptor on the BBB to allow self-passage and tumor accumulation. The nanoparticle converts absorbed microwaves into ultrasonic shockwaves via the thermoacoustic cavitation effect. The ultrasonic shockwave can mechanically destroy tumor cells within a short range with minimal damage to adjacent normal brain tissue due to the rapid decay of the ultrasonic shockwave intensity. The deep tissue penetration characteristics of the microwave and the rapid decay of the ultrasonic shockwave make MTA therapy a promising glioblastoma cure including intact skin and skull.

Therapeutic Opportunities and Delivery Strategies for Brain Revascularization in Stroke, Neurodegeneration, and Aging

Central nervous system (CNS) diseases, especially acute ischemic events and neurodegenerative disorders, constitute a public health problem with no effective treatments to allow a persistent solution. Failed therapies targeting neuronal recovery have revealed the multifactorial and intricate pathophysiology underlying such CNS disorders as ischemic stroke, Alzheimeŕs disease, amyotrophic lateral sclerosis, vascular Parkisonism, vascular dementia, and aging, in which cerebral microvasculature impairment seems to play a key role. In fact, a reduction in vessel density and cerebral blood flow occurs in these scenarios, contributing to neuronal dysfunction and leading to loss of cognitive function. In this review, we provide an overview of healthy brain microvasculature structure and function in health and the effect of the aforementioned cerebral CNS diseases. We discuss the emerging new therapeutic opportunities, and their delivery approaches, aimed at recovering brain vascularization in this context. SIGNIFICANCE STATEMENT: The lack of effective treatments, mainly focused on neuron recovery, has prompted the search of other therapies to treat cerebral central nervous system diseases. The disruption and degeneration of cerebral microvasculature has been evidenced in neurodegenerative diseases, stroke, and aging, constituting a potential target for restoring vascularization, neuronal functioning, and cognitive capacities by the development of therapeutic pro-angiogenic strategies.

Improved Immunotherapy Efficacy by Vascular Modulation

Several strategies have been developed to modulate the tumour vasculature for cancer therapy including anti-angiogenesis and vascular normalisation. Vasculature modulation results in changes to the tumour microenvironment including oxygenation and immune cell infiltration, therefore lending itself to combination with cancer therapy. The development of immunotherapies has led to significant improvements in cancer treatment. Particularly promising are immune checkpoint blockade and CAR T cell therapies, which use antibodies against negative regulators of T cell activation and T cells reprogrammed to better target tumour antigens, respectively. However, while immunotherapy is successful in some patients, including those with advanced or metastatic cancers, only a subset of patients respond. Therefore, better predictors of patient response and methods to overcome resistance warrant investigation. Poor, or periphery-limited, T cell infiltration in the tumour is associated with poor responses to immunotherapy. Given that (1) lymphocyte recruitment requires leucocyte-endothelial cell adhesion and (2) the vasculature controls tumour oxygenation and plays a pivotal role in T cell infiltration and activation, vessel targeting strategies including anti-angiogenesis and vascular normalisation in combination with immunotherapy are providing possible new strategies to enhance therapy. Here, we review the progress of vessel modulation in enhancing immunotherapy efficacy.

Expression Analysis of α5 Integrin Subunit Reveals Its Upregulation as a Negative Prognostic Biomarker for Glioblastoma

Integrin α5β1 was suggested to be involved in glioblastoma (GBM) aggressiveness and treatment resistance through preclinical studies and genomic analysis in patients. However, further protein expression data are still required to confirm this hypothesis. In the present study, we investigated by immunofluorescence the expression of integrin α5 and its prognostic impact in a glioblastoma series of patients scheduled to undergo the Stupp protocol as first-line treatment for GBM. The integrin α5 protein expression level was estimated in each tumor by the mean fluorescence intensity (MFI) and allowed us to identify two subpopulations showing either a high or low expression level. The distribution of patients in both subpopulations was not significantly different according to age, gender, recursive partitioning analysis (RPA) prognostic score, molecular markers or surgical and medical treatment. A high integrin α5 protein expression level was associated with a high risk of recurrence (HR = 1.696, 95% CI 1.031-2.792, p = 0.0377) and reduced overall survival (OS), even more significant in patients who completed the Stupp protocol (median OS: 15.6 vs. 22.8 months; HR = 2.324; 95% CI 1.168-4.621, p = 0.0162). In multivariate analysis, a high integrin α5 protein expression level was confirmed as an independent prognostic factor in the subpopulation of patients who completed the temozolomide-based first-line treatment for predicting OS over age, extent of surgery, RPA score and O-6-methylguanine-DNA methyltransferase (MGMT) promoter methylation (p = 0.029). In summary, for the first time, our study validates that a high integrin α5 protein expression level is associated with poor prognosis in GBM and confirms its potential as a therapeutic target implicated in the Stupp protocol resistance.

RGD-Binding Integrins Revisited: How Recently Discovered Functions and Novel Synthetic Ligands (Re-)Shape an Ever-Evolving Field

Integrins have been extensively investigated as therapeutic targets over the last decades, which has been inspired by their multiple functions in cancer progression, metastasis, and angiogenesis as well as a continuously expanding number of other diseases, e.g., sepsis, fibrosis, and viral infections, possibly also Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2). Although integrin-targeted (cancer) therapy trials did not meet the high expectations yet, integrins are still valid and promising targets due to their elevated expression and surface accessibility on diseased cells. Thus, for the future successful clinical translation of integrin-targeted compounds, revisited and innovative treatment strategies have to be explored based on accumulated knowledge of integrin biology. For this, refined approaches are demanded aiming at alternative and improved preclinical models, optimized selectivity and pharmacological properties of integrin ligands, as well as more sophisticated treatment protocols considering dose fine-tuning of compounds. Moreover, integrin ligands exert high accuracy in disease monitoring as diagnostic molecular imaging tools, enabling patient selection for individualized integrin-targeted therapy. The present review comprehensively analyzes the state-of-the-art knowledge on the roles of RGD-binding integrin subtypes in cancer and non-cancerous diseases and outlines the latest achievements in the design and development of synthetic ligands and their application in biomedical, translational, and molecular imaging approaches. Indeed, substantial progress has already been made, including advanced ligand designs, numerous elaborated pre-clinical and first-in-human studies, while the discovery of novel applications for integrin ligands remains to be explored.

Targeting Intercellular Communication in the Bone Microenvironment to Prevent Disseminated Tumor Cell Escape from Dormancy and Bone Metastatic Tumor Growth

Metastasis to the bone is a common feature of many cancers including those of the breast, prostate, lung, thyroid and kidney. Once tumors metastasize to the bone, they are essentially incurable. Bone metastasis is a complex process involving not only intravasation of tumor cells from the primary tumor into circulation, but extravasation from circulation into the bone where they meet an environment that is generally suppressive of their growth. The bone microenvironment can inhibit the growth of disseminated tumor cells (DTC) by inducing dormancy of the DTC directly and later on following formation of a micrometastatic tumour mass by inhibiting metastatic processes including angiogenesis, bone remodeling and immunosuppressive cell functions. In this review we will highlight some of the mechanisms mediating DTC dormancy and the complex relationships which occur between tumor cells and bone resident cells in the bone metastatic microenvironment. These inter-cellular interactions may be important targets to consider for development of novel effective therapies for the prevention or treatment of bone metastases.

