CXCR4-based imaging agents

PET imaging of CXCR4 expression using [18F]AlF-NOTA-QHY-04 for hematologic malignancy and solid tumors

C-X-C motif chemokine receptor 4 (CXCR4) is an attractive target for the diagnosis and treatment of cancers. Here, we aimed to develop a new CXCR4-targeted PET tracer, and to investigate the translational potential for noninvasive imaging of CXCR4 expression in various cancer entities through preclinical and pilot clinical studies. Methods [18F]AlF-NOTA-QHY-04 was synthesized and evaluated by cellular uptake, blocking and biolayer interferometry studies in vitro. The pharmacokinetics, biodistribution, and imaging specificity were researched in tumor-bearing mice. [18F]AlF-NOTA-QHY-04 PET/CT imaging was performed on 55 patients with different types of cancers. Correlations between ex vivo CXCR4 expression and PET parameters, and CXCR4 expression characteristics in different tumors were analyzed by histopathological staining in patients. Results [18F]AlF-NOTA-QHY-04 was prepared with high radiolabeling yield and radiochemical purity, exhibiting good stability, high binding affinity and specificity for CXCR4. NCI-H69 (small cell lung cancer, SCLC) tumor-bearing mice showed the highest tumor uptake (4.98 ± 0.98%ID/mL, P < 0.0001) on PET imaging except for Daudi lymphoma xenograft model, which was consistent with the results of cellular and histological analyses. Patients with diffuse large B-cell lymphoma showed the highest tumor uptake (SUVmax, 11.10 ± 4.79) followed by SCLC patients (SUVmax, 7.51 ± 3.01), which were both significantly higher than other solid tumors (P < 0.05). The radiotracer uptake of high-grade gliomas is significantly higher than that of low-grade gliomas (3.13 ± 0.58 vs. 1.18 ± 0.51, P = 0.005). Significant higher tumor-to-normal brain ratio of [18F]AlF-NOTA-QHY-04 than [18F]FDG was found in primary brain tumors (62.55 ± 43.24 vs 1.70 ± 0.25, P = 0.027). Positive correlations between ex vivo CXCR4 expression and [18F]AlF-NOTA-QHY-04 uptake (all P < 0.01) were recorded. Multicolor immunofluorescence staining indicated the high tracer uptake in certain patients was mainly due to the high expression of CXCR4 in tumor cells, followed by macrophages. Conclusion The CXCR4-targeted radiotracer [18F]AlF-NOTA-QHY-04 was successfully prepared with favorable yield, high specificity and binding affinity to CXCR4. Preclinical and pilot clinical studies demonstrated its feasibility and potential application in precise diagnosis for not only lymphoma but also SCLC and glioma. [18F]AlF-NOTA-QHY-04 PET/CT can also provide a complementary mapping for brain tumors to [18F]FDG PET/CT.

Chemokine Receptor 4-Targeted PET/CT with [68Ga]pentixather in Newly Diagnosed Multiple Myeloma: a Comparative Study with [68Ga]pentixafor PET/CT

PURPOSE

This study aimed to compare the detection rate of [68Ga]pentixather PET/CT and [68Ga]pentixafor PET/CT in newly diagnosed multiple myeloma (NDMM) patients, and to explore the value of [68Ga]pentixather PET/CT for tumor load assessment.

METHODS

Nineteen NDMM Patients were prospectively recruited and underwent both [68Ga]pentixather PET/CT and [68Ga]pentixafor PET/CT. A positive PET scan was defined as the presence of PET-positive focal bone lesions, paraskeletal disease, extramedullary plasmacytoma, or diffuse bone marrow uptake. Lesion numbers, SUVmax and PET-related tumor burden values were compared. The correlations between PET-related tumor burden and clinical risk stratification were analyzed.

RESULTS

[68Ga]pentixather PET/CT showed a tendency of higher positive rate compared with [68Ga]pentixafor PET/CT [94.7% (18/19) vs. 78.9% (15/19), p > 0.05]. Among 14 patients with 151 matched focal bone lesions, [68Ga]pentixather PET detected more or equal number of lesions in 13 patients, and demonstrated higher uptake value than 68 Ga-pentixafor PET [SUVmax, 16.8 (9.0, 23.8) vs. 13.4 (6.5, 20.4), p < 0.001]. For PET related-tumor burden, positive correlations of total bone marrow uptake (TBmU) (r = 0.9540, p < 0.0001) and SUVmean of total bone marrow (r = 0.9632, p < 0.0001) in two PET scans were observed. Higher TBmU [7864.9 (5549.2, 11,616.2) vs. 5383.4(4102.7, 11,041.8), p < 0.001], SUVmean of total bone marrow [1.4 (1.1, 2.2) vs. 1.1 (0.7, 2.1), p < 0.001] were demonstrated on [68Ga]pentixather PET than [68Ga]pentixafor PET. And the level of TBmU in [68Ga]pentixather PET and [68Ga]pentixafor PET were both elevated in Durie-Salmon Staging (DSS) III than DSS I (p < 0.01).

CONCLUSIONS

[68Ga]pentixather PET/CT performed a non-inferior capability for tumor detection compared to [68Ga]pentixafor PET/CT in NDMM patients. [68Ga]pentixather PET/CT can assess tumor load in MM patients and depict a significantly higher PET-related total tumor burden than [68Ga]pentixafor PET/CT.

Construction of CXCR4 Receptor-Targeted CuFeSe2 Nano Theranostic Platform and Its Application in MR/CT Dual Model Imaging and Photothermal Therapy

Introduction

Targeting, imaging, and treating tumors represent major clinical challenges. Developing effective theranostic agents to address these issues is an urgent need.

Methods

We introduce an "all-in-one" tumor-targeted theranostic platform using CuFeSe2-based composite nanoparticles (CuFeSe2@PA) for magnetic resonance (MR) and computed tomography (CT) dual model imaging-guided hyperthermia tumor ablation. Plerixafor (AMD3100) is bonded to the surface of CuFeSe2 as a targeting unit. Due to the robust interaction between AMD3100 and the overexpressed Chemokine CXC type receptor 4 (CXCR4) on the membrane of 4T1 cancer cells, CuFeSe2@PA specifically recognizes 4T1 cancer cells, enriching the tumor region.

