Dual-Targeted Molecular Imaging of Cancer

Development of a PSMA and EphA2 dual-receptor-activated fluorescent probe for wash-free prostate cancer cell imaging

Prostate cancer (PCa) remains a leading cause of cancer-related mortality in men, underscoring the need for improved diagnostic tools. In this study, a novel dual-receptor-activated fluorescence probe (9) designed to simultaneously bind to prostate-specific membrane antigen (PSMA) and erythropoietin-producing hepatocellular receptor type A2 (EphA2), two key biomarkers in PCa, was developed and applied for wash-free cell imaging. The probe was synthesized by conjugating both PSMA- and EphA2-targeting ligands with a sulfonated benzothiazole environment-sensitive dye. 9 demonstrated good binding affinity (Kd = 34 nM for PSMA, 9.70 nM for EphA2) with significant fluorescence activation upon receptor binding (14.1-fold for PSMA; 8.6-fold for EphA2). Cell studies demonstrated 9 showed negligible cytotoxicity and good targeting specificity, which could enable convenient monitoring of the dynamic biological processes in PCa, such as ligand-receptor interactions. The study may also provide insights into the design and applications of multiple-receptor-activated fluorescence probes.

Dual-Labeled Small Peptides in Cancer Imaging and Fluorescence-Guided Surgery: Progress and Future Perspectives

Dual-labeled compounds that combine radiolabeling and fluorescence labeling represent a significant advancement in precision oncology. Their clinical implementation enhances patient care and outcomes by leveraging the high sensitivity of radioimaging for tumor detection and taking advantage of fluorescence-based optical visualization for surgical guidance. Non-invasive radioimaging facilitates immediate identification of both primary tumors and metastases, while fluorescence imaging assists in decision-making during surgery by offering a spatial distinction between malignant and non-malignant tissue. These advancements hold promise for enhancing patient outcomes and personalization of cancer treatment. The development of dual-labeled molecular probes targeting various cancer biomarkers is crucial in addressing the heterogeneity inherent in cancer pathology and recent studies had already demonstrated the impact of dual-labeled compounds in surgical decision-making (NCT03699332, NCT03407781). This review focuses on the development and application of small dual-labeled peptides in the imaging and treatment of various cancer types. It summarizes the biomarkers targeted to date, tracing their development from initial discovery to the latest advancements in peptidomimetics. Through comprehensive analysis of recent preclinical and clinical studies, the review demonstrates the potential of these dual-labeled peptides to improve tumor detection, localization, and resection. Additionally, it highlights the evolving landscape of dual-modality imaging, emphasizing its critical role in advancing personalized and effective cancer therapy. This synthesis of current research underscores the promise of dual-labeled peptides in enhancing diagnostic accuracy and therapeutic outcomes in oncology.

Synthesis and Evaluation of 99mTc-Labeled l-Aspartic Acid as a EuK Polymer Linker for Targeting PSMA to a Novel SPECT Tumor Tracer

The development of novel tracers targeting prostate-specific membrane antigen (PSMA) has great potential for improving the diagnosis and treatment of prostate cancer (PCa). This study aimed to improve the absolute tumor uptake and tumor-to-background ratios (TBRs) of this novel PSMA tracer by increasing the number of pharmacophores, Glu-urea-Lys (EuK), that specifically bind to PSMA. We successfully synthesized four radioligands and prepared a total of 12 stable radiotracers by coordinating 99mTc with various coligands. [99mTc]Tc-EUKD-EDDA showed the best pharmacokinetic properties both in vitro and in vivo. It effectively increased the absolute uptake in tumors and resulted in good tumor retention. Rapid clearance in nontarget organs resulted in high TBRs. High-contrast SPECT/CT images were obtained within 2-6 h after injection, suggesting that [99mTc]Tc-EUKD-EDDA has great application potential in time-lapse imaging of PCa, which is important for improving the diagnostic accuracy of PCa in clinical practice.

Application of rare earth elements in dual-modality molecular probes

The unique 4f subshell electronic structure of rare earth elements endows them with exceptional properties in electrical, magnetic, and optical domains. These properties include prolonged fluorescence lifetimes, large Stokes shifts, distinctive spectral bands, and strong resistance to photobleaching, making them ideal for the synthesis of molecular probes. Each imaging technique possesses unique advantages and specific applicabilities but also inherent limitations due to its operational principles. Dual-modality molecular probes effectively address these limitations, particularly in applications involving high-resolution Magnetic Resonance Imaging (MRI) such as MRI/OI, MRI/PET, MRI/CT, and MRI/US. This review summarizes the applications, advantages, challenges, and current research status of rare earth elements in these four dual imaging modalities, providing a theoretical basis for the future development and application of rare earth elements in the field of dual-modality molecular probes.

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.

Integrin αvβ3 and EGFR dual-targeted [64Cu]Cu-NOTA-RGD-GE11 heterodimer for PET imaging in pancreatic cancer mouse model

PURPOSE

Radiolabeled heterodimeric peptide has emerged as a highly promising targeting strategy for PET imaging due to their superior properties. RGD and GE11 are two peptides binding to receptor integrin αvβ3 and EGFR, respectively, which both overexpress in many different types of tumors. This study focuses on the synthesis and evaluation of a RGD and GE11-containing heterodimeric radiotracer [64Cu]Cu-NOTA-RGD-GE11 for PET imaging of tumors that simultaneously overexpress integrin αvβ3 and EGFR.

PROCEDURES

[64Cu]Cu-NOTA-RGD-GE11 was prepared by the conjugation of RGD-PEG4-NOTA-N3 and GE11-PEG4-BCN via metal-free click chemistry, followed by radiolabeling with 64Cu. Cell uptake and efflux studies, saturation binding assay, the animal PET/CT and biodistribution studies were conducted to characterize the biological properties of [64Cu]Cu-NOTA-RGD-GE11.