Integrin Signaling in Glioma Pathogenesis: From Biology to Therapy

Integrins are a large family of transmembrane adhesion receptors, which play a key role in interactions of a cell with the surrounding stroma. Integrins are comprised of non-covalently linked α and β chains, which form heterodimeric receptor complexes. The signals from integrin receptors are combined with those originating from growth factor receptors and participate in orchestrating morphological changes of cells, organization of the cytoskeleton, stimulation of cell proliferation and rescuing cells from programmed cell death induced by extracellular matrix (ECM) detachment. Upon binding to specific ligands or ECM components, integrin dimers activate downstream signaling pathways, including focal adhesion kinase, phosphoinositide-3-kinase (PI3K) and AKT kinases, which regulate migration, invasion, proliferation and survival. Expression of specific integrins is upregulated in both tumor cells and stromal cells in a tumor microenvironment. Therefore, integrins became an attractive therapeutic target for many cancers, including the most common primary brain tumors-gliomas. In this review we provide an overview of the involvement of integrin signaling in glioma pathogenesis, formation of the tumor niche and brain tissue infiltration. We will summarize up-to-date therapeutic strategies for gliomas focused on interference with integrin ligand-receptor signaling.

Peptides derived from the integrin β cytoplasmic tails inhibit angiogenesis

BACKGROUND

Integrins are essential regulators of angiogenesis. However, the antiangiogenic potential of peptides derived from the integrin cytoplasmic tails (CT) remains mostly undetermined.

METHODS

Here we designed a panel of membrane-penetrating peptides (termed as mβCTPs), each comprising a C-terminal NxxY motif from one of the conserved integrin β CTs, and evaluated their antiangiogenic ability using both in vitro and in vivo approaches.

RESULTS

We found that mβ3CTP, mβ5CTP and mβ6CTP, derived respectively from the integrin β3, β5 and β6 CTs, but not others, exhibit antiangiogenic ability. Interestingly, we observed that the integrin β3, β5 and β6 CTs but not others are able to interact with β₃-endonexin. In addition, the antiangiogenic core in mβ3CTP is identical to a previously identified β₃-endonexin binding region in the integrin β3 CT, indicating that the antiangiogenic mβCTPs may function via their binding to β₃-endonexin. Consistently, knockdown of endogenous β₃-endonexin in HUVECs significantly suppresses tube formation, suggesting that β₃-endonexin is proangiogenic. However, neither treatment with the antiangiogenic mβCTPs nor knockdown of endogenous β₃-endonexin affects integrin-mediated HUVEC adhesion and migration, indicating that their antiangiogenic effect may not rely on directly regulating integrin activity. Importantly, both treatment with the antiangiogenic mβCTPs and knockdown of endogenous β₃-endonexin in HUVECs inhibit VEGF expression and cell proliferation, thereby providing mechanistic explanations for the functional consequences.

CONCLUSION

Our results suggest that the antiangiogenic mβCTPs can interact with β₃-endonexin in vascular endothelial cells and suppress its function in regulating VEGF expression and cell proliferation, thus disclosing a unique pathway that may be useful for developing novel antiangiogenic strategies.

Targeting αvβ3 and αvβ5 integrins inhibits pulmonary metastasis in an intratibial xenograft osteosarcoma mouse model

Osteosarcoma is an aggressive bone cancer that has a high propensity for metastasis to the lungs. Patients with metastatic disease face a very poor prognosis. Therefore, novel therapeutics, efficiently suppressing the metastatic process, are urgently needed. Integrins play a pivotal role in tumor cell adhesion, motility and metastasis. Here, we evaluated αvβ3 and αvβ5 integrin inhibition with cilengitide as a novel metastasis-suppressive therapeutic approach in osteosarcoma. Immunohistochemical analysis of αvβ3 and αvβ5 integrins expression in a tissue microarray of tumor specimens collected from osteosarcoma patients revealed that αvβ5 integrin is mainly found on tumor cells, whereas αvβ3 is predominantly expressed by stromal cells. In vitro functional assays demonstrated that cilengitide dose-dependently inhibited de novo adhesion, provoked detachment and inhibited migration of osteosarcoma cell lines. Cilengitide induced a decline in cell viability, blocked the cell cycle in the G1 phase and caused anoikis by activation of the Hippo pathway. In a xenograft orthotopic mouse model cilengitide minimally affected intratibial primary tumor growth but, importantly, suppressed pulmonary metastasis. The data demonstrate that targeting αvβ3 and αvβ5 integrins in osteosarcoma should be considered as a novel therapeutic option for patients with metastatic disease.

Cilengitide in newly diagnosed glioblastoma: biomarker expression and outcome

Integrins αvβ3 and αvβ5 regulate angiogenesis and invasiveness in cancer, potentially by modulating activation of the transforming growth factor (TGF)-β pathway. The randomized phase III CENTRIC and phase II CORE trials explored the integrin inhibitor cilengitide in patients with newly diagnosed glioblastoma with versus without O⁶-methylguanine DNA methyltransferase (MGMT) promoter methylation. These trials failed to meet their primary endpoints.

Immunohistochemistry was used to assess the levels of the target integrins of cilengitide, αvβ3 and αvβ5 integrins, of αvβ8 and of their putative target, phosphorylation of SMAD2, in tumor tissues from CENTRIC (n=274) and CORE (n=224).

αvβ3 and αvβ5 expression correlated well in tumor and endothelial cells, but showed little association with αvβ8 or pSMAD2 levels. In CENTRIC, there was no interaction between the biomarkers and treatment for prediction of outcome. In CORE, higher αvβ3 levels in tumor cells were associated with improved progression-free survival by central review and with improved overall survival in patients treated with cilengitide.

Integrins αvβ3, αvβ5 and αvβ8 are differentially expressed in glioblastoma. Integrin levels do not correlate with the activation level of the canonical TGF-β pathway. αvβ3 integrin expression may predict benefit from integrin inhibition in patients with glioblastoma lacking MGMT promoter methylation.

Reduced Cytokine Release in Ex Vivo Response to Cilengitide and Cetuximab Is a Marker for Improved Survival of Head and Neck Cancer Patients

Targeting of α_Vβ3 and α_Vβ5 integrins by cilengitide may reduce growth of solid tumors including head and neck squamous cell carcinoma (HNSCC). Preclinical investigations suggest increased activity of cilengitide in combination with other treatment modalities. The only published trial in HNSCC (ADVANTAGE) investigated cisplatin, 5-fluorouracil, and cetuximab (PFE) without or with once (PFE+CIL1W) or twice weekly cilengitide (PFE+CIL2W) in recurrent/metastatic HNSCC. ADVANTAGE showed good tolerability of the cilengitide arms and even lower adverse events (AEs) compared to PFE but not the benefit in overall survival expected based on preclinical data. As we found in the FLAVINO assay, a short-time ex vivo assay for prediction of chemosensitivity, only a subgroup of HNSCC had an increased suppressive effect of cilengitide containing combination therapies on colony formation of epithelial cells (CF_ec) and release of pro-angiogenetic and pro-inflammatory cytokines, whereas other HNSCC failed to respond. Response to α_Vβ3 and α_Vβ5 integrin targeting by cilengitide classifies HNSCC regarding outcome. We present FLAVINO data arguing for further development of cilengitide plus cetuximab in treatment of a subgroup of HNSCC potentially identified by the FLAVINO assay using a set of biomarkers for response evaluation.

