RGD-based PET tracers for imaging receptor integrin αv β3 expression

A robust lyophilized kit for convenient one-step formulation of [68Ga]Ga-DOTA-E-[c(RGDfK)]2 in hospital radiopharmacy for clinical PET imaging

The present article describes the development of robust lyophilized kit for convenient formulation of [⁶⁸Ga]Ga-DOTA-E-[c(RGDfK)]₂ (E = glutamic acid, R = arginine, G = glycine, D = aspartic acid, f = phenylalanine, K = lysine) radiopharmaceutical for clinical use in non-invasive monitoring of malignancies overexpressing integrin α_vβ₃ receptors. Five batches of the kit were prepared with optimized kit contents, all of which showed high ⁶⁸Ga-radiolabeling yield (>98%). Pre-clinical evaluation of the [⁶⁸Ga]Ga-radiotracer in SCID mice bearing FTC133 tumour exhibited significant accumulation in the tumor xenograft. Preliminary human clinical investigation carried out in a 60 year old male patient with metastatic lung cancer revealed high radiotracer uptake in the tumor along with satisfactory target to non-target contrast. The developed kit formulation also showed a long shelf-life of at least 12 months on storage at 0 °C. All these results point towards the promising attributes of the developed kit formulation for convenient preparation of [⁶⁸Ga]Ga-DOTA-E-[c(RGDfK)]₂ for routine clinical use.

Fluorine-18: Radiochemistry and Target-Specific PET Molecular Probes Design

The positron emission tomography (PET) molecular imaging technology has gained universal value as a critical tool for assessing biological and biochemical processes in living subjects. The favorable chemical, physical, and nuclear characteristics of fluorine-18 (97% β⁺ decay, 109.8 min half-life, 635 keV positron energy) make it an attractive nuclide for labeling and molecular imaging. It stands that 2-[¹⁸F]fluoro-2-deoxy-D-glucose ([¹⁸F]FDG) is the most popular PET tracer. Besides that, a significantly abundant proportion of PET probes in clinical use or under development contain a fluorine or fluoroalkyl substituent group. For the reasons given above, ¹⁸F-labeled radiotracer design has become a hot topic in radiochemistry and radiopharmaceutics. Over the past decades, we have witnessed a rapid growth in ¹⁸F-labeling methods owing to the development of new reagents and catalysts. This review aims to provide an overview of strategies in radiosynthesis of [¹⁸F]fluorine-containing moieties with nucleophilic [¹⁸F]fluorides since 2015.

Real-time in vivo imaging reveals specific nanoparticle target binding in a syngeneic glioma mouse model

Nanomaterial-based drug delivery is a promising strategy for glioma treatment. However, the detailed dynamics of nanoparticles in solid glioma are still a mystery, including their intratumoral infiltration depth, penetration, retention time, and distribution. Revealing these processes in detail requires repeated intravital imaging of the corresponding brain tumor regions over time during glioma growth. Hereby, we established a syngeneic orthotopic cerebral glioma mouse model by combining the chronic cranial window and two-photon microscopy. Thus, we were able to investigate the dynamics of the nanoparticles during long-term glioma growth. Three hours after the intravenous (i.v.) injection of integrin α_Vβ₃ binding conjugated silicon nanoparticles (SNPs-PEG-RGD-FITC), green nanoparticles had already infiltrated the brain glioma, and then more nanoparticles penetrated into the solid brain tumor and were retained for at least 8 days. However, the amount of control SNPs-PEG-FITC that infiltrated into the solid brain tumor was very low. Moreover, we found that SNPs-PEG-RGD-FITC were not only located in the tumor border but could also infiltrate into the core region of the solid tumor. In vitro assay also confirmed the high binding affinity between GL-261-Tdtomato cells and SNPs-PEG-RGD-FITC. Our results indicate that SNPs-PEG-RGD-FITC has high penetration and retention in a solid glioma and our model provides novel ideas for the investigation of nanoparticle dynamics in brain tumors.

Biological Relevance of RGD-Integrin Subtype-Specific Ligands in Cancer

Integrins are heterodimeric transmembrane proteins able to connect cells with the micro-environment. They represent a family of receptors involved in almost all the hallmarks of cancer. Integrins recognizing the Arg-Gly-Asp (RGD) peptide in their natural extracellular matrix ligands have been particularly investigated as tumoral therapeutic targets. In the last 30 years, intense research has been dedicated to designing specific RGD-like ligands able to discriminate selectively the different RGD-recognizing integrins. Chemists' efforts have led to the proposition of modified peptide or peptidomimetic libraries to be used for tumor targeting and/or tumor imaging. Here we review, from the biological point of view, the rationale underlying the need to clearly delineate each RGD-integrin subtype by selective tools. We describe the complex roles of RGD-integrins (mainly the most studied αvβ3 and α5β1 integrins) in tumors, the steps towards selective ligands and the current usefulness of such ligands. Although the impact of integrins in cancer is well acknowledged, the biological characteristics of each integrin subtype in a specific tumor are far from being completely resolved. Selective ligands might help us to reconsider integrins as therapeutic targets in specific clinical settings.

Noninvasive Molecular Imaging of the Enhanced Permeability and Retention Effect by 64Cu-Liposomes: In vivo Correlations with 68Ga-RGD, Fluid Pressure, Diffusivity and 18F-FDG

Background

The accumulation of liposome encapsulated chemotherapy in solid cancers is dependent on the presence of the enhanced permeability and retention (EPR) effect. Positron emission tomography (PET) imaging with a liposome encapsulated radioisotope, such as liposome encapsulated Cu-64 (⁶⁴Cu-liposome) may help to identify tumors with high liposome accumulation, and thereby stratify patients based on expected benefit from liposomal chemotherapy. However, intravenous administration of liposomes without a cytotoxic content is complicated by the accelerated blood clearance (ABC) phenomenon for succeeding therapeutic liposome dosing. Alternative markers for assessing the tumor’s EPR level are therefore warranted.

Materials and Methods

To increase our understanding of EPR variations and to ultimately identify an alternative marker for the EPR effect, we investigated the correlation between ⁶⁴Cu-liposome PET/CT (EPR effect) and ⁶⁸Ga-RGD PET/CT (neoangiogenesis), ¹⁸F-FDG PET/CT (glycolysis), diffusion-weighted MRI (diffusivity) and interstitial fluid pressure in two experimental cancer models (CT26 and COLO 205).

Results

⁶⁴Cu-liposome and ⁶⁸Ga-RGD SUV_max displayed a significant moderate correlation, however, none of the other parameters evaluated displayed significant correlations. These results indicate that differences in neoangiogenesis may explain some EPR variability, however, as correlations were only moderate and not observed for SUV_mean, ⁶⁸Ga-RGD is probably insufficient to serve as a stand-alone surrogate marker for quantifying the EPR effect and stratifying patients.

