Imaging agents for the chemokine receptor 4 (CXCR4)

Inductively Coupled Plasma-Mass Spectrometry (ICP-MS): An Emerging Tool in Radiopharmaceutical Science

Although radioactive experiments are necessary in radiopharmaceutical drug discovery and theranostic cancer research, they are expensive, require special facilities, and face certain restrictions. Thus, finding techniques not involving radioactivity is highly beneficial for minimizing these disadvantages in such research. In this regard, methods using inductively coupled plasma-mass spectrometry (ICP-MS) have emerged as viable alternatives to traditional radioactive approaches. Despite its potential, practical applications of ICP-MS in radiopharmaceutical cancer research have only emerged in recent years. This Perspective focuses on the development and implementation of nonradioactive ICP-MS-based assays in radiopharmaceutical research and aims to inspire future research efforts in this area.

68Ga-pentixafor PET/CT in the localization diagnosis of primary aldosteronism concurrent subclinical cushing's syndrsome: two case reports

PURPOSE

Adrenal venous sampling (AVS) is recommended for subtyping primary aldosteronism (PA). However, in cases of PA, concurrent subclinical Cushing's syndrome (SCS) has the potential to confound AVS results. Pentixafor, a CXC chemokine receptor type 4-specific ligand, has been reported as a promising marker to evaluate functional nature of adrenal adenomas. This study aims to investigate the clinical value of Gallium-68 Pentixafor Positron Emission Tomography-Computed Tomography (68Ga-Pentixafor PET/CT) in the localization diagnosis of patients with PA plus SCS.

METHODS

Two patients with a confirmed diagnosis of PA plus SCS underwent AVS and 68Ga-Pentixafor PET/CT.

RESULTS

AVS results revealed no lateralization for both patients while 68Ga-Pentixafor PET/CT showed a unilateral adrenal nodule with increased uptake of 68Ga-Pentixafor. Unilateral adrenalectomy was performed based on the results of 68Ga-Pentixafor PET/CT. Subsequently, complete biochemical remission of autonomous aldosterone and cortisol secretion were achieved in both cases.

CONCLUSIONS

68Ga-Pentixafor PET/CT shows promising potential for the localization of aldosterone and cortisol co-secreting adrenal adenoma in patients with PA plus SCS.

Lessons learned in application driven imaging agent design for image-guided surgery

To meet the growing demand for intraoperative molecular imaging, the development of compatible imaging agents plays a crucial role. Given the unique requirements of surgical applications compared to diagnostics and therapy, maximizing translational potential necessitates distinctive imaging agent designs. For effective surgical guidance, exogenous signatures are essential and are achievable through a diverse range of imaging labels such as (radio)isotopes, fluorescent dyes, or combinations thereof. To achieve optimal in vivo utility a balanced molecular design of the tracer as a whole is required, which ensures a harmonious effect of the imaging label with the affinity and specificity (e.g., pharmacokinetics) of a pharmacophore/targeting moiety. This review outlines common design strategies and the effects of refinements in the molecular imaging agent design on the agent's pharmacological profile. This includes the optimization of affinity, pharmacokinetics (including serum binding and target mediated background), biological clearance route, the achievable signal intensity, and the effect of dosing hereon.

Theranostic Diagnostics

Diagnosing and then treating disease defines theranostics. The approach holds promise by facilitating targeted disease outcomes. The simultaneous analysis of finding the presence of disease pathophysiology while providing a parallel in treatment is a novel and effective strategy for seeking improved medical care. We discuss how theranostics improves disease outcomes is discussed. The chapter reviews the delivery of targeted therapies. Bioimaging techniques are highlighted as early detection and tracking systems for microbial infections, degenerative diseases, and cancers.

Cell Surface Engineering Tools for Programming Living Assemblies

Breakthroughs in precision cell surface engineering tools are supporting the rapid development of programmable living assemblies with valuable features for tackling complex biological problems. Herein, the authors overview the most recent technological advances in chemically- and biologically-driven toolboxes for engineering mammalian cell surfaces and triggering their assembly into living architectures. A particular focus is given to surface engineering technologies for enabling biomimetic cell-cell social interactions and multicellular cell-sorting events. Further advancements in cell surface modification technologies may expand the currently available bioengineering toolset and unlock a new generation of personalized cell therapeutics with clinically relevant biofunctionalities. The combination of state-of-the-art cell surface modifications with advanced biofabrication technologies is envisioned to contribute toward generating living materials with increasing tissue/organ-mimetic bioactivities and therapeutic potential.

Development of a Rare Earth Nanoprobe Enables In Vivo Real-Time Detection of Sentinel Lymph Node Metastasis of Breast Cancer Using NIR-IIb Imaging

Sentinel lymph node (SLN) biopsy plays a critical role in axillary staging of breast cancer. However, traditional SLN mapping does not accurately discern the presence or absence of metastatic disease. Detection of SLN metastasis largely hinges on examination of frozen sections or paraffin-embedded tissues post-SLN biopsy. To improve detection of SLN metastasis, we developed a second near-infrared (NIR-II) in vivo fluorescence imaging system, pairing erbium-based rare-earth nanoparticles (ErNP) with bright down-conversion fluorescence at 1,556 nm. To visualize SLNs bearing breast cancer, ErNPs were modified by balixafortide (ErNPs@POL6326), a peptide antagonist of the chemokine receptor CXCR4. The ErNPs@POL6326 probes readily drained into SLNs when delivered subcutaneously, entering metastatic breast tumor cells specifically via CXCR4-mediated endocytosis. NIR fluorescence signals increased significantly in tumor-positive versus tumor-negative SLNs, enabling accurate determination of SLN breast cancer metastasis. In a syngeneic mouse mammary tumor model and a human breast cancer xenograft model, sensitivity for SLN metastasis detection was 92.86% and 93.33%, respectively, and specificity was 96.15% and 96.08%, respectively. Of note, the probes accurately detected both macrometastases and micrometastases in SLNs. These results overall underscore the potential of ErNPs@POL6326 for real-time visualization of SLNs and in vivo screening for SLN metastasis.

SIGNIFICANCE

NIR-IIb imaging of a rare-earth nanoprobe that is specifically taken up by breast cancer cells can accurately detect breast cancer macrometastases and micrometastases in sentinel lymph nodes.

The Role of [68Ga]Ga-Pentixafor PET/CT or PET/MRI in Lymphoma: A Systematic Review

The aim of this systematic review was to investigate published data about the role of gallium-68 Pentixafor positron emission tomography/computed tomography ([⁶⁸Ga]Ga-Pentixafor PET/CT) or PET/magnetic resonance imaging (PET/MRI) in patients affected by lymphoma. A comprehensive computer literature search of the Scopus, PubMed/MEDLINE, and Embase databases was conducted including articles indexed up to June 2022. In total, 14 studies or subsets in studies were eligible for inclusion. From the analyses of the selected studies, the following main findings have been found: (1) lymphomas can be considered [⁶⁸Ga]Ga-Pentixafor avid diseases, also in cases of fluorine-18 fluorodeoxyglucose [¹⁸F]FDG-not avid forms such as lymphoplasmacytic lymphoma (LPL), chronic lymphocytic leukemia (CLL), marginal zone lymphoma (MZL) and central nervous system lymphoma (CNSL); (2) among lymphomas, mantle cell lymphoma (MCL) and MZL are those with highest [⁶⁸Ga]Ga-Pentixafor uptake; (3) [⁶⁸Ga]Ga-Pentixafor PET/CT or PET/MRI is a useful tool for the staging and treatment response evaluation; (4) [⁶⁸Ga]Ga-Pentixafor PET seems to have a better diagnostic performance than [¹⁸F]FDG PET in evaluating lymphomas. Despite several limitations affecting this analysis, especially related to the heterogeneity of the included studies, [⁶⁸Ga]Ga-Pentixafor PET may be considered a useful imaging method for staging and treatment response evaluation of several lymphomas, especially MZL, CNSL and LPL.

