A first-in-human clinical trial of ultrasmall inorganic hybrid nanoparticles, “C dots” (Cornell dots), in patients with metastatic melanoma is described for the imaging of cancer. These renally excreted silica particles were labeled with 124I for positron emission tomography (PET) imaging and modified with cRGDY peptides for molecular targeting. 124I-cRGDY–PEG–C dot particles are inherently fluorescent, containing the dye, Cy5, so they may be used as hybrid PET-optical imaging agents for lesion detection, cancer staging, and treatment management in humans. However, the clinical translation of nanoparticle probes, including quantum dots, has not kept pace with the accelerated growth in minimally invasive surgical tools that rely on optical imaging agents. The safety, pharmacokinetics, clearance properties, and radiation dosimetry of 124I-cRGDY–PEG–C dots were assessed by serial PET and computerized tomography after intravenous administration in patients. Metabolic profiles and laboratory tests of blood and urine specimens, obtained before and after particle injection, were monitored over a 2-week interval. Findings are consistent with a well-tolerated inorganic particle tracer exhibiting in vivo stability and distinct, reproducible pharmacokinetic signatures defined by renal excretion. No toxic or adverse events attributable to the particles were observed. Coupled with preferential uptake and localization of the probe at sites of disease, these first-in-human results suggest safe use of these particles in human cancer diagnostics.

Optical imaging has emerged as a powerful modality for studying molecular recognitions and molecular imaging in a noninvasive, sensitive, and real-time way. Some advantages of optical imaging include cost-effectiveness, convenience, and non-ionization safety as well as complementation with other imaging modalities such as positron emission tomography (PET), single-photon emission computed tomography (SPECT), and magnetic resonance imaging (MRI). Over the past decade, considerable advances have been made in tumor optical imaging by targeting integrin receptors in preclinical studies. This review has emphasized the construction and evaluation of diverse integrin targeting agents for optical imaging of tumors in mouse models. They mainly include some near-infrared fluorescent dye-RGD peptide conjugates, their multivalent analogs, and nanoparticle conjugates for targeting integrin αvβ3. Some compounds targeting other integrin subtypes such as α4β1 and α3 for tumor optical imaging have also been included. Both in vitro and in vivo studies have revealed some promising integrin-targeting optical agents which have further enhanced our understanding of integrin expression and targeting in cancer biology as well as related anticancer drug discovery. Especially, some integrin-targeted multifunctional optical agents including nanoparticle-based optical agents can multiplex optical imaging with other imaging modalities and targeted therapy, serving as an attractive type of theranostics for simultaneous imaging and targeted therapy. Continued efforts to discover and develop novel, innovative integrin-based optical agents with improved targeting specificity and imaging sensitivity hold great promises for improving cancer early detection, diagnosis, and targeted therapy in clinic.

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.

mouse ͉ optical imaging ͉ RGD peptides ͉ tumor ͉ near-infrared A ngiogenesis, the formation of new blood vessels, is the cardinal feature of virtually all malignant tumors (1). Because of this commonality, probing tumor-induced angiogenesis and associated proteins is a viable approach to detect and treat a wide range of cancers. Angiogenesis is stimulated by integrins, a large family of transmembrane proteins that mediate dynamic linkages between extracellular adhesion molecules and the intracellular actin skeleton. Integrins are composed of two different subunits, ␣ and ␤, which are noncovalently bound into ␣␤ complexes (2-4). Particularly, the expression of ␣ v ␤ 3 integrin (ABI) in tumor cells undergoing angiogenesis and on the epithelium of tumor-induced neovasculature alters the interaction of cells with the extracellular matrix, thereby increasing tumorigenicity and invasiveness of cancers (5-9).Numerous studies have shown that ABI and more than seven other heterodimeric integrins recognize proteins and low molecular weight ligands containing RGD (arginine-glycineaspartic acid) motifs in proteins and small peptides (10). Based on structural and bioactivity considerations, cyclic RGD peptide ligands are preferentially used as delivery vehicles for molecular probes for imaging (8,(11)(12)(13) and treating (14-17) ABI-positive tumors and proliferating blood vessels. Until recently, most of the in vivo imaging studies were performed with radiopharmaceuticals because of the high sensitivity and clinical utility of nuclear imaging methods. Particularly, the use of small monoatomic radioisotopes does not generally interfere with the biodistribution and bioactivity of ligands. Despite these advantages, nuclear imaging is currently only performed in specialized centers because of regulatory, production, and handling issues associated with radiopharmaceuticals. Optical imaging is an alternative but complementary method to interrogate molecular processes in vivo and in vitro.Optical imaging for biomedical applications typically relies on activating chromophore systems with low energy radiation between 400 -and 1,500-nm wavelengths and monitoring the propagation of light in deep tissues with a charge-coupled device camera or other point source detectors (18). Molecular optical imaging of diseases with molecular probes is attractive because of the flexibility of altering the detectable spectral properties of the probes, especially in the fluorescence detection mode. The probes can be designed to target cellular and molecular processes at functional physiological concentrations. For deep-tissue imaging, molecular probes that are photoactive in the near-infrared (NIR) instead of visible wavelengths are preferred to minimize background tissue autof luorescence and light attenuation caused by absorption by intrinsic chromophores (19). In contrast to radioisotopes, the NIR antennas are usually large heteroatomic molecules that could impact the biodistribution and activity of conjugated bioactive ligands. However, previous s...

Objectives-The α v β 3 integrin is a cell adhesion molecule known to be involved in stages of angiogenesis and metastasis. In this study, the chelators CB-TE2A and diamsar were conjugated to cyclic RGDyK and RGDfD and the biological properties of 64 Cu labeled peptides were compared.Methods-CB-TE2A-c(RGDyK) and diamsar-c(RGDfD) were labeled with 64 Cu in 0.1 M NH 4 OAc (pH = 8) at 95 °C and 25 °C, respectively. PET and biodistribution studies were carried out on M21 (α v β 3 -positive) and M21L (α v -negative) melanoma-bearing mice. Binding affinity of the Cu-chelator-RGD peptides to α v β 3 integrins was determined by a competitive binding affinity assay.Results-Biological studies showed higher concentration of 64 Cu-CB-TE2A-c(RGDyK) in M21 tumor compared to M21L tumor at 1 h and 4 h p.i. Tumor concentration of 64 Cu-CB-TE2A-c (RGDyK) was higher than that of 64 Cu-diamsar-c(RGDfD). The difference is not due to differing binding affinities, since similar values were obtained for the agents. Compared to 64 Cu-diamsar-c (RGDfD), there is more rapid liver and blood clearance of 64 Cu-CB-TE2A-c(RGDyK), resulting in a lower liver and blood concentration at 24 h p.i.. Both 64 Cu labeled RGD peptides show similar binding affinities to α v β 3 . The differences in their biodistribution properties are likely related to different linkers, charges and lipophilicities. The M21 tumor is clearly visualized with 64 Cu-CB-TE2A-c(RGDyK) by microPET imaging. Administration of c(RGDyK) as a block significantly reduced the tumor concentration; however, the radioactivity background was also decreased by the blocking dose. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. the Cu-chelator moiety and the RGD peptide to achieve optimal in vivo tumor concentration and clearance from non-target organs. Conclusions-Both NIH Public Access