68Ga-DOTA-E[c(RGDfK)]2 PET Imaging of SHARPIN-Regulated Integrin Activity in Mice

A novel PET tracer for noninvasive imaging the checkpoints expression of innate and adaptive immunity in tumors by simultaneously targeting CD24 and PD-L1

The success of tumor immunotherapy depends on the innate and adaptive immune responses, with CD24 and PD-L1 being key targets. DBP1 peptide is a novel bispecific D-peptide, targeting both CD24 and PD-L1 simultaneously. In this study, by radiolabeling DBP1 peptide, we developed a novel PET modality to noninvasively evaluate CD24 and PD-L1 expressions in tumors. To enhance the solubility of DBP1, a hydrophilic lysine was added into C-terminal residue of the peptide, which was then modified with a chelator NOTA to produce the radiotracer precursor NOTA-DBP1k. NOTA-DBP1k showed high affinity for CD24 (KD = 10.70 ± 0.70 nM) and PD-L1 (KD = 5.40 ± 0.61 nM). [68Ga]Ga-NOTA-DBP1k was synthesized with a high radiochemical yield (71 ± 3.0 %) and exhibited high hydrophilicity and stability. [68Ga]Ga-NOTA-DBP1k showed higher uptake in high CD24/PD-L1 expressed MCF-7 cells than that in low CD24/PD-L1 expressed U-87MG cells in vitro. In vivo, [68Ga]Ga-NOTA-DBP1k showed high uptake in MCF-7 tumors and had favorable tumor-to-background ratios by microPET imaging. On the contrary, low uptake was found in U-87MG tumors, which was significantly lower than that in MCF-7 tumors (0.42 ± 0.02 %ID/g vs. 1.01 ± 0.06 %ID/g, p < 0.05). The biodistribution study was consistent with the findings of microPET imaging results. These results demonstrated that [68Ga]Ga-NOTA-DBP1k can noninvasively image the CD24 and PD-L1 checkpoint expression of innate and adaptive immunity in tumors and may be helpful for guiding the CD24/PD-L1 dual-checkpoints blockage immunotherapy.

The role and regulation of integrins in cell migration and invasion

Integrin receptors are the main molecular link between cells and the extracellular matrix (ECM) as well as mediating cell-cell interactions. Integrin-ECM binding triggers the formation of heterogeneous multi-protein assemblies termed integrin adhesion complexes (IACs) that enable integrins to transform extracellular cues into intracellular signals that affect many cellular processes, especially cell motility. Cell migration is essential for diverse physiological and pathological processes and is dysregulated in cancer to favour cell invasion and metastasis. Here, we discuss recent findings on the role of integrins in cell migration with a focus on cancer cell dissemination. We review how integrins regulate the spatial distribution and dynamics of different IACs, covering classical focal adhesions, emerging adhesion types and adhesion regulation. We discuss the diverse roles integrins have during cancer progression from cell migration across varied ECM landscapes to breaching barriers such as the basement membrane, and eventual colonization of distant organs.

Development and Evaluation of [68Ga]Ga-Labeled Riboflavin Derivative for RFVT3-Targeted PET Imaging of Melanoma in Mice

