Synthesis, in vitro, and in vivo characterization of an integrin alpha(v)beta(3)-targeted molecular probe for optical imaging of tumor

Combination Therapy with LXW7 and Ceria Nanoparticles Protects against Acute Cerebral Ischemia/Reperfusion Injury in Rats

Ischemia/reperfusion is known to greatly increase oxidative stress in the penumbra, which results in brain damage. Integrin αvβ3 is selectively up-regulated with ischemic injury to the brain and remains elevated throughout reperfusion. We determined whether or not a new compound biotinylated-LXW7-ceria nanoparticle (CeNP) (bLXW7-CeNP) plays a role in brain protection in the rat model of middle cerebral artery occlusion/reperfusion and shows better effects than CeNPs alone in improving the outcomes of focal oxidative stress and apoptosis more effectively. Male Sprague-Dawley rats were subjected to focal cerebral ischemia for 2 h followed by a 24-h reperfusion. Drug treatment was intravenously administered via the caudal vein 1 h after occlusion. Rats were randomly divided into the following 4 groups: bLXW7-CeNP treatment group (0.5 mg/kg); CeNP treatment group (0.5 mg/kg); control saline group; and sham group. Brains were harvested 24 h after reperfusion, and the neurologic deficit scores, infarction volume, blood-brain barrier (BBB) disruption, and the level of oxidative stress and apoptosis were determined. Results showed that the bLXW7-CeNP and CeNP treatments could improve neurologic deficit scores, infarction volume, BBB disruption, and the level of oxidative stress and apoptosis. Compound bLXW7-CeNP treatment exhibited better effects than CeNp treatment and showed remarkable statistical differences in the infarction volume, the degree of BBB breakdown, the apoptosis and oxidative stress, apart from neurologic deficit scores. Thus, we concluded that bLXW7-CeNP protects against acute cerebral ischemia/reperfusion injury. BLXW7, as a ligand of integrin αvβ3, may be able to effectively localize the anti-oxidant CeNPs to the ischemic penumbra region, which may provide more adequate opportunities for CeNPs to exert anti-oxidative stress effects and subsequently reduce apoptosis in acute cerebral ischemia/reperfusion.

Enhancing tissue permeability with MRI guided preclinical focused ultrasound system in rabbit muscle: From normal tissue to VX2 tumor

High Intensity Focused Ultrasound (HIFU) is an emerging noninvasive, nonionizing physical energy based modality to ablate solid tumors with high power, or increase local permeability in tissues/tumors in pulsed mode with relatively low power. Compared with traditional ablative HIFU, nondestructive pulsed HIFU (pHIFU) is present in the majority of novel applications recently developed for enhancing the delivery of drugs and genes. Previous studies have demonstrated the capability of pHIFU to change tissue local permeability for enhanced drug delivery in both mouse tumors and mouse muscle. Further study based on bulk tissues in large animals and clinical HIFU system revealed correlation between therapeutic effect and thermal parameters, which was absent in the previous mouse studies. In this study, we further investigated the relation between the therapeutic effect of pHIFU and thermal parameters in bulky normal muscle tissues based on a rabbit model and a preclinical HIFU system. Correlation between therapeutic effect and thermal parameters was confirmed in our study on the same bulk tissues although different HIFU systems were used. Following the study in bulky normal muscle tissues, we further created bulky tumor model with VX2 tumors implanted on both hind limbs of rabbits and investigated the feasibility to enhance tumor permeability in bulky VX2 tumors in a rabbit model using pHIFU technique. A radiolabeled peptidomimetic integrin antagonist, 111In-DOTA-IA, was used following pHIFU treatment in our study to target VX2 tumor and serve as the radiotracer for follow-up single-photon emission computed tomography (SPECT) scanning. The results have shown significantly elevated uptake of 111In-DOTA-IA in the area of VX2 tumors pretreated by pHIFU compared with the control VX2 tumors not being pretreated by pHIFU, and statistical analysis revealed averaged 34.5% enhancement 24h after systematic delivery of 111In-DOTA-IA in VX2 tumors pretreated by pHIFU compared with the control VX2 tumors.

Alpha Particle Enhanced Blood Brain/Tumor Barrier Permeabilization in Glioblastomas Using Integrin Alpha-v Beta-3-Targeted Liposomes

Glioblastoma (GBM) is the most common primary malignant astrocytoma characterized by extensive invasion, angiogenesis, hypoxia, and micrometastasis. Despite the relatively leaky nature of GBM blood vessels, effective delivery of antitumor therapeutics has been a major challenge due to the complications caused by the blood-brain barrier (BBB) and the highly torturous nature of newly formed tumor vasculature (blood tumor barrier-BTB). External beam radiotherapy was previously shown to be an effective means of permeabilizing central nervous system (CNS) barriers. By using targeted short-ranged radionuclides, we show for the first time that our targeted actinium-225-labeled α_vβ₃-specific liposomes (²²⁵Ac-IA-TLs) caused catastrophic double stranded DNA breaks and significantly enhanced the permeability of BBB and BTB in mice bearing orthotopic GBMs. Histologic studies revealed characteristic α-particle induced double strand breaks within tumors but was not significantly present in normal brain regions away from the tumor where BBB permeability was observed. These findings indicate that the enhanced vascular permeability in these distal regions did not result from direct α-particle-induced DNA damage. On the basis of these results, in addition to their direct antitumor effects, ²²⁵Ac-IA-TLs can potentially be used to enhance the permeability of BBB and BTB for effective delivery of systemically administered antitumor therapeutics. Mol Cancer Ther; 16(10); 2191-200. ©2017 AACR.

