[68Ga]Ga-Pentixafor PET/MRI for CXCR4 Imaging of Chronic Lymphocytic Leukemia: Preliminary Results

New PET Tracers for Lymphoma

While functional imaging with [18F]Fluoro-deoxy-glucose positron emission tomography (PET)/computed tomography is a well-established imaging modality in most lymphoma entities, novel tracers addressing cell surface receptors, tumor biology, and the microenvironment are being developed. Especially, with the emergence of immuno-PET targeting surface markers of lymphoma cells, a new imaging modality of immunotherapies is evolving, which might especially aid in relapsed and refractory disease stages. This review highlights different new PET tracers in indolent and aggressive lymphoma subtypes and summarizes the current state of immuno-PET imaging in lymphoma.

PET/CT in leukemia: utility and future directions

2-Deoxy-2-[ 18 F]fluoro- d -glucose PET/computed tomography ([ 18 F]FDG PET/CT) has proven to be a sensitive method for the detection and evaluation of hematologic malignancies, especially lymphoma. The increasing incidence and mortality rates of leukemia have raised significant concerns. Through the utilization of whole-body imaging, [ 18 F]FDG PET/CT provides a thorough assessment of the entire bone marrow, complementing the limited insights provided by biopsy samples. In this regard, [ 18 F]FDG PET/CT has the ability to assess diverse types of leukemia The utilization of [ 18 F]FDG PET/CT has been found to be effective in evaluating leukemia spread beyond the bone marrow, tracking disease relapse, identifying Richter's transformation, and assessing the inflammatory activity associated with acute graft versus host disease. However, its role in various clinical scenarios in leukemia remains unacknowledged. Despite their less common use, some novel PET/CT radiotracers are being researched for potential use in specific scenarios in leukemia patients. Therefore, the objectives of this review are to provide a thorough assessment of the current applications of [ 18 F]FDG PET/CT in the staging and monitoring of leukemia patients, as well as the potential for an expanding role of PET/CT in leukemia patients.

The Clinical Role of CXCR4-Targeted PET on Lymphoproliferative Disorders: A Systematic Review

Background/Objectives: We conducted a comprehensive investigation to explore the pathological expression of the CXCR4 receptor in lymphoproliferative disorders (LPDs) using [68Ga]Ga-Pentixafor PET/CT or PET/MRI technology. The PICO question was as follows: What is the diagnostic role (outcome) of [68Ga]Ga-Pentixafor PET (intervention) in patients with LPDs (problem/population)? Methods: The study was written based on the reporting items for systematic reviews and meta-analyses (PRISMA) 2020 guidelines, and it was registered on the prospective register of systematic reviews (PROSPERO) website (CRD42024506866). A comprehensive computer literature search of Scopus, MEDLINE, Scholar, and Embase databases was conducted, including articles indexed up to February 2024. To the methodological evaluation of the studies used the quality assessment of diagnosis accuracy studies-2 (QUADAS-2) tool. Results: Of the 8380 records discovered, 23 were suitable for systematic review. Fifteen studies (on 571 LPD patients) focused on diagnosis and staging, and eight trials (194 LPD patients) assessed treatment response. Conclusions: The main conclusions that can be inferred from the published studies are as follows: (a) [68Ga]Ga-Pentixafor PET may have excellent diagnostic performance in the study of several LPDs; (b) [68Ga]Ga-Pentixafor PET may be superior to [18F]FDG or complementary in some LPDs variants and settings; (c) multiple myeloma seems to have a high uptake of [68Ga]Ga-Pentixafor. Overall, this technique is probably suitable for imaging, staging, and follow-up on patients with LPD. Due to limited data, further studies are warranted to confirm the promising role of [68Ga]Ga-Pantixafor in this context.

Different extramedullary disease shown in chemokine receptor 4 targeted PET/CT with [68Ga]Ga-pentixafor in patients with Waldenström macroglobulinemia and smoldering disease

INTRODUCTION

It is important to distinguish Waldenström macroglobulinemia from smoldering Waldenström macroglobulinemia (sWM), because only patients with Waldenström macroglobulinemia require treatment, however the distinction can be clinically complex. The aim of this study is to investigate whether [68Ga]Ga-pentixafor PET/CT shows different characteristics in sWM and Waldenström macroglobulinemia patients and therefore can help to differentiate Waldenström macroglobulinemia and sWM.

RESULTS

Thirty-seven patients with newly diagnosed Waldenström macroglobulinemia and 11 sWM patients were analyzed [35 men and 13 women; 64.3 ± 10.7 (range, 29-87) years old]. The SUVmax of bone marrow disease, lymph nodes, and other extramedullary diseases on [68Ga]Ga-pentixafor were significantly higher than those on 2-[18F]FDG PET/CT (P < 0.05). On [68Ga]Ga-pentixafor PET/CT, patients with Waldenström macroglobulinemia had more lymph node regions involved, significantly higher incidence of involvement in more than three lymph node regions, larger nodal disease, and higher incidence of other extramedullary disease when compared with sWM patients (P < 0.05). Waldenström macroglobulinemia patients showed significantly higher total lesions uptake, total lesion volume, and SUVmax of extramedullary disease than sWM patients did (P < 0.05). None of the visual or semiquantitative indexes in 2-[18F]FDG PET/CT showed significant difference between Waldenström macroglobulinemia and sWM patients.

CONCLUSION

[68Ga]Ga-pentixafor PET/CT had better diagnostic performance than 2-[18F]FDG PET/CT in Waldenström macroglobulinemia. Patients with Waldenström macroglobulinemia presented with more extensive extramedullary disease shown in [68Ga]Ga-pentixafor PET/CT than sWM patients did.

The Diagnostic Performance of 2-[18F]FDG PET/CT in Identifying Richter Transformation in Chronic Lymphocytic Leukemia: An Updated Systematic Review and Bivariate Meta-Analysis

Richter transformation is a rare phenomenon characterized by the transformation of cell chronic lymphocytic leukemia (CLL) into a more aggressive lymphoma variant. The early identification of CLLs with a high risk of RT is fundamental. In this field, 2-deoxy-2-[18F]-fluoro-D-glucose positron emission tomography/computed tomography (2-[18F]FDG PET/CT) has been shown to be a non-invasive and promising tool, but apparently, unclear data seem to be present in the literature. This systematic review and bivariate meta-analysis aimed to investigate the diagnostic performance of 2-[18F]FDG PET/CT and its parameters in predicting RT. Between 2006 and 2024, 15 studies were published on this topic, including 1593 CLL patients. Among semiquantitative variables, SUVmax was the most investigated, and the best threshold derived for detecting RT was five. With this cut-off value, a pooled sensitivity of 86.8% (95% CI: 78.5-93.3), a pooled specificity of 48.1% (95% CI: 27-69.9), a pooled negative predictive value of 90.5% (95% CI: 88.4-92.4), a pooled negative likelihood ratio of 0.35 (95% CI: 0.17-0.70), a pooled positive likelihood ratio of 1.8 (95% CI: 1.3-2.4), and a pooled diagnostic odds ratio of 6.7 (3.5-12.5) were obtained. With a higher cut-off (SUVmax = 10), the specificity increased while the sensitivity reduced. The other metabolic features, like metabolic tumor volume, total lesion glycolysis, and radiomic features, were only marginally investigated with controversial evidence.