Natural-based Hydrogels: A Journey from Simple to Smart Networks for Medical Examination

Natural hydrogels, due to their unique biological properties, have been used extensively for various medical and clinical examinations that are performed to investigate the signs of disease. Recently, complex-crosslinking strategies improved the mechanical properties and advanced approaches have resulted in the introduction of naturally derived hydrogels that exhibit high biocompatibility, with shape memory and self-healing characteristics. Moreover, the creation of self-assembled natural hydrogels under physiological conditions has provided the opportunity to engineer fine-tuning properties. To highlight recent studies of natural-based hydrogels and their applications for medical investigation, a critical review was undertaken using published papers from the Science Direct database. This review presents different natural-based hydrogels (natural, natural-synthetic hybrid and complex-crosslinked hydrogels), their historical evolution, and recent studies of medical examination applications. The application of natural-based hydrogels in the design and fabrication of biosensors, catheters and medical electrodes, detection of cancer, targeted delivery of imaging compounds (bioimaging) and fabrication of fluorescent bioprobes is summarised here. Without doubt, in future, more useful and practical concepts will be derived to identify natural-based hydrogels for a wide range of clinical examination applications.

Synthesis and 18F-radiolabeling of thymidine AMBF3 conjugates

In pursuit of ¹⁸F-labeled nucleosides for positron emission tomography (PET) imaging, we report on the chemical and radiochemical synthesis of two thymidine (dT) analogs, dT-C⁵-AMBF₃ and dT-N³-AMBF₃, that are radiofluorinated by isotope exchange (IEX) and studied as PET imaging agents in mice with tumor xenografts. dT-C⁵-AMBF₃ shows preferential, and tumor-specific, uptake over dT-N³-AMBF₃. This work provides a new synthetic method in order to access new nucleoside tracers for PET imaging.

An improved kit formulation for one-pot synthesis of [99m Tc]Tc-HYNIC-E[c(RGDfK)]2 for routine clinical use in cancer imaging

Radiolabeled Arg-Gly-Asp (RGD) peptide derivatives have immense potential for non-invasive monitoring of malignancies overexpressing integrin α_v β₃ receptors. Easy availability of suitable radiotracers would augment the utility of this class of molecular imaging agents. Towards this, the present article describes the development of an improved lyophilized kit for the routine clinical formulation of [^99m Tc]Tc complex of HYNIC-conjugated dimeric cyclic RGD peptide derivative E-[c(RGDfK)]₂ (E = glutamic acid, f = phenyl alanine, K = lysine) without using Sn²⁺ and systematic evaluation of its efficacy. Five batches of the kits were prepared, and [^99m Tc]Tc-HYNIC-E[c(RGDfK)]₂ radiotracer was synthesized with high radiochemical purity (98.6 ± 0.5%) and specific activity (124.8 GBq/μmol) using the kits. Biodistribution studies in C57BL/6 mice bearing melanoma tumor exhibited significant accumulation of the radiotracer in tumor (5.32 ± 0.56 %ID/g at 60 min p.i.), and this uptake was also found to be receptor-specific by blocking studies. Preliminary human clinical investigations carried out in 10 breast cancer patients revealed high radiotracer uptake in the tumor along with good tumor-to-background contrast. The developed kit formulation showed an exceptionally high shelf-life of at least 18 months. These results demonstrated promising attributes of the developed kit formulation and warrant more extensive clinical investigations.

Al18F-labeled alpha-melanocyte-stimulating hormone (α-MSH) peptide derivative for the early detection of melanoma

OBJECTIVE

Early detection plays a role in the prognosis of melanoma, the most aggressive skin cancer. ⁶⁴Cu- and ⁶⁸Ga-labeled alpha-melanocyte-stimulating hormone (α-MSH) analogs targeting the melanocortin-1 receptor are promising positron emission tomography (PET) tracers for detecting melanoma, and the use of ¹⁸F-labeling will further contribute to the detectability and availability. However, the high radiochemistry demand related to the conventional ¹⁸F-labeling methods has restricted the development of ¹⁸F-labeled α-MSH analogs. A recently developed radiofluorination method using aluminum-fluoride (Al¹⁸F) offers a simple, efficient, and time-saving labeling procedure compared to the conventional ¹⁸F-labeling methods. Herein, we sought to establish a simple preparation method for an ¹⁸F-labeled α-MSH analog using Al¹⁸F, and we examined its potential for the early detection of melanoma.

METHODS

A 1,4,7-triazacyclononane-N,N',N″-triacetic acid (NOTA)-conjugated α-MSH analog (NOTA-GGNle-CycMSH_hex) was prepared by the Fmoc solid-phase strategy. NOTA-GGNle-CycMSH_hex was labeled with Al¹⁸F by heating at 105 °C using a microwave synthesizer for 15 min. Biodistribution study was conducted on B16/F10-luc melanoma-bearing mice at 30 min, 1 h and 3 h after injection of Al¹⁸F-NOTA-GGNle-CycMSH_hex. PET imaging was conducted on melanoma-bearing mice at 1 h post-injection. One day prior to the PET imaging, bioluminescence imaging was also performed.

RESULTS

Al¹⁸F-NOTA-GGNle-CycMSH_hex was readily prepared with a high radiochemical yield (94.0 ± 2.8%). The biodistribution study showed a high accumulation of Al¹⁸F-NOTA-GGNle-CycMSH_hex in the tumor at 30 min and 1 h post-injection (6.69 ± 1.49 and 7.70 ± 1.71%ID/g, respectively). The tumor-to-blood ratio increased with time: 3.46 ± 0.89, 12.67 ± 1.29, and 35.27 ± 9.12 at 30 min, 1 h, and 3 h post-injection, respectively. In the PET imaging, Al¹⁸F-NOTA-GGNle-CycMSH_hex clearly visualized the tumors and depicted very small tumors (< 3 mm).

CONCLUSIONS

We successfully prepared Al¹⁸F-NOTA-GGNle-CycMSH_hex in a simple and efficient manner. Al¹⁸F-NOTA-GGNle-CycMSH_hex showed high tumor accumulation and clearly visualized very small tumors in melanoma-bearing mice. These findings suggest that Al¹⁸F-NOTA-GGNle-CycMSH_hex will be a promising PET tracer for melanoma imaging at an earlier stage.

Surface Modification with Lactadherin Augments the Attachment of Sonazoid Microbubbles to Glycoprotein IIb/IIIa

Arginine-glycine-aspartate (RGD)-carrying microbubbles (MBs) have been utilized as a specific contrast agent for glycoprotein IIb/IIIa (α_IIbβ₃ integrin)-expressing activated platelets in ultrasound molecular imaging. Recently, we found that surface modification with lactadherin provides the RGD motif on the surface of phosphatidylserine-containing clinically available MBs, Sonazoid. Here, we examined the potential of lactadherin-bearing Sonazoid MBs to be targeted MBs for glycoprotein IIb/IIIa using the custom-designed in vitro settings with recombinant α_IIbβ₃ integrin, activated platelets or erythrocyte-rich human clots. By modification of the surface with lactadherin, a large number of Sonazoid MBs were attached to the α_IIbβ₃ integrin-coated and platelet-immobilized plate. Additionally, the video intensity of clots after incubation with lactadherin-bearing Sonazoid MBs was significantly higher than that with unmodified Sonazoid MBs, implying the number of attached Sonazoid MBs was increased by the modification with lactadherin. Our results suggest that the lactadherin-bearing Sonazoid MBs have the potential to be thrombus-targeted MBs.

