Immunohistochemical analysis of integrin alpha vbeta3 expression on tumor-associated vessels of human carcinomas

Peptide-Based Agents for Cancer Treatment: Current Applications and Future Directions

Peptide-based strategies have received an enormous amount of attention because of their specificity and applicability. Their specificity and tumor-targeting ability are applied to diagnosis and treatment for cancer patients. In this review, we will summarize recent advancements and future perspectives on peptide-based strategies for cancer treatment. The literature search was conducted to identify relevant articles for peptide-based strategies for cancer treatment. It was performed using PubMed for articles in English until June 2023. Information on clinical trials was also obtained from ClinicalTrial.gov. Given that peptide-based strategies have several advantages such as targeted delivery to the diseased area, personalized designs, relatively small sizes, and simple production process, bioactive peptides having anti-cancer activities (anti-cancer peptides or ACPs) have been tested in pre-clinical settings and clinical trials. The capability of peptides for tumor targeting is essentially useful for peptide-drug conjugates (PDCs), diagnosis, and image-guided surgery. Immunomodulation with peptide vaccines has been extensively tested in clinical trials. Despite such advantages, FDA-approved peptide agents for solid cancer are still limited. This review will provide a detailed overview of current approaches, design strategies, routes of administration, and new technological advancements. We will highlight the success and limitations of peptide-based therapies for cancer treatment.

Exploration of tumor penetrating peptide iRGD as a potential strategy to enhance tumor penetration of cancer nanotherapeutics

Cancer therapy continues to be a huge challenge as most chemotherapeutic agents exert serious adverse effects on healthy organs. Chemotherapeutic agents lack selective targeting and even the existing target specific therapies are failing due to poor distribution into the tumor microenvironment. Nanotechnology offers multiple advantages to address the limitations encountered by conventional therapy. However, the delivery of nanotherapeutics to tumor tissue has not improved over the years partly due to the poor and inadequate distribution of nanotherapeutics into deeper tumor regions resulting in resistance and relapse. To curb the penetration concerns, iRGD was explored and found to be highly effective in improving the delivery of cancer nanomedicine. The preclinical observations are highly encouraging; however, the clinical translation is at a nascent stage. Based on this, we have made an elaborative effort to give a detailed account of various promising applications of iRGD to increase anticancer and tumor imaging potential. Importantly, we have comprehensively discussed the shortcomings and uncertainties associated with the clinical translation of iRGD-based therapeutic approaches and future directions.

Ligand fishing as a tool to screen natural products with anticancer potential

Cancer is the second leading cause of death in the world and its incidence is expected to increase with the aging of the world's population and globalization of risk factors. Natural products and their derivatives have provided a significant number of approved anticancer drugs and the development of robust and selective screening assays for the identification of lead anticancer natural products are essential in the challenge of developing personalized targeted therapies tailored to the genetic and molecular characteristics of tumors. To this end, a ligand fishing assay is a remarkable tool to rapidly and rigorously screen complex matrices, such as plant extracts, for the isolation and identification of specific ligands that bind to relevant pharmacological targets. In this paper, we review the application of ligand fishing with cancer-related targets to screen natural product extracts for the isolation and identification of selective ligands. We provide critical analysis of the system configurations, targets, and key phytochemical classes related to the field of anticancer research. Based on the data collected, ligand fishing emerges as a robust and powerful screening system for the rapid discovery of new anticancer drugs from natural resources. It is currently an underexplored strategy according to its considerable potential.

Synthesis, Radiolabeling, and In Vitro and In Vivo Characterization of Heterobivalent Peptidic Agents for Bispecific EGFR and Integrin αvβ3 Targeting

Radiolabeled heterobivalent peptidic ligands (HBPLs) are a highly promising compound class for the sensitive and specific visualization of tumors as they often exhibit superior properties compared to their monospecific counterparts and are able to concomitantly or complementarily address different receptor types. The combination of two receptor-specific agents targeting the epidermal growth factor receptor (EGFR) and the integrin α_vβ₃ in one HBPL would constitute a synergistic combination of binding motifs as these two receptor types are concurrently overexpressed on several human tumor types and are closely associated with disease progression and metastasis. Here, we designed and synthesized two heterobivalent radioligands consisting of the EGFR-specific peptide GE11 and α_vβ₃-specific cyclic RGD peptides, bearing a (1,4,7-triazacyclononane-4,7-diyl)diacetic acid-1-glutaric acid chelator for efficient radiolabeling and linkers of different lengths between both peptides. Both HBPLs were radiolabeled with ⁶⁸Ga³⁺ in high radiochemical yields, purities of 96-99%, and molar activities of 36-88 GBq/μmol. [⁶⁸Ga]Ga-1 and [⁶⁸Ga]Ga-2 were evaluated for their log _D(7.4) and stability toward degradation by human serum peptidases, showing a high hydrophilicity for both agents of -3.07 ± 0.01 and -3.44 ± 0.08 as well as a high stability toward peptidase degradation in human serum with half-lives of 272 and 237 min, respectively. Further on, the in vitro receptor binding profiles of both HBPLs to the target EGF and integrin α_vβ₃ receptors were assessed on EGFR-positive A431 and α_vβ₃-positive U87MG cells. Finally, we investigated the in vivo pharmacokinetics of HBPL [⁶⁸Ga]Ga-1 by positron emission tomography/computed tomography imaging in A431 tumor-bearing xenograft mice to assess its potential for the receptor-specific visualization of EGFR- and/or α_vβ₃-expressing tumors. In these experiments, [⁶⁸Ga]Ga-1 demonstrated a tumor uptake of 2.79 ± 1.66% ID/g, being higher than in all other organs and tissues apart from kidneys and blood at 2 h p.i. Receptor blocking studies revealed the observed tumor uptake to be solely mediated by integrin α_vβ₃, whereas no contribution of the GE11 peptide sequence to tumor uptake via the EGFR could be determined. Thus, the approach to develop radiolabeled EGFR- and integrin α_vβ₃-bispecific HBPLs is in general feasible although another peptide lead structure than GE11 should be used as the basis for the EGFR-specific part of the agents.

The natural compound atraric acid suppresses androgen-regulated neo-angiogenesis of castration-resistant prostate cancer through angiopoietin 2

Castration-resistant prostate cancer (CRPC) is an aggressive lethal form of prostate cancer (PCa). Atraric acid (AA) not only inhibits the wild-type androgen receptor (AR) but also those AR mutants that confer therapy resistance to other clinically used AR antagonists, indicating a different mode of AR antagonism. AA induces cellular senescence and inhibits CRPC tumour growth in in vivo xenograft mouse model associated with reduced neo-angiogenesis suggesting the repression of intratumoural neo-angiogenesis by AA. In line with this, the secretome of CRPC cells mediates neo-angiogenesis in an androgen-dependent manner, which is counteracted by AA. This was confirmed by two in vitro models using primary human endothelial cells. Transcriptome sequencing revealed upregulated angiogenic pathways by androgen, being however VEGF-independent, and pointing to the pro-angiogenic factor angiopoietin 2 (ANGPT2) as a key driver of neo-angiogenesis induced by androgens and repressed by AA. In agreement with this, AA treatment of native patient-derived PCa tumour samples ex vivo inhibits ANGPT2 expression. Mechanistically, in addition to AA, immune-depletion of ANGPT2 from secretome or blocking ANGPT2-receptors inhibits androgen-induced angiogenesis. Taken together, we reveal a VEGF-independent ANGPT2-mediated angiogenic pathway that is inhibited by AA leading to repression of androgen-regulated neo-angiogenesis.

Current understandings and clinical translation of nanomedicines for breast cancer therapy

Breast cancer is one of the most frequently diagnosed cancers that is threatening women's life. Current clinical treatment regimens for breast cancer often involve neoadjuvant and adjuvant systemic therapies, which somewhat are associated with unfavorable features. Also, the heterogeneous nature of breast cancers requires precision medicine that cannot be fulfilled by a single type of systemically administered drug. Taking advantage of the nanocarriers, nanomedicines emerge as promising therapeutic agents for breast cancer that could resolve the defects of drugs and achieve precise drug delivery to almost all sites of primary and metastatic breast tumors (e.g. tumor vasculature, tumor stroma components, breast cancer cells, and some immune cells). Seven nanomedicines as represented by Doxil® have been approved for breast cancer clinical treatment so far. More nanomedicines including both non-targeting and active targeting nanomedicines are being evaluated in the clinical trials. However, we have to realize that the translation of nanomedicines, particularly the active targeting nanomedicines is not as successful as people have expected. This review provides a comprehensive landscape of the nanomedicines for breast cancer treatment, from laboratory investigations to clinical applications. We also highlight the key advances in the understanding of the biological fate and the targeting strategies of breast cancer nanomedicine and the implications to clinical translation.