The limited progress in treatment options and the alarming survival rates in advanced melanoma emphasize the significant research importance of early melanoma diagnosis. RFVT3, a crucial protein at the core of energy metabolism reprogramming in melanoma, might play a pivotal role in early detection. In this study, [68Ga]Ga-NOTA-RF, based on riboflavin (RF), was rationally developed and validated, serving as an innovative tool for positron emission tomography (PET) imaging of RFVT3 expression in melanoma. The in vitro assays of RFVT3 specificity of [68Ga]Ga-NOTA-RF were performed on B16F10 melanoma cells. Then, PET imaging of melanoma was investigated in B16F10 allograft mouse models with varying volumes. Biodistribution studies are used to clarify the behavior of [68Ga]Ga-NOTA-RF in vivo. [68Ga]Ga-NOTA-RF was obtained with high radiochemical purity (>95%). A significant uptake (37.79 ± 6.86%, n = 4) of [68Ga]Ga-NOTA-RF was observed over time in B16F10 melanoma cells, which was significantly inhibited by RFVT3 inhibitors RF or methylene blue (MB), demonstrating the specific binding of [68Ga]Ga-NOTA-RF. At 60 min postinjection, the tumor-to-muscle (T/M) ratio of [68Ga]Ga-NOTA-RF was 4.03 ± 0.34, higher than that of the RF-blocked group (2.63 ± 0.19) and MB-blocked group (2.14 ± 0.20). The T/M ratios for three distinct tumor volumes-small (5 mm), medium (10 mm), and large (15 mm) were observed to be 5.25 ± 0.28, 4.03 ± 0.34, and 3.19 ± 0.55, respectively. The expression of RFVT3 was validated by immunohistochemical staining in various tumor models, with small B16F10 tumors exhibiting the highest expression. [68Ga]Ga-NOTA-RF demonstrates promising properties for the early diagnosis of melanoma and the examination of minute metastatic lesions, indicating its potential to assist in guiding clinical treatment decisions.

Beyond Small Molecules: Antibodies and Peptides for Fibroblast Activation Protein Targeting Radiopharmaceuticals

Fibroblast activation protein (FAP) is a serine protease characterized by its high expression in cancer-associated fibroblasts (CAFs) and near absence in adult normal tissues and benign lesions. This unique expression pattern positions FAP as a prospective biomarker for targeted tumor radiodiagnosis and therapy. The advent of FAP-based radiotheranostics is anticipated to revolutionize cancer management. Among various types of FAP ligands, peptides and antibodies have shown advantages over small molecules, exemplifying prolonged tumor retention in human volunteers. Within its scope, this review summarizes the recent research progress of the FAP radiopharmaceuticals based on antibodies and peptides in tumor imaging and therapy. Additionally, it incorporates insights from recent studies, providing valuable perspectives on the clinical utility of FAP-targeted radiopharmaceuticals.

Integrins in cancer: Emerging mechanisms and therapeutic opportunities

Integrins are vital surface adhesion receptors that mediate the interactions between the extracellular matrix (ECM) and cells and are essential for cell migration and the maintenance of tissue homeostasis. Aberrant integrin activation promotes initial tumor formation, growth, and metastasis. Recently, many lines of evidence have indicated that integrins are highly expressed in numerous cancer types and have documented many functions of integrins in tumorigenesis. Thus, integrins have emerged as attractive targets for the development of cancer therapeutics. In this review, we discuss the underlying molecular mechanisms by which integrins contribute to most of the hallmarks of cancer. We focus on recent progress on integrin regulators, binding proteins, and downstream effectors. We highlight the role of integrins in the regulation of tumor metastasis, immune evasion, metabolic reprogramming, and other hallmarks of cancer. In addition, integrin-targeted immunotherapy and other integrin inhibitors that have been used in preclinical and clinical studies are summarized.

[68Ga]Ga-DOTA-Siglec-9 Detects Pharmacodynamic Changes of FAP-Targeted IL2 Variant Immunotherapy in B16-FAP Melanoma Mice

