[18F]galacto-RGD positron emission tomography for imaging of alphavbeta3 expression on the neovasculature in patients with squamous cell carcinoma of the head and neck

Integrin Targeting and Beyond: Enhancing Cancer Treatment with Dual-Targeting RGD (Arginine-Glycine-Aspartate) Strategies

Integrins, an important superfamily of cell adhesion receptors, play an essential role in cancer progression, metastasis, and angiogenesis, establishing them as prime targets for both diagnostic and therapeutic applications. Despite their significant potential, integrin-targeted therapies have faced substantial challenges in clinical trials, including variable efficacy and unmet high expectations. Nevertheless, the consistent expression of integrins on tumor and stromal cells underscores their ongoing relevance and potential. Traditional RGD-based imaging and therapeutic agents have faced limitations, such as inconsistent target expression and rapid systemic clearance, which have reduced their effectiveness. To overcome these challenges, recent research has focused on advancing RGD-based strategies and exploring innovative solutions. This review offers a thorough analysis of the latest developments in the RGD-integrin field, with a particular focus on addressing previous limitations. It delves into new dual-targeting approaches and cutting-edge RGD-based agents designed to improve both tumor diagnosis and therapeutic outcomes. By examining these advancements, this review illuminates new pathways for enhancing the specificity and efficacy of integrin-targeted therapies, paving the way for more effective cancer diagnosis and treatment strategies.

Emerging Head and Neck Tumor Targeting Contrast Agents for the Purpose of CT, MRI, and Multimodal Diagnostic Imaging: A Molecular Review

BACKGROUND

The diagnosis and treatment of head and neck tumors present significant challenges due to their infiltrative nature and diagnostic hindrances such as the blood-brain barrier. The intricate anatomy of the head and neck region also complicates the clear identification of tumor boundaries and assessment of tumor characteristics.

AIM

This review aims to explore the efficacy of molecular imaging techniques that employ targeted contrast agents in head and neck cancer imaging. Head and neck cancer imaging benefits significantly from the combined advantages of CT and MRI. CT excels in providing swift, high-contrast images, enabling the accurate localization of tumors, while MRI offers superior soft tissue resolution, contributing to the detailed evaluation of tumor morphology in this region of the body. Many of these novel contrast agents have integration of dual-modal, triple-modal, or even dual-tissue targeting imaging, which have expanded the horizons of molecular imaging. Emerging contrast agents for the purpose of MRI and CT also include the widely used standards in imaging such as gadolinium and iodine-based agents, respectively, but with peptide, polypeptide, or polymeric functionalizations. Relevance for patients. For patients, the development and use of these targeted contrast agents have potentially significant implications. They benefit from the enhanced accuracy of tumor detection and characterization, which are critical for effective treatment planning. Additionally, these agents offer improved imaging contrast with the added benefit of reduced toxicity and bioaccumulation. The summarization of preclinical nanoparticle research in this review serves as a valuable resource for scientists and students working towards advancing tumor diagnosis and treatment with targeted contrast agents.

18F-alfatide II internal dosimetry using the ICRP 110 adult reference phantoms and the ICRP 103 tissue weighting factors

PURPOSE

¹⁸F-alfatide II is an arginine-glycine-aspartate (RGD) peptide-based PET tracer with promising imaging properties and pharmacokinetics. This study aims to calculate the absorbed and effective doses of ¹⁸F-alfatide II using the ICRP 110 adult reference phantoms and the ICRP 103 tissue weighting factors.

METHODS

The MIRD method was used in this study to calculate the absorbed dose of organs and tissues. The biokinetic data were taken from a previous study. These data are based on the whole-body PET imaging of mice.

RESULTS

The results show that the effective dose per unit activity administered of ¹⁸F-alfatide II is 1.33E-02 mSv/MBq. The urinary bladder wall receives the highest absorbed dose due to the administration of this radiopharmaceutical. Also, the effective dose of ¹⁸F-alfatide II is lower than that of ¹⁸F-FDG and some other RGD peptide-based tracers.

CONCLUSIONS

Dose calculation using ICRP 110 voxelized adult reference phantoms and ICRP 103 tissue weighting factors leads to more realistic and accurate results for 18F-alfatide II compared to the stylized phantoms. The calculated effective dose of ¹⁸F-alfatide II in the present study is lower than that of previously published data.

Improved Boron Neutron Capture Therapy Using Integrin αvβ3-Targeted Long-Retention-Type Boron Carrier in a F98 Rat Glioma Model

Integrin αvβ3 is more highly expressed in high-grade glioma cells than in normal tissues. In this study, a novel boron-10 carrier containing maleimide-functionalized closo-dodecaborate (MID), serum albumin as a drug delivery system, and cyclic arginine-glycine-aspartate (cRGD) that can target integrin αvβ3 was developed. The efficacy of boron neutron capture therapy (BNCT) targeting integrin αvβ3 in glioma cells in the brain of rats using a cRGD-functionalized MID-albumin conjugate (cRGD-MID-AC) was evaluated. F98 glioma cells exposed to boronophenylalanine (BPA), cRGD-MID-AC, and cRGD + MID were used for cellular uptake and neutron-irradiation experiments. An F98 glioma-bearing rat brain tumor model was used for biodistribution and neutron-irradiation experiments after BPA or cRGD-MID-AC administration. BNCT using cRGD-MID-AC had a sufficient cell-killing effect in vitro, similar to that with BNCT using BPA. In biodistribution experiments, cRGD-MID-AC accumulated in the brain tumor, with the highest boron concentration observed 8 h after administration. Significant differences were observed between the untreated group and BNCT using cRGD-MID-AC groups in the in vivo neutron-irradiation experiments through the log-rank test. Long-term survivors were observed only in BNCT using cRGD-MID-AC groups 8 h after intravenous administration. These findings suggest that BNCT with cRGD-MID-AC is highly selective against gliomas through a mechanism that is different from that of BNCT with BPA.

Skin Cancer Pathobiology at a Glance: A Focus on Imaging Techniques and Their Potential for Improved Diagnosis and Surveillance in Clinical Cohorts

Early diagnosis is essential for completely eradicating skin cancer and maximizing patients' clinical benefits. Emerging optical imaging modalities such as reflectance confocal microscopy (RCM), optical coherence tomography (OCT), magnetic resonance imaging (MRI), near-infrared (NIR) bioimaging, positron emission tomography (PET), and their combinations provide non-invasive imaging data that may help in the early detection of cutaneous tumors and surgical planning. Hence, they seem appropriate for observing dynamic processes such as blood flow, immune cell activation, and tumor energy metabolism, which may be relevant for disease evolution. This review discusses the latest technological and methodological advances in imaging techniques that may be applied for skin cancer detection and monitoring. In the first instance, we will describe the principle and prospective clinical applications of the most commonly used imaging techniques, highlighting the challenges and opportunities of their implementation in the clinical setting. We will also highlight how imaging techniques may complement the molecular and histological approaches in sharpening the non-invasive skin characterization, laying the ground for more personalized approaches in skin cancer patients.