Results

CuFeSe2@PA serves as a contrast agent for T2-weighted MR imaging (relaxivity value of 1.61 mM-1 s-1) and CT imaging. Moreover, it effectively suppresses tumor growth through photothermal therapy (PTT) owing to its high photothermal conversion capability and stability, with minimized side effects demonstrated both in vitro and in vivo.

Discussion

CuFeSe2@PA nanoparticles show potential as dual-mode imaging contrast agents for MR and CT and provide an effective means of tumor treatment through photothermal therapy. The surface modification with Plerixafor enhances the targeting ability of the nanoparticles, performing more significant efficacy and biocompatibility in the 4T1 cancer cell model. The study demonstrates that CuFeSe2@PA is a promising multifunctional theranostic platform with clinical application potential.

Chemokine receptor PET imaging: Bridging molecular insights with clinical applications

Chemokine receptors are important components of cellular signaling and play a critical role in directing leukocytes during inflammatory reactions. Their importance extends to numerous pathological processes, including tumor differentiation, angiogenesis, metastasis, and associations with multiple inflammatory disorders. The necessity to monitor the in vivo interactions of cellular chemokine receptors has been driven the recent development of novel positron emission tomography (PET) imaging agents. This imaging modality provides non-invasive localization and quantitation of these receptors that cannot be provided through blood or tissue-based assays. Herein, we provide a review of PET imaging of the chemokine receptors that have been imaged to date, namely CXCR3, CXCR4, CCR2, CCR5, and CMKLR1. The quantification of these receptors can aid in understanding various diseases, including cancer, atherosclerosis, idiopathic pulmonary fibrosis, and acute respiratory distress syndrome. The development of specific radiotracers targeting these receptors will be discussed, including promising results for disease diagnosis and management. However, challenges persist in fully translating these imaging advancements into practical therapeutic applications. Given the success of CXCR4 PET imaging to date, future research should focus on clinical translation of these approaches to understand their role in the management of a wide variety of diseases.

[68 Ga]Ga-PentixaFor: Development of a fully automated in hospital production on the Trasis miniAllinOne synthesizer

[68 Ga]Ga-PentixaFor is a frequently used radiotracer to image the CXCR4/CXCL12 axis in various malignancies, infections, and cardiovascular diseases. To answer increasing clinical needs, an automatized synthesis process ensuring efficient and reproducible production and improving operator's radioprotection is needed. [68 Ga]Ga-PentixaFor synthesis has been described on other synthesizers but not on the miniAiO. In this work, we defined automated synthesis process and an analytical method for the quality control of [68 Ga]Ga-PentixaFor. Validation batches were performed under aseptic conditions in a class A hotcell. All the quality controls required by the European Pharmacopea (Eur. Ph) were performed. The analytical methods were validated according to the International Conference Harmonization (ICH) recommendations. Validation batches were performed with a radiochemical yield of 94.8 ± 2.6%. All the quality controls were in conformity with the Eur. Ph, and the validation of the analytical method complied with the ICH. The environmental monitoring performed during the synthesis process showed that the aseptic conditions were ensured. [68 Ga]Ga-PentixaFor was successfully synthesized with the miniAiO by a fully automated process. This robust production mode and the quality control have been validated in this study allowing to increase the access of patients to this new promising radiopharmaceutical.

LPA1-mediated inhibition of CXCR4 attenuates CXCL12-induced signaling and cell migration

BACKGROUND

G protein-coupled receptor heteromerization is believed to exert dynamic regulatory impact on signal transduction. CXC chemokine receptor 4 (CXCR4) and its ligand CXCL12, both of which are overexpressed in many cancers, play a pivotal role in metastasis. Likewise, lysophosphatidic acid receptor 1 (LPA1) is implicated in cancer cell proliferation and migration. In our preliminary study, we identified LPA1 as a prospective CXCR4 interactor. In the present study, we investigated in detail the formation of the CXCR4-LPA1 heteromer and characterized the unique molecular features and function of this heteromer.

METHODS

We employed bimolecular fluorescence complementation, bioluminescence resonance energy transfer, and proximity ligation assays to demonstrate heteromerization between CXCR4 and LPA1. To elucidate the distinctive molecular characteristics and functional implications of the CXCR4-LPA1 heteromer, we performed various assays, including cAMP, BRET for G protein activation, β-arrestin recruitment, ligand binding, and transwell migration assays.

RESULTS

We observed that CXCR4 forms heteromers with LPA1 in recombinant HEK293A cells and the human breast cancer cell line MDA-MB-231. Coexpression of LPA1 with CXCR4 reduced CXCL12-mediated cAMP inhibition, ERK activation, Gαi/o activation, and β-arrestin recruitment, while CXCL12 binding to CXCR4 remained unaffected. In contrast, CXCR4 had no impact on LPA1-mediated signaling. The addition of lysophosphatidic acid (LPA) further hindered CXCL12-induced Gαi/o recruitment to CXCR4. LPA or alkyl-OMPT inhibited CXCL12-induced migration in various cancer cells that endogenously express both CXCR4 and LPA1. Conversely, CXCL12-induced calcium signaling and migration were increased in LPAR1 knockout cells, and LPA1-selective antagonists enhanced CXCL12-induced Gαi/o signaling and cell migration in the parental MDA-MB-231 cells but not in LPA1-deficient cells. Ultimately, complete inhibition of cell migration toward CXCL12 and alkyl-OMPT was only achieved in the presence of both CXCR4 and LPA1 antagonists.

CONCLUSIONS

The presence and impact of CXCR4-LPA1 heteromers on CXCL12-induced signaling and cell migration have been evidenced across various cell lines. This discovery provides crucial insights into a valuable regulatory mechanism of CXCR4 through heteromerization. Moreover, our findings propose a therapeutic potential in combined CXCR4 and LPA1 inhibitors for cancer and inflammatory diseases associated with these receptors, simultaneously raising concerns about the use of LPA1 antagonists alone for such conditions. Video Abstract.