Association of high microvessel αvβ3 and low PTEN with poor outcome in stage 3 neuroblastoma: rationale for using first in class dual PI3K/BRD4 inhibitor, SF1126

Neuroblastoma (NB) is the most common extracranial solid tumor in children. Our previous studies showed that the angiogenic integrin α_vβ₃ was increased in high-risk metastatic (stage 4) NB compared with localized neuroblastomas. Herein, we show that integrin α_vβ₃ was expressed on 68% of microvessels in MYCN-amplified stage 3 neuroblastomas, but only on 34% (means) in MYCN-non-amplified tumors (p < 0.001; n = 54). PTEN, a tumor suppressor involved in α_vβ₃ signaling, was expressed in neuroblastomas either diffusely, focally or not at all (immunohistochemistry). Integrin α_vβ₃ was expressed on 60% of tumor microvessels when PTEN was negative or focal, as compared to 32% of microvessels in tumors with diffuse PTEN expression (p < 0.001). In a MYCN transgenic mouse model, loss of one allele of PTEN promoted tumor growth, illustrating the potential role of PTEN in neuroblastoma pathogenesis. Interestingly, we report the novel dual PI-3K/BRD4 activity of SF1126 (originally developed as an RGD-conjugated pan PI3K inhibitor). SF1126 inhibits BRD4 bromodomain binding to acetylated lysine residues with histone H3 as well as PI3K activity in the MYCN amplified neuroblastoma cell line IMR-32. Moreover, SF1126 suppressed MYCN expression and MYCN associated transcriptional activity in IMR-32 and CHLA136, resulting in overall decrease in neuroblastoma cell viability. Finally, treatment of neuroblastoma tumors with SF1126 inhibited neuroblastoma growth in vivo. These data suggest integrin α_vβ₃, MYCN/BRD4 and PTEN/PI3K/AKT signaling as biomarkers and hence therapeutic targets in neuroblastoma and support testing of the RGD integrin α_vβ₃-targeted PI-3K/BRD4 inhibitor, SF1126 as a therapeutic strategy in this specific subgroup of high risk neuroblastoma.

Identifying novel therapeutic agents using xenograft models of pediatric cancer

In the USA, the overall cure rate for all childhood cancers is seventy percent, and in many patients that ultimately fail curative therapy, initial responses to current multimodality treatments (surgery, radiation therapy and chemotherapy) is good, with overall 5-year event-free survival approaching 80 %. However, current approaches to curative therapy result in significant morbidity and long-term sequelae, including cardiac dysfunction and cognitive impairment. Furthermore, dose-intensive chemotherapy with conventional agents has not significantly improved outcomes for patients that present with advanced or metastatic disease. Classical cytotoxic agents remain the backbone for curative therapy of both hematologic and solid tumors of childhood. While 'molecularly' targeted agents have shown some clinical activity, responses are often modest and of short duration; hence, there is a need to identify new classes of cytotoxic agent that are effective in patients at relapse and that have reduced or different toxicity profiles to normal tissues. Here we review the pediatric preclinical testing program experience of testing novel agents, and the value and limitations of preclinical xenograft models and genetically engineered mouse models for developing novel agents for treatment of childhood cancer.

In vitro and in vivo drug disposition of cilengitide in animals and human

Cilengitide is very low permeable (1.0 nm/sec) stable cyclic pentapeptide containing an Arg-Gly-Asp motif responsible for selective binding to αvβ3 and αvβ5 integrins administered intravenously (i.v.). In vivo studies in the mouse and Cynomolgus monkeys showed the major component in plasma was unchanged drug (>85%). These results, together with the absence of metabolism in vitro and in animals, indicate minimal metabolism in both species. The excretion of [(14)C]-cilengitide showed profound species differences, with a high renal excretion of the parent drug observed in Cynomolgus monkey (50% dose), but not in mouse (7 and 28%: m/f). Consistently fecal (biliary) secretion was high in mouse (87 and 66% dose: m/f) but low in Cynomolgus monkey (36.5%). Human volunteers administrated with [(14)C]-cilengitide showed that most of the dose was recovered in urine as unchanged drug (77.5%, referred to Becker et al. 2015), indicating that the Cynomolgus monkey was the closer species to human. In order to better understand the species difference between human and mouse, the hepatobiliary disposition of [(14)C]-cilengitide was determined in sandwich-cultured hepatocytes. Cilengitide exhibited modest biliary efflux (30-40%) in mouse, while in human hepatocytes this was negligible. Furthermore, it was confirmed that the uptake of cilengitide into human hepatocytes was minor and appeared to be passive. In summary, the extent of renal and biliary secretion of cilengitide appears to be highly species specific and is qualitatively well explained using sandwich hepatocyte culture models.

Tumor Microenvironment-Mediated Construction and Deconstruction of Extracellular Drug-Delivery Depots

Protein therapy has been considered the most direct and safe approach to treat cancer. Targeting delivery of extracellularly active protein without internalization barriers, such as membrane permeation and endosome escape, is efficient and holds vast promise for anticancer treatment. Herein, we describe a "transformable" core-shell based nanocarrier (designated CS-NG), which can enzymatically assemble into microsized extracellular depots at the tumor site with assistance of hyaluronidase (HAase), an overexpressed enzyme at the tumor microenvironment. Equipped with an acid-degradable modality, the resulting CS-NG can substantially release combinational anticancer drugs-tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL) and antiangiogenic cilengitide toward the membrane of cancer cells and endothelial cells at the acidic tumor microenvironment, respectively. Enhanced cytotoxicity on MDA-MB-231 cells and improved antitumor efficacy were observed using CS-NG, which was attributed to the inhibition of cellular internalization and prolonged retention time in vivo.

The Effect of Stromal Integrin β3-Deficiency on Two Different Tumors in Mice

There is an increasing focus on the tumor microenvironment in carcinogenesis. Integrins are important receptors and adhesion molecules in this environment and have been shown to be involved in cell adhesion, proliferation, differentiation and migration. The present study aimed to evaluate the effect of stromal integrin β3-deficiency on tumor growth, angiogenesis, interstitial fluid pressure (PIF), fibrosis and metastasis in a murine breast cancer (4T1) and a prostate tumor (RM11) model. We showed that stromal integrin β3-deficiency led to an elevation in PIF that correlated to a shift towards thicker collagen fibrils in the 4T1 mammary tumor. In the RM11 prostate carcinoma model there was no effect of integrin β3-deficiency on PIF and collagen fibril thickness. These findings support the notion that changes in the collagen scaffold influence PIF, and also indicate that there must be important crosstalk between the stroma and tumor cells, in a tumor cell line specific manner. Furthermore, stromal integrin β3-deficiency had no effect on tumor growth or angiogenesis in both tumor models and no effect on lung metastasis in the 4T1 mammary tumor model. In conclusion, the stromal β3 integrin influence PIF, possibly via its effect on the structure of the collagen network, in a tumor cell line dependent manner.

Characterization of the blood brain barrier in pediatric central nervous system neoplasms

Objective

The normal blood–brain barrier (BBB) is composed of tight junctions between endothelial cells and surrounding astrocyte foot processes. Breakdown of the physiological astrocyte-endothelial cell relationship occurs in adult metastatic and primary brain tumors. However, the astrocyte-endothelial cell relationship has not been studied in pediatric tumors.

Materials and Methods

Utilizing specimens from cases of pilocytic astrocytoma (n = 5), medulloblastoma (n = 5), and low-grade diffuse astrocytoma (n = 1), immunofluorescence were performed using primary antibodies against CD31, glial fibrillary acidic protein (GFAP), and aquaporin 4 (AQ4). Clinical, magnetic resonance imaging, operative, and histopathological findings were analyzed.