Structural Biology of the Tumor Microenvironment

Cancers can be described as "rogue organs" (Balkwill FR, Capasso M, Hagemann T, J Cell Sci 125:5591-5596, 2012) because they are composed of multiple cell types and tissues. The transformed cells can recruit and alter healthy cells from surrounding tissues for their own benefit. It is these interactions that create the tumor microenvironment (TME). The TME describes the cells, factors, and extracellular matrix proteins that make up the tumor and the area around it; the biology of the TME influences tumor progression. Changes in the TME can lead to the growth and development of the tumor, the death of the tumor, or tumor metastasis. Metastasis is the process by which cancer spreads from its initial site to a different part of the body. Metastasis occurs when cancer cells enter the circulatory system or lymphatic system after they break away from a tumor. Once the cells leave, they can travel to a different part of the body and form new tumors. Therefore, understanding the TME is critical to fully understand cancer and find a way to successfully combat it. Knowledge of the TME can better inform researchers of the ability of potential therapies to reach tumor cells. It can also give researchers potential targets to kill the tumor. Instead of directly killing the cancer cells, therapies can target an aspect of the TME which could then halt tumor development or lead to tumor death. In other cases, targeting another aspect of the TME could make it easier for another therapy to kill the cancer cells, for example, using nanoparticles with collagenases to target the collagen in the surrounding environment to expose the cancer cells to drugs (Zinger A, et al, ACS Nano 13(10):11008-11021, 2019).The TME can be split simply into cells and the structural matrix. Within these groups are fibroblasts, structural proteins, immune cells, lymphocytes, bone marrow-derived inflammatory cells, blood vessels, and signaling molecules (Spill F, et al, Curr Opin Biotechnol 40:41-48, 2016; Del Prete A, et al, Curr Opin Pharmacol 35:40-47, 2017; Arneth B, Medicina (Kaunas) 56(1), 2019). From structure to providing nutrients for growth, each of these components plays a critical role in tumor maintenance. Together these components impact cancer growth, development, and resistance to therapies (Hanahan D, Coussens LM, Cancer Cell 21:309-322, 2012). In this chapter, we will describe the TME and express the importance of the cellular and structural elements of the TME.

Synergistic cytotoxicity and co-autophagy inhibition in pancreatic tumor cells and cancer-associated fibroblasts by dual functional peptide-modified liposomes

Pancreatic ductal adenocarcinoma (PDA) is a highly fatal disease with 5-year survival of ∼8.5%. Nanoplatforms such as nab-paclitaxel and nanoliposomal irinotecan demonstrate superiority and utility in treating different progressions of PDA by prolonging the median overall survival by only a few months. Due to the dense surrounding stroma and the high autophagy in pancreatic cancer, integrin ɑ_vβ₃ targeting, acid environmental sensitive, TR peptide-modified liposomal platforms loaded with combined autophagy inhibiting hydroxychloroquine (HCQ), and cytotoxic paclitaxel (PTX) were designed (TR-PTX/HCQ-Lip) to accomplish the aim of synergistically killing tumor cells while inhibiting stroma fibrosis. The results showed that TR peptide-modified liposomes (TR-Lip) have superior targeting and penetrating effects both in vitro and in vivo. TR-PTX/HCQ-Lip efficiently inhibited autophagy in pancreatic cells and surrounding cancer-associated fibroblasts. The synergistic anti-fibrosis roles were also confirmed both in vitro and in vivo, all of which contributes to the enhanced curative effects of TR-PTX/HCQ-Lip in both heterogenetic and orthotopic pancreatic cancer models. STATEMENT OF SIGNIFICANCE: Autophagy plays a significant role in pancreatic ductal adenocarcinoma, especially in activating cancer associated fibroblasts which is also related to collagen generation that promotes the formation of dense stroma, which hinder the cytotoxic drugs to target and kill cancer cells. In this study, we designed integrin ɑvβ3 targeting, acid environmental sensitive liposomal platforms to co-loaded paclitaxel and the autophagy inhibitor hydroxychloroquine. The results showed that the muti-functional liposomes can target to the pancreatic tumor and efficiently kill tumor cells and inhibit stroma fibrosis, thus improve the therapeutic effect in orthotopic pancreatic cancer models.

Osteoblasts grown on microroughened titanium surfaces regulate angiogenic growth factor production through specific integrin receptors

Cellular attachment and response to biomaterials are mediated by integrin receptor binding to extracellular matrix proteins adsorbed onto the material surface. Osteoblasts interact with their substrates via several integrin complexes including fibronectin-binding α5β1 and collagen-binding α1β1 and α2β1. Knockdown of α2 or β1 integrin subunits inhibits the production of factors that promote an osteogenic microenvironment, including osteocalcin, osteoprotegerin, and TGFβ1. Osteoblasts also secrete several angiogenic growth factors such as VEGF-A (VEGF¹⁶⁵), FGF-2, and angiopoietin 1, which are regulated by titanium surface topography and surface energy. Here, we examined whether signaling through integrin receptor complexes regulates production and secretion of angiogenic factors during osteoblast differentiation on microtextured Ti surfaces. To do this, integrin subunits α1, α2, α5, and β1 were stably silenced in MG63 osteoblast-like cells cultured on grit-blasted/acid-etched hydrophobic Ti (SLA) or on hydrophilic SLA (modSLA). VEGF-A production increased in response to Ti surface topography and energy in integrin α2, α5, and β1 silenced cells but decreased in α1-silenced cells. FGF-2 decreased on modSLA substrates in both α1 and α2-silenced cells but was unchanged in response to silencing of either α5 or β1. In integrin α1, α2, and β1-silenced cells, Ang-1 increased on modSLA but α5-silencing did not affect Ang-1 production during surface mediated differentiation. These results suggest that signaling through specific integrin receptor complexes during osteoblast differentiation on microstructured Ti substrates, regulates the production of angiogenic factors by those cells, and this is differentially regulated by surface hydrophilicity. STATEMENT OF SIGNIFICANCE: Successful implantation of synthetic biomaterials into bone depends on the biological process known as osseointegration. Osseointegration is a highly regulated communication of cells that orchestrates the migration of progenitor cells towards the implant site and promotes the deposition and mineralization of extracellular matrix proteins within the implant microenvironment, to tightly join the implant to native bone. In this process, angiogenesis functions as the initiation site of progenitor cell migration and is necessary for matrix deposition by providing the necessary nutrients for bone formation. In the present study, we show a novel regulation of specific angiogenic growth factors by integrin receptor complexes. This research is important to develop biomaterials that promote and maintain osseointegration through proper vascularization and prevent implant failure in patients lacking sufficient angiogenesis.

A Clinical Feasibility Study to Image Angiogenesis in Patients with Arteriovenous Malformations Using 68Ga-RGD PET/CT

Arteriovenous malformations (AVMs) have an inherent capacity to form new blood vessels, resulting in excessive lesion growth, and this process is further triggered by the release of angiogenic factors. ⁶⁸Ga-labeled arginine-glycine-aspartate tripeptide sequence (RGD) PET/CT imaging may provide insight into the angiogenic status and treatment response of AVMs. This clinical feasibility study was performed to demonstrate that ⁶⁸Ga-RGD PET/CT imaging can be used to quantitatively assess angiogenesis in peripheral AVMs. Methods: Ten patients with a peripheral AVM (mean age, 40 y; 4 men and 6 women) and scheduled for endovascular embolization treatment were prospectively included. All patients underwent ⁶⁸Ga-RGD PET/CT imaging 60 min after injection (mean dose, 207 ± 5 MBq). Uptake in the AVM, blood pool, and muscle was quantified as SUV_max and SUV_peak, and a descriptive analysis of the PET/CT images was performed. Furthermore, immunohistochemical analysis was performed on surgical biopsy sections of peripheral AVMs to investigate the expression pattern of integrin α_vβ₃ Results: ⁶⁸Ga-RGD PET/CT imaging showed enhanced uptake in all AVM lesions (mean SUV_max, 3.0 ± 1.1; mean SUV_peak, 2.2 ± 0.9). Lesion-to-blood and lesion-to-muscle ratios were 3.5 ± 2.2 and 4.6 ± 2.8, respectively. Uptake in blood and muscle was significantly higher in AVMs than in background tissue (P = 0.0006 and P = 0.0014, respectively). Initial observations included uptake in multifocal AVM lesions and enhanced uptake in intraosseous components in those AVM cases affecting bone integrity. Immunohistochemical analysis revealed cytoplasmatic and membranous integrin α_vβ₃ expression in the endothelial cells of AVMs. Conclusion: This feasibility study showed increased uptake in AVMs with angiogenic activity, compared with surrounding tissue without angiogenic activity, suggesting that ⁶⁸Ga-RGD PET/CT imaging can be used as a tool to quantitatively determine angiogenesis in AVMs. Further studies will be conducted to explore the potential of ⁶⁸Ga-RGD PET/CT imaging for guiding current treatment decisions and for assessing response to antiangiogenic treatment.