Small-Molecule Fluorescent Ligands for the CXCR4 Chemokine Receptor

The C-X-C chemokine receptor type 4, or CXCR4, is a chemokine receptor found to promote cancer progression and metastasis of various cancer cell types. To investigate the pharmacology of this receptor, and to further elucidate its role in cancer, novel chemical tools are a necessity. In the present study, using classic medicinal chemistry approaches, small-molecule-based fluorescent probes were designed and synthesized based on previously reported small-molecule antagonists. Here, we report the development of three distinct chemical classes of fluorescent probes that show specific binding to the CXCR4 receptor in a novel fluorescence-based NanoBRET binding assay (pK_D ranging 6.6-7.1). Due to their retained affinity at CXCR4, we furthermore report their use in competition binding experiments and confocal microscopy to investigate the pharmacology and cellular distribution of this receptor.

Radiometal-theranostics: the first 20 years*

This review describes the basic principles of radiometal-theranostics and its dawn based on the development of the positron-emitting 86Y and 86Y-labeled radiopharmaceuticals to quantify biodistribution and dosimetry of 90Y-labeled analogue therapeutics. The nuclear and inorganic development of 86Y (including nuclear and cross section data, irradiation, radiochemical separation and recovery) led to preclinical and clinical evaluation of 86Y-labeled citrate and EDTMP complexes and yielded organ radiation doses in terms of mGy/MBq 90Y. The approach was extended to [86/90Y]Y-DOTA-TOC, yielding again yielded organ radiation doses in terms of mGy/MBq 90Y. The review further discusses the consequences of this early development in terms of further radiometals that were used (68Ga, 177Lu etc.), more chelators that were developed, new biological targets that were addressed (SSTR, PSMA, FAP, etc.) and subsequent generations of radiometal-theranostics that resulted out of that.

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.

CXCR4-targeted theranostics in oncology

A growing body of literature reports on the upregulation of C-X-C motif chemokine receptor 4 (CXCR4) in a variety of cancer entities, rendering this receptor as suitable target for molecular imaging and endoradiotherapy in a theranostic setting. For instance, the CXCR4-targeting positron emission tomography (PET) agent [⁶⁸ Ga]PentixaFor has been proven useful for a comprehensive assessment of the current status quo of solid tumors, including adrenocortical carcinoma or small-cell lung cancer. In addition, [⁶⁸ Ga]PentixaFor has also provided an excellent readout for hematological malignancies, such as multiple myeloma, marginal zone lymphoma, or mantle cell lymphoma. PET-based quantification of the CXCR4 capacities in vivo allows for selecting candidates that would be suitable for treatment using the theranostic equivalent [¹⁷⁷Lu]/[⁹⁰Y]PentixaTher. This CXCR4-directed theranostic concept has been used as a conditioning regimen prior to hematopoietic stem cell transplantation and to achieve sufficient anti-lymphoma/-tumor activity in particular for malignant tissues that are highly sensitive to radiation, such as the hematological system. Increasing the safety margin, pretherapeutic dosimetry is routinely performed to determine the optimal activity to enhance therapeutic efficacy and to reduce off-target adverse events. The present review will provide an overview of current applications for CXCR4-directed molecular imaging and will introduce the CXCR4-targeted theranostic concept for advanced hematological malignancies.

A Rapid and Specific HPLC Method to Determine Chemical and Radiochemical Purity of [68Ga]Ga-DOTA-Pentixafor (PET) Tracer: Development and Validation

BACKGROUND

Due to its overexpression in a variety of tumor types, the chemokine receptor 4 (CXCR4) represents a highly relevant diagnostic and therapeutic target in nuclear oncology. Recently, [⁶⁸Ga]Ga-DOTA-Pentixafor has emerged as an excellent imaging agent for positron emission tomography (PET) of CXCR4 expression in vivo. Preparation conditions may influence the quality and in vivo behaviour of this tracer and no standard procedure for the quality controls (QCs) is available.

OBJECTIVE

The developed analytical test method was validated because a specific monograph in the Pharmacopoeia is not available for [68Ga]Ga-DOTA-Pentixafor.

METHOD

A stepwise approach was used based on the quality by design (QbD) concept of the ICH Q2 (R1) and Q8 (Pharmaceutical Development) guidelines in accordance with the regulations and requirements of EANM, SNM, IAEA and WHO.

RESULTS

The purity and quality of the radiopharmaceutical obtained according to the proposed method were found to be high enough to safely administrate it to patients. Excellent linearity was found between 0.5 and 4 μg/mL, with a correlation coefficient (r²) for calibration curves being equal to 0.999, the average coefficient of variation (CV%) < 2% and average bias% that did not deviate more than 5% for all concentrations.

CONCLUSION

This study developed a new rapid and simple HPLC method of analysis for the routine QCs of [⁶⁸Ga]Ga-DOTA-Pentixafor to guarantee the high quality of the finished product before release.

Small Molecular Immune Modulators as Anticancer Agents

After decades of intense effort, immune checkpoint inhibitors have been conclusively demonstrated to be effective in cancer treatments and thus are revolutionizing the concepts in the treatment of cancers. Immuno-oncology has arrived and will play a key role in cancer treatment in the foreseeable future. However, efforts to find novel methods to improve the immune response to cancer have not ceased. Small-molecule approaches offer inherent advantages over biologic immunotherapies since they can cross cell membranes, penetrate into tumor tissue and tumor microenvironment more easily, and are amenable to be finely controlled than biological agents, which may help reduce immune-related adverse events seen with biologic therapies and provide more flexibility for the combination use with other therapies and superior clinical benefit. On the one hand, small-molecule therapies can modulate the immune response to cancer by restoring the antitumor immunity, promoting more effective cytotoxic lymphocyte responses, and regulating tumor microenvironment, either directly or epigenetically. On the other hand, the combination of different mechanisms of small molecules with antibodies and other biologics demonstrated admirable synergistic effect in clinical settings for cancer treatment and may expand antibodies' usefulness for broader clinical applications. This chapter provides an overview of small-molecule immunotherapeutic approaches either as monotherapy or in combination for the treatment of cancer.