LXW7 ameliorates focal cerebral ischemia injury and attenuates inflammatory responses in activated microglia in rats

Inflammation plays a pivotal role in ischemic stroke, when activated microglia release excessive pro-inflammatory mediators. The inhibition of integrin αvβ3 improves outcomes in rat focal cerebral ischemia models. However, the mechanisms by which microglia are neuroprotective remain unclear. This study evaluated whether post-ischemic treatment with another integrin αvβ3 inhibitor, the cyclic arginine-glycine-aspartic acid (RGD) peptide-cGRGDdvc (LXW7), alleviates cerebral ischemic injury. The anti-inflammatory effect of LXW7 in activated microglia within rat focal cerebral ischemia models was examined. A total of 108 Sprague-Dawley rats (250–280 g) were subjected to middle cerebral artery occlusion (MCAO). After 2 h, the rats were given an intravenous injection of LXW7 (100 μg/kg) or phosphate-buffered saline (PBS). Neurological scores, infarct volumes, brain water content (BWC) and histology alterations were determined. The expressions of pro-inflammatory cytokines [tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β)], and Iba1-positive activated microglia, within peri-ischemic brain tissue, were assessed with ELISA, western blot and immunofluorescence staining. Infarct volumes and BWC were significantly lower in LXW7-treated rats compared to those in the MCAO + PBS (control) group. The LXW7 treatment lowered the expression of pro-inflammatory cytokines. There was a reduction of Iba1-positive activated microglia, and the TNF-α and IL-1β expressions were attenuated. However, there was no difference in the Zea Longa scores between the ischemia and LXW7 groups. The results suggest that LXW7 protected against focal cerebral ischemia and attenuated inflammation in activated microglia. LXW7 may be neuroprotective during acute MCAO-induced brain damage and microglia-related neurodegenerative diseases.

First-In-Human Study Demonstrating Tumor-Angiogenesis by PET/CT Imaging with (68)Ga-NODAGA-THERANOST, a High-Affinity Peptidomimetic for αvβ3 Integrin Receptor Targeting

(68)Ga-NODAGA-THERANOST™ is an αvβ3 integrin antagonist and the first radiolabeled peptidomimetic to reach clinical development for targeting integrin receptors. In this first-in-human study, the feasibility of integrin receptor peptidomimetic positron emission tomography/computed tomography (PET/CT) imaging was confirmed in patients with non-small-cell lung cancer and breast cancer.

METHODS

Patients underwent PET/CT imaging with (68)Ga NODAGA-THERANOST. PET images were analyzed qualitatively and quantitatively and compared to 2-deoxy-2-((18)F) fluoro-d-glucose ((18)F-FDG) findings. Images were obtained 60 minutes postinjection of 300-500 MBq of (68)Ga-NODAGA-THERANOST.

RESULTS

(68)Ga-NODAGA-THERANOST revealed high tumor-to-background ratios (SUVmax=4.8) and uptake at neoangiogenesis sites. Reconstructed fused images distinguished cancers with high malignancy potential and enabled enhanced bone metastasis detection. (18)F-FDG-positive lung and lymph node metastases did not show uptake, indicating the absence of neovascularization.

CONCLUSIONS

(68)Ga-NODAGA-THERANOST was found to be safe and effective, exhibiting in this study rapid blood clearance, stability, rapid renal excretion, favorable biodistribution and PK/PD, low irradiation burden (μSv/MBq/μg), and convenient radiolabeling. This radioligand might enable theranostics, that is, a combination of diagnostics followed by the appropriate therapeutics, namely antiangiogenic therapy, image-guided presurgical assessment, treatment response evaluation, prediction of pathologic response, neoadjuvant-peptidomimetic-radiochemotherapy, and personalized medicine strategies. Further clinical trials evaluating (68)Ga-NODAGA-THERANOST are warranted.

Synthesis and characterization of gadolinium-Peptidomimetic complex as an αvβ3 integrin targeted MR contrast agent

There is growing interest in small and rigid peptidomimetic αvβ3 integrin antagonists that are readily synthesized and characterized and amenable to physiological conditions. Peptidomimetic 4-[2-(3,4,5,6-tetrahydropyrimidine-2-ylamino)ethyloxy]benzoyl-2-[N-(3-amino-neopenta-1-carbamyl)]-aminoethylsulfonyl-amino-β-alanine (IAC) was successfully conjugated to DOTA, complexed with Gd(III) and radiolabeled with (153)Gd. Radioassay results demonstrated specificity of the labeled conjugate by blocking ∼95% binding with the addition of a 50-fold molar excess of cold IAC to the reaction solution. Relaxometry was used to support the hypothesis that the specificity of the Gd-peptidomimetic targeting αvβ3 integrin would increase the contrast and therefore enhance the sensitivity of an MRI scan of αvβ3 integrin positive tissues. Magnetic resonance imaging of cell pellets (M21 human melanoma) was also performed, and the images clearly show that cells reacted with Gd(III)-DOTA-IAC display a brighter image than cells without the Gd(III)-DOTA-IAC contrast agent. In addition, Gd(III)-DOTA-IAC and IAC, with IC50 of 300nM and 230nM, respectively, are 2.1 and 2.7 times more potent than c(RGDfK) whose IC50 is 625nM. This promising preliminary data fuels further investigation of DOTA-IAC conjugates for targeting tumor associated angiogenesis and αvβ3 integrin positive tumors using magnetic resonance imaging.