Non-genomic Actions of Thyroid Hormones Regulate the Growth and Angiogenesis of T Cell Lymphomas

T-cell lymphomas (TCL) are a heterogeneous group of aggressive clinical lymphoproliferative disorders with considerable clinical, morphological, immunophenotypic, and genetic variation, including ~10-15% of all lymphoid neoplasms. Several evidences indicate an important role of the non-neoplastic microenvironment in promoting both tumor growth and dissemination in T cell malignancies. Thus, dysregulation of integrin expression and activity is associated with TCL survival and proliferation. We found that thyroid hormones acting via the integrin αvβ3 receptor are crucial factors in tumor microenvironment (TME) affecting the pathophysiology of TCL cells. Specifically, TH-activated αvβ3 integrin signaling promoted TCL proliferation and induced and an angiogenic program via the up-regulation of the vascular endothelial growth factor (VEGF). This was observed both on different TCL cell lines representing the different subtypes of human hematological malignancy, and in preclinical models of TCL tumors xenotransplanted in immunodeficient mice as well. Moreover, development of solid tumors by inoculation of murine TCLs in syngeneic hyperthyroid mice, showed increased tumor growth along with increased expression of cell cycle regulators. The genomic or pharmacological inhibition of integrin αvβ3 decreased VEGF production, induced TCL cell death and decreased in vivo tumor growth and angiogenesis. Here, we review the non-genomic actions of THs on TCL regulation and their contribution to TCL development and evolution. These actions not only provide novel new insights on the endocrine modulation of TCL, but also provide a potential molecular target for its treatment.

Synthesis and In Vitro Study of a Dual-Mode Probe Targeting Integrin αvβ3

Malignant tumors constitute a serious disease that threaten human life, and early diagnosis and metastasis prediction are critical to the choice of treatment plan and the timing of treatment. Integrin α_vβ₃, which has received broad attention as a molecular marker of the tumor neovasculature, is an important target for monitoring tumorigenesis and progression in molecular imaging research. This study reports a magnetic resonance (MR)/fluorescence dual-mode molecular probe, cRGD-Gd-Cy5.5, which targets the integrin α_vβ₃ receptor and uses liposomes as carrier. The obtained nanoprobe had a size of 60.08 ± 0.45 nm, with good dispersion in water, a uniform distribution of sizes, desirable stability, and high relaxivity. Its r1 relaxation rate was 10.515 mM^-1 s^-1, much higher than that of other Gd chelates in clinical use. The probe showed no cytotoxicity at the tested concentrations in vitro, and its ability to target A549 cells and SUNE-1-5-8F cells was preliminarily evaluated through in vitro fluorescence imaging and MR imaging. The results demonstrated that the cRGD-Gd-Cy5.5 nanoprobe had good characteristics, showing desirable stability and biosafety, a high T1 relaxation rate, and strong targeting and binding to tumors with high expression of integrin α_vβ₃. Therefore, cRGD-Gd-Cy5.5 is a promising agent for the visual monitoring of tumor metastasis.

Synthesis and photophysical studies of a multivalent photoreactive RuII-calix[4]arene complex bearing RGD-containing cyclopentapeptides

Photoactive ruthenium-based complexes are actively studied for their biological applications as potential theragnostic agents against cancer. One major issue of these inorganic complexes is to penetrate inside cells in order to fulfil their function, either sensing the internal cell environment or exert a photocytotoxic activity. The use of lipophilic ligands allows the corresponding ruthenium complexes to passively diffuse inside cells but limits their structural and photophysical properties. Moreover, this strategy does not provide any cell selectivity. This limitation is also faced by complexes anchored on cell-penetrating peptides. In order to provide a selective cell targeting, we developed a multivalent system composed of a photoreactive ruthenium(II) complex tethered to a calix[4]arene platform bearing multiple RGD-containing cyclopentapeptides. Extensive photophysical and photochemical characterizations of this Ru(II)–calixarene conjugate as well as the study of its photoreactivity in the presence of guanosine monophosphate have been achieved. The results show that the ruthenium complex should be able to perform efficiently its photoinduced cytotoxic activity, once incorporated into targeted cancer cells thanks to the multivalent platform.

In Vivo Characterization of 4 68Ga-Labeled Multimeric RGD Peptides to Image αvβ3 Integrin Expression in 2 Human Tumor Xenograft Mouse Models

α_vβ₃ integrins play an important role in angiogenesis and cell migration in cancer and are highly expressed on the activated endothelial cells of newly formed blood vessels. Here, we compare the targeting characteristics of 4 ⁶⁸Ga-labeled multimeric cyclic arginine-glycine-aspartate (RGD)-based tracers in an α_vβ₃ integrin-expressing tumor model and a tumor model in which α_vβ₃ integrin is expressed solely on the neovasculature. Methods: Female BALB/c nude mice were subcutaneously injected with SK-RC-52 (α_vβ₃ integrin-positive) or FaDu (α_vβ₃ integrin-negative) tumor cells. ⁶⁸Ga-labeled DOTA-(RGD)₂, TRAP-(RGD)₃, FSC-(RGD)₃, or THP-(RGD)₃ was intravenously administered to the mice (0.5 nmol per mouse, 10-20 MBq), followed by small-animal PET/CT imaging and ex vivo biodistribution studies 1 h after injection. Nonspecific uptake of the tracers in both models was determined by coinjecting an excess of unlabeled DOTA-(RGD)₂ (50 nmol) along with the radiolabeled tracers. Results: Imaging and biodistribution data showed specific uptake in the tumors for each tracer in both models. Tumor uptake of ⁶⁸Ga-FSC-(RGD)₃ was significantly higher than that of ⁶⁸Ga-DOTA-(RGD)₂, ⁶⁸Ga-TRAP-(RGD)₃, or ⁶⁸Ga-THP-(RGD)₃ in the SK-RC-52 model but not in the FaDu model, in which ⁶⁸Ga-FSC-(RGD)₃ showed significantly higher tumor uptake than ⁶⁸Ga-TRAP-(RGD)₃ Most importantly, differences were also observed in normal tissues and in tumor-to-blood ratios. Conclusion: All tracers showed sufficient targeting of α_vβ₃ integrin expression to allow for tumor detection. Although the highest tumor uptake was found for ⁶⁸Ga-FSC-(RGD)₃ and ⁶⁸Ga-THP-(RGD)₃ in the SK-RC-52 and FaDu models, respectively, selection of the optimal tracer for specific diagnostic applications also depends on tumor-to-blood ratio and uptake in normal tissues; these factors should therefore also be considered.

A Pilot Study of 18F-Alfatide PET/CT Imaging for Detecting Lymph Node Metastases in Patients with Non-Small Cell Lung Cancer

Angiogenesis plays a key role in tumor development and α_vβ₃ integrin are overexpressed on the endothelial cell surface of newly forming vessels. ¹⁸F-Alfatide has favorable properties for α_vβ₃ integrin targeting and showed potential for imaging angiogenesis with Positron Emission Tomography (PET)/computed tomography (CT). In this study, 13 patients with non-small cell lung cancer (NSCLC) who underwent ¹⁸F-Alfatide PET/CT before surgery were enrolled. The uptake of all dissected lymph nodes (LNs) of ¹⁸F-Alfatide were assessed visually and analyzed with a maximum and mean standard uptake value (SUV_max, SUV_mean) and SUV ratios. LN metastases were pathologically confirmed and 20 of 196 LNs were malignant. All malignant LNs were successfully visualized on ¹⁸F-Alfatide PET/CT in patients and the sensitivity, specificity and accuracy was 100.0%, 94.9% and 95.4%, respectively. SUV_max, SUV_mean and SUV ratios in malignant LNs were significantly higher than in benign LNs for NSCLC patients (P < 0.001). The same result was observed in patients with adenocarcinoma and squamous cell carcinoma (P < 0.001). The ¹⁸F-Alfatide parameter shows high sensitivity (83.9-100%), specificity (78.6-96.7%) and accuracy (81.7-96.9%) according to thresholds calculated from receiver operating characteristic curve. Our results suggest that ¹⁸F-Alfatide PET/CT is valuable in the diagnosis of metastatic LNs for NSCLC patients.