Theranostics: Leveraging Molecular Imaging and Therapy to Impact Patient Management and Secure the Future of Nuclear Medicine

Nuclear medicine is experiencing a renaissance, with U.S. Food and Drug Administration approval recently being obtained for theranostic agents and a wide variety of such agents soon to impact patient care significantly in the era of precision medicine. The NETTER-1 trial demonstrated the therapeutic effect of a theranostic agent in markedly improving progression-free survival in patients with metastatic gastroenteropancreatic neuroendocrine tumors. Predominantly retrospective studies have demonstrated a significant response to ¹⁷⁷Lu-labeled agents targeting prostate-specific membrane antigen (PSMA) in patients with prostate cancer. At least 2 prospective clinical trials involving ¹⁷⁷Lu-PSMA agents are under way that will likely pave the way for Food and Drug Administration approval in the United States. A significant upside to theranostics is that patients tend to tolerate these agents better than chemotherapy. Theranostic compounds are likely to impact many cancers in the near future, not only through improvements in quality of life but also in terms of survival. This article provides an overview of already approved agents as well as those on the horizon. It is important that as these agents are clinically onboarded, nuclear medicine physicians have the expertise to deploy theranostics safely and efficiently, ensuring that these agents attain and maintain their position as leading lines of therapy in managing patients with cancer as well as becoming an important aspect of nuclear medicine practice in the future.

CP-25 exerts anti-angiogenic effects on a rat model of adjuvant-induced arthritis by promoting GRK2-induced downregulation of CXCR4-ERK1/2 signaling in endothelial cells

Angiogenesis can produce an invasive and destructive front, also named a pannus, comprised of inflammatory vascular tissue that covers and erodes articular cartilage, subchondral bone and peri‑articular soft tissues in rheumatoid arthritis (RA). Paeoniflorin‑6'‑O‑benzene sulfonate (CP‑25) is a novel ester derivative of paeoniflorin. We previously demonstrated that CP‑25 exerts anti‑inflammatory and immunoregulatory effects. CP‑25 also exhibits a marked therapeutic effect on adjuvant‑induced arthritis (AA), and is able to inhibit synovial and immune cell function, according to our previous study. However, the effect of CP‑25 on angiogenesis remains unclear. In the present study, AA was initiated in Sprague‑Dawley rats via intradermal immunization in the right hind metatarsal footpad with heat‑killed Mycobacterium butyricum in liquid paraffin, and rats were divided into four groups: Normal, AA rat model, CP‑25 (50 mg/kg) and methotrexate (0.5 mg/kg) groups (n=10 rats/group). Subsequently, joint synovium in AA rats was pathologically evaluated by hematoxylin and eosin staining, synovial vascular proliferation was evaluated by immunofluorescence, the synovial expression levels of C‑X‑C motif chemokine ligand 12 (CXCL12) were detected by immunohistochemistry and ELISA, and synovial C‑X‑C chemokine receptor type 4 (CXCR4) was detected by western blotting. The results demonstrated that CP‑25 ameliorated clinical signs and pannus formation in the ankle joint in rats with AA. Furthermore, there was a positive correlation between pannus score and CXCL12 and CXCR4 expression. In addition, the effects of CP‑25 on endothelial cell function and CXCL12/CXCR4 signaling were studied in vitro using human umbilical vein endothelial cells (HUVECs). The results demonstrated that CXCL12 significantly promoted HUVEC proliferation, migration and tube formation, and that CP‑25 could reverse these abnormalities by inhibiting plasma membrane localization of G protein‑coupled receptor kinase 2 (GRK2) in HUVECs. These findings suggested that CP‑25 may markedly inhibit pannus formation in AA. This effect may be associated with a reduction in the plasma membrane localization of GRK2 in endothelial cells, an enhancement of the inhibitory effect of GRK2 on ERK1/2 in the cytoplasm, a reduction in the phosphorylation of ERK1/2 and in the function of HUVECs.

Repopulating hematopoietic stem cells from steady-state blood before and after ex vivo culture are enriched in the CD34+CD133+CXCR4low fraction

The feasibility of ex vivo expansion allows us to consider the steady-state peripheral blood as an alternative source of hematopoietic stem progenitor cells for transplantation when growth factor-induced cell mobilization is contraindicated or inapplicable. Ex vivo expansion dramatically enhances the in vivo reconstituting cell population from steady-state blood. In order to investigate phenotype and the expression of homing molecules, the expression of CD34, CD133, CD90, CD45RA, CD26 and CD9 was determined on sorted CD34⁺ cells according to CXCR4 (“neg”, “low” “bright”) and CD133 expression before and after ex vivo expansion. Hematopoietic stem cell activity was determined in vivo on the basis of hematopoietic repopulation of primary and secondary recipients - NSG immuno-deficient mice. In vivo reconstituting cells in the steady-state blood CD34⁺ cell fraction before expansion belong to the CD133⁺ population and are CXCR4^low or, to a lesser extent, CXCR4^neg, while after ex vivo expansion they are contained only in the CD133⁺CXCR4^low cells. The failure of the CXCR4^bright population to engraft is probably due to the exclusive expression of CD26 by these cells. The limiting-dilution analysis showed that both repopulating cell number and individual proliferative capacity were enhanced by ex vivo expansion. Thus, steady-state peripheral blood cells exhibit a different phenotype compared to mobilized and cord blood cells, as well as to those issued from the bone marrow. These data represent the first phenotypic characterization of steady-state blood cells exhibiting short- and long-term hematopoietic reconstituting potential, which can be expanded ex vivo, a sine qua non for their subsequent use for transplantation.

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.

A Flow Cytometry-based Assay to Identify Compounds That Disrupt Binding of Fluorescently-labeled CXC Chemokine Ligand 12 to CXC Chemokine Receptor 4

Pharmacological targeting of G protein-coupled receptors (GPCRs) is of great importance to human health, as dysfunctional GPCR-mediated signaling contributes to the progression of many diseases. The ligand/receptor pair CXC chemokine ligand 12 (CXCL12)/CXC chemokine receptor 4 (CXCR4) has raised significant clinical interest, for instance as a potential target for the treatment of cancer and inflammatory diseases. Small molecules as well as therapeutic antibodies that specifically target CXCR4 and inhibit the receptor's function are therefore considered to be valuable pharmacological tools. Here, a flow cytometry-based cellular assay that allows identification of compounds (e.g., small molecules) that abrogate CXCL12 binding to CXCR4, is described. Essentially, the assay relies on the competition for receptor binding between a fixed amount of fluorescently labeled CXCL12, the natural chemokine agonist for CXCR4, and unlabeled compounds. Hence, the undesirable use of radioactively labeled probes is avoided in this assay. In addition, living cells are used as the source of receptor (CXCR4) instead of cell membrane preparations. This allows easy adaptation of the assay to a plate format, which increases the throughput. This assay has been shown to be a valuable generic drug discovery assay to identify CXCR4-targeting compounds. The protocol can likely be adapted to other GPCRs, at least if fluorescently labeled ligands are available or can be generated. Prior knowledge concerning the intracellular signaling pathways that are induced upon activation of these GPCRs, is not required.