Advanced Techniques in Head and Neck Cancer Imaging: Guide to Precision Cancer Management

Precision treatment requires precision imaging. With the advent of various advanced techniques in head and neck cancer treatment, imaging has become an integral part of the multidisciplinary approach to head and neck cancer care from diagnosis to staging and also plays a vital role in response evaluation in various tumors. Conventional anatomic imaging (CT scan, MRI, ultrasound) remains basic and focuses on defining the anatomical extent of the disease and its spread. Accurate assessment of the biological behavior of tumors, including tumor cellularity, growth, and response evaluation, is evolving with recent advances in molecular, functional, and hybrid/multiplex imaging. Integration of these various advanced diagnostic imaging and nonimaging methods aids understanding of cancer pathophysiology and provides a more comprehensive evaluation in this era of precision treatment. Here we discuss the current status of various advanced imaging techniques and their applications in head and neck cancer imaging.

Personalized Targeted Therapeutic Strategies against Oral Squamous Cell Carcinoma. An Evidence-Based Review of Literature

Oral squamous cell carcinoma (OSCC) is the most common type of malignant tumor in the head and neck, with a poor prognosis mainly due to recurrence and metastasis. Classical treatment modalities for OSCC like surgery and radiotherapy have difficulties in dealing with metastatic tumors, and together with chemotherapy, they have major problems related to non-specific cell death. Molecular targeted therapies offer solutions to these problems through not only potentially maximizing the anticancer efficacy but also minimizing the treatment-related toxicity. Among them, the receptor-mediated targeted delivery of anticancer therapeutics remains the most promising one. As OSCC exhibits a heterogeneous nature, selecting the appropriate receptors for targeting is the prerequisite. Hence, we reviewed the OSCC-associated receptors previously used in targeted therapy, focused on their biochemical characteristics and expression patterns, and discussed the application potential in personalized targeted therapy of OSCC. We hope that a better comprehension of this subject will help to provide the fundamental information for OSCC personalized therapeutic planning.

Advances in nuclear medicine-based molecular imaging in head and neck squamous cell carcinoma

Head and neck squamous cell carcinomas (HNSCCs) are often aggressive, making advanced disease very difficult to treat using contemporary modalities, such as surgery, radiation therapy, and chemotherapy. However, targeted therapy, e.g., cetuximab, an epidermal growth factor receptor inhibitor, has demonstrated survival benefit in HNSCC patients with locoregional failure or distant metastasis. Molecular imaging aims at various biomarkers used in targeted therapy, and nuclear medicine-based molecular imaging is a real-time and non-invasive modality with the potential to identify tumor in an earlier and more treatable stage, before anatomic-based imaging reveals diseases. The objective of this comprehensive review is to summarize recent advances in nuclear medicine-based molecular imaging for HNSCC focusing on several commonly radiolabeled biomarkers. The preclinical and clinical applications of these candidate imaging strategies are divided into three categories: those targeting tumor cells, tumor microenvironment, and tumor angiogenesis. This review endeavors to expand the knowledge of molecular biology of HNSCC and help realizing diagnostic potential of molecular imaging in clinical nuclear medicine.

Investigational PET tracers in neuro-oncology-What's on the horizon? A report of the PET/RANO group

Many studies in patients with brain tumors evaluating innovative PET tracers have been published in recent years, and the initial results are promising. Here, the Response Assessment in Neuro-Oncology (RANO) PET working group provides an overview of the literature on novel investigational PET tracers for brain tumor patients. Furthermore, newer indications of more established PET tracers for the evaluation of glucose metabolism, amino acid transport, hypoxia, cell proliferation, and others are also discussed. Based on the preliminary findings, these novel investigational PET tracers should be further evaluated considering their promising potential. In particular, novel PET probes for imaging of translocator protein and somatostatin receptor overexpression as well as for immune system reactions appear to be of additional clinical value for tumor delineation and therapy monitoring. Progress in developing these radiotracers may contribute to improving brain tumor diagnostics and advancing clinical translational research.

Preliminary Clinical Application of RGD-Containing Peptides as PET Radiotracers for Imaging Tumors

Angiogenesis is a common feature of many physiological processes and pathological conditions. RGD-containing peptides can strongly bind to integrin αvβ3 expressed on endothelial cells in neovessels and several tumor cells with high specificity, making them promising molecular agents for imaging angiogenesis. Although studies of RGD-containing peptides combined with radionuclides, namely, 18F, 64Cu, and 68Ga for positron emission tomography (PET) imaging have shown high spatial resolution and accurate quantification of tracer uptake, only a few of these radiotracers have been successfully translated into clinical use. This review summarizes the RGD-based tracers in terms of accumulation in tumors and adjacent tissues, and comparison with traditional 18F-fluorodeoxyglucose (FDG) imaging. The value of RGD-based tracers for diagnosis, differential diagnosis, tumor subvolume delineation, and therapeutic response prediction is mainly discussed. Very low RGD accumulation, in contrast to high FDG metabolism, was found in normal brain tissue, indicating that RGD-based imaging provides an excellent tumor-to-background ratio for improved brain tumor imaging. However, the intensity of the RGD-based tracers is much higher than FDG in normal liver tissue, which could lead to underestimation of primary or metastatic lesions in liver. In multiple studies, RGD-based imaging successfully realized the diagnosis and differential diagnosis of solid tumors and also the prediction of chemoradiotherapy response, providing complementary rather than similar information relative to FDG imaging. Of most interest, baseline RGD uptake values can not only be used to predict the tumor efficacy of antiangiogenic therapy, but also to monitor the occurrence of adverse events in normal organs. This unique dual predictive value in antiangiogenic therapy may be better than that of FDG-based imaging.

