Bimodal MRI/Fluorescence Nanoparticle Imaging Contrast Agent Targeting Prostate Cancer

We developed a novel site-specific bimodal MRI/fluorescence nanoparticle contrast agent targeting gastrin-releasing peptide receptors (GRPrs), which are overexpressed in aggressive prostate cancers. Biocompatible ultra-small superparamagnetic iron oxide (USPIO) nanoparticles were synthesized using glucose and casein coatings, followed by conjugation with a Cy7.5-K-8AOC-BBN [7-14] peptide conjugate. The resulting USPIO(Cy7.5)-BBN nanoparticles were purified by 100 kDa membrane dialysis and fully characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier transform infrared (FTIR) spectroscopy, and magnetic resonance imaging (MRI) relaxivity, as well as evaluated for in vitro and in vivo binding specificity and imaging efficacy in PC-3 prostate cancer cells and xenografted tumor-bearing mice. The USPIO(Cy7.5)-BBN nanoparticles had a core diameter of 4.93 ± 0.31 nm and a hydrodynamic diameter of 35.56 ± 0.58 nm. The r2 relaxivity was measured to be 70.2 ± 2.5 s-1 mM-1 at 7T MRI. The Cy7.5-K-8AOC-BBN [7-14] peptide-to-nanoparticle ratio was determined to be 21:1. The in vitro GRPr inhibitory binding (IC50) value was 2.5 ± 0.7 nM, indicating a very high binding affinity of USPIO(Cy7.5)-BBN to the GRPr on PC-3 cells. In vivo MRI showed significant tumor-to-muscle contrast enhancement in the uptake group at 4 h (31.1 ± 3.4%) and 24 h (25.7 ± 2.1%) post-injection compared to the blocking group (4 h: 15.3 ± 2.0% and 24 h: -2.8 ± 6.8%; p < 0.005). In vivo and ex vivo near-infrared fluorescence (NIRF) imaging revealed significantly increased fluorescence in tumors in the uptake group compared to the blocking group. These findings demonstrate the high specificity of bimodal USPIO(Cy7.5)-BBN nanoparticles towards GRPr-expressing PC-3 cells, suggesting their potential for targeted imaging in aggressive prostate cancer.

Peptide-based diagnostic and therapeutic agents: Where we are and where we are heading?

Peptides are increasingly present in all branches of medicine as innovative drugs, imaging agents, theragnostic, and constituent moieties of other sophisticated drugs such as peptide-drug conjugates. Due to new developments in chemical synthesis strategies, computational biology, recombinant technology, and chemical biology, peptide drug development has made a great progress in the last decade. Numerous natural peptides and peptide mimics have been obtained and studied, covering multiple therapeutic areas. Even though peptides have been investigated across the wide therapeutic spectrum, oncology, metabolism, and endocrinology are the most frequent medical indications of them. This review summarizes the current use of and the emerging new opportunities of peptides for diagnosis and treatment of various diseases.

Towards Selective Delivery of a Ruthenium(II) Polypyridyl Complex-Containing Bombesin Conjugate into Cancer Cells

An increasing number of novel Ru(II) polypyridyl complexes have been successfully applied as photosensitizers (PSs) for photodynamic therapy (PDT). Despite recent advances in optimized PSs with refined photophysical properties, the lack of tumoral selectivity is often a major hurdle for their clinical development. Here, classical maleimide and versatile NHS-activated acrylamide strategies were employed to site-selectively conjugate a promising Ru(II) polypyridyl complex to the N-terminally Cys-modified Bombesin (BBN) targeting unit. Surprisingly, the decreased cell uptake of these novel Ru-BBN conjugates in cancer cells did not hamper the high phototoxic activity of the Ru-containing bioconjugates and even decreased the toxicity of the constructs in the absence of light irradiation. Overall, although deceiving in terms of selectivity, our new bioconjugates could still be useful for advanced cancer treatment due to their nontoxicity in the dark.

pH-responsive graphene oxide loaded with targeted peptide and anticancer drug for OSCC therapy