RESULTS

[64Cu]Cu-NOTA-RGD-GE11 was synthesized with a radiochemical purity of >97 % and molar activity of 23 GBq/μmol at the end of synthesis. [64Cu]Cu-NOTA-RGD-GE11 showed moderate hydrophilicity, good stability in mouse serum and high specific uptake by the human pancreatic cancer cell line (BxPC3) in the in vitro studies. Compared to the two monomeric counterparts [64Cu]Cu-NOTA-RGD and [64Cu]Cu-NOTA-GE11, [64Cu]Cu-NOTA-RGD-GE11 demonstrated significantly improved tumor uptakes (e.g. 4.63 ± 0.25 %ID/g vs 1.24 ± 0.18 %ID/g and 0.77 ± 0.13 %ID/g, 2 h after injection, p < 0.05) in the subsequent in vivo evaluation in mice bearing BxPC3 xenograft. Tumor uptake could be blocked in the presence of both non-radioactive c(RGDyK) and GE11 peptides, indicating good tumor specificity of [64Cu]Cu-NOTA-RGD-GE11 in vivo.

CONCLUSION

The results suggested that the as-developed [64Cu]Cu-NOTA-RGD-GE11 could serve as a potential PET tracer for the noninvasive imaging of integrin αvβ3 and EGFR expression in tumors.

Non-invasive molecular imaging for precision diagnosis of metastatic lymph nodes: opportunities from preclinical to clinical applications

Lymph node metastasis is an indicator of the invasiveness and aggressiveness of cancer. It is a vital prognostic factor in clinical staging of the disease and therapeutic decision-making. Patients with positive metastatic lymph nodes are likely to develop recurrent disease, distant metastasis, and succumb to death in the coming few years. Lymph node dissection and histological analysis are needed to detect whether regional lymph nodes have been infiltrated by cancer cells and determine the likely outcome of treatment and the patient's chances of survival. However, these procedures are invasive, and tissue biopsies are prone to sampling error. In recent years, advanced molecular imaging with novel imaging probes has provided new technologies that are contributing to comprehensive management of cancer, including non-invasive investigation of lymphatic drainage from tumors, identifying metastatic lymph nodes, and guiding surgeons to operate efficiently in patients with complex lesions. In this review, first, we outline the current status of different molecular imaging modalities applied for lymph node metastasis management. Second, we summarize the multi-functional imaging probes applied with the different imaging modalities as well as applications of cancer lymph node metastasis from preclinical studies to clinical translations. Third, we describe the limitations that must be considered in the field of molecular imaging for improved detection of lymph node metastasis. Finally, we propose future directions for molecular imaging technology that will allow more personalized treatment plans for patients with lymph node metastasis.

Multifunctional stimuli-responsive hybrid nanogels for cancer therapy: Current status and challenges

With cancer research shifting focus to achieving multifunctionality in cancer treatment strategies, hybrid nanogels are making a rapid rise to the spotlight as novel, multifunctional, stimuli-responsive, and biocompatible cancer therapeutic strategies. They can possess cancer cell-specific cytotoxic effects themselves, carry drugs or enzymes that can produce cytotoxic effects, improve imaging modalities, and target tumor cells over normal cells. Hybrid nanogels bring together a wide range of desirable properties for cancer treatment such as stimuli-responsiveness, efficient loading and protection of molecules such as drugs or enzymes, and effective crossing of cellular barriers among other properties. Despite their promising abilities, hybrid nanogels are still far from being used in the clinic, and their available data remains relatively limited. However, many studies can be done to facilitate this clinical transition. This review is critically summarizing and analyzing the recent information and progress on the use of hybrid nanogels particularly inorganic nanoparticle-based and organic nanoparticle-based hybrid nanogels in the field of oncology and future directions to aid in transferring those results to the clinic. This work concludes that the future of hybrid nanogels is greatly impacted by therapeutic and non-therapeutic factors. Therapeutic factors include the lack of hemocompatibility studies, acute and chronic toxicological studies, and information on agglomeration capability and extent, tumor heterogeneity, interaction with proteins in physiological fluids, endocytosis-exocytosis, and toxicity of the nanogels' breakdown products. Non-therapeutic factors include the lack of clear regulatory guidelines and standardized assays, limitations of animal models, and difficulties associated with good manufacture practices (GMP).

The Dual-Targeted Peptide Conjugated Probe for Depicting Residual Nasopharyngeal Carcinoma and Guiding Surgery

Detecting residual nasopharyngeal carcinoma (rNPC) can be difficult because of the coexistence of occult tumours and post-chemoradiation changes, which poses a challenge for both radiologists and surgeons using current imaging methods. Currently, molecular imaging that precisely targets and visualises particular biomarkers in tumours may exceed the specificity and sensitivity of traditional imaging techniques, providing the potential to distinguish tumours from non-neoplastic lesions. Here, we synthesised a HER2/SR-BI-targeted tracer to efficiently position NPC and guide surgery in living mice. This bispecific tracer contained the following two parts: IRDye 800 CW, as an imaging reagent for both optical and optoacoustic imaging, and a fusion peptide (FY-35), as the targeting reagent. Both in vitro and in vivo tests demonstrated that the tracer had higher accumulation and longer retention (up to 48 h) in tumours than a single-targeted probe, and realised sensitive detection of tumours with a minimum size of 3.9 mm. By visualising the vascular network via a customised handheld optoacoustic scan, our intraoperative fluorescence molecular imaging system provides accurate guidance for intraoperative tumour resection. Integrating the advantages of both optical and optoacoustic scanning in an intraoperative image-guided system, this method holds promise for depicting rNPC and guiding salvage surgery.

