Monitoring Breast Tumor Lung Metastasis by U-SPECT-II/CT with an Integrin α(v)β(3)-Targeted Radiotracer( 99m)Tc-3P-RGD(2)

Synthesis and characterization of 64Cu-labeled Geldanamycin derivative for imaging HSP90 expression in breast cancer

Heat shock protein 90 (HSP90) plays a crucial role in cancer cell growth and metastasis by stabilizing overexpressed signaling proteins. Inhibiting HSP90 has emerged as a promising anti-cancer strategy. In this study, we aimed to develop and characterize a HSP90-targeted molecular imaging probe, [64Cu]Cu-DOTA-BDA-GM, based on a specific HSP90 inhibitor, geldanamycin (GM), for PET imaging of cancers. GM is modified at the C-17 position with 1,4-butane-diamine (BDA) and linked to 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) for 64Cu radiolabeling. We evaluated the probe's specific binding to HSP90-expressing cells using Chinese hamster ovary (CHO) cells and breast cancer cells including MDA-MB-231, MDA-MB-435S, MCF7, and KR-BR-3 cell lines. A competition study with non-radioactive GM-BDA yielded an IC50 value of 1.35 ± 0.14 nM, underscoring the probe's affinity for HSP90. In xenograft models of MDA-MB-231 breast cancer, [64Cu]Cu-DOTA-BDA-GM showcased targeted tumor localization, with significant radioactivity observed up to 18 h post-injection. Blocking studies using unlabeled GM-BDA and treatment with the anticancer drug Vorinostat (SAHA), which can affect the expression and activity of numerous proteins, such as HSPs, confirmed the specificity and sensitivity of the probe in cancer targeting. Additionally, PET/CT imaging in a lung metastasis mouse model revealed increased lung uptake of [64Cu]Cu-DOTA-BDA-GM in metastatic sites, significantly higher than in non-metastatic lungs, illustrating the probe's ability to detect metastatic breast cancer. In conclusion, [64Cu]Cu-DOTA-BDA-GM represents a sensitive and specific approach for identifying HSP90 expression in breast cancer and metastases, offering promising implications for clinical diagnosis and monitoring.

Characterization of a multi-pinhole molecular breast tomosynthesis scanner

In recent years, breast imaging using radiolabelled molecules has attracted significant interest. Our group has proposed a multi-pinhole molecular breast tomosynthesis (MP-MBT) scanner to obtain 3D functional molecular breast images at high resolutions. After conducting extensive optimisation studies using simulations, we here present a first prototype of MP-MBT and evaluate its performance using physical phantoms. The MP-MBT design is based on two opposing gamma cameras that can image a lightly compressed pendant breast. Each gamma camera consists of a 250 × 150 mm² detector equipped with a collimator with multiple pinholes focusing on a line. The NaI(Tl) gamma detector is a customised design with 3.5 mm intrinsic spatial resolution and high spatial linearity near the edges due to a novel light-guide geometry and the use of square PMTs. A volume-of-interest is scanned by translating the collimator and gamma detector together in a sequence that optimises count yield from the scan region. Derenzo phantom images showed that the system can reach 3.5 mm resolution for a clinically realistic ^99mTc activity concentration in an 11-minute scan, while in breast phantoms the smallest spheres visible were 6 mm in diameter for the same scan time. To conclude, the experimental results of the novel MP-MBT scanner showed that the setup had sub-centimetre breast tumour detection capability which might facilitate 3D molecular breast cancer imaging in the future.

Preclinical SPECT and SPECT-CT in Oncology

Molecular imaging enables both spatial and temporal understanding of the complex biologic systems underlying carcinogenesis and malignant spread. Single-photon emission tomography (SPECT) is a versatile nuclear imaging-based technique with ideal properties to study these processes in vivo in small animal models, as well as to identify potential drug candidates and characterize their antitumor action and potential adverse effects. Small animal SPECT and SPECT-CT (single-photon emission tomography combined with computer tomography) systems continue to evolve, as do the numerous SPECT radiopharmaceutical agents, allowing unprecedented sensitivity and quantitative molecular imaging capabilities. Several of these advances, their specific applications in oncology as well as new areas of exploration are highlighted in this chapter.

18F-labeled magnetic nanoparticles for monitoring anti-angiogenic therapeutic effects in breast cancer xenografts

PURPOSE

To develop a novel fluorine-18 (¹⁸F)-labeled arginine-glycine-aspartic acid (RGD)-coupled ultra-small iron oxide nanoparticle (USPIO) (hereafter, referred to as ¹⁸F-RGD@USPIO) and conduct an in-depth investigation to monitor the anti-angiogenic therapeutic effects by using a novel dual-modality PET/MRI probe.

METHODS

The RGD peptide and ¹⁸F were coupled onto USPIO by click chemistry. In vitro experiments including determination of stability, cytotoxicity, cell binding of the obtained ¹⁸F-RGD@USPIO were carried out, and the targeting kinetics and bio-distribution were tested on an MDA-MB-231 tumor model. A total of 20 (n = 10 per group) MDA-MB-231 xenograft-bearing mice were treated with bevacizumab or placebo (intraperitoneal injections of bevacizumab or a volume-equivalent placebo solution at the dose of 5 mg/kg for consecutive 7 days, respectively), and underwent PET/CT and MRI examinations with ¹⁸F-RGD@USPIO before and after treatment. Imaging findings were validated by histological analysis with regard to β₃-integrin expression (CD61 expression), microvascular density (CD31 expression), and proliferation (Ki-67 expression).

RESULTS

Excellent stability, low toxicity, and good specificity to endothelial of ¹⁸F-RGD@USPIO were confirmed. The best time point for MRI scan was 6 h post-injection. No intergroup differences were observed in tumor volume development between baseline and day 7. However, ¹⁸F-RGD@USPIO binding was significantly reduced after bevacizumab treatment compared with placebo, both on MRI (P < 0.001) and PET/CT (P = 0.002). Significantly lower microvascular density, tumor cell proliferation, and integrin β₃ expression were noted in the bevacizumab therapy group than the placebo group, which were consistent with the imaging results.

CONCLUSION

PET/MRI with the dual-modality nanoprobe, ¹⁸F-RGD@USPIO, can be implemented as a noninvasive approach to monitor the therapeutic effects of anti-angiogenesis in breast cancer model in vivo.

Targeted imaging and inhibition of triple-negative breast cancer metastases by a PDGFRβ aptamer

While the overall mortality for breast cancer has recently declined, management of triple-negative breast cancer (TNBC) is still challenging because of its aggressive clinical behavior and the lack of targeted therapies. Genomic profiling studies highlighted the high level of heterogeneity of this cancer, which comprises different subtypes with unique phenotypes and response to treatment. Platelet-derived growth factor receptor β (PDGFRβ) is an established mesenchymal/stem cell-specific marker in human glioblastoma and, as recently suggested, it may uniquely mark breast cancer cells with stem-like characteristics and/or that have undergone epithelial-mesenchymal transition.

Methods: Immunohistochemical analysis for PDGFRβ expression was performed on a human TNBC tissue microarray. Functional assays were conducted on mesenchymal-like TNBC cells to investigate the effect of a previously validated PDGFRβ aptamer on invasive cell growth in three-dimensional culture conditions, migration, invasion and tube formation. The aptamer was labeled with a near-infrared (NIR) dye and its binding specificity to PDGFRβ was assessed both in vitro (confocal microscopy and flow cytometry analyses) and in vivo (fluorescence molecular tomography in mice bearing TNBC xenografts). A mouse model of TNBC lung metastases formation was established and NIR-labeled PDGFRβ aptamer was used to detect lung metastases in mice untreated or intravenously injected with unlabeled aptamer.