Oral squamous cell carcinoma (OSCC) is the most common type of cancer occurring in the oral and maxillofacial regions. Despite of the advances in the diagnosis and treatment, the overall 5-year survival rate has remained about 40%–50% in the past decades. Various nanotechnology-based carrier systems have been investigated for their potentials in the OSCC treatment. However, because of the lack of active targeting of tumors, their application is limited. Studies have shown that gastrin-releasing peptide receptors (GRPRs) are overexpressed on many human cancers, including head and neck squamous cell carcinoma. Herein, we aimed to develop a GRPR-targeted nano-graphene oxide (NGO) nanoprobe drug delivery system for OSCC therapy. DOX@NGO-BBN-AF750 was synthesized by the non-covalent bonding method to couple carboxylated NGO with BBN-AF750 (bombesin antagonist peptides conjugated to Alexa Fluor 750) and DOX (doxorubicin) through π-π and hydrogen bonding. Internalization and antitumor activities were carried out in human HSC-3 cancer cells. The tumor pH microenvironment was simulated to study the release of antitumor drug DOX from the DOX@NGO-ant BBN-AF750 complex under different pH conditions. DOX@NGO-BBN-AF750 showed internalization into HSC-3 cells. The IC50 (50% inhibitory concentration) was 5 µg/ml for DOX@NGO-BBN-AF750 in HSC-3 cells. Furthermore, DOX@NGO-BBN-AF750 showed a pH-sensitive drug release rate, and a dose-dependent and pH-responsive cytotoxicity in HSC-3 cells. DOX@NGO-BBN-AF750 presents the characteristics ensuring a slow release of DOX from the nanoprobe, thereby protecting the drug from degradation and prolonging the half-life of the drug. This report provides a versatile strategy to achieving targeted and imaging-guided therapy of OSCC.

Peptide-Pegylated Lipid Conjugation Via Copper-Catalyzed Alkyne-Azide 1,3-Dipolar Cycloaddition

Targeted drug delivery is an important strategy in the treatment of many diseases. However, cancer cells are very difficult to target, making this a substantial obstacle in chemotherapy treatment. Bombesin fragment (BBN(6-14)) has been found to target gastrin-releasing peptide receptor (GRPR), which is overexpressed in many cancer cells. In this chapter, BBN peptide was used as a targeting moiety on the surface of polymeric-based nanoparticles to deliver its payload into prostate cancer PC-3 cell lines. Copper-catalyzed alkyne-azide 1,3-dipolar cycloaddition (CuAAC) click reaction was utilized to link the BBN peptide with an alkyne derivative of Pegylated lipid.

GRPr-mediated photothermal and thermodynamic dual-therapy for prostate cancer with synergistic anti-apoptosis mechanism

Conventional prostate cancer treatment strategies, including chemotherapy and radiotherapy, cannot effectively eradicate prostate cancer, especially castration resistance prostate cancer. Herein, we developed a novel nanotherapy platform that consists of synergic photothermal and photodynamic therapy via the unique properties of photothermal conversion by gold nanorods and free radicals generation by encapsulated initiators (AIPH). Mesoporous silica was employed as a coating material, and the bombesin peptide was conjugated onto the mesoporous silica coating layer as the targeting moiety to prostate cancer via its overexpressed gastrin-releasing peptide receptors. An in vitro study with the castration resistance prostate cancer cell exhibited a significant photothermal therapeutic effect as well as enhanced thermodynamic therapy via generating free radicals. P-p38 and p-JNK proteins, as key proteins involved in the cells' stress responses, were found to be upregulated by the synergetic treatment. The in vivo study demonstrated that a significant eradication of prostate tumour could be achieved by the nanoparticle therapeutic platform with a good biocompatibility profile. This work pioneers a novel approach for high-efficient castration resistance prostate cancer treatment by combining photothermal, thermodynamic, and site-specific drug delivery directed by an integrated nanoparticle system.

Advances in Targeted Gene Delivery

Gene therapy has the potential to treat both acquired and inherited genetic diseases. Generally, two types of gene delivery vectors are used - viral vectors and non-viral vectors. Non-viral gene delivery systems have attracted significant interest (e.g. 115 gene therapies approved for clinical trials in 2018; clinicaltrials.gov) due to their lower toxicity, lack of immunogenicity and ease of production compared to viral vectors. To achieve the goal of maximal therapeutic efficacy with minimal adverse effects, the cell-specific targeting of non-viral gene delivery systems has attracted research interest. Targeting through cell surface receptors; the enhanced permeability and retention effect, or pH differences are potential means to target genes to specific organs, tissues, or cells. As for targeting moieties, receptorspecific ligand peptides, antibodies, aptamers and affibodies have been incorporated into synthetic nonviral gene delivery vectors to fulfill the requirement of active targeting. This review provides an overview of different potential targets and targeting moieties to target specific gene delivery systems.