Clinical Applications of Immuno-PET in Lymphoma: A Systematic Review

Simple Summary

A systematic review of the published literature was performed to assess current clinicalapplications of immuno-PET in patients diagnosed with any histological type of lymphoma. The initial search yielded 1407 articles from PubMed/Medline and Scopus databases, but only 2 articles were found to comply with the inclusion criteria and 2 more were found during the cross-reference check. All four articles were deemed of sufficient methodological quality according to the QUADAS-2 assessment and were included in the review. Among the four included articles, three described the use of ⁸⁹Zr-labelled antibodies targeting CD20+ relapsed/refractory B-cell lymphomas and one concerned the use of ⁶⁸Ga-labelled mAb targeting CXCR4 in patients with non-Hodgkin lymphomas. Very limited literature data are currently available on the use of iPET in patients with lymphoma. However, iPET may represent a useful tool to non-invasively visualize the heterogeneous individual immunological environment, thus potentially guiding treatment-planning in lymphoma patients, and hence deserves further exploitation.

Abstract

Objective: Immuno-positron emission tomography (iPET) combines the sensitivity of the PET imaging technique and the targeting specificity of radio-labelled monoclonal antibodies (mAb). Its first clinical applications in humans were described in the late 1990s, and several pathologies have benefitted from this molecular imaging modality since then. Our scope was to assess current clinical applications of immuno-PET in patients with lymphoma. Therefore, a systematic review of the published literature was performed. Methods: PubMed/Medline and Scopus databases were independently searched by two nuclear medicine physicians, to identify studies describing the clinical use of immuno-PET in patients with lymphoma. Methodological quality of the included articles was assessed by using the Quality Assessment of Diagnostic Accuracy Studies criteria. The studies were then analyzed concerning the molecular target of interest. Results: The initial search yielded 1407 articles. After elimination of duplicates, 1339 titles/abstracts were evaluated. Only two articles were found to comply with the inclusion criteria and two more were found during the cross-reference check. Among the four included articles, three described the use of ⁸⁹Zr-labelled antibodies targeting CD20+ relapsed/refractory B-cell lymphomas and one concerned the use of ⁶⁸Ga-labelled mAb targeting CXCR4 in patients with non-Hodgkin lymphomas. Conclusions: Very limited literature data are currently available on the clinical use of iPET in patients with lymphoma. This technique is encountering obstacles in its wider use, possibly because of the need of specific facilities, unfavorable dosimetry, and unclear correlation of immuno-tracer biodistribution with patients’ clinical and tumors’ molecular characteristics. However, iPET may represent a useful tool to non-invasively visualize the heterogenous individual immunological environment, thus potentially guiding treatment-planning in lymphoma patients, and hence deserves further exploitation.

C-X-C Chemokine Receptor Type 4-Targeted Imaging in Glioblastoma Multiforme Using 64Cu-Radiolabeled Ultrasmall Gold Nanoclusters

Glioblastoma multiforme (GBM) is the most prevalent and aggressive primary malignant brain cancer in adults, and it carries a poor prognosis. Despite the current multimodality treatment, including surgery, radiation, and chemotherapy, the overall survival is still poor. Neurooncological imaging plays an important role in the initial diagnosis and prediction of the treatment response of GBM. Positron emission tomography (PET) imaging using radiotracers that target disease-specific hallmarks, which are both noninvasive and specific, has drawn much attention. C-X-C chemokine receptor 4 (CXCR4) plays an important role in neoangiogenesis and vasculogenesis, and, moreover, it is reported to be overexpressed in GBM, which is associated with poor patient survival; thus, CXCR4 can be an ideal candidate for PET imaging of GBM. Nanomaterials, which possess multifunctional capabilities, effective drug delivery, and favorable pharmacokinetics, are now being applied to improve the diagnosis and therapy of the most difficult-to-treat cancers. Herein, we engineered an ultrasmall, renal-clearable gold nanoclusters intrinsically radiolabeled with ⁶⁴Cu (⁶⁴Cu-AuNCs-FC131) for targeted PET imaging of CXCR4 in a U87 intracranial GBM mouse model. These targeted nanoclusters demonstrated specific binding to U87 cells with minimal cytotoxicity. The in vivo biodistribution showed favorable pharmacokinetics and efficient renal clearance. PET/computed tomography imaging of the U87 model revealed the effective delivery of ⁶⁴Cu-AuNCs-FC131 into the tumors. In vivo toxicity studies demonstrated insignificant safety concerns at various dosages, indicating its potential as a useful platform for GBM imaging and drug delivery.

In Vivo Targeting of CXCR4-New Horizons

Given its pre-eminent role in the context of tumor cell growth as well as metastasis, the C-X-C motif chemokine receptor 4 (CXCR4) has attracted a lot of interest in the field of nuclear oncology, and clinical evidence on the high potential of CXCR4-targeted theranostics is constantly accumulating. Additionally, since CXCR4 also represents a key player in the orchestration of inflammatory responses to inflammatory stimuli, based on its expression on a variety of pro- and anti-inflammatory immune cells (e.g., macrophages and T-cells), CXCR4-targeted inflammation imaging has recently gained considerable attention. Therefore, after briefly summarizing the current clinical status quo of CXCR4-targeted theranostics in cancer, this review primarily focuses on imaging of a broad spectrum of inflammatory diseases via the quantification of tissue infiltration with CXCR4-expressing immune cells. An up-to-date overview of the ongoing preclinical and clinical efforts to visualize inflammation and its resolution over time is provided, and the predictive value of the CXCR4-associated imaging signal for disease outcome is discussed. Since the sensitivity and specificity of CXCR4-targeted immune cell imaging greatly relies on the availability of suitable, tailored imaging probes, recent developments in the field of CXCR4-targeted imaging agents for various applications are also addressed.

The role of fluorescent and hybrid tracers in radioguided surgery in urogenital malignancies

The increasing availability of new imaging technologies and tracers has enhanced the application of nuclear molecular imaging in urogenital interventions. In this context, preoperative nuclear imaging and radioactivity-based intraoperative surgical guidance have become important tools for the identification and anatomical allocation of tumor lesions and/or suspected lymph nodes. Fluorescence guidance can provide visual identification of the preoperatively defined lesions during surgery. However, the added value of fluorescence guidance is still mostly unknown. This review provides an overview of the role of fluorescence imaging in radioguided surgery in urogenital malignancies. The sentinel node (SN) biopsy procedure using hybrid tracers (radioactive and fluorescent component) serves as a prominent example for in-depth evaluation of the complementary value of radio- and fluorescence guidance. The first large patient cohort and long-term follow-up studies show: 1) improvement in the SN identification rate compared to blue dye; 2) improved detection of cancer-positive SNs; and 3) hints towards a positive effect on (biochemical) recurrence rates compared to extended lymph node dissection. The hybrid tracer approach also highlights the necessity of a preoperative roadmap in preventing incomplete resection. Recent developments focus on receptor-targeted approaches that allow intraoperative identification of tumor tissue. Here radioguidance is still leading, but fluorescent and hybrid tracers are also finding their way into the clinic. Emerging multiwavelength approaches that allow concomitant visualization of different anatomical features within the surgical field may provide the next step towards even more refined procedures.

Intraoperative visualization of nerves using a myelin protein-zero specific fluorescent tracer

BACKGROUND

Surgically induced nerve damage is a common but debilitating side effect in oncological surgery. With the aim to use fluorescence guidance to enable nerve-sparing interventions in future surgery, a fluorescent tracer was developed that specifically targets myelin protein zero (P0).

RESULTS

Truncated homotypic P0 protein-based peptide sequences were C-terminally functionalized with the far-red cyanine dye Cy5. The lead compound Cy5-P0101-125 was selected after initial solubility, (photo)physical and in vitro evaluation (including P0-blocking experiments). Cy5-P0101-125 (KD = 105 ± 17 nM) allowed in vitro and ex vivo P0-related staining. Furthermore, Cy5-P0101-125  enabled in vivo fluorescence imaging of the Sciatic nerve in mice after local intravenous (i.v.) administration and showed compatibility with a clinical fluorescence laparoscope during evaluation in a porcine model undergoing robot-assisted surgery. Biodistribution data revealed that i.v. administered [111In]In-DTPA-P0101-125 does not enter the central nervous system (CNS).