Results: Here, we present novel data showing that tumor cell expression of PDGFRβ identifies a subgroup of mesenchymal tumors with invasive and stem-like phenotype, and propose a previously unappreciated role for PDGFRβ in driving TNBC cell invasiveness and metastases formation. We show that the PDGFRβ aptamer blocked invasive growth and migration/invasion of mesenchymal TNBC cell lines and prevented TNBC lung metastases formation. Further, upon NIR-labeling, the aptamer specifically bound to TNBC xenografts and detected lung metastases.

Conclusions: We propose PDGFRβ as a reliable biomarker of a subgroup of mesenchymal TNBCs with invasive and stem-like phenotype as well as the use of the PDGFRβ aptamer as a high efficacious tool for imaging and suppression of TNBC lung metastases. This study will allow for the significant expansion of the current repertoire of strategies for managing patients with more aggressive TNBC.

Negative feedback between TAp63 and Mir-133b mediates colorectal cancer suppression

Background

TAp63 is known as the most potent transcription activator and tumor suppressor. microRNAs (miRNAs) are increasingly recognized as essential components of the p63 pathway, mediating downstream post-transcriptional gene repression. The aim of present study was to investigate a negative feedback loop between TAp63 and miR-133b.

Results

Overexpression of TAp63 inhibited HCT-116 cell proliferation, apoptosis and invasion via miR-133b. Accordingly, miR-133b inhibited TAp63 expression through RhoA and its downstream pathways. Moreover, we demonstrated that TAp63/miR-133b could inhibit colorectal cancer proliferation and metastasis in vivo and vitro.

Materials and Methods

We evaluated the correlation between TAp63 and miR-133b in HCT-116 cells and investigated the roles of the TAp63/miR-133b feedback loop in cell proliferation, apoptosis and metastasis via MTT, flow cytometry, Transwell, and nude mouse xenograft experiments. The expression of TAp63, miR-133b, RhoA, α-tubulin and Akt was assessed via qRT-PCR, western blot and immunofluorescence analyses. miR-133b target genes were identified through luciferase reporter assays.

Conclusions

miR-133b plays an important role in the anti-tumor effects of TAp63 in colorectal cancer. miR-133b may represent a tiemolecule between TAp63 and RhoA, forming a TAp63/miR-133b/RhoA negative feedback loop, which could significantly inhibit proliferation, apoptosis and metastasis.

Evaluation of 99mTc-3PRGD2 integrin receptor imaging in hepatocellular carcinoma tumour-bearing mice: comparison with 18F-FDG metabolic imaging

Objective

Our study was designed to explore the utility of ^99mTc-HYNIC-PEG₄-E[PEG₄-c(RGDfK)]₂ (^99mTc-3PRGD₂) for the detection of hepatocellular carcinoma (HCC) and specifically to compare the diagnostic performance of ^99mTc-3PRGD₂ integrin receptor imaging and 2-18-fluoro-2-deoxy-d-glucose (¹⁸F-FDG) metabolic imaging in a nude mouse model.

Methods

^99mTc-3PRGD₂ was synthesized using a HYNIC-3PRGD₂ lyophilized kit with ^99mTcO₄ labelling. The nude mouse animal model was established by subcutaneously injecting 5 × 10⁷/ml HepG2 cells into the shoulder flank of each mouse. Biodistribution studies were performed at 0.5, 1, 2 and 4 h after intravenous administration of 0.37 MBq of ^99mTc-3PRGD₂. Immunohistochemistry was performed to evaluate the expression level of integrin αvβ3 in the HCC tissues. Dynamic imaging was performed using list-mode after the administration of 55.5 MBq of ^99mTc-3PRGD₂, to reconstruct the multiphase images and acquire the best initial scan time. At 8, 12, 16, 20 and 24 days after inoculation with HepG2 cells, 55.5 MBq of ^99mTc-3PRGD₂ and 37 MBq of ¹⁸F-FDG were injected successively into the nude mouse model, subsequently, simultaneous SPECT/PET imaging was performed to calculate the tumour volume and tumour uptake of ^99mTc-3PRGD₂ and ¹⁸F-FDG.

Results

The biodistribution study first validated that the tumour uptake of ^99mTc-3PRGD₂ at the different time points was higher than that of all the other organs tested in the experiment, except for the kidney. Integrin αvβ3 expressed highly in early stage HCC and declined for further necrosis of the tumour tissue. Subcutaneous tumours were visualized clearly with excellent contrast under ^99mTc-3PRGD₂ SPECT/CT imaging, and the multiphase imaging comparison showed the tumours were prominent at 0.5 h, suggesting that the best initial scan time is 0.5 h post-injection. The comparison of the imaging results of the two methods showed that ^99mTc-3PRGD₂ integrin receptor imaging was more sensitive than ¹⁸F-FDG metabolic imaging for the detection of early stage HCC, meanwhile the tumour uptake of ^99mTc-3PRGD₂ was consistently higher than that of ¹⁸F-FDG. However, as tumour necrosis further increased in HCC tissues, the uptake of ¹⁸F-FDG was higher than that of ^99mTc-3PRGD₂.

Conclusion

Our study demonstrated that ^99mTc-3PRGD₂ is a valuable tumour molecular probe for the detection of early stage HCC compared with ¹⁸F-FDG, meriting further investigation of ^99mTc-3PRGD₂ as a novel SPECT tracer for tumour imaging.

Comparison of the accuracy of 99mTc-3P4-RGD2 SPECT and CT in diagnosing solitary pulmonary nodules

The aim of the present study was to compare technetium-99m-(polyethylene glycol-4)₃-(Arg-Gly-Asp)₂ (99mTc-3P₄-RGD₂) single-photon emission computed tomography (SPECT) and computed tomography (CT) in the noninvasive differentiation of solitary pulmonary nodules (SPNs). The present study prospectively investigated a consecutive series of 24 patients with SPN, who were newly diagnosed using radiography between September 2012 and January 2014. All patients underwent 99mTc-3P₄-RGD₂ SPECT and CT scans using a dual-head variable-angle γ-camera equipped with high-resolution collimators. A blinded panel of two thoracic radiologists for CT and three nuclear physicians for SPECT analyzed the images using a 5-grade scale. The SPECT images were also semi-quantitatively evaluated using tumor to non-tumor localization ratios (T/NT). The results were verified by pathological examination of the biopsy material obtained from each patient with SPN, and receiver operating characteristic (ROC) curves were generated from these results. The present results revealed that there were 17 malignant and 7 benign SPNs among the 24 patients with SPN. The mean size of the SPN was 2.1±0.6 cm. Sensitivity of visual analysis for SPECT and CT were 100.0 and 82.4%, respectively, and specificity was 71.4% for the two methods. When the T/NT SPECT semiquantitative analysis (ratio, 1.64) was used as a cut-off, the sensitivity and specificity of SPECT were 100.0 and 71.4%, respectively. The areas under the ROC curves were 0.840 for visual analysis of SPECT [95% confidence interval (CI), 0.600–1.000], 0.849 for semiquantitative analysis of SPECT (95% CI, 0.618–1.000) and 0.815 for CT (95% CI, 0.626–1.000). In conclusion, the present results suggest that 99mTc-3P₄-RGD₂ SPECT is more accurate than CT in the detection of malignant SPN, and visual analysis appears to be sufficient for the characterization of SPN.