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.

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.

Synthesis, ADMET Properties, and Biological Evaluation of Benzothiazole Compounds Targeting Chemokine Receptor 2 (CXCR2)

Herein we describe the synthesis and biological evaluation of a series of novel benzothiazoles based on a diaryl urea scaffold previously reported in some allosteric chemokine receptor 2 (CXCR2) inhibitors. From a library of 41 new compounds, 17 showed significant inhibition of CXCR2, with IC₅₀ values less than 10 μm and selectivity over CXCR4. Our ADMET simulations suggest favorable drug-like properties for the active compounds. Importantly, we developed a predictive model that can distinguish active from inactive compounds; this will serve as a valuable tool to guide the design of optimized compounds to be evaluated in preclinical models.

A novel CXCR4-targeted near-infrared (NIR) fluorescent probe (Peptide R-NIR750) specifically detects CXCR4 expressing tumors

C-X-C chemokine receptor 4 (CXCR4) is over-expressed in multiple human cancers and correlates with tumor aggressiveness, poor prognosis and increased risk for distant metastases. Imaging agents for CXCR4 are thus highly desirable. We developed a novel CXCR4-targeted near-infrared (NIR) fluorescent probe (Peptide R-NIR750) conjugating the new developed CXCR4 peptidic antagonist Peptide R with the NIR fluorescent dye VivoTag-S750. Specific CXCR4 binding was obtained in cells overexpressing human CXCR4 (B16-hCXCR4 and human melanoma cells PES43), but not in CXCR4 low expressing cells (FB-1). Ex vivo evaluation demonstrated that PepR-NIR750 specifically detects B16-hCXCR4-derived subcutaneous tumors and lung metastases. Fluorescence Molecular Tomography (FMT) in vivo imaging was performed on mice carrying subcutaneous CHO and CHO-CXCR4 tumors. PepR-NIR750 accumulates only in CXCR4-positive expressing subcutaneous tumors. Additionally, an intense NIR fluorescence signal was detected in PES43-derived lung metastases of nude mice injected with PepR-NIR750 versus mice injected with VivoTag-S750. With a therapeutic intent, mice bearing PES43-derived lung metastases were treated with Peptide R. A the dramatic reduction in PES43-derived lung metastases was detected through a decrease of the PepR-NIR750 signal. PepR-NIR750 is a specific probe for non-invasive detection of human high CXCR4-expressing tumors and metastatic lesion and thus a valuable tool for cancer molecular imaging.

Molecular imaging to guide systemic cancer therapy: Illustrative examples of PET imaging cancer biomarkers

Molecular imaging agents have the ability to non-invasively visualize, characterize, and quantify the molecular biology of disease. Recent advances in nuclear probe development, particularly in PET radiotracers, have generated many new imaging agents with precise molecular targets. With such specificity, PET probes may be utilized as biomarkers to objectively interrogate and evaluate pathology. Whereas the current indications for PET imaging are predominately confined to staging and restaging of malignancy, the utility of PET greatly expands when utilized as a biomarker, the topic of this review. As an imaging biomarker, PET may be used to (1) measure target expression to select subsets of patients who would most benefit from targeted therapy; (2) measure early treatment response to predict therapeutic efficacy; and (3) relate tumor response to survival. This review will discuss the application of radiotracers to targeted cancer therapy. Particular attention is given to new radiotracers evaluated in recently completed clinical trials and those with current or potential clinical utility. The diverse roles of PET in clinical trails for drug development are also examined.

The influence of different metal-chelate conjugates of pentixafor on the CXCR4 affinity

Background

The overexpression of the chemokine receptor 4 (CXCR4) in different epithelial, mesenchymal, and hematopoietic cancers makes CXCR4 an attractive diagnostic and therapeutic target. However, targeting the CXCR4 receptor with small cyclic pentapeptide-based radiopharmaceuticals remains challenging because minor structural modifications within the ligand-linker-chelate structure often significantly affect the receptor affinity. Based on the excellent in vivo properties of CXCR4-directed pentapeptide [⁶⁸Ga]pentixafor (cyclo(-d-Tyr-N-Me-d-Orn(AMB-DOTA)-l-Arg-l-2-Nal-Gly-)), this study aims to broaden the spectrum of applicable (radio)metal-labeled pentixafor analogs.

Methods

Cyclic pentapeptides, based on the pentixafor scaffold, were synthesized by a combined solid- and solution-phase peptide synthesis. The CXCR4 receptor affinities of the cold reference compounds were determined in competitive binding assays using CXCR4-expressing Jurkat T - cell leukemia cells and [¹²⁵I]FC131 as the radioligand.

Results

Metalated pentixafor derivatives with cyclic and acyclic chelators were synthesized by solid-phase peptide synthesis and evaluated in vitro. The resulting CXCR4 affinities (IC₅₀) were highly dependent on the chelator and metal used. Two pentapeptides, Ga-NOTA and Bi-DOTA conjugates, offer an improved affinity compared to [⁶⁸Ga]pentixafor.

Conclusions

Based on the pentapeptide [⁶⁸Ga]pentixafor, a broad range of metal-labeled analogs were investigated. The affinities of the new compounds were found to be strongly dependent on both the chelator and the metal used. Bi-labeled pentixafor showed high receptor affinity and seems to be a promising ligand for further preclinical evaluation and future α-emitter-based endoradiotherapy.

Symmetrical bis-tertiary amines as novel CXCR4 inhibitors

CXCR4 inhibitors are promising agents for the treatment of cancer metastasis and inflammation. A series of novel tertiary amine derivatives targeting CXCR4 were designed, synthesized, and evaluated. The central benzene ring linker and side chains were modified and optimized to study the structure-activity relationship. Seven compounds displayed much more potent activity than the reference drug, AMD3100, in both the binding affinity assay and the blocking of Matrigel invasion functional assay. These compounds exhibited effective concentration ranging from 1 to 100 nM in the binding affinity assay and inhibited invasion from 65.3% to 100% compared to AMD3100 at 100 nM. Compound IIn showed a 50% suppressive effect against carrageenan-induced paw inflammation in a mouse model, which was as effective as the peptidic antagonist, TN14003 (48%). These data demonstrate that symmetrical bis-tertiary amines are unique CXCR4 inhibitors with high potency.