A novel peptide targeting gastrin releasing peptide receptor for pancreatic neoplasm detection

The designed novel peptide GB-6 with targeted GRPR-binding possesses more favorable pharmacokinetic properties and metabolic stability, as well as superior tumor-targeting ability in pancreatic cancer models, relative to BBN_7–14.

Peptide-based targeted polymeric nanoparticles for siRNA delivery

The development of polymer-based nanoparticulate delivery systems for siRNA is important for the clinical success of gene therapy. However, there are some major drawbacks that need to be overcome. Short interfering RNA (siRNA) has been investigated as a potential therapeutic drug to silence disease-associated genes, but its usage is limited due to the lack of effective and safe nanocarriers. In this study, DOPE-PEI, a nanoparticle consisting of the fusogenic lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) conjugated with low-molecular-weight, 600 Da, branched polyethylenimine (PEI) was produced and optimized for siRNA delivery. This delivery system was modified with other components such as 1,2-dioleoyl-sn-glycerol-3-phosphoethanolamine-N-[methoxy(polyethyleneglycol)2000] (DOPE-PEG2K), DOPE-PEG3.4K-bombesin and 1,2-dioleoyl-sn-glycerol-3-phosphoethanolamine/1,2-dioleoyl-3-trimethylammonium-propane (DOPE/DOTAP) and tested on PC-3 cells. The conjugation of DOPE to PEI polymer (DOPE-PEI) improved the efficiency of PEI to deliver siRNA into the cytosol and knockdown genes, but demonstrated high toxicity. The addition of DOPE-PEG2K reduced cellular toxicity by masking the surface positive charge of the DOPE-PEI/siRNA complex, with the incorporation of a gastrin-releasing peptide receptor (GRPR) targeting peptide and DOPE/DOTAP components improving the cellular uptake of siRNA into targeted cells and the siRNA knockdown efficiency.

Gastrin-Releasing Peptide Receptor- and Prostate-Specific Membrane Antigen-Specific Ultrasmall Gold Nanoparticles for Characterization and Diagnosis of Prostate Carcinoma via Fluorescence Imaging

Gold nanoparticles (AuNPs) have widely been used for 70 years in cancer treatment, but only in the last 15 years has the focus been on specific AuNPs with homogeneous size and shape for various areas in science. They constitute a perfect platform for multifunctionalization and therefore enable the enhancement of target affinity. Here we report on the development of tumor specific AuNPs as diagnostic tools intended for the detection of prostate cancer via fluorescence imaging and positron emission tomography (PET). The AuNPs were further evaluated in vitro and in vivo and exhibited favorable diagnostic properties concerning tumor cell uptake, biodistribution, clearance, and tumor retention.

Direct subphthalocyanine conjugation to bombesin vs. indirect conjugation to its lipidic nanocarrier

Bombesin (BBN) was covalently bound to graftable subphthalocyanine (SubPc) or to a cholesterol derivative, a component of a liposome that encapsulates non-graftable SubPc. The latter bioconjugation approach was suitable to address the stability of SubPc and was achieved by copper-free click-chemistry on the outer-face of the liposome. Liposomes were purified (FPLC) and then analyzed in size (outer diameter about 60 nm measured by DLS). In vitro binding studies allowed to determine the IC50 13.9 nM for one component of the liposome, cholesterol, conjugated to BBN. Hence, azido- (or alkynyl-) liposomes give fluorophores with no reactive functional group available on their backbone a second chance to be (indirectly) bioconjugated (with bombesin).

Next generation NIR fluorophores for tumor imaging and fluorescence-guided surgery: A review

Cancer is a group of diseases responsible for the major causes of mortality and morbidity among people of all ages. Even though medical sciences have made enormous growth, complete treatment of this deadly disease is still a challenging task. Last few decades witnessed an impressive growth in the design and development of near infrared (NIR) fluorophores with and without recognition moieties for molecular recognitions, imaging and image guided surgeries. The present article reviews recently reported NIR emitting organic/inorganic fluorophores that targets and accumulates in organelle/organs specifically for molecular imaging of cancerous cells. Near infrared (NIR probe) with or without a tumor-targeting warhead have been considered and discussed for their applications in the field of cancer imaging. In addition, challenges persist in this area are also delineated in this review.