Gelatin Methacrylate Hydrogels as Biomimetic Three-Dimensional Matrixes for Modeling Breast Cancer Invasion and Chemoresponse in Vitro

Recent studies have shown that three-dimensional (3D) culture environments allow the study of cellular responses in a setting that more closely resembles the in vivo milieu. In this context, hydrogels have become popular scaffold options for the 3D cell culture. Because the mechanical and biochemical properties of culture matrixes influence crucial cell behavior, selecting a suitable matrix for replicating in vivo cellular phenotype in vitro is essential for understanding disease progression. Gelatin methacrylate (GelMA) hydrogels have been the focus of much attention because of their inherent bioactivity, favorable hydration and diffusion properties, and ease-of-tailoring of their physicochemical characteristics. Therefore, in this study we examined the efficacy of GelMA hydrogels as a suitable platform to model specific attributes of breast cancer. We observed increased invasiveness in vitro and increased tumorigenic ability in vivo in breast cancer cells cultured on GelMA hydrogels. Further, cells cultured on GelMA matrixes were more resistant to paclitaxel treatment, as shown by the results of cell-cycle analysis and gene expression. This study, therefore, validates GelMA hydrogels as inexpensive, cell-responsive 3D platforms for modeling key characteristics associated with breast cancer metastasis, in vitro.

(99m)Tc-3PRGD2 SPECT/CT Imaging for Monitoring Early Response of EGFR-TKIs Therapy in Patients with Advanced-Stage Lung Adenocarcinoma

OBJECTIVE

This study was aimed to assess the efficacy of (99m)Tc-3PRGD2 imaging for evaluating both early treatment response to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) and prognosis in advanced-stage lung adenocarcinoma.

MATERIAL AND METHODS

Eighteen patients with lung adenocarcinoma were enrolled for EGFR-TKIs therapy. (99m)Tc-3PRGD2 SPECT/CT and planar imaging were performed pre- and post-therapy. The tumor to nontumor (T/NT) ratio and percentage change in T/NT ratio were assessed for the treatment response. Receiver operator characteristic (ROC) analysis was utilized to analyze the power of identifying responders based on the changes in T/NT ratios.

RESULTS

After treatment, 10 patients had partial response (PR), and 6 patients stable disease (SD), while 2 patients progressive disease (PD). The mean changes in T/NT ratios on SPECT/CT and planar images in PR group were 35.8% and 15.0% and in SD group were 8.9% and 0.7%, while in PD group were 76.1% and 18.7%, respectively. For ROC analysis, using a cutoff value of 23.8% decrease in T/NT ratio on SPECT/CT images, the sensitivity and specificity in identifying responders were 80.0% and 87.5%, respectively. The median progression-free survival (PFS) for patients with responders and nonresponders (on (99m)Tc-3PRGD2 SPECT/CT) was 18 months (95% CI 5.8-30.2 months) and 7 months (95% CI 5.2-8.8 months), respectively (p = 0.006).

CONCLUSION

(99m)Tc-3PRGD2 imaging can evaluate the early response to EGFR-targeted therapy and predict the PFS of lung adenocarcinoma patients.

Comparison of biological properties of 99mTc-labeled cyclic RGD Peptide trimer and dimer useful as SPECT radiotracers for tumor imaging

INTRODUCTION

This study sought to evaluate a ^99mTc-labeled trimeric cyclic RGD peptide (^99mTc-4P-RGD₃) as the new radiotracer for tumor imaging. The objective was to compare its biological properties with those of ^99mTc-3P-RGD₂ in the same animal model.

METHODS

HYNIC-4P-RGD₃ was prepared by reacting 4P-RGD₃ with excess HYNIC-OSu in the presence of diisopropylethylamine. ^99mTc-4P-RGD₃ was prepared using a kit formulation, and evaluated for its tumor-targeting capability and biodistribution properties in the BALB/c nude mice with U87MG human glioma xenografts. Planar and SPECT imaging studies were performed in athymic nude mice with U87MG glioma xenografts. For comparison purpose, ^99mTc-3P-RGD₂ (a α_vβ₃-targeted radiotracer currently under clinical evaluation for tumor imaging in cancer patients) was also evaluated in the same animal models. Blocking experiments were used to demonstrate the α_vβ₃ specificity of ^99mTc-4P-RGD₃.

RESULTS

^99mTc-4P-RGD₃ was prepared with >95% RCP and high specific activity (~200GBq/μmol). ^99mTc-4P-RGD₃ and ^99mTc-3P-RGD₂ shared almost identical tumor uptake and similar biodistribution properties. ^99mTc-4P-RGD₃ had higher uptake than ^99mTc-3P-RGD₂ in the intestines and kidneys; but it showed better metabolic stability. The U87MG tumors were clearly visualized by SPECT with excellent contrast with ^99mTc-4P-RGD₃ and ^99mTc-3P-RGD₂.

CONCLUSION

Increasing peptide multiplicity from 3P-RGD₂ to 4P-RGD₃ offers no advantages with respect to the tumor-targeting capability. ^99mTc-4P-RGD₃ is as good a SPECT radiotracer as ^99mTc-3P-RGD₂ for imaging α_vβ₃-positive tumors.

A pH-Responsive Host-guest Nanosystem Loading Succinobucol Suppresses Lung Metastasis of Breast Cancer

Cancer metastasis is the leading reason for the high mortality of breast cancer. Herein, we report on a pH-responsive host-guest nanosystem of succinobucol (PHN) with pH-stimuli controlled drug release behavior to improve the therapeutic efficacy on lung metastasis of breast cancer. PHN was composed of the host polymer of β-cyclodextrin linked with multiple arms of N,N-diisopropylethylenediamine (βCD-DPA), the guest polymer of adamantyl end-capped methoxy poly(ethylene glycol) (mPEG-Ad), and the active agent of succinobucol. PHN comprises nanometer-sized homogenous spherical particles, and exhibits specific and rapid drug release in response to the intracellular acidic pH-stimuli. Then, the anti-metastatic efficacy of PHN is measured in metastatic 4T1 breast cancer cells, which effectively confirms the superior inhibitory effects on cell migration and invasion activities, VCAM-1 expression and cell-cell binding of RAW 264.7 to 4T1 cells. Moreover, PHN can be specifically delivered to the sites of metastatic nodules in lungs, and result in an obviously improved therapeutic efficacy on lung metastasis of breast cancer. Thereby, the pH-responsive host-guest nanosystem can be a promising drug delivery platform for effective treatment of cancer metastasis.