RGD-Binding Integrins in Head and Neck Cancers

Alterations in integrin expression and function promote tumour growth, invasion, metastasis and neoangiogenesis. Head and neck cancers are highly vascular tumours with a tendency to metastasise. They express a wide range of integrin receptors. Expression of the αv and β1 subunits has been explored relatively extensively and linked to tumour progression and metastasis. Individual receptors αvβ3 and αvβ5 have proved popular targets for diagnostic and therapeutic agents but lesser studied receptors, such as αvβ6, αvβ8, and β1 subfamily members, also show promise. This review presents the current knowledge of integrin expression and function in squamous cell carcinoma of the head and neck (HNSCC), with a particular focus on the arginine-glycine-aspartate (RGD)-binding integrins, in order to highlight the potential of integrins as targets for personalised tumour-specific identification and therapy.

A phase I study of cilengitide and paclitaxel in patients with advanced solid tumors

PURPOSE

Cilengitide is a potent and selective inhibitor of the integrins αvβ3 and αvβ5. The primary objective of this phase I clinical trial was to establish the maximum tolerated dose and determine safety/tolerability of cilengitide in combination with paclitaxel in patients with advanced solid tumors. Secondary objectives included the evaluation of the preliminary clinical outcomes.

PATIENTS AND METHODS

Patients with advanced solid tumors experiencing disease progression on standard treatment were assigned to two different dose levels of cilengitide (2000 mg intravenously once or twice weekly) in combination with fixed-dose, weekly paclitaxel (90 mg/m² intravenously).

RESULTS

Twelve evaluable patients were treated per protocol. A single dose limiting toxicity (DLT) of grade 4 neutropenia was observed at the starting dose level of once weekly cilengitide. There were no grade ≥3 adverse events that occurred with >10% frequency. One patient achieved a partial response to therapy. Five patients experienced stable disease as best response, 3 of which discontinued study participation due to progressive, peripheral neuropathy.

CONCLUSIONS

Cilengitide in combination with paclitaxel was well tolerated. Antitumor activity was observed. The recommended phase II dose is twice weekly cilengitide (2000 mg) with weekly paclitaxel (90 mg/m²). Further studies evaluating drugs that target this pathway are warranted.

Onto better TRAILs for cancer treatment

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), also known as Apo-2 ligand (Apo2L), is a member of the TNF cytokine superfamily. By cross-linking TRAIL-Receptor (TRAIL-R) 1 or TRAIL-R2, also known as death receptors 4 and 5 (DR4 and DR5), TRAIL has the capability to induce apoptosis in a wide variety of tumor cells while sparing vital normal cells. The discovery of this unique property among TNF superfamily members laid the foundation for testing the clinical potential of TRAIL-R-targeting therapies in the cancer clinic. To date, two of these therapeutic strategies have been tested clinically: (i) recombinant human TRAIL and (ii) antibodies directed against TRAIL-R1 or TRAIL-R2. Unfortunately, however, these TRAIL-R agonists have basically failed as most human tumors are resistant to apoptosis induction by them. It recently emerged that this is largely due to the poor agonistic activity of these agents. Consequently, novel TRAIL-R-targeting agents with increased bioactivity are currently being developed with the aim of rendering TRAIL-based therapies more active. This review summarizes these second-generation novel formulations of TRAIL and other TRAIL-R agonists, which exhibit enhanced cytotoxic capacity toward cancer cells, thereby providing the potential of being more effective when applied clinically than first-generation TRAIL-R agonists.

Can an ¹⁸F-ALF-NOTA-PRGD2 PET/CT Scan Predict Treatment Sensitivity to Concurrent Chemoradiotherapy in Patients with Newly Diagnosed Glioblastoma?

This study examined the value of a novel 1-step labeled integrin α(v)β3-targeting (18)F-AlF-NOTA-PRGD2 (denoted as (18)F-RGD) scan in assessing sensitivity to concurrent chemoradiotherapy (CCRT) in patients with newly diagnosed glioblastoma multiforme (GBM).

METHODS

Twenty-five patients with newly diagnosed GBM were enrolled in this study 3-5 wk after surgical resection. All participants were investigated with (18)F-RGD PET/CT on baseline (T1) and at the third week (T2) after the start of CCRT. Tumor volume, maximal and mean standardized uptake value of the tumor (SUVmax, SUVmean), and tumor-to-nontumor ratios of the tumor volume were obtained. The MRI treatment response was assessed at the 11th week (T3). The change in the lesion volume from T1 to T3 on MRI was used as an endpoint to evaluate the predictive ability of (18)F-RGD PET/CT.

RESULTS

With (18)F-RGD PET/CT imaging, we successfully visualized the residual lesions of GBM. Twenty-five and 23 (18)F-RGD PET/CT scans at baseline and the third week, respectively, were available for analysis. We found that (18)F-RGD PET/CT parameters, both pretreatment SUVmax on baseline (P< 0.05) and intratreatment SUVmax at the third week (SUV(maxT2)) (P< 0.05) and tumor-to-nontumor ratios at the third week (P< 0.05), were predictive of treatment sensitivity to CCRT. Additionally, the change of volume from T1 to T2 on MRI was also predictive (P< 0.05). According to receiver-operating-characteristic curve analysis, the most significant parameter was SUV(maxT2) (area under the curve, 0.846). The threshold of SUV(maxT2) was 1.35, and its sensitivity, specificity, and accuracy were 84.6%, 90.0% and 87.0%, respectively.

CONCLUSION

(18)F-RGD PET/CT allows for the noninvasive visualization of GBM lesions and the prediction of sensitivity to CCRT as early as 3 wk after treatment initiation.

Exploration of peptide T7 and its derivative as integrin αvβ3-targeted imaging agents

OBJECTIVE

The aim of the present study was to develop potential candidates of integrin αvβ3-targeted imaging agent, which can facilitate the diagnosis and treatment of malignant solid tumors.

METHODS

Peptides derived from tumstatin, named T7 and T7-6H, were derivatized to contain histidine in the C-terminus of their sequence and were labeled with (99m)Tc via nitrido and carbonyl precursors. The radiochemical purity and stability of (99m)Tc-labeled T7 and T7-6H were characterized by thin-layer chromatography. The whole body biodistribution was studied in NCI-H157-bearing BALB/c nude mice.

RESULTS

The (99m)Tc-labeled T7 and T7-6H showed adequate in vitro stability, with a high radiochemical purity of over 90%. The dissociation constant (Kd) value of the (99m)Tc-labeled T7 and T7-6H ranged from 68.5 nM to 140.8 nM in U251 and NCI-H157 cell lines. (99m)Tc-labeled T7 and T7-6H showed no significant difference of biodistribution in mice. Furthermore, both T7 and T7-6H exhibited a poor blood-brain barrier penetration and a transient accumulation in lung; the uptake in tumor tissues was significantly higher than in muscle tissue, with a ratio of 5.8.

CONCLUSION

(99m)Tc-labeled T7 and T7-6H can be regarded as promising single-photon emission computed tomography probes for imaging integrin αvβ3, and need to be further studied for noninvasive detection of tumors.

Biodistribution of the ¹⁸F-FPPRGD₂ PET radiopharmaceutical in cancer patients: an atlas of SUV measurements

PURPOSE

The aim of this study was to investigate the biodistribution of 2-fluoropropionyl-labeled PEGylated dimeric arginine-glycine-aspartic acid (RGD) peptide (PEG3-E[c{RGDyk}]2) ((18)F-FPPRGD2) in cancer patients and to compare its uptake in malignant lesions with (18)F-FDG uptake.

METHODS

A total of 35 patients (11 men, 24 women, mean age 52.1 ± 10.8 years) were enrolled prospectively and had (18)F-FPPRGD2 PET/CT prior to treatment. Maximum standardized uptake values (SUVmax) and mean SUV (SUVmean) were measured in 23 normal tissues in each patient, as well as in known or suspected cancer lesions. Differences between (18)F-FPPRGD2 uptake and (18)F-FDG uptake were also evaluated in 28 of the 35 patients.

RESULTS

Areas of high (18)F-FPPRGD2 accumulation (SUVmax range 8.9 - 94.4, SUVmean range 7.1 - 64.4) included the bladder and kidneys. Moderate uptake (SUVmax range 2.1 - 6.3, SUVmean range 1.1 - 4.5) was found in the choroid plexus, salivary glands, thyroid, liver, spleen, pancreas, small bowel and skeleton. Compared with (18)F-FDG, (18)F-FPPRGD2 showed higher tumor-to-background ratio in brain lesions (13.4 ± 8.5 vs. 1.1 ± 0.5, P < 0.001), but no significant difference in body lesions (3.2 ± 1.9 vs. 4.4 ± 4.2, P = 0.10). There was no significant correlation between the uptake values (SUVmax and SUVmean) for (18)F FPPRGD2 and those for (18)F-FDG.