CONCLUSION

P0101-125 has proven to be a potent nerve-specific agent that is able to target P0/myelin under in vitro, ex vivo, and in vivo conditions without posing a threat for CNS-related toxicity.

Translation of c-Met Targeted Image-Guided Surgery Solutions in Oral Cavity Cancer-Initial Proof of Concept Data

Simple Summary

Translation of tumor-specific fluorescent tracers is crucial in the realization intraoperative of tumor identification during fluorescence-guided surgery. Ex vivo assessment of surgical specimens after topical tracer application has the potential to reveal the suitability of a potential surgical target prior to in vivo use in patients. In this study, the c-Met receptor was identified as a possible candidate for fluorescence-guided surgery in oral cavity cancer. Freshly excised tumor specimens obtained from ten patients with squamous cell carcinoma of the tongue were incubated with EMI-137 and imaged with a clinical-grade Cy5 prototype fluorescence camera. In total, 9/10 tumors were fluorescently illuminated, while non-visualization could be linked to non-superficial tumor localization. Immunohistochemistry revealed c-Met expression in all ten specimens. Tumor assessment was improved via video representation of the tumor-to-background ratio.

Abstract

Intraoperative tumor identification (extension/margins/metastases) via receptor-specific targeting is one of the ultimate promises of fluorescence-guided surgery. The translation of fluorescent tracers that enable tumor visualization forms a critical component in the realization of this approach. Ex vivo assessment of surgical specimens after topical tracer application could help provide an intermediate step between preclinical evaluation and first-in-human trials. Here, the suitability of the c-Met receptor as a potential surgical target in oral cavity cancer was explored via topical ex vivo application of the fluorescent tracer EMI-137. Freshly excised tumor specimens obtained from ten patients with squamous cell carcinoma of the tongue were incubated with EMI-137 and imaged with a clinical-grade Cy5 prototype fluorescence camera. In-house developed image processing software allowed video-rate assessment of the tumor-to-background ratio (TBR). Fluorescence imaging results were related to standard pathological evaluation and c-MET immunohistochemistry. After incubation with EMI-137, 9/10 tumors were fluorescently illuminated. Immunohistochemistry revealed c-Met expression in all ten specimens. Non-visualization could be linked to a more deeply situated lesion. Tumor assessment was improved via video representation of the TBR (median TBR: 2.5 (range 1.8–3.1)). Ex vivo evaluation of tumor specimens suggests that c-Met is a possible candidate for fluorescence-guided surgery in oral cavity cancer.

Automated Synthesis of Fluorine-18 Labeled CXCR4 Ligand via the Conjugation with Nicotinic Acid N-Hydroxysuccinimide Ester (6-[18F]SFPy)

The C-X-C motif chemokine receptor 4 (CXCR4) is a seven-transmembrane G protein-coupled receptor that is overexpressed in numerous diseases, particularly in various cancers and is a powerful chemokine, attracting cells to the bone marrow niche. Therefore, CXCR4 is an attractive target for imaging and therapeutic purposes. The goal of this study is to develop an efficient, reproducible, and straightforward method to prepare a fluorine-18 labeled CXCR4 ligand. 6-[18F]Fluoronicotinic acid-2,3,5,6-tetrafluorophenyl ester (6-[18F]FPy-TFP) and nicotinic acid N-hydroxysuccinimide ester (6-[18F]SFPy) have been prepared using 'fluorination on the Sep-Pak' method. Conjugation of 6-[18F]SFPy or 6-[18F]FPy-TFP with the alpha-amino group at the N terminus of the protected T140 precursor followed by deprotection, yielded the final product 6-[18F]FPy-T140. The overall radiochemical yields were 6-17% (n = 15, decay-corrected) in a 90-min radiolabeling time with a radiochemical purity >99%. 6-[18F]FPy-T140 exhibited high specific binding and nanomolar affinity for CXCR4 in vitro, indicating that the biological activity of the peptide was preserved. For the first time, [18F]SFPy has been prepared using 'fluorination on the Sep-Pak' method that allows rapid automated synthesis of 6-[18F]FPy-T140. In addition to increased synthetic efficiency, this construct binds with CXCR4 in high affinity and may have potential as an in vivo positron emission tomography (PET) imaging agent. This radiosynthesis method should encourage wider use of this PET agent to quantify CXCR4 in both research and clinical settings.

CXCR4 antagonist AMD3100 (plerixafor): From an impurity to a therapeutic agent

AMD3100 (plerixafor), a CXCR4 antagonist, has opened a variety of avenues for potential therapeutic approaches in different refractory diseases. The CXCL12/CXCR4 axis and its signaling pathways are involved in diverse disorders including HIV-1 infection, tumor development, non-Hodgkin lymphoma, multiple myeloma, WHIM Syndrome, and so on. The mechanisms of action of AMD3100 may relate to mobilizing hematopoietic stem cells, blocking infection of X4 HIV-1, increasing circulating neutrophils, lymphocytes and monocytes, reducing myeloid-derived suppressor cells, and enhancing cytotoxic T-cell infiltration in tumors. Here, we first revisit the pharmacological discovery of AMD3100. We then review monotherapy of AMD3100 and combination use of AMD3100 with other agents in various diseases. Among those, we highlight the perspective of AMD3100 as an immunomodulator to regulate immune responses particularly in the tumor microenvironment and synergize with other therapeutics. All the pre-clinical studies support the clinical testing of the monotherapy and combination therapies with AMD3100 and further development for use in humans.

Design, synthesis, and biological characterization of a new class of symmetrical polyamine-based small molecule CXCR4 antagonists

CXCR4, a well-studied coreceptor of human immunodeficiency virus type 1 (HIV-1) entry, recognizes its cognate ligand SDF-1α (also named CXCL12) which plays many important roles, including regulating immune cells, controlling hematopoietic stem cells, and directing cancer cells migration. These pleiotropic roles make CXCR4 an attractive target to mitigate human disorders. Here a new class of symmetrical polyamines was designed and synthesized as potential small molecule CXCR4 antagonists. Among them, a representative compound 21 (namely HF50731) showed strong CXCR4 binding affinity (mean IC₅₀ = 19.8 nM) in the CXCR4 competitive binding assay. Furthermore, compound 21 significantly inhibited SDF-1α-induced calcium mobilization and cell migration, and blocked HIV-1 infection via antagonizing CXCR4 coreceptor function. The structure-activity relationship analysis, site-directed mutagenesis, and molecular docking were conducted to further elucidate the binding mode of compound 21, suggesting that compound 21 could primarily occupy the minor subpocket of CXCR4 and partially bind in the major subpocket by interacting with residues W94, D97, D171, and E288. Our studies provide not only new insights for the fragment-based design of small molecule CXCR4 antagonists for clinical applications, but also a new and effective molecular probe for CXCR4-targeting biological studies.

A benzenesulfonamide derivative as a novel PET radioligand for CXCR4

CXCR4 is involved in various diseases such as inflammation, tumor growth, and cancer metastasis through the interaction with its natural endogenous ligand, chemokine CXCL12. In an effort to develop imaging probes for CXCR4, we developed a novel small molecule CXCR4-targeted PET agent (compound 5) by combining our established benzenesulfonamide scaffold with a labeling component by virtue of click chemistry. 5 shows nanomolar affinity (IC50 = 6.9 nM) against a known CXCR4 antagonist (TN14003) and inhibits more than 65% chemotaxis at 10 nM in vitro assays. Radiofluorinated compound 5 ([18F]5) demonstrates a competitive cellular uptake against CXCL12 in a dose-dependent manner. Further, microPET images of [18F]5 exhibits preferential accumulation of radioactivity in the lesions of λ-carrageenan-induced paw edema, human head and neck cancer orthotopic xenograft, and metastatic lung cancer of each mouse model.

Potential targets for tumor-specific imaging of vulvar squamous cell carcinoma: A systematic review of candidate biomarkers

INTRODUCTION

Vulvar squamous cell carcinoma (VSCC) is a rare malignancy with an increasing incidence, especially in young women. Surgical treatment of VSCC is associated with significant morbidity and high recurrence rates, which is related to the limited ability to distinguish (pre)malignant from healthy tissue. There is a need for new tools for specific real-time detection of occult tumor lesions and localization of cancer margins in patients with VSCC. Several tumor-specific imaging techniques are developed to recognize malignant tissue by targeting tumor markers. We present a systematic review to identify, evaluate, and summarize potential markers for tumor-specific imaging of VSCC.