Gelatinase activity imaged by activatable cell-penetrating peptides in cell-based and in vivo models of stroke

Matrix metalloproteinases (MMPs), particularly gelatinases (MMP-2/-9), are involved in neurovascular impairment after stroke. Detection of gelatinase activity in vivo can provide insight into blood-brain barrier disruption, hemorrhage, and nerve cell injury or death. We applied gelatinase-activatable cell-penetrating peptides (ACPP) with a cleavable l-amino acid linker to examine gelatinase activity in primary neurons in culture and ischemic mouse brain in vivo We found uptake of Cy5-conjugated ACPP (ACPP-Cy5) due to gelatinase activation both in cultured neurons exposed to n-methyl-d-aspartate and in mice after cerebral ischemia. Fluorescence intensity was significantly reduced when cells or mice were treated with MMP inhibitors or when a cleavage-resistant ACPP-Cy5 was substituted. We also applied an ACPP dendrimer (ACPPD) conjugated with multiple Cy5 and/or gadolinium moieties for fluorescence and magnetic resonance imaging (MRI) in intact animals. Fluorescence analysis showed that ACPPD was detected in sub-femtomole range in ischemic tissues. Moreover, MRI and inductively coupled plasma mass spectrometry revealed that ACPPD produced quantitative measures of gelatinase activity in the ischemic region. The resulting spatial pattern of gelatinase activity and neurodegeneration were very similar. We conclude that ACPPs are capable of tracing spatiotemporal gelatinase activity in vivo, and will therefore be useful in elucidating mechanisms of gelatinase-mediated neurodegeneration after stroke.

GRPR-targeted Protein Contrast Agents for Molecular Imaging of Receptor Expression in Cancers by MRI

Gastrin-releasing peptide receptor (GRPR) is differentially expressed on the surfaces of various diseased cells, including prostate and lung cancer. However, monitoring temporal and spatial expression of GRPR in vivo by clinical MRI is severely hampered by the lack of contrast agents with high relaxivity, targeting capability and tumor penetration. Here, we report the development of a GRPR-targeted MRI contrast agent by grafting the GRPR targeting moiety into a scaffold protein with a designed Gd³⁺ binding site (ProCA1.GRPR). In addition to its strong binding affinity for GRPR (K_d = 2.7 nM), ProCA1.GRPR has high relaxivity (r₁ = 42.0 mM⁻¹s⁻¹ at 1.5 T and 25 °C) and strong Gd³⁺ selectivity over physiological metal ions. ProCA1.GRPR enables in vivo detection of GRPR expression and spatial distribution in both PC3 and H441 tumors in mice using MRI. ProCA1.GRPR is expected to have important preclinical and clinical implications for the early detection of cancer and for monitoring treatment effects.

Insights into bombesin receptors and ligands: Highlighting recent advances

This following article is written for Prof. Abba Kastin's Festschrift, to add to the tribute to his important role in the advancement of the role of peptides in physiological, as well as pathophysiological processes. There have been many advances during the 35 years of his prominent role in the Peptide field, not only as editor of the journal Peptides, but also as a scientific investigator and editor of two volumes of the Handbook of Biological Active Peptides [146,147]. Similar to the advances with many different peptides, during this 35 year period, there have been much progress made in the understanding of the pharmacology, cell biology and the role of (bombesin) Bn receptors and their ligands in various disease states, since the original isolation of bombesin from skin of the European frog Bombina bombina in 1970 [76]. This paper will briefly review some of these advances over the time period of Prof. Kastin 35 years in the peptide field concentrating on the advances since 2007 when many of the results from earlier studies were summarized [128,129]. It is appropriate to do this because there have been 280 articles published in Peptides during this time on bombesin-related peptides and it accounts for almost 5% of all publications. Furthermore, 22 Bn publications we have been involved in have been published in either Peptides [14,39,55,58,81,92,93,119,152,216,225,226,231,280,302,309,355,361,362] or in Prof. Kastin's Handbook of Biological Active Peptides [137,138,331].

Advances in imaging probes and optical microendoscopic imaging techniques for early in vivo cancer assessment

A new chapter in the history of medical diagnosis happened when the first X-ray technology was invented in the late 1800s. Since then, many non-invasive and minimally invasive imaging techniques have been invented for clinical diagnosis to research in cellular biology, drug discovery, and disease monitoring. These imaging modalities have leveraged the benefits of significant advances in computer, electronics, and information technology and, more recently, targeted molecular imaging. The development of targeted contrast agents such as fluorescent and nanoparticle probes coupled with optical imaging techniques has made it possible to selectively view specific biological events and processes in both in vivo and ex vivo systems with great sensitivity and selectivity. Thus, the combination of targeted molecular imaging probes and optical imaging techniques have become a mainstay in modern medicinal and biological research. Many promising results have demonstrated great potentials to translate to clinical applications. In this review, we describe a discussion of employing imaging probes and optical microendoscopic imaging techniques for cancer diagnosis.