Development and Evaluation of a Peptide Heterodimeric Tracer Targeting CXCR4 and Integrin αvβ3 for Pancreatic Cancer Imaging

Nowadays, pancreatic cancer is still a formidable disease to diagnose. The CXC chemokine receptor 4 (CXCR4) and integrin αvβ3 play important roles in tumor development, progression, invasion, and metastasis, which are overexpressed in many types of human cancers. In this study, we developed a heterodimeric tracer 68Ga-yG5-RGD targeting both CXCR4 and integrin αvβ3, and evaluated its feasibility and utility in PET imaging of pancreatic cancer. The 68Ga-yG5-RGD could accumulate in CXCR4/integrin αvβ3 positive BxPC3 tumors in a high concentration and was much higher than that of 68Ga-yG5 (p < 0.001) and 68Ga-RGD (p < 0.001). No increased uptake of 68Ga-yG5-RGD was found in MX-1 tumors (CXCR4/integrin αvβ3, negative). In addition, the uptake of 68Ga-yG5-RGD in BxPC3 was significantly blocked by excess amounts of AMD3100 (an FDA-approved CXCR4 antagonist) and/or unlabeled RGD (p < 0.001), confirming its dual-receptor targeting properties. The ex vivo biodistribution and immunohistochemical results were consistent with the in vivo imaging results. The dual-receptor targeting strategy achieved improved tumor-targeting efficiency and prolonged tumor retention in BxPC3 tumors, suggesting 68Ga-yG5-RGD is a promising tracer for the noninvasive detection of tumors that express either CXCR4 or integrin αvβ3 or both, and therefore may have good prospects for clinical translation.

Positron emission tomography molecular imaging-based cancer phenotyping

During the past several decades, numerous studies have provided insights into biological characteristics of cancer cells and identified various hallmarks of cancer acquired in the tumorigenic processes. However, it is still challenging to image these distinctive traits of cancer to facilitate the management of patients in clinical settings. The rapidly evolving field of positron emission tomography (PET) imaging has provided opportunities to investigate cancer's biological characteristics in vivo. This article reviews the current status of PET imaging on characterizing hallmarks of cancer and discusses the future directions of PET imaging strategies facilitating in vivo cancer phenotyping.

Systematic Review: Targeted Molecular Imaging of Angiogenesis and Its Mediators in Rheumatoid Arthritis

Extensive angiogenesis is a characteristic feature in the synovial tissue of rheumatoid arthritis (RA) from a very early stage of the disease onward and constitutes a crucial event for the development of the proliferative synovium. This process is markedly intensified in patients with prolonged disease duration, high disease activity, disease severity, and significant inflammatory cell infiltration. Angiogenesis is therefore an interesting target for the development of new therapeutic approaches as well as disease monitoring strategies in RA. To this end, nuclear imaging modalities represent valuable non-invasive tools that can selectively target molecular markers of angiogenesis and accurately and quantitatively track molecular changes in multiple joints simultaneously. This systematic review summarizes the imaging markers used for single photon emission computed tomography (SPECT) and/or positron emission tomography (PET) approaches, targeting pathways and mediators involved in synovial neo-angiogenesis in RA.

Engineering AND-Gate Aptamer-Signal Base Conjugates for Targeted Magnetic Resonance Molecular Imaging of Metastatic Cancer

In vivo noninvasive molecular imaging requires precise recognition and in situ, real-time imaging of specific cellular and molecular signatures at the site of interest. However, this is often hindered by issues of current imaging probes relating to either the lack of active recognition or the overall nonspecific mechanism of action. Here, we present an aptamer-signal base conjugate (ApSC) concept to engineer AND-gate molecular tools for tumor-targeted molecular imaging. Superior to conventional synthetic methods for imaging probes, our design enables programmable and precise conjugation between recognition and signaling units in a modular synthesis manner with high fidelity for both the conjugating chemistry and binding affinity to the molecular target. Moreover, this design is endowed with simultaneous multivariate activation that readily adapts to tumor microenvironments for signal output, thus providing improved imaging specificity and sensitivity. Such a concept has been successfully shown in magnetic resonance imaging (MRI), the modality of choice for in vivo noninvasive molecular imaging. The engineered ApSC can produce amplified MR signals only after activation by the unique metabolism and dysregulation of redox balance in cancer. In mouse models of xenograft and metastatic breast cancer, the AND-gate molecular MRI probe elicits high imaging contrast in primary tumors and micrometastases. This study promises to provide synthetically accessible scaffolds that can be extended to a large library of advanced molecular imaging tools with varied imaging modalities and mechanisms of action for preventative, predictive, and personalized medicine.

Advanced Tumor Imaging Approaches in Human Tumors

The management of cancer has always relied heavily on the imaging modalities used to detect and monitor it. While many of these modalities have been around for decades, the technology surrounding them is always improving, and much has been discovered in recent years about the nature of tumors because of this. There have been several areas that have aided those discoveries. The use of artificial intelligence has already helped immensely in the quality of images taken but has not yet been widely implemented in clinical settings. Molecular imaging has proven to be useful in diagnosing different types of cancers based on the specificity of the probes/contrast agents used. Intravital imaging has already uncovered new information regarding the heterogeneity of the tumor vasculature. These three areas have provided a lot of useful information for the diagnosis and treatment of cancer, but further research and development in human trials is necessary to allow these techniques to fully utilize the information obtained thus far.

Synthesis of 68Ga-Labeled cNGR-Based Glycopeptides and In Vivo Evaluation by PET Imaging

Tumor hypoxia induces angiogenesis, which is required for tumor cell survival. The aminopeptidase N receptor (APN/CD13) is an excellent marker of angiogenesis since it is overexpressed in angiogenic blood vessels and in tumor cells. Asparagine-glycine-arginine (NGR) peptide analogs bind selectively to the APN/CD13 recepto, therefore, they are important vector molecules in the development of a PET radiotracer which is capable of detecting APN-rich tumors. To investigate the effect of glycosylation and pegylation on in-vivo efficacy of an NGR-based radiotracer, two ⁶⁸Ga-labeled radioglycopeptides were synthesized. A lactosamine derivative was applied to glycosylation of the NGR derivative and PEG₄ moiety was used for pegylation. The receptor targeting potential and biodistribution of the radiopeptides were evaluated with in vivo PET imaging studies and ex vivo tissue distribution studies using B16-F10 melanoma tumor-bearing mice. According to these studies, all synthesized radiopeptides were capable of detecting APN expression in B16-F10 melanoma tumor. In addition, lower hepatic uptake, higher tumor-to background (T/M) ratio and prolonged circulation time were observed for the novel [⁶⁸Ga]-10 radiotracer due to pegylation and glycosylation, resulting in more contrasting PET imaging. These in vivo PET imaging results correlated well with the ex vivo tissue distribution data.