METHODS

Relevant papers were identified by a systematic cross-database literature search developed with assistance of an experienced librarian. Data were extracted from eligible papers and reported based on the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. VSCC-specific tumor markers were valued based on a weighted scoring system, in which each biomarker was granted points based on ranked eligibility criteria: I) percentage expression, II) sample size, and III) in vivo application.

RESULTS

In total 627 papers were included of which 22 articles met the eligibility criteria. Twelve VSCC-specific tumor markers were identified and of these 7 biomarkers were considered most promising: EGFR, CD44v6, GLUT1, MRP1, MUC1, CXCR-4 and VEGF-A.

DISCUSSION

This overview identified 7 potential biomarkers that can be used in the development of VSCC-specific tracers for real-time and precise localization of tumor tissue before, during, and after treatment. These biomarkers were identified in a small number of samples, without discriminating for VSCC-specific hallmarks such as HPV-status. Before clinical development, experimental studies should first aim at validation of these biomarkers using immunohistochemistry and cell line-based examination, discriminating for HPV-status and the expression rate in lymph nodes and precursor lesions.

64Cu-Labeled Ubiquitin for PET Imaging of CXCR4 Expression in Mouse Breast Tumor

Ubiquitin has been recently identified as a chemokine receptor 4 (CXCR4) natural ligand, offering great potential for positron emission computed tomography (PET) imaging of CXCR4 expression. This study reports the preparation and evaluation of (64Cu)-radiolabeled ubiquitin for CXCR4 imaging. The ubiquitin was first fused with a C-terminal GGCGG sequence, and the resulting recombinant ubiquitin derivative UbCG4 was then functionalized with the trans-cyclooctene (TCO) moiety via thiol-maleimide click reaction, followed by 64Cu-radiolabeling through the TCO/Tz (tetrazine)-based Diels-Alder click reaction. In the prepared in vitro studies, the prepared (64Cu)-UbCG4 showed significantly higher specific uptakes in the 4T1 breast cancer cells compared with the uptakes in the CXCR4-knockdown 4T1 cells. In the in vivo evaluation in the 4T1-xenograft mouse model, (64Cu)-UbCG4 demonstrated a similar tumor uptake but much lower backgrounds compared with 64Cu-labeled AMD3465. These results suggested that (64Cu)-UbCG4 could serve as a potent PET tracer for the noninvasive imaging of CXCR4 expression in tumors.

Biomedical applications of radioiodinated peptides

The overexpression of peptide receptors in certain tumors as compared to endogeneous expression levels represents the molecular basis for the design of peptide-based tools for targeted nuclear imaging and therapy. Receptor targeting with radiolabelled peptides became a very important imaging and/or therapeutic approach in nuclear medicine and oncology. A great variety of peptides has been radiolabelled with clinical relevant radionuclides, such as radiometals and radiohalogens. However, to the best of our knowledge concise and updated reviews providing information about the biomedical application of radioiodinated peptides are still missing. This review outlines the synthetic efforts in the preparation of radioiodinated peptides highlighting the importance of radioiodine in nuclear medicine, giving an overview of the most relevant radioiodination strategies that have been employed and describes relevant examples of their use in the biomedical field.

High-resolution imaging and single-cell analysis via laser ablation-inductively coupled plasma-mass spectrometry for the determination of membranous receptor expression levels in breast cancer cell lines using receptor-specific hybrid tracers

This work evaluates the possibility of placement of high-resolution imaging and single-cell analysis via laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) within precision medicine by assessing the suitability of LA-ICP-MS as a micro-analytical technique for the localization and quantification of membranous receptors in heterogeneous cell samples that express both the membrane-bound receptors C-X-C chemokine receptor type 4 (CXCR4) and epidermal growth factor receptor (EGFR). Staining of the breast cancer cell lines MDA-MB-231 X4 and MDA-MB-468 was achieved using receptor-specific hybrid tracers, containing both a fluorophore and a DTPA single-lanthanide chelate. Prior to LA-ICP-MS imaging, fluorescence confocal microscopy (FCM) imaging was performed to localize the receptors, hereby enabling direct comparison. Based on the different expression levels of CXCR4 and EGFR, a distinction could be made between the cell lines using both imaging modalities. Furthermore, FCM and LA-ICP-MS demonstrated complementary characteristics, as a more distinct discrimination could be made between both cell lines based on the EGFR-targeting hybrid tracer via LA-ICP-MS, due to the intrinsic CXCR4-related green fluorescent protein (GFP) signal present in the MDA-MB-231 X4 cells. Employing state-of-the-art LA-ICP-MS instrumentation in bidirectional area scanning mode for sub-cellular imaging of MDA-MB-231 X4 cells enabled the specific binding of the CXCR4-targeting hybrid tracer to the cell membrane to be clearly demonstrated. The stretching of cells over the glass substrate led to a considerably higher signal response for pixels at the cell edges, relative to the more central pixels. The determination of the expression levels of CXCR4 and EGFR for the MDA-MB-468 cell line was performed using LA-ICP-MS single-cell analysis (sc-LA-ICP-MS) and external calibration, based on the quantitative ablation of Ho-spiked dried gelatin droplet standards. Additionally, a second calibration approach was applied based on spot ablation of highly homogeneous dried gelatin gels in combination with the determination of the ablated volume using atomic force microscopy (AFM) and yielded results which were in good agreement with the expression levels determined via flow cytometry (FC) and mass cytometry (MC). Hybrid tracers enable a direct comparison between (i) FCM and LA-ICP-MS imaging for the evaluation of the microscopic binding pattern and between (ii) FC, MC and sc-LA-ICP-MS for the quantification of receptor expression levels in single cells.

Radionuclide-Labeled Peptides for Imaging and Treatment of CXCR4- Overexpressing Malignant Tumors

Malignant tumors are a major cause of death. The lack of methods that provide an early diagnosis and adequate treatment of cancers is the main obstacle to precision medicine. The C-X-C chemokine receptor 4 (CXCR4) is overexpressed in various tumors and plays a key role in tumor pathogenesis. Therefore, CXCR4-targeted molecular imaging can quickly and accurately detect and quantify CXCR4 abnormalities in real time. The expression level and activation status of CXCR4 are very important for screening susceptible populations and providing an accurate diagnosis and optimal treatment. In view of the fact that radionuclide-labeled peptides have become widely used for the diagnosis and treatment of tumors, this manuscript reviews the potential of different radionuclide-labeled peptide inhibitors for the targeted imaging of CXCR4- positive tumors and targeted treatment. The article also discusses the specificity and in vivo distribution of radionuclide-labeled peptide inhibitors, and translation of these inhibitors to the clinic.

The progression of HMGB1-induced autophagy in cancer biology

Autophagy is an important process of cellular degradation and has been proven to contribute to tumorigenesis. High-mobility group box 1 (HMGB1) is an abundant nonhistone protein that has been widely reported to play a central role in the induction of autophagy. In nucleus, HMGB1 upregulates the expression of HSP27 to induce autophagy. In cytoplasm, the Beclin-1/PI3K-III complex can be activated by HMGB1 to promote autophagy. Extracellular HMGB1 binds to the receptor for advanced glycation end products to induce autophagy. Recent studies have shown that HMGB1-induced autophagy exerts multiple functions in various cancers like proliferation. Moreover, inhibition of HMGB1-induced autophagy can reverse chemoresistance, which is regulated by noncoding RNAs such as microRNAs and lncRNAs. Here, we provide a brief introduction to HMGB1 and HMGB1-induced autophagy in cancer. We also discuss the challenges associated with performing further investigations on this issue. HMGB1-induced autophagy exerts significant functions in cancer and has potential utility for new strategy to reverse drug resistance.