Single-Molecule Force Probing of RGD-Binding Integrins on Pancreatic Cancer Cells

Integrin-targeting arginine-glycine-aspartic acid (RGD)-based nanocarriers have been widely used for tumor imaging, monitoring of tumor development, and delivery of anticancer drugs. However, the thermodynamics of an RGD-integrin formation and dissociation associated with binding dynamics, affinity, and stability remains unclear. Here, we probed the binding strength of the binary complex to live pancreatic cancer cells using single-molecule binding force spectroscopy methods, in which RGD peptides were functionalized on a force probe tip through poly(ethylene glycol) (PEG)-based bifunctional linker molecules. While the density of integrin α_V receptors on the cell surface varies more than twofold from cell line to cell line, the individual RGD-integrin complexes exhibited a cell type-independent, monovalent bond strength. The load-dependent bond strength of multivalent RGD-integrin interactions scaled sublinearly with increasing bond number, consistent with the noncooperative, parallel bond model. Furthermore, the multivalent bonds ruptured sequentially either by one or in multiples, and the force strength was comparable to the synchronous rupture force. Comparison of energy landscapes of the bond number revealed a substantial decrease of kinetic off-rates for multivalent bonds, along with the increased width of the potential well and the increased potential barrier height between bound and unbound states, enhancing the stability of the multivalent bonds between them.

Clinical evaluation of kit based Tc-99m-HYNIC-RGD2 for imaging angiogenesis in breast carcinoma patients

BACKGROUND

Radiolabeled RGD peptide can be used for noninvasive in vivo imaging of αvβ3 integrin receptors leading to early detection of tumor cells and hence improving the clinical outcomes. In the present study single vial kit based HYNIC RGD2 was radiolabeled with Tc-99m and evaluated in patients with breast carcinoma.

METHODS

Radiolabeling was performed via bifunctional chelator method. Tc-99m 1110-2960 MBq (30-80 mCi) was added to the HYNIC-RGD2 vial. The reaction mixture was heated for 20 minutes at 100°C. After performing the quality checks, whole-body planar imaging was performed in 20 patients at 2-2.5 h post i.v. injection of 555-740 MBq (15-20 mCi) of the radiotracer.

RESULTS

Radiolabeling yield of ≥98% was observed in all the formulations. Quality control tests indicated the suitability of radiopharmaceutical for intravenous administration. Physiological uptake of Tc-99m HYNIC-RGD2 was observed in the nasopharynx, salivary glands, liver, spleen, and intestine. Good uptake of radiotracer was observed in breast lesions of 18 patients. Two patients were observed to be negative. Increased uptake was also seen in metastatic sites in two patients and in lymph nodes in three patients. Scintigraphy findings were in corroboration with pathological observations.

CONCLUSION

The single vial cold kit based radiolabeling of Tc-99m HYNIC-RGD2 is facile leading to its easy availability. Tc-99m HYNIC-RGD2 is a promising radiopharmaceutical which can be used for the molecular imaging of angiogenesis in breast carcinoma patients.

Imaging methods to evaluate tumor microenvironment factors affecting nanoparticle drug delivery and antitumor response

Standard small molecule and nanoparticulate chemotherapies are used for cancer treatment; however, their effectiveness remains highly variable. One reason for this variable response is hypothesized to be due to nonspecific drug distribution and heterogeneity of the tumor microenvironment, which affect tumor delivery of the agents. Nanoparticle drugs have many theoretical advantages, but due to variability in tumor microenvironment (TME) factors, the overall drug delivery to tumors and associated antitumor response are low. The nanotechnology field would greatly benefit from a thorough analysis of the TME factors that create these physiological barriers to tumor delivery and treatment in preclinical models and in patients. Thus, there is a need to develop methods that can be used to reveal the content of the TME, determine how these TME factors affect drug delivery, and modulate TME factors to increase the tumor delivery and efficacy of nanoparticles. In this review, we will discuss TME factors involved in drug delivery, and how biomedical imaging tools can be used to evaluate tumor barriers and predict drug delivery to tumors and antitumor response.

Molecular Imaging and Preclinical Studies of Radiolabeled Long-Term RGD Peptides in U-87 MG Tumor-Bearing Mice

The Arg–Gly–Asp (RGD) peptide shows a high affinity for α_vβ₃ integrin, which is overexpressed in new tumor blood vessels and many types of tumor cells. The radiolabeled RGD peptide has been studied for cancer imaging and radionuclide therapy. We have developed a long-term tumor-targeting peptide DOTA-EB-cRGDfK, which combines a DOTA chelator, a truncated Evans blue dye (EB), a modified linker, and cRGDfK peptide. The aim of this study was to evaluate the potential of indium-111(¹¹¹In) radiolabeled DOTA-EB-cRGDfK in α_vβ₃ integrin-expressing tumors. The human glioblastoma cell line U-87 MG was used to determine the in vitro binding affinity of the radiolabeled peptide. The in vivo distribution of radiolabeled peptides in U-87 MG xenografts was investigated by biodistribution, nanoSPECT/CT, pharmacokinetic and excretion studies. The in vitro competition assay showed that ¹¹¹In-DOTA-EB-cRGDfK had a significant binding affinity to U-87 MG cancer cells (IC₅₀ = 71.7 nM). NanoSPECT/CT imaging showed ¹¹¹In-DOTA-EB-cRGDfK has higher tumor uptake than control peptides (¹¹¹In-DOTA-cRGDfK and ¹¹¹In-DOTA-EB), and there is still a clear signal until 72 h after injection. The biodistribution results showed significant tumor accumulation (27.1 ± 2.7% ID/g) and the tumor to non-tumor ratio was 22.85 at 24 h after injection. In addition, the pharmacokinetics results indicated that the ¹¹¹In-DOTA-EB-cRGDfK peptide has a long-term half-life (T_1/2λz = 77.3 h) and that the calculated absorbed dose was safe for humans. We demonstrated that radiolabeled DOTA-EB-cRGDfK may be a promising agent for glioblastoma tumor imaging and has the potential as a theranostic radiopharmaceutical.

Targeted molecular imaging of head and neck squamous cell carcinoma: a window into precision medicine

Tumor biomarkers play important roles in tumor growth, invasion, and metastasis. Imaging of specific biomarkers will help to understand different biological activities, thereby achieving precise medicine for each head and neck squamous cell carcinoma (HNSCC) patient. Here, we describe various molecular targets and molecular imaging modalities for HNSCC imaging. An extensive search was undertaken in the PubMed database with the keywords including “HNSCC,” “molecular imaging,” “biomarker,” and “multimodal imaging.” Imaging targets in HNSCC consist of the epidermal growth factor receptor, cluster of differentiation 44 variant 6 (CD44v6), and mesenchymal-epithelial transition factor and integrins. Targeted molecular imaging modalities in HNSCC include optical imaging, ultrasound, magnetic resonance imaging, positron emission tomography, and single-photon emission computed tomography. Making the most of each single imaging method, targeted multimodal imaging has a great potential in the accurate diagnosis and therapy of HNSCC. By visualizing tumor biomarkers at cellular and molecular levels in vivo, targeted molecular imaging can be used to identify specific genetic and metabolic aberrations, thereby accelerating personalized treatment development for HNSCC patients.