Rapid one-step 18F-radiolabeling of biomolecules in aqueous media by organophosphine fluoride acceptors

Currently, only a few ¹⁸F-radiolabeling methods were conducted in aqueous media, with non-macroelement fluoride acceptors and stringent conditions required. Herein, we describe a one-step non-solvent-biased, room-temperature-driven ¹⁸F-radiolabeling methodology based on organophosphine fluoride acceptors. The high water tolerance for this isotope-exchange-based ¹⁸F-labeling method is attributed to the kinetic and thermodynamic preference of F/F over the OH/F substitution based on computational calculations and experimental validation. Compact [^18/19F]di-tert-butyl-organofluorophosphine and its derivatives used as ¹⁸F-labeling synthons exhibit excellent stability in vivo. The synthons are further conjugated to several biomolecular ligands such as c(RGDyk) and human serum albumin. The one-step labeled biomolecular tracers demonstrate intrinsic target imaging ability and negligible defluorination in vivo. The current method thus offers a facile and efficient ¹⁸F-radiolabeling pathway, enabling further widespread application of ¹⁸F.

The synthesis of ¹⁸F-labeled positron emission tomography (PET) tracers is difficult and typically requires anhydrous conditions. Here, the authors developed organophosphine precursors that allow for quick, high-yield synthesis of ¹⁸F-labeled probes in either organic solvents or aqueous media.

Design of RGD-ATWLPPR peptide conjugates for the dual targeting of αVβ3 integrin and neuropilin-1

Targeting the tumour microenvironment is a promising strategy to detect and/or treat cancer. The design of selective compounds that co-target several receptors frequently overexpressed in solid tumours may allow a reliable and selective detection of tumours. Here we report the modular synthesis of compounds encompassing ligands of αVβ3 integrin and neuropilin-1 that are overexpressed in the tumour microenvironment. These compounds were then evaluated through cellular experiments and imaging of tumours in mice. We observed that the peptide that displays both ligands is more specifically accumulating in the tumours than in controls. Simultaneous interaction with αVβ3 integrin and NRP1 induces NRP1 stabilization at the cell membrane surface which is not observed with the co-injection of the controls.

Fully automated radiosynthesis of [18F]fluoro-C-glyco-c(RGDfC): exploiting all the abilities of the AllInOne synthesizer

Fully automated and modular radiosynthesis of [¹⁸F]fluoro-C-glyco-RGD conjugate.

Visualisation of interstitial lung disease by molecular imaging of integrin αvβ3 and somatostatin receptor 2

OBJECTIVE

To evaluate integrin αvβ3 (alpha-v-beta-3)-targeted and somatostatin receptor 2 (SSTR2)-targeted nuclear imaging for the visualisation of interstitial lung disease (ILD).

METHODS

The pulmonary expression of integrin αvβ3 and SSTR2 was analysed in patients with different forms of ILD as well as in bleomycin (BLM)-treated mice and respective controls using immunohistochemistry. Single photon emission CT/CT (SPECT/CT) was performed on days 3, 7 and 14 after BLM instillation using the integrin αvβ3-targeting ¹⁷⁷Lu-DOTA-RGD and the SSTR2-targeting ¹⁷⁷Lu-DOTA-NOC radiotracer. The specific pulmonary accumulation of the radiotracers over time was assessed by in vivo and ex vivo SPECT/CT scans and by biodistribution studies.

RESULTS

Expression of integrin αvβ3 and SSTR2 was substantially increased in human ILD regardless of the subtype. Similarly, in lungs of BLM-challenged mice, but not of controls, both imaging targets were stage-specifically overexpressed. While integrin αvβ3 was most abundantly upregulated on day 7, the inflammatory stage of BLM-induced lung fibrosis, SSTR2 expression peaked on day 14, the established fibrotic stage. In agreement with the findings on tissue level, targeted nuclear imaging using SPECT/CT specifically detected both imaging targets ex vivo and in vivo, and thus visualised different stages of experimental ILD.

CONCLUSION

Our preclinical proof-of-concept study suggests that specific visualisation of molecular processes in ILD by targeted nuclear imaging is feasible. If transferred into clinics, where imaging is considered an integral part of patients' management, the additional information derived from specific imaging tools could represent a first step towards precision medicine in ILD.

Site-Specific Deoxyfluorination of Small Peptides with [18 F]Fluoride

Radiolabeled receptor-binding peptides are an important class of positron emission tomography tracers owing to achievable high binding affinities and their rapid blood clearance. Herein, a method to introduce a 4-[¹⁸ F]fluoro-phenylalanine residue into peptide sequences is reported, by chemoselective radio-deoxyfluorination of a tyrosine residue using a traceless activating group. The replacement of only one hydrogen atom with [¹⁸ F]fluoride results in minimal structural perturbation of the peptide, which is desirable in the labeling of tracer candidates.

Biodistribution and toxicity assessment of intratumorally injected arginine-glycine-aspartic acid peptide conjugated to CdSe/ZnS quantum dots in mice bearing pancreatic neoplasm

Quantum dots (QDs) conjugated with arginine-glycine-aspartic acid (RGD) peptides (which are integrin antagonists) are novel nanomaterials with the unique optical property of high molar extinction coefficient, and they have potential utility as photosensitizers in photodynamic therapy (PDT). Our group previously demonstrated significant benefits of using PDT with QD-RGD on pancreatic tumor cells. This study aimed to evaluate the biodistribution and toxicity of QD-RGD in mice prior to in vivo application. Mice with pancreatic neoplasms were intratumorally injected with varying doses of QD-RGD, and the biodistribution 0-24 h post injection was compared to that in control mice (intravenously injected with unconjugated QD). Various tissue samples were collected for toxicity analyses, which included inductively coupled plasma mass spectrometry (ICP-MS) to assess Cd²⁺ concentrations and hematoxylin-eosin staining for histopathological examination. Fluorescent imaging revealed relatively sufficient radiant efficiency in mice under specific conditions. The ICP-MS and HE data showed no significant signs of necrosis due to Cd²⁺ release by QDs. The mice survived well and had no apparent weakness or weight loss during the 4 weeks post injection. These findings provide novel insights into the biodistribution of QD-RGD and encourage profound in vivo studies regardless of safety concerns. These findings alleviate safety concerns and provide novel insights into the biodistribution of QD-RGD, offering a solid foundation for comprehensive in vivo studies.

Preparation and preclinical evaluation of a 68Ga-labelled c(RGDfK) conjugate comprising the bifunctional chelator NODIA-Me

Background

We recently developed a chelating platform based on the macrocycle 1,4,7-triazacyclononane with up to three, five-membered azaheterocyclic arms for the development of ⁶⁸Ga- and ⁶⁴Cu-based radiopharmaceuticals. Here, a ⁶⁸Ga-labelled conjugate comprising the bifunctional chelator NODIA-Me in combination with the α_vß₃-targeting peptide c(RGDfK) has been synthesized and characterized. The primary aim was to evaluate further the potential of our NODIA-Me chelating system for the development of ⁶⁸Ga-labelled radiotracers.