AMD3100: A Versatile Platform for CXCR4 Targeting (68)Ga-Based Radiopharmaceuticals

CXCR4 is a G protein-coupled receptor (GPCR), which is overexpressed in numerous diseases, particularly in multiple cancers. Therefore, this receptor represents a valuable target for imaging and therapeutic purposes. Among the different approaches, which were developed for CXCR4 imaging, a CXCR4 antagonist biscyclam system (AMD3100, also called Mozobil), currently used in the clinic for the mobilization of hematopoietic stem cells, was radiolabeled with different radiometals such as (62)Zn, (64)Cu, (67)Ga, or (99m)Tc. However, cyclam is not an ideal chelator for most of these radiometals, and could lead to the release of the radionuclide in vivo. In the current study, a new family of CXCR4 imaging agents is presented, in which AMD3100 is used as a carrier for specific delivery of an imaging reporter, i.e., a (68)Ga complex for PET imaging. AMD3100 was functionalized on the phenyl moiety with different linkers, either ethylenediamine or diamino-polyethylene glycol 3 (PEG3). The resulting AMD3100 analogues were further coupled with two different chelators, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) or 1,4,7-triazacyclononane-1-glutaric acid-4,7-acetic acid (NODAGA). Five potential CXCR4 targeting agents were obtained. The derived AMD3100-based ligands were labeled with (68)Ga, highlighting the influence of the spacer nature on the (68)Ga-labeling yield. The lipophilic character of the different systems was also investigated, as well as their affinity for the CXCR4 receptor. The most promising compound was further evaluated in vivo in H69 tumor xenografts by biodistribution and PET imaging studies, validating the proof of principle of our concept.

Positron emission tomographic imaging of CXCR4 in cancer: challenges and promises

Molecular imaging is an attractive platform for noninvasive detection and assessment of cancer. In recent years, the targeted imaging of the C-X-C chemokine receptor 4 (CXCR4), a chemokine receptor that has been associated with tumor metastasis, has become an area of intensive research. This review article focuses on positron emission tomography (PET) and aims to provide useful and critical insights into the application of PET to characterize CXCR4 expression, including the chemical, radiosynthetic, and biological requirements for PET radiotracers. This discussion is informed by a summary of the different approaches taken so far and a comparison of their clinical translation. Finally, our expert opinions as to potential future advances in the field are expressed.

Prospective Study of (68)Ga-NOTA-NFB: Radiation Dosimetry in Healthy Volunteers and First Application in Glioma Patients

Purpose: The chemokine receptor CXCR4 is overexpressed in various types of human cancers. As a specific imaging agent of CXCR4, ⁶⁸Ga-NOTA-NFB was investigated in this study to assess its safety, biodistribution and dosimetry properties in healthy volunteers, and to preliminarily evaluate its application in glioma patients.

Methods: Six healthy volunteers underwent whole-body PET scans at 0, 0.5, 1, 2 and 3 h after ⁶⁸Ga-NOTA-NFB injection (mean dose, 182.4 ± 3.7 MBq (4.93 ± 0.10 mCi)). For time-activity curve calculations, 1 mL blood samples were obtained at 1, 3, 5, 10, 30, 60, 90, 120, 150 and 180 min after the injection. The estimated radiation doses were calculated by OLINDA/EXM software. Eight patients with glioma were enrolled and underwent both ⁶⁸Ga-NOTA-NFB and ¹⁸F-FDG PET/CT scans before surgery. The expression of CXCR4 on the resected brain tumor tissues was determined by immunohistochemical staining.

Results:⁶⁸Ga-NOTA-NFB was safe and well tolerated by all subjects. A rapid activity clearance from the blood circulation was observed. The organs with the highest absorbed doses were spleen (193.8 ± 32.5 μSv/MBq) and liver (119.3 ± 25.0 μSv/MBq). The mean effective dose was 25.4 ± 6.1 μSv/MBq. The maximum standardized uptake values (SUV_max) and the maximum target to non-target ratios (T/NT_max) of ⁶⁸Ga-NOTA-NFB PET/CT in glioma tissues were 4.11 ± 2.90 (range, 0.45-8.21) and 9.21 ± 8.75 (range, 3.66-24.88), respectively, while those of ¹⁸F-FDG PET/CT were 7.34 ± 2.90 (range, 3.50-12.27) and 0.86 ± 0.41 (range, 0.35-1.59). The histopathological staining confirmed that CXCR4 was overexpressed on resected tumor tissues with prominent ⁶⁸Ga-NOTA-NFB uptake.

Conclusion: With a favorable radiation dosimetry profile, ⁶⁸Ga-NOTA-NFB is safe for clinical imaging. Compared to ¹⁸F-FDG PET/CT, ⁶⁸Ga-NOTA-NFB PET/CT is more sensitive in detecting glioma and could have potential in diagnosing and treatment planning for CXCR4 positive patients.

Structural characterization and in vivo evaluation of β-Hairpin peptidomimetics as specific CXCR4 imaging agents

The CXCR4 chemokine receptor is integral to several biological functions and plays a pivotal role in the pathophysiology of many diseases. As such, CXCR4 is an enticing target for the development of imaging and therapeutic agents. Here we report the evaluation of the POL3026 peptidomimetic template for the development of imaging agents that target CXCR4. Structural and conformational analyses of POL3026 and two of its conjugates, DOTA (POL-D) and PEG12-DOTA (POL-PD), by circular dichroism, two-dimensional NMR spectroscopy and molecular dynamics calculations are reported. In silico observations were experimentally verified with in vitro affinity assays and rationalized using crystal structure-based molecular modeling studies. [(111)In]-labeled DOTA conjugates were assessed in vivo for target specificity in CXCR4 expressing subcutaneous U87 tumors (U87-stb-CXCR4) through single photon emission computed tomography (SPECT/CT) imaging and biodistribution studies. In silico and in vitro studies show that POL3026 and its conjugates demonstrate similar interactions with different micelles that mimic cellular membrane and that the ε-NH2 of lysine(7) is critical to maintain high affinity to CXCR4. Modification of this group with DOTA or PEG12-DOTA led to the decrease of IC50 value from 0.087 nM for POL3026 to 0.47 nM and 1.42 nM for POL-D and POL-PD, respectively. In spite of the decreased affinity toward CXCR4, [(111)In]POL-D and [(111)In]POL-PD demonstrated high and significant uptake in U87-stb-CXCR4 tumors compared to the control U87 tumors at 90 min and 24 h post injection. Uptake in U87-stb-CXCR4 tumors could be blocked by unlabeled POL3026, indicating specificity of the agents in vivo. These results suggest POL3026 as a promising template to develop new imaging agents that target CXCR4.