Multiparametric PET and MRI of myocardial damage after myocardial infarction: correlation of integrin αvβ3 expression and myocardial blood flow

PURPOSE

Increased angiogenesis after myocardial infarction is considered an important favorable prognostic parameter. The αvβ3 integrin is a key mediator of cell-cell and cell-matrix interactions and an important molecular target for imaging of neovasculature and repair processes after MI. Thus, imaging of αvβ3 expression might provide a novel biomarker for assessment of myocardial angiogenesis as a prognostic marker of left ventricular remodeling after MI. Currently, there is limited data available regarding the association of myocardial blood flow and αvβ3 integrin expression after myocardial infarction in humans.

METHODS

Twelve patients were examined 31 ± 14 days after MI with PET/CT using [18F]Galacto-RGD and [13N]NH3 and with cardiac MRI including late enhancement on the same day. Normal myocardium (remote) and areas of infarction (lesion) were identified on the [18F]Galacto-RGD PET/CT images by correlation with [13N]NH3 PET and cardiac MRI. Lesion/liver-, lesion/blood-, and lesion/remote ratios were calculated. Blood flow and [18F]Galacto-RGD uptake were quantified and correlated for each myocardial segment (AHA 17-segment model).

RESULTS

In 5 patients, increased [18F]Galacto-RGD uptake was notable within or adjacent to the infarction areas with a lesion/remote ratio of 46% (26-83%; lesion/blood 1.15 ± 0.06; lesion/liver 0.61 ± 0.18). [18F]Galacto-RGD uptake correlated significantly with infarct size (R = 0.73; p = 0.016). Moreover, it correlated significantly with restricted blood flow for all myocardial segments (R = - 0.39; p < 0.0001) and even stronger in severely hypoperfused areas (R = - 0.75; p < 0.0001).

CONCLUSION

[18F]Galacto-RGD PET/CT allows the visualization and quantification of myocardial αvβ3 expression as a key player in angiogenesis in a subset of patients after MI. αvβ3 expression was more pronounced in patients with larger infarcts and was generally more intense but not restricted to areas with more impaired blood flow, proving that tracer uptake was largely independent of unspecific perfusion effects. Based on these promising results, larger prospective studies are warranted to evaluate the potential of αvβ3 imaging for assessment of myocardial angiogenesis and prediction of ventricular remodeling.

Head and neck tumors angiogenesis imaging with 68Ga-NODAGA-RGD in comparison to 18F-FDG PET/CT: a pilot study

Background

Angiogenesis plays an important role in head and neck squamous cell carcinoma (HNSCC) progression. This pilot study was designed to compare the distribution of ⁶⁸Ga-NODAGA-RGD PET/CT for imaging α_vβ₃ integrins involved in tumor angiogenesis to ¹⁸F-FDG PET/CT in patients with HNSCC.

Material and methods

Ten patients (aged 58.4 ± 8.3 years [range, 44–73 years], 6 males, 4 females) with a total of 11 HNSCC were prospectively enrolled. Activity mapping and standard uptake values (SUV) from both ⁶⁸Ga-NODAGA-RGD and ¹⁸F-FDG PET/CT scans were recorded for primary tumor and compared with the Wilcoxon signed-rank test. The relation between the SUV of both tracers was assessed using the Spearman correlation.

Results

All HNSCC tumors were visible with both tracers. Quantitative analysis showed higher ¹⁸F-FDG SUV_max in comparison to ⁶⁸Ga-NODAGA-RGD (14.0 ± 6.1 versus 3.9 ± 1.1 g/mL, p = 0.0017) and SUV_mean (8.2 ± 3.1 versus 2.0 ± 0.8 g/mL, p = 0.0017). Both ¹⁸F-FDG and ⁶⁸Ga-NODAGA-RGD uptakes were neither correlated with grade, HPV status nor p16 protein expression (p ≥ 0.17).

Conclusion

All HNSCC tumors were detected with both tracers with higher uptake with ¹⁸F-FDG, however. ⁶⁸Ga-NODAGA-RGD has a different spatial distribution than ¹⁸F-FDG bringing different tumor information.

Trial registration

NCT, NCT02666547. Registered 12.8.2012.

[18F]Fluciclatide PET as a biomarker of response to combination therapy of pazopanib and paclitaxel in platinum-resistant/refractory ovarian cancer

BACKGROUND

Angiogenesis is a driver of platinum resistance in ovarian cancer. We assessed the effect of combination pazopanib and paclitaxel followed by maintenance pazopanib in patients with platinum-resistant/refractory ovarian cancer. Integrins αvβ3 and αvβ5 are both upregulated in tumor-associated vasculature. [18F]Fluciclatide is a novel PET tracer that has high affinity for integrins αvβ3/5, and was used to assess the anti-angiogenic effect of pazopanib.

PATIENTS AND METHODS

We conducted an open-label, phase Ib study in patients with platinum-resistant/refractory ovarian cancer. Patients received 1 week of single-agent pazopanib (800 mg daily) followed by combination therapy with weekly paclitaxel (80 mg/m2). Following completion of 18 weeks of combination therapy, patients continued with single-agent pazopanib until disease progression. Dynamic [18F]fluciclatide-PET imaging was conducted at baseline and after 1 week of pazopanib. Response (RECIST 1.1), toxicities, and survival outcomes were recorded. Circulating markers of angiogenesis were assessed with therapy.

RESULTS

Fourteen patients were included in the intention-to-treat analysis. Complete and partial responses were seen in seven patients (54%). Median progression-free survival (PFS) was 10.63 months, and overall survival (OS) was 18.5 months. Baseline [18F]fluciclatide uptake was predictive of long PFS. Elevated baseline circulating angiopoietin and fibroblast growth factor (FGF) were predictive of greater reduction in SUV60,mean following pazopanib. Kinetic modeling of PET data indicated a reduction in K1 and Ki following pazopanib indicating reduced radioligand delivery and retention.

CONCLUSIONS

Combination therapy followed by maintenance pazopanib is effective and tolerable in platinum-resistant/refractory ovarian cancer. [18F]Fluciclatide-PET uptake parameters predict clinical outcome with pazopanib therapy indicating an anti-angiogenic response.

Imaging angiogenesis in patients with head and neck squamous cell carcinomas by [68Ga]Ga-DOTA-E-[c(RGDfK)]2 PET/CT

Purpose

Angiogenesis plays an important role in the growth and metastatic spread of solid tumours and is characterised by the expression of integrins on the cell surface of endothelial cells. Radiolabelled RGD peptides specifically target angiogenesis-related α_vβ₃ integrins, expressed on the activated endothelial cells of sprouting blood vessels. Here, we validated the feasibility of ⁶⁸Ga[Ga]-DOTA-E-[c(RGDfK)]₂ (⁶⁸Ga-RGD) PET/CT to visualise angiogenesis in patients with oral squamous cell carcinoma (OSCC).