One-step (18)F labeling of non-peptidic bivalent integrin αvβ3 antagonist for cancer imaging

A rapid one-step ¹⁸F labeling reaction with fluoridealuminum complex, which is based on chelation chemistry, has received a surge of interest for ¹⁸F radiolabeling of peptides. In this study, a non-peptidic bivalent integrin α_vβ₃ antagonist (bivalent-IA) was conjugated with 1,4,7-triazacyclononane-1,4-diiacetic acid (NODA). A novel ¹⁸F labeled radiotracer, ¹⁸F-bivalent-IA, was developed via one step ¹⁸F–AlF/NODA chelation reaction in aqueous phase with high radiochemical yield (65–75%, decay corrected) and good specific activity (750–850 mCi/μmol). The tumor integrin targeting efficiency and in vivo pharmacokinetic profile of ¹⁸F-bivalent-IA were evaluated in U-87 MG (integrin positive) and MDA-MB-231 (integrin negative) models by small-animal PET/CT scan followed by a biodistribution study. The PET/CT and ROI results showed high tumor uptake of ¹⁸F-bivalent-IA in U-87 MG tumor-bearing mice from 5 to 120 min p.i. with good contrast, and the U-87 MG tumor uptake values (6.35 ± 0.67%ID/g, at 1 h p.i.) were 6 times higher than those of MDA-MB-231 tumor (1.05 ± 0.12%ID/g, at 1 h p.i.) (P < 0.0001) which correlated with the integrin α_vβ₃ expression in tumor tissues confirmed by immunohistochemistry. Co-injection of the ¹⁸F-bivalent-IA with 6 nmol (6 μg) of nonradioactive bivalent-IA effectively blocked tumor uptake demonstrating the integrin α_vβ₃-specificity. In conclusion, the first ¹⁸F labeled non-peptidic bivalent integrin α_vβ₃ targeting radiotracer, ¹⁸F-bivalent-IA, was developed and proved to be a highly potent and specific PET radiopharmaceutical for noninvasive imaging of integrin α_vβ₃, which plays a critical role in tumor angiogenesis and metastasis.

Effects of integrins and integrin αvβ3 inhibitor on angiogenesis in cerebral ischemic stroke

Integrins such as αvβ3, α5β1 play a key role in angiogenesis regulation, invasion and metastasis, inflammation, wound healing, etc. The up-regulation of integrin αvβ3 after cerebral ischemic stroke can promote angiogenesis, which in turn improves functional recovery. In addition, the integrin αvβ3 inhibitor can block the blood-brain barrier (BBB) leakage induced by vascular endothelial growth factor (VEGF) and also can reduce inflammatory reaction, decrease the deposition of fibrinogen. Other studies showed that integrin αvβ3 is not essential in revascularization. Therefore, the effect of integrin αvβ3 in the whole process of brain function recovery merits further study.

Multivalency of non-peptide integrin αVβ3 antagonist slows tumor growth

Multivalency is a powerful strategy for achieving high-affinity molecular binding of compounds to increase their therapeutic potency or imaging potential. In our study, multivalent non-peptide integrin αvβ3 antagonists (IA) were designed for antitumor therapy. Docking and molecular dynamics were employed to explore the binding modes of IA monomer, dimer, and trimer. In silico, one IA unit binds tightly in the active site with similar pose to native ligand RGD and other parts of dimer and trimer contribute extra binding affinities by interacting with residues in vicinity of the original site. In vitro studies demonstrated that increasing valency results in increasing antiproliferative and antiorganizational effects against endothelial cells (HUVECs), and a much weaker effect on melanoma B16F10 cells. The antitumor efficacies of the IA multivalent compounds were evaluated in subcutaneous B16F10 melanoma tumor-bearing mice. At 30 mg/kg dose, the mean masses of tumors harvested 18 days after inoculation were significantly reduced (p<10(-7)) by 36±9%, 49±8%, and 71±7% for the IA monomer, dimer, and trimer groups, relative to control. The importance of multivalency was demonstrated to be highly significant beyond the additive effect of the extra pharmacological sites (p=0.00011). These results suggest that the major target of these anti-αvβ3 compounds is the neovasculature rather than the cancer cells, and the success of a multivalent strategy depends on the details of the components and linker. This is the first integrin αvβ3 multivalent ligand showing clear enhancement in antitumor effectiveness.