2-[18F]-FDG PET/CT Semiquantitative and Radiomics Predictive Parameters of Richter's Transformation in CLL Patients

Background and Objectives: Chronic lymphocytic leukemia (CLL) is the most common type of leukemia in developed countries, which can evolve into aggressive lymphoma variants, a process called Richter transformation (RT). The aim of this retrospective study was to analyze the role of 2-deoxy-2-[18F]fluoro-D-glucose positron emission tomography/computed tomography (2-[18F]-FDG PET/CT) and its semiquantitative and radiomics features in detecting RT and evaluate the impact on overall survival (OS). Materials and Methods: One hundred and thirty-seven patients with histologically proven CLL were retrospectively recruited. PET/CT images were qualitatively and semiquantitatively examined by estimating the main metabolic parameters (the maximum standardized uptake value body weight (SUVbw), lean body mass (SUVlbm), body surface area (SUVbsa), lesion-to-blood-pool SUV ratio (L-BP SUV R), lesion-to-liver SUV ratio (L-L SUV R), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) and radiomics first- and second- order variables of the lesion with highest uptake. The role of these parameters in predicting RT and OS was analyzed. Results: One hundred and thirty (95%) PET/CT scans were positive, showing an increased tracer uptake at the site of disease, whereas the remaining 7 (5%) scans were negative. SUVbw, SUVlbm, SUVbsa, L-L SUV ratio, and L-BP SUV ratio were significantly higher in the RT group (p < 0.001 in all cases). Radiomics first- and second-order features were not significantly associated with RT. After a median follow-up of 44 months, 56 patients died; OS was significantly shorter in patients with RT than patients without RT (28 vs. 34 months; p = 0.002). Binet-stage, RT, and L-BP SUV R were shown to be independent prognostic features. Conclusions: Semiquantitative PET/CT parameters such as SUVbw, SUVlbm, SUVbsa, L-L SUV ratio and L-BP SUV ratio may be useful in discriminating patients with a high risk of developing RT, whereas Binet-stage, RT, and L-BP SUV R are also significant in predicting OS.

First reported case of splenic diffuse red pulp small B-cell lymphoma with novel mutations in CXCR4 and TRAF3 genes

Splenic diffuse red pulp small B-cell lymphoma (SDRPL) is a rare B-cell tumor whose genetic characteristics are poorly understood. Here, we introduce the case of a 62-year-old patient with SDRPL who showed progressive elevation of lymphocytes and progressive spleen enlargement. Immunohistochemistry showed that CD20 and CD79a were positive, and the Ki-67 labelling index was approximately 5%, consistent with the pathological features of splenic B-cell lymphoma. Spleen tissue and peripheral blood samples from the patient were sequenced using a next-generation sequencing platform, and mutations possibly were detected in the CXCR4 and TRAF3 genes that may be related to the pathogenesis of the disease. This finding may provide insights into the molecular pathogenesis of SDRPL and assist in molecular diagnosis and targeted therapy for SDRPL.

Research Progress of CXCR4-Targeting Radioligands for Oncologic Imaging

C-X-C motif chemokine receptor 4 (CXCR4) plays a key role in various physiological functions, such as immune processes and disease development, and can influence angiogenesis, proliferation, and distant metastasis in tumors. Recently, several radioligands, including peptides, small molecules, and nanoclusters, have been developed to target CXCR4 for diagnostic purposes, thereby providing new diagnostic strategies based on CXCR4. Herein, we focus on the recent research progress of CXCR4-targeting radioligands for tumor diagnosis. We discuss their application in the diagnosis of hematological tumors, such as lymphomas, multiple myelomas, chronic lymphocytic leukemias, and myeloproliferative tumors, as well as nonhematological tumors, including tumors of the esophagus, breast, and central nervous system. Additionally, we explored the theranostic applications of CXCR4-targeting radioligands in tumors. Targeting CXCR4 using nuclear medicine shows promise as a method for tumor diagnosis, and further research is warranted to enhance its clinical applicability.

68Ga-Pentixafor PET/MRI for Treatment Response Assessment in Mantle Cell Lymphoma: Comparison Between Changes in Lesion CXCR4 Expression on PET and Lesion Size and Diffusivity on MRI

PURPOSE

The aim of this study was to compare CXCR4 imaging with 68Ga-pentixafor PET to MRI for treatment response assessment in patients with mantle cell lymphoma (MCL).

PATIENTS AND METHODS

Twenty-two posttreatment 68Ga-pentixafor PET/MRI scans of 16 patients (7 women and 9 men; mean age, 69.9 ± 7.9) with a total of 67 target lesions on baseline PET/MRI were analyzed. Rates of complete remission per lesion and per scan, according to MRI (based on lesion size) and 68Ga-pentixafor PET (based on SUV decrease to lower than liver and blood pool uptake), were compared using McNemar tests. The t tests and Pearson correlation coefficients (r) were used to compare rates of change in lesion diameter products (DPs) on MRI, and standardized uptake values (SUVmax, SUVmean) on PET, relative to baseline.

RESULTS

At interim PET/MRI, 18/32 (56.3%) target lesions met CR criteria on 68Ga-pentixafor PET, and 16/32 (50.0%) lesions met size-based MRI criteria for CR (P = 0.63). At end-of-treatment PET/MRI, 40/57 (70.2%) target lesions met 68Ga-pentixafor PET criteria for CR, and 27/57 (47.4%) lesions met size-based MRI criteria for CR (P = 0.021). Complete remission after treatment was observed more frequently on 68Ga-pentixafor PET (11/22 scans, 54.5%) than on MRI (6/22 scans, 27.3%) (P = 0.031). Rates of change did not differ significantly between lesion DP (-69.20% ± 34.62%) and SUVmax (-64.59% ± 50.78%, P = 0.22), or DP and SUVmean (-60.15 ± 64.58, P = 0.064). Correlations were strong between DP and SUVmax (r = 0.71, P < 0.001) and DP and SUVmean (r = 0.73, P < 0.001).

CONCLUSIONS

In MCL patients, 68Ga-pentixafor PET may be superior for assessment of complete remission status than anatomic MRI using lesion size criteria, especially at the end of treatment.

Theranostics in Hematooncology

In the early 2000s, major clinical trials provided evidence of a favorable outcome from antibody-mediated radioimmunotherapy for hematologic neoplasms, which then led to Food and Drug Administration approval. For instance, the theranostic armamentarium for the referring hematooncologist now includes ⁹⁰Y-ibritumomab tiuxetan for refractory low-grade follicular lymphoma or transformed B-cell non-Hodgkin lymphoma, as well as ¹³¹I-tositumomab for rituximab-refractory follicular lymphoma. Moreover, the first interim results of the SIERRA phase III trial reported beneficial effects from the use of ¹³¹I-anti-CD45 antibodies (Iomab-B) in refractory or relapsed acute myeloid leukemia. During the last decade, the concept of theranostics in hematooncology has been further expanded by C-X-C motif chemokine receptor 4-directed molecular imaging. Beyond improved detection rates of putative sites of disease, C-X-C motif chemokine receptor 4-directed PET/CT also selects candidates for radioligand therapy using β-emitting radioisotopes targeting the identical chemokine receptor on the lymphoma cell surface. Such image-piloted therapeutic strategies provided robust antilymphoma efficacy, along with desired eradication of the bone marrow niche, such as in patients with T- or B-cell lymphoma. As an integral part of the treatment plan, such radioligand therapy-mediated myeloablation also allows one to line up patients for stem cell transplantation, which leads to successful engraftment during the further treatment course. In this continuing education article, we provide an overview of the current advent of theranostics in hematooncology and highlight emerging clinical applications.