Methods

Ten patients with OSCC and scheduled for surgical resection including elective neck dissection received an intravenously administration of ⁶⁸Ga-RGD (42 ± 8 μg; 214 ± 9 MBq). All patients subsequently underwent dynamic (n = 5) or static PET/CT imaging (n = 5) for 60 min or for 4 min/bed position at 30, 60 and 90 min after injection, respectively. Quantitative tracer uptake in tumour lesions was expressed as standardised uptake values (SUV). Additionally, tumour tissue was immunohistochemically stained for α_vβ₃ integrin to assess the expression pattern.

Results

⁶⁸Ga-RGD tumour accumulation was observed in all patients. At 60 min post injection, tumour SUV_max ranged between 4.0 and 12.7. Tracer accumulation in tumour tissue plateaued at 10 min after injection. Uptake in background tissue did not change over time, resulting in tumour-to-muscle tissue of 6.4 ± 0.7 at 60 min post injection.

Conclusions

⁶⁸Ga-RGD PET/CT of α_vβ₃ integrin expression in OSCC patients is feasible with adequate tumour-to-background ratios. It will provide more insight in angiogenesis as a hallmark of the head and neck squamous cell carcinomas’ tumour microenvironment.

Trial registration

https://eudract.ema.europa.eu no. 2015-000917-31

Electronic supplementary material

The online version of this article (10.1007/s00259-020-04766-2) contains supplementary material, which is available to authorized users.

Radiolabelled Peptides for Positron Emission Tomography and Endoradiotherapy in Oncology

This review deals with the development of peptide-based radiopharmaceuticals for the use with positron emission tomography and peptide receptor radiotherapy. It discusses the pros and cons of this class of radiopharmaceuticals as well as the different labelling strategies, and summarises approaches to optimise metabolic stability. Additionally, it presents different target structures and addresses corresponding tracers, which are already used in clinical routine or are being investigated in clinical trials.

Diagnostic and Predictive Value of Using RGD PET/CT in Patients with Cancer: A Systematic Review and Meta-Analysis

The purpose of this study was to assess the diagnostic value of arginine-glycine-aspartic acid (RGD) PET/CT for tumor detection in patients with suspected malignant lesions and to determine the predictive performance of RGD PET/CT in identifying responders. Methods. The PubMed (Medline), EMBASE, Cochrane Library, and Web of Science databases were systematically searched for potentially relevant publications (last updated on July 28th, 2018) reporting the performance of RGD PET in the field of oncology. Pooled sensitivities, specificities, and diagnostic odds ratios (DORs) were calculated for parameters. The areas under the curve (AUCs) and Q⁎ index scores were determined from the constructed summary receiver operating characteristic (SROC) curve. We explored heterogeneity by metaregression. Results. Nine studies, five including 216 patients that determined diagnostic performance and three including 75 patients that determined the predictive value of parameters, met our inclusion criteria. The pooled sensitivity, pooled specificity, DOR, AUC, and Q⁎ index score of RGD PET/CT for the detection of underlying malignancy were 0.85 (0.79-0.89), 0.93 (0.90-0.96), 48.35 (18.95-123.33), 0.9262 (standard error=0.0216), and 0.8606 for SUVmax and 0.86 (0.80-0.91), 0.92 (0.88-0.94), 40.49 (14.16-115.77), 0.9312 (SE=0.0177), and 0.8665 for SUVmean, respectively. The pooled sensitivity, pooled specificity, DOR, AUC, and Q⁎ index score of RGD PET/CT for identifying responders were 0.80 (0.59-0.93), 0.74 (0.60-0.85), 15.76 (4.33-57.32), 0.8682 (0.0539), and 0.7988, respectively, for SUVmax at baseline. Conclusion. The interesting but preliminary data in this meta-analysis demonstrate that RGD PET/CT may be an ideal diagnostic tool for detecting underlying malignancies in patients suspected of having tumors and may be able to efficiently predict short-term outcomes.

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.

Three-Dimensional Tumor Margin Demarcation Using the Hybrid Tracer Indocyanine Green-99mTc-Nanocolloid: A Proof-of-Concept Study in Tongue Cancer Patients Scheduled for Sentinel Node Biopsy

For radical resection of squamous cell carcinoma of the oral cavity, a tumor-free margin of at least 5 mm is required. Unfortunately, establishing in-depth margins is a surgical conundrum. Knowing that the hybrid sentinel node (SN) tracer indocyanine green (ICG)-^99mTc-nanocolloid generates temporary tattoolike markings at the site of administration, we studied the ability to apply this tracer for tumor margin demarcation combined with SN biopsy. Methods: Nineteen patients with clinical T1-T2 oral tongue tumors received the traditional superficial 3 or 4 deposits of ICG-^99mTc-nanocolloid (0.1 mL each), and in 12 patients additional deposits were placed deeply using ultrasound guidance (total of 6; 0.07 mL each). SN mapping was performed using lymphoscintigraphy and SPECT/CT. Before and directly after tumor excision, fluorescence imaging was performed to monitor the tracer deposits in the patient (fluorescent deposits were not used to guide the surgical excision). At pathologic examination, primary tumor samples were studied in detail. Results: The number of tracer depositions did not induce a significant difference in the number of SNs visualized (P = 0.836). Reproducible and deep tracer deposition proved to be challenging. The fluorescent nature of ICG-^99mTc-nanocolloid supported in vivo and ex vivo identification of the tracer deposits surrounding the tumor. Pathologic examination indicated that in 66.7% (8/12), all fluorescence was observed within the resection margins. Conclusion: This study indicates that tumor margin demarcation combined with SN identification has potential but that some practical challenges need to be overcome if this technique is to mature as a surgical guidance concept. Future studies need to define whether the technology can improve the radical nature of the resections.