Biometabolic Distribution of 99mTc-3PRGD2 and Its Potential Value in Monitoring Chemotherapeutic Effects

Previous studies have reported that 99mTc-3PRGD2 is an excellent tumor imaging agent that showed a good correlation with integrin αvβ3, a main factor of tumor-induced angiogenesis. In this study, we investigated the biometabolic distribution characteristics of 99mTc-3PRGD2 with a continuous dynamic acquisition mode to explore the potential value of 99mTc-3PRGD2 in monitoring chemotherapeutic effects in VX2 tumor models. Eighteen rabbits with 27 implanted VX2 squamous cell tumors were randomly divided into a nontreated control group (NTG, n = 8; 12 tumors) and a treatment group (TG, n = 10; 15 tumors). 99mTc-3PRGD2 imaging was performed prior to cisplatin injection and repeated on days 0, 1, 7, and 14 postinjection. Continuous dynamic scanning up to 30 minutes; static imaging at 0.5 hours, 1 hour, and 3 hours; and single-photon emission computed tomography/computed tomography (SPECT/CT)-integrated imaging at 3 hours post-99mTc-3PRGD2 injection were performed. The peak time (time to reach peak in dynamic curve), tumor to normal (T/N) ratios, and their change rates relative to pretherapy were calculated. Autoradiography, hematoxylin-eosin (H&E) staining, and CD31 and integrin αv immunohistochemical staining were examined. VX2 tumors were clearly visualized at 3 hours post-99mTc-3PRGD2 injection. Tumors in the TG shrank significantly on day 7 after cisplatin administration (p < .05). The half-life (t1/2) of the radiotracer in heart, liver, and tumor in the NTG were 3.43 ± 0.94 minutes, 13.41 ± 9.17 minutes, and 70.83 ± 33.37 minutes, respectively. The peak time was delayed in the TG immediately and continuously after cisplatin administration compared to the peak time in the NTG. The T/N values and their change rates decreased significantly in the TG compared to the NTG after therapy (p < .05). The immunostained areas were significantly decreased in the TG (p < .05) compared to the NTG. 99mTc-3PRGD2 was an excellent imaging agent for demonstrating tumor angiogenesis. The peak time, T/N values, and their change rates were sensitive parameters to monitor early chemotherapeutic effects. Due to the specific target mechanism and the cost-effective value of 99mTc-3PRGD2, 99mTc-3PRGD2 SPECT imaging may have potential in detecting the therapeutic effects of anticancer therapy.

Quarter-millimeter-resolution molecular mouse imaging with U-SPECT⁺

Limited spatial resolution of preclinical positron emission tomography (PET) and single-photon emission computed tomography (SPECT) has slowed down applications of molecular imaging in small animals. Here we present the latest-generation U-SPECT system (U-SPECT⁺, MILabs, Utrecht, the Netherlands) enabling radionuclide imaging of mice with quarter-millimeter resolution. The system was equipped with the newest high-resolution collimator with 0.25 mm diameter circular pinholes. It was calibrated with technetium-99 m point source measurements from which the system matrix was calculated. Images were reconstructed using pixel-based ordered subset expectation maximization (OSEM). Various phantoms and mouse SPECT scans were acquired. The reconstructed spatial resolution (the smallest visible capillary diameter in a hot-rod resolution phantom) was 0.25 mm. Knee joint images show tiny structures such as the femur epicondyle sulcus, as well as a clear separation between cortical and trabecular bone structures. In addition, time-activity curves of the lumbar spine illustrated that tracer dynamics in tiny tissue amounts could be measured. U-SPECT⁺ allows discrimination between molecular concentrations in adjacent volumes of as small as 0.015 μL, which is significantly better than can be imaged by any existing SPECT or PET system. This increase in the level of detail makes it more and more attractive to replace ex vivo methods and allows monitoring biological processes in tiny parts of organs in vivo.

Preclinical imaging and translational animal models of cancer for accelerated clinical implementation of nanotechnologies and macromolecular agents

The majority of animal models of cancer have performed poorly in terms of predicting clinical performance of new therapeutics, which are most often first evaluated in patients with advanced, metastatic disease. The development and use of metastatic models of cancer may enhance clinical translatability of preclinical studies focused on the development of nanotechnology-based drug delivery systems and macromolecular therapeutics, potentially accelerating their clinical implementation. It is recognized that the development and use of such models are not without challenge. Preclinical imaging tools offer a solution by allowing temporal and spatial characterization of metastatic lesions. This paper provides a review of imaging methods applicable for evaluation of novel therapeutics in clinically relevant models of advanced cancer. An overview of currently utilized models of oncology in small animals is followed by image-based development and characterization of visceral metastatic cancer models. Examples of imaging tools employed for metastatic lesion detection, evaluation of anti-tumor and anti-metastatic potential and biodistribution of novel therapies, as well as the co-development and/or use of imageable surrogates of response, are also discussed. While the focus is on development of macromolecular and nanotechnology-based therapeutics, examples with small molecules are included in some cases to illustrate concepts and approaches that can be applied in the assessment of nanotechnologies or macromolecules.

Radiolabeled Cyclic RGD Peptide Bioconjugates as Radiotracers Targeting Multiple Integrins

Angiogenesis is a requirement for tumor growth and metastasis. The angiogenic process depends on vascular endothelial cell migration and invasion, and is regulated by various cell adhesion receptors. Integrins are such a family of receptors that facilitate the cellular adhesion to and migration on extracellular matrix proteins in the intercellular spaces and basement membranes. Among 24 members of the integrin family, αvβ3 is studied most extensively for its role in tumor angiogenesis and metastasis. The αvβ3 is expressed at relatively low levels on epithelial cells and mature endothelial cells, but it is highly expressed on the activated endothelial cells of tumor neovasculature and some tumor cells. This restricted expression makes αvβ3 an excellent target to develop antiangiogenic drugs and diagnostic molecular imaging probes. Since αvβ3 is a receptor for extracellular matrix proteins with one or more RGD tripeptide sequence, many radiolabeled cyclic RGD peptides have been evaluated as "αvβ3-targeted" radiotracers for tumor imaging over the past decade. This article will use the dimeric and tetrameric cyclic RGD peptides developed in our laboratories as examples to illustrate basic principles for development of αvβ3-targeted radiotracers. It will focus on different approaches to maximize the radiotracer tumor uptake and tumor/background ratios. This article will also discuss some important assays for preclinical evaluations of integrin-targeted radiotracers. In general, multimerization of cyclic RGD peptides increases their integrin binding affinity and the tumor uptake and retention times of their radiotracers. Regardless of their multiplicity, the capability of cyclic RGD peptides to bind other integrins (namely, αvβ5, α5β1, α6β4, α4β1, and αvβ6) is expected to enhance the radiotracer tumor uptake due to the increased integrin population. The results from preclinical and clinical studies clearly show that radiolabeled cyclic RGD peptides (such as (99m)Tc-3P-RGD2, (18)F-Alfatide-I, and (18)F-Alfatide-II) are useful as the molecular imaging probes for early cancer detection and noninvasive monitoring of the tumor response to antiangiogenic therapy.

Influence of mesenchymal stem cells on metastasis development in mice in vivo

INTRODUCTION

In recent years, mesenchymal stem cells (MSCs) have been demonstrated to play an important role in carcinogenesis. However, the effect of MSCs on tumor and metastasis development and the mechanisms underlying the interaction of cancer and stem cells are not completely understood. This study investigated the effect of MSCs on breast cancer metastasis formation by using the methods of in vivo fluorescence and luminescence imaging.