Overview and Future Perspectives on Tumor-Targeted Positron Emission Tomography and Fluorescence Imaging of Pancreatic Cancer in the Era of Neoadjuvant Therapy

BACKGROUND

Despite recent advances in the multimodal treatment of pancreatic ductal adenocarcinoma (PDAC), overall survival remains poor with a 5-year cumulative survival of approximately 10%. Neoadjuvant (chemo- and/or radio-) therapy is increasingly incorporated in treatment strategies for patients with (borderline) resectable and locally advanced disease. Neoadjuvant therapy aims to improve radical resection rates by reducing tumor mass and (partial) encasement of important vascular structures, as well as eradicating occult micrometastases. Results from recent multicenter clinical trials evaluating this approach demonstrate prolonged survival and increased complete surgical resection rates (R0). Currently, tumor response to neoadjuvant therapy is monitored using computed tomography (CT) following the RECIST 1.1 criteria. Accurate assessment of neoadjuvant treatment response and tumor resectability is considered a major challenge, as current conventional imaging modalities provide limited accuracy and specificity for discrimination between necrosis, fibrosis, and remaining vital tumor tissue. As a consequence, resections with tumor-positive margins and subsequent early locoregional tumor recurrences are observed in a substantial number of patients following surgical resection with curative intent. Of these patients, up to 80% are diagnosed with recurrent disease after a median disease-free interval of merely 8 months. These numbers underline the urgent need to improve imaging modalities for more accurate assessment of therapy response and subsequent re-staging of disease, thereby aiming to optimize individual patient's treatment strategy. In cases of curative intent resection, additional intra-operative real-time guidance could aid surgeons during complex procedures and potentially reduce the rate of incomplete resections and early (locoregional) tumor recurrences. In recent years intraoperative imaging in cancer has made a shift towards tumor-specific molecular targeting. Several important molecular targets have been identified that show overexpression in PDAC, for example: CA19.9, CEA, EGFR, VEGFR/VEGF-A, uPA/uPAR, and various integrins. Tumor-targeted PET/CT combined with intraoperative fluorescence imaging, could provide valuable information for tumor detection and staging, therapy response evaluation with re-staging of disease and intraoperative guidance during surgical resection of PDAC.

METHODS

A literature search in the PubMed database and (inter)national trial registers was conducted, focusing on studies published over the last 15 years. Data and information of eligible articles regarding PET/CT as well as fluorescence imaging in PDAC were reviewed. Areas covered: This review covers the current strategies, obstacles, challenges, and developments in targeted tumor imaging, focusing on the feasibility and value of PET/CT and fluorescence imaging for integration in the work-up and treatment of PDAC. An overview is given of identified targets and their characteristics, as well as the available literature of conducted and ongoing clinical and preclinical trials evaluating PDAC-targeted nuclear and fluorescent tracers.

Functionalized niosomes as a smart delivery device in cancer and fungal infection

Various diseases remain untreated due to lack of suitable therapeutic moiety or a suitable drug delivery device, especially where toxicities and side effects are the primary reason for concern. Cancer and fungal infections are diseases where treatment schedules are not completed due to severe side effects or lengthy treatment protocols. Advanced treatment approaches such as active targeting and inhibition of angiogenesis may be preferred method for the treatment for malignancy over the conventional method. Niosomes may be a better alternative drug delivery carrier for various therapeutic moieties (either hydrophilic or hydrophobic) and also due to ease of surface modification, non-immunogenicity and economical. Active targeting approach may be done by targeting the receptors through coupling of suitable ligand on niosomal surface. Moreover, various receptors (CD44, folate, epidermal growth factor receptor (EGFR) & Vascular growth factor receptor (VGFR)) expressed by malignant cells have also been reviewed. The preparation of suitable niosomal formulation also requires considerable attention, and its formulation depends upon various factors such as selection of non-ionic surfactant, method of fabrication, and fabrication parameters. A combination therapy (dual drug and immunotherapy) has been proposed for the treatment of fungal infection with special consideration for surface modification with suitable ligand on niosomal surface to sensitize the receptors (C-type lectin receptors, Toll-like receptors & Nucleotide-binding oligomerization domain-like receptors) present on immune cells involved in fungal immunity. Certain gene silencing concept has also been discussed as an advanced alternative treatment for cancer by silencing the mRNA at molecular level using short interfering RNA (si-RNA).

High-performance renal imaging with a radiolabeled, non-excretable chimeric fusion protein

Ideal nuclear imaging tracers should exhibit high target uptake and low background signal. Traditional renal scintigraphy and SPECT scans examine kidney function via static or dynamic tracing of radioactive probes in the kidneys. The lack of tracer affinity to specific biological processes and high background uptake from urinary excretion have added many difficulties to precision renal diagnosis. In this issue of Theranostics, Jin and colleagues innovatively devised a recombinant probe for preferential kidney imaging through targeting of tubular neonatal Fc receptor and proximal tubular basement membrane for sustained tubular reabsorption and accumulation. This work has broad implications regarding how an in depth understanding of physiology and pathology may be of service for tracer development, renal diagnosis, and disease theranostics.

Next-Generation Molecular Imaging of Thyroid Cancer

An essential aspect of thyroid cancer (TC) management is personalized and precision medicine. Functional imaging of TC with radioiodine and [18F]FDG has been frequently used in disease evaluation for several decades now. Recently, advances in molecular imaging have led to the development of novel tracers based on aptamer, peptide, antibody, nanobody, antibody fragment, and nanoparticle platforms. The emerging targets-including HER2, CD54, SHP2, CD33, and more-are promising targets for clinical translation soon. The significance of these tracers may be realized by outlining the way they support the management of TC. The provided examples focus on where preclinical investigations can be translated. Furthermore, advances in the molecular imaging of TC may inspire the development of novel therapeutic or theranostic tracers. In this review, we summarize TC-targeting probes which include transporter-based and immuno-based imaging moieties. We summarize the most recent evidence in this field and outline how these emerging strategies may potentially optimize clinical practice.