18F-Alfatide II PET/CT for Identification of Breast Cancer: A Preliminary Clinical Study

¹⁸F-alfatide II has been proven to have excellent clinical translational potential. In this study, we investigated ¹⁸F-alfatide II for identifying breast cancer and compared the performances between ¹⁸F-alfatide II and ¹⁸F-FDG. Methods: Forty-four female patients with suspected primary breast cancer were recruited. PET/CT images using ¹⁸F-alfatide II and ¹⁸F-FDG were acquired within 7 d. Tracer uptake in breast lesions was evaluated by visual analysis, and semiquantitative analysis with SUV_max and SUV_mean Results: Forty-two breast cancer lesions and 11 benign breast lesions were confirmed by histopathology in 44 patients. Both ¹⁸F-alfatide II and ¹⁸F-FDG had higher uptake in breast cancer lesions than in benign breast lesions (P < 0.05 for ¹⁸F-alfatide II, P < 0.05 for ¹⁸F-FDG). The area under the curve of ¹⁸F-alfatide II was slightly less than that of ¹⁸F-FDG. Both ¹⁸F-alfatide II and ¹⁸F-FDG had high sensitivity (88.1% vs. 90.5%), high positive predictive value (88.1% vs. 88.4%), moderate specificity (54.5% vs. 54.5%), and moderate negative predictive value (54.5% vs. 60.0%) for differentiating breast cancer from benign breast lesions. By combining ¹⁸F-alfatide II and ¹⁸F-FDG, the sensitivity and negative predictive value significantly increased to 97.6% and 85.7%, respectively, with positive predictive value slightly increased to 89.1% and no change to the specificity (54.5%). The uptake of ¹⁸F-alfatide II (SUV_max: 3.77 ± 1.78) was significantly lower than that of ¹⁸F-FDG (SUV_max: 7.37 ± 4.48) in breast cancer lesions (P < 0.05). ¹⁸F-alfatide II uptake in triple-negative subtype was significantly lower than that in luminal A and luminal B subtypes. By contrast, human epidermal growth factor receptor-2 (HER-2)-overexpressing subtype had higher ¹⁸F-FDG uptake than the other 3 subtypes. There were 8 breast cancer lesions with higher ¹⁸F-alfatide II uptake than ¹⁸F-FDG uptake, which all had a common characteristic that HER-2 expression was negative and estrogen receptor expression was strongly positive. Conclusion: ¹⁸F-alfatide II is suitable for clinical use in breast cancer patients. ¹⁸F-alfatide II is of good performance, but not superior to ¹⁸F-FDG in identifying breast cancer. ¹⁸F-alfatide II may have superiority to ¹⁸F-FDG in detecting breast cancer with strongly positive estrogen receptor expression and negative HER-2 expression.

In Vivo Characterization of 4 68Ga-Labeled Multimeric RGD Peptides to Image αvβ3 Integrin Expression in 2 Human Tumor Xenograft Mouse Models

α_vβ₃ integrins play an important role in angiogenesis and cell migration in cancer and are highly expressed on the activated endothelial cells of newly formed blood vessels. Here, we compare the targeting characteristics of 4 ⁶⁸Ga-labeled multimeric cyclic arginine-glycine-aspartate (RGD)-based tracers in an α_vβ₃ integrin-expressing tumor model and a tumor model in which α_vβ₃ integrin is expressed solely on the neovasculature. Methods: Female BALB/c nude mice were subcutaneously injected with SK-RC-52 (α_vβ₃ integrin-positive) or FaDu (α_vβ₃ integrin-negative) tumor cells. ⁶⁸Ga-labeled DOTA-(RGD)₂, TRAP-(RGD)₃, FSC-(RGD)₃, or THP-(RGD)₃ was intravenously administered to the mice (0.5 nmol per mouse, 10-20 MBq), followed by small-animal PET/CT imaging and ex vivo biodistribution studies 1 h after injection. Nonspecific uptake of the tracers in both models was determined by coinjecting an excess of unlabeled DOTA-(RGD)₂ (50 nmol) along with the radiolabeled tracers. Results: Imaging and biodistribution data showed specific uptake in the tumors for each tracer in both models. Tumor uptake of ⁶⁸Ga-FSC-(RGD)₃ was significantly higher than that of ⁶⁸Ga-DOTA-(RGD)₂, ⁶⁸Ga-TRAP-(RGD)₃, or ⁶⁸Ga-THP-(RGD)₃ in the SK-RC-52 model but not in the FaDu model, in which ⁶⁸Ga-FSC-(RGD)₃ showed significantly higher tumor uptake than ⁶⁸Ga-TRAP-(RGD)₃ Most importantly, differences were also observed in normal tissues and in tumor-to-blood ratios. Conclusion: All tracers showed sufficient targeting of α_vβ₃ integrin expression to allow for tumor detection. Although the highest tumor uptake was found for ⁶⁸Ga-FSC-(RGD)₃ and ⁶⁸Ga-THP-(RGD)₃ in the SK-RC-52 and FaDu models, respectively, selection of the optimal tracer for specific diagnostic applications also depends on tumor-to-blood ratio and uptake in normal tissues; these factors should therefore also be considered.

The feasibility of 18F-AlF-NOTA-PRGD2 PET/CT for monitoring early response of Endostar antiangiogenic therapy in human nasopharyngeal carcinoma xenograft model compared with 18F-FDG

Purpose

Radiolabeled arginine-glycine-aspartic acid (RGD) peptides have been developed for PET imaging of integrin avβ3 in the tumor vasculature, leading to great potential for noninvasively evaluating tumor angiogenesis and monitoring antiangiogenic treatment. The aim of this study was to investigate a novel one-step labeled integrin-targeted tracer, ¹⁸F-AlF-NOTA-PRGD2, for PET/CT for detecting tumor angiogenesis and monitoring the early therapeutic efficacy of antiangiogenic agent Endostar in human nasopharyngeal carcinoma (NPC) xenograft model.

Experimental design and results

Mice bearing NPC underwent ¹⁸F-AlF-NOTA-PRGD2 PET/CT at baseline and after 2, 4, 7, and 14 days of consecutive treatment with Endostar or PBS, compared with ¹⁸F-FDG PET/CT. Tumors were harvested at all imaging time points for histopathological analysis with H & E and microvessel density (MVD) and integrin avβ3 immunostaining. The maximum percent injected dose per gram of body weight (%ID/gmax) tumor uptake of ¹⁸F-AlF-NOTA-PRGD2 PET/CT was significantly lower than that in the control group starting from day 2 (p < 0.01), much earlier and more accurately than that of ¹⁸F-FDG PET/CT. Moreover, a moderate linear correlation was observed between tumor MVD and the corresponding tumor uptake of ¹⁸F-AlF-NOTA-PRGD2 PET/CT (r = 0.853, p < 0.01).

Conclusions

¹⁸F-AlF-NOTA-PRGD2 PET/CT can be used for in vivo angiogenesis imaging and monitoring early response to Endostar antiangiogenic treatment in NPC xenograft model, favoring its potential clinical translation.

RGD-Binding Integrins in Head and Neck Cancers

Alterations in integrin expression and function promote tumour growth, invasion, metastasis and neoangiogenesis. Head and neck cancers are highly vascular tumours with a tendency to metastasise. They express a wide range of integrin receptors. Expression of the αv and β1 subunits has been explored relatively extensively and linked to tumour progression and metastasis. Individual receptors αvβ3 and αvβ5 have proved popular targets for diagnostic and therapeutic agents but lesser studied receptors, such as αvβ6, αvβ8, and β1 subfamily members, also show promise. This review presents the current knowledge of integrin expression and function in squamous cell carcinoma of the head and neck (HNSCC), with a particular focus on the arginine-glycine-aspartate (RGD)-binding integrins, in order to highlight the potential of integrins as targets for personalised tumour-specific identification and therapy.