METHODS

MSCs were isolated from bone marrow of normal donors, characterized, and genetically labeled with luciferase (luc2). The effects of MSCs on MDA-MB-231 cancer cell proliferation were evaluated in conditioned medium from MSCs. To generate lung metastases, MDA-MB-231 cells stably expressing red fluorescent protein Turbo FP650 were injected intravenously into nude mice. On day 10 after the cancer cell injection, mice were injected via the tail vein with MSCs-luc2 cells (the MET+MSCs group). Animals that received the injection of MDA-MB-231-Turbo FP650 alone (the MET group) and no injections (the intact control group) served as controls. Fluorescence and bioluminescence imaging was performed for monitoring of the metastasis formation and MSC distribution in the recipient's body.

RESULTS

We found that the proliferative activity of the cancer cells in the presence of MSC conditioned medium was lower than that of the cells grown in conventional culture medium. The metastasis formation in the MET+MSCs group was delayed in time as compared with the MET group. Macroscopic and histological examination of isolated lungs 8 weeks after cancer cell injection showed that the total number of metastases in animals of the MET+MSCs group was significantly lower. Using bioluminescence imaging in vivo, we found that MSCs-luc2 cells survived in the host animal for at least 7 weeks and re-migrated to the lung 6 to 7 weeks after injection. Immunohistochemical analysis revealed the presence of MSCs-luc2 in metastases and lung tissue.

CONCLUSIONS

Long-term in vivo bioluminescence imaging of intravenously injected MSCs-luc2 cells showed distribution of MSCs to the lungs and abdominal organs within the first 2 to 3 weeks and re-migration to the lungs in weeks 6 to 7. It was found that MSCs reduced the proliferative activity of cancer cells in vitro and lung metastasis formation in mice.

Assessing activation of hepatic stellate cells by (99m)Tc-3PRGD2 scintigraphy targeting integrin αvβ3: a feasibility study

OBJECTIVE

Hepatic stellate cell (HSC) activation, which is accompanied by increased expression of integrin αvβ3, is an important factor in liver fibrogenesis. Molecular imaging targeting the integrin αvβ3 could provide a non-invasive method for evaluating the expression and the function of the integrin αvβ3 on the activated HSCs (aHSCs) in the injured liver, and then provide important prognostic information. (99m)Tc-3PRGD2 is such a radiotracer specific for integrin αvβ3. In this study, we aimed to compare the differences in liver uptake and retention of the (99m)Tc-3PRGD2 between normal liver and injured liver to evaluate the feasibility of (99m)Tc-3PRGD2 scintigraphy for this purpose.

METHODS

We used planar scintigraphy to assess changes in integrin αvβ3 binding of intravenously-administered (99m)Tc-3PRGD2 in the livers of rats with thioacetamide (TAA)-induced liver fibrosis compared with the controls. We co-injected cold c(RGDyK) with (99m)Tc-3PRGD2 to assess the specific binding of the radiotracer. We performed Sirius red staining to assess liver fibrosis, immunofluorescent colocalization to identify the location of integrin αvβ3 expressed in the fibrotic liver, and we measured protein and messenger RNA expression of integrin αvβ3 and alpha smooth muscle actin (α-SMA) in the control and fibrotic livers.

RESULTS

The fibrotic livers showed enhanced (99m)Tc-3PRGD2 uptake and retention. The radiotracer was demonstrated to bind specifically with the integrin αvβ3 mainly expressed on the aHSCs. The liver-to-heart ratio at 30 min post-injection was higher in the fibrotic livers than in the control livers (TAA, 1.98±0.08 vs. control, 1.50±0.12, p<0.01). The liver t1/2 was longer than in the controls (TAA, 27.07±10.69 min vs. control, 12.67±4.10 min, p<0.01). The difference of heart t1/2 between the two groups was not statistically significant (TAA, 3.13±0.63 min vs. control, 3.41±0.77 min, p=0.94).

CONCLUSIONS

(99m)Tc-3PRGD2 molecular imaging can provide a non-invasive method for assessing activation of HSCs.

Evaluation of ανβ3-mediated tumor expression with a 99mTc-labeled ornithine-modified RGD derivative during glioblastoma growth in vivo

In this study, a novel way of distinguishing the intrinsic relationship between ανβ3 integrin targeting and detection of tumor growth by using a radiolabeled tracer based on a cyclic Arg-Gly-Asp (RGD) peptide was provided. The potential of the in vivo scintigraphic imaging of the developing vasculature from the early stage of tumor growth was evaluated. Alongside with the scintigraphic images, biodistribution studies were performed at distinct time points to validate this noninvasive imaging approach. The ability to noninvasively assess the tumor growth of ανβ3 integrin-positive glioblastoma tumors provides a method to better understand tumor angiogenesis in vivo and allows for a direct assessment of anti-integrin treatment efficacy.

Comparison of three dimeric 18F-AlF-NOTA-RGD tracers

PURPOSE

RGD peptide-based radiotracers are well established as integrin αvβ3 imaging probes to evaluate tumor angiogenesis or tissue remodeling after ischemia or infarction. In order to optimize the labeling process and pharmacokinetics of the imaging probes, we synthesized three dimeric RGD peptides with or without PEGylation and performed in vivo screening.

PROCEDURES

Radiolabeling was achieved through the reaction of F-18 aluminum-fluoride complex with the cyclic chelator, 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA). Three imaging probes were synthesized as (18)F-AlF-NOTA-E[c(RGDfK)]2, (18)F-AlF-NOTA-PEG4-E[c(RGDfK)]2, and (18)F-AlF-NOTA-E[PEG4-c(RGDfk)]2. The receptor binding affinity was determined by competitive cell binding assay, and the stability was evaluated by mouse serum incubation. Tumor uptake and whole body distribution of the three tracers were compared through direct tissue sampling and PET quantification of U87MG tumor-bearing mice.

RESULTS

All three compounds remained intact after 120 min incubation with mouse serum. They all had a rapid and relatively high tracer uptake in U87MG tumors with good target-to-background ratios. Compared with the other two tracers, (18)F-AlF-NOTA-E[PEG4-c(RGDfk)]2 had the highest tumor uptake and the lowest accumulation in the liver. The integrin receptor specificity was confirmed by co-injection of unlabeled dimeric RGD peptide.

CONCLUSION

The rapid one-step radiolabeling strategy by the complexation of (18)F-aluminum fluoride with NOTA-peptide conjugates was successfully applied to synthesize three dimeric RGD peptides. Among the three probes developed, (18)F-AlF-NOTA-E[PEG4-c(RGDfk)]2 with relatively low liver uptake and high tumor accumulation appears to be a promising candidate for further translational research.

U-SPECT-BioFluo: an integrated radionuclide, bioluminescence, and fluorescence imaging platform

Background

In vivo bioluminescence, fluorescence, and single-photon emission computed tomography (SPECT) imaging provide complementary information about biological processes. However, to date these signatures are evaluated separately on individual preclinical systems. In this paper, we introduce a fully integrated bioluminescence-fluorescence-SPECT platform. Next to an optimization in logistics and image fusion, this integration can help improve understanding of the optical imaging (OI) results.

Methods

An OI module was developed for a preclinical SPECT system (U-SPECT, MILabs, Utrecht, the Netherlands). The applicability of the module for bioluminescence and fluorescence imaging was evaluated in both a phantom and in an in vivo setting using mice implanted with a 4 T1-luc + tumor. A combination of a fluorescent dye and radioactive moiety was used to directly relate the optical images of the module to the SPECT findings. Bioluminescence imaging (BLI) was compared to the localization of the fluorescence signal in the tumors.