Biodistribution of99mTc Labeled Integrin Antagonist

The selective targeting of an integrin α_vβ₃ receptor using radioligands may enable the assessment of angiogenesis and integrin α_vβ₃ receptor status in tumors. The aim of this research was to label a peptidomimetic integrin α_vβ₃ antagonist (PIA) with ^99mTc(CO)₃ and to test its receptor targeting properties in nude mice bearing receptor-positive tumors. PIA was reacted with tris-succinimidyl aminotriacetate (TSAT) (20 mM) as a PIA per TSAT. The product, PIA-aminodiacetic acid (ADA), was radiolabeled with [^99mTc(CO)₃(H₂O)₃]⁺¹, and purified sequentially on a Sep-Pak C-18 cartridge followed by a Sep-Pak QMA anion exchange cartridge. Using gradient C-18 reverse-phase HPLC, the radiochemical purity of ^99mTc(CO)₃-ADA-PIA (retention time, 10.5 min) was confirmed to be > 95%. Biodistribution analysis was performed in nude mice (n = 5 per time point) bearing receptor-positive M21 human melanoma xenografts. The mice were administered ^99mTc(CO)₃-ADA-PIA intravenously. The animals were euthanized at 0.33, 1, and 2 hr after injection for the biodistribution study. A separate group of mice were also co-injected with 200 μg of PIA and euthanized at 1 hr to quantify tumor uptake. ^99mTc(CO)₃-ADA-PIA was stable in phosphate buffer for 21 hr, but at 3 and 6 hr, 7.9 and 11.5% of the radioactivity was lost as histidine, respectively. In tumor bearing mice, ^99mTc(CO)₃-ADA-PIA accumulated rapidly in a receptor-positive tumor with a peak uptake at 20 min, and rapid clearance from blood occurring primarily through the hepatobiliary system. At 20 min, the tumor-toblood ratio was 1.8. At 1 hr, the tumor uptake was 0.47% injected dose (ID)/g, but decreased to 0.12% ID/g when co-injected with an excess amount of PIA, indicating that accumulation was receptor mediated. These results demonstrate successful ^99mTc labeling of a peptidomimetic integrin antagonist that accumulated in a tumor via receptor-specific binding. However, tumor uptake was very low because of low blood concentrations that likely resulted from rapid uptake of the agent into the hepatobiliary system. This study suggests that for ^99mTc(CO)₃-ADA-PIA to be useful as a tumor detection agent, it will be necessary to improve receptor binding affinity and increase the hydrophilicity of the product to minimize rapid hepatobiliary uptake.

Combined MR, fluorescence and histology imaging strategy in a human breast tumor xenograft model

Applications of molecular imaging in cancer and other diseases frequently require the combination of in vivo imaging modalities, such as MR and optical imaging, with ex vivo optical, fluorescence, histology and immunohistochemical imaging to investigate and relate molecular and biological processes to imaging parameters within the same region of interest. We have developed a multimodal image reconstruction and fusion framework that accurately combines in vivo MRI and MRSI, ex vivo brightfield and fluorescence microscopic imaging and ex vivo histology imaging. Ex vivo brightfield microscopic imaging was used as an intermediate modality to facilitate the ultimate link between ex vivo histology and in vivo MRI/MRSI. Tissue sectioning necessary for optical and histology imaging required the generation of a three-dimensional reconstruction module for two-dimensional ex vivo optical and histology imaging data. We developed an external fiducial marker-based three-dimensional reconstruction method, which was able to fuse optical brightfield and fluorescence with histology imaging data. The registration of the three-dimensional tumor shape was pursued to combine in vivo MRI/MRSI and ex vivo optical brightfield and fluorescence imaging data. This registration strategy was applied to in vivo MRI/MRSI, ex vivo optical brightfield/fluorescence and histology imaging datasets obtained from human breast tumor models. Three-dimensional human breast tumor datasets were successfully reconstructed and fused with this platform.

Synthesis and characterization of αvβ₃-targeting peptidomimetic chelate conjugates for PET and SPECT imaging

There is growing interest in small peptidomimetic α(v)β(3) integrin antagonists that are readily synthesized and characterized and can be easily handled using physiological conditions. Peptidomimetic 4-[2-(3,4,5,6-tetrahydropyrimidine-2-ylamino)ethyloxy]benzoyl-2-[N-(3-amino-neopenta-1-carbamyl)]-aminoethylsulfonyl-amino-β-alanine (IAC) was successfully conjugated to 1-(1-carboxy-3-carbo-t-butoxypropyl)-4,7-(carbo-tert-butoxymethyl)-1,4,7-triazacyclononane (NODA-GA(tBu)(3)) and 1-(1-carboxy-3-carbotertbutoxymethyl)-1,4,7,10-tetraazacyclododecane (DOTA-GA(tBu)(4)) and radiolabeled with (111)In, (67)Ga and (203)Pb. Results of a radioimmunoassay demonstrated binding to purified α(v)β(3) integrin when 1-4equiv of integrin were added to the reaction. Based on this promising result, investigations are moving forward to evaluate the NODA-GA-IAC and DOTA-GA-IAC conjugates for targeting tumor associated angiogenesis and α(v)β(3) integrin positive tumors to define their PET and SPECT imaging qualities as well as their potential for delivery of therapeutic radionuclides.

RGD-targeted paramagnetic liposomes for early detection of tumor: in vitro and in vivo studies

Magnetic resonance molecular imaging has emerged as a potential approach for tumor diagnosis in the last few decades. This approach consists of the delivery of MR contrast agents to the tumor by specific targeted carriers. For this purpose, a lipopeptide was constructed by using a cyclic RGD peptide headgroup coupled to palmitic acid anchors via a KGG tripeptide spacer. Targeted paramagnetic liposomes were then prepared by the incorporation of RGD-coupled-lipopeptides into lipid bilayers for specific bounding to tumor. In vitro, study demonstrated that RGD-targeted liposomes exhibited a better binding affinity to targeted cells than non-targeted liposomes. MR imaging of mice bearing A549 tumors with the RGD-targeted paramagnetic liposomes also resulted in a greater signal enhancement of tumor compared to non-targeted liposomes and pure contrast agents groups. In addition, biodistribution study also showed specific tumor targeting of RGD-targeted paramagnetic liposomes in vivo. Therefore, RGD-targeted paramagnetic liposomes prepared in the present study may be a more promising method for early tumor diagnosis.