Less Exploited GPCRs in Precision Medicine: Targets for Molecular Imaging and Theranostics

Precision medicine relies on individually tailored therapeutic intervention taking into account individual variability. It is strongly dependent on the availability of target-specific drugs and/or imaging agents that recognize molecular targets and patient-specific disease mechanisms. The most sensitive molecular imaging modalities, Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET), rely on the interaction between an imaging radioprobe and a target. Moreover, the use of target-specific molecular tools for both diagnostics and therapy, theranostic agents, represent an established methodology in nuclear medicine that is assuming an increasingly important role in precision medicine. The design of innovative imaging and/or theranostic agents is key for further accomplishments in the field. G-protein-coupled receptors (GPCRs), apart from being highly relevant drug targets, have also been largely exploited as molecular targets for non-invasive imaging and/or systemic radiotherapy of various diseases. Herein, we will discuss recent efforts towards the development of innovative imaging and/or theranostic agents targeting selected emergent GPCRs, namely the Frizzled receptor (FZD), Ghrelin receptor (GHSR-1a), G protein-coupled estrogen receptor (GPER), and Sphingosine-1-phosphate receptor (S1PR). The pharmacological and clinical relevance will be highlighted, giving particular attention to the studies on the synthesis and characterization of targeted molecular imaging agents, biological evaluation, and potential clinical applications in oncology and non-oncology diseases. Whenever relevant, supporting computational studies will be also discussed.

Bioorthogonally Applicable Fluorescence Deactivation Strategy for Receptor Kinetics Study and Theranostic Pretargeting Approaches

The availability of a receptor for theranostic pretargeting approaches was assessed by use of a new click-chemistry-based deactivatable fluorescence-quenching concept. The efficacy was evaluated in a cell-based model system featuring both membranous (available) and internalized (unavailable) receptor fractions of the clinically relevant receptor chemokine receptor 4 (CXCR4). Proof of concept was achieved with a deactivatable tracer consisting of a CXCR4-specific peptide functionalized with a Cy5 dye bearing a chemoselective azide handle (N3 -Cy5-AcTZ14011). Treatment with a Cy7 quencher dye (Cy7-DBCO) resulted in optically silent Cy7-[click]-Cy5-AcTZ14011. In situ, a >90 % FRET-based reduction of the signal intensity of N3 -Cy5-AcTZ14011 [KD =(222.4±25.2) nm] was seen within minutes after quencher addition. In cells, discrimination between the membranous and the internalized receptor fraction could be achieved through quantitative assessment of quenching/internalization kinetics. Similar evaluation of an activatable tracer variant based on the same targeting moiety (Cy5-S-S-Cy3-AcTZ14011) was unsuccessful in vitro. As such, using the described deactivatable approach to screen membrane receptors and their applicability in receptor-(pre-)targeted theranostics can become straightforward.

Heightened CXCR4 and CXCL12 expression in NF1-associated neurofibromas

BACKGROUND

Neurofibromatosis type 1 (NF1) is a common autosomal dominantly inherited disorder that affects both the skin and the nervous system. NF1 occurs due to the mutations in the NF1 gene. Neurofibromas are the most common Schwann cell-based tumors in NF1 patients, which are mainly categorized into dermal and plexiform neurofibromas. Studies on different tumor types demonstrate that CXCR4 expression increases in tumor tissues and is linked to metastasis and cancer progression.

PURPOSE

In the present study, we aimed to analyze the gene expression of CXCR4, and its ligand CXCL12, in human neurofibromas.

METHODS

Eight NF1 patients aged between 5 and 37 (2 males, 6 females) were selected. The patient group comprised 1 plexiform neurofibroma, 1 pheochromocytoma, and 6 dermal neurofibromas. Following pathological examination and diagnosis, tumors were co-stained with antibodies against Schwann cell marker S100 and target molecule CXCR4. CXCR4 expression in Schwann cell-based tumors was detected at the protein level. RNA isolated from the same tumors was used for RT-PCR-based studies to measure the quantitative expression of CXCR4 and CXCL12.

RESULTS

CXCR4 gene expression increased 3- to 120-fold and CXCL12 gene expression increased 33- to 512-fold in all human Schwann cell-based tumors.

CONCLUSION

In order to validate the role of CXCR4 and its relationship with CXCL12 in NF1, future studies should be performed with additional tumors and different tumor types.

Radiotheranostics in Cancer Diagnosis and Management

The fundamental foundation for precision medicine is accurate and specific targeting of cancer cells. Advances in the understanding of cancer biology, developments in diagnostic technologies, and expansion of therapeutic options have all contributed to the concept of personalized cancer care. Theranostics is the systematic integration of targeted diagnostics and therapeutics. The theranostic platform includes an imaging component that "sees" the lesions followed by administration of the companion therapy agent that "treats" the same lesions. This strategy leads to enhanced therapy efficacy, manageable adverse events, improved patient outcome, and lower overall costs. Radiotheranostics refers to the use of radionuclides for the paired imaging and therapy agents. Radioiodine is the classic radiotheranostic agent that has been used clinically in management of thyroid diseases for nearly 75 years. More recently there have been major exciting strides in radiotheranostics for neuroendocrine tumors and prostate cancer, among other conditions. Regulatory approval of a number of radiotheranostic pairs is anticipated in the near future. Continued support will be needed in research and development to keep pace with the current momentum in radiotheranostics innovations. Moreover, regulatory and reimbursement agencies need to streamline their requirements for seamless transfer of the radiotheranostic agents from the bench to the bedside. In this review, the concept, history, recent developments, current challenges, and outlook for radiotheranostics in the treatment of patients with cancer will be discussed. ^© RSNA, 2018.

The chemical diversity and structure-based evolution of non-peptide CXCR4 antagonists with diverse therapeutic potential

The CXC chemokine receptor 4 (CXCR4) is a highly reserved G-protein coupled 7-transmembrane (TM) chemokine receptor which consists of 352 amino acids. CXCR4 has only one endogenous chemokine ligand of CXCL12, besides several other natural nonchemokine ligands such as extracellular ubiquitin and noncognate ligand of MIF. CXCR4 strongly binds to CXCL12 and the resulting CXCLl2/CXCR4 axis is the molecular basis of their various biological functions, which include: (1) mediating immune and inflammatory response; (2) regulation of hematopoietic stem cell migration and homing; (3) an essential co-receptor for HIV entry into host cells; (4) participation in the process of embryonic development; (5) malignant tumor invasion and metastasis; (6) myocardial infarction, ischemic stroke and acute kidney injury. Correspondingly, CXCR4 antagonists find potential therapeutic applications in HIV infection, as well as hematopoietic stem cell migration, inflammation, immune-related diseases, tumor and ischemic diseases. Recently, great achievements have been made and a number of non-peptide CXCR4 antagonists with diversity scaffolds have been discovered. In this review, the discovery of small molecule CXCR4 antagonists focused on the structures, activities, evolution and development of representative CXCR4 antagonists is comprehensively described. The central role of CXCR4 in diverse cellular signaling pathways and its involvement in several diseases progressions are discussed as well.

High expression of SDF-1 and VEGF is associated with poor prognosis in patients with synovial sarcomas

Stromal cell-derived factor-1 (SDF-1) predicts poor clinical outcomes of certain types of cancer. Furthermore, vascular endothelial growth factor (VEGF) promotes the growth and metastasis of solid tumors. The aim of the present study was to examine the expression of SDF-1 and VEGF in patients with synovial sarcoma and to determine their expression is correlated with unfavorable outcomes. Levels of SDF-1 and VEGF proteins were evaluated in 54 patients with synovial sarcoma using immunohistochemical and immunofluorescence staining. Potential associations between the expression of SDF-1 and VEGF and various clinical parameters were analyzed using Pearson's χ² test and the Spearman-rho test. Additionally, univariate and multivariate Cox regression analyses were used to identify potential prognostic factors, and the Kaplan-Meier method was used to analyze the overall survival rates of patients. Low SDF-1 and VEGF expression was detected in 20.4% (11/54) and 22.2% (12/54) of patients with synovial sarcoma; moderate expression was detected in 35.2% (19/54) and 37.0% (20/54) of patients and high expression was detected in 44.4% (24 of 54) and 40.7% (22 of 54) of patients, respectively. Levels of SDF-1 and VEGF proteins were significantly associated with histological grade (P<0.05), metastasis (P<0.05) and American Joint Committee on Cancer staging (P<0.05). In addition, levels of SDF-1 and VEGF expression were positively correlated with each other (P<0.001). Univariate analysis also indicated that VEGF expression was associated with shorter overall survival rates in (P<0.05), whereas multivariate analysis demonstrated that SDF-1 expression was associated with shorter patient survival rates (P<0.05). Finally, both SDF-1 and VEGF expression were associated with various characteristics of synovial sarcoma. Therefore, SDF-1 expression may be a potential independent prognostic indicator in patients with synovial sarcomas.