CXCR4 as biomarker for radioresistant cancer stem cells

PURPOSE

Radioresistance of cancer cells remains a fundamental barrier for maximum efficient radiotherapy. Tumor heterogeneity and the existence of distinct cell subpopulations exhibiting different genotypes and biological behaviors raise difficulties to eradicate all tumorigenic cells. Recent evidence indicates that a distinct population of tumor cells, called cancer stem cells (CSC), is involved in tumor initiation and recurrence and is a putative cause of tumor radioresistance. There is an urgent need to identify the intrinsic molecular mechanisms regulating the generation and maintenance of resistance to radiotherapy, especially within the CSC subset. The chemokine C-X-C motif receptor 4 (CXCR4) has been found to be a prognostic marker in various types of cancer, being involved in chemotaxis, stemness and drug resistance. The interaction of CXCR4 with its ligand, the chemokine C-X-C motif ligand 12 (CXCL12), plays an important role in modulating the tumor microenvironment, angiogenesis and CSC niche. Moreover, the therapeutic inhibition of the CXCR4/CXCL12 signaling pathway is sensitizing the malignant cells to conventional anti-cancer therapy.

CONTENT

Within this review we are summarizing the role of the CXCR4/CXCL12 axis in the modulation of CSC properties, the regulation of the tumor microenvironment in response to irradiation, therapy resistance and tumor relapse.

CONCLUSION

In light of recent findings, the inhibition of the CXCR4/CXCL12 signaling pathway is a promising therapeutic option to refine radiotherapy.

Synthesis and Evaluation of [(67)Ga]-AMD3100: A Novel Imaging Agent for Targeting the Chemokine Receptor CXCR4

In order to develop a possible C-X-C chemokine receptor type 4 (CXCR4) imaging agent for oncological scintigraphy, [⁶⁷Ga]-labeled 1,1′-[1,4-Phenylene-bis(methylene)]bis(1,4,8,11-tetraazacyclotetradecane) ([⁶⁷Ga]-AMD3100) was prepared by using [⁶⁷Ga]GaCl₃ and AMD-3100 for 2 h at 50 °C (radiochemical purity: >95% ITLC, >99% HPLC, specific activity: 1800–2000 TBq/mmol) in acetate buffer. The stability of the complex was checked in the presence of human serum (37 °C) and in the final formulation for four days. The biodistribution of the labeled compound in the vital organs of wild type Sprague-Dawley rats was determined and compared with that of the free Ga³⁺ cation up to 48 h. Considering the spleen as the target organ, the best target:non target ratios were obtained 48 h post-injection (spleen:blood ratio; 14.5 and spleen:muscle ratio; 88.4). Initial SPECT images and biodistribution results in the wild type rats matched each other and demonstrated rapid washout of the tracer from the urinary tract. SPECT images in human breast carcinoma-bearing mice demonstrated a detectable tumor uptake in 48 h post-injection.

Scavenging strategy for specific activity improvement: application to a new CXCR4-specific cyclopentapeptide positron emission tomography tracer

Huisgen cycloaddition is attractive to label peptide because of its rapidity and bioorthogonality. However, for larger tracers, the physico-chemical differences between the precursor and the tracer are usually insufficient to allow their separation by HPLC, reducing the specific activity. This is of importance for peptidic tracers because the combination of their high-affinity receptor with low specific activity results in the precursor saturating the receptors, causing non-specific tracer binding. Here, we report a fast, one-pot, general strategy to circumvent this issue, yielding a tracer of improved specific activity. It consists in adding a lipophilic azide after the labeling step to scavenge unreacted precursor into a more lipophilic species that does not co-elute with the tracer. We applied this strategy to a new fluorinated cyclopentapeptidic CXCR4 antagonist for the PET imaging of cancer, CCIC15, for which we managed to reduce the apparent peptide concentration by a factor of 34 in 10 min. This tracer was radiolabeled by click chemistry with 2-[(18) F]fluoroethylazide, yielding the tracer in 18 ± 6% (n = 5) end-of-synthesis radiochemical yields (EOS-RCY) in 1.5 h from [(18) F]fluoride with a specific activity of 19.4 GBq µmol(-1) . Preliminary biological evaluation of the probe confirmed potency and specificity for CXCR4; further biological evaluation is underway.

Small molecule inhibitors of CXCR4

CXCR4 is a G-protein-coupled receptor involved in a number of physiological processes in the hematopoietic and immune systems. The SDF-1/CXCR4 axis is significantly associated with several diseases, such as HIV, cancer, WHIM syndrome, rheumatoid arthritis, pulmonary fibrosis and lupus. For example, CXCR4 is one of the major co-receptors for HIV entry into target cells, while in cancer it plays an important role in tumor cell metastasis. Several promising CXCR4 antagonists have been developed to block SDF-1/CXCR4 interactions that are currently under different stages of development. The first in class CXCR4 antagonist, plerixafor, was approved by the FDA in 2008 for the mobilization of hematopoietic stem cells and several other drugs are currently in clinical trials for cancer, HIV, and WHIM syndrome. While the long-term safety data for the first generation CXCR4 antagonists are not yet available, several new compounds are under preclinical development in an attempt to provide safer and more efficient treatment options for HIV and cancer patients.

Effective inhibition of metastases and primary tumor growth with CTCE-9908 in esophageal cancer

BACKGROUND

In spite of multimodular treatment, the therapeutic options for esophageal carcinoma are limited, and metastases remain the leading cause of tumor-related mortality. Expression of the chemokine receptor CXCR4 significantly correlates with poor survival rates in patients with esophageal carcinoma and is associated with lymph node and bone marrow metastases. The aim of this study was to evaluate the effect of the CXCR4 antagonist CTCE-9908 on metastatic homing and primary tumor growth in vitro and in vivo in an orthotopic xenograft model of esophageal cancer.