CONCLUSION

The biodistribution of (18)F-FPPRGD2 in cancer patients is similar to that of other RGD dimer peptides and it is suitable for clinical use. The lack of significant correlation between (18)F-FPPRGD2 and (18)F-FDG uptake confirms that the information provided by each PET tracer is different.

(44)Sc: an attractive isotope for peptide-based PET imaging

The overexpression of integrin α_vβ₃ has been linked to tumor aggressiveness and metastasis in several cancer types. Because of its high affinity, peptides containing the arginine–glycine–aspartic acid (RGD) motif have been proven valuable vectors for noninvasive imaging of integrin α_vβ₃ expression and for targeted radionuclide therapy. In this study, we aim to develop a ⁴⁴Sc-labeled RGD-based peptide for in vivo positron emission tomography (PET) imaging of integrin α_vβ₃ expression in a preclinical cancer model. High quality ⁴⁴Sc (t_1/2, 3.97 h; β⁺ branching ratio, 94.3%) was produced inexpensively in a cyclotron, via proton irradiation of natural Ca metal targets, and separated by extraction chromatography. A dimeric cyclic-RGD peptide, (cRGD)₂, was conjugated to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and radiolabeled with ⁴⁴Sc in high yield (>90%) and specific activity (7.4 MBq/nmol). Serial PET imaging of mice bearing U87MG tumor xenografts showed elevated ⁴⁴Sc-DOTA-(cRGD)₂ uptake in the tumor tissue of 3.93 ± 1.19, 3.07 ± 1.17, and 3.00 ± 1.25 %ID/g at 0.5, 2, and 4 h postinjection, respectively (n = 3), which were validated by ex vivo biodistribution experiments. The integrin α_vβ₃ specificity of the tracer was corroborated, both in vitro and in vivo, by competitive cell binding and receptor blocking assays. These results parallel previously reported studies showing similar tumor targeting and pharmacokinetic profiles for dimeric cRGD peptides labeled with ⁶⁴Cu or ⁶⁸Ga. Our findings, together with the advantageous radionuclidic properties of ⁴⁴Sc, capitalize on the relevance of this isotope as an attractive alternative isotope to more established radiometals for small molecule-based PET imaging, and as imaging surrogate of ⁴⁷Sc in theranostic applications.

Multimeric disintegrin protein polymer fusions that target tumor vasculature

Recombinant protein therapeutics have increased in number and frequency since the introduction of human insulin, 25 years ago. Presently, proteins and peptides are commonly used in the clinic. However, the incorporation of peptides into clinically approved nanomedicines has been limited. Reasons for this include the challenges of decorating pharmaceutical-grade nanoparticles with proteins by a process that is robust, scalable, and cost-effective. As an alternative to covalent bioconjugation between a protein and nanoparticle, we report that biologically active proteins may themselves mediate the formation of small multimers through steric stabilization by large protein polymers. Unlike multistep purification and bioconjugation, this approach is completed during biosynthesis. As proof-of-principle, the disintegrin protein called vicrostatin (VCN) was fused to an elastin-like polypeptide (A192). A significant fraction of fusion proteins self-assembled into multimers with a hydrodynamic radius of 15.9 nm. The A192-VCN fusion proteins compete specifically for cell-surface integrins on human umbilical vein endothelial cells (HUVECs) and two breast cancer cell lines, MDA-MB-231 and MDA-MB-435. Confocal microscopy revealed that, unlike linear RGD-containing protein polymers, the disintegrin fusion protein undergoes rapid cellular internalization. To explore their potential clinical applications, fusion proteins were characterized using small animal positron emission tomography (microPET). Passive tumor accumulation was observed for control protein polymers; however, the tumor accumulation of A192-VCN was saturable, which is consistent with integrin-mediated binding. The fusion of a protein polymer and disintegrin results in a higher intratumoral contrast compared to free VCN or A192 alone. Given the diversity of disintegrin proteins with specificity for various cell-surface integrins, disintegrin fusions are a new source of biomaterials with potential diagnostic and therapeutic applications.

Evaluation of the microvessel density and the expression of metalloproteases 2 and 9 and ttf1 in the different subtypes of lung adenocarcinoma in Tunisia: a retrospective study of 46 cases

Despite the new available histologic classification of lung cancers, it remains difficult to assess the real prognostic relevance of the different subtypes of lung adenocarcinomas. Facing the prognostic relevance of microvessel density (MVD) and the expression of metalloproteases and thyroid tyrosine factor 1 (TTF1) in different cancers, we tried to compare these parameters in the different subtypes of lung adenocarcinomas. We conducted a retrospective study of 46 adenocarcinomas surgically resected. An immunohistochemical study using the cluster of differentiation 34 (CD34), TTF1, metalloproteases 2 (MMP2), and metalloproteases 9 (MMP9) antibodies was performed on all samples while MVD was evaluated using CD34 antibody. The analyzed cases included 19 acinar, 7 papillary, 1 lepidic, and 19 solid predominant American Thoracic Classification of lung adenocarcinomas (ASK). The higher MVD levels were observed in papillary and acinar subtypes types and a statically significant difference in the MVD was observed in the different subtypes (p< 0,001). This study didn't show significant statistical results concerning MMP and TTF1 expression but it revealed a tendency to an equal expression of these antibodies in the different subtypes. The difference in the MVD between the different subtypes of adenocarcinoma puts emphasis on their prognostic relevance.

Atomic basis for the species-specific inhibition of αV integrins by monoclonal antibody 17E6 is revealed by the crystal structure of αVβ3 ectodomain-17E6 Fab complex

The function-blocking, non-RGD-containing, and primate-specific mouse monoclonal antibody 17E6 binds the αV subfamily of integrins. 17E6 is currently in phase II clinical trials for treating cancer. To elucidate the structural basis of recognition and the molecular mechanism of inhibition, we crystallized αVβ3 ectodomain in complex with the Fab fragment of 17E6. Protein crystals grew in presence of the activating cation Mn(2+). The integrin in the complex and in solution assumed the genuflected conformation. 17E6 Fab bound exclusively to the Propeller domain of the αV subunit. At the core of αV-Fab interface were interactions involving Propeller residues Lys-203 and Gln-145, with the latter accounting for primate specificity. The Propeller residue Asp-150, which normally coordinates Arg of the ligand Arg-Gly-Asp motif, formed contacts with Arg-54 of the Fab that were expected to reduce soluble FN10 binding to cellular αVβ3 complexed with 17E6. This was confirmed in direct binding studies, suggesting that 17E6 is an allosteric inhibitor of αV integrins.

Strategies to inhibit tumor associated integrin receptors: rationale for dual and multi-antagonists

The integrins are a family of 24 heterodimeric transmembrane cell surface receptors. Involvement in cell attachment to the extracellular matrix, motility, and proliferation identifies integrins as therapeutic targets in cancer and associated conditions: thrombosis, angiogenesis, and osteoporosis. The most reported strategy for drug development is synthesis of an agent that is highly selective for a single integrin receptor. However, the ability of cancer cells to change their integrin repertoire in response to drug treatment renders this approach vulnerable to the development of resistance and paradoxical promotion of tumor growth. Here, we review progress toward development of antagonists targeting two or more members of the Arg-Gly-Asp (RGD) binding integrins, notably αvβ3, αvβ5, αvβ6, αvβ8, α5β1, and αIIbβ3, as anticancer therapeutics.

Near-infrared fluorescence imaging of both colorectal cancer and ureters using a low-dose integrin targeted probe

BACKGROUND

Irradical tumor resections and iatrogenic ureteral injury remain a significant problem during lower abdominal surgery. The aim of the current study was to intraoperatively identify both colorectal tumors and ureters in subcutaneous and orthotopic animal models using cRGD-ZW800-1 and near-infrared (NIR) fluorescence.

METHODS

The zwitterionic fluorophore ZW800-1 was conjugated to the tumor specific peptide cRGD (targeting integrins) and to the a-specific peptide cRAD. One nmol cRGD-ZW800-1, cRAD-ZW800-1, or ZW800-1 alone was injected in mice bearing subcutaneous HT-29 human colorectal tumors. Subsequently, cRGD-ZW800-1 was injected at dosages of 0.25 and 1 nmol in mice bearing orthotopic HT-29 tumors transfected with luciferase2. In vivo biodistribution and ureteral visualization were investigated in rats. Fluorescence was measured intraoperatively at several time points after probe administration using the FLARE imaging system.

RESULTS

Both subcutaneous and orthotopic tumors could be clearly identified using cRGD-ZW800-1. A significantly higher signal-to-background ratio was observed in mice injected with cRGD-ZW800-1 (2.42 ± 0.77) compared with mice injected with cRAD-ZW800-1 or ZW800-1 alone (1.21 ± 0.19 and 1.34 ± 0.19, respectively) when measured at 24 h after probe administration. The clearance of cRGD-ZW800-1 permitted visualization of the ureters and also generated minimal background fluorescence in the gastrointestinal tract.