A fully human CXCR4 antibody demonstrates diagnostic utility and therapeutic efficacy in solid tumor xenografts

For physiologically important cancer therapeutic targets, use of non-invasive imaging for therapeutic guidance and monitoring may improve outcomes for treated patients. The CXC chemokine receptor 4 (CXCR4) is overexpressed in many cancers including non-small cell lung cancer (NSCLC) and triple negative breast cancer (TNBC). CXCR4 overexpression contributes to tumor growth, progression and metastasis. There are several CXCR4-targeted therapeutic agents currently in clinical trials. Since CXCR4 is also crucial for normal biological functions, its prolonged inhibition could lead to unwanted toxicities. While CXCR4-targeted imaging agents and inhibitors have been reported and evaluated independently, there are currently no studies demonstrating CXCR4-targeted imaging for therapeutic guidance.

Monoclonal antibodies (mAbs) are commonly used for cancer therapy and imaging. Here, an ⁸⁹Zr-labeled human CXCR4-mAb (⁸⁹Zr-CXCR4-mAb) was evaluated for detection of CXCR4 expression with positron emission tomography (PET) while its native unmodified analogue was evaluated for therapy in relevant models of NSCLC and TNBC. In vitro and in vivo evaluation of ⁸⁹Zr-CXCR4-mAb showed enhanced uptake in NSCLC xenografts with a high expression of CXCR4. It also had the ability to detect lymph node metastases in an experimental model of metastatic TNBC. Treatment of high and low CXCR4 expressing NSCLC and TNBC xenografts with CXCR4-mAb demonstrated a therapeutic response correlating with the expression of CXCR4. Considering the key role of CXCR4 in normal biological functions, our results suggest that combination of ⁸⁹Zr-CXCR4-mAb-PET with non-radiolabeled mAb therapy may provide a precision medicine approach for selecting patients with tumors that are likely to be responsive to this treatment.

In vivo Evaluation of an Engineered Cyclotide as Specific CXCR4 Imaging Reagent

The CXCR4 chemokine receptor plays a key regulatory role in many biological functions, including embryonic development and controlling leukocyte functions during inflammation and immunity. CXCR4 has been also associated with multiple types of cancers where its overexpression/activation promotes metastasis, angiogenesis, and tumor growth and/or survival. Furthermore, CXCR4 is involved in HIV replication, as it is a co-receptor for viral entry into host cells. Altogether, these features make CXCR4 a very attractive target for the development of imaging and therapeutic agents. Here, the in vivo evaluation of the MCoTI-based cyclotide, MCo-CVX-5c, for the development of imaging agents that target CXCR4 is reported. Cyclotide MCo-CVX-5c is a potent CXCR4 antagonist with a remarkable in vivo resistance to biological degradation in serum. A [64 Cu]-DOTA-labeled version of this cyclotide demonstrated high and significant uptake in U87-stb-CXCR4 tumors compared to the control U87 tumors. Furthermore, protracted imaging studies demonstrated radiotracer retention in the U87-stb-CXCR4 tumor at 24 h post injection. Uptake in U87-stb-CXCR4 tumors could be blocked by unlabeled MCo-CVX-5c, showing high in vivo specificity. These results demonstrate the in vivo specificity and retention of a bioactive molecularly targeted cyclotide and highlight the potential of bioactive cyclotides for the development of new imaging agents that target CXCR4.

Screening of cancer tissue arrays identifies CXCR4 on adrenocortical carcinoma: correlates with expression and quantification on metastases using 64Cu-plerixafor PET

Expression of the chemokine receptor CXCR4 by many cancers correlates with aggressive clinical behavior. As part of the initial studies in a project whose goal was to quantify CXCR4 expression on cancers non-invasively, we examined CXCR4 expression in cancer samples by immunohistochemistry using a validated anti-CXCR4 antibody. Among solid tumors, we found expression of CXCR4 on significant percentages of major types of kidney, lung, and pancreatic adenocarcinomas, and, notably, on metastases of clear cell renal cell carcinoma and squamous cell carcinoma of the lung. We found particularly high expression of CXCR4 on adrenocortical cancer (ACC) metastases. Microarrays of ACC metastases revealed correlations between expression of CXCR4 and other chemokine system genes, particularly CXCR7/ACKR3, which encodes an atypical chemokine receptor that shares a ligand, CXCL12, with CXCR4. A first-in-human study using ⁶⁴Cu-plerixafor for PET in an ACC patient prior to resection of metastases showed heterogeneity among metastatic nodules and good correlations among PET SUVs, CXCR4 staining, and CXCR4 mRNA. Additionally, we were able to show that CXCR4 expression correlated with the rates of growth of the pulmonary lesions in this patient. Further studies are needed to understand better the role of CXCR4 in ACC and whether targeting it may be beneficial. In this regard, non-invasive methods for assessing CXCR4 expression, such as PET using ⁶⁴Cu-plerixafor, should be important investigative tools.

Cyclotides: Overview and Biotechnological Applications

Cyclotides are globular microproteins with a unique head-to-tail cyclized backbone, stabilized by three disulfide bonds forming a cystine knot. This unique circular backbone topology and knotted arrangement of three disulfide bonds makes them exceptionally stable to chemical, thermal, and biological degradation compared to other peptides of similar size. In addition, cyclotides have been shown to be highly tolerant to sequence variability, aside from the conserved residues forming the cystine knot. Cyclotides can also cross cellular membranes and are able to modulate intracellular protein-protein interactions, both in vitro and in vivo. All of these features make cyclotides highly promising as leads or frameworks for the design of peptide-based diagnostic and therapeutic tools. This article provides an overview on cyclotides and their applications as molecular imaging agents and peptide-based therapeutics.

Fluorescent CXCR4 targeting peptide as alternative for antibody staining in Ewing sarcoma

Background

Ewing sarcoma is an aggressive, highly metastatic primary bone and soft tissue tumor most frequently occurring in the bone of young adolescents. Patients, especially those diagnosed with a metastatic disease, have a poor overall survival. Chemokine receptor CXCR4 has a key pro-tumorigenic role in the tumor microenvironment of Ewing sarcoma and has been suggested to be involved in the increased metastatic propensity. Earlier studies on CXCR4 protein expression in Ewing sarcoma yielded contradictory results when compared to CXCR4 RNA expression studies. Previously, we demonstrated that CXCR4 expression could be detected in vivo using the fluorescently tagged CXCR4-specific peptide MSAP-Ac-TZ14011. Therefore, we studied the membranous CXCR4 expression in Ewing sarcoma cell lines using MSAP-Ac-TZ14011.

Methods

The CXCR4 membrane expression levels were studied in EWS cell lines by flow cytometry using the hybrid peptide MSAP-Ac-TZ14011 and were correlated to CXCR4 RNA expression levels. The measurements were compared to levels detected using the CXCR4 antibody ab2074 under various cell preparation conditions. In addition, the staining patterns were analyzed by confocal fluorescence microscopy over time.

Results

The hybrid peptide MSAP-Ac-TZ14011 levels showed a strong and better correlation of CXCR4 membrane expression with the CXCR4 RNA expression levels than observed with the anti-CXCR4 antibody ab2074. With the hybrid peptide MSAP-Ac-TZ14011 using live cell confocal microscopy CXCR4 membrane staining and internalization was detected and the signal intensity correlated well with CXCR4 mRNA expression levels.