Preparation and Preliminary Evaluation of 68Ga-Acridine: An Attempt to Study the Potential of Radiolabeled DNA Intercalator as a PET Radiotracer for Tumor Imaging

INTRODUCTION

Acridine is a well-known DNA intercalator and thereby gets easily inserted within DNA. As uncontrolled rapid cell division is one of the primary characteristics of the tumors, it is expected that acridine or its suitable derivatives will have preferential accumulation in the tumorous lesions. Therefore, an attempt was made to radiolabel an acridine derivative with 68Ga and study the potential of the 68Ga-acridine complex as a PET agent for tumor imaging.

METHODS

9-aminoacridine was coupled with p-NCS-benzyl-DOTA to render it suitable for labeling with 68Ga. The purified acridine-DOTA conjugate was radiolabeled with 68Ga, eluted from a 68Ge/68Ga radionuclide generator. Various radiolabeling parameters were optimized and the stability of the radiolabeled preparation was studied. The biological behavior of the 68Ga-acridine complex was studied both in vitro and in vivo using Raji cell line and fibrosarcoma tumor bearing Swiss mice, respectively.

RESULTS

68Ga-acridine complex was obtained with ~100% radiochemical purity under the optimized reaction conditions involving incubation of 2mg/mL of ligand at 100°C for 30 minutes. The complex maintained a radiochemical purity of >95% in normal saline and >65% in human blood serum at 3h post-incubation. In vitro cellular study showed (3.2±0.1)% uptake of the radiotracer in the Raji cells. Biodistribution study revealed significant tumor accumulation [(11.41±0.41)% injected activity in per gram] of the radiotracer within 1h postadministration along with uptake in other non-target organs such as, blood, liver, GIT kidney etc. Conclusion: The present study indicates the potential of 68Ga-acridine as a PET agent for imaging of tumorous lesions. However, further detailed evaluation of the agent is warranted to explore its actual potential.

Syntheses and Preliminary Evaluation of Dual Target PET Probe [18F]-NOTA-Gly3- E (2PEG4-RGD-WH701) for PET Imaging of Breast Cancer

PURPOSE

Tumor Necrosis Factor Receptor 1 (TNFR1) and integrin αvβ3 receptor are overexpressed in breast cancer. We hypothesized that a peptide ligand recognizing both receptors in a single receptor-binding probe would be advantageous. Here, we developed a novel 18F-labeled fusion peptide probe [18F]-NOTA-Gly3- E(2PEG4-RGD-WH701) targeting dual receptors (TNFR1 and αvβ3) and evaluated the diagnostic efficacy of this radioactive probe in both MDA-MB-231 and MCF-7 xenograft models in mice.

METHODS

The NOTA-conjugated RGD-WH701 analog was radiolabeled with 18F using NOTA-AlF chelation method. We used two PEG4 molecules and Glutamic acid (Glu) to covalently link c(RGDyK) with WH701. Gly3 was also added to further improve the water solubility and pharmacokinetic properties of the probe. The expression of TNFR1 and Integrin αvβ3 in MCF-7 and MDA-MB-231 cells was detected by western blot analysis and immunofluorescence staining. The tumor-targeting characteristics of [18F]-NOTA-Gly3-E(2PEG4-RGDWH701) were assessed in nude mice bearing MDA-MB-231 and MCF-7 xenografts.

RESULTS

HPLC analysis of the product NOTA-G3-E (2P4-RGD-WH701) revealed a purity >95%. The yield after attenuation correction was approximately 33.5%±2.8% (n=5), and the radiochemical purity was above 95%. The MDA-MB-231 tumor uptake of [18F]-NOTA-Gly3-E(2PEG4-RGD-WH701) was 1.14±0.14%ID/g, as measured by PET at 40min postinjection (p.i.). In comparison, the tumor uptake of [18F]-NOTA-RGD and [18F]- NOTA-WH701 in MDA-MB-231 xenografts was 0.96±0.13%ID/g and 0.93±0.28%ID/g, respectively. The MCF-7 tumor uptake of [18F]-NOTA-Gly3-E(2PEG4-RGD-WH701) was 1.22±0.11%ID/g, as measured by PET at 40min postinjection (p.i.). In comparison, the tumor uptake of [18F]-NOTA-RGD and [18F]-NOTA-WH701 in MCF-7 xenografts was 0.99±0.18%ID/g and 0.57±0.08%ID/g, respectively.

CONCLUSION

[18F]AlF-NOTA-Gly3-E(2PEG4-RGD-WH701) was successfully synthesized and labeled with 18F. The results from the microPET/CT and biodistribution studies of [18F]AlF-NOTA-Gly3-E(2PEG4-RGDWH701) showed that the tracer could specifically target TNFR1 and integrin αvβ3 receptors.

Synthesis of Novel, Dual-Targeting 68Ga-NODAGA-LacN-E[c(RGDfK)]2 Glycopeptide as a PET Imaging Agent for Cancer Diagnosis

Radiolabeled peptides possessing an Arg-Gly-Asp (RGD) motif are widely used radiopharmaceuticals for PET imaging of tumor angiogenesis due to their high affinity and selectivity to α_vβ₃ integrin. This receptor is overexpressed in tumor and tumor endothelial cells in the case of numerous cancer cell lines, therefore, it is an excellent biomarker for cancer diagnosis. The galectin-3 protein is also highly expressed in tumor cells and N-acetyllactosamine is a well-established ligand of this receptor. We have developed a synthetic method to prepare a lactosamine-containing radiotracer, namely ⁶⁸Ga-NODAGA-LacN-E[c(RGDfK)]₂, for cancer diagnosis. First, a lactosamine derivative with azido-propyl aglycone was synthetized. Then, NODAGA-NHS was attached to the amino group of this lactosamine derivative. The obtained compound was conjugated to an E[c(RGDfK)]₂ peptide with a strain-promoted click reaction. We have accomplished the radiolabeling of the synthetized NODAGA-LacN-E[c(RGDfK)]₂ precursor with a positron-emitting ⁶⁸Ga isotope (radiochemical yield of >95%). The purification of the labeled compound with solid-phase extraction resulted in a radiochemical purity of >99%. Subsequently, the octanol–water partition coefficient (log P) of the labeled complex was determined to be −2.58. In addition, the in vitro stability of ⁶⁸Ga-NODAGA-LacN-E[c(RGDfK)]₂ was investigated and it was found that it was stable under the examined conditions.