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.

Synthesis and evaluation of a near-infrared fluorescent non-peptidic bivalent integrin alpha(v)beta(3) antagonist for cancer imaging

Computer modeling approaches to identify new inhibitors are essentially a very sophisticated and efficient way to design drugs. In this study, a bivalent nonpeptide intergrin alpha(v)beta(3) antagonist (bivalent IA) has been synthesized on the basis of an in silico rational design approach. A near-infrared (NIR) fluorescent imaging probe has been developed from this bivalent compound. In vitro binding assays have shown that the bivalent IA (IC(50) = 0.40 +/- 0.11 nM) exhibited improved integrin alpha(v)beta(3) affinity in comparison with the monovalent IA (IC(50) = 22.33 +/- 4.51 nM), resulting in an over 50-fold improvement in receptor affinity. NIR imaging probe, bivalent-IA-Cy5.5 conjugate, also demonstrated significantly increased binding affinity (IC(50) = 0.13 +/- 0.02 nM). Fluorescence microscopy studies showed integrin-mediated endocytosis of bivalent-IA-Cy5.5 in U87 cells which was effectively blocked by nonfluorescent bivalent IA. We also demonstrated tumor accumulation of this NIR imaging probe in U87 mouse xenografts.

High-affinity alphavbeta3 integrin targeted optical probe as a new imaging biomarker for early atherosclerosis: initial studies in Watanabe rabbits

PURPOSE

A newly developed synthetic alpha v beta 3 integrin targeted optical probe (ITOP) has been demonstrated to target cancer cells, in vivo. Compared to the commercially available cyclic peptide c[RGDfv], this optical probe has at least 20 times better binding affinity for the alpha v beta 3 receptor. The present in vitro study was designed to investigate the possibility of detecting early atherosclerotic plaque by using this ITOP.

PROCEDURES

Experiments were performed on five Watanabe heritable hyperlipidemic rabbits and two New Zealand White rabbits for control. Our ITOP was used for detecting the presence of alpha v beta 3 receptors in vitro.

RESULTS

Segments of plaque accumulation from two distinct regions of ascending and descending aortas were labeled in Watanabe rabbits. The signal was found principally in the adventitia and proximal intima of the aortic vessel, corresponding directly to the expression of integrin alpha v beta 3 as determined by antibody assay. Moreover, there was a close association between the level of labeling with the alpha v beta 3 targeted probe and the thickness of the adventitia.

CONCLUSIONS

This high-affinity ITOP identifies the site and extent of alpha v beta 3 expression and correlates with adventitial thickness. Recent evidence associates alpha v beta 3 expression with the inflammatory process in early vulnerable plaque, making this compound a promising potential biomarker for early atherosclerotic disease.

Tc-labeling of Peptidomimetic Antagonist to Selectively Target alpha(v)beta(3) Receptor-Positive Tumor: Comparison of PDA and EDDA as co-Ligands

OBJECTIVES: The aim of this research was to synthesize radiolabeled peptidomimetic integrin alpha(v)beta(3) antagonist with (99m)Tc for rapid targeting of integrin alpha(v)beta(3) receptors in tumor to produce a high tumor to background ratio. METHODS: The amino terminus of 4-[2-(3,4,5,6-tetra-hydropyrimidin-2-ylamino)-ethyloxy]benzoyl-2-(S)-[N-(3-amino-neopenta-1-carbamyl)]-aminoethylsulfonyl-amino-beta-alanine hydrochloride (IAC) was conjugated with N-hydroxysuccinimide ester of HYNIC and labeled with (99m)Tc using tricine with either 1,5-pyridinedicarboxylic acid (PDA) or ethylenediamine-N,N'-diacetic acid (EDDA) as the co-ligand. The products, (99m)Tc EDDA(2)/HYNIC-IAC (P1) and (99m)Tc PDA (tricin)/HYNIC-IAC (P2) were subjected to in vitro serum stability, receptor-binding, biodistribution and imaging studies. RESULTS: P1 and P2 were synthesized with an overall yield of >80%. P1 was slightly more stable than P2 when incubated in serum at 37 degrees C for 18 hrs (84 vs 77% intact). The In vitro receptor-binding of P1 was higher than that of P2 (78.02 +/- 13.48 vs 51.05 +/- 14.05%) when incubated with alpha(v)beta(3) at a molar excess (0.8 muM). This receptor binding was completely blocked by a molar excess of an unlabeled peptidomimetic antagonist. Their differences shown in serum stability and the receptor-binding appeared to be related to their biological behaviors in tumor uptake and retention; the 1 h tumor uptakes of P1 and P2 were 3.17+/-0.52 and 2.13+/-0.17 % ID/g, respectively. P1 was retained in the tumor longer than P2. P1 was excreted primarily through the renal system whereas P2 complex was excreted equally via both renal and hepatobiliary systems. Thus, P1 was retained in the whole-body with 27.25 +/- 3.67% ID at 4 h whereas 54.04 +/- 3.57% ID of P2 remained in the whole-body at 4 h. This higher whole-body retention of P2 appeared to be resulted from a higher amount of radioactivity retained in liver and intestine. These findings were supported by imaging studies showing higher tumor-to-abdominal contrast for P1 than for P2 at 3 h postinjection. CONCLUSIONS: P1 showed good tumor targeting properties with a rapid tumor uptake, prolonged tumor retention and fast whole-body clearance kinetics. These findings warrant further investigation of the HYNIC method of (99m)Tc labeling of other peptidomimetic antagonists using EDDA as a coligand.