Conclusions

The fluorescently labeled CXCR4 targeting peptide-based method provides a reliable alternative to antibody staining to study the CXCR4 membrane expression in live cells using either flow cytometry or live cell fluorescence microscopy. The fluorescently tagged CXCR4 targeting peptide could enable in vivo detection of CXCR4 expression in Ewing sarcoma which may help to stratify cases for anti-CXCR4 therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3352-z) contains supplementary material, which is available to authorized users.

Molecular imaging probes derived from natural peptides

Covering: up to the end of 2015.Peptides are naturally occurring compounds that play an important role in all living systems and are responsible for a range of essential functions. Peptide receptors have been implicated in disease states such as oncology, metabolic disorders and cardiovascular disease. Therefore, natural peptides have been exploited as diagnostic and therapeutic agents due to the unique target specificity for their endogenous receptors. This review discusses a variety of natural peptides highlighting their discovery, endogenous receptors, as well as their derivatization to create molecular imaging agents, with an emphasis on the design of radiolabelled peptides. This review also highlights methods for discovering new and novel peptides when knowledge of specific targets and endogenous ligands are not available.

The dual role and therapeutic potential of high-mobility group box 1 in cancer

High-mobility group box 1 (HMGB1) is an abundant protein in most eukaryocytes. It can bind to several receptors such as advanced glycation end products (RAGE) and Toll-like receptors (TLRs), in direct or indirect way. The biological effects of HMGB1 depend on its expression and subcellular location. Inside the nucleus, HMGB1 is engaged in many DNA events such as DNA repair, transcription, telomere maintenance, and genome stability. While outside the nucleus, it possesses more complicated functions, including regulating cell proliferation, autophagy, inflammation and immunity. During tumor development, HMGB1 has been characterized as both a pro- and anti-tumoral protein by either promoting or suppressing tumor growth, proliferation, angiogenesis, invasion and metastasis. However, the current knowledge concerning the positive and negative effects of HMGB1 on tumor development is not explicit. Here, we evaluate the role of HMGB1 in tumor development and attempt to reconcile the dual effects of HMGB1 in carcinogenesis. Furthermore, we would like to present current strategies targeting against HMGB1, its receptor or release, which have shown potentially therapeutic value in cancer intervention.

[64Cu]NOTA-pentixather enables high resolution PET imaging of CXCR4 expression in a preclinical lymphoma model

BACKGROUND

The chemokine receptor 4 (CXCR4) is an important molecular target for both visualization and therapy of tumors. The aim of the present study was the synthesis and preclinical evaluation of a 64Cu-labeled, CXCR4-targeting peptide for positron emission tomography (PET) imaging of CXCR4 expression in vivo.

METHODS

For this purpose, 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA), or 1,4,7-triazacyclononane-triacetic acid (NOTA) was conjugated to the highly affine CXCR4-targeting pentixather scaffold. Affinities were determined using Jurkat T-lymphocytes in competitive binding assays employing [125I]FC131 as the radioligand. Internalization and efflux studies of [64Cu]NOTA-pentixather were performed in chem-1 cells, stably transfected with hCXCR4. The stability of the tracer was evaluated in vitro and in vivo. Small-animal PET and biodistribution studies at different time points were performed in Daudi lymphoma-bearing severe combined immunodeficiency (SCID) mice.

RESULTS

[64Cu]NOTA-pentixather was rapidly radiolabeled at 60 °C with high radiochemical yields ≥90% and purities >99%. [64Cu]NOTA-pentixather offered the highest affinity of the evaluated peptides in this study (IC50 = 14.9 ± 2.1 nM), showed efficient CXCR4-targeting in vitro and was stable in blood and urine with high resistance to transchelation in ethylenediaminetetraacetic acid (EDTA) challenge studies. Due to the enhanced lipophilicity of [64Cu]NOTA-pentixather (logP = -1.2), biodistribution studies showed some nonspecific accumulation in the liver and intestines. However, tumor accumulation (13.1 ± 1.5% ID/g, 1.5 h p.i.) was CXCR4-specific and higher than in all other organs and resulted in high resolution delineation of Daudi tumors in PET/CT images in vivo.

CONCLUSIONS

[64Cu]NOTA-pentixather was fast and efficiently radiolabeled, showed effective CXCR4-targeting, high stability in vitro and in vivo and resulted in high resolution PET/CT images accompanied with a suitable biodistribution profile, making [64Cu]NOTA-pentixather a promising tracer for future application in humans.

Hybrid Imaging Labels: Providing the Link Between Mass Spectrometry-Based Molecular Pathology and Theranostics

Background: Development of theranostic concepts that include inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS (LA-ICP-MS) imaging can be hindered by the lack of a direct comparison to more standardly used methods for in vitro and in vivo evaluation; e.g. fluorescence or nuclear medicine. In this study a bimodal (or rather, hybrid) tracer that contains both a fluorescent dye and a chelate was used to evaluate the existence of a direct link between mass spectrometry (MS) and in vitro and in vivo molecular imaging findings using fluorescence and radioisotopes. At the same time, the hybrid label was used to determine whether the use of a single isotope label would allow for MS-based diagnostics.

Methods: A hybrid label that contained both a DTPA chelate (that was coordinated with either ¹⁶⁵Ho or ¹¹¹In) and a Cy5 fluorescent dye was coupled to the chemokine receptor 4 (CXCR4) targeting peptide Ac-TZ14011 (hybrid-Cy5-Ac-TZ4011). This receptor targeting tracer was used to 1) validate the efficacy of (¹⁶⁵Ho-based) mass-cytometry in determining the receptor affinity via comparison with fluorescence-based flow cytometry (Cy5), 2) evaluate the microscopic binding pattern of the tracer in tumor cells using both fluorescence confocal imaging (Cy5) and LA-ICP-MS-imaging (¹⁶⁵Ho), 3) compare in vivo biodistribution patterns obtained with ICP-MS (¹⁶⁵Ho) and radiodetection (¹¹¹In) after intravenous administration of hybrid-Cy5-Ac-TZ4011 in tumor-bearing mice. Finally, LA-ICP-MS-imaging (¹⁶⁵Ho) was linked to fluorescence-based analysis of excised tissue samples (Cy5).

Results: Analysis with both mass-cytometry and flow cytometry revealed a similar receptor affinity, respectively 352 ± 141 nM and 245 ± 65 nM (p = 0.08), but with a much lower detection sensitivity for the first modality. In vitro LA-ICP-MS imaging (¹⁶⁵Ho) enabled clear discrimination between CXCR4 positive and negative cells, but fluorescence microscopy was required to determine the intracellular distribution. In vivo biodistribution patterns obtained with ICP-MS (¹⁶⁵Ho) and radiodetection (¹¹¹In) of the hybrid peptide were shown to be similar. Assessment of tracer distribution in excised tissues revealed the location of tracer uptake with both LA-ICP-MS-imaging and fluorescence imaging.

Conclusion: Lanthanide-isotope chelation expands the scope of fluorescent/radioactive hybrid tracers to include MS-based analytical tools such as mass-cytometry, ICP-MS and LA-ICP-MS imaging in molecular pathology. In contradiction to common expectations, MS detection using a single chelate imaging agent was shown to be feasible, enabling a direct link between nuclear medicine-based imaging and theranostic methods.

Obtaining control of cell surface functionalizations via Pre-targeting and Supramolecular host guest interactions

The use of mammalian cells for therapeutic applications is finding its way into modern medicine. However, modification or "training" of cells to make them suitable for a specific application remains complex. By envisioning a chemical toolbox that enables specific, but straight-forward and generic cellular functionalization, we investigated how membrane-receptor (pre)targeting could be combined with supramolecular host-guest interactions based on β-cyclodextrin (CD) and adamantane (Ad). The feasibility of this approach was studied in cells with membranous overexpression of the chemokine receptor 4 (CXCR4). By combining specific targeting of CXCR4, using an adamantane (Ad)-functionalized Ac-TZ14011 peptide (guest; KD = 56 nM), with multivalent host molecules that entailed fluorescent β-CD-Poly(isobutylene-alt-maleic-anhydride)-polymers with different fluorescent colors and number of functionalities, host-guest cell-surface modifications could be studied in detail. A second set of Ad-functionalized entities enabled introduction of additional surface functionalities. In addition, the attraction between CD and Ad could be used to drive cell-cell interactions. Combined we have shown that supramolecular interactions, that are based on specific targeting of an overexpressed membrane-receptor, allow specific and stable, yet reversible, surface functionalization of viable cells and how this approach can be used to influence the interaction between cells and their surroundings.