[68Ga]Ga-Pentixafor PET/CT imaging for in vivo CXCR4 receptor mapping in different lung cancer histologic sub-types: correlation with quantitative receptors' density by immunochemistry techniques

PURPOSE

In vivo CXCR4 receptor quantification in different lung cancer (LC) sub-types using [⁶⁸Ga]Ga-Pentixafor PET/CT and to study correlation with quantitative CXCR4 receptors' tissue density by immunochemistry analyses.

METHODS

[⁶⁸Ga]Ga-Pentixafor PET/CT imaging was performed prospectively in 94 (77 M: 17F, mean age 60.1 ± 10.1 years) LC patients. CXCR4 receptors' expression on lung mass in all the patients was estimated by immunohistochemistry (IHC) and fluorescence-activated cell sorting (FACS) analyses. SUV_max on PET, intensity score on IHC, and mean fluorescence index (MFI) on FACS analyses were measured.

RESULTS

A total of 75/94 (79.8%) cases had non-small cell lung cancer (NSCLC), 14 (14.9%) had small cell lung cancer (SCLC), and 5 (5.3%) had lung neuroendocrine neoplasm (NEN). All LC types showed increased CXCR4 expression on PET (SUV_max) and FACS (MFI). However, both these parameters (mean SUV_max = 10.3 ± 5.0; mean MFI = 349.0 ± 99.0) were significantly (p = 0.005) higher in SCLC as compared to those in NSCLC and lung NEN. The mean SUV_max in adenocarcinoma (n = 16) was 8.0 ± 1.9 which was significantly (p = 0.003) higher than in squamous cell carcinoma (n = 54; 6.2 ± 2.1) and in not-otherwise specified (NOS) sub-types (n = 5; 5.8 ± 1.5) of NSCLC. A significant correlation (r = 0.697; p = 001) was seen between SUV_max and MFI values in squamous cell NSCLC as well as in NSCLC adenocarcinoma (r = 0.538, p = 0.031) which supports the specific in vivo uptake of [⁶⁸Ga]Ga-Pentixafor by CXCR4 receptors. However, this correlation was not significant in SCLC (r = 0.435, p = 0.121) and NEN (r = 0.747, p = 0.147) which may be due to the small sample size. [⁶⁸Ga]Ga-Pentixafor PET/CT provided good sensitivity (85.7%) and specificity (78.1%) for differentiating SCLC from NSCLC (ROC cutoff SUV_max = 7.2). This technique presented similar sensitivity (87.5%) and specificity (71.4%) (ROC cutoff SUV_max = 6.7) for differentiating adenocarcinoma and squamous cell variants of NSCLC.

CONCLUSION

The high sensitivity and specificity of [⁶⁸Ga]Ga-Pentixafor PET/CT for in vivo targeting of CXCR4 receptors in lung cancer can thus be used effectively for the response assessment and development of CXCR4-based radioligand therapies in LC.

Automated synthesis and quality control of [68Ga]Ga-PentixaFor using the Gaia/Luna Elysia-Raytest module for CXCR4 PET imaging

BACKGROUND

[⁶⁸Ga]Ga-PentixaFor is a promising radiotracer for positron emission tomography imaging of several human tumors overexpressing the chemokine receptor-4 (CXCR4). CXCR4 overexpression has been demonstrated in patients with hematologic malignancies, solid cancers, as well as cardiovascular pathologies of inflammatory origins. However, its radio synthesis is not yet fully developed in France, and existing methods do not use our type of synthesis module. Therefore, we aimed at developing a [⁶⁸Ga]Ga-PentixaFor synthesis with Gaia/Luna Elysia-Raytest module to use it in clinical purpose.

RESULTS

12 syntheses were carried out by varying the temperature conditions and radiolabeling times, and led to choose specific labelling conditions with the Gaia/Luna Elysia-Raytest module: 97 °C, 4 min. The mean synthesis time of the 3 validation runs under good manufacturing practice (GMP) was 24 min 27 s (± 8 s), and the mean radiochemical yield was 87.0% [standard deviation (SD) 6.67%]. Different quality control parameters were also evaluated in accordance with European Pharmacopeia: radiochemical and radionuclidic purity, pH, sterility, stability and endotoxins levels. The average radiochemical purity was 99.1% (SD 0.25%) assessed by instant thin layer chromatography and 99.8% (SD 0.092%) assessed by high pressure liquid chromatography. average [⁶⁸Ge] breakthrough was 1.48 × 10^-5%, under the recommended level of 0.001%. We assessed the stability of the radiotracer up to 4 h at room temperature (no augmentation of the [⁶⁸Ga] chloride in the final product, i.e. radiochemical purity (RCP) > 98.5%). The endotoxins levels were < 5 EU/mL, and the pH was 6.5 (same for the three syntheses).

CONCLUSION

The [⁶⁸Ga]Ga-PentixaFor synthesis process developed on the Gaia/Luna Elysia-Raytest module has fulfilled all acceptance criteria for injectable radiopharmaceutical products regarding the European Pharmacopeia. The radiochemical purity, stability, efficacy, as well as the microbiological quality of the three GMP batches were found to be good. The robustness of the synthesis process may be suitable for multi-dose application in clinical settings.

Radiotheranostics in oncology: Making precision medicine possible

A quintessential setting for precision medicine, theranostics refers to a rapidly evolving field of medicine in which disease is diagnosed followed by treatment of disease-positive patients using tools for the therapy identical or similar to those used for the diagnosis. Against the backdrop of only-treat-when-visualized, the goal is a high therapeutic index with efficacy markedly surpassing toxicity. Oncology leads the way in theranostics innovation, where the approach has become possible with the identification of unique proteins and other factors selectively expressed in cancer versus healthy tissue, advances in imaging technology able to report these tissue factors, and major understanding of targeting chemicals and nanodevices together with methods to attach labels or warheads for imaging and therapy. Radiotheranostics-using radiopharmaceuticals-is becoming routine in patients with prostate cancer and neuroendocrine tumors who express the proteins PSMA (prostate-specific membrane antigen) and SSTR2 (somatostatin receptor 2), respectively, on their cancer. The palpable excitement in the field stems from the finding that a proportion of patients with large metastatic burden show complete and partial responses, and this outcome is catalyzing the search for more radiotheranostics approaches. Not every patient will benefit from radiotheranostics; but, for those who cross the target-detected line, the likelihood of response is very high.

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.