Results

The BFC NODIA-Me was conjugated to c(RGDfK) by standard peptide chemistry to obtain the final bioconjugate NODIA-Me-c(RGDfK) 3 in 72% yield. Labelling with [⁶⁸Ga]GaCl₃ was accomplished in a fully automated, cGMP compliant process to give [⁶⁸Ga]3 in high radiochemical yield (98%) and moderate specific activity (~ 8 MBq nmol− ¹). Incorporation of the Ga-NODIA-Me chelate to c(RGDfK) 2 had only minimal influence on the affinity to integrin α_vß₃ (IC₅₀ values [^natGa]3 = 205.1 ± 1.4 nM, c(RGDfK) 2 = 159.5 ± 1.3 nM) as determined in competitive cell binding experiments in U-87 MG cell line. In small-animal PET imaging and ex vivo biodistribution studies, the radiotracer [⁶⁸Ga]3 showed low uptake in non-target organs and specific tumor uptake in U-87 MG tumors.

Conclusion

The results suggest that the bifunctional chelator NODIA-Me is an interesting alternative to existing ligands for the development of ⁶⁸Ga-labelled radiopharmaceuticals.

Comparison and evaluation of two RGD peptides labelled with 68Ga or 18F for PET imaging of angiogenesis in animal models of human glioblastoma or lung carcinoma

The aim of this study was to evaluate two RGD radiotracers radiolabelled with fluorine-18 or gallium-68, in detecting angiogenesis in grafted human tumours and monitoring their treatment with the anti-angiogenic agent bevacizumab.

Sixteen mice bearing an U87MG tumour in one flank and a contralateral A549 tumour were treated with intravenous injections of bevacizumab twice a week for 3 weeks. PET images with ¹⁸F-RGD-K5 and ⁶⁸Ga-RGD were acquired before treatment (baseline), after three bevacizumab injections (t1) and after seven bevacizumab injections (t2).

In A549 tumours, the treatment stopped the tumour growth, with a tumour volume measured by calliper remaining between 0.28 and 0.40 cm³. The decrease in tumour uptake of both RGD tracers was non-significant. Therefore it was not possible to predict this efficacy on tumour growth based on RGD PET results, whereas ex vivo measurements showed a significantly lower tumour uptake of both tracers in mice sacrificed at t2 vs. at baseline.

In U87MG tumours, the uptake measured on PET decreased during treatment, reflecting the partial therapeutic effect observed on tumour volume, consisting in a decrease in the slope of tumour growth. Using ¹⁸F-RGD-K5, this decrease in tumour SUVmax became significant at t1, whereas it was also observed with the ⁶⁸Ga-RGD tracer, but only at t2. ¹⁸F-RGD-K5 appeared more efficient than ⁶⁸Ga-RGD in the visualisation and follow-up of U87MG tumours.

The comparison of those results with those of immunohistochemistry at baseline and at t2 favoured the hypothesis that tumour RGD uptake reflects other cancer properties than just its angiogenic capacity.

Non-invasive assessment of inter-and intrapatient variability of integrin expression in metastasized prostate cancer by PET

Purpose

Due to the high expression of the integrin αvβ3 not only on endothelial cells, but also on mature osteoclasts and prostate cancer cells, imaging of osseous metastases with αvβ3-targeted tracers seems promising. However, little is known about the patterns of αvβ3-expression in metastasized prostate cancer lesions in-vivo. Thus we evaluated the uptake of the αvβ3-specific PET tracer [¹⁸F]Galacto-RGD for assessment of bone metastases in prostate cancer patients.

Results

[¹⁸F]Galacto-RGD PET identified 58/74 bone-lesions (detection rate of 78.4%) and lymph node metastases in 2/5 patients. The SUV_mean was 2.12+/−0.94 (range 0.70–4.38; tumor/blood 1.36+/−0.53; tumor/muscle 2.82+/−1.31) in bone-lesions and 2.21+/−1.18 (range 0.75–3.56) in lymph node metastases. Good visualization and detection of bone metastases was feasible due to a low background activity of the surrounding normal bone tissue.

Methods

12 patients with known metastasized prostate cancer according to conventional staging (including bone-scintigraphy and contrast-enhanced CT; median PSA 68.63 ng/ml, range 3.72-1935) were examined with PET after i.v.-injection of [¹⁸F]Galacto-RGD. Two blinded nuclear-medicine physicians evaluated the PET-scans in consensus concerning lesion detectability. Volumes-of-interest were drawn in the PET-scans over all metastases defined by conventional staging (maximum of 11 lesions/patient), over the left ventricle, liver and muscle and standardized-uptake-values (SUVs) were calculated.

Conclusions

Our data show generally elevated uptake of [¹⁸F]Galacto-RGD in bone metastases from prostate cancer with a marked inter- and intrapatient variability. While [¹⁸F]Galacto-RGD PET is inferior to bone scintigraphy for detection of osseous metastases, it might be valuable in patient screening and monitoring of αvβ3-targeted therapies due to the high variability of αvβ3-expression.

Prospective of 68Ga Radionuclide Contribution to the Development of Imaging Agents for Infection and Inflammation

During the last decade, the utilization of ⁶⁸Ga for the development of imaging agents has increased considerably with the leading position in the oncology. The imaging of infection and inflammation is lagging despite strong unmet medical needs. This review presents the potential routes for the development of ⁶⁸Ga-based agents for the imaging and quantification of infection and inflammation in various diseases and connection of the diagnosis to the treatment for the individualized patient management.

A Systematic Comparative Evaluation of 68Ga-Labeled RGD Peptides Conjugated with Different Chelators

Purpose

The present paper reports a systematic study on the effect of bifunctional chelators (BFC) namely, NOTA, DOTA, and DTPA, on the radiochemical formulation, in vitro stability, and in vivo biological properties of ⁶⁸Ga-labeled RGD peptide derivatives.

Methods

The three RGD conjugates namely, NOTA-Bn-E-[c(RGDfk)]₂, DOTA-Bn-E-[c(RGDfk)]₂, and DTPA-Bn-E-[c(RGDfk)]₂ were radiolabeled with ⁶⁸Ga and the radiolabeling was optimized with respect to the ligand amount, radiolabeling time, and temperature. Further, the ⁶⁸Ga complexes were assessed for their in vitro and in vivo stabilities. The biodistribution studies of the three radiolabeled conjugates were carried out in C57BL/6 mice bearing melanoma tumor at 30 min and 1 h post-adimistration.