MATERIALS AND METHODS

OE19 cells were examined for stromal cell-derived factor 1 alpha-mediated migration under CTCE-9908 treatment. The CTCE-9908 treatment was further evaluated in an in vitro proliferation assay and orthotopic esophageal model, accompanied by magnetic resonance imaging. Tumor and metastases were immunohistochemically examined for CXCR4 expression.

RESULTS

CTCE-9908 has an inhibitory effect on stromal cell-derived factor 1 alpha-mediated migration and proliferation of OE19 cells. Treatment with CTCE-9908 in the orthotopic esophageal model leads to a reduction of metastatic spread and primary tumor growth. This was confirmed by magnetic resonsance imaging. Treatment with CTCE-9908 results in altered CXCR4 expression pattern exhibiting a high degree of variability.

CONCLUSION

CTCE-9908 effectively inhibits OE19 cell migration and proliferation in vitro, reduces metastases to lung, liver, and lymph nodes in vivo, and moreover leads to tumor growth reduction in an orthotopic model of esophageal carcinoma.

In vivo imaging of therapy-induced anti-cancer immune responses in humans

Immunotherapy aims to re-engage and revitalize the immune system in the fight against cancer. Research over the past decades has shown that the relationship between the immune system and human cancer is complex, highly dynamic, and variable between individuals. Considering the complexity, enormous effort and costs involved in optimizing immunotherapeutic approaches, clinically applicable tools to monitor therapy-induced immune responses in vivo are most warranted. However, the development of such tools is complicated by the fact that a developing immune response encompasses several body compartments, e.g., peripheral tissues, lymph nodes, lymphatic and vascular systems, as well as the tumor site itself. Moreover, the cells that comprise the immune system are not static but constantly circulate through the vascular and lymphatic system. Molecular imaging is considered the favorite candidate to fulfill this task. The progress in imaging technologies and modalities has provided a versatile toolbox to address these issues. This review focuses on the detection of therapy-induced anticancer immune responses in vivo and provides a comprehensive overview of clinically available imaging techniques as well as perspectives on future developments. In the discussion, we will focus on issues that specifically relate to imaging of the immune system and we will discuss the strengths and limitations of the current clinical imaging techniques. The last section provides future directions that we envision to be crucial for further development.

Influence of DOTA chelator position on biodistribution and targeting properties of (111)In-labeled synthetic anti-HER2 affibody molecules

Affibody molecules are a class of affinity proteins. Their small size (7 kDa) in combination with the high (subnanomolar) affinity for a number of cancer-associated molecular targets makes them suitable for molecular imaging. Earlier studies demonstrated that the selection of radionuclide and chelator may substantially influence the tumor-targeting properties of affibody molecules. Moreover, the placement of chelators for labeling of affibody molecules with (99m)Tc at different positions in affibody molecules influenced both blood clearance rate and uptake in healthy tissues. This introduces an opportunity to improve the contrast of affibody-mediated imaging. In this comparative study, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was conjugated to the synthetic affibody molecule Z(HER2:S1) at three different positions: DOTA-A1-Z(HER2:S1) (N-terminus), DOTA-K58-Z(HER2:S1) (C-terminus), and DOTA-K50-Z(HER2:S1) (middle of helix 3). The affinity for HER2 differed slightly among the variants and the K(D) values were determined to be 133 pM, 107 pM and 94 pM for DOTA-A1-Z(HER2:S1), DOTA-K50-Z(HER2:S1), and DOTA-K58-Z(HER2:S1), respectively. Z(HER2:S1)-K50-DOTA showed a slightly lower melting point (57 °C) compared to DOTA-A1-Z(HER2:S1) (64 °C) and DOTA-K58-Z(HER2:S1) (62 °C), but all variants showed good refolding properties after heat treatment. All conjugates were successfully labeled with (111)In resulting in a radiochemical yield of 99% with preserved binding capacity. In vitro specificity studies using SKOV-3 and LS174T cell lines showed that the binding of the radiolabeled compounds was HER2 receptor-mediated, which also was verified in vivo using BALB/C nu/nu mice with LS174T and Ramos lymphoma xenografts. The three conjugates all showed specific uptake in LS174T xenografts in nude mice, where DOTA-A1-Z(HER2:S1)and DOTA-K58-Z(HER2:S1) showed the highest uptake. Overall, DOTA-K58-Z(HER2:S1) provided the highest tumor-to-blood ratio, which is important for a high-contrast imaging. In conclusion, the positioning of the DOTA chelator influences the cellular processing and the biodistribution pattern of radiolabeled affibody molecules, creating preconditions for imaging optimization.

Imaging agents for the chemokine receptor 4 (CXCR4)

The interaction between the chemokine receptor 4 (CXCR4) and stromal cell-derived factor-1 (SDF-1, also known as CXCL12) is a natural regulatory process in the human body. However, CXCR4 over-expression is also found in diseases such as cancer, where it plays a role in, among others, the metastatic spread. For this reason it is an interesting biomarker for the field of diagnostic oncology, and therefore, it is gaining increasing interest for applications in molecular imaging. Especially "small-molecule" imaging agents based on T140, FC131 and AMD3100 have been extensively studied. SDF-1, antibodies, pepducins and bioluminescence have also been used to visualize CXCR4. In this critical review reported CXCR4 targeting imaging agents are described based on their affinity, specificity and biodistribution. The level wherein CXCR4 is up-regulated in cancer patients and its relation to the different cell lines and animal models used to evaluate the efficacy of the imaging agents is also discussed (221 references).

Differential Expression of Chemokine Receptors and their Roles in Cancer Imaging

Chemokine/chemokine receptor interactions play diverse roles in cell migration and homeostasis. Emerging evidence suggests that cancer cells co-opt chemokine networks for survival, proliferation, immune evasion, and metastasis. Most of the chemokine receptors are reported to be involved in tumor progression. Given their extensive implication in cancer progression, several chemokine receptor/ligand axes are considered as potential therapeutic targets. This review provides a survey of chemokine receptor expression in cancer and evaluates the potential of chemokine receptor imaging as a tool for molecular characterization of cancer.