Vascular Integrins in Tumor Angiogenesis: Mediators and Therapeutic Targets

The notion that tumor angiogenesis may have therapeutic implications in the control of tumor growth was introduced by Dr. Judah Folkman in 1971. The approval of Avastin in 2004 as the first antiangiogenic systemic drug to treat cancer patients came as a validation of this visionary concept and opened new perspectives to the treatment of cancer. In addition, this success boosted the field to the quest for new therapeutic targets and antiangiogenic drugs. Preclinical and clinical evidence indicate that vascular integrins may be valid therapeutic targets. In preclinical studies, pharmacological inhibition of integrin function efficiently suppressed angiogenesis and inhibited tumor progression. alphaVbeta3 and alphaVbeta5 were the first vascular integrins targeted to suppress tumor angiogenesis. Subsequent experiments revealed that at least four additional integrins (i.e., alpha1beta1, alpha2beta1, alpha5beta1, and alpha6beta4) might be potential therapeutic targets. In clinical studies low-molecular-weight integrin inhibitors and anti-integrin function-blocking antibodies demonstrated low toxicity and good tolerability and are now being tested in combination with radiotherapy and chemotherapy for anticancer activity in patients. In this article the authors review the role of integrins in angiogenesis, present recent development in the use of alphaVbeta3 and alpha5beta1 integrin antagonists as potential therapeutics in cancer, and discuss future perspectives.

Inhibition of integrin alphavbeta3 prevents urokinase plasminogen activator-mediated impairment of cerebrovasodilation after cerebral hypoxia/ischemia

Cerebral hypoxia (10 min) followed immediately by ischemia (20 min) (H/I) impairs cerebrovasodilation in response to hypercapnia and hypotension in the newborn pig; exogenous urokinase plasminogen activator (uPA) potentiates this effect, whereas the blockade of endogenous uPA-mediated vasoactivity prevents it completely. This study investigated the role of integrin alpha(V)beta(3) in the uPA-mediated impairment of cerebrovasodilation after H/I in piglets equipped with a closed cranial window. Pial artery dilation induced by hypercapnia (Pco(2), 75 mmHg) and hypotension (mean arterial blood pressure, decreased by 45%) was blunted after H/I, reversed to vasconstriction in piglets treated with uPA (10(-7) M), a concentration observed in cerebrospinal fluid after H/I, but reverted to a dilation no different than preinsult in piglets administered an anti-alpha(V)beta(3) antibody (10 ng/ml) in addition to uPA (26 +/- 1, 9 +/- 1, -10 +/- 3, and 22 +/- 3% for hypercapnia before H/I, after H/I, after H/I with uPA, and after H/I with combined uPA and anti-alpha(V)beta(3) antibody, respectively). Responses to isoproterenol were unchanged after H/I and combined uPA and anti-alpha(V)beta(3) antibody. Similar results were obtained for the combined administration of uPA with the alpha(V)beta(3) antagonist Arg-Gly-Asp-d-Phe-Val and Arg-Gly-Asp-Ser, but not for the inactive analog Arg-Gly-Asp-Glu-Ser acetate. These data show that the activation of the integrin alpha(V)beta(3) contributes to the uPA-mediated impairment of pial artery dilation after H/I. These data suggest that the inhibition of uPA and integrin signaling may preserve cerebrohemodynamic control after H/I.

Radiolabeled high affinity peptidomimetic antagonist selectively targets alpha(v)beta(3) receptor-positive tumor in mice

OBJECTIVES

The aim of this research was to synthesize radiolabeled peptidomimetic integrin alpha(v)beta(3) antagonists that selectively target integrin alpha(v)beta(3) receptor and clear rapidly from the whole body.

METHODS

Integrin alpha(v)beta(3) antagonists, 4-[2-(3,4,5,6-tetrahydropyrimidine-2-ylamino)ethyloxy]benzoyl-2-(S)-aminoethylsulfonyl-amino-beta-alanine (IA) and 4-[2-(3,4,5,6-tetrahydro-pyrimidin-2-ylamino)-ethyloxy]benzoyl-2-(S)-[N-(3-amino-neopenta-1-carbamyl)]-aminoethylsulfonylamino-beta-alanine hydrochloride (IAC), a hydrophobic carbamate derivative of IA, were conjugated with 2-p-isothiocyanatobenzyl-DOTA at the amino terminus and labeled with (111)In. The (111)In labeled IA and IAC were subjected to in vitro receptor binding, biodistribution and imaging studies using nude mice bearing the receptor-positive M21 human melanoma xenografts.