Results

NOTA-Bn-E-[c(RGDfk)]₂ could be radiolabeled with ⁶⁸Ga at room temperature while DOTA-Bn-E-[c(RGDfk)]₂ and DTPA-Bn-E-[c(RGDfk)]₂ were radiolabeled at high temperature. ⁶⁸Ga-NOTA-Bn-E-[c(RGDfk)]₂ was found to be the most kinetically rigid in in vitro stability assay. The uptake of the three radiolabeled peptide conjugates in melanoma tumor was comparable at 1 h post-administration (NOTA; DOTA; DTPA (% I.D./g):: 2.78 ± 0.38; 3.08 ± 1.1; 3.36 ± 0.49). However, the tumor/background ratio of ⁶⁸Ga-NOTA-Bn-E-[c(RGDfk)]₂ was the best amongst the three radiotracers. ⁶⁸Ga-complexes of NOTA-Bn-E-[c(RGDfk)]₂ and DOTA-Bn-E-[c(RGDfk)]₂ showed excellent in vivo stability while ⁶⁸Ga-DTPA-Bn-E-[c(RGDfk)]₂ showed significant metabolic degradation.

Conclusion

These studies show that ⁶⁸Ga-NOTA-Bn-E-[c(RGDfk)]₂ would be the most appropriate ⁶⁸Ga-labeled radiotracer and the most amenable for kit formulation.

18 F-Labeling of Sensitive Biomolecules for Positron Emission Tomography

Positron emission tomography (PET) imaging study of fluorine-18 labeled biomolecules is an emerging and rapidly growing area for preclinical and clinical research. The present review focuses on recent advances in radiochemical methods for incorporating fluorine-18 into biomolecules via "direct" or "indirect" bioconjugation. Recently developed prosthetic groups and pre-targeting strategies, as well as representative examples in 18 F-labeling of biomolecules in PET imaging research studies are highlighted.

Molecular Ultrasound Imaging of αvβ3-Integrin Expression in Carotid Arteries of Pigs After Vessel Injury

OBJECTIVES

Interventions such as balloon angioplasty can cause vascular injury leading to platelet activation, thrombus formation, and inflammatory response. This induces vascular smooth muscle cell activation and subsequent re-endothelialization with expression of αvβ3-integrin by endothelial cells and vascular smooth muscle cell. Thus, poly-N-butylcyanoacrylate microbubbles (MBs) targeted to αvβ3-integrin were evaluated for monitoring vascular healing after vessel injury in pigs using molecular ultrasound imaging.

MATERIALS AND METHODS

Approval for animal experiments was obtained. The binding specificity of αvβ3-integrin-targeted MB to human umbilical vein endothelial cells was tested with fluorescence microscopy. In vivo imaging was performed using a clinical ultrasound system and an 8-MHz probe. Six mini pigs were examined after vessel injury in the left carotid artery. The right carotid served as control. Uncoated MB, cDRG-coated MB, and αvβ3-integrin-specific cRGD-coated MB were injected sequentially. Bound MBs were assessed 8 minutes after injection using ultrasound replenishment analysis. Measurements were performed 2 hours, 1 and 5 weeks, and 3 and 6 months after injury. In vivo data were validated by immunohistochemistry.

RESULTS

Significantly stronger binding of cRGD-MB than MB and cDRG-MB to human umbilical vein endothelial cells was found (P < 0.01). As vessel injury leads to upregulation of αvβ3-integrin, cRGD-MBs bound significantly stronger (P < 0.05) in injured carotid arteries than at the counter side 1 week after vessel injury and significant differences could also be observed after 5 weeks. After 3 months, αvβ3-integrin expression decreased to baseline and binding of cRGD-MB was comparable in both vessels. Values remained at baseline also after 6 months.

CONCLUSIONS

Ultrasound imaging with RGD-MB is promising for monitoring vascular healing after vessel injury. This may open new perspectives to assess vascular damage after radiological interventions.

Synthesis, Chemical Characterization and Multiscale Biological Evaluation of a Dimeric-cRGD Peptide for Targeted Imaging of α V β 3 Integrin Activity

Cyclic peptides containing the Arg-Gly-Asp (RGD) sequence have been shown to specifically bind the angiogenesis biomarker α_Vβ₃ integrin. We report the synthesis, chemical characterization, and biological evaluation of two novel dimeric cyclic RGD-based molecular probes for the targeted imaging of α_Vβ₃ activity (a radiolabeled version, ⁶⁴Cu-NOTA-PEG₄-cRGD₂, for PET imaging, and a fluorescent version, FITC-PEG₄-cRGD₂, for in vitro work). We investigated the performance of this probe at the receptor, cell, organ, and whole-body levels, including its use to detect diabetes associated impairment of ischemia-induced myocardial angiogenesis. Both versions of the probe were found to be stable, demonstrated fast receptor association constants, and showed high specificity for α_Vβ₃ in HUVECs (K_d ~ 35 nM). Dynamic PET-CT imaging indicated rapid blood clearance via kidney filtration, and accumulation within α_Vβ₃-positive infarcted myocardium. ⁶⁴Cu-NOTA-PEG₄-cRGD₂ demonstrated a favorable biodistribution, slow washout, and excellent performance with respect to the quality of the PET-CT images obtained. Importantly, the ratio of probe uptake in infarcted heart tissue compared to normal tissue was significantly higher in non-diabetic rats than in diabetic ones. Overall, our probes are promising agents for non-invasive quantitative imaging of α_Vβ₃ expression, both in vitro and in vivo.

Angiogenesis Imaging Using (68)Ga-RGD PET/CT: Therapeutic Implications

Angiogenesis imaging is important for diagnostic and therapeutic treatment of various malignant and nonmalignant diseases. The Arg-Gly-Asp (RGD) sequence has been known to bind with the αvβ3 integrin that is expressed on the surface of angiogenic blood vessels or tumor cells. Thus, various radiolabeled derivatives of RGD peptides have been developed for angiogenesis imaging. Among the various radionuclides, (68)Ga was the most widely studied for RGD peptide imaging because of its excellent nuclear physical properties, easy-to-label chemical properties, and cost-effectiveness owing to the availability of a (68)Ge-(68)Ga generator. Thus, various (68)Ga-labeled RGD derivatives have been developed and applied for preclinical and clinical studies. Clinical trials were performed for both malignant and nonmalignant diseases. Breast cancer, glioma, and lung cancer were malignant, and myocardial infarction, atherosclerosis, and moyamoya disease were nonmalignant among the investigated diseases. Further, these (68)Ga-labeled RGD derivatives could be applied to assess the effects of antiangiogenic treatment or theragnosis or both, of cancers. In conclusion, the angiogenesis imaging technology using (68)Ga-labeled RGD derivatives might be useful for the development of new therapeutic assessments, and for diagnostic and theragnostic applications.

