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

Novel Theranostic Approaches Targeting CCR4-Receptor, Current Status and Translational Prospectives: A Systematic Review

Background: With the high mortality rate of malignant tumors, there is a need to find novel theranostic approaches to provide an early diagnosis and targeted therapy. The chemokine receptor 4 (CCR4) is highly expressed in various tumors and plays an important role in tumor pathogenesis. This systematic review aims to provide a complete overview on clinical and preclinical applications of the CCR4 receptor as a target for theranostics, using a systematic approach to classify and assemble published studies performed on humans and animals, sorted by field of application and specific tumor. Methods: A systematic literature search of articles suiting the inclusion criteria was conducted on Pubmed, Scopus, Central, and Web of Science databases, including papers published from January 2006 to November 2022. Eligible studies had to be performed on humans and/or in vivo/in vitro studying CCR4 expression in tumors. The methodological quality was assessed through the Critical Appraisal Skills Programme (CASP) assessing only the studies performed on humans. Results: A total of 17 articles were screened. The articles were assessed for eligibility with the exclusion of 4 articles. Ultimately, 13 articles were selected for the qualitative analysis, and six articles were selected for the critical appraisal skills program. Conclusions: The development of new radionuclides and radiopharmaceuticals targeting CCR4 show promising results in the theranostics of CCR4 sensible tumors. Although to widen its use in clinical practice, further translation of preclinical to clinical data is needed.

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

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

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.

18F-PEG1-Vinyl Sulfone-Labeled Red Blood Cells as Positron Emission Tomography Agent to Image Intra-Abdominal Bleeding

¹⁸F-Labeled blood pool agents (BPAs) have attracted great attention for identifying bleeding sites. However, many BPAs are not sufficiently evaluated partially due to the limitations of labeling methods. In our previous work, we noticed that ¹⁸F-PEG1-vinyl sulfone (¹⁸F-VS) could efficiently label red blood cells (RBCs) ex vivo and in situ. However, its application as BPA is not fully evaluated. In this study, we systematically explored the feasibility of using ¹⁸F-VS-labeled RBCs as a positron emission tomography (PET) BPA for intra-abdominal bleeding diagnosis. In brief, we first optimized the labeling conditions, which lead to an 80% labeling yield of RBCs after incubating with ¹⁸F-VS in phosphate-buffered saline (PBS) at 37°C for 20 min. ¹⁸F-VS-labeled RBCs were found to be stable in vitro, which could simplify its transportation/storage for in vivo applications. In normal rat PET study, the cardiovascular system could be clearly imaged up to 5 h post injection (p.i.). An intra-abdominal hemorrhage rat model demonstrated that the ¹⁸F-VS-labeled RBCs clearly showed the dynamic changes of extravascular radioactivity due to intra-abdominal hemorrhage. Validation in the model of gastrointestinal bleeding clearly demonstrated the great potential of using ¹⁸F-VS-labeled RBCs as a BPA, which could be further evaluated in future studies.

Novel Peptide-Based PET Probe for Non-invasive Imaging of C-X-C Chemokine Receptor Type 4 (CXCR4) in Tumors

The recently reported CXCR4 antagonist 3 (Ac-Arg-Ala-[DCys-Arg-2Nal-His-Pen]-CO₂H) was investigated as a molecular scaffold for a CXCR4-targeted positron emission tomography (PET) tracer. Toward this end, 3 was functionalized with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and 1,4,7-triazacyclononanetriacetic acid (NOTA). On the basis of convincing affinity data, both tracers, [⁶⁸Ga]NOTA analogue ([⁶⁸Ga]-5) and [⁶⁸Ga]DOTA analogue ([⁶⁸Ga]-4), were evaluated for PET imaging in "in vivo" models of CHO-hCXCR4 and Daudi lymphoma cells. PET imaging and biodistribution studies revealed higher CXCR4-specific tumor uptake and high tumor/background ratios for the [⁶⁸Ga]NOTA analogue ([⁶⁸Ga]-5) than for the [⁶⁸Ga]DOTA analogue ([⁶⁸Ga]-4) in both in vivo models. Moreover, [⁶⁸Ga]-4 and [⁶⁸Ga]-5 displayed rapid clearance and very low levels of accumulation in all nontarget tissues but the kidney. Although the high tumor/background ratios observed in the mouse xenograft model could partially derive from the hCXCR4 selectivity of [⁶⁸Ga]-5, our results encourage its translation into a clinical context as a novel peptide-based tracer for imaging of CXCR4-overexpressing tumors.

Targeting CXCR4 in AML and ALL

The interaction of acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) blasts with the bone marrow microenvironment regulates self-renewal, growth signaling, as well as chemotherapy resistance. The chemokine receptor, CXC receptor 4 (CXCR4), with its ligand chemokine ligand 12 (CXCL12), plays a key role in the survival and migration of normal and malignant stem cells to the bone marrow. High expression of CXCR4 on AML and ALL blasts has been shown to be a predictor of poor prognosis for these diseases. Several small molecule inhibitors, short peptides, antibodies, and antibody drug conjugates have been developed for the purposes of more effective targeting and killing of malignant cells expressing CXCR4. In this review we will discuss recent results and strategies in targeting CXCR4 with these agents in patients with AML or ALL.