CONCLUSIONS

This study appears to be the first to demonstrate both clear tumor demarcation and ureteral visualization after a single intravenous injection of a targeted NIR fluorophore. As a low dose of cRGD-ZW800-1 provided clear tumor identification, clinical translation of these results should be possible.

Optimized multimodal nanoplatforms for targeting α(v)β3 integrins

Magnetic Resonance Imaging (MRI) using contrast agents is a very powerful technique for diagnosis in clinical medicine and biomedical research. The synthesis of ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles targeting αvβ3 integrins and acting as new MRI contrast agents seems to be a promising way for cancer diagnosis. Indeed, it is well established that αvβ3 integrin plays a key role in tumor angiogenesis acting like a receptor for the extracellular matrix proteins like vitronectin, fibronectin through the arginine-glycine-aspartic acid (RGD) sequence. Up-regulation of αvβ3 has been found to be associated with a wide range of cancers, making it a broad-spectrum tumor-marker. In this study, USPIO nanocrystals were synthesized and surface passivated with caffeic acid. The large number of the carboxylic acid functions at the outer surface of the nanoplatforms was used for the covalent coupling of Rhodamine123, polyethylene glycol (PEG) and cyclic RGD. Soluble carbodiimide (EDC) and N-hydroxysuccinimide (NHS) were used to crosslink carboxylic acid with the amino group of the ligands. We examined the design of the nanoplatforms with each individual entity and then the combination of two and three of them. Several methods were used to characterize the nanoparticle surface functionalization and the magnetic properties of these contrast agents were studied using a 1.5 T clinical MRI scanner. The affinity towards integrins was evidenced by surface plasmon resonance and solid-phase receptor-binding assay.

Imaging integrin alpha-v-beta-3 expression in tumors with an 18F-labeled dimeric RGD peptide

Integrin αv β3 receptors are expressed on activated endothelial cells during neovascularization to maintain tumor growth. Many radiolabeled probes utilize the tight and specific association between the arginine-glycine-aspartatic acid (RGD) peptide and integrin αv β3 , but one main obstacle for any clinical application of these probes is the laborious multistep radiosynthesis of (18)F. In this study, the dimeric RGD peptide, E-[c(RGDfK)]2, was conjugated with NODAGA and radiolabeled with (18)F in a simple one-pot process with a radiolabeling yield of 20%, the whole process lasting only 45 min. NODAGA-E-[c(RGDfK)]2 labeled with (18)F at a specific activity of 1.8 MBq nmol(-1) and a radiochemical purity of 100% could be achieved. The logP value of (18)F-labeled NODAGA-E-[c(RGDfK)]2 was -4.26 ± 0.02. In biodistribution studies, (18)F-NODAGA-E-[c(RGDfK)]2 cleared rapidly from the blood with 0.03 ± 0.01 percentage injected dose per gram (%ID g(-1)) in the blood at 2 h p.i., mainly via the kidneys, and showed good in vivo stability. Tumor uptake of (18)F-NODAGA-E-[c(RGDfK)]2 (3.44 ± 0.20 %ID g(-1), 2 h p.i.) was significantly lower than that of reference compounds (68) Ga-labeled NODAGA-E-[c(RGDfK)]2 (6.26 ± 0.76 %ID g(-1) ; p <0.001) and (111) In-labeled NODAGA-E-[c(RGDfK)]2 (4.99 ± 0.64 %ID g(-1) ; p < 0.01). Co-injection of an excess of unlabeled NODAGA-E-[c(RGDfK)]2 along with (18)F-NODAGA-E-[c(RGDfK)]2 resulted in significantly reduced radioactivity concentrations in the tumor (0.85 ± 0.13 %ID g(-1)). The αv β3 integrin-expressing SK-RC-52 tumor could be successfully visualized by microPET with (18)F-labeled NODAGA-E-[c(RGDfK)]2 . In conclusion, NODAGA-E-[c(RGDfK)]2 could be labeled rapidly with (18)F using a direct aqueous, one-pot method and it accumulated specifically in αv β3 integrin-expressing SK-RC-52 tumors, allowing for visualization by microPET.

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.

Synstatin: a selective inhibitor of the syndecan-1-coupled IGF1R-αvβ3 integrin complex in tumorigenesis and angiogenesis

The syndecans are a family of heparan sulfate-decorated cell-surface proteoglycans: matrix receptors with roles in cell adhesion and growth factor signaling. Their heparan sulfate chains recognize 'heparin-binding' motifs that are ubiquitously present in the extracellular matrix, providing the means for syndecans to constitutively bind and cluster to sites of cell-matrix adhesion. Emerging evidence suggests that specialized docking sites in the syndecan extracellular domains may serve to localize other receptors to these sites as well, including integrins and growth factor receptor tyrosine kinases. A prototype of this mechanism is capture of the αvβ3 integrin and insulin-like growth factor 1 receptor (IGF1R) by syndecan-1 (Sdc1), forming a ternary receptor complex in which signaling downstream of IGF1R activates the integrin. This Sdc1-coupled ternary receptor complex is especially prevalent on tumor cells and activated endothelial cells undergoing angiogenesis, reflecting the up-regulated expression of αvβ3 integrin in such cells. As such, much effort has focused on developing therapeutic agents that target this integrin in various cancers. Along these lines, the site in the Sdc1 ectodomain that is responsible for capture and activation of the αvβ3 or αvβ5 integrins by IGF1R can be mimicked by a short peptide called 'synstatin', which competitively displaces the integrin and IGF1R kinase from the syndecan and inactivates the complex. This review summarizes our current knowledge of the Sdc1-coupled ternary receptor complex and the efficacy of synstatin as an emerging therapeutic agent to target this signaling mechanism.

Vascular endothelial-cadherin stimulates syndecan-1-coupled insulin-like growth factor-1 receptor and cross-talk between αVβ3 integrin and vascular endothelial growth factor receptor 2 at the onset of endothelial cell dissemination during angiogenesis

Vascular endothelial growth factor (VEGF)-stimulated angiogenesis depends on a cross-talk mechanism involving VEGF receptor 2 (VEGFR2), vascular endothelial (VE)-cadherin and the αVβ3 integrin. Because we have shown that αVβ3 integrin activation is dependent on its incorporation, along with the insulin-like growth factor-1 receptor (IGF1R) kinase, into a ternary receptor complex organized by the matrix receptor syndecan-1 (Sdc1), we questioned the role of this core complex in VEGF-stimulated angiogenesis. We find that the Sdc1-coupled ternary receptor complex is required for VEGF signalling and for stimulation of vascular endothelial cell migration by vascular endothelial cadherin (VE-cadherin) engagement. VE-cadherin binding to Fc/VE-cadherin extracellular domain chimera activates Sdc1-coupled IGF1R and αvβ3 integrin; this depends on VEGFR2 and c-Src activated by the cadherin. Blocking homotypic VE-cadherin engagement disrupts VEGF-stimulated cell migration, which is restored by clustering the cadherin in the absence of cell-cell adhesion. This cadherin-dependent stimulation requires VEGFR2 and IGF1R and is blocked by synstatin (SSTN)(92-119), a peptide that competitively disrupts the Sdc1-coupled ternary complex and prevents the αVβ3 integrin activation required for VEGFR2 activation. VEGFR2-stimulated angiogenesis in the mouse aortic ring explant assay is disrupted by SSTN, although only early in the process, suggesting that IGF1R coupling to Sdc1 and αVβ3 integrin comprises a core activation mechanism activated by VE-cadherin that is necessary for VEGFR2 and integrin activation in the initial stages of endothelial cell dissemination during angiogenesis.

Cilengitide affects tumor compartment, vascularization and microenvironment in experimental bone metastases as shown by longitudinal ¹⁸F-FDG PET and gene expression analysis

PURPOSE

Aim of this study was to investigate the specific treatment effects of inhibiting αvβ3/αvβ5 integrins by cilengitide in an animal model of breast cancer bone metastases using dynamic (18)F-FDG PET and gene expression analysis.

METHODS

For this purpose, nude rats bearing bone metastases were treated with cilengitide, a small molecule inhibitor of αvβ3 and αvβ5 integrins, from day 30 to 55 after tumor cell inoculation of MDA-MB-231 breast cancer cells (25 mg/kg, 5 days per week; n = 8 rats) and compared to control rats (n = 8). Dynamic (18)F-FDG PET data were assessed at days 30, 35 and 55 after tumor cell inoculation determining the vascular fraction VB and the metabolic variables k1-k4. At day 55, genome-wide mRNA expression analysis was performed to assess the treatment-specific expression changes from cilengitide-treated and control rats.