Structural Engineering of Fluorescent Self-Threaded Peptide Probes for Targeted Cell Imaging†

Squaraine figure-eight (SF8) molecules are a new class of deep-red fluorescent probes that are well suited for fluorescence cell microscopy due to their very high fluorescence brightness and excellent stability. Three homologous SF8 probes, with peptidyl loops that differ by very minor changes in the peptide sequence, were synthesized and assessed for probe uptake by cancer cells. One of probes included the RGD motif that is recognized by many classes of integrin receptors that reside on the surface of the cancer cells, and it permeated the cells by receptor-mediated endocytosis. In contrast, cell microscopy showed that there was negligible cell uptake of the two homologous SF8 probes indicating differences in probe targeting capability. The synthetic method allows for easy alteration of the peptide sequence; thus, it is straightforward to develop new classes of peptidyl SF8 probes with loop sequences that target other cancer biomarkers.

Preclinical Advances in Theranostics for the Different Molecular Subtypes of Breast Cancer

Breast cancer is the most common cancer in women worldwide. The heterogeneity of breast cancer and drug resistance to therapies make the diagnosis and treatment difficult. Molecular imaging methods with positron emission tomography (PET) and single-photon emission tomography (SPECT) provide useful tools to diagnose, predict, and monitor the response of therapy, contributing to precision medicine for breast cancer patients. Recently, many efforts have been made to find new targets for breast cancer therapy to overcome resistance to standard of care treatments, giving rise to new therapeutic agents to offer more options for patients with breast cancer. The combination of diagnostic and therapeutic strategies forms the foundation of theranostics. Some of these theranostic agents exhibit high potential to be translated to clinic. In this review, we highlight the most recent advances in theranostics of the different molecular subtypes of breast cancer in preclinical studies.

Molecular Targeting of Epidermal Growth Factor Receptor (EGFR) and Vascular Endothelial Growth Factor Receptor (VEGFR)

Epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor (VEGFR) are two extensively studied membrane-bound receptor tyrosine kinase proteins that are frequently overexpressed in many cancers. As a result, these receptor families constitute attractive targets for imaging and therapeutic applications in the detection and treatment of cancer. This review explores the dynamic structure and structure-function relationships of these two growth factor receptors and their significance as it relates to theranostics of cancer, followed by some of the common inhibition modalities frequently employed to target EGFR and VEGFR, such as tyrosine kinase inhibitors (TKIs), antibodies, nanobodies, and peptides. A summary of the recent advances in molecular imaging techniques, including positron emission tomography (PET), single-photon emission computerized tomography (SPECT), computed tomography (CT), magnetic resonance imaging (MRI), and optical imaging (OI), and in particular, near-IR fluorescence imaging using tetrapyrrolic-based fluorophores, concludes this review.

Nuclear Medicine in Times of COVID-19: How Radiopharmaceuticals Could Help to Fight the Current and Future Pandemics

The emergence and global spread of COVID-19, an infectious disease caused by the novel coronavirus SARS-CoV-2, has resulted in a continuing pandemic threat to global health. Nuclear medicine techniques can be used for functional imaging of (patho)physiological processes at the cellular or molecular level and for treatment approaches based on targeted delivery of therapeutic radionuclides. Ongoing development of radiolabeling methods has significantly improved the accessibility of radiopharmaceuticals for in vivo molecular imaging or targeted radionuclide therapy, but their use for biosafety threats such as SARS-CoV-2 is restricted by the contagious nature of these agents. Here, we highlight several potential uses of nuclear medicine in the context of SARS-CoV-2 and COVID-19, many of which could also be performed in laboratories without dedicated containment measures. In addition, we provide a broad overview of experimental or repurposed SARS-CoV-2-targeting drugs and describe how radiolabeled analogs of these compounds could facilitate antiviral drug development and translation to the clinic, reduce the incidence of late-stage failures and possibly provide the basis for radionuclide-based treatment strategies. Based on the continuing threat by emerging coronaviruses and other pathogens, it is anticipated that these applications of nuclear medicine will become a more important part of future antiviral drug development and treatment.

Anticancer peptide: Physicochemical property, functional aspect and trend in clinical application (Review)

Cancer is currently ineffectively treated using therapeutic drugs, and is also able to resist drug action, resulting in increased side effects following drug treatment. A novel therapeutic strategy against cancer cells is the use of anticancer peptides (ACPs). The physicochemical properties, amino acid composition and the addition of chemical groups on the ACP sequence influences their conformation, net charge and orientation of the secondary structure, leading to an effect on targeting specificity and ACP-cell interaction, as well as peptide penetrating capability, stability and efficacy. ACPs have been developed from both naturally occurring and modified peptides by substituting neutral or anionic amino acid residues with cationic amino acid residues, or by adding a chemical group. The modified peptides lead to an increase in the effectiveness of cancer therapy. Due to this effectiveness, ACPs have recently been improved to form drugs and vaccines, which have sequentially been evaluated in various phases of clinical trials. The development of the ACPs remains focused on generating newly modified ACPs for clinical application in order to decrease the incidence of new cancer cases and decrease the mortality rate. The present review could further facilitate the design of ACPs and increase efficacious ACP therapy in the near future.

ImmunoPET: Concept, Design, and Applications

Immuno-positron emission tomography (immunoPET) is a paradigm-shifting molecular imaging modality combining the superior targeting specificity of monoclonal antibody (mAb) and the inherent sensitivity of PET technique. A variety of radionuclides and mAbs have been exploited to develop immunoPET probes, which has been driven by the development and optimization of radiochemistry and conjugation strategies. In addition, tumor-targeting vectors with a short circulation time (e.g., Nanobody) or with an enhanced binding affinity (e.g., bispecific antibody) are being used to design novel immunoPET probes. Accordingly, several immunoPET probes, such as 89Zr-Df-pertuzumab and 89Zr-atezolizumab, have been successfully translated for clinical use. By noninvasively and dynamically revealing the expression of heterogeneous tumor antigens, immunoPET imaging is gradually changing the theranostic landscape of several types of malignancies. ImmunoPET is the method of choice for imaging specific tumor markers, immune cells, immune checkpoints, and inflammatory processes. Furthermore, the integration of immunoPET imaging in antibody drug development is of substantial significance because it provides pivotal information regarding antibody targeting abilities and distribution profiles. Herein, we present the latest immunoPET imaging strategies and their preclinical and clinical applications. We also emphasize current conjugation strategies that can be leveraged to develop next-generation immunoPET probes. Lastly, we discuss practical considerations to tune the development and translation of immunoPET imaging strategies.