[PET-CT in head and neck cancer]

The importance of ¹⁸F-fluorodesoxyglucose positron-emission tomography (FDG-PET) for the diagnosis of malignant disease is increasing. On one hand, this is due to the high sensitivity of this method, on the other, because the entire body can be examined. FDG-PET can be particularly advantageous for the diagnosis of head and neck tumors, where tumor staging is an important prognostic parameter and essentially determines the therapeutic regimen. This article presents the different possibilities for combined evaluation with PET and computed tomography (CT) for the diagnosis of patients with head and neck cancer. Special focus is placed on primary staging and tumor follow-up, as well as on the role of PET-CT in the diagnosis of patients with cancer of unknown primary origin (CUP). The use of PET-CT for radiotherapy planning and new aspects of PET technology are also discussed.

Noninvasive monitoring of early antiangiogenic therapy response in human nasopharyngeal carcinoma xenograft model using MRI with RGD-conjugated ultrasmall superparamagnetic iron oxide nanoparticles

Purpose

Arginine-glycine-aspartic acid (RGD)-based nanoprobes allow specific imaging of integrin αvβ3, a protein overexpressed during angiogenesis. Therefore, this study applied a novel RGD-coupled, polyacrylic acid (PAA)-coated ultrasmall superparamagnetic iron oxide (USPIO) (referred to as RGD-PAA-USPIO) in order to detect tumor angiogenesis and assess the early response to antiangiogenic treatment in human nasopharyngeal carcinoma (NPC) xenograft model by magnetic resonance imaging (MRI).

Materials and methods

The binding specificity of RGD-PAA-USPIO with human umbilical vein endothelial cells (HUVECs) was confirmed by Prussian blue staining and transmission electron microscopy in vitro. The tumor targeting of RGD-PAA-USPIO was evaluated in the NPC xenograft model. Later, mice bearing NPC underwent MRI at baseline and after 4 and 14 days of consecutive treatment with Endostar or phosphate-buffered saline (n=10 per group).

Results

The specific uptake of the RGD-PAA-USPIO nanoparticles was mainly dependent on the interaction between RGD and integrin αvβ3 of HUVECs. The tumor targeting of RGD-PAA-USPIO was observed in the NPC xenograft model. Moreover, the T2 relaxation time of mice in the Endostar-treated group decreased significantly compared with those in the control group both on days 4 and 14, consistent with the immunofluorescence results of CD31 and CD61 (P<0.05).

Conclusion

This study demonstrated that the magnetic resonance molecular nanoprobes, RGD-PAA-USPIOs, allow noninvasive in vivo imaging of tumor angiogenesis and assessment of the early response to antiangiogenic treatment in NPC xenograft model, favoring its potential clinical translation.

Molecular Imaging and Precision Medicine in Head and Neck Cancer

The concept of using tumor genomic profiling information has revolutionized personalized cancer treatment. Head and neck (HN) cancer management is being influenced by recent discoveries of activating mutations in epidermal growth factor receptor and related targeted therapies with tyrosine kinase inhibitors, targeted therapies for Kristen Rat Sarcoma, and MET proto-oncogenes. Molecular imaging using PET plays an important role in assessing the biologic behavior of HN cancer with the goal of delivering individualized cancer treatment. This review summarizes recent genomic discoveries in HN cancer and their implications for functional PET imaging in assessing response to targeted therapies, and drug resistance mechanisms.

SPECT and PET imaging of angiogenesis and arteriogenesis in pre-clinical models of myocardial ischemia and peripheral vascular disease

Purpose

The extent of neovascularization determines the clinical outcome of coronary artery disease and other occlusive cardiovascular disorders. Monitoring of neovascularization is therefore highly important. This review article will elaborately discuss preclinical studies aimed at validating new nuclear angiogenesis and arteriogenesis tracers. Additionally, we will briefly address possible obstacles that should be considered when designing an arteriogenesis radiotracer.

Methods

A structured medline search was the base of this review, which gives an overview on different radiopharmaceuticals that have been evaluated in preclinical models.

Results

Neovascularization is a collective term used to indicate different processes such as angiogenesis and arteriogenesis. However, while it is assumed that sensitive detection through nuclear imaging will facilitate translation of successful therapeutic interventions in preclinical models to the bedside, we still lack specific tracers for neovascularization imaging. Most nuclear imaging research to date has focused on angiogenesis, leaving nuclear arteriogenesis imaging largely overlooked.

Conclusion

Although angiogenesis is the process which is best understood, there is no scarcity in theoretical targets for arteriogenesis imaging.

Radiolabeled cyclic RGD peptides as radiotracers for tumor imaging

The integrin family comprises 24 transmembrane receptors, each a heterodimeric combination of one of 18α and one of 8β subunits. Their main function is to integrate the cell adhesion and interaction with the extracellular microenvironment with the intracellular signaling and cytoskeletal rearrangement through transmitting signals across the cell membrane upon ligand binding. Integrin α_vβ₃ is a receptor for the extracellular matrix proteins containing arginine–glycine–aspartic (RGD) tripeptide sequence. The α_vβ₃ is generally expressed in low levels on the epithelial cells and mature endothelial cells, but it is highly expressed in many solid tumors. The α_vβ₃ levels correlate well with the potential for tumor metastasis and aggressiveness, which make it an important biological target for development of antiangiogenic drugs, and molecular imaging probes for early tumor diagnosis. Over the last decade, many radiolabeled cyclic RGD peptides have been evaluated as radiotracers for imaging tumors by SPECT or PET. Even though they are called “α_vβ₃-targeted” radiotracers, the radiolabeled cyclic RGD peptides are also able to bind α_vβ₅, α₅β₁, α₆β₄, α₄β₁, and α_vβ₆ integrins, which may help enhance their tumor uptake due to the “increased receptor population.” This article will use the multimeric cyclic RGD peptides as examples to illustrate basic principles for development of integrin-targeted radiotracers and focus on different approaches to maximize their tumor uptake and T/B ratios. It will also discuss important assays for pre-clinical evaluations of the integrin-targeted radiotracers, and their potential applications as molecular imaging tools for noninvasive monitoring of tumor metastasis and early detection of the tumor response to antiangiogenic therapy.