Positron emission tomography/magnetic resonance imaging (PET/MRI) vs. gastroscopy: Can it improve detection of extranodal marginal zone lymphomas of the stomach following H. pylori treatment?

INTRODUCTION

The stomach is the most common site of origin for extranodal marginal zone B-cell lymphoma of the mucosa-associated lymphoid tissue (MALT lymphoma). Antibiotic eradication of Helicobacter pylori (H. pylori) is the standard first-line treatment, with response assessment being performed by histological evaluation of multiple gastric biopsies.

AREAS COVERED

The objective of this review is to provide an update on results obtained using noninvasive methods, including magnetic resonance imaging (MRI), positron emission tomography combined with computed tomography (PET/CT), and most recently, PET/MRI for the assessment of disease extent and response to treatment in patients with gastric MALT lymphoma.

EXPERT OPINION

While CT is the officially recommended imaging technique, few studies in small cohorts have suggested that diffusion-weighted MRI shows higher sensitivity, also relative to 18 F-FDG PET/CT, for both gastric and nongastric MALT lymphomas. A recent prospective study using PET/MRI with the novel CXCR4-targeting radiotracer 68 Ga-Pentixafor suggested that, for patients with gastric MALT lymphoma after H. pylori eradication, this imaging technique may provide excellent accuracy (97%) for assessment of residual or recurrent disease. Although recent studies on CXCR4-targeting PET and to some extent also diffusion-weighted MRI are promising, there is insufficient evidence to suggest a change in clinical practice.

Extranodal Marginal Zone Lymphoma: Pathogenesis, Diagnosis and Treatment

Simple Summary

Extranodal marginal zone lymphoma (EMZL) is an indolent lymphoproliferative disease morphologically composed of small heterogeneous B lymphocytes. It generally occurs with a localized stage and can arise in various organs, the most frequent being the stomach, lung, and ocular adnexa. Depending on the presentation and the possible association with infectious agents, different therapeutic approaches are to be undertaken. The purpose of this review is to describe the biology underlying this pathology, the diagnostic, and therapeutic approach.

Abstract

Extranodal Marginal Zone Lymphoma (EMZL lymphoma) is an indolent B-cell lymphoma with a median age at diagnosis of about 60 years. It accounts for 7–8% of all B-cell lymphomas. It can occur in various extranodal sites, including stomach, lung, ocular adnexa, and skin; furthermore, the disseminated disease can be found in 25–50% of cases. Several infectious agents, such as Helicobacter pylori (H. Pylori) in the case of gastric Mucosa Associated Lymphoid Tissue (MALT) Lymphoma, can drive the pathogenesis of this cancer, through the autoantigenic stimulation of T cells, but there may also be other factors participating such autoimmune diseases. Initial staging should include total body computed tomography, bone marrow aspirate, and endoscopic investigation if indicated. Fluorescence in situ hybridization (FISH), should be performed to detect the presence of specific chromosomal translocations involving the MALT1 and BCL10 genes, which leads to the activation of the NF-κB signaling pathway. Depending on the location and dissemination of the disease, different therapeutic choices may include targeted therapy against the etiopathogenetic agent, radiotherapy, immunochemotherapy, and biological drugs. The purpose of this review is to illustrate the complex biology and the diagnosis of this disease and to better define new treatment strategies.

Burkitt Lymphoma/Leukemia Presented on 68Ga-Pentixafor and 18F-FDG PET/CT

ABSTRACT

An 18-year-old man with newly diagnosed Burkitt lymphoma/leukemia was referred for 18F-FDG and 68Ga-Pentixafor PET/CT. 68Ga-Pentixafor PET/CT revealed similar radioactivity uptake pattern to the 18F-FDG PET/CT in superior phrenic lymph node, ascending colon, ileocecum, peritoneal, marrow, and spleen. This case highlighted that it might be interesting to further investigate the role of 68Ga-Pentixafor PET/CT imaging in staging, treatment evaluation, and especially the feasibility of CXCR4-directed radioligand therapy in Burkitt lymphoma with positive expression of CXCR4.

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.

ImmunoPET imaging of hematological malignancies: From preclinical promise to clinical reality

Immuno-positron emission tomography (immunoPET) imaging is a paradigm-shifting imaging technique for whole-body and all-lesion tumor detection, based on the combined specificity of tumor-targeting vectors [e.g., monoclonal antibodies (mAbs), nanobodies, and bispecific antibodies] and the sensitivity of PET imaging. By noninvasively, comprehensively, and serially revealing heterogeneous tumor antigen expression, immunoPET imaging is gradually improving the theranostic prospects for hematological malignancies. In this review, we summarize the available literature regarding immunoPET in imaging hematological malignancies. We also highlight the pros and cons of current conjugation strategies, and modular chemistry that can be leveraged to develop novel immunoPET probes for hematological malignancies. Lastly, we discuss the use of immunoPET imaging in guiding antibody drug development.

What you always wanted to know about gastric MALT-lymphoma: a focus on recent developments

The stomach is the most common site of origin for extranodal lymphomas, with extranodal marginal zone B-cell of the mucosa associated lymphoid tissue (MALT-lymphoma) being the predominant subtype. MALT-lymphoma develops in mucosa associated lymphoid structures acquired by infection or chronic antigenic stimuli and may therefore arise in almost any organ of the human body. In spite of histopathologic similarities between various organs upon first glance, recent findings suggest pronounced differences between different sites, with a variety of features specific to gastric MALT-lymphoma. The objective of this review is to sum up the current knowledge on pathogenesis, molecular pathology, clinical presentation and therapeutic approaches to gastric MALT-lymphoma with in-depth discussion of recent developments.

CXCR4 hyperactivation cooperates with TCL1 in CLL development and aggressiveness

Aberrant CXCR4 activity has been implicated in lymphoma pathogenesis, disease progression, and resistance to therapies. Using a mouse model with a gain-of-function CXCR4 mutation (CXCR4C1013G) that hyperactivates CXCR4 signaling, we identified CXCR4 as a crucial activator of multiple key oncogenic pathways. CXCR4 hyperactivation resulted in an expansion of transitional B1 lymphocytes, which represent the precursors of chronic lymphocytic leukemia (CLL). Indeed, CXCR4 hyperactivation led to a significant acceleration of disease onset and a more aggressive phenotype in the murine Eµ-TCL1 CLL model. Hyperactivated CXCR4 signaling cooperated with TCL1 to cause a distinct oncogenic transcriptional program in B cells, characterized by PLK1/FOXM1-associated pathways. In accordance, Eµ-TCL1;CXCR4C1013G B cells enriched a transcriptional signature from patients with Richter's syndrome, an aggressive transformation of CLL. Notably, MYC activation in aggressive lymphoma was associated with increased CXCR4 expression. In line with this finding, additional hyperactive CXCR4 signaling in the Eµ-Myc mouse, a model of aggressive B-cell cancer, did not impact survival. In summary, we here identify CXCR4 hyperactivation as a co-driver of an aggressive lymphoma phenotype.

CXCR4 PET/MRI for follow-up of gastric mucosa-associated lymphoid tissue lymphoma after first-line H. pylori eradication

[⁶⁸Ga]Pentixafor is a novel PET tracer that targets the chemokine receptor CXCR4, which is overexpressed in MALT lymphoma.