68Ga-Chelation and comparative evaluation of N,N'-bis-[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N'-diacetic acid (HBED-CC) conjugated NGR and RGD peptides as tumor targeted molecular imaging probes

Peptides containing RGD and NGR motifs display high affinity towards tumor vasculature molecular markers, integrin α_vβ₃ and CD13 receptors, respectively. In the present study, RGD and NGR peptides were conjugated with the novel acyclic chelator N,N'-bis-[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N'-diacetic acid (HBED-CC) for radiolabeling with ⁶⁸Ga. The radiotracers [⁶⁸Ga-HBED-CC-c(NGR)] and [⁶⁸Ga-HBED-CC-c(RGD)] were quite hydrophilic with respective log P values being -2.8 ± 0.14 and -2.1 ± 0.17. ⁶⁸Ga-HBED-CC-c(RGD) displayed a significantly higher (p < 0.05) uptake in murine melanoma B16F10 tumors as compared to ⁶⁸Ga-HBED-CC-c(NGR) indicating its higher specificity towards integrin α_vβ₃-positive tumors. The two radiotracers showed similar uptake in CD13-positive human fibrosarcoma HT-1080 tumor xenografts (∼1.5 ± 0.2% ID g^-1). The tumor uptake of the two radiotracers was significantly reduced (p < 0.05) in both animal models during blocking studies. The tumor-to-blood ratio was observed to be ∼2-2.5 for the two radiotracers, whereas the tumor-to-muscle ratio was significantly higher (p < 0.005) for ⁶⁸Ga-HBED-CC-c(RGD) in the two animal models. The two radiotracers ⁶⁸Ga-HBED-CC-c(NGR) and ⁶⁸Ga-HBED-CC-c(RGD) exhibited renal excretion with rapid clearance from blood and other non-target organs. Thus, ⁶⁸Ga-chelated HBED-CC conjugated NGR and RGD peptides expressed features conducive towards development as tumor targeted molecular imaging probes. This study further opens avenues for the successful conjugation of different peptides with the acyclic chelator HBED-CC and expansion of ⁶⁸Ga-based radiopharmaceuticals.

Peptide-based imaging agents for cancer detection

Selective receptor-targeting peptide based agents have attracted considerable attention in molecular imaging of tumor cells that overexpress corresponding peptide receptors due to their unique properties such as rapid clearance from circulation as well as high affinities and specificities for their targets. The rapid growth of chemistry modification techniques has enabled the design and development of various peptide-based imaging agents with enhanced metabolic stability, favorable pharmacokinetics, improved binding affinity and selectivity, better imaging ability as well as biosafety. Among them, many radiolabeled peptides have already been translated into the clinic with impressive diagnostic accuracy and sensitivity. This review summarizes the current status in the development of peptide-based imaging agents with an emphasis on the consideration of probe design including the identification of suitable peptides, the chemical modification of probes and the criteria for clinical translation. Specific examples in clinical trials have been provided as well with respect to their diagnostic capability compared with other FDA approved imaging agents.

Preclinical validations of [18F]FPyPEGCBT-c(RGDfK): a 18F-labelled RGD peptide prepared by ligation of 2-cyanobenzothiazole and 1,2-aminothiol to image angiogenesis

Background

α_Vβ₃, α_Vβ₅ and α₅β₁ integrins are known to be involved in carcinogenesis and are overexpressed in many types of tumours compared to healthy tissues; thereby they have been selected as promising therapeutic targets. Positron emission tomography (PET) is providing a unique non-invasive screening assay to discriminate which patient is more prone to benefit from antiangiogenic therapies, and extensive research has been carried out to develop a clinical radiopharmaceutical that binds specifically to integrin receptors. We recently reported the synthesis of a new ¹⁸F-labelled RGD peptide prepared by 2-cyanobenzothiazole (CBT)/1,2-aminothiol conjugation. This study aims at characterising the preclinical biologic properties of this new tumour-targeting ligand, named [¹⁸F]FPyPEGCBT-c(RGDfK).

The in vitro binding properties of [¹⁸F]FPyPEGCBT-c(RGDfK) were analysed by standard binding assay in U-87 MG and SKOV-3 cancer models and its selectivity towards integrins by siRNA depletions. Its preclinical potential was studied in mice bearing subcutaneous tumours by ex vivo biodistribution studies and in vivo microPET/CT imaging.

Results

In vitro, FPyPEGCBT-c(RGDfK) efficiently bound RGD-recognising integrins as compared to a control c(RGDfV) peptide (IC₅₀ = 30.8 × 10⁻⁷ M vs. 6.0 × 10⁻⁷ M). [¹⁸F]FPyPEGCBT-c(RGDfK) cell uptake was mediated by an active transport through binding to α_V, β₃ and β₅ but not to β₁ subunits. In vivo, this new tracer demonstrated specific tumour uptake with %ID/g of 2.9 and 2.4 in U-87 MG and SKOV-3 tumours 1 h post injection. Tumour-to-muscle ratios of 4 were obtained 1 h after intravenous administration of the tracer allowing good visualisation of the tumours. However, unfavourable background accumulation and high hepatobiliary excretion were observed.

Conclusion

[¹⁸F]FPyPEGCBT-c(RGDfK) specifically detects tumours expressing RGD-recognising integrin receptors in preclinical studies. Further optimisation of this radioligand may yield candidates with improved imaging properties and would warrant the further use of this efficient labelling technique for alternative targeting vectors.

Electronic supplementary material

The online version of this article (doi:10.1186/s41181-016-0019-z) contains supplementary material, which is available to authorized users.

Structure-activity relationship study towards non-peptidic positron emission tomography (PET) radiotracer for gastrin releasing peptide receptors: Development of [18F] (S)-3-(1H-indol-3-yl)-N-[1-[5-(2-fluoroethoxy)pyridin-2-yl]cyclohexylmethyl]-2-methyl-2-[3-(4-nitrophenyl)ureido]propionamide

Gastrin-releasing peptide receptors (GRP-Rs, also known as bombesin 2 receptors) are overexpressed in a variety of human cancers, including prostate cancer, and therefore they represent a promising target for in vivo imaging of tumors using positron emission tomography (PET). Structural modifications of the non-peptidic GRP-R antagonist PD-176252 ((S)-1a) led to the identification of the fluorinated analog (S)-3-(1H-indol-3-yl)-N-[1-[5-(2-fluoroethoxy)pyridin-2-yl]cyclohexylmethyl]-2-methyl-2-[3-(4-nitrophenyl)ureido]propionamide ((S)-1m) that showed high affinity and antagonistic properties for GRP-R. This antagonist was stable in rat plasma and towards microsomal oxidative metabolism in vitro. (S)-1m was successfully radiolabeled with fluorine-18 through a conventional radiochemistry procedure. [¹⁸F](S)-1m showed high affinity and displaceable interaction for GRP-Rs in PC3 cells in vitro.