RGD-K5 PET/CT in patients with advanced head and neck cancer treated with concurrent chemoradiotherapy: Results from a pilot study

BACKGROUND/AIM

We prospectively investigated the potential usefulness of PET using a new tracer targeting integrin αvβ3 (termed RGD-K5) in patients with head and neck cancer (HNC) undergoing definitive concurrent chemoradiotherapy (CCRT).

PATIENTS AND METHODS

Newly diagnosed patients with locally advanced HNC scheduled for definitive CCRT were eligible. RDG-K5 PET and FDG PET scans were performed at three different time points (baseline, 2 weeks, and 3 months post-treatment).

RESULTS

Nine patients completed all of the three scans, whereas two patients withdrew after two scans only. Uptake of both RGD-K5 and FDG generally decreased following CCRT. However, the observed decrease did not differ significantly between complete responders and non-responders. At 3 months post-treatment, the uptake of both RGD-K5 and FDG at the main tumors was significantly lower in those who achieved complete responses than in those with residual tumors.

CONCLUSION

RGD-K5 PET has the potential to identify patients with incomplete responses to CCRT.

In vivo monitoring of the anti-angiogenic therapeutic effect of the pan-deacetylase inhibitor panobinostat by small animal PET in a mouse model of gastrointestinal cancers

INTRODUCTION

Deacetylase inhibitors have recently been established as a novel therapeutic approach to solid and hematologic cancers and have also been demonstrated to possess anti-angiogenic properties. Although these compounds show a good efficacy in vitro and in vivo, no data on monitoring and predicting treatment response are currently available. We therefore investigated the effect of the pan-deacetylase inhibitor panobinostat (LBH589) on gastrointestinal cancer models and the suitability of 2-[(18)F]FGlc-RGD as a specific agent for imaging integrin αvβ3 expression during tumor angiogenesis using small animal positron emission tomography (PET).

METHODS

The effect of panobinostat on cell viability in vitro was assessed with a label-free impedance based real-time analysis. Nude mice bearing HT29 and HepG2 tumors were treated with daily i.p. injections of 10mg/kg panobinostat for 4 weeks. During this time, tumor size was determined with a calliper and mice were repeatedly subjected to PET imaging. Tumor tissues were analyzed immunohistochemically with a focus on proliferation and endothelial cell markers (Ki-67, Meca-32) and by Western blot applying specific markers of apoptosis.

RESULTS

In vitro, panobinostat inhibited the proliferation of HepG2 and HT29 cells. Contrary to the situation in HepG2 tumors in vivo, where panobinostat treatment is known to reduce proliferation and vascularization resulting in a decreased tumor growth, HT29 tumors did not show any effect on these parameters. We demonstrated by Western blotting, that panobinostat induced apoptosis in HT29 tumors in vivo. Longitudinal PET imaging studies in HepG2 tumor-bearing mice using 2-[(18)F]FGlc-RGD demonstrated that the standard uptake value (SUVmax) in HepG2 tumors was significantly decreased by 39% at day 7 after treatment. The comparative PET study using HT29 tumor-bearing animals did not reveal any response of the tumors to panobinostat treatment.

CONCLUSIONS

Small-animal PET imaging using 2-[(18)F]FGlc-RGD was successfully applied to the non-invasive monitoring of the HepG2-tumor response to panobinostat in nude mice early after begin of treatment. Thus, PET imaging of angiogenesis using 2-[(18)F]FGlc-RGD could be a valuable tool to monitor panobinostat therapy in further preclinical studies.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

When successfully translated to the clinical surrounding, PET imaging of angiogenesis could therefore facilitate therapy planning and monitoring of therapy success with panobinostat in hepatocellular carcinoma.

Clinical Application of Radiolabeled RGD Peptides for PET Imaging of Integrin αvβ3

Molecular imaging for non-invasive assessment of angiogenesisis is of great interest for clinicians because of the wide-spread application of anti-angiogenic cancer therapeutics. Besides, many other interventions that involve the change of blood vessel/tumor microenvironment would also benefit from such imaging strategies. Of the imaging techniques that target angiogenesis, radiolabeled Arg-Gly-Asp (RGD) peptides have been a major focus because of their high affinity and selectivity for integrin α_vβ₃--one of the most extensively examined target of angiogenesis. Since the level of integrin α_vβ₃ expression has been established as a surrogate marker of angiogenic activity, imaging α_vβ₃ expression can potentially be used as an early indicator of effectiveness of antiangiogenic therapy at the molecular level. In this review, we summarize RGD-based PET tracers that have already been used in clinical trials and intercompared them in terms of radiosynthesis, dosimetry, pharmacokinetics and clinical applications. A perspective of their future use in the clinic is also provided.

Multicenter Reproducibility of 18F-Fluciclatide PET Imaging in Subjects with Solid Tumors

Integrins are upregulated on both tumor cells and associated vasculature, where they play an important role in angiogenesis and metastasis. Fluciclatide is an arginine-glycine-aspartic acid peptide with high affinity for αvβ3/αvβ5 integrin, which can be radiolabeled for PET imaging of angiogenesis. Thus, (18)F-fluciclatide is a potential biomarker of therapeutic response to antiangiogenic inhibitors. The aim of this study was to evaluate the reproducibility of (18)F-fluciclatide in multiple solid-tumor types.

METHODS

Thirty-nine patients underwent PET/CT scanning at 40, 65, and 90 min after injection of (18)F-fluciclatide (maximum, 370 MBq) on 2 separate days (2-9 d apart). Patients did not receive any therapy between PET/CT scans. (18)F-fluciclatide images were reported and quantitative measures of uptake were extracted using the PERCIST methodology. Intrasubject reproducibility of PET uptake in all measurable lesions was evaluated by calculating relative differences in SUV between PET scans for each lesion during the 2 imaging sessions.

RESULTS

Thirty-nine measurable lesions were detected in 26 patients. Lesion uptake correlated strongly across imaging sessions (r = 0.92, P < 0.05, at 40 min; r = 0.94, P < 0.05, at 65 min; r = 0.94, P < 0.05, at 90 min) with a mean relative difference and SD of the relative difference of 0.006 ± 0.18 at 40 min, 0.003 ± 0.19 at 65 min, and 0.025 ± 0.20 at 90 min. This reflects 95% limits of repeatability of 35%-39% for the difference between the 2 SUV measurements or a variability of 18%-20% in agreement from that observed in well-calibrated multicenter (18)F-FDG studies.

CONCLUSION

The test-retest reproducibility of (18)F-fluciclatide across multiple tumor types has been measured and shown to be acceptable. This is an important step in the development of this in vivo biomarker to identify and quantify response to antiangiogenic therapy in cancer patients.

(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.

Radiolabeled Cyclic RGD Peptide Bioconjugates as Radiotracers Targeting Multiple Integrins

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