In gastric MALT lymphoma after H pylori eradication, [⁶⁸Ga]Pentixafor–PET shows high accuracy for detection of residual disease.

Posttreatment evaluation of gastric mucosa-associated lymphoid tissue (MALT) lymphoma currently relies on esophagogastroduodenoscopy with histological assessment of biopsies. Overexpression of the G protein–coupled C-X-C chemokine receptor type 4 (CXCR4) has been previously observed in MALT lymphoma. The aim of this prospective study was to evaluate positron emission tomography (PET) with the novel CXCR4 tracer [⁶⁸Ga]Pentixafor as a potential alternative to follow up biopsies for assessment of residual disease (noncomplete remission [CR]) after first-line Helicobacter pylori eradication. Forty-six post–H pylori eradication [⁶⁸Ga]Pentixafor–PET/magnetic resonance imaging (MRI) examinations of 26 gastric MALT lymphoma patients, and 20 [⁶⁸Ga]Pentixafor–PET/MRI examinations of 20 control group patients without lymphoma, were analyzed. In the MALT lymphoma group, time-matched gastric biopsies were used as reference standard and showed CR in 6 cases. Pooled examination-based accuracy, sensitivity, specificity, and positive and negative predictive values of [⁶⁸Ga]Pentixafor–PET for detection of residual gastric MALT lymphoma at follow-up were 97.0%, 95.0%, 100.0%, 100.0%, and 92.9%, respectively. Maximum and mean PET standardized uptake values showed moderate correlation with immunohistochemistry-based CXCR4⁺ cell counts, with correlation coefficients of r = 0.51 and r = 0.52 (P = .008 and P = .006). In summary, CXCR4 imaging with [⁶⁸Ga]Pentixafor–PET may represent a promising test for assessment of residual gastric MALT lymphomas after H pylori eradication.

Chronic lymphocytic leukaemia and Richter's transformation: multimodal review and new imaging paradigms

Chronic lymphocytic leukaemia (CLL) is the most common leukaemia in adults. It is a malignancy of CD5 B-cells characterised by small, mature-appearing lymphocytes accumulating in the blood, bone marrow, and lymphoid tissues. Richer transformation (RT) is an important adverse complication. Detection of RT is critical to allow initiation of appropriate therapy. CLL staging and response evaluation is complicated and nuanced. From our extensive tertiary centre experience of several hundred CLL cases over the last decade, we detail key computed tomography (CT) and positron-emission tomography (PET) imaging features of the natural history of CLL. The authors present an original imaging-based patient-management paradigm for the investigation of potential RT, which will inform global practice. Potential applications of whole-body diffusion weighted imaging, novel PET radiotracers, minimal residual disease, and ct-DNA are addressed.

68Ga-Pentixafor-PET/CT imaging represents a novel approach to detect chemokine receptor CXCR4 expression in myeloproliferative neoplasms

C-X-C motif chemokine receptor 4 (CXCR4) is an attractive target for cancer diagnosis and treatment, as it is overexpressed in many solid and hematological malignancies. This study investigated the feasibility of CXCR4-directed imaging with positron emission tomography/computed tomography (PET/CT) using ⁶⁸Ga-Pentixafor to visualize and quantify disease involvement in myeloproliferative neoplasms (MPNs). Methods: 12 patients with MPNs (n = 4 primary myelofibrosis, n = 6 essential thrombocythemia, n = 2 polycythemia vera) and 5 controls underwent ⁶⁸Ga-Pentixafor-PET/CT. Imaging findings were compared with immunohistochemical stainings, laboratory data and splenic volume. Results: ⁶⁸Ga-Pentixafor-PET/CT was visually positive in 12/12 patients and CXCR4 target specificity could be confirmed by immunohistochemical staining. A significantly higher tracer uptake could be detected in the bone marrow of MPN patients (SUVmean 6.45±2.34 vs. 4.44±1.24). Dynamic changes of CXCR4 expression determined by ⁶⁸Ga-Pentixafor-PET/CT corresponded with treatment response. Conclusion: ⁶⁸Ga-Pentixafor-PET/CT represents a novel diagnostic tool to non-invasively detect and quantify the extent of disease involvement in MPNs.

The Role of 2-[18F]-FDG PET/CT in Detecting Richter Transformation in Chronic Lymphocytic Leukemia: A Systematic Review

Richter transformation (RT) is a condition wherein B cell chronic lymphocytic leukemia (CLL) transforms into a more aggressive lymphoma variant. The incidence and the significance of RT detected by 2-[18F]-FDG PET/CT is a clinical challenge and it is not widely investigated in the literature. The aim of this systematic review was to analyze published data about the potential role of 2-[18F]-FDG PET/CT in detecting RT. A comprehensive computer literature search of the PubMed/MEDLINE, Embase and Cochrane library databases was conducted up to December 2020. Thirteen studies (1336 patients with CLL) were selected. The maximum standardized uptake value (SUVmax) was the most common metabolic parameter used to detect RT. An SUVmax of 5 had an average overall sensitivity of 87% (range: 71–96%), an average overall specificity of 49% (range: 4–80%), an average positive predictive value of 41% (range: 16–53%) and an average negative predictive value of 84% (range: 33–97%). Other metabolic variables were only marginally investigated, with promising results. 2-[18F]-FDG PET/CT imaging may play an important role in the detection of RT in CLL, based on the high metabolic activity of the nodal lesions that transformed into aggressive lymphomas. 2-[18F]-FDG PET/CT has high negative predictive value for evaluating RT.

CXCR4 PET imaging of mantle cell lymphoma using [68Ga]Pentixafor: comparison with [18F]FDG-PET

For PET imaging of mantle cell lymphoma (MCL), [18F]FDG (2-deoxy-2-[18F]fluoro-D-glucose) is the currently recommended radiotracer, although uptake is variable and bone marrow evaluation is limited. In this prospective study, we evaluated the novel CXCR4 (G-protein-coupled C-X-C chemokine receptor type 4) tracer [68Ga]Pentixafor in MCL patients, and compared it to [18F]FDG. Methods: MCL patients underwent [68Ga]Pentixafor-PET/MRI, and, if required for routine purposes, also [18F]FDG-PET/MRI, before treatment. PET was evaluated separately for 23 anatomic regions (12 lymph node stations and 11 organs/tissues), using MRI as the main reference standard. Standardized uptake values (SUVmax and SUVmean) and tumor-to-background ratios (TBRblood and TBRliver) were calculated. General Estimation Equations (GEE) were used to compare [68Ga]Pentixafor-PET and [18F]FDG-PET sensitivities and positive predictive values (PPV). For bone marrow involvement, where biopsy served as the main reference standard, and splenic involvement, receiver operating characteristic curves were used to determine the optimal SUV and TBR cut-off values, and areas under the curve (AUC) were calculated. Results: Twenty-two MCL patients were included. [68Ga]Pentixafor-PET sensitivity (100%) was significantly higher than for [18F]FDG-PET (75.2%) (P<0.001), and PPV was slightly, but not significantly lower (94.0%.vs. 96.5%; P=0.21). SUVs and TBRs were significantly higher for [68Ga]Pentixafor-PET than for [18F]FDG-PET (P<0.001 in all cases); the greatest difference was observed for mean TBRblood, with 4.9 for [68Ga]Pentixafor-PET and 2.0 for [18F]FDG-PET. For bone marrow involvement, [68Ga]Pentixafor-PET SUVmean showed an AUC of 0.92; and for splenic involvement, TBRblood showed an AUC of 0.81. Conclusion: [68Ga]Pentixafor-PET may become an alternative to [18F]FDG-PET in MCL patients, showing clearly higher detection rates and better tumor-to-background contrast.