Straightforward synthesis of bis-tetraazacycloalkanes: towards new potential CXCR4 antagonists?

We report herein an efficient and general method for the synthesis of new bismacrocyclic compounds, structural analogues of biscyclam AMD3100, in which the two macrocycles are linked together through carbon atoms of the cycles.

Al[18F]NOTA-T140 Peptide for Noninvasive Visualization of CXCR4 Expression

PURPOSE

Chemokine receptor CXCR4 plays an important role in tumor aggressiveness, invasiveness, and metastasis formation. Quantification of CXCR4 expression by tumors may have an impact on prediction and evaluation of tumor response to therapies. In this study, we developed a robust and straightforward F-18 labeling route of T140, a CXCR4 peptide-based antagonist.

PROCEDURES

T140 derivative was conjugated to 1,4,7-triazacyclononane-triacetic acid (NOTA) and labeled with Al[(18)F]. Al[(18)F]NOTA-T140 was evaluated in vitro in cell-based assay and stability in mouse serum and in vivo using CXCR4 positive and negative tumor xenograft models.

RESULTS

Labeling of Al[(18)F]NOTA-T140 was completed within 30 min with a radiochemical yield of 58 ± 5.3 % at the end of synthesis, based on fluoride-18 activity. Al[(18)F]NOTA-T140 accumulated in CHO-CXCR4 positive but not negative tumors. Al[(18)F]NOTA-T140 uptake in the tumors correlated with CXCR4 protein expression. Moreover, Al[(18)F]NOTA-T140 had high accumulation in CXCR4-positive metastatic tumors.

CONCLUSIONS

The simplicity of Al[(18)F]NOTA-T140 labeling along with its properties to specifically image CXCR4 expression by tumors warrant further clinical application for the diagnosis of CXCR4 clinically.

Selecting Targets for Tumor Imaging: An Overview of Cancer-Associated Membrane Proteins

Tumor targeting is a booming business: The global therapeutic monoclonal antibody market accounted for more than $78 billion in 2012 and is expanding exponentially. Tumors can be targeted with an extensive arsenal of monoclonal antibodies, ligand proteins, peptides, RNAs, and small molecules. In addition to therapeutic targeting, some of these compounds can also be applied for tumor visualization before or during surgery, after conjugation with radionuclides and/or near-infrared fluorescent dyes. The majority of these tumor-targeting compounds are directed against cell membrane-bound proteins. Various categories of targetable membrane-bound proteins, such as anchoring proteins, receptors, enzymes, and transporter proteins, exist. The functions and biological characteristics of these proteins determine their location and distribution on the cell membrane, making them more, or less, accessible, and therefore, it is important to understand these features. In this review, we evaluate the characteristics of cancer-associated membrane proteins and discuss their overall usability for cancer targeting, especially focusing on imaging applications.

Gold Nanoclusters Doped with (64)Cu for CXCR4 Positron Emission Tomography Imaging of Breast Cancer and Metastasis

As an emerging class of nanomaterial, nanoclusters hold great potential for biomedical applications due to their unique sizes and related properties. Herein, we prepared a (64)Cu doped gold nanocluster ((64)CuAuNC, hydrodynamic size: 4.2 ± 0.5 nm) functionalized with AMD3100 (or Plerixafor) for targeted positron emission tomography (PET) imaging of CXCR4, an up-regulated receptor on primary tumor and lung metastasis in a mouse 4T1 orthotopic breast cancer model. The preparation of targeted (64)CuAuNCs-AMD3100 (4.5 ± 0.4 nm) was done via one-step reaction with controlled conjugation of AMD3100 and specific activity, as well as improved colloid stability. In vivo pharmacokinetic evaluation showed favorable organ distribution and significant renal and fecal clearance within 48 h post injection. The expression of CXCR4 in tumors and metastasis was characterized by immunohistochemistry, Western blot, and reverse transcription polymerase chain reaction analysis. PET imaging with (64)CuAuNCs-AMD3100 demonstrated sensitive and accurate detection of CXCR4 in engineered tumors expressing various levels of the receptor, while competitive receptor blocking studies confirmed targeting specificity of the nanoclusters. In contrast to nontargeted (64)CuAuNCs and (64)Cu-AMD3100 alone, the targeted (64)CuAuNCs-AMD3100 detected up-regulated CXCR4 in early stage tumors and premetastatic niche of lung earlier and with greater sensitivity. Taken together, we believe that (64)CuAuNCs-AMD3100 could serve as a useful platform for early and accurate detection of breast cancer and metastasis providing an essential tool to guide the treatment.

First 18F-Labeled Pentixafor-Based Imaging Agent for PET Imaging of CXCR4 Expression In Vivo

In vivo quantification of CXCR4 expression using [⁶⁸Ga]pentixafor for positron emission tomography (PET) imaging has gained significant clinical interest as CXCR4 plays a fundamental role in oncology and possesses potential prognostic value when overexpressed. To combine the excellent CXCR4-targeting properties of pentixafor-based tracers with the favorable radionuclide properties of ¹⁸F for high-resolution PET imaging, we developed an Al¹⁸F-labeled 1,4,7-triazacyclononane-triacetic acid (NOTA) analog of pentixather. Al¹⁸F-labeling of NOTA-pentixather was performed in aqueous dimethyl sulfoxide (DMSO) at pH = 4 (105°C, 15 minutes). CXCR4 affinities were determined in competitive binding assays, and both biodistribution and small-animal PET studies were performed in Daudi lymphoma-bearing mice. Under non-optimized conditions, [¹⁸F]AlF-NOTA-pentixather was obtained in radiochemical yields of 45.5% ± 13.3% and specific activities of up to 24.8 GBq/μmol. Compared with [^natGa]pentixafor, [^natF]AlF-NOTA-pentixather showed 1.4-fold higher CXCR4 affinity. [¹⁸F]AlF-NOTA-pentixather displayed high and CXCR4-specific in vivo uptake in Daudi xenografts (13.9% ± 0.8% injected dose per gram [ID/g] at 1 hour post injection [p.i.]). Because of its enhanced lipophilicity (logP = -1.4), [¹⁸F]AlF-NOTA-pentixather showed increased accumulation in the gall bladder and intestines. However, tumor/background ratios of 7.0 ± 1.2, 2.0 ± 0.3, 2.2 ± 0.4, 16.5 ± 6.5, and 29.2 ± 4 for blood, liver, small intestine, gut, and muscle, respectively, allowed for high-contrast visualization of Daudi tumors using PET (1 hour p.i.). The relatively straightforward radiosynthesis and efficient CXCR4 targeting of [¹⁸F]AlF-NOTA-pentixather demonstrate the successful implementation of ¹⁸F-complexation chemistry and pentixather-based CXCR4 targeting. Upon pharmacokinetic optimization, this class of tracers holds great promise for future application in humans.

Tailoring Fluorescent Dyes To Optimize a Hybrid RGD-Tracer

Quantitative assessment of affinity and kinetics is a critical component in the development of (receptor-targeted) radiotracers. For fluorescent tracers, such an assessment is currently not yet applied, while (small) changes in chemical composition of the fluorescent component might have substantial influence on the overall properties of a fluorescent tracer. Hybrid imaging labels that contain both a radiolabel and a fluorescent dye can be used to evaluate both the affinity (fluorescent label) and the in vivo distribution (radiolabel) of a targeted tracer. We present a hybrid label oriented and matrix-based scoring approach that enabled quantitative assessment of the influence of (overall) charge and lipophilicity of the fluorescent label on the (in vivo) characteristics of αvβ3-integrin targeted tracers. Systematic chemical alterations in the fluorescent dye were shown to result in a clear difference in the in vivo distribution of the different hybrid tracers. The applied evaluation technique resulted in an optimized targeted tracer for αvβ3-integrin, which combined the highest T/M ratio with the lowest uptake in other organs. Obviously this selection concept would also be applicable during the development of other (receptor-targeted) imaging tracers.