Results

Strongly-enhancing areas of medulloblastoma exhibited complete BBB breakdown with sparse GFAP and AQ4 staining around CD31-positive vessels. Moderately enhancing regions of pilocytic astrocytomas exhibited regions of intact BBB and vasculature surrounded by dense GFAP staining but reduced and disorganized AQ4 staining, suggesting tumor cells could not fulfill physiological BBB support. Non-enhancing low-grade diffuse astrocytoma demonstrated intact BBB with intense peri-microvasculature GFAP and AQ4 staining. AQ4 stained so strongly that AQ4 visualization alone delineated CD31-positive vessels.

Conclusion

Taken together, BBB breakdown in pediatric tumors corresponds to a loss of normal endothelial cell-astrocyte foot process relationships. Further development of pharmaceutical agents capitalizing on this disrupted BBB is warranted in medulloblastoma and pilocytic astrocytoma. However, BBB integrity remains a challenge in treating low-grade diffuse astrocytoma before progression toward secondary glioblastoma.

Glioblastomas require integrin αvβ3/PAK4 signaling to escape senescence

Integrin αvβ3 has been implicated as a driver of aggressive and metastatic disease, and is upregulated during glioblastoma progression. Here, we demonstrate that integrin αvβ3 allows glioblastoma cells to counteract senescence through a novel tissue-specific effector mechanism involving recruitment and activation of the cytoskeletal regulatory kinase PAK4. Mechanistically, targeting either αvβ3 or PAK4 led to emergence of a p21-dependent, p53-independent cell senescence phenotype. Notably, glioblastoma cells did not exhibit a similar requirement for either other integrins or additional PAK family members. Moreover, αvβ3/PAK4 dependence was not found to be critical in epithelial cancers. Taken together, our findings established that glioblastomas are selectively addicted to this pathway as a strategy to evade oncogene-induced senescence, with implications that inhibiting the αvβ3-PAK4 signaling axis may offer novel therapeutic opportunities to target this aggressive cancer.

Integrin antagonist augments the therapeutic effect of adenovirus-mediated REIC/Dkk-3 gene therapy for malignant glioma

Reduced expression in immortalized cells/Dickkopf-3 (REIC/Dkk-3) was identified as a gene whose expression is reduced in many human cancers. REIC/Dkk-3 expression is also downregulated in malignant glioma and regulates cell growth through caspase-dependent apoptosis. cRGD (EMD121974), an antagonist of integrins, has demonstrated preclinical efficacy against malignant glioma. In this study, we investigated the antiglioma effect of combination therapy using an adenovirus vector carrying REIC/Dkk-3 (Ad-REIC) and cRGD. Quantitative real-time reverse-transcription PCR revealed the reduction of REIC/Dkk-3 mRNA levels in malignant glioma cell lines. The reduction of REIC/Dkk-3 protein expression in malignant glioma cell lines was also confirmed with western blot analysis. After treatment with Ad-REIC and cRGD, the proliferative rate of malignant glioma cells was significantly reduced in a time-dependent manner. In vivo, there was a statistically significant increase in the survival of mice treated with Ad-REIC and cRGD combination therapy compared with Ad-REIC monotherapy. We identified an apoptotic effect following monotherapy with Ad-REIC. Moreover, cRGD augmented the antiglioma efficacy of Ad-REIC. These results may lead to a promising new approach for the treatment of malignant glioma.

Contemporary murine models in preclinical astrocytoma drug development

Despite 6 decades of research, only 3 drugs have been approved for astrocytomas, the most common malignant primary brain tumors. However, clinical drug development is accelerating with the transition from empirical, cytotoxic therapy to precision, targeted medicine. Preclinical animal model studies are critical for prioritizing drug candidates for clinical development and, ultimately, for their regulatory approval. For decades, only murine models with established tumor cell lines were available for such studies. However, these poorly represent the genomic and biological properties of human astrocytomas, and their preclinical use fails to accurately predict efficacy in clinical trials. Newer models developed over the last 2 decades, including patient-derived xenografts, genetically engineered mice, and genetically engineered cells purified from human brains, more faithfully phenocopy the genomics and biology of human astrocytomas. Harnessing the unique benefits of these models will be required to identify drug targets, define combination therapies that circumvent inherent and acquired resistance mechanisms, and develop molecular biomarkers predictive of drug response and resistance. With increasing recognition of the molecular heterogeneity of astrocytomas, employing multiple, contemporary models in preclinical drug studies promises to increase the efficiency of drug development for specific, molecularly defined subsets of tumors.

Cilengitide inhibits attachment and invasion of malignant pleural mesothelioma cells through antagonism of integrins αvβ3 and αvβ5

Malignant pleural mesothelioma (MPM) is an almost invariably fatal, asbestos-related malignancy arising from the mesothelial membrane lining the thoracic cavities. Despite some improvements in treatment, therapy is not considered curative and median survival following diagnosis is less than 1 year. Although still classed as a rare cancer, the incidence of MPM is increasing, and the limited progress in treating the disease makes the identification of new therapies a priority. As there is evidence for expression of the integrins αvβ3 and αvβ5 in MPM, there is a rationale for investigating the effects on MPM of cilengitide, a synthetic peptide inhibitor of integrin αv heterodimer with high specificity for αvβ3 and αvβ5. In mesothelial cells (MC) and 7 MPM cell lines, growth inhibition by cilengitide was associated with the expression level of its target integrins. Furthermore, cilengitide caused cell detachment and subsequent death of anoikis-sensitive cells. It also suppressed invasion of MPM cells in monolayer and three-dimensional cultures. Gene knockdown experiments indicated that these effects of cilengitide were, at least partly, due to antagonism of αvβ3 and αvβ5.

Cilengitide-induced temporal variations in transvascular transfer parameters of tumor vasculature in a rat glioma model: identifying potential MRI biomarkers of acute effects

Increased efficacy of radiotherapy (RT) 4-8 h after Cilengitide treatment has been reported. We hypothesized that the effects of Cilengitide on tumor transvascular transfer parameters might underlie, and thus predict, this potentiation. Athymic rats with orthotopic U251 glioma were studied at ~21 days after implantation using dynamic contrast-enhanced (DCE)-MRI. Vascular parameters, viz: plasma volume fraction (v_p), forward volume transfer constant (K^trans) and interstitial volume fraction (v_e) of a contrast agent, were determined in tumor vasculature once before, and again in cohorts 2, 4, 8, 12 and 24 h after Cilengitide administration (4 mg/kg; N = 31; 6-7 per cohort). Perfusion-fixed brain sections were stained for von Willebrand factor to visualize vascular segments. A comparison of pre- and post-treatment parameters showed that the differences between MR indices before and after Cilengitide treatment pivoted around the 8 h time point, with 2 and 4 h groups showing increases, 12 and 24 h groups showing decreases, and values at the 8 h time point close to the baseline. The vascular parameter differences between group of 2 and 4 h and group of 12 and 24 h were significant for K^trans (p = 0.0001 and v_e (p = 0,0271). Vascular staining showed little variation with time after Cilengitide. The vascular normalization occurring 8 h after Cilengitide treatment coincided with similar previous reports of increased treatment efficacy when RT followed Cilengitide by 8 h. Pharmacological normalization of vasculature has the potential to increase sensitivity to RT. Evaluating acute temporal responses of tumor vasculature to putative anti-angiogenic drugs may help in optimizing their combination with other treatment modalities.

Combination therapy targeting integrins reduces glioblastoma tumor growth through antiangiogenic and direct antitumor activity and leads to activation of the pro-proliferative prolactin pathway

Background

Tumors may develop resistance to specific angiogenic inhibitors via activation of alternative pathways. Therefore, multiple angiogenic pathways should be targeted to achieve significant angiogenic blockade. In this study we investigated the effects of a combined application of the angiogenic inhibitors endostatin and tumstatin in a model of human glioblastoma multiforme.