Assessment of Central Nervous System Lymphoma Based on CXCR4 Expression In Vivo Using 68Ga-Pentixafor PET/MRI

PURPOSE OF THE REPORT

F-FDG PET is limited for assessment of central nervous system lymphoma (CNSL) due to physiologic tracer accumulation in the brain. We prospectively evaluated the novel PET tracer Ga-pentixafor, which targets the C-X-C chemokine receptor 4 (CXCR4), for lesion visualization and response assessment of CNSL.

MATERIALS AND METHODS

Seven CNSL patients underwent Ga-pentixafor PET/MRI with contrast enhancement (CE-MRI) and diffusion-weighted sequences. The accuracy of Ga-pentixafor PET for CNSL lesion detection relative to the CE-MRI reference standard was determined. Standardized uptake values (SUVmean and SUVmax), PET-based (PTV) and MRI-based (VOLMRI) tumor volumes, and apparent diffusion coefficients (ADCs) were assessed, and correlation coefficients were calculated. Three SUVmax thresholds (41%, 50%, and 70%) were evaluated for PTV definitions (PTV41%, PTV50%, and PTV70%) and tested against VOLMRI using paired sample t tests.

RESULTS

Twelve Ga-pentixafor PET/MRI examinations (including 5 follow-up scans) of 7 patients were evaluated. Ga-pentixafor PET demonstrated 18 lesions, all of which were confirmed by CE-MRI; there were no false-positive lesions on PET (accuracy, 100%). PTV41% showed the highest concordance with lesion morphology, with no significant difference compared with VOLMRI (mean difference, -0.24 cm; P = 0.45). The correlation between ADCmean and SUVmean41% (r = 0.68) was moderate. Changes in PTV41% on follow-up PET/MRI showed the same trend as VOLMRI changes, including progression of 1 lesion each in patient 1 (+456.0% PTV41% and +350.8% VOLMRI) and patient 3 (+110.4% PTV41% and +85.1% VOLMRI).

CONCLUSIONS

Ga-pentixafor PET may be feasible for assessment and follow-up of CNSL. Future studies need to focus on testing its clinical value to distinguish between glioma and CNSL, and between radiation-induced inflammation and viable residual tumor.

Increased Uptake of 68Ga-Pentixafor in Thymic Rebound After Chemotherapy in a Patient With Multiple Myeloma

A 38-year-old man with newly diagnosed multiple myeloma underwent Ga-pentixafor PET/CT for baseline assessment. Ga-pentixafor PET/CT demonstrated multiple focal bone and bone marrow lesions with intense radioactivity. After 9 cycles of chemotherapy against multiple myeloma, the patient experienced serologically complete remission of myeloma. Consistently, the follow-up Ga-pentixafor PET/CT for PET response showed significantly reduced uptake in the previously chemokine receptor 4-positive bone lesions. However, intense and homogeneous uptake of Ga-pentixafor was noted in the thymus with a smooth contour and slightly increased density, which is possibly caused by thymic hyperplasia after chemotherapy.

At the Bedside: Profiling and treating patients with CXCR4-expressing cancers

The chemokine receptor, C-X-C chemokine receptor type 4 (CXCR4) and its ligand, C-X-C motif chemokine 12, are key mediators of hematopoietic cell trafficking. Their roles in the proliferation and metastasis of tumor cells, induction of angiogenesis, and invasive tumor growth have been recognized for over 2 decades. CXCR4 is a promising target for imaging and therapy of both hematologic and solid tumors. To date, Sanofi Genzyme's plerixafor is the only marketed CXCR4 inhibitor (i.e., Food and Drug Administration-approved in 2008 for stem cell mobilization). However, several new CXCR4 inhibitors are now being investigated as potential therapies for a variety of fluid and solid tumors. These small molecules, peptides, and Abs include balixafortide (POL6326, Polyphor), mavorixafor (X4P-001, X4 Pharmaceuticals), motixafortide (BL-8040, BioLineRx), LY2510924 (Eli Lilly), and ulocuplumab (Bristol-Myers Squibb). Early clinical evidence has been encouraging, for example, with motixafortide and balixafortide, and the CXCR4 inhibitors appear to be generally safe and well tolerated. Molecular imaging is increasingly being used for effective patient selection before, or early during CXCR4 inhibitor treatment. The use of radiolabeled theranostics that combine diagnostics and therapeutics is an additional intriguing approach. The current status and future directions for radioimaging and treating patients with CXCR4-expressing hematologic and solid malignancies are reviewed. See related review - At the Bench: Pre-Clinical Evidence for Multiple Functions of CXCR4 in Cancer. J. Leukoc. Biol. xx: xx-xx; 2020.

Applications of PET in Diagnosis and Prognosis of Leukemia

As a malignant hematopoietic stem cell disease, leukemia remains life-threatening due to its increasing incidence rate and mortality rate. Therefore, its early diagnosis and treatment play a very important role. In the present work, we systematically reviewed the current applications and future directions of positron emission tomography (PET) in patients with leukemia, especially ¹⁸F-FDG PET/CT. As a useful imaging approach, PET significantly contributes to the diagnosis and treatment of different types of leukemia, especially in the evaluation of extramedullary infiltration, monitoring of leukemia relapse, detection of Richter’s transformation (RT), and assessment of the inflammatory activity associated with acute graft versus host disease. Future investigations should be focused on the potential of PET/CT in the prediction of clinical outcomes in patients with leukemia and the utility of novel radiotracers.

Preliminary evidence of imaging of chemokine receptor-4-targeted PET/CT with [68Ga]pentixafor in non-Hodgkin lymphoma: comparison to [18F]FDG

BACKGROUND

In order to study the CXCR4 expression with [⁶⁸Ga]pentixafor PET in different types of non-Hodgkin lymphoma, we performed a retrospective study to describe the [⁶⁸Ga]pentixafor PET/CT imaging in a spectrum of lymphomas and to compare it with [¹⁸F]FDG PET/CT.

RESULTS

Twenty-seven patients with newly diagnosed non-Hodgkin lymphoma were recruited retrospectively. [⁶⁸Ga]pentixafor PET showed increased radioactivity in lymphoplasmacytic lymphoma (n = 8), marginal zone lymphoma (n = 4), diffuse large B cell lymphoma (n = 3), follicular lymphoma (n = 2), mantle cell lymphoma (n = 1), unclassified indolent B cell lymphoma (n = 3), and enteropathy associated T cell lymphoma (n = 3). However, peripheral T cell lymphoma, not otherwise specified (n = 1), and NK/T cell lymphoma (n = 2) were not avid for [⁶⁸Ga]pentixafor. In comparison to [¹⁸F]FDG PET, [⁶⁸Ga]pentixafor PET demonstrated more extensive disease and higher radioactivity in lymphoplasmacytic lymphoma and marginal zone lymphoma.