Engineered Gold Nanoshells Killing Tumor Cells: New Perspectives

The current strategies to treat different kinds of cancer are mainly based on chemotherapy, surgery and radiation therapy. Unfortunately, these approaches are not specific and rather invasive as well. In this scenario, metal nano-shells, in particular gold-based nanoshells, offer interesting perspectives in the effort to counteract tumor cells, due to their unique ability to tune Surface Plasmon Resonance in different light-absorbing ranges. In particular, the Visible and Near Infrared Regions of the electromagnetic spectrum are able to penetrate through tissues. In this way, the light absorbed by the gold nanoshell at a specific wavelength is converted into heat, inducing photothermal ablation in treated cancer cells. Furthermore, inert gold shells can be easily functionalized with different types of molecules in order to bind cellular targets in a selective manner. This review summarizes the current state-of-art of nanosystems embodying gold shells, regarding methods of synthesis, bio-conjugations, bio-distribution, imaging and photothermal effects (in vitro and in vivo), providing new insights for the development of multifunctional antitumor drugs.

Dual Imaging Gold Nanoplatforms for Targeted Radiotheranostics

Gold nanoparticles (AuNPs) are interesting for the design of new cancer theranostic tools, mainly due to their biocompatibility, easy molecular vectorization, and good biological half-life. Herein, we report a gold nanoparticle platform as a bimodal imaging probe, capable of coordinating Gd³⁺ for Magnetic Resonance Imaging (MRI) and ⁶⁷Ga³⁺ for Single Photon Emission Computed Tomography (SPECT) imaging. Our AuNPs carry a bombesin analogue with affinity towards the gastrin releasing peptide receptor (GRPr), overexpressed in a variety of human cancer cells, namely PC3 prostate cancer cells. The potential of these multimodal imaging nanoconstructs was thoroughly investigated by the assessment of their magnetic properties, in vitro cellular uptake, biodistribution, and radiosensitisation assays. The relaxometric properties predict a potential T₁- and T₂- MRI application. The promising in vitro cellular uptake of ⁶⁷Ga/Gd-based bombesin containing particles was confirmed through biodistribution studies in tumor bearing mice, indicating their integrity and ability to target the GRPr. Radiosensitization studies revealed the therapeutic potential of the nanoparticles. Moreover, the DOTA chelating unit moiety versatility gives a high theranostic potential through the coordination of other therapeutically interesting radiometals. Altogether, our nanoparticles are interesting nanomaterial for theranostic application and as bimodal T₁- and T₂- MRI / SPECT imaging probes.

Furin-Guided Intracellular 68Ga Nanoparticle Formation Enhancing Tumor MicroPET Imaging

Positron-emission tomography (PET) is routinely used in the clinic for tumor imaging with ultrahigh sensitivity, but tumor-targeted PET imaging probes are quite few. In this work, we rationally designed a furin-responsive radiotracer Acetyl-Arg-Val-Arg-Arg-Cys(StBu)-Lys(DOTA-⁶⁸Ga)-CBT (CBT-⁶⁸Ga) and demonstrated that coinjection of the radiotracer with its cold analogue CBT-Ga instructed the formation of ⁶⁸Ga nanoparticles in furin-overexpressing MDA-MB-468 cancer cells, which significantly enhanced microPET imaging of the tumor in vivo. In vitro results showed that CBT-Ga subjected to furin-initiated CBT-Cys condensation reaction and self-assembly to form the nanoparticles CBT-Ga-NPs with an average diameter of 258.3 nm. In vivo microPET imaging results indicate that the mice coinjected with CBT-⁶⁸Ga and CBT-Ga, which warrants ⁶⁸Ga nanoparticle formation in their MDA-MB-468 tumors, had a tumor/liver ratio 9.1-fold of that of the mice only injected with CBT-⁶⁸Ga. We envisioned that, by replacing the RVRR substrate of CBT-⁶⁸Ga with other enzyme-specific ones and using the strategy of intracellular nanoparticle formation, a series of radioactive probes could be developed for more sensitive and precise tumor microPET imaging in the near future.

Carboxylesterase-Cleavable Biotinylated Nanoparticle for Tumor-Dual Targeted Imaging

Near-infrared (NIR) nanoprobes with fluorescence "Turn-On" property are advantageous in cancer diagnosis but, to the best of our knowledge, "smart" nanoprobe that simultaneously targets both biotin receptor and carboxylesterase (CES) for HepG2 tumor-dual targeted imaging has not been reported. Methods: Using CBT-Cys click condensation reaction, we rationally designed a "smart" NIR fluorescence probe H2N-Cys(StBu)-Lys(Biotin)-Ser(Cy5.5)-CBT (NIR-CBT) and used it to facilely prepare the fluorescence-quenched nanoparticle NIR-CBT-NP. Results: In vitro results indicated that, after NIR-CBT-NP was incubated with CES for 6 h, its fluorescence was turned "On" by 69 folds. Cell experiments verified that NIR-CBT-NP was uptaken by HepG2 cells via biotin receptor-assisted endocytosis and its fluorescence was turned "On" by intracellular CES hydrolysis. Moreover, NIR-CBT-NP was successfully applied to image both biotin receptor- and CES-overexpressing HepG2 tumors. Conclusion: Fluorescence-quenched nanoparticle NIR-CBT-NP was facilely prepared to actively target biotin receptor-overexpressing HepG2 cancer cells and turn the fluorescence "On" by intracellular CES hydrolysis for tumor-dual targeted imaging. We anticipate that our fluorescence "Turn-On" nanoparticle could be applied for liver cancer diagnosis in clinic in the near future.