Vascular adhesion protein-1 (VAP-1) is an inflammation-inducible adhesion molecule, which supports contact between leukocytes and inflamed endothelium. There is evidence that VAP-1 is involved in the recruitment of leukocytes to melanoma tumors. Interleukin-2 (IL-2)-based immunotherapy is an efficient therapy that promotes immune system activity against cancers but is associated with toxicity. In the present study, we evaluated the feasibility of PET/CT imaging using the radiotracer [⁶⁸Ga]Ga-DOTA-Siglec-9, which is targeted to VAP-1, to monitor pharmacodynamic effects of a novel FAP-IL2v immunocytokine (a genetically engineered variant of IL-2 fused with fibroblast activation protein) in the B16-FAP melanoma model. At 9 days after the inoculation of B16-FAP melanoma cells, mice were studied with [⁶⁸Ga]Ga-DOTA-Siglec-9 PET/CT as a baseline measurement. Immediately after baseline imaging, mice were treated with FAP-IL2v or vehicle, and treatment was repeated 3 days later. Subsequent PET/CT imaging was performed 3, 5, and 7 days after baseline imaging. In addition to in vivo PET imaging, ex vivo autoradiography, histology, and immunofluorescence staining were performed on excised tumors. B16-FAP tumors were clearly detected with [⁶⁸Ga]Ga-DOTA-Siglec-9 PET/CT during the follow-up period, without differences in tumor volume between FAP-IL2v-treated and vehicle-treated groups. Tumor-to-muscle uptake of [⁶⁸Ga]Ga-DOTA-Siglec-9 was significantly higher in the FAP-IL2v-treated group than in the vehicle-treated group 7 days after baseline imaging, and this was confirmed by tumor autoradiography analysis. FAP-IL2v treatment did not affect VAP-1 expression on the tumor vasculature. However, FAP-IL2v treatment increased the number of CD8⁺ T cells and natural killer cells in tumors. The present study showed that [⁶⁸Ga]Ga-DOTA-Siglec-9 can detect B16-FAP tumors and allows monitoring of FAP-IL2v treatment.

SHARPIN: Role in Finding NEMO and in Amyloid-Beta Clearance and Degradation (ABCD) Pathway in Alzheimer's Disease?

SHANK- associated RH domain-interacting protein (SHARPIN) is a multifunctional protein associated with numerous physiological functions and many diseases. The primary role of the protein as a LUBAC-dependent component in regulating the activation of the transcription factor NF-κB accounts to its role in inflammation and antiapoptosis. Hence, an alteration of SHARPIN expression or genetic mutations or polymorphisms leads to the alteration of the above-mentioned primary physiological functions contributing to inflammation-associated diseases and cancer, respectively. However, there are complications of targeting SHARPIN as a therapeutic approach, which arises from the wide-range of LUBAC-independent functions and yet unknown roles of SHARPIN including neuronal functions. The identification of SHARPIN as a postsynaptic protein and the emerging studies indicating its role in several neurodegenerative diseases including Alzheimer's disease suggests a strong role of SHARPIN in neuronal functioning. This review summarizes the functional roles of SHARPIN in normal physiology and disease pathogenesis and strongly suggests a need for concentrating more studies on identifying the unknown neuronal functions of SHARPIN and hence its role in neurodegenerative diseases.

Evaluation of [68Ga]Ga-NODAGA-RGD for PET Imaging of Rat Autoimmune Myocarditis

The ⁶⁸Gallium-labeled 1,4,7-triazacyclononane-1-glutaric acid-4,7-diacetic acid conjugated radiolabelled arginine-glycine-aspartic acid peptide ([⁶⁸Ga]Ga-NODAGA-RGD) is a positron emission tomography (PET) tracer binding to cell surface receptor α_vβ₃ integrin that is upregulated during angiogenesis and inflammation. We studied whether α_vβ₃ targeting PET imaging can detect myocardial inflammation in a rat model of autoimmune myocarditis. To induce myocarditis, rats (n = 8) were immunized with porcine cardiac myosin in complete Freund's adjuvant on days 0 and 7. Control rats (n = 8) received Freund's adjuvant alone. On day 21, in vivo PET/CT imaging with [⁶⁸Ga]Ga-NODAGA-RGD followed by ex vivo autoradiography and immunohistochemistry were carried out. Inflammatory lesions were detected histologically in the myocardium of 7 out of 8 immunized rats. In vivo PET images showed higher [⁶⁸Ga]Ga-NODAGA-RGD accumulation in the myocardium of rats with inflammation than the non-inflamed myocardium of control rats (SUV_mean 0.4 ± 0.1 vs. 0.1 ± 0.02; P = 0.00006). Ex vivo autoradiography and histology confirmed that [⁶⁸Ga]Ga-NODAGA-RGD uptake co-localized with inflammatory lesions containing α_vβ₃ integrin-positive capillary-like structures. A non-specific [⁶⁸Ga]Ga-DOTA-(RGE)₂ tracer showed 76% lower uptake than [⁶⁸Ga]Ga-NODAGA-RGD in the inflamed myocardium. Our results indicate that α_vβ₃ integrin-targeting [⁶⁸Ga]Ga-NODAGA-RGD is a potential PET tracer for the specific detection of active inflammatory lesions in autoimmune myocarditis.