Results

Inhibitors released by stably transfected porcine aortic endothelial cells (PAE) showed anti-angiogenic activity in proliferation and wound-healing assays with endothelial cells (EC). Interestingly, combination of endostatin and tumstatin (ES + Tum) also reduced proliferation of glioma cells and additionally induced morphological changes and apoptosis in vitro. Microencapsulated PAE-cells producing these inhibitors were applied for local therapy in a subcutaneous glioblastoma model. When endostatin or tumstatin were applied separately, in vivo tumor growth was inhibited by 58% and 50%, respectively. Combined application of ES + Tum, in comparison, resulted in a significantly more pronounced inhibition of tumor growth (83%). cDNA microarrays of tumors treated with ES + Tum revealed an up-regulation of prolactin receptor (PRLR). ES + Tum-induced up-regulation of PRLR in glioma cells was also found in in vitro. Moreover, exogenous PRLR overexpression in vitro led to up-regulation of its ligand prolactin and increased proliferation suggesting a functional autocrine growth loop in these cells.

Conclusion

Our data indicate that integrin-targeting factors endostatin and tumstatin act additively by inhibiting glioblastoma growth via reduction of vessel density but also directly by affecting proliferation and viability of tumor cells. Treatment with the ES + Tum-combination activates the PRLR pro-proliferative pathway in glioblastoma. Future work will show whether the prolactin signaling pathway represents an additional target to improve therapeutic strategies in this entity.

Mechanisms of tumor development and anti-angiogenic therapy in glioblastoma multiforme

Despite advances in surgical and medical therapy, glioblastoma multiforme (GBM) remains a fatal disease. There has been no significant increase in survival for patients with this disease over the last 20 years. Tumor vasculature formation and glioma cell invasion along the white matter tracts both play a pivotal role in glioma development. Angiogenesis and invasion are the major factors believed to be responsible for treatment resistance in tumors, and a better understanding of the glioma invasion and angiogenesis mechanisms will lead to the development of potential new treatments. In this review, we focus on the molecular characteristics of angiogenesis and invasion in human malignant glioma. We discuss bevacizumab and cilengitide, which are used to inhibit angiogenesis in GBM.

Phase II study of cilengitide in the treatment of refractory or relapsed high-grade gliomas in children: a report from the Children's Oncology Group

BACKGROUND

Cilengitide, an αv integrin antagonist, has demonstrated activity in recurrent adult glioblastoma (GBM). The Children's Oncology Group ACNS0621 study thus evaluated whether cilengitide is active as a single agent in the treatment of children with refractory high-grade glioma (HGG). Secondary objectives were to investigate the pharmacokinetics and pharmacogenomics of cilengitide in this population.

METHODS

Cilengitide (1800 mg/m(2)/dose intravenous) was administered twice weekly until evidence of disease progression or unacceptable toxicity. Thirty patients (age range, 1.1-20.3 years) were enrolled, of whom 24 were evaluable for the primary response end point.

RESULTS

Toxicity was infrequent and mild, with the exception of one episode of grade 2 pain possibly related to cilengitide. Two intratumoral hemorrhages were reported, but only one (grade 2) was deemed to be possibly related to cilengitide and was in the context of disease progression. One patient with GBM received cilengitide for 20 months and remains alive with continuous stable disease. There were no other responders, with median time to tumor progression of 28 days (range, 11-114 days). Twenty-one of the 24 evaluable patients died, with a median time from enrollment to death of 172 days (range, 28-325 days). The 3 patients alive at the time of this report had a follow-up time of 37, 223, and 1068 days, respectively.

CONCLUSIONS

We conclude that cilengitide is not effective as a single agent for refractory pediatric HGG. However, further study evaluating combination therapy with cilengitide is warranted before a role for cilengitide in the treatment of pediatric HGG can be excluded.

Cilengitide response in ultra-low passage glioblastoma cell lines: relation to molecular markers

PURPOSE

In glioblastoma multiforme (GBM), a tumor still characterized by dismal prognosis, recent research focuses on novel-targeted compounds, in addition to standard temozolomide (TMZ) chemotherapy. One of these emerging compounds is cilengitide (CGT), which by binding to integrins (i.e., αvβ3 and αvβ5) may inhibit angiogenesis and also is directly cytotoxic to tumor cells by interfering with intracellular signaling pathways.

METHODS

A total of ten patient-derived ultra-low passage GBM cell lines were treated with increasing doses of CGT, TMZ, and a combination of both substances. Inhibitory concentrations of 50% (IC₅₀) were determined for the single agents and as a combination. Cell lines were stratified according to MGMT promoter methylation. The expression of relevant integrins was assessed by flow cytometry.

RESULTS

In monotherapy, all GBM cell lines showed higher sensitivity to CGT than to TMZ, as determined by IC₅₀ values in relation to clinically relevant patient plasma levels. MGMT promoter methylation correlated with a significantly higher TMZ response, but tended to be associated with a lower CGT response. Response to CGT was not correlated with cell surface integrin expression as measured by flow cytometry. Finally, addition of CGT to TMZ enhanced growth inhibition, but only in those cell lines with a methylated MGMT promoter.

CONCLUSIONS

As suggested by this analysis, patients with MGMT promoter-methylated GBM may benefit from addition of CGT to the standard TMZ treatment, while patients with MGMT promoter-unmethylated GBM may better respond to CGT monotherapy.

The integrin inhibitor cilengitide enhances the anti-glioma efficacy of vasculostatin-expressing oncolytic virus

Oncolytic viral (OV) therapy has been considered as a promising treatment modality for brain tumors. Vasculostatin, the fragment of brain-specific angiogenesis inhibitor-1, shows anti-angiogenic activity against malignant gliomas. Previously, a vasculostatin-expressing oncolytic herpes simplex virus-1, Rapid Antiangiogenesis Mediated By Oncolytic virus (RAMBO), was reported to have a potent antitumor effect. Here, we investigated the therapeutic efficacy of RAMBO and cilengitide, an integrin inhibitor, combination therapy for malignant glioma. In vitro, tube formation was significantly decreased in RAMBO and cilengitide combination treatment compared with RAMBO or cilengitide monotherapy. Moreover, combination treatment induced a synergistic suppressive effect on endothelial cell migration compared with the control virus. RAMBO, combined with cilengitide, induced synergistic cytotoxicity on glioma cells. In the caspase-8 and -9 assays, the relative absorption of U87ΔEGFR cell clusters treated with cilengitide and with RAMBO was significantly higher than that of those treated with control. In addition, the activity of caspase 3/7 was significantly increased with combination therapy. In vivo, there was a significant increase in the survival of mice treated with combination therapy compared with RAMBO or cilengitide monotherapy. These results indicate that cilengitide enhanced vasculostatin-expressing OV therapy for malignant glioma and provide a rationale for designing future clinical trials combining these two agents.

Gene expression profiling of the anti-glioma effect of Cilengitide

Cilengitide (EMD121974), an inhibitor of the adhesive function of integrins, demonstrated preclinical efficacy against malignant glioma. It is speculated that cilengitide can inhibit tumor growth, invasion, and angiogenesis. However, the effects of cilengitide on these processes have not been sufficiently examined. In this study, we investigated the anti-glioma effect of cilengitide using DNA microarray analysis. U87ΔEGFR cells (human malignant glioma cell line) were used for this experiment. The cells were harvested after 16 h of cilengitide treatment, and mRNA was extracted. Gene expression and pathway analyses were performed using a DNA microarray (CodeLink™Human Whole Genome Bioarray). The expression of 265 genes was changed with cilengitide treatment. The expression of 214 genes was up-regulated by more than 4-fold and the expression of 51 genes was down-regulated by more than 4-fold compared to the controls. In pathway analysis, “apoptotic cleavage of cellular proteins” and “TNF receptor signaling pathway” were over-represented. Apoptotic-associated genes such as caspase 8 were up-regulated. Gene expression profiling revealed more detailed mechanism of the anti-glioma effect of cilengitide. Genes associated with apoptosis were over-represented following cilengitide treatment.