RESULTS

In a longitudinal (18)F-FDG PET study, the vascular fraction VB was significantly decreased in bone metastases between days 30/35, 30/55 and 35/55, whereas the kinetic parameters k1 and k4 were significantly decreased between days 30/55 in skeletal lesions of treated animals. Gene expression analysis from bone metastases at day 55 revealed that tumor-produced integrins (αvβ5) as well as factors relevant for angiogenesis (αvβ3, VEGF, PDGF), bone resorption (PTHrP and RANKL), extracellular matrix remodeling (collagen, CD44) and bone marrow microenvironment (CXCR4) were significantly reduced upon therapy with cilengitide.

CONCLUSIONS

Here, we provide evidence that cilengitide inhibits pivotal factors of all compartments of bone metastases including tumor cells, vasculature and bone microenvironment in vivo and by whole-genome transcriptome analysis.

The αVβ3/αVβ5 integrin inhibitor cilengitide augments tumor response to melphalan isolated limb perfusion in a sarcoma model

Isolated limb perfusion (ILP) with melphalan and tumor necrosis factor (TNF)-α is used to treat bulky, locally advanced melanoma and sarcoma. However, TNF toxicity suggests a need for better-tolerated drugs. Cilengitide (EMD 121974), a novel cyclic inhibitor of alpha-V integrins, has both anti-angiogenic and direct anti-tumor effects and is a possible alternative to TNF in ILP. In this study, rats bearing a hind limb soft tissue sarcoma underwent ILP using different combinations of melphalan, TNF and cilengitide in the perfusate. Further groups had intra-peritoneal (i.p.) injections of cilengitide or saline 2 hr before and 3 hr after ILP. A 77% response rate (RR) was seen in animals treated i.p. with cilengitide and perfused with melphalan plus cilengitide. The RR was 85% in animals treated i.p. with cilengitide and ILP using melphalan plus both TNF and cilengitide. Both RRs were significantly greater than those seen with melphalan or cilengitide alone. Histopathology showed that high RRs were accompanied by disruption of tumor vascular endothelium and tumor necrosis. Compared with ILP using melphalan alone, the addition of cilengitide resulted in a three to sevenfold increase in melphalan concentration in tumor but not in muscle in the perfused limb. Supportive in vitro studies indicate that cilengitide both inhibits tumor cell attachment and increases endothelial permeability. Since cilengitide has low toxicity, these data suggest the agent is a good alternative to TNF in the ILP setting.

Endogenous ribosomal protein L29 (RPL29): a newly identified regulator of angiogenesis in mice

Cellular ribosomal protein L29 (RPL29) is known to be important in protein synthesis, but its function during angiogenesis has never been described before. We have shown previously that mice lacking β3-integrins support enhanced tumour angiogenesis and, therefore, deletion of endothelial αvβ3 can provide a method for discovery of novel regulators of tumour angiogenesis. Here, we describe significant upregulation of RPL29 in β3-null endothelial cells at both the mRNA and protein level. Ex vivo, we show that VEGF-stimulated microvessel sprouting was reduced significantly in Rpl29-heterozygous and Rpl29-null aortic ring assays compared with wild-type controls. Moreover, we provide in vivo evidence that RPL29 can regulate tumour angiogenesis. Tumour blood vessel density in subcutaneously grown Lewis lung carcinomas was reduced significantly in Rpl29-mutant mice. Additionally, depletion of Rpl29 using RNA interference inhibited VEGF-induced aortic ring sprouting, suggesting that anti-RPL29 strategies might have anti-angiogenic potential. Overall, our results identify that loss or depletion of RPL29 can reduce angiogenesis in vivo and ex vivo.

Vascular density and endothelial cell expression of integrin alpha v beta 3 and E-selectin in murine tumours

The endothelial cell adhesion molecules, including the integrin alpha v beta 3 (αvβ3) and E-selectin, are involved in the process of angiogenesis required for tumour growth, cell migration and metastasis. The purpose of this study was to assess and compare widely used tumour models to select the ones most suitable for angiogenesis research. Fifteen murine tumours were selected including melanoma (B16), colon (C26, C38, C51), mammary (MA13, MA16, MA16/Adr, MA17, MA17/Adr, MA25, MA44), pancreatic (PO2, PO3), Glasgow osteogenic sarcoma (GOS) and Lewis lung carcinoma (LLC). The tumour vascular density, assessed using the platelet endothelial cell adhesion molecule 1 (PECAM-1; CD31) immunostaining, revealed that B16 melanoma was poorly vascularized (<5 %), whereas the colon and mammary tumours were well vascularized (5-15 %). The most vascularized tumours (>15 %) were the pancreatic tumours (PO2 and PO3), the sarcoma (GOS) and the lung tumour (LLC). The integrin αvβ3 and E-selectin, evaluated by immunohistology, showed that 7/15 tumours expressed the αvβ3 integrin which was homogeneously distributed on all tumour sections (B16, C26, MA17/Adr, MA25, MA44, PO2, LLC). E-selectin was expressed in 4/15 tumours and its expression was restricted to the tumour periphery. Only 2/15 tumours (B16 and C26) were shown to express both integrin αvβ3 and E-selectin. In conclusion, these data not only contribute to a better understanding of the tumour biology of murine tumours but can also guide the choice of appropriate models for antiangiogenic therapy, for selective drug delivery to tumours and the validation of tumour imaging modalities targeting these endothelial cell adhesion molecules.

A novel PET tracer for the imaging of αvβ3 and αvβ5 integrins in experimental breast cancer bone metastases

The aim of this study was the evaluation of (68)Ga-DOTA-E-[c(RGDfK)](2) as a novel PET tracer to image αvβ3 and αvβ5 integrins. For this purpose, DOTA-E-[c(RGDfK)](2) was labeled with (68)Ga, which was obtained from a (68)Ge/(68)Ga generator, purified by solid-phase extraction and the radiochemical purity analyzed by radio-RP-HPLC. (68) Ga-DOTA-E-[c(RGDfK)](2) was obtained reproducibly in radiochemical yields of 60 ± 6% and with an excellent radiochemical purity of >99%. In nude rats bearing bone metastases after injection of MDA-MB-231 human breast cancer cells, biodistribution studies were performed to evaluate the accumulation of the radiotracer in selected organs, blood and bone metastases 0.5, 1, 2 and 3 h post injection. A rapid uptake into the bone metastases and rapid blood clearance was observed, resulting in tumor-blood ratios of up to 26.6 (3 h post injection) and tumor-muscle ratios of up to 7.9 (3 h post injection). A blocking experiment with coinjected αvβ3/αvβ5 antagonist showed the tumor uptake to be receptor-specific. In an initial in vivo micro PET evaluation of the tracer using the same animal model, the bone metastasis was clearly visualized. These results suggest that (68)Ga-DOTA-E-[c(RGDfK)](2) is a promising PET tracer suitable for the imaging of αvβ3 and αvβ5 integrins in bone metastases. This novel PET tracer should be further evaluated concerning its usefulness for early detection of bone metastases and monitoring treatment response of these lesions.

Absence of integrin αvβ3 enhances vascular leak in mice by inhibiting endothelial cortical actin formation

RATIONALE

Sepsis and acute lung injury (ALI) have devastatingly high mortality rates. Both are associated with increased vascular leak, a process regulated by complex molecular mechanisms.

OBJECTIVES

We hypothesized that integrin αvβ3 could be an important determinant of vascular leak and endothelial permeability in sepsis and ALI.

METHODS

β3 subunit knockout mice were tested for lung vascular leak after endotracheal LPS, and systemic vascular leak and mortality after intraperitoneal LPS and cecal ligation and puncture. Possible contributory effects of β3 deficiency in platelets and other hematopoietic cells were excluded by bone marrow reconstitution experiments. Endothelial cells treated with αvβ3 antibodies were evaluated for sphingosine-1 phosphate (S1P)–mediated alterations in barrier function, cytoskeletal arrangement, and integrin localization.

MEASUREMENTS AND MAIN RESULTS

β3 knockout mice had increased vascular leak and pulmonary edema formation after endotracheal LPS, and increased vascular leak and mortality after intraperitoneal LPS and cecal ligation and puncture. In endothelial cells, αvβ3 antibodies inhibited barrier-enhancing and cortical actin responses to S1P. Furthermore, S1P induced translocation of αvβ3 from discrete focal adhesions to cortically distributed sites through Gi- and Rac1-mediated pathways. Cortical αvβ3 localization after S1P was decreased by αvβ3 antibodies, suggesting that ligation of the αvβ3 with its extracellular matrix ligands is required to stabilize cortical αvβ3 focal adhesions.