In Vivo Imaging of Biodegradable Implants and Related Tissue Biomarkers

Non-invasive longitudinal imaging of osseointegration of bone implants is essential to ensure a comprehensive, physical and biochemical understanding of the processes related to a successful implant integration and its long-term clinical outcome. This study critically reviews the present imaging techniques that may play a role to assess the initial stability, bone quality and quantity, associated tissue remodelling dependent on implanted material, implantation site (surrounding tissues and placement depth), and biomarkers that may be targeted. An updated list of biodegradable implant materials that have been reported in the literature, from metal, polymer and ceramic categories, is provided with reference to the use of specific imaging modalities (computed tomography, positron emission tomography, ultrasound, photoacoustic and magnetic resonance imaging) suitable for longitudinal and non-invasive imaging in humans. The advantages and disadvantages of the single imaging modality are discussed with a special focus on preclinical imaging for biodegradable implant research. Indeed, the investigation of a new implant commonly requires histological examination, which is invasive and does not allow longitudinal studies, thus requiring a large number of animals for preclinical testing. For this reason, an update of the multimodal and multi-parametric imaging capabilities will be here presented with a specific focus on modern biomaterial research.

PET Diagnostic Molecules Utilizing Multimeric Cyclic RGD Peptide Analogs for Imaging Integrin αvβ3 Receptors

Multimeric ligands consisting of multiple pharmacophores connected to a single backbone have been widely investigated for diagnostic and therapeutic applications. In this review, we summarize recent developments regarding multimeric radioligands targeting integrin α_vβ₃ receptors on cancer cells for molecular imaging and diagnostic applications using positron emission tomography (PET). Integrin α_vβ₃ receptors are glycoproteins expressed on the cell surface, which have a significant role in tumor angiogenesis. They act as receptors for several extracellular matrix proteins exposing the tripeptide sequence arginine-glycine-aspartic (RGD). Cyclic RDG peptidic ligands c(RGD) have been developed for integrin α_vβ₃ tumor-targeting positron emission tomography (PET) diagnosis. Several c(RGD) pharmacophores, connected with the linker and conjugated to a chelator or precursor for radiolabeling with different PET radionuclides (¹⁸F, ⁶⁴Cu, and ⁶⁸Ga), have resulted in multimeric ligands superior to c(RGD) monomers. The binding avidity, pharmacodynamic, and PET imaging properties of these multimeric c(RGD) radioligands, in relation to their structural characteristics are analyzed and discussed. Furthermore, specific examples from preclinical studies and clinical investigations are included.

Keratinocyte-specific deletion of SHARPIN induces atopic dermatitis-like inflammation in mice

Spontaneous mutations in the SHANK-associated RH domain interacting protein (Sharpin) resulted in a severe autoinflammatory type of chronic proliferative dermatitis, inflammation in other organs, and lymphoid organ defects. To determine whether cell-type restricted loss of Sharpin causes similar lesions, a conditional null mutant was created. Ubiquitously expressing cre-recombinase recapitulated the phenotype seen in spontaneous mutant mice. Limiting expression to keratinocytes (using a Krt14-cre) induced a chronic eosinophilic dermatitis, but no inflammation in other organs or lymphoid organ defects. The dermatitis was associated with a markedly increased concentration of serum IgE and IL18. Crosses with S100a4-cre resulted in milder skin lesions and moderate to severe arthritis. This conditional null mutant will enable more detailed studies on the role of SHARPIN in regulating NFkB and inflammation, while the Krt14-Sharpin-/- provides a new model to study atopic dermatitis.