Results

Both the phantom and in vivo mouse studies showed that superficial fluorescence signals could be imaged accurately. The SPECT and bioluminescence images could be used to place the fluorescence findings in perspective, e.g. by showing tracer accumulation in non-target organs such as the liver and kidneys (SPECT) and giving a semi-quantitative read-out for tumor spread (bioluminescence).

Conclusions

We developed a fully integrated multimodal platform that provides complementary registered imaging of bioluminescent, fluorescent, and SPECT signatures in a single scanning session with a single dose of anesthesia. In our view, integration of these modalities helps to improve data interpretation of optical findings in relation to radionuclide images.

Impact of multiple negative charges on blood clearance and biodistribution characteristics of 99mTc-labeled dimeric cyclic RGD peptides

This study sought to evaluate the impact of multiple negative charges on blood clearance kinetics and biodistribution properties of ^99mTc-labeled RGD peptide dimers. Bioconjugates HYNIC-P6G-RGD₂ and HYNIC-P6D-RGD₂ were prepared by reacting P6G-RGD₂ and P6D-RGD₂, respectively, with excess HYNIC-OSu in the presence of diisopropylethylamine. Their IC₅₀ values were determined to be 31 ± 5 and 41 ± 6 nM, respectively, against ¹²⁵I-echistatin bound to U87MG glioma cells in a whole-cell displacement assay. Complexes [^99mTc(HYNIC-P6G-RGD₂)(tricine)(TPPTS)] (^99mTc-P6G-RGD₂) and [^99mTc(HYNIC-P6D-RGD₂)(tricine)(TPPTS)] (^99mTc-P6D-RGD₂) were prepared in high radiochemical purity (RCP > 95%) and specific activity (37–110 GBq/μmol). They were evaluated in athymic nude mice bearing U87MG glioma xenografts for their biodistribution. The most significant difference between ^99mTc-P6D-RGD₂ and ^99mTc-P6G-RGD₂ was their blood radioactivity levels and tumor uptake. The initial blood radioactivity level for ^99mTc-P6D-RGD₂ (4.71 ± 1.00%ID/g) was ∼5× higher than that of ^99mTc-P6G-RGD₂ (0.88 ± 0.05%ID/g), but this difference disappeared at 60 min p.i. ^99mTc-P6D-RGD₂ had much lower tumor uptake (2.20–3.11%ID/g) than ^99mTc-P6G-RGD₂ (7.82–9.27%ID/g) over a 2 h period. Since HYNIC-P6D-RGD₂ and HYNIC-P6G-RGD₂ shared a similar integrin α_vβ₃ binding affinity (41 ± 6 nM versus 31 ± 5 nM), the difference in their blood activity and tumor uptake is most likely related to the nine negative charges and high protein binding of ^99mTc-P6D-RGD₂. Despite its low uptake in U87MG tumors, the tumor uptake of ^99mTc-P6D-RGD₂ was integrin α_vβ₃-specific. SPECT/CT studies were performed using ^99mTc-P6G-RGD₂ in athymic nude mice bearing U87MG glioma and MDA-MB-231 breast cancer xenografts. The SPECT/CT data demonstrated the tumor-targeting capability of ^99mTc-P6G-RGD₂, and its tumor uptake depends on the integrin α_vβ₃ expression levels on tumor cells and neovasculature. It was concluded that the multiple negative charges have a significant impact on the blood clearance kinetics and tumor uptake of ^99mTc-labeled dimeric cyclic RGD peptides.

The role of molecular imaging in diagnosis of deep vein thrombosis

Venous thromboembolism (VTE) mostly presenting as deep venous thrombosis (DVT) and pulmonary embolism (PE) affects up to 600,000 individuals in United States each year. Clinical symptoms of VTE are nonspecific and sometimes misleading. Additionally, side effects of available treatment plans for DVT are significant. Therefore, medical imaging plays a crucial role in proper diagnosis and avoidance from over/under diagnosis, which exposes the patient to risk. In addition to conventional structural imaging modalities, such as ultrasonography and computed tomography, molecular imaging with different tracers have been studied for diagnosis of DVT. In this review we will discuss currently available and newly evolving targets and tracers for detection of DVT using molecular imaging methods.

Different molecular profiles are associated with breast cancer cell homing compared with colonisation of bone: evidence using a novel bone-seeking cell line

Advanced breast cancer is associated with the development of incurable bone metastasis. The two key processes involved, tumour cell homing to and subsequent colonisation of bone, remain to be clearly defined. Genetic studies have indicated that different genes facilitate homing and colonisation of secondary sites. To identify specific changes in gene and protein expression associated with bone-homing or colonisation, we have developed a novel bone-seeking clone of MDA-MB-231 breast cancer cells that exclusively forms tumours in long bones following i.v. injection in nude mice. Bone-homing cells were indistinguishable from parental cells in terms of growth rate in vitro and when grown subcutaneously in vivo. Only bone-homing ability differed between the lines; once established in bone, tumours from both lines displayed similar rates of progression and caused the same extent of lytic bone disease. By comparing the molecular profile of a panel of metastasis-associated genes, we have identified differential expression profiles associated with bone-homing or colonisation. Bone-homing cells had decreased expression of the cell adhesion molecule fibronectin and the migration and calcium signal binding protein S100A4, in addition to increased expression of interleukin 1B. Bone colonisation was associated with increased fibronectin and upregulation of molecules influencing signal transduction pathways and breakdown of extracellular matrix, including hRAS and matrix metalloproteinase 9. Our data support the hypothesis that during early stages of breast cancer bone metastasis, a specific set of genes are altered to facilitate bone-homing, and that disruption of these may be required for effective therapeutic targeting of this process.

Three-dimensional histologic validation of high-resolution SPECT of antibody distributions within xenografts

Longitudinal imaging of intratumoral distributions of antibodies in vivo in mouse cancer models is of great importance for developing cancer therapies. In this study, multipinhole SPECT with sub-half-millimeter resolution was tested for exploring intratumoral distributions of radiolabeled antibodies directed toward the epidermal growth factor receptor (EGFr) and compared with full 3-dimensional target expression assessed by immunohistochemistry.

METHODS

(111)In-labeled zalutumumab, a human monoclonal human EGFr-targeting antibody, was administered at a nonsaturating dose to 3 mice with xenografted A431 tumors exhibiting high EGFr expression. Total-body and focused in vivo tumor SPECT was performed at 0 and 48 h after injection and compared both visually and quantitatively with full 3-dimensional immunohistochemical staining for EGFr target expression.

RESULTS

SPECT at 48 h after injection showed that activity was predominantly concentrated in the tumor (10.5% ± 1.3% of the total-body activity; average concentration, 30.1% ± 4.6% of the injected dose per cubic centimeter). (111)In-labeled EGFr-targeting antibodies were distributed heterogeneously throughout the tumor. Some hot spots were observed near the tumor rim. Immunohistochemistry indicated that the antibody distributions obtained by SPECT were morphologically similar to those obtained for ex vivo EGFr target expression. Regions showing low SPECT activity were necrotic or virtually negative for EGFr target expression. A good correlation (r = 0.86, P < 0.0001) was found between the percentage of regions showing low activity on SPECT and the percentage of necrotic tissue on immunohistochemistry.

CONCLUSION

Multipinhole SPECT enables high-resolution visualization and quantification of the heterogeneity of (111)In-zalutumumab concentrations in vivo.