Longitudinal expression analysis of αv integrins in human gliomas reveals upregulation of integrin αvβ3 as a negative prognostic factor

Integrin inhibitors targeting αv series integrins are being tested for their therapeutic potential in patients with brain tumors, but pathologic studies have been limited by lack of antibodies suitable for immunohistochemistry (IHC) on formalin-fixed, paraffin-embedded specimens. We compared the expression of αv integrins by IHC in brain tumor and normal human brain samples with gene expression data in a public database using new rabbit monoclonal antibodies against αvβ3, αvβ5, αvβ6, and αvβ8 complexes using both manual and automated microscopy analyses. Glial tumors usually shared an αvβ3-positive/αvβ5-positive/αvβ8-positive/αvβ6-negative phenotype. In 94 WHO (World Health Organization) grade II astrocytomas, 85 anaplastic astrocytomas WHO grade III, and 324 glioblastomas from archival sources, expression of integrins generally increased with grade of malignancy. Integrins αvβ3 and αvβ5 were expressed in many glioma vessels; the intensity of vascular expression of αvβ3 increased with grade of malignancy, whereas αvβ8 was absent. Analysis of gene expression in an independent cohort showed a similar increase in integrin expression with tumor grade, particularly of ITGB3 and ITGB8; ITGB6 was not expressed, consistent with the IHC data. Parenchymal αvβ3 expression and ITGB3 gene overexpression in glioblastomas were associated with a poor prognosis, as revealed by survival analysis (Kaplan-Meier logrank, p = 0.016). Together, these data strengthen the rationale for anti-integrin treatment of glial tumors.

Integrins and metastasis

Metastasis is a combination of biological events that makes the difference between cancer and other diseases. Metastasis requires flow of erroneous but precisely coordinated basic cellular activities like cell migration-invasion, cell survival-apoptosis, cell proliferation, etc. All of these processes require efficient regulation of cell attachment and detachment, which recruit integrin receptors in this flow of events. World literatures show several aspects of interrelation of integrins and metastasis. Integrin molecules are being used as prime target to battle metastasis. In this review we are collating the observations showing importance of integrin biology in regulation of metastasis and the strategies where integrin receptors are being used as targets to regulate metastasis.

αV integrins in angiogenesis and cancer

During angiogenesis, αv integrins are overexpressed on the endothelial cell surface to facilitate the growth and survival of newly forming vessels. Accordingly, blocking αv integrin function by disrupting ligand binding can produce an antiangiogenic effect. Although the integrin ectodomain regulates ligand binding specificity, the short cytoplasmic tail facilitates intracellular signaling pathways through the recruitment and activation of specific kinases and signaling intermediates. This in turn controls endothelial cell adhesion, morphology, migration, invasion, proliferation, and survival. These same integrin-mediated signaling pathways are exploited in cancer to promote the invasiveness and survival of tumor cells and to manipulate the host microenvironment to provide ample blood vessel and stromal resources to support tumor growth and metastatic spread. Because expression of αv integrins on distinct cell types contributes to cancer growth, αv integrin antagonists have the potential to disrupt multiple aspects of disease progression.

Bimodal anti-glioma mechanisms of cilengitide demonstrated by novel invasive glioma models

Integrins are expressed in tumor cells and tumor endothelial cells, and likely play important roles in glioma angiogenesis and invasion. We investigated the anti-glioma mechanisms of cilengitide (EMD121974), an αvβ3 integrin inhibitor, utilizing the novel invasive glioma models, J3T-1 and J3T-2. Immunohistochemical staining of cells in culture and brain tumors in rats revealed positive αvβ3 integrin expression in J3T-2 cells and tumor endothelial cells, but not in J3T-1 cells. Established J3T-1 and J3T-2 orthotopic gliomas in athymic rats were treated with cilengitide or solvent. J3T-1 gliomas showed perivascular tumor cluster formation and angiogenesis, while J3T-2 gliomas showed diffuse single-cell infiltration without obvious angiogenesis. Cilengitide treatment resulted in a significantly decreased diameter of the J3T-1 tumor vessel clusters and its core vessels when compared with controls, while an anti-invasive effect was shown in the J3T-2 glioma with a significant reduction of diffuse cell infiltration around the tumor center. The survival of cilengitide-treated mice harboring J3T-1 tumors was significantly longer than that of control animals (median survival: 57.5 days and 31.8 days, respectively, P < 0.005), while cilengitide had no effect on the survival of mice with J3T-2 tumors (median survival: 48.9 days and 48.5, P = 0.69). Our results indicate that cilengitide exerts a phenotypic anti-tumor effect by inhibiting angiogenesis and glioma cell invasion. These two mechanisms are clearly shown by the experimental treatment of two different animal invasive glioma models.

c-Abl is an upstream regulator of acid sphingomyelinase in apoptosis induced by inhibition of integrins αvβ3 and αvβ5

Inhibition of integrins αvβ3/αvβ5 by the cyclic function-blocking peptide, RGDfV (Arg-Gly-Asp-Phe-Val) can induce apoptosis in both normal cells and tumor cells. We show that RGDfV induced apoptosis in ECV-304 carcinoma cells, increased activity and mRNA expression of acid sphingomyelinase (ASM), and increased ceramides C₁₆, C_18∶0, C_24∶0 and C_24∶1 while decreasing the corresponding sphingomyelins. siRNA to ASM decreased RGDfV-induced apoptosis as measured by TUNEL, PARP cleavage, mitochondrial depolarization, and caspase-3 and caspase-8 activities, as well as by annexinV in a 3D collagen model. These findings indicate a causal role for ASM in RGDfV-induced apoptosis in ECV-304. We have shown that c-Abl, a non-receptor tyrosine kinase, also mediates RGDfV-induced apoptosis. However, c-Abl, has not been previously linked to ASM in any system. Here we show that STI-571 (imatinib, inhibitor of c-Abl) inhibited RGDfV-induced ASM activity. Furthermore, STI-571 and c-Abl-siRNA both inhibited RGDfV-induced increase in ASM mRNA, but ASM-siRNA did not affect c-Abl phosphorylation or expression, supporting that c-Abl regulates the RGDfV-induced increase in ASM expression. These studies implicate ASM as a mediator of apoptosis induced by inhibition of integrins αvβ3/αvβ5, and for the first time place c-Abl as an upstream regulator of ASM expression and activity.