A high-affinity, high-stability photoacoustic agent for imaging gastrin-releasing peptide receptor in prostate cancer

PURPOSE

To evaluate the utility of targeted photoacoustic imaging (PAI) in providing molecular information to complement intrinsic functional and anatomical details of the vasculature within prostate lesion.

EXPERIMENTAL DESIGN

We developed a PAI agent, AA3G-740, that targets gastrin-releasing peptide receptor (GRPR), found to be highly overexpressed in prostate cancer. The binding specificity of the agent was evaluated in human prostate cancer cell lines, PC3 and LNCaP, and antagonist properties determined by cell internalization and intracellular calcium mobilization studies. The imaging sensitivity was assessed for the agent itself and for the PC3 cells labeled with agent. The in vivo stability of the agent was determined in human plasma and in the blood of living mice. The in vivo binding of the agent was evaluated in PC3 prostate tumor models in mice, and was validated ex vivo by optical imaging.

RESULTS

AA3G-740 demonstrated strong and specific binding to GRPR. The sensitivity of detection in vitro indicated suitability of the agent to image very small lesions. In mice, the agent was able to bind to GRPR even in poorly vascularized tumors leading to nearly 2-fold difference in photoacoustic signal relative to the control agent.

CONCLUSIONS

The ability to image both vasculature and molecular profile outside the blood vessels gives molecular PAI a unique advantage over currently used imaging techniques. The imaging method presented here can find application both in diagnosis and in image-guided biopsy.

Dual-band Fourier domain optical coherence tomography with depth-related compensations

Dual-band Fourier domain optical coherence tomography (FD-OCT) provides depth-resolved spectroscopic imaging that enhances tissue contrast and reduces image speckle. However, previous dual-band FD-OCT systems could not correctly give the tissue spectroscopic contrast due to depth-related discrepancy in the imaging method and attenuation in biological tissue samples. We designed a new dual-band full-range FD-OCT imaging system and developed an algorithm to compensate depth-related fall-off and light attenuation. In our imaging system, the images from two wavelength bands were intrinsically overlapped and their intensities were balanced. The processing time of dual-band OCT image reconstruction and depth-related compensations were minimized by using multiple threads that execute in parallel. Using the newly developed system, we studied tissue phantoms and human cancer xenografts and muscle tissues dissected from severely compromised immune deficient mice. Improved spectroscopic contrast and sensitivity were achieved, benefiting from the depth-related compensations.

Near-infrared fluorescence imaging of gastrin releasing peptide receptor targeting in prostate cancer lymph node metastases

BACKGROUND

Development of high affinity and specificity molecular imaging probes that increase accuracy for early detection of lymph node (LN) metastases is important for improving survivorship in prostate cancer. We evaluated the specificity, sensitivity, and accuracy of fluorescence-labeled bombesin (BBN) peptides to detect LN and systematic metastases in orthotopic mouse models bearing gastrin releasing peptide receptor (GRPR)-positive human prostate cancer.

METHODS

PC-3 cells were orthotopically implanted in severe combined immunedeficient or thymic nude (nu/nu) male mice. Tumor growth was monitored using magnetic resonance imaging. Alexa Fluor 680 conjugated BBN[7-14]NH2 (AF680-BBN) peptides were administered intravenously at 4-7 weeks post-tumor-implantation. Near-infrared fluorescence (NIRF) imaging was performed for up to 6 hr post-injection. The imaging sensitivity and specificity were assessed by co-registration of AF680-BBN NIRF imaging and luciferase bioluminescence imaging of the PC-3/Luc+ orthotopic mouse model.

RESULTS

AF680-BBN showed a high binding affinity and selectivity to GRPR-positive cancer in vitro and in vivo. LN and peritoneal metastases were detected by NIRF imaging, and confirmed by histopathology. Tumor-to-muscle (T/M) ratio was the highest at 2-hr post-injection (4.12 ± 1.77). Blocking experiments, using unlabeled BBN as the inhibiting agent, significantly reduced the T/M ratio (1.64 ± 0.21, P = 0.02). AF680-BBN NIRF imaging had a sensitivity of 89.4%, specificity of 92.9%, and accuracy of 90.2% for the detection of metastases in mice.