[Radio-labeling of T7 peptide with 99mTc and its biodistribution in nude mice bearing non-small cell lung cancer]

BACKGROUND

Lung cancer is a malignant tumor with high mortality rates. This study aims to develop potential candidates of integrin αvβ3 imaging agents, which can facilitate the diagnosis and treatment of lung cancer.

METHODS

The T7 peptide was labeled with carbonyl technetium. The thin layer chromatography with acetone as the development system was performed to investigate the purity and stability of (99m)Tc-T7. The binding affinity of (99m)Tc-T7 with NCI-H157 tumor cells was determined. The biodistribution of (99m)Tc-T7 in nude mice bearing non-small cell lung carcinoma was observed after injection of (99m)Tc-T7 at 0.5 h, 1 h, 2 h, 4 h, and 8 h, and the radioactive ratio of tumor (T) and non-tumor tissues (NT) was calculated.

RESULTS

99mTc labeled T7 had high radiochemical purity of more than 90%, which does not require further purification, with good stability in vitro. The association and dissociation constant (KD) of (99m)Tc-T7 with NCI-H157 tumor cells was 196.1 nM. (99m)Tc-T7 was mainly metabolism through the internal organs with rapid blood removal. Moreover, the uptake in tumor tissue was significantly higher than the muscle with tumor/muscle ratio of 5.8. In addition, the (99m)Tc-T7 exhibited a transient accumulation in the lungs.

CONCLUSIONS

The (99m)Tc-T7 could be prepared using a simple method, had high labeling rate and good stability, and could be accumulated at tumor site. Thus, (99m)Tc-T7 is a potential lung cancer SPECT/CT imaging agent.

pH-responsive near-infrared nanoprobe imaging metastases by sensing acidic microenvironment

A pH responsive near-infrared fluorescence nanoprobe was developed and visualized pulmonary metastases in a mouse model with a volume as small as 0.5 mm³ by sensing the acidic tumor microenvironment.

Integrin α(v)β₃-targeted radiotracer (99m)Tc-3P-RGD₂ useful for noninvasive monitoring of breast tumor response to antiangiogenic linifanib therapy but not anti-integrin α(v)β₃ RGD₂ therapy

Purpose: ^99mTc-3P-RGD₂ is a ^99mTc-labeled dimeric cyclic RGD peptide that binds to integrin α_vβ₃ with high affinity and specificity. The purpose of this study was to demonstrate the utility of ^99mTc-3P-RGD₂ SPECT/CT (single photon emission computed tomography/computed tomography) as a molecular imaging tool for noninvasive monitoring breast tumor early response to antiangiogenesis therapy with linifanib, and to illustrate its limitations in monitoring the efficacy of anti-α_vβ₃ treatment.

Methods: To support SPECT/CT imaging, biodistribution and therapy studies, the xenografted breast cancer model was established by subcutaneous injection of 5 × 10⁶ MDA-MB-435 cells into the fat pad of each athymic nude mouse. Linifanib (ABT-869) was used as antiangiogenesis agent. The tumor volume was 180 ± 90 mm³ on the day (-1 day) before baseline SPECT/CT. Each animal was treated twice daily with vehicle or 12.5 mg/kg linifanib. Longitudinal ^99mTc-3P-RGD₂ SPECT/CT imaging was performed on days -1, 1, 4 and 11. Tumors were harvested at each time point for pathological analysis of hematoxylin and eosin (H&E) and immunohistochemistry (IHC). Tumor uptake of ^99mTc-3P-RGD₂ was calculated from SPECT/CT quantification. When cyclic peptide E[c(RGDfK)]₂ (RGD₂) was used as the anti-α_vβ₃ agent, SPECT/CT images were obtained only at 7 and 21 days after last RGD₂ dose.

Results: The tumor uptake of ^99mTc-3P-RGD₂ from SPECT/CT quantification was almost identical to that from biodistribution. There was a dramatic reduction in both %ID and %ID/cm³ tumor uptake of ^99mTc-3P-RGD₂ during the first 24 hours of linifanib therapy. The therapeutic effect of linifanib was on both tumor cells and vasculature, as determined by IHC analysis of integrin α_vβ₃ and CD31. Changes in tumor vasculature were further confirmed by pathological H&E analysis of tumor tissues. While its %ID tumor uptake increased steadily in vehicle-treated group, the %ID tumor uptake of ^99mTc-3P-RGD₂ decreased in linifanib-treated group slowly over the 11-day study period. The degree of tumor response to linifanib therapy correlated well to the integrin α_vβ₃ expression levels before linifanib therapy.

Conclusion: ^99mTc-3P-RGD₂ is an excellent radiotracer for monitoring integrin α_vβ₃ expression during and after linifanib therapy. ^99mTc-3P-RGD₂ SPECT/CT is an useful molecular imaging tool for patient selection before antiangiogenic and anti-α_vβ₃ therapy; but it would be difficult to use ^99mTc-3P-RGD₂ for accurate and noninvasive monitoring of early tumor response to anti-α_vβ₃ therapy.

(99m)Tc-Galacto-RGD2: a novel 99mTc-labeled cyclic RGD peptide dimer useful for tumor imaging

This study sought to evaluate [(99m)Tc(HYNIC-Galacto-RGD2)(tricine)(TPPTS)] ((99m)Tc-Galacto-RGD2: HYNIC = 6-hydrazinonicotinyl; Galacto-RGD2 = Glu[cyclo[Arg-Gly-Asp-D-Phe-Lys(SAA-PEG2-(1,2,3-triazole)-1-yl-4-methylamide)]]2 (SAA = 7-amino-L-glycero-L-galacto-2,6-anhydro-7-deoxyheptanamide, and PEG2 = 3,6-dioxaoctanoic acid); and TPPTS = trisodium triphenylphosphine-3,3',3″-trisulfonate) as a new radiotracer for tumor imaging. Galacto-RGD2 was prepared via the copper(I)-catalyzed 1,3-dipolar azide-alkyne Huisgen cycloaddition. HYNIC-Galacto-RGD2 was prepared by reacting Galacto-RGD2 with sodium succinimidyl 6-(2-(2-sulfonatobenzaldehyde)hydrazono)nicotinate (HYNIC-OSu) in the presence of diisopropylethylamine, and was evaluated for its integrin αvβ3 binding affinity against (125)I-echistatin bound to U87MG glioma cells. The IC50 value for HYNIC-Galacto-RGD2 was determined to be 20 ± 2 nM. (99m)Tc-Galacto-RGD2 was prepared in high specific activity (∼ 185 GBq/μmol) and high radiochemical purity (>95%), and was evaluated in athymic nude mice bearing U87MG glioma xenografts for its tumor-targeting capability and biodistribution. The tumor uptake of (99m)Tc-Galacto-RGD2 was 10.30 ± 1.67, 8.37 ± 2.13, 6.86 ± 1.33, and 5.61 ± 1.52%ID/g at 5, 30, 60, and 120 min p.i., respectively, which was in agreement with high integrin αvβ3 expression on glioma cells and neovasculature. Its lower uptake in intestines, lungs, and spleen suggests that (99m)Tc-Galacto-RGD2 has advantages over (99m)Tc-3P-RGD2 ([(99m)Tc(HYNIC-3P-RGD2)(tricine)(TPPTS)]: 3P-RGD2 = PEG4-E[PEG4-c(RGDfK)]2; PEG4 = 15-amino-4,7,10,13-tetraoxapentadecanoic acid) for imaging tumors in the chest and abdominal regions. U87MG tumors were readily detected by SPECT and the tumor uptake of (99m)Tc-Galacto-RGD2 was integrin αvβ3-specific. (99m)Tc-Galacto-RGD2 also had very high metabolic stability. On the basis of results from this study, it was concluded that (99m)Tc-Galacto-RGD2 is an excellent radiotracer for imaging integrin αvβ3-positive tumors and related metastases.