PET Imaging of Receptor Tyrosine Kinases in Cancer

Overexpression and/or mutations of the receptor tyrosine kinase (RTK) subfamilies, such as epidermal growth factor receptors (EGFR) and vascular endothelial growth factor receptors (VEGFR), are closely associated with tumor cell growth, differentiation, proliferation, apoptosis, and cellular invasiveness. Monoclonal antibodies (mAb) and tyrosine kinase inhibitors (TKI) specifically inhibiting these RTKs have shown remarkable success in improving patient survival in many cancer types. However, poor response and even drug resistance inevitably occur. In this setting, the ability to detect and visualize RTKs with noninvasive diagnostic tools will greatly refine clinical treatment strategies for cancer patients, facilitate precise response prediction, and improve drug development. Positron emission tomography (PET) agents using targeted radioactively labeled antibodies have been developed to visualize tumor RTKs and are changing clinical decisions for certain cancer types. In the present review, we primarily focus on PET imaging of RTKs using radiolabeled antibodies with an emphasis on the clinical applications of these immunoPET probes. Mol Cancer Ther; 17(8); 1625-36. ©2018 AACR.

Seeing Is Believing: Nuclear Imaging of HIV Persistence

A major obstacle to HIV eradication is the presence of infected cells that persist despite suppressive antiretroviral therapy (ART). HIV largely resides outside of the peripheral circulation, and thus, numerous anatomical and lymphoid compartments that have the capacity to harbor HIV are inaccessible to routine sampling. As a result, there is a limited understanding of the tissue burden of HIV infection or anatomical distribution of HIV transcriptional and translational activity. Novel, non-invasive, in vivo methods are urgently needed to address this fundamental gap in knowledge. In this review, we discuss past and current nuclear imaging approaches that have been applied to HIV infection with an emphasis on current strategies to implement positron emission tomography (PET)-based imaging to directly visualize and characterize whole-body HIV burden. These imaging approaches have various limitations, such as the potential for limited PET sensitivity and specificity in the setting of ART suppression or low viral burden. However, recent advances in high-sensitivity, total-body PET imaging platforms and development of new radiotracer technologies that may enhance anatomical penetration of target-specific tracer molecules are discussed. Potential strategies to image non-viral markers of HIV tissue burden or focal immune perturbation are also addressed. Overall, emerging nuclear imaging techniques and platforms may play an important role in the development of novel therapeutic and HIV reservoir eradication strategies.

Mini-review: Targeted radiopharmaceuticals incorporating reversible, low molecular weight albumin binders

The combination of low molecular weight, reversible human serum albumin (HSA) binders with targeted radiopharmaceuticals in dual-targeted radioconjugates holds great promise, in particular for endoradiotherapy. Attachment of HSA-binders to radiopharmaceuticals extends their blood circulation time and results in an enhanced tumour uptake as well as often in an improved pharmacokinetic profile. In this mini-review, an overview of currently pursued approaches of this novel strategy is provided.

Dual integrin αvβ 3 and NRP-1-Targeting Paramagnetic Liposome for Tumor Early Detection in Magnetic Resonance Imaging

Enhanced MRI (magnetic resonance imaging) plays a vital role in the early detection of tumor but with low specificity. Molecular imaging of angiogenesis could efficiently deliver contrast agents to the tumor site by specific targeted carriers. We designed and synthesized dual-targeted paramagnetic liposomes functionalized with two angiogenesis-targeting ligands, the αVβ3 integrin-specific RGD (Arg-Gly-Asp) and the neuropilin-1 (NRP-1) receptor-specific ATWLPPR (Ala-Thr-Trp-Leu-Pro-Pro-Arg) (A7R). These liposomes were proved to be in the nanoparticle range and demonstrated to effectively encapsulate paramagnetic MRI contrast agents Gd-DTPA (gadolinium-diethylenetriamine pentaacetic acid). T1 relaxivity of various liposome formulations was lower than pure Gd-DTPA but with no statistically significant difference. In vitro cellular uptake and competitive inhibition assay showed the higher binding affinity of dual-targeted liposomes to HUVECs (human umbilical vein endothelial cells) and A549 cells compared with pure Gd-DTPA, non-targeted, and single-targeted liposomes, which was proved to be mediated by the binding of RGD/ανβ3-integrin and A7R/NRP1. For MR imaging of mice bearing A549 cells in vivo, dual-targeted liposomes reached the highest SER (signal enhancement rate) value with a significant difference at all experimental time points. It was about threefold increase compared to pure Gd-DTPA and non-targeted liposomes and was 1.5-fold of single-targeted liposomes at 2 h post injection. The SER was lowered gradually and decreased only by 40% of the peak value in 6 h. Dual-targeted liposomes were likely to exert a synergistic effect and the specificity of delivering Gd-DTPA to the tumor site. Therefore, dual-ανβ3-integrin-NRP1-targeting paramagnetic liposome with a RGD-ATWLPPR heterodimeric peptide might be a potent system for molecular imaging of tumor.

Utilizing Peptide Ligand GPCRs to Image and Treat Pancreatic Cancer

It is estimated that early detection of pancreatic ductal adenocarcinoma (PDAC) could increase long-term patient survival by as much as 30% to 40% (Seufferlein, T. et al., Nat. Rev. Gastroenterol. Hepatol.2016, 13, 74–75). There is an unmet need for reagents that can reliably identify early cancerous or precancerous lesions through various imaging modalities or could be employed to deliver anticancer treatments specifically to tumor cells. However, to date, many PDAC tumor-targeting strategies lack selectivity and are unable to discriminate between tumor and nontumor cells, causing off-target effects or unclear diagnoses. Although a variety of approaches have been taken to identify tumor-targeting reagents that can effectively direct therapeutics or imaging agents to cancer cells (Liu, D. et al., J. Controlled Release2015, 219, 632–643), translating these reagents into clinical practice has been limited, and it remains an area open to new methodologies and reagents (O’Connor, J.P. et al., Nat. Rev. Clin. Oncol. 2017, 14, 169–186). G protein–coupled receptors (GPCRs), which are key target proteins for drug discovery and comprise a large proportion of currently marketed therapeutics, hold significant promise for tumor imaging and targeted treatment, particularly for pancreatic cancer.