Targeting αV-integrins decreased metastasis and increased survival in a nude rat breast cancer brain metastasis model

Brain metastases commonly occur in patients with breast, lung and melanoma systemic cancers. The anti-α(V) integrin monoclonal antibody intetumumab binds cell surface proteins important for adhesion, invasion and angiogenesis in the metastatic cascade. The objective of this study was to investigate the anti-metastatic effect of intetumumab in a hematogenous breast cancer brain metastasis model. Female nude rats received intra-carotid infusion of human brain-seeking metastatic breast cancer cells (231BR-HER2) and were randomly assigned into four groups: (1) control; (2) intetumumab mixed with cells in vitro 5 min before infusion without further treatment; (3) intetumumab intravenously 4 h before and weekly after cell infusion; (4) intetumumab intravenously weekly starting 7 days after cell infusion. Brain metastases were detected by magnetic resonance imaging (MRI) and immunohistochemistry. Comparisons were made using the Kruskal-Wallis test and Dunnett's test. Survival times were estimated using Kaplan-Meier analysis. All control rats with brain tissue available for histology (9 of 11 rats) developed multiple brain metastases (median = 14). Intetumumab treatment either in vitro prior to cell infusion or intravenous before or after cell infusion prevented metastasis formation on MRI and decreased the number of metastases on histology (median = 2, p = 0.0055), including 30 % of animals without detectable tumors at the end of the study. The overall survival was improved by intetumumab compared to controls (median 77+ vs. 52 days, p = 0.0277). Our results suggest that breast cancer patients at risk of metastases might benefit from early intetumumab treatment.

A safety run-in and randomized phase 2 study of cilengitide combined with chemoradiation for newly diagnosed glioblastoma (NABTT 0306)

BACKGROUND

Cilengitide is a selective integrin inhibitor that is well tolerated and has demonstrated biologic activity in patients with recurrent malignant glioma. The primary objectives of this randomized phase 2 trial were to determine the safety and efficacy of cilengitide when combined with radiation and temozolomide for patients with newly diagnosed glioblastoma multiforme and to select a dose for comparative clinical testing.

METHODS

In total, 112 patients were accrued. Eighteen patients received standard radiation and temozolomide with cilengitide in a safety run-in phase followed by a randomized phase 2 trial with 94 patients assigned to either a 500 mg dose group or 2000 mg dose group. The trial was designed to estimate overall survival benefit compared with a New Approaches to Brain Tumor Therapy (NABTT) Consortium internal historic control and data from the published European Organization for Research and Treatment of Cancer (EORTC) trial EORTC 26981.

RESULTS

Cilengitide at all doses studied was well tolerated with radiation and temozolomide. The median survival was 19.7 months for all patients, 17.4 months for the patients in the 500 mg dose group, 20.8 months for patients in the 2000 mg dose group, 30 months for patients who had methylated O6-methylguanine-DNA methyltransferase (MGMT) status, and 17.4 months for patients who had unmethylated MGMT status. For patients aged ≤70 years, the median survival and survival at 24 months was superior to what was observed in the EORTC trial (20.7 months vs 14.6 months and 41% vs 27%, respectively; P = .008).

CONCLUSIONS

Cilengitide was well tolerated when combined with standard chemoradiation and may improve survival for patients newly diagnosed with glioblastoma multiforme regardless of MGMT methylation status. The authors concluded that, from an efficacy and safety standpoint, future trials of this agent in this population should use the 2000 mg dose.

Cilengitide: a prototypic integrin inhibitor for the treatment of glioblastoma and other malignancies

Integrins are critical intermediaries in a wide spectrum of cancer cell activities and thus represent a highly attractive target in oncology therapy. Nonetheless, successful exploitation of anti-integrin therapeutics has proven challenging to date for cancer patients. In this review, we will focus on cilengitide, an RGD pentapeptide inhibitor of α V integrins. Although several integrin inhibitors are under clinical evaluation, cilengitide is the most clinically advanced and is emerging as a prototype for this class of anticancer therapy. A foundation of encouraging preclinical studies led to a well-designed clinical development plan that culminated in a pivotal phase III study of cilengitide in combination with radiation therapy and temozolomide chemotherapy for newly diagnosed glioblastoma patients. Accrual to this study recently completed, while phase II studies of cilengitide are ongoing for head and neck cancer as well as lung cancer. Important future considerations for cilengitide and other integrin-targeting agents will likely include the identification of optimal combinatorial regimens and the delineation of biomarkers associated with efficacy.

A review of VEGF/VEGFR-targeted therapeutics for recurrent glioblastoma

Glioblastoma, the most common primary malignant brain tumor among adults, is a highly angiogenic and deadly tumor. Angiogenesis in glioblastoma, driven by hypoxia-dependent and independent mechanisms, is primarily mediated by vascular endothelial growth factor (VEGF), and generates blood vessels with distinctive features. The outcome for patients with recurrent glioblastoma is poor because of ineffective therapies. However, recent encouraging rates of radiographic response and progression-free survival, and adequate safety, led the FDA to grant accelerated approval of bevacizumab, a humanized monoclonal antibody against VEGF, for the treatment of recurrent glioblastoma in May 2009. These results have triggered significant interest in additional antiangiogenic agents and therapeutic strategies for patients with both recurrent and newly diagnosed glioblastoma. Given the potent antipermeability effect of VEGF inhibitors, the Radiologic Assessment in Neuro-Oncology (RANO) criteria were recently implemented to better assess response among patients with glioblastoma. Although bevacizumab improves survival and quality of life, eventual tumor progression is the norm. Better understanding of resistance mechanisms to VEGF inhibitors and identification of effective therapy after bevacizumab progression are currently a critical need for patients with glioblastoma.

Cilengitide: an RGD pentapeptide ανβ3 and ανβ5 integrin inhibitor in development for glioblastoma and other malignancies

Cilengitide, a cyclicized arginine-glycine-aspartic acid-containing pentapeptide, potently blocks ανβ3 and ανβ5 integrin activation. Integrins are upregulated in many malignancies and mediate a wide variety of tumor-stroma interactions. Cilengitide and other integrin-targeting therapeutics have preclinical activity against many cancer subtypes including glioblastoma (GBM), the most common and deadliest CNS tumor. Cilengitide is active against orthotopic GBM xenografts and can augment radiotherapy and chemotherapy in these models. In Phase I and II GBM trials, cilengitide and the combination of cilengitide with standard temozolomide and radiation demonstrate consistent antitumor activity and a favorable safety profile. Cilengitide is currently under evaluation in a pivotal, randomized Phase III study (Cilengitide in Combination With Temozolomide and Radiotherapy in Newly Diagnosed Glioblastoma Phase III Randomized Clinical Trial [CENTRIC]) for newly diagnosed GBM. In addition, randomized controlled Phase II studies with cilengitide are ongoing for non-small-cell lung cancer and squamous cell carcinoma of the head and neck. Cilengitide is the first integrin inhibitor in clinical Phase III development for oncology.

Cilengitide in patients with recurrent glioblastoma: the results of NABTC 03-02, a phase II trial with measures of treatment delivery

Cilengitide is a cyclic pentapeptide that is a specific inhibitor of the αvβ3 and αvβ5 integrins. Preclinical studies demonstrate antiangiogenic activity and anti-invasive activity in a number of glioma models. This study was designed to evaluate the efficacy and tumor delivery of cilengitide in patients with recurrent glioblastoma. Patients with recurrent glioblastoma who require a surgical resection for optimal clinical care received 3 intravenous doses of cilengitide at either 500 or 2000 mg (day -8, -4, -1) prior to undergoing tumor resection with corresponding blood samples for plasma to tumor comparisons. After recovery from surgery, patients were treated with cilengitide (2000 mg i.v. twice weekly, maximum of 2 years of treatment). The study accrued 30 patients with recurrent glioblastoma, 26 were evaluable for efficacy. The 6-month progression free survival rate was 12%. Cilengitide was detected in all tumor specimens with higher levels in the group receiving 2000 mg dosing while corresponding plasma concentrations were low, often below the lower limit of detection. These results confirm drug delivery and possibly retention in tumor. This study provides evidence that with established dosing, cilengitide is adequately delivered to the tumor, although as a single agent, efficacy in recurrent glioblastoma is modest. However, these results demonstrating drug delivery to tumor do support continued investigation of this agent as preliminary results from recent studies combining cilengitide with cytotoxic therapies are promising.