CONCLUSION

CXCR4 expression varies in different types of non-Hodgkin lymphoma. Overexpression of CXCR4 was detected with [⁶⁸Ga]pentixafor PET/CT in lymphoplasmacytic lymphoma, marginal zone lymphoma, diffuse large B cell lymphoma, follicular lymphoma, mantle cell lymphoma, unclassified indolent B cell lymphoma, and enteropathy associated T cell lymphoma. The uptake of [⁶⁸Ga]pentixafor was higher than [¹⁸F]FDG in lymphoplasmacytic lymphoma and marginal zone lymphoma.

A new class of PentixaFor- and PentixaTher-based theranostic agents with enhanced CXCR4-targeting efficiency

Non-invasive PET imaging of CXCR4 expression in cancer and inflammation as well as CXCR4-targeted radioligand therapy (RLT) have recently found their way into clinical research by the development of the theranostic agents [⁶⁸Ga]PentixaFor (cyclo(D-Tyr¹-D-[NMe]Orn²(AMBS-[⁶⁸Ga]DOTA)-Arg³-Nal⁴-Gly⁵) = [⁶⁸Ga]DOTA-AMBS-CPCR4) and [¹⁷⁷Lu/⁹⁰Y]PentixaTher (cyclo(D-3-iodo-Tyr¹-D-[NMe]Orn²(AMBS-[¹⁷⁷Lu/⁹⁰Y]DOTA)-Arg³-Nal⁴-Gly⁵) = [¹⁷⁷Lu/⁹⁰Y]DOTA-AMBS-iodoCPCR4). Although convincing clinical results have already been obtained with both agents, this study was designed to further investigate the required structural elements for improved ligand-receptor interaction for both peptide cores (CPCR4 and iodoCPCR4). To this aim, a series of DOTA-conjugated CPCR4- and iodoCPCR4-based ligands with new linker structures, replacing the AMBA-linker in PentixaFor and PentixaTher, were synthesized and evaluated. Methods: The in vitro investigation of the novel compounds alongside with the reference peptides PentixaFor and PentixaTher encompassed the determination of hCXCR4 and mCXCR4 affinity (IC₅₀) of the respective ^natGa-, ^natLu-, ^natY- and ^natBi-complexes in Jurkat and Eμ-myc 1080 cells using [¹²⁵I]FC-131 and [¹²⁵I]CPCR4.3 as radioligands, respectively, as well as the evaluation of the internalization and externalization kinetics of selected ⁶⁸Ga- and ¹⁷⁷Lu-labeled compounds in hCXCR4-transfected Chem-1 cells. Comparative small animal PET imaging studies (1h p.i.) as well as in vivo biodistribution studies (1, 6 and 48h p.i.) were performed in Daudi (human B cell lymphoma) xenograft bearing CB17 SCID mice. Results: Based on the affinity data and cellular uptake studies, [⁶⁸Ga/¹⁷⁷Lu]DOTA-r-a-ABA-CPCR4 and [⁶⁸Ga/¹⁷⁷Lu]DOTA-r-a-ABA-iodoCPCR4 (with r-a-ABA = D-Arg-D-Ala-4-aminobenzoyl-) were selected for further evaluation. Both analogs show app. 10-fold enhanced hCXCR4 affinity compared to the respective references [⁶⁸Ga]PentixaFor and [¹⁷⁷Lu]PentixaTher, four times higher cellular uptake in hCXCR4 expressing cells and improved cellular retention. Unfortunately, the improved in vitro binding and uptake characteristics of [⁶⁸Ga]DOTA-r-a-ABA-CPCR4 and -iodoCPCR4 could not be recapitulated in initial PET imaging studies; both compounds showed similar uptake in the Daudi xenografts as [⁶⁸Ga]PentixaFor, alongside with higher background accumulation, especially in the kidneys. However, the subsequent biodistribution studies performed for the corresponding ¹⁷⁷Lu-labeled analogs revealed a clear superiority of [¹⁷⁷Lu]DOTA-r-a-ABA-CPCR4 and [¹⁷⁷Lu]DOTA-r-a-ABA-iodoCPCR4 over [¹⁷⁷Lu]PentixaTher with respect to tumor uptake (18.3±3.7 and 17.2±2.0 %iD/g, respectively, at 1h p.i. vs 12.4±3.7%iD/g for [¹⁷⁷Lu]PentixaTher) as well as activity retention in tumor up to 48h. Especially for [¹⁷⁷Lu]DOTA-r-a-ABA-CPCR4 with its low background accumulation, tumor/organ ratios at 48h were 2- to 4-fold higher than those obtained for [¹⁷⁷Lu]PentixaTher (except for kidney). Conclusions: The in-depth evaluation of a series of novel CPCR4- and iodoCPCR4 analogs with modified linker structure has yielded reliable structure-activity relationships. It was generally observed that a) AMBA-by-ABA-substitution leads to enhanced ligand internalization, b) the extension of the ABA-linker by two additional amino acids (DOTA-Xaa₂-Xaa₁-ABA-) provides sufficient linker length to minimize the interaction of the [M³⁺]DOTA-chelate with the receptor, and that c) introduction of a cationic side chain (Xaa₂) greatly enhances receptor affinity of the constructs, obliterating the necessity for Tyr¹-iodination of the pentapeptide core to maintain high receptor affinity (such as in [¹⁷⁷Lu]PentixaTher). As a result, [¹⁷⁷Lu]DOTA-r-a-ABA-CPCR4 has emerged from this study as a powerful second-generation therapeutic CXCR4 ligand with greatly improved targeting efficiency and tumor retention and will be further evaluated in preclinical and clinical CXCR4-targeted dosimetry and RLT studies.

In Human Visualization of Ibrutinib-Induced CLL Compartment Shift

Bruton tyrosine kinase inhibitor ibrutinib is effective in treating chronic lymphocytic leukemia (CLL). However, after ibrutinib treatment initiation, patients frequently experience an increase of CLL blood cell count. This phenomenon in clinical practice is thought to reflect a "compartment shift" of CLL cells from lymph nodes to the peripheral blood, but the actual shifting has not yet been demonstrated. Using [⁶⁸Ga]Pentixafor-PET/MRI for in vivo CXCR4 visualization, we here provide images of topical changes of CLL cells upon ibrutinib treatment. Within the first month of ibrutinib treatment, mean standardized [⁶⁸Ga]Pentixafor uptake decreased in the bone marrow and lymph nodes, whereas [⁶⁸Ga]Pentixafor uptake increased in the spleen. Leukocytosis rose, as did numbers of CXCR4^high (tissue-resident) CLL cells. Volumes of lymph nodes and spleen decreased. Upon longer ibrutinib treatment, leukocytosis decreased, followed by a decrease of [⁶⁸Ga]Pentixafor uptake in the spleen. These results support the preexisting clinical hypothesis of a "compartment shift" of CLL cells from the lymph nodes to the peripheral blood, but also refine the mechanistic model by describing early clearing of the bone marrow and redistribution of CLL cells to the orthotopic splenic cavernous system in response to ibrutinib treatment.