Mechanochemical synthesis of mesoporous tin oxide: a new generation nanosorbent for (68)Ge/(68)Ga generator technology

The present article reports the synthesis and characterization of mesoporous tin oxide (MTO) nanoparticles by a solid-state mechanochemical route. The synthesized material was used as an advanced sorbent material for (68)Ge/(68)Ga radionuclide generator technology. Gallium-68 (t½ = 68 min) obtained from the (68)Ge/(68)Ga generator is an important diagnostic radioisotope which holds tremendous potential in the non-invasive monitoring of various diseases, including cancer, using positron emission tomography (PET). The crystallite size of the MTO nanoparticles was in the range of 6-12 nm with a large surface area of 265 ± 16 m(2) g(-1), while the mean pore radius was found to be 2.1 ± 0.6 nm. Determination of the zeta-potential of the MTO nanoparticles dispersed in solutions at different pH values aided in understanding the sorption and separation mechanisms, which were based on the surface charge developed on the nanosorbent. The sorption capacity observed under column-flow conditions was 85 ± 5 mg Ge per g of nanosorbent. A clinical-scale (68)Ge/(68)Ga generator (740 MBq) was developed using this nanosorbent. Gallium-68 could be regularly eluted from this generator over a prolonged period of 1 year with >70% elution yield and met all the requirements for clinical use. The suitability of (68)Ga obtained from it was evaluated in preclinical settings by the preparation of a (68)Ga-labeled peptide containing the arginine-glycine-aspartic acid (RGD) motif. To the best of our knowledge, this is the first report on the synthesis of MTO nanoparticles by a mechanochemical route which could be effectively utilized for the routine preparation of clinical-scale (68)Ge/(68)Ga generators. The promising results obtained in this study would facilitate greater implementation of mechanochemistry for the synthesis of nanosorbents for radionuclide generator technology since this method is simple, economical and convenient.

Optical imaging probes in oncology

Cancer is a complex disease, characterized by alteration of different physiological molecular processes and cellular features. Keeping this in mind, the possibility of early identification and detection of specific tumor biomarkers by non-invasive approaches could improve early diagnosis and patient management.Different molecular imaging procedures provide powerful tools for detection and non-invasive characterization of oncological lesions. Clinical studies are mainly based on the use of computed tomography, nuclear-based imaging techniques and magnetic resonance imaging. Preclinical imaging in small animal models entails the use of dedicated instruments, and beyond the already cited imaging techniques, it includes also optical imaging studies. Optical imaging strategies are based on the use of luminescent or fluorescent reporter genes or injectable fluorescent or luminescent probes that provide the possibility to study tumor features even by means of fluorescence and luminescence imaging. Currently, most of these probes are used only in animal models, but the possibility of applying some of them also in the clinics is under evaluation.The importance of tumor imaging, the ease of use of optical imaging instruments, the commercial availability of a wide range of probes as well as the continuous description of newly developed probes, demonstrate the significance of these applications. The aim of this review is providing a complete description of the possible optical imaging procedures available for the non-invasive assessment of tumor features in oncological murine models. In particular, the characteristics of both commercially available and newly developed probes will be outlined and discussed.

New Glucocyclic RGD Dimers for Positron Emission Tomography Imaging of Tumor Integrin Receptors

Most studies of radiolabeled arginine-glycine-aspartic acid (RGD) peptides have shown in vitro affinity for integrin ανβ3, allowing for the targeting of receptor-positive tumors in vivo. However, major differences have been found in the pharmacokinetic profiles of different radiolabeled RGD peptide analogs. The purposes of this study were to prepare (64)Cu-DOTA-gluco-E[c(RGDfK)]2 (R8), (64)Cu-NOTA-gluco-E[c(RGDfK)]2 (R9), and (64)Cu-NODAGA-gluco-E[c(RGDfK)]2 (R10) and compare their pharmacokinetics and tumor imaging properties using small-animal positron emission tomography (PET). All three compounds were produced with high specific activity within 10 minutes. The IC50 values were similar for all the substances, and their affinities were greater than that of c(RGDyK). R8, R9, and R10 were stable for 24 hours in human and mouse serums and showed high uptake in U87MG tumors with high tumor-to-blood ratios. Compared to the control, a cyclic RGD peptide dimer without glucosamine, R10, showed low uptake in the liver. Because of their good imaging qualities and improved pharmacokinetics, (64)Cu-labeled dimer RGD conjugates (R8, R9, and R10) may have potential applications as PET radiotracers. R9 (NOTA) with highly in vivo stability consequentially showed an improved PET tumor uptake than R8 (DOTA) or R10 (NODAGA).

[(68)Ga]NODAGA-RGD - Metabolic stability, biodistribution, and dosimetry data from patients with hepatocellular carcinoma and liver cirrhosis

Purpose

This study was designed to determine safety, tolerability, and radiation burden of a [⁶⁸Ga]NODAGA-RGD-PET for imaging integrin α_vβ₃ expression in patients with hepatocellular carcinoma (HCC) and liver cirrhosis. Moreover, metabolic stability and biokinetic data were compiled.

Methods

After injection of 154–184 MBq [⁶⁸Ga]NODAGA-RGD three consecutive PET/CT scans were acquired starting 8.3 ± 2.1, 36.9 ± 2.8, and 75.1 ± 3.4 min after tracer injection. For metabolite analysis, blood and urine samples were analyzed by HPLC. For dosimetry studies, residence time VOIs were placed in the corresponding organs. The OLINDA/EXM program was used to estimate the absorbed radiation dose.

Results

The radiopharmaceutical was well tolerated and no drug-related adverse effects were observed. No metabolites could be detected in blood (30 and 60 min p.i.) and urine (60 min p.i.). [⁶⁸Ga]NODAGA-RGD showed rapid and predominantly renal elimination. Background radioactivity in blood, intestine, lung, and muscle tissue was low (%ID/l 60 min p.i. was 0.56 ± 0.43, 0.54 ± 0.39, 0.22 ± 0.05, and 0.16 ± 0.8, respectively). The calculated effective dose was 21.5 ± 5.4 μSv/MBq, and the highest absorbed radiation dose was found for the urinary bladder wall (0.26 ± 0.09 mSv/MBq). No increased uptake of the tracer was found in HCC compared with the background liver tissue.

Conclusions

[⁶⁸Ga]NODAGA-RGD uptake in the HCCs lesions was not sufficient to use this tracer for imaging these tumors. [⁶⁸Ga]NODAGA-RGD was well tolerated and metabolically stable. Due to rapid renal excretion, background radioactivity was low in most of the body, resulting in low radiation burden and indicating the potential of [⁶⁸Ga]NODAGA-RGD PET for non-invasive determination of integrin α_vβ₃ expression.

Ultrasmall inorganic nanoparticles: State-of-the-art and perspectives for biomedical applications

Ultrasmall nanoparticulate materials with core sizes in the 1-3nm range bridge the gap between single molecules and classical, larger-sized nanomaterials, not only in terms of spatial dimension, but also as regards physicochemical and pharmacokinetic properties. Due to these unique properties, ultrasmall nanoparticles appear to be promising materials for nanomedicinal applications. This review overviews the different synthetic methods of inorganic ultrasmall nanoparticles as well as their properties, characterization, surface modification and toxicity. We moreover summarize the current state of knowledge regarding pharmacokinetics, biodistribution and targeting of nanoscale materials. Aside from addressing the issue of biomolecular corona formation and elaborating on the interactions of ultrasmall nanoparticles with individual cells, we discuss the potential diagnostic, therapeutic and theranostic applications of ultrasmall nanoparticles in the emerging field of nanomedicine in the final part of this review.