CONCLUSIONS

Our studies identify a novel mechanism by which αvβ3 mitigates increased vascular leak, a pathophysiologic function central to sepsis and ALI. These studies suggest that drugs designed to block αvβ3 may have the unexpected side effect of intensifying sepsis- and ALI-associated vascular endothelial leak.

Novel tetrapeptide, RGDF, mediated tumor specific liposomal doxorubicin (DOX) preparations

Arginine-glycine-aspartate (RGD) has been shown to possess a strong affinity for the integrins overexpressed in tumor cells, especially during tumor invasion, angiogenesis and metasis. Based on work from others, a novel tetrapeptide, arginine-glycine-aspartate-phenylanaline (RGDF), has been designed and studied as a homing device to direct liposomal doxorubicin (DOX) to tumor cells in this work. In order to incorporate RGDF into liposomal DOX preparations, RGDF was conjugated with three different fatty alcohols to achieve RGDF-fatty alcohol conjugates. Glycine-glycine-aspartate-phenylanaline (GGDF)-lauryl alcohol conjugate was synthesized as a negative control. RGDF-fatty alcohol conjugates (RGDFO(CH(2))(n)CH(3)) and GGDF-lauryl alcohol conjugate (L-GGDFC12-DOX) incorporated liposomal preparations were obtained by first preparing liposomes using the film dispersion method followed by loading DOX using a transmembrane pH gradient method. Because of their amphipathic nature, RGDF- or GGDF-fatty alcohol conjugates are expected to be readily incorporated into liposomes with their fatty alkanyl chains being intercalated between fatty acyl chains of liposomal bilayers and the hydrophilic peptide moiety (RGDF or GGDF) being anchored on the surface of liposomes. The particle size and zeta potential of liposomal DOX preparations containing RGDF-fatty alcohol conjugate (L-RGDF-DOXs) or L-GGDFC12-DOX were measured, and their morphology was studied using transmission electron microscopy. In vitro DOX release profile from RGDF incorporated liposomal DOX was measured. The antitumor activities of RGDF incorporated liposomal DOX preparations were evaluated in ICR mice inoculated with sarcoma S(180), which is known to express α(v)β(3) integrin. Both conventional liposomal DOX preparation (L-DOX) without RGDFO(CH(2))(n)CH(3) and L-GGDFC12-DOX were used as negative controls. Our results showed improved tumor growth inhibition with L-RGDF-DOXs over doxorubicin hydrochloride solution, L-DOX and L-GGDFC12-DOX. Pathological examination of tumor biopsy demonstrated that L-RGDF-DOXs induced enhanced tumor cell death in comparison to negative controls. Pharmacokinetic studies showed that the concentrations of DOX found in tumor sites were increased by 1.7-4.5-fold when liposomal DOX preparation containing RGDF-lauryl alcohol conjugate (L-RGDFC12-DOX) was administered in comparison to when L-GGDFC12-DOX or doxorubicin hydrochloride solution was administered. The concentrations of DOX found in the heart, which is the main site of toxic effects of DOX, were significantly reduced when L-RGDFC12-DOX was administered in comparison to when L-GGDFC12-DOX or doxorubicin hydrochloride solution was administered.

Cilengitide inhibits progression of experimental breast cancer bone metastases as imaged noninvasively using VCT, MRI and DCE-MRI in a longitudinal in vivo study

The aim of this study was to investigate the effect of inhibiting αvβ(3)/α(v) β(5) integrins by cilengitide in experimentally induced breast cancer bone metastases using noninvasive imaging techniques. For this purpose, nude rats bearing established breast cancer bone metastases were treated with cilengitide, a small molecule inhibitor of αvβ(3) and αvβ(5) integrins (75 mg/kg, five days per week; n = 12 rats) and compared to vehicle-treated control rats (n = 12). In a longitudinal study, conventional magnetic resonance imaging (MRI) and flat panel volumetric computed tomography were used to assess the volume of the soft tissue tumor and osteolysis, respectively, and dynamic contrast-enhanced (DCE-) MRI was performed to determine functional parameters of the tumor vasculature reflecting blood volume and blood vessel permeability. In rats treated with cilengitide, VCT and MRI showed that osteolytic lesions and the respective bone metastatic soft tissue tumors progressed more slowly than in vehicle-treated controls. DCE-MRI indicated a decrease in blood volume and an increase in vessel permeability and immunohistology revealed increased numbers of immature vessels in cilengitide-treated rats compared to vehicle controls. In conclusion, treatment of experimental breast cancer bone metastases with cilengitide resulted in pronounced antiresorptive and antitumor effects, suggesting that αvβ(3)/αvβ(5) inhibition may be a promising therapeutic approach for bone metastases.

Integrin αvβ3-targeted gold nanoshells augment tumor vasculature-specific imaging and therapy

PURPOSE

Gold nanoshells (NSs) have already shown great promise as photothermal actuators for cancer therapy. Integrin αvβ3 is a marker that is specifically and preferentially overexpressed on multiple tumor types and on angiogenic tumor neovasculature. Active targeting of NSs to integrin αvβ3 offers the potential to increase accumulation preferentially in tumors and thereby enhance therapy efficacy.

METHODS

Enzyme-linked immunosorbent assay (ELISA) and cell binding assay were used to study the in vitro binding affinities of the targeted nanoconjugate NS-RGDfK. In vivo biodistribution and tumor specificity were analyzed using 64Cu-radiolabeled untargeted and targeted NSs in live nude rats bearing head and neck squamous cell carcinoma (HNSCC) xenografts. The potential thermal therapy applications of NS-RGDfK were evaluated by subablative thermal therapy of tumor xenografts using untargeted and targeted NSs.

RESULTS

ELISA and cell binding assay confirmed the binding affinity of NS-RGDfK to integrin αvβ3. Positron emission tomography/computed tomography imaging suggested that tumor targeting is improved by conjugation of NSs to cyclo(RGDfK) and peaks at ~20 hours postinjection. In the subablative thermal therapy study, greater biological effectiveness of targeted NSs was implied by the greater degree of tumor necrosis.

CONCLUSION

The results presented in this paper set the stage for the advancement of integrin αvβ3-targeted NSs as therapeutic nanoconstructs for effective cancer therapy.

Immunohistochemical analysis of integrins αvβ3, αvβ5 and α5β1, and their ligands, fibrinogen, fibronectin, osteopontin and vitronectin, in frozen sections of human oral head and neck squamous cell carcinomas

Integrins mediate the interaction of cells with the extracellular matrix and are believed to be involved in tumor cell survival and metastasis, and in tumor angiogenesis. We used immunohistochemistry of fresh-frozen human tumor tissues to analyze the presence of integrins αvβ3, αvβ5 and α5β1, which are believed to be involved in tumor growth and migration, together with integrin ligands, vitronectin, osteopontin, fibronectin and fibrinogen, in human oral squamous cell carcinomas. Samples of squamous cell carcinomas and control tissues from patients without cancer undergoing oral or maxillofacial surgery were frozen in liquid nitrogen within 30 min of removal. Frozen sections were prepared, and the presence of integrins or ligands was visualized using standard immunohistochemistry (APAAP) with a blinded evaluation. Comparison of samples from the 40 oral cancer patients and the 20 controls revealed increased staining in tumors compared with the controls, and staining was demonstrated for αvβ3 in endothelia. αvβ5 staining was increased in the tumor samples, but this was associated with increased expression in stroma rather than in endothelia. Modestly increased expression of α5β1 was observed in the tumor samples, and this was associated with tumor cells, endothelia and stroma. Expression of ligands for the integrins varied between tissue types, with increased fibrinogen and fibronectin expression in tumor endothelia. Confirmation of the presence of these integrins and their association with tumor cells, endothelia or stroma suggests their potential for these integrins in human oral tumors. Overall, the increased expression of integrins within tumors, particularly expression associated with endothelial cells, supports the principle of selective integrin blockade as a novel anticancer strategy.

Stimulus-responsive macromolecules and nanoparticles for cancer drug delivery

Nanoparticles and macromolecular carriers have been widely used to increase the efficacy of chemotherapeutics, largely through passive accumulation provided by the enhanced permeability and retention effect. Stimulus-responsive peptide and polymer vehicles can further enhance the efficacy of antitumor therapeutics compared with the administration of free drug by three mechanisms: increasing the overall accumulation within solid tumors; providing a homogeneous spatial distribution in tumor tissues; and increasing the intracellular localization of anticancer therapeutics. This article highlights recent developments in 'smart' - stimulus-responsive - peptide, polymer and lipid drug carriers designed to enhance the localization and efficacy of therapeutic payloads as compared with free drug.