Targeted delivery of antisense oligonucleotides by chemically self-assembled nanostructures

Synthetic nucleic acids have shown great potential in the treatment of various diseases. Nevertheless, the selective delivery to a target tissue has proved challenging. The coupling of nucleic acids to targeting peptides, proteins, and antibodies has been explored as an approach for their selective tissue delivery. Nevertheless, the preparation of covalently coupled peptides and proteins that can also undergo intracellular release as well as deliver more than one copy of the nucleic acid has proved challenging. Recently, we have developed a novel method for the rapid noncovalent conjugation of nucleic acids to targeting single chain antibodies (scFv) using chemically self-assembled nanostructures (CSANs). CSANs have been prepared by the self-assembly of two dihydrofolate reductase molecules (DHFR(2)) and a targeting scFv in the presence of bis-methotrexate (bis-MTX). The valency of the nanorings can be tuned from one to eight subunits, depending on the length and composition of the linker between the dihydrofolate reductase molecules. To explore their potential for the therapeutic delivery of nucleic acids as well as the ability to expand the capabilities of CSANs by incorporating smaller cyclic targeting peptides, we prepared DHFR(2) proteins fused through a flexible peptide linker to cyclic-RGD, which targets αvβ3 integrins, and a bis-MTX chemical dimerizer linked to an antisense oligonucleotide (bis-MTX-ASO) that has been shown to silence expression of eukaryotic translation initiation factor 4E (eIF4E). Monomeric and multimeric cRGD-CSANs were then prepared with bis-MTX-ASO and shown to undergo endocytosis in the breast cancer cell line, MDA-MB-231, which overexpresses αvβ3. The bis-MTX-ASO was shown to undergo endosomal escape resulting in the knock down of eIF4E with at least the same efficiency as ASO delivered by oligofectamine. The modularity, flexibility, and common method of conjugation may prove to be a useful general approach for the targeted delivery of ASOs, as well as other nucleic acids to cells.

Monitoring tumor response to linifanib therapy with SPECT/CT using the integrin αvβ3-targeted radiotracer 99mTc-3P-RGD2

The objective of this study was to determine the utility of (99m)Tc-3P-Arg-Gly-Asp (RGD2) single photon emission computed tomography (SPECT)/computed tomography (CT) for noninvasive monitoring of integrin αvβ3-expression response to antiangiogenic treatment with linifanib. Linifanib or vehicle therapy was carried out in female athymic nu/nu mice bearing U87MG glioma (high αvβ3 expression) or PC-3 prostate (low αvβ3 expression) tumors at 12.5 mg/kg twice daily. The average tumor volume was 180 ± 90 mm(3) the day prior to baseline SPECT/CT. Longitudinal (99m)Tc-3P-RGD2 SPECT/CT imaging was performed at baseline (-1 day) and days 1, 4, 11, and 18. Tumors were harvested at all imaging time points for histopathological analysis with H&E and immunohistochemistry. A significant difference in tumor volumes between vehicle- and linifanib-treated groups was observed after 4 days of linifanib therapy in the U87MG model. The percent injected dose (%ID) tumor uptake of (99m)Tc-3P-RGD2 peaked in the vehicle-treated group at day 11, while the %ID/cm(3) tumor uptake decreased slowly over the whole study period. During the first 2 days of linifanib treatment, a rapid decrease in both %ID/cm(3) tumor uptake and tumor/muscle ratios of (99m)Tc-3P-RGD2 was observed, followed by a slow decrease until day 18. No decrease in tumor uptake of (99m)Tc-3P-RGD2 or tumor volume was observed for either treatment group in the PC-3 model. Changes in tumor vasculature were confirmed by histopathological H&E analysis and immunohistochemistry. Longitudinal imaging using (99m)Tc-3P-RGD2 SPECT/CT may be a useful tool for monitoring the downstream biologic effects of linifanib therapy.

Evaluation of K(HYNIC)(2) as a bifunctional chelator for (99m)Tc-labeling of small biomolecules

This study sought to evaluate K(HYNIC)(2) (K = lysine and HYNIC = 6-hydrazinonicotinyl) as a bifunctional chelator for (99m)Tc-labeling of biomolecule. In this study, four K(HYNIC)(2)-conjugated cyclic RGD peptides, K(HYNIC)(2)-RGD(2) (RGD(2) = E[c(RGDfK)](2)), K(HYNIC)(2)-3G-RGD(2) (3G-RGD(2) = Gly-Gly-Gly-E[Gly-Gly-Gly-c(RGDfK)](2)), K(HYNIC)(2)-2P-RGD(2) (2P-RGD(2) = E[PEG4-c(RGDfK)](2), and PEG(4) = 15-amino-4,7,10,13-tetraoxapentadecanoic acid), and K(HYNIC)(2)-3P-RGD(2) (3P-RGD(2) = PEG4-E[PEG4-c(RGDfK)]2) were prepared, and evaluated for their integrin αvβ3 binding affinity. IC(50) values were determined to be 47 ± 2, 35 ± 2, 37 ± 2, 85 ± 2, and 422 ± 15 nM for K(HYNIC)(2)-2P-RGD(2), K(HYNIC)(2)-3P-RGD(2), K(HYNIC)(2)-3G-RGD(2), K(HYNIC)(2)-RGD(2), and c(RGDyK), respectively, against (125)I-echistatin bound to U87MG cells. Macrocyclic complexes [(99m)Tc(K(HYNIC)(2)-RGD(2))(tricine)] (1), [(99m)Tc(K(HYNIC)(2)-3G-RGD(2))(tricine)] (2), [(99m)Tc(K(HYNIC)(2)-2P-RGD(2))(tricine)] (3), and [(99m)Tc(K(HYNIC)(2)-3P-RGD(2))(tricine)] (4) were prepared, and evaluated in athymic nude mice bearing U87MG glioma xenografts for their tumor targeting capability and biodistribution. It was found that 1-4 all had high solution stability and more than two isomers, as evidenced by the presence of multiple radiometric peaks in their radio-HPLC chromatograms. The tumor uptake of 1-4 was 3.78 ± 0.81, 7.46 ± 1.68, 9.74 ± 1.65, and 8.59 ± 1.52%ID/g, respectively, which was completely consistent with trend of integrin α(v)β(3) binding affinity for cyclic RGD peptides. Replacing [(99m)Tc(HYNIC)(tricine)(TPPTS)] (TPPTS = trisodium triphenylphosphine-3,3',3"-trisulfonate) with [(99m)Tc(K(HYNIC)(2))(tricine)] had little impact on radiotracer tumor uptake; but it had significant effect on the uptake of radiotracer in kidneys, lungs, and spleen. The tumor was clearly visualized by SPECT/CT with excellent contrast in a glioma-bearing mouse administered with 4. K(HYNIC)(2) would be particularly useful for (99m)Tc-labeling of small biomolecules with one or more disulfide linkages.