68Gallium-Arginine-Glycine-Aspartic Acid and 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in Chondroblastic Osteosarcoma of the Skull

We report the case of a 32 year-old male with Chondroblastic Osteosarcoma of the skull, which was imaged with both ¹⁸[F]fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) and ⁶⁸Gallium-arginine-glycine-aspartic acid (⁶⁸Ga-RGD) PET/CT. The ¹⁸F-FDG PET/CT did not demonstrate the tumour, whereas the ⁶⁸Ga-RGD PET/CT clearly depicted a left-sided frontal tumour. ⁶⁸Ga-RGD PET/CT may be a clinically useful imaging modality for early detection of recurrent osteosarcoma, considering the limitations of ¹⁸F-FDG PET in a setting of low glycolytic activity.

Detailed evaluation of different (68)Ge/(68)Ga generators: an attempt toward achieving efficient (68)Ga radiopharmacy

The present study is aimed at carrying out a comparative performance evaluation of different types of (68)Ge/(68)Ga generators to identify the best choice for use in (68)Ga-radiopharmacy. Over the 1 year period of evaluation, the elution yields from the CeO2-based and SiO2-based (68)Ge/(68) Ga generators remained almost consistent, in contrast to the sharp decrease observed in the elution yields from TiO2 and SnO2-based generators. The level of (68)Ge impurity in (68)Ga eluates from the CeO2 and SiO2-based (68)Ge/(68)Ga generator was always <10(-3)%, while this level increased from 10(-3)% to 10(-1)% in case of TiO2 and SnO2-based generators. The level of chemical impurities in (68)Ga eluates from CeO2 and SiO2-based (68)Ge/(68)Ga generators was negligibly low (<0.1 ppm) in contrast to the significantly higher level (1-20 ppm) of such impurities in eluates from other two generators. As demonstrated by radiolabeling studies carried out using DOTA-coupled dimeric cyclic RGD peptide derivative (DOTA-RGD2), CeO2-PAN and SiO2-based generators are directly amenable for radiopharmaceutical preparation, whereas the other generators can be only used after post-elution purification of (68)Ga eluates. Clinically relevant dose of (68)Ga-DOTA-RGD2 was prepared in a hospital radiopharmacy for non-invasive visualization of tumors in breast cancer patients using positron emission tomography.

(18)F-Alfatide II PET/CT in healthy human volunteers and patients with brain metastases

PURPOSE

We report the biodistribution and radiation dosimetry of an integrin αvβ3 specific PET tracer (18)F-AlF-NOTA-E[PEG4-c(RGDfk)]2) (denoted as (18)F-Alfatide II). We also assessed the value of (18)F-Alfatide II in patients with brain metastases.

METHODS

A series of torso (from the skull to the thigh) static images were acquired in five healthy volunteers (3 M, 2 F) at 5, 10, 15, 30, 45, and 60 min after injection of (18)F-Alfatide II (257 ± 48 MBq). Regions of interest (ROIs) were drawn manually, and the time-activity curves (TACs) were obtained for major organs. Nine patients with brain metastases were examined by static PET imaging with (18)F-FDG (5.55 MBq/kg) and (18)F-Alfatide II.

RESULTS

Injection of (18)F-Alfatide II was well tolerated in all healthy volunteers, with no serious tracer-related adverse events found. (18)F-Alfatide II showed rapid clearance from the blood pool and kidneys. The total effective dose equivalent (EDE) and effective dose (ED) were 0.0277 ± 0.003 mSv/MBq and 0.0198 ± 0.002 mSv/MBq, respectively. The organs with the highest absorbed dose were the kidneys and the spleen. Nine patients with 20 brain metastatic lesions identified by MRI and/or CT were enrolled in this study. All 20 brain lesions were visualized by (18)F-Alfatide II PET, while only ten lesions were visualized by (18)F-FDG, and 13 by CT.

CONCLUSION

F-Alfatide II is a safe PET tracer with a favorable dosimetry profile. The observed ED suggests that (18)F-Alfatide II is feasible for human studies. (18)F-Alfatide II has potential value in finding brain metastases of different cancers as a biomarker of angiogenesis.

Toward realization of 'mix-and-use' approach in ⁶⁸Ga radiopharmacy: preparation, evaluation and preliminary clinical utilization of ⁶⁸Ga-labeled NODAGA-coupled RGD peptide derivative

INTRODUCTION

The present article demonstrates a 'mix-and-use' approach for radiolabeling RGD peptide derivative with (68)Ga, which is easily adaptable in hospital radiopharmacy practice. The radiotracer thus formulated was successfully used for positron emission tomography (PET) imaging of breast cancer in human patients.

METHODS

The conditions for radiolabeling NODAGA-coupled dimeric cyclic RGD peptide derivative [NODAGA-(RGD)2] with (68)Ga were optimized using (68)Ga obtained from a (68)Ge/(68)Ga generator developed in-house with CeO2-PAN composite sorbent as well as from a commercial (68)Ge/(68)Ga generator obtained from ITG, Germany. Preclinical studies were carried out in C57BL/6 mice bearing melanoma tumors. The radiotracer was prepared in a hospital radiopharmacy using (68)Ga obtained from ITG generator and used for monitoring breast cancer patients by positron emission tomography (PET) imaging.

RESULTS

(68)Ga-NODAGA-(RGD)2 could be prepared with high radiolabeling yield (>98%) and specific activity (~50 GBq/μmol) within 10 min at room temperature by mixing (68)Ga with the solution of the peptide conjugate. In vivo biodistribution studies showed significant uptake (5.24±0.39% ID/g) in melanoma tumor at 30 min post-injection, with high tumor-to-background contrast. The integrin αvβ3 specificity of the tracer was corroborated by blocking study. Preliminary clinical studies in locally advanced breast cancer (LABC) patients indicated specifically high tumor uptake (SUVmax 10-15) with good contrast.

CONCLUSIONS

This is one of the very few reports which presents preliminary clinical data on use of (68)Ga-NODAGA-(RGD)2 and the developed 'mix-and-use' holds tremendous prospect in clinical PET imaging using (68)Ga.

Integration of imaging into clinical practice to assess the delivery and performance of macromolecular and nanotechnology-based oncology therapies

Functional and molecular imaging has become increasingly used to evaluate interpatient and intrapatient tumor heterogeneity. Imaging allows for assessment of microenvironment parameters including tumor hypoxia, perfusion and proliferation, as well as tumor metabolism and the intratumoral distribution of specific molecular markers. Imaging information may be used to stratify patients for targeted therapies, and to define patient populations that may benefit from alternative therapeutic approaches. It also provides a method for non-invasive monitoring of treatment response at earlier time-points than traditional cues, such as tumor shrinkage. Further, companion diagnostic imaging techniques are becoming progressively more important for development and clinical implementation of targeted therapies. Imaging-based companion diagnostics are likely to be essential for the validation and FDA approval of targeted nanotherapies and macromolecular medicines. This review describes recent clinical advances in the use of functional and molecular imaging to evaluate the tumor microenvironment. Additionally, this article focuses on image-based assessment of distribution and anti-tumor effect of nano- and macromolecular systems.