RESULTS

The (111)In-labeled IA (40%) and -IAC (72%) specifically bound in vitro to alpha(v)beta(3) (0.8 microM) at a molar excess. This receptor binding was completely blocked by a molar excess of cold IA to alpha(v)beta(3). The higher receptor-binding affinity of the (111)In-labeled IAC was reflected in higher tumor uptake and retention: 5.6+/-1.4 and 4.5+/-0.7 %ID/g vs. 3.8+/-0.9 and 2.0+/-0.3 %ID/g for the (111)In-labeled IA at 0.33 and 2 h. The tumor uptakes were inhibited by the co-injection of 200 microg of IA, indicating that the uptake was receptor mediated. These antagonists were excreted primarily via the renal system. The (111)In activity retained in the whole body was quite comparable between the (111)In-labeled IA (24% ID) and the (111)In-labeled IAC (33% ID) at 2 h. The higher peak tumor uptake and longer retention resulted in higher tumor-to-background ratios for the (111)In-labeled IAC at 2 h with 9.7, 2.3, 0.8, 1.9, 7.1, 2.2, 0.9, 3.7 and 9.9 for blood, liver, kidney, lung, heart, stomach, intestine, bone and muscle, respectively. The imaging studies with the (111)In-labeled IAC also clearly visualized the receptor-positive tumor at 4 h.

CONCLUSIONS

The (111)In-labeled IAC showed an improve tumor targeting kinetics with rapid accumulation and prolonged retention in the alpha(v)beta(3) receptor-positive tumor. This together with the rapid whole-body clearance pharmacokinetics warrants further studies on this IAC analog for molecular imaging of tumor-induced angiogenic vessels and various malignant human tumors expressing the receptor.

Bifunctional ligands that target cells displaying the alpha v beta3 integrin

Strategies to eliminate tumor cells have long been sought. We envisioned that a small molecule could be used to decorate the offending cells with immunogenic carbohydrates and evoke an immune response. To this end, we describe the synthesis of bifunctional ligands possessing two functional motifs: one binds a cell-surface protein and the other binds a naturally occurring human antibody. Our conjugates combine an RGD-based peptidomimetic, to target cells displaying the alpha v beta3 integrin, with the carbohydrate antigen galactosyl-alpha(1-3)galactose [Galalpha(1-3)Gal or alpha-Gal]. To generate such bifunctional ligands, we designed and synthesized RGD mimetics 1 b and 2 c, which possess a free amino group for modification. These compounds were used to generate bifunctional derivatives 1 c and 2 d, with dimethyl squarate serving as the linchpin; thus, our synthetic approach is modular. To evaluate the binding of our peptidomimetics to the target alpha v beta3-displaying cells, we implemented a cell-adhesion assay. Results from this assay indicate that the designed, small-molecule ligands inhibit alpha v beta3-dependent cell adhesion. Additionally, our most effective bifunctional ligand exhibits a high degree of selectivity (4000-fold) for alpha v beta3 over the related alpha v beta5 integrin, a result that augurs its utility in specific cell targeting. Finally, we demonstrate that the bifunctional ligands can bind to alpha v beta3-positive cells and recruit human anti-Gal antibodies. These results indicate that both the integrin-binding and the anti-Gal-binding moieties can act simultaneously. Bifunctional conjugates of this type can facilitate the development of new methods for targeting cancer cells by exploiting endogenous antibodies. We anticipate that our modifiable alpha v beta3-binding ligands will be valuable in a variety of applications, including drug delivery and tumor targeting.

Inhibition of integrin alphavbeta3 reduces blood-brain barrier breakdown in focal ischemia in rats

Ischemic stroke is a major cause of morbidity and mortality in industrialized nations. We tested the effect of postischemic treatment of cyclo-RGDfV (cRGDfV), a selective inhibitor of integrin alphavbeta3, in the middle cerebral artery occlusion (MCAO) model of ischemic stroke in rats. Rats were randomly divided into three groups: sham operation (n = 13), MCAO with no treatment (n = 18), and MCAO with cRGDfV treatment (n = 28). Focal ischemia was induced with the suture occlusion method for 2 hr, and treatment was given 1 hr after reperfusion (3 hr after ischemia). All animals were sacrificed 24 hr after reperfusion. Assessment included neurological scores, infarction volumes, brain water content, Evans blue exudation, IgG exudation, histology, immunohistochemistry, and Western blotting. Treatment with cRGDfV ameliorated neurological deficits, reduced brain edema, and reduced exudation of Evans blue dye and IgG, but failed to reduce infarction volumes. Western blotting showed a reduction in phosphorylation of one subset of vascular endothelial growth factor (VEGF) receptors in the cRGDfV treatment group. Western blotting also demonstrated a significant reduction of fibrinogen in the cRGDfV treatment group. We conclude that poststroke treatment with cRGDfV reduces blood-brain barrier breakdown in focal ischemia, possibly through inhibition of VEGF-mediated vascular breakdown.