Cilengitide: the first anti-angiogenic small molecule drug candidate design, synthesis and clinical evaluation

Cilengitide, a cyclic RGD pentapeptide, is currently in clinical phase III for treatment of glioblastomas and in phase II for several other tumors. This drug is the first anti-angiogenic small molecule targeting the integrins αvβ3, αvβ5 and αvβ1. It was developed by us in the early 90s by a novel procedure, the spatial screening. This strategy resulted in c(RGDfV), the first superactive αvβ3 inhibitor (100 to 1000 times increased activity over the linear reference peptides), which in addition exhibited high selectivity against the platelet receptor αIIbβ3. This cyclic peptide was later modified by N-methylation of one peptide bond to yield an even greater antagonistic activity in c(RGDf(NMe)V). This peptide was then dubbed Cilengitide and is currently developed as drug by the company Merck-Serono (Germany). This article describes the chemical development of Cilengitide, the biochemical background of its activity and a short review about the present clinical trials. The positive anti-angiogenic effects in cancer treatment can be further increased by combination with "classical" anti-cancer therapies. Several clinical trials in this direction are under investigation.

Integrin targeted therapeutics

Integrins are heterodimeric, transmembrane receptors that function as mechanosensors, adhesion molecules and signal transduction platforms in a multitude of biological processes. As such, integrins are central to the etiology and pathology of many disease states. Therefore, pharmacological inhibition of integrins is of great interest for the treatment and prevention of disease. In the last two decades several integrin-targeted drugs have made their way into clinical use, many others are in clinical trials and still more are showing promise as they advance through preclinical development. Herein, this review examines and evaluates the various drugs and compounds targeting integrins and the disease states in which they are implicated.

Angiogenesis and invasion in glioma

Despite advances in surgical and medical therapy, glioblastoma consistently remains a fatal disease. Over the last 20 years, no significant increase in survival has been achieved for patients with this disease. The formation of abnormal tumor vasculature and glioma cell invasion along white matter tracts are believed to be the major factors responsible for the resistance of these tumors to treatment. Therefore, investigation of angiogenesis and invasion in glioblastoma is essential for the development of a curative therapy. In our report, we first reviewed certain histopathological studies that focus on angiogenesis and invasion of human malignant gliomas. Second, we considered several animal models of glioma available for studying angiogenesis and invasion, including our novel animal models. Third, we focused on the molecular aspects of glioma angiogenesis and invasion, and the key mediators of these processes. Finally, we discussed the recent and ongoing clinical trials targeting tumor angiogenesis and invasion in glioma patients. A better understanding of the mechanism of glioma angiogenesis and invasion will lead to the development of new treatment methods.

Dynamic magnetic resonance imaging assessment of vascular targeting agent effects in rat intracerebral tumor models

We used dynamic MRI to evaluate the effects of monoclonal antibodies targeting brain tumor vasculature. Female athymic rats with intracerebral human tumor xenografts were untreated or treated with intetumumab, targeting α(V)-integrins, or bevacizumab, targeting vascular endothelial growth factor (n = 4-6 per group). Prior to treatment and at 1, 3, and 7 days after treatment, we performed standard MRI to assess tumor volume, dynamic susceptibility-contrast MRI with the blood-pool iron oxide nanoparticle ferumoxytol to evaluate relative cerebral blood volume (rCBV), and dynamic contrast-enhanced MRI to assess tumor vascular permeability. Tumor rCBV increased by 27 ± 13% over 7 days in untreated rats; intetumumab increased tumor rCBV by 65 ± 10%, whereas bevacizumab reduced tumor rCBV by 31 ± 10% at 7 days (P < .001 for group and day). Similarly, intetumumab increased brain tumor vascular permeability compared with controls at 3 and 7 days after treatment, whereas bevacizumab decreased tumor permeability within 24 hours (P = .0004 for group, P = .0081 for day). All tumors grew over the 7-day assessment period, but bevacizumab slowed the increase in tumor volume on MRI. We conclude that the vascular targeting agents intetumumab and bevacizumab had diametrically opposite effects on dynamic MRI of tumor vasculature in rat brain tumor models. Targeting α(V)-integrins increased tumor vascular permeability and blood volume, whereas bevacizumab decreased both measures. These findings have implications for chemotherapy delivery and antitumor efficacy.

Phase II study of cilengitide (EMD 121974, NSC 707544) in patients with non-metastatic castration resistant prostate cancer, NCI-6735. A study by the DOD/PCF prostate cancer clinical trials consortium

BACKGROUND

Integrins mediate invasion and angiogenesis in prostate cancer bone metastases. We conducted a phase II study of cilengitide, a selective antagonist of α(v)β(3) and α(v)β(5) integrins, in non-metastatic castration resistant prostate cancer with rising PSA.

METHODS

Patients were observed for 4 weeks with PSA monitoring, and then treated with 2,000 mg IV of cilengitide twice weekly until toxicity/progression. PSA, circulating tumor cells (CTCs) and circulating endothelial cells (CECs) were monitored each cycle with imaging performed every three cycles. Primary end point was PSA decline by ≥ 50%. Secondary endpoints were safety, PSA slope, time to progression (TTP), overall survival (OS), CTCs, CECs and gene expression.

RESULTS

16 pts were enrolled; 13 were eligible with median age 65.5 years, baseline PSA 8.4 ng/mL and median Gleason sum 7. Median of three cycles was administered. Treatment was well tolerated with two grade three toxicities and no grade four toxicities. There were no PSA responses; 11 patients progressed by PSA after three cycles. Median TTP was 1.8 months and median OS has not been reached. Median pre- and on-treatment PSA slopes were 1.1 and 1.8 ng/mL/month. Baseline CTCs were detected in 1/9 patients. CTC increased (0 to 1; 2 pts), remained at 0 (2 pts) or decreased (23 to 0; 1 patient) at progression. Baseline median CEC was 26 (0-61) and at progression, 47 (15-148). Low cell counts precluded gene expression studies.

CONCLUSIONS

Cilengitide was well tolerated but had no detectable clinical activity. CTCs are of questionable utility in non-metastatic prostate cancer.

Jekyll and Hyde: the role of the microenvironment on the progression of cancer

It is now recognized that the host microenvironment undergoes extensive change during the evolution and progression of cancer. This involves the generation of cancer-associated fibroblasts (CAFs), which, through release of growth factors and cytokines, lead to enhanced angiogenesis, increased tumour growth and invasion. It has also been demonstrated that CAFs may modulate the cancer stem cell (CSC) phenotype, which has therapeutic implications. The altered fibroblast phenotype also contributes to the development of an altered extracellular matrix (ECM), with synthesis of ECM isoforms rarely found in normal tissues, including tenascin-C isoforms and the fibronectin EDA isoform. There is also emerging evidence of how the tensile strength of the tumour-associated ECM may be modified and lead to altered signalling in tumour cells. The hypoxic environment of the tumour stimulates angiogenesis and also impacts on other aspects of cell signalling, including the c-met pathway and lysyl oxidase-mediated signalling, which can directly promote tumour cell invasion. The inflammatory infiltrate associated with many solid tumours also modulates tumour function, having both anti- and pro-tumour effects. All of these components of the microenvironment provide potential targets for therapeutic attack, with a number of molecules already in clinical trials. It is also becoming evident that characterizing the tumour microenvironment can provide important prognostic and predictive information about tumours, independent of the tumour cell phenotype.