[Hybrid imaging in lymphoma]

Hybrid imaging using the tracer [18F]FDG (2‑deoxy-2-fluoro-D-glucose) is regarded as the backbone of the diagnostic workup of lymphomas. All international guidelines, and especially the Lugano and RECIL (Response Evaluation Criteria in Lymphoma) guidelines, currently recommend [18F]FDG-PET/CT (positron emission tomography/computed tomography) for staging and treatment response assessment. With the exception of pediatric lymphomas, neither PET/MRI (magnetic resonance imaging) nor whole-body MRI are currently endorsed by international guidelines, despite the fact that both techniques have clear advantages over [18F]FDG-PET/CT in the assessment of lymphomas with variable FDG avidity. Of the new, more specific PET tracers that are being evaluated for the use in lymphomas, the CXCR4 (CXC motif chemokine receptor 4) tracer [68Ga]Pentixafor is of particular interest, as initial studies have shown that it may be used to visualize frequently non-FDG-avid lymphomas such as small-cell lymphocytic lymphoma, mucosa-associated lymphoid tissue (MALT) lymphoma and lymphomplasmacytic lymphoma.

Fully-automated production of [68Ga]Ga-PentixaFor on the module Modular Lab-PharmTracer

Background

PentixaFor is a promising radiopharmaceutical for positron emission tomography in the detection of different tumor entities and other diseases. Until now, the synthesis of [⁶⁸Ga]Ga-PentixaFor was reported for the automated synthesis module from Scintomics® only. Our aim was to evaluate the automated synthesis of this radiopharmaceutical on a different module in order to make it available for a broader community.

Results

The synthesis of [⁶⁸Ga]Ga-PentixaFor with different amounts of PentixaFor (50 μg, 30 μg and 20 μg) on the Modular Lab PharmTracer (MLPT) from Eckert & Ziegler with the already established synthesis template for [⁶⁸Ga]Ga-DOTATOC yielded best results with 50 μg PentixaFor for clinical multi-dose application. All different quality control parameters tested (e.g. sterility, stability and radiochemical purity) were in accordance with the European Pharmacopoeia.

Conclusions

[⁶⁸Ga]Ga-PentixaFor was successfully synthesized fully-automated on the synthesis module Modular Lab PharmTracer and can be used for multi-dose application in clinical settings.

Radiolabelled Peptides for Positron Emission Tomography and Endoradiotherapy in Oncology

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

Posttreated POEMS Syndrome With Concurrent Follicular Lymphoma Revealed by 18F-FDG and 68Ga-Pentixafor PET/CT

A 59-year-old man with history of POEMS syndrome was found with a painless mass in the right neck for 9 months. In F-FDG and Ga-pentixafor PET/CT, there were multiple neck nodes and left inguinal nodes that showed intense F-FDG and Ga-pentixafor uptake. In addition, osteoblastic bone lesions with mild F-FDG and Ga-pentixafor uptake were noted in the pelvis, which was consistent with posttreated osseous involvement of POEMS syndrome. However, considering lymphoadenopathy with such intense F-FDG uptake is not usually seen in POEMS syndrome, the patient underwent biopsy of the right cervical nodes. The histopathology with immunohistochemistry confirmed follicular lymphoma.

Radiolabeled Protein-inhibitor Peptides with Rapid Clinical Translation towards Imaging and Therapy

Protein interactions are the basis for the biological functioning of human beings. However, many of these interactions are also responsible for diseases, including cancer. Synthetic inhibitors of protein interactions based on small molecules are widely investigated in medicinal chemistry. The development of radiolabeled protein-inhibitor peptides for molecular imaging and targeted therapy with quickstep towards clinical translation is an interesting and active research field in the radiopharmaceutical sciences. In this article, recent achievements concerning the design, translational research and theranostic applications of structurally-modified small radiopeptides, such as prostate-specific membrane antigen (PSMA) inhibitors, fibroblast activation protein (FAP) inhibitors and antagonists of chemokine-4 receptor ligands (CXCR-4-L), with high affinity for cancer-associated target proteins, are reviewed and discussed.

Consensus criteria for diagnosis, staging, and treatment response assessment of T-cell prolymphocytic leukemia

T-cell prolymphocytic leukemia (T-PLL) is a rare, mature T-cell neoplasm with a heterogeneous clinical course. With the advent of novel treatment options that will potentially change the management of patients with T-PLL, it has become necessary to produce consensus guidelines for the design and conduct of clinical trials. The T-PLL International Study group (TPLL-ISG) set out to define standardized criteria for diagnosis, treatment indication, and evaluation of response. These criteria will facilitate comparison of results from clinical trials in T-PLL, and will thus support clinical decision making, as well as the approval of new therapeutics by healthcare authorities.

MRI and PET/MRI in hematologic malignancies

The role of MRI differs considerably between the three main groups of hematological malignancies: lymphoma, leukemia, and myeloma. In myeloma, whole‐body MRI (WB‐MRI) is recognized as a highly sensitive test for the assessment of myeloma, and is also endorsed by clinical guidelines, especially for detection and staging. In lymphoma, WB‐MRI is presently not recommended, and merely serves as an alternative technique to the current standard imaging test, [¹⁸F]FDG‐PET/CT, especially in pediatric patients. Even for lymphomas with variable FDG avidity, such as extranodal mucosa‐associated lymphoid tissue lymphoma (MALT), contrast‐enhanced computed tomography (CT), but not WB‐MRI, is presently recommended, despite the high sensitivity of diffusion‐weighted MRI and its ability to capture treatment response that has been reported in the literature. In leukemia, neither MRI nor any other cross‐sectional imaging test (including positron emission tomography [PET]) is currently recommended outside of clinical trials. This review article discusses current clinical applications as well as the main research topics for MRI, as well as PET/MRI, in the field of hematological malignancies, with a focus on functional MRI techniques such as diffusion‐weighted imaging and dynamic contrast‐enhanced MRI, on the one hand, and novel, non‐FDG PET imaging probes such as the CXCR4 radiotracer [⁶⁸Ga]Ga‐Pentixafor and the amino acid radiotracer [¹¹C]methionine, on the other hand.

Level of Evidence: 5

Technical Efficacy Stage: 3

J. Magn. Reson. Imaging 2020;51:1325–1335.

CXCR4-directed theranostics in oncology and inflammation

Given its prominent role in inflammation and cancer biology, the C-X-C motif chemokine receptor 4 (CXCR4) has gained a lot of attention in the recent years. This review gives a short overview of the physiology and pathology of chemokines and chemokine receptors and then focuses on the current experience of targeting CXCR4, using radiolabeled receptor ligands suitable for positron emission tomography (PET) imaging, in both hematologic and solid malignancy as well as in inflammatory conditions. Additionally, CXCR4-directed endoradiotherapy (ERT) as a new treatment option is discussed.