Synthesis of DOTA-conjugated multivalent cyclic-RGD peptide dendrimers via 1,3-dipolar cycloaddition and their biological evaluation: implications for tumor targeting and tumor imaging purposes

This report describes the design and synthesis of a series of alpha(V)beta(3) integrin-directed monomeric, dimeric and tetrameric cyclo[Arg-Gly-Asp-d-Phe-Lys] dendrimers using "click chemistry". It was found that the unprotected N-epsilon-azido derivative of cyclo[Arg-Gly-Asp-d-Phe-Lys] underwent a highly chemoselective conjugation to amino acid-based dendrimers bearing terminal alkynes using a microwave-assisted Cu(I)-catalyzed 1,3-dipolar cycloaddition. The alpha(V)beta(3) binding characteristics of the dendrimers were determined in vitro and their in vivoalpha(V)beta(3) targeting properties were assessed in nude mice with subcutaneously growing human SK-RC-52 tumors. The multivalent RGD-dendrimers were found to have enhanced affinity toward the alpha(V)beta(3) integrin receptor as compared to the monomeric derivative as determined in an in vitro binding assay. In case of the DOTA-conjugated (111)In-labeled RGD-dendrimers, it was found that the radiolabeled multimeric dendrimers showed specifically enhanced uptake in alpha(V)beta(3) integrin expressing tumors in vivo. These studies showed that the tetrameric RGD-dendrimer had better tumor targeting properties than its dimeric and monomeric congeners.

Inhibition of integrin alphavbeta3 ameliorates focal cerebral ischemic damage in the rat middle cerebral artery occlusion model

BACKGROUND AND PURPOSE

Recent studies have shown that selective inhibition of specific subsets of intercellular adhesion molecules protects the brain during ischemia. We studied selective inhibition of integrin alphavbeta3 with cyclo [Arg-Gly-Asp-D-Phe-Val] (cRGDfV) in the rat middle cerebral artery occlusion model (MCAO).

METHODS

Rats were treated before and after MCAO with cRGDfV. Physiological parameters, expression of integrin alphavbeta3, infarction volume, brain water content, Evans Blue exudation, IgG exudation, histology, immunohistochemistry, and western blotting were studied in 4 groups of animals: sham operation (n=13), untreated (n=18), nonfunctioning peptide treatment (n=19), and cRGDfV treatment (n=27).

RESULTS

Treatment with cRGDfV reduced infarction, reduced brain edema, reduced exudation of Evans blue and IgG, and prevented fibrinogen deposition. Western blotting showed reduction of phosphorylated Flk-1 (a vascular endothelial growth factor [VEGF] receptor), reduction of phosphorylated FAK (an intracellular kinase phosphorylated in the presence of VEGF), reduction of VEGF, and reduction of fibrinogen in the cRGDfV treatment group.

CONCLUSIONS

The selective integrin alphavbeta3 inhibitor cRGDfV improves outcomes in the MCAO model by preserving the blood-brain barrier, which mechanistically may occur in a VEGF- and VEGF-receptor-dependent manner.

Design, synthesis, and evaluation of near infrared fluorescent multimeric RGD peptides for targeting tumors

Molecular interactions between RGD peptides and integrins are known to mediate many biological and pathological processes. This has led to an increased interest in the development of RGD compounds with high affinity and improved selectivity for integrin receptors. In this study, we synthesized and evaluated a series of multimeric RGD compounds constructed on a dicarboxylic acid-containing near-infrared (NIR) fluorescent dye (cypate) for tumor targeting. An array of NIR fluorescent RGD compounds was prepared efficiently, including one RGD monomer (cypate-(RGD)(2)-NH(2)), two RGD dimers (cypate-(RGD)(2)-NH(2) and cypate-(RGD-NH(2))(2)), one trimer (cypate-(RGD)(3)-NH(2)), two tetramers (cypate-(RGD)(4)-NH(2) and cypate-[(RGD)(2)-NH(2)](2)), one hexamer (cypate-[(RGD)(3)-NH(2)](2)), and one octamer (cypate-[(RGD)(4)-NH(2)](2)). The binding affinity of the multimeric RGD compounds for alpha(v)beta(3) integrin receptor (ABIR) showed a remarkable increase relative to the monomer cypate-RGD-NH(2). Generally, the divalent linear arrays of the multimeric RGD units bound the ABIR with slightly higher affinity than their monovalent analogues. These results suggest that the receptor binding affinity was not only dependent on the number of RGD moieties but also on the spatial alignments of the pendant peptides. Internalization of the compounds by ABIR-positive tumor cells (A549) was monitored by NIR fluorescence microscopy. The data showed that endocytosis of the octameric RGD derivative was significantly higher by comparison to other compounds in this study. In vivo noninvasive optical imaging and biodistribution data showed that the compounds were retained in A549 tumor tissue. These results clearly demonstrated that an array of simple RGD tripeptides on a NIR fluorescent dye core can be recognized by ABIR. Optimization of the spatial alignment of the RGD moieties through careful molecular design and library construction could induce multivalent ligand-receptor interactions useful for in vivo tumor imaging and tumor-targeted therapy.

Multimodality tumor imaging targeting integrin αvβ3

The cell adhesion molecule integrin αvβ3 is an important player in the process of tumor angiogenesis and metastasis. Antibodies, peptides, peptidomimetics, and small molecule antagonists against integrin αvβ3 have been shown to induce endothelial apoptosis, to inhibit tumor angiogenesis, and to increase endothelial permeability. The ability to quantitatively image integrin αvβ3 expression in vivo in a noninvasive manner may shed new light into the mechanism of angiogenesis and antiangiogenic treatment efficacy based on integrin antagonism. Tumor integrin expression imaging will also aid in lesion detection, patient stratification, new anti-integrin drug development/validation, as well as treatment monitoring and optimization. This review summarizes the recent advances in multimodality imaging of tumor integrin αvβ3 expression using magnetic resonance imaging (MRI), ultrasound, near-infrared (NIR) fluorescence, single photon emission computed tomography (SPECT), and positron emission tomography (PET).