CONCLUSIONS

[corrected] The studies suggest the potential of use and development of NIR-fluorescent BBN probes as site-directed agents to help improve the current detection and LN staging accuracy in prostate cancer.

Exogenous Molecular Probes for Targeted Imaging in Cancer: Focus on Multi-modal Imaging

Cancer is one of the major causes of mortality and morbidity in our health care system. Molecular imaging is an emerging methodology for the early detection of cancer, and the development of exogenous molecular probes that can be labeled for multi-modality imaging is critical to this process. Today, molecular imaging is at crossroad, and new targeted imaging agents are expected to broadly expand our ability to detect pre-malignant lesions. This integrated imaging strategy will permit clinicians to not only localize lesions within the body, but also to visualize the expression and activity of specific molecules. This information is expected to have a major impact on diagnosis, therapy, drug development and understanding of basic cancer biology. At this time, a number of molecular probes have been developed by conjugating various labels to affinity ligands for targeting in different imaging modalities. This review will describe the current status of exogenous molecular probes for optical, nuclear and MRI imaging platforms. Furthermore, we will also shed light on how these techniques can be used synergistically in multi-modal platforms and how these techniques are being employed in current research.

Surface activation and targeting strategies of superparamagnetic iron oxide nanoparticles in cancer-oriented diagnosis and therapy

The advanced fabrication and surface engineering of superparamagnetic iron oxide nanoparticles (SPIONs) could offer excellent physiochemical features for noninvasive tumor imaging and drug delivery. The key issues of realization of maximized selective cancer targeting of SPIONs are minimization of uptake by macrophages, preferential binding to cancerous cells over neighboring normal cells, visualization of tumor cells prior to and after treatment and triggered drug release into target cells in a controlled fashion. In this article, we summarize the current status of fabrication of multifunctional SPION-based nanodevices specially designed for cancer-oriented diagnosis and therapy, with a focus on potential malignancy-targeting ligands’ identification and development as nanocarriers. A number of examples of passive and active targeting strategies – lymphoangiogenesis markers, cellular metabolite receptors, extracellular matrix component receptors, neuropeptide receptors and receptor-mediated bypass of the blood–brain barrier – are described in detail.

In vitro and in vivo analysis of [(64)Cu-NO2A-8-Aoc-BBN(7-14)NH(2)]: a site-directed radiopharmaceutical for positron-emission tomography imaging of T-47D human breast cancer tumors

INTRODUCTION

Human breast cancer, from which the T-47D cell line was derived, is known to overexpress the gastrin-releasing peptide receptor (GRPR) in some cases. Bombesin (BBN), an agonist for the GRPR, has been appended with a radionuclide capable of positron-emission tomography (PET) imaging and therapy. (64)Cu-NO2A-8-Aoc-BBN(7-14)NH(2) (NO2A=1,4,7-triazacyclononane-1,4-diacetate) has produced high-quality microPET images of GRPR-positive breast cancer xenografted tumors in mice.

METHODS

The imaging probe was synthesized by solid-phase peptide synthesis followed by manual conjugation of the 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) bifunctional chelator and radiolabeling in aqueous solution. The radiolabeled conjugate was subjected to in vitro and in vivo studies to determine its specificity for the GRPR and its pharmacokinetic profile. A T-47D tumor-bearing mouse was imaged with microPET/CT and microMRI imaging.

RESULTS

The (64)Cu-NO2A-8-Aoc-BBN(7-14)NH(2) targeting vector was determined to specifically localize in GRPR-positive tissue. Accumulation was observed in the tumor in sufficient quantities to allow for identification of tumors in microPET imaging procedures. For example, uptake and retention in T-47D xenografts at 1, 4 and 24 h were determined to be 2.27+/-0.08, 1.35+/-0.14 and 0.28+/-0.07 % ID/g, respectively.

CONCLUSIONS

The (64)Cu-NO2A-8-Aoc-BBN(7-14)NH(2) produced high-quality microPET images. The pharmacokinetic profile justifies investigation of this bioconjugate as a potentially useful diagnostic/therapeutic agent. Additionally, the bioconjugate would serve as a good starting point for modification and optimization of similar agents to maximize tumor uptake and